A study on the interfacial reaction and dielectric properties of Ba0.88(Nd1.40Bi0.42La0.30)Ti4O12alk
SiC与耐热钢在高温真空中的界面反应机制研究
第42卷第6期2023年6月硅㊀酸㊀盐㊀通㊀报BULLETIN OF THE CHINESE CERAMIC SOCIETY Vol.42㊀No.6June,2023SiC 与耐热钢在高温真空中的界面反应机制研究谢莹莹1,陈㊀毛1,宋子杰1,范冰冰1,张㊀锐1,2,陈勇强1(1.郑州大学材料科学与工程学院,郑州㊀450001;2.洛阳理工学院材料科学与工程学院,洛阳㊀471023)摘要:碳化硅陶瓷可用作镁冶炼还原钢罐的内衬㊂在真空和1200ħ条件下,通过扩散偶试验,对SiC 与耐热钢的界面反应进行了系统研究㊂结果表明,在反应初期,界面反应的主要产物为金属硅化物和石墨,其中分布在界面的片状石墨阻碍了界面反应㊂由于界面上低熔点硅镍化合物的熔化,片状石墨在Ni 的催化作用下转变为纤维状石墨,失去了对碳化硅的保护作用㊂界面反应由固-固反应转变为固-液反应,界面反应过程加快,加速了钢对碳化硅的侵蚀㊂与耐热钢相比,SiC 与纯铁的界面反应速率明显降低,金属熔化所需温度也显著升高㊂减少耐热钢中的Ni 含量,可以有效阻止耐热钢和SiC 之间的反应㊂关键词:SiC;耐热钢;界面;石墨;固相反应中图分类号:TQ174㊀㊀文献标志码:A ㊀㊀文章编号:1001-1625(2023)06-2161-11Interfacial Reaction Mechanism of Silicon Carbide and Heat Resistant Steel in High-Temperature VacuumXIE Yingying 1,CHEN Mao 1,SONG Zijie 1,FAN Bingbing 1,ZHANG Rui 1,2,CHEN Yongqiang 1(1.School of Materials Science and Engineering,Zhengzhou University,Zhengzhou 450001,China;2.School of Materials Science and Engineering,Luoyang Institute of Science and Technology,Luoyang 471023,China)Abstract :Silicon carbide (SiC)ceramics can be used as inner lining of reduction tank for magnesium smelting.The interfacial reaction between SiC and heat resistant steel was systematically investigated by diffusion couple experiment under vacuum and 1200ħ.The results show that at the early stage of reaction,the main products of interfacial reaction are metal silicide and graphite,and the lamellar graphite distributing at the interface hinders the interfacial reaction.However,due to the melting of silicon-nickel compounds with low melting point at interface,the lamellar graphite is transformed into fibrous graphite under the catalysis of Ni,losing its protective effect on silicon carbide.In addition,the interface reaction changes from solid-solid reaction to solid-liquid reaction,and the interfacial reaction process is accelerated,which accelerates the corrosion of silicon carbide by pared with heat resistant steel,the interfacial reaction rate between SiC and pure iron is obviously decreased,and the temperature required for the reaction is obviously increased.Reducing Ni content in heat resistant steel can effectively prevent the reaction between heat resistant steel and SiC.Key words :SiC;heat resistant steel;interfacial;graphite;solid phase reaction收稿日期:2023-02-23;修订日期:2023-03-27基金项目:国家自然科学基金青年项目(52202072)作者简介:谢莹莹(2000 ),女㊂主要从事冶金用耐火材料方面的研究㊂E-mail:2428230514@通信作者:陈勇强,博士,讲师㊂E-mail:chenyq@ 0㊀引㊀言碳化硅(SiC)陶瓷具有高强度㊁高硬度㊁耐磨损㊁耐氧化和良好的高温力学性能等诸多特性,在碳化硅基电子器件的金属化和高温航空航天技术中有着重要应用[1-2]㊂然而,碳化硅陶瓷存在脆性较大㊁难加工和高孔隙率等缺陷,应用范围受到限购[3-5]㊂目前,SiC 与金属通常被复合成复合材料,从而改变了单一陶瓷或单一金属材料应用的局限性,扩大了应用范围[6-7]㊂但是,各组分在复合材料中无论如何连接和重新组合,总会有一定的界面存在㊂因此,SiC 和金属材料的界面结构和反应对碳化硅/金属复合材料的性能和应用起着2162㊀陶㊀瓷硅酸盐通报㊀㊀㊀㊀㊀㊀第42卷决定性作用[8-9]㊂在皮江法炼镁过程中,镁在1200ħ㊁10Pa条件下被还原[10-11]㊂因此,耐热钢在工业生产中被用作还原罐㊂金属材料本身存在局限性,在高温下会发生蠕变,导致罐体坍塌而无法继续使用㊂因为还原罐的坍塌和变形,一些机械化的操作设备无法使用,只能依靠人工取罐和排渣㊂由Cr24Ni7S制成的传统还原罐寿命约为60天,使用寿命短,这不仅提高了冶炼成本,还严重影响了生产效率㊂有学者提出,在金属罐内安装陶瓷内衬来支撑金属罐,可以延缓金属罐在高温下的蠕变行为㊂据估计,该方法可将还原罐的使用寿命提高三倍以上,但目前该设计尚未应用到实际生产中㊂考虑到常用陶瓷的高温强度㊁高温氧化性能㊁抗热震性能以及生产成本等因素,碳化硅陶瓷可以用作镁冶炼还原罐的衬里材料㊂然而,作为还原罐内衬材料的SiC与Cr24Ni7S在1200ħ㊁10Pa条件下的物理化学相互作用尚未被研究㊂目前的研究主要集中于液态金属对SiC复合材料的侵蚀[12-14],而对于固态金属对SiC的侵蚀机理研究较少[15-16]㊂其他研究学者[17-20]也重点研究SiC与Fe㊁Ti㊁Ni㊁Cr等金属的扩散偶之间的界面反应,而对SiC 与合金之间的高温反应,特别是对真空条件下的高温反应研究较少[20-22]㊂本文将Cr24Ni7S和SiC组成的扩散偶置于模拟皮江法炼镁的环境中(1200ħ㊁10Pa),详细研究了SiC/钢界面反应和侵蚀过程㊂对不同时间段的样品进行采样和分析,并利用XRD㊁SEM㊁TEM/EDS等方法对其微观结构进行了详细表征和分析,以期为碳化硅陶瓷衬里在皮江法炼镁中的应用提供理论指导㊂1㊀实㊀验1.1㊀材料及样本制备试验中使用的碳化硅(华盛碳化硅有限公司)的主要成分是SiC和SiO2㊂碳化硅陶瓷的主要物理性能如表1所示㊂ZG30Cr24Ni7钢(Cr24Ni7S)的材质与常规镁冶炼还原罐相同,主要成分如表2所示㊂另外,选择纯度为99.9%的铁进行对照试验㊂表1㊀碳化硅陶瓷的物理特性Table1㊀Physical properties of SiC ceramicProperty IndexFlexural strengthσ/MPa522ʃ5Bulk density/(g㊃cm-3) 2.98ʃ0.14Apparent porosity/%14.01ʃ0.21Diffusivity(25ħ)/(mm2㊃s-1) 4.8ʃ0.3Thermal conductivity(25ħ)/(W㊃m-1㊃K-1)18.3ʃ4.8Thermal expansion coefficient(25ħ)/% 5.6ˑ10-6表2㊀ZG30Cr24Ni7钢的主要成分Table2㊀Main composition of ZG30Cr24Ni7steelComposition Cr Ni C Si Mn P N S Mass fraction/%23.76 6.910.29 1.03 1.960.040.120.03首先将SiC和Cr24Ni7S钢分别加工成20mmˑ20mmˑ5mm和5mmˑ5mmˑ5mm的试样㊂通过粗磨㊁细磨去除表面氧化皮,再经过金相抛光得到表面光滑的样品㊂最后将SiC和金属样品的抛光表面拼接在一起,形成紧密接触的扩散偶㊂1.2㊀试验设备和程序利用可视化高温相变仪(TA-16A,CTJZH,中国)观察SiC与金属界面反应过程中的形态变化㊂该设备主体为卧式管式炉,由硅钼棒加热,最高加热温度为1600ħ,且配有真空和气体保护系统,样品可在真空环境或大气保护下进行测试㊂此外,该设备配备了专业的摄像设备和专用软件系统,可以观察样品在不同加热温度下的形态变化,并按照设定的时间进行拍照㊂在利用辅助光源的情况下,从室温到1600ħ都可以达到同样的成像效果㊂本试验所采用镁冶炼生产条件为:真空度保持在10Pa左右,试验温度设定在1200ħ㊂试验前,将制备第6期谢莹莹等:SiC 与耐热钢在高温真空中的界面反应机制研究2163㊀好的扩散偶样品装入设备的炉管中,调整样品角度㊁光源和摄像机位置,以保证观察到清晰的样品图像㊂打开真空泵,将炉膛内的压力调至10Pa㊂将加热程序和摄影参数输入计算机,依次点击启动任务开始加热,设备开始运行㊂以10ħ/min 的速率升温至1200ħ,并分别保温1㊁2㊁4和8h 得到样品㊂1.3㊀界面和微观结构表征将样品嵌入树脂中,然后用金刚石线切割器(STX-202A,中国沈阳科晶自动化设备有限公司)纵向切割㊂用金相砂纸对样品进行细磨,并对抛光后的组织进行分析㊂通过光学显微镜(OM,Axioscope,德国)观察Cr 24Ni 7S 的显微组织结构演变㊂利用X 射线衍射仪(XRD-6100,SHIMADZU,日本)分析样品的物相组成,扫描速度为4(ʎ)/min㊂使用扫描电子显微镜(SEM,JEOL JSM-7001F,Japan)在15kV 加速电压下,观察样品的微观结构以及SiC 和Cr 24Ni 7S 之间的反应界面㊂利用能谱仪(EDS,Ultim Extreme,Oxford,德国)对界面反应产物的元素组成和分布进行了检测㊂利用透射电子显微镜(TEM,JEOL JEOM 2100,日本)对物质的微观结构进行进一步观察和表征㊂2㊀结果与讨论2.1㊀SiC 与Cr 24Ni 7S的界面反应过程图1㊀在界面反应过程中碳化硅陶瓷和Cr 24Ni 7S 接触角随时间和温度的变化曲线Fig.1㊀Contact angle of SiC ceramics and Cr 24Ni 7S varies with time and temperature during interfacial reaction 图1显示了由SiC 和Cr 24Ni 7S 组成的扩散偶从50ħ加热到1200ħ,并在1200ħ保持8h 的界面反应过程,整个反应过程在真空度为10Pa 的条件下进行,与皮江法镁冶炼的条件相同㊂图2为在界面反应过程中碳化硅陶瓷和Cr 24Ni 7S 接触角(θ)随时间和温度的变化图像㊂从图1可以看出,在温度升高到1000ħ之前接触角没有明显变化㊂然而,当温度达到1000ħ时,接触角出现较大的波动,表明在界面上发生了化学反应,导致界面失稳,接触角随之变化㊂当温度继续升高到1200ħ时,接触角的变化幅度逐渐变小,表明界面反应趋于平衡㊂当保温时间为90min 时,接触角开始急剧增加,此时Cr 24Ni 7S 与SiC 接触面处部分出现熔化,导致金属块倾斜,如图2(c)所示㊂随着保温时间的延长,Cr 24Ni 7S 在接触面处出现大面积的熔化,使Cr 24Ni 7S 试样左右摆动(图2(d)),与碳化硅陶瓷的接触角也出现不连续的剧烈波动㊂然而,当保温时间超过240min 时,接触角趋于稳定,这是因为与SiC 接触的Cr 24Ni 7S 已全部熔化,界面不再变化,而远离界面的Cr 24Ni 7S 则没有继续熔化,如图2(f)所示㊂在1200ħ㊁10Pa 的高温条件下,耐热钢与SiC 接触反应后会出现熔化现象,此时耐热钢中的组织结构和物相也发生了变化㊂样品的物相变化通过XRD 来分析,结果如图3所示㊂从图3(a)可以看出,原始的Cr 24Ni 7S 中主要含有Fe㊁Cr 和CrFeNi 相,这是耐热钢熔点高㊁强度高㊁抗高温蠕变性能好的原因㊂当Cr 24Ni 7S 与SiC 发生接触反应后,界面处主要的第二相是金属硅化物,如Fe 3Si [23]和CrFe 8Si,样品顶部上部主要为金属相和金属碳化物㊂出现这种现象可能是由于硅镍相和硅铁相具有较低的反应焓,在SiC 与Cr 24Ni 7S 的界面上优先生成了Fe 3Si㊁Ni 3Si [24]和石墨,而铬元素更容易与C 结合形成碳化物[25]㊂硅以金属硅化物的形式在界面处富集,而C 则在金属试样内部扩散,导致熔融试样的顶部和底部形成不同的物相㊂图3(b)表明,SiC 与耐热钢反应后,SiO 2的峰强度明显减弱,同时出现了碳元素的衍射峰㊂在真空条件下,SiO 2易与SiC 发生反应并分解[26-27],从而降低界面处的SiO 2含量㊂Park 等[28-29]认为,对于SiC /金属界面反应,相平衡原理和质量守恒原则是影响新生相形成顺序的主要因素㊂由于碳化硅/金属界面反应的局部平衡,反应产物中不可能生成单质Si,所以硅化物和碳是碳化硅与金属反应的主要反应产物[30]㊂2164㊀陶㊀瓷硅酸盐通报㊀㊀㊀㊀㊀㊀第42卷图2㊀在界面反应过程中碳化硅陶瓷和Cr 24Ni 7S 接触角随时间和温度的变化Fig.2㊀Contact angle of SiC ceramics and Cr 24Ni 7S varies with time and temperature during interfacialreaction 图3㊀SiC 和Cr 24Ni 7S 反应前后的XRD 谱Fig.3㊀XRD patterns of SiC and Cr 24Ni 7S before and after reaction ㊀㊀图4是Cr 24Ni 7S 与SiC 反应前后的金相照片㊂从图4(a)可以看出,原始的Cr 24Ni 7S 内部是奥氏体组织㊂铬元素主要分布在晶粒内部,镍元素和硅元素在晶界处富集,少量的碳元素分布在基体中㊂然而,当Cr 24Ni 7S 与SiC 反应后,耐热钢的组织结构和元素分布都发生了变化㊂如图4(b)所示,在熔化的样品中没有观察到奥氏体组织,基体中出现白色的第二相㊂通过高倍物镜观察,发现这些白色相呈现不同的尺寸和形状,随机分布在基体上㊂根据图3中的XRD 结果,这些白色物质可能是富铬相㊂此外,由于Cr 24Ni 7S 熔化后部分高熔点金属元素从基体中析出并形成一些新的物相,如出现铬元素的富集,导致基体不同位置的耐蚀性不一致,腐蚀后的颜色也不一致㊂对熔化后的样品进行SEM 和能谱分析,结果如图5所示㊂基体中主要的第二相是白色的富硌相和灰色的富镍相㊂此外,基体中含有较多的硅元素,主要以硅镍化合物的形式存在㊂从Ni Si 相图可知,Si Ni 二元体系的共晶温度为1143ħ,生成的Si Ni 相大多是低熔点化合物[31]㊂例如,NiSi 相的液相温度只有992ħ[32]㊂因此,Ni Si 相的形成是界面融化的原因㊂基体中白色的富铬区最有可能是Cr 23C 6[15],铬元素第6期谢莹莹等:SiC与耐热钢在高温真空中的界面反应机制研究2165㊀与碳元素反应具有较低的反应焓,碳元素的增多可能是基体中铬元素析出的主要原因㊂通过上文分析可知,碳化硅与耐热钢反生应生成的主要产物是金属硅化物㊁碳化物以及单质碳㊂因此,在真空条件下,耐热钢与碳化硅的反应如式(1)所示㊂SiC+Steel(Fe,Cr,Ni)ң(Cr,Ni)x Fe y Si z+Cr x C y+C(1)图4㊀Cr24Ni7S熔化前后的金相照片Fig.4㊀Metallography of Cr24Ni7S before and aftermelting2166㊀陶㊀瓷硅酸盐通报㊀㊀㊀㊀㊀㊀第42卷图5㊀熔融金属样品的SEM 照片和元素分布Fig.5㊀SEM image and elemental distribution of molten metal sample ㊀㊀一般来说,Cr 24Ni 7S 的熔点在1500ħ左右,1200ħ时不会出现熔化现象㊂为了确定Cr 24Ni 7S 熔化的原因,本文对Cr 24Ni 7S 反应前后样品的熔点进行了分析㊂图6为Cr 24Ni 7S 熔化前后的DTA 曲线㊂原始的Cr 24Ni 7S 样品在1250ħ前没有明显的吸热峰,表明其熔点在1250ħ以上㊂而反应后的样品在1139.8ħ时表现出强烈的吸热峰,表明样品在该温度下已开始熔化㊂参考相图可以看出,在由Fe㊁Cr㊁Ni㊁C 和Si 组成的二元相图中,只有Fe C 和Ni Si 二元体系的熔点低于1200ħ㊂通过检测发现样品中碳元素的含量是初始样品碳含量的10倍,而硅元素的含量只增加了32.6%,因此导致耐热钢熔点降低的主要元素是碳㊂本文以纯铁为参照样品对耐热钢熔化的原因进一步分析㊂用纯铁代替Cr 24Ni 7S 进行重复试验,结果如图7所示㊂当试样温度上升到1000ħ时,接触角开始波动,接触表面上发生化学反应,这与Cr 24Ni 7S 的试验现象一致㊂然而,纯铁在1200ħ甚至1300ħ长时间保温都不会发生熔化,这可能是因为体系内缺少熔点较低的硅镍化合物㊂但是,当温度升高到1400ħ并且保持10min 后,样品的底部首先出现熔化,并且整个金属样品在短时间内发生完全熔化㊂这可能是因为界面反应生成的碳元素逐渐扩散到样品内部,使纯铁转化为具有一定碳含量的碳钢,耐热钢的熔点降低到1400ħ左右并发生熔化,这与Cr 24Ni 7S 从底部向顶部逐渐熔化的过程有明显差别㊂图6㊀Cr 24Ni 7S 熔化前后的DTA 曲线Fig.6㊀DTA curves of Cr 24Ni 7S before and aftermelting 图7㊀在界面反应过程中碳化硅陶瓷和铁接触角随时间和温度的变化Fig.7㊀Contact angle of SiC ceramics and Fe varies with time and temperature during interfacial reaction ㊀㊀图8为在界面反应过程中碳化硅陶瓷和Fe 接触角随时间和温度的变化图像㊂从图8可以看出,在温度升高到1400ħ之前,长时间的保温并会使纯铁发生熔化㊂当温度逐渐升高到1400ħ过程中,纯铁样品的仍保持最初的形状,如图8(c)所示㊂但是随着在1400ħ的保温时间延长,纯铁在短时内整体熔化㊂说明第6期谢莹莹等:SiC 与耐热钢在高温真空中的界面反应机制研究2167㊀该样品在1400ħ因达到熔点而发生了熔化,这与之前观察到的耐热钢逐层熔化现象有着本质差别㊂图8㊀在界面反应过程中碳化硅陶瓷和Fe 接触角随时间和温度的变化Fig.8㊀Contact angle of SiC ceramics and Fe varies with time and temperature during interfacial reaction 2.2㊀Cr 24Ni 7S 在1200ħ、10Pa 条件下对SiC 的侵蚀过程图9为碳化硅复合材料在1200ħ㊁10Pa 条件下,与耐热钢反应2h 前后的微观形貌㊂对碳化硅样品进行试验之前,需将其表面打磨和抛光,如图9(a)所示㊂SiC 样品表面光滑,并且有一些不规则的孔隙,这些孔隙是在烧结过程中形成的㊂然而,碳化硅表面经耐热钢侵蚀后变得非常粗糙(图9(b)),表面分布大量的纤维状结构㊂对图9(b)中区域1进行放大,如图9(c)所示,可以看到一层直径约100nm 的纳米线附着在碳化硅表面㊂根据EDS 分析(图9(d))结果可知,这些纳米线的主要成分是C,可能是由碳化硅分解形成的碳转变而来㊂对被腐蚀后的SiC 表面取样进行TEM 分析,结果如图10所示㊂SiC 表面的腐蚀产物主要是各种形态的碳,如石墨片(图10(a))㊁碳纳米线(图10(b))和碳纳米管(图10(c))㊂通过分析碳纳米管的衍射图像,可以发现纳米管为立方晶体结构㊂图10(d)是由图10(e)中a 区域的反傅里叶变化得到的㊂在Fe /Ni 等金属的催化作用下,无定形碳通过原子重排形成碳纳米线,转换界面上分布着大量位错,由无序状态转变为规则的晶体结构㊂纳米线沿着(100)平面生长,生长机制可能是固-液-固(S-L-S)[33]㊂从图9(e)可以看出,碳纳米线的形成与末端的金属有关㊂从EDS 图谱(图10(f))来看,末端金属的主要成分是Ni,还含有Fe 和Cr㊂从文献[34]中可以知,金属具有催化碳纳米形成的作用,但是不同的金属对碳的形态有不同的影响㊂Fe 可以促进片状石墨的形成,而Ni 有助于碳纳米线的形成[34]㊂为了确定Cr 24Ni 7S 对碳化硅陶瓷的腐蚀机制,本文对扩散偶的侵蚀界面进行了分析㊂图11和图12是SiC 陶瓷分别与Cr 24Ni 7S 和纯铁在1200ħ㊁10Pa 条件下反应2h 后的微观界面图㊂从图11(a)可以看出,SiC 被纯铁腐蚀后,在界面处出现了明显碳过渡区㊂这是因为SiC 和纯铁反应形成了FeSi 3,并且生成的C 除部分溶解在金属基体中[35],大部分仍残留在界面处㊂许多结果[36-37]已经证实Fe 与碳化物在高温下反应会生成石墨㊂然而,当SiC 被Cr 24Ni 7S 腐蚀时,其腐蚀界面与纯铁有很大不同,如图12(a)所示㊂在相同条件下,SiC 被Cr 24Ni 7S 腐蚀的情况更为严重,形成的腐蚀层也更大㊂图11(a)和图12(a)的明显区别是,图11(a)界面处形成了不规则的界面侵蚀区域,金属和生成的碳交错分布在一起,没有明显的界面㊂这是因为耐热钢在反应过程中,界面处最先出现熔化,生成的碳部分溶解到金属中,Fe㊁Ni 等金属原子也逐渐向SiC 界面扩散㊂因此,Cr 24Ni 7S 比纯铁对SiC 的侵蚀速率更高,主要是因为反应界面处生成液相,以及碳及金属原子在2168㊀陶㊀瓷硅酸盐通报㊀㊀㊀㊀㊀㊀第42卷液体中快速扩散㊂图9㊀试验前后碳化硅复合材料的微观结构演变Fig.9㊀Microstructural evolution of SiC composites before and aftertest 图10㊀在1200ħ㊁10Pa 条件下,2h 后侵蚀产物的TEM 图像Fig.10㊀TEM images of corrosion products at 1200ħ,10Pa for 2h.第6期谢莹莹等:SiC 与耐热钢在高温真空中的界面反应机制研究2169㊀图11㊀SiC 复合材料与铁在1200ħ㊁10Pa 条件下腐蚀2h 后的腐蚀层SEM 照片和EDS 谱Fig.11㊀SEM image and EDS spectra of corrosion layer of SiC composite with iron after corrosion at 1200ħ,10Pa for 2h 图12㊀SiC 复合材料与Cr 24Ni 7S 在1200ħ㊁10Pa 条件下腐蚀2h 后的腐蚀层SEM 照片和EDS 谱Fig.12㊀SEM image and EDS spectra of corrosion layer of the SiC composite with Cr 24Ni 7S after corrosion at 1200ħ,10Pa for 2h3㊀结㊀论1)在1200ħ㊁10Pa 的条件下,SiC 与Cr 24Ni 7S 能够发生剧烈的界面反应,生成金属硅化物和无定形碳单质㊂由于硅镍相的熔点较低,硅镍相在界面处熔化后使界面反应由固-固界面转变为固-液界面㊂液相的2170㊀陶㊀瓷硅酸盐通报㊀㊀㊀㊀㊀㊀第42卷存在促进了原子的扩散,导致耐热钢从界面处向外逐渐熔化㊂2)在固-液界面处,无定形碳在金属Ni的催化作用下转化为碳纳米线,生长机制是固-液-固机制㊂随着保温时间的延长,纳米线逐渐聚集并长大,导致界面处的碳层消失㊂3)纯铁与SiC在相同的反应条件下,只能形成片层状石墨,而且界面处没有液相生成,样品在温度升高到某一数值时发生整体熔化㊂Ni是导致耐热钢与SiC反应并在低温下逐步熔化的关键因素㊂参考文献[1]㊀LI T,ZHANG Y L,LI J C,et al.Improved mechanical strength and oxidation resistance of SiC/SiC-MoSi2-ZrB2coated C/C composites by anovel strategy[J].Corrosion Science,2022,205:10.[2]㊀LIU G W,ZHANG X Z,YANG J,et al.Recent advances in joining of SiC-based materials(monolithic SiC and SiC f/SiC composites):joiningprocesses,joint strength,and interfacial behavior[J].Journal of Advanced Ceramics,2019,8(1):19-38.[3]㊀CAO L,WANG J,LIU Y,et al.Effect of heat transfer channels on thermal conductivity of silicon carbide composites reinforced with pitch-basedcarbon fibers[J].Journal of the European Ceramic Society,2022,42(2):420-431.[4]㊀GOMEZ E,ECHEBERRIA J,ITURRIZA I,et al.Liquid phase sintering of SiC with 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2题名+单位英文名
当有介词by时, 应保留investigation 之类 的词。
Investigation of phase behavior of polymer blends by thermal methods. A study of rate constants for two-phase electron-transfer reaction by A.C. impedance → A.C. impedance study of rate constants for two-phase electron-transfer reaction
The synthesis of a novel alcoholsoluble polyamide resin → Synthesis of a novel alcoholsoluble polyamide resin
• Avoid nonquantitative , meaningless words like “rapid” and “new”
“Speciation”(鉴别 分类)含义已经包括物质 的 各 种 化 学 形 态 、 形 态 分 析 。 “Chemical”、“Analysis”应删去。
举例
在三个升温速率下用热天平研究 煤的热解及其反应动力学 → 煤的热解及其反应动力学 PES/PC 共混体系的研究 → PES/PC 共混体系的力学性能； PES/PC 共混体系的相容性与力学性能
• In most cases, omit “the” at beginning of the title
The microstructure of microcrystalline cellulose → Microsபைடு நூலகம்ructure of microcrystalline cellulose
甘阳
科研成果
an overview article). J. Shen, D. Zhang, Y. Wang, Y. Gan, AFM and SEM Study on Crystallographic and Topographical Evolution of Wet-Etched Patterned Sapphire Substrates (PSS): I. Cone-Shaped PSS Etched in Sulfuric Acid and Phosphoric Acid Mixture (3:1) at 230°C, ECS nol., 6 (2017) R24. 所有文章（All Publications）
谢谢观看
科研成果
） Y. Yuan, D. Zhang, F. Zhang, , Y. Gan, Crystallographic Orientation Dependence of Nanopattern Morphology and Size in Electropolished Polycrystalline and Monocrystalline Aluminum: An EBSD and SEM Study, ., 167 (2020) . （多晶和单晶铝， 一定条件下电解抛光后，表面会产生纳米图案（如平行条纹或短条或无序结构），这不奇怪。但 是，结合系统的EBSD、SEM表征和深入系统的数据分析，发现了意想不到的结果——纳米图案的 类型和周期具有明显的晶粒取向和晶面取向依赖性。在机理方面也提出了一个改进的框架。后续 还有更多结果。。。
目录
01 研究方向
02 主要贡献
研究方向
研究方向
主要研究方向：新能源材料与器件、电池、石墨烯纳米材料等的表面和界面物理化学。无机氧化 物和陶瓷材料的表面微观结构与表面化学性质的关系，纳米材料制备、表征和应用。
Phase transfer catalyzed esterification modeling and experimental studies in a microreactor
RESEARCH PAPERPhase transfer catalyzed esterification:modelingand experimental studies in a microreactor under parallel flow conditionsErvin Sˇinkovec •Andrej Pohar •Matjaz ˇKrajnc Received:28June 2012/Accepted:20September 2012/Published online:7October 2012ÓSpringer-Verlag Berlin Heidelberg 2012Abstract A liquid–liquid phase transfer catalyzed (PTC)esterification reaction of 4-t -butylphenol in aqueous phase (1M sodium hydroxide solution)and 4-methoxybenzoyl chloride in organic phase (dichloromethane)in a micro-channel under parallel laminar flow conditions was studied in this work.Tetrabutylammonium bromide was used as the PTC.Stable liquid–liquid hydrodynamic flow and a defined specific interfacial area in a microreactor offer considerable benefits over conventional batch reactors and are crucial to study interactions between kinetics and mass transfer effects.Mentioned features were used to develop a 3D mathematical model considering convection in the flow direction,diffusion in all spatial directions,and reactions in organic and aqueous phases.Results have shown a much higher mass transfer rate of the PTC between both phases as the one predicted by the 3D mathematical model.It may be assumed that the instability of parallel flow,along with the mass transfer of catalyst between both phases,causes rippling and erratic pulsation at the interface which then leads to interfacial convection and increased mass transfer rates.With a proposed correlation for mass transfer enhancement due to interfacial convection,all the experi-mental data were successfully predicted by the model.Keywords Phase transfer catalysis ÁMicrofluidic ÁParallel flow ÁMass transfer ÁMathematical model1IntroductionIn the fine chemical,pharmaceutical,analytical,and bio-chemical industry,microstructured devices have impres-sively demonstrated several decisive advantages,such as better heat and mass transfer due to a very large surface-to-volume ratio and superior mixing of the fluid phases(Ehrfeld et al.2000;Ja¨hnisch et al.2004;Wirth 2008).An important feature of microstructured reactors is the hydrodynamic flow in the microchannel.In liquid–liquid microchannel flow,different flow patterns such as annular flow,parallel flow,droplet flow,or slug flow are found.Circulation patterns vary with the physical properties of liquids as well as with operating parameters such as the flow ratio of two immiscible liquids,mixing elements geometry,channel geometry,and capillary dimensions (Zhao et al.2006).In a glass microreactor with a rectan-gular microchannel,a high degree of control over parallel flow can be achieved and under precisely controlled con-ditions,the liquid–liquid interfacial surface-to-volume ratio may be strictly defined.Mentioned features enable the prediction and calculation of mass transport between two phases and offer considerable benefits over conventional batch reactors.In spite of its industrial importance,the details of mass transfer and the role of the interfacial area on transport enhancements for liquid–liquid two-phase microsystems are still not very well understood,especially in those where mass transfer and chemical reaction occur simultaneously,such as in two-phase phase transfer cata-lyzed reactions (PTC reactions).PTC is one of the most important and useful techniques when anionic activation is concerned.It is estimated that PTC is used in as many as 500commercial processes with a wide range of applications (Starks et al.1994).General PTC reaction systems consist of two mass transfer stepsE.Sˇinkovec ÁA.Pohar ÁM.Krajnc (&)Faculty of Chemistry and Chemical Technology,Universityof Ljubljana,Asˇkerc ˇeva cesta 5,1000Ljubljana,Slovenia e-mail:matjaz.krajnc@fkkt.uni-lj.siMicrofluid Nanofluid (2013)14:489–498DOI 10.1007/s10404-012-1067-7and two reaction steps in the organic and aqueous phases. The key factor is the ability of small quantities of an agent (PTC)to transfer one reactant across the interface between two immiscible liquid–liquid phases so that the reaction can proceed.The regenerated catalyst is then transferred into another phase where it participates in another catalytic cycle(Starks1971;Dehmlow1974).Despite many publications on the chemistry and appli-cations of PTC,only few of them involve the role of interfacial mass transfer and mathematical modeling which include reaction kinetics in both phases and mass transport between and within each phase(Wang and Wu1990;Asai et al.1993;Wu1993;Wang and Chang1994;Bhattach-arya1996;Yang1998).Thefirst study of a PTC reaction in a microreactor was performed by Hisamoto et al.(2001)on a diazo-coupling reaction.Ueno et al.(2003)investigated PTC alkylation and Ahmed-Omer et al.(2008)investigated a number of process-intensification techniques in a two-phase slugflow reaction system.The influence of the surface-to-volume ratio on mass transfers and consequently on the overall chemical reaction rate of the Wittig reaction in a microtube reactor under liquid–liquid slugflow pattern was investi-gated in our previous work(Sinkovec and Krajnc2011). Efficient liquid–liquid PTC reactions due to more effective mass transfer between two immiscible phases,which can be attributed to the high surface-to-volume ratio and internalflow circulation in the droplets,compared to con-ventional dispersion techniques were reported by Ji et al. (2012).Aljbour et al.(2010)investigated a PTC reaction with continuous phase separation by utilizing a parallel flow pattern in a rectangular microchannel.In this work,a PTC esterification reaction of sodium4-t-butylphenolate(MY)in the aqueous phase(1M sodium hydroxide solution)and4-methoxybenzoyl chloride(RX) in the organic phase(dichloromethane)in a microreactor with a rectangular microchannel under parallel pressure drivenflow was studied.Quaternary salt tetrabutylammo-nium bromide(QX)was used as the PT catalyst.4-t-butylphenol dissolved in1M NaOH forms with sodium hydroxide MY.QX picks up the nucleophile Y and ferries it in the form QY(tetrabutylammonium4-t-butylpheno-late)into the organic phase where the reaction with the organic substrate RX occurs,giving the desired product 4-t-butylphenyl4-methoxybenzoate(RY)and regenerated QX that continues the next PTC cycle in the aqueous phase.The reactions were performed at different ratios between organic and aqueous phaseflow rates,different temperatures,and at different amounts of PT catalyst. Furthermore,a3D mathematical model considering con-vection in theflow direction(z),diffusion in x,y,z direc-tions,and reactions in organic and aqueous phases was developed to analyze the experimental data and to predict reactor performance.The reaction kinetics in the organic phase and distribution coefficients of MY,QX,QY,RX, and RY were determined experimentally,whereas an empirical correlation was used to estimate molecular dif-fusion coefficients in the aqueous and organic phase.2Experimental section2.1Materials4-t-butylphenol(C98%,Merck),4-methoxybenzoyl chloride (RX,C99%,Sigma-Aldrich),tetrabutylammonium bromide (QX,C99%,Sigma-Aldrich),1,3,5-trimethoxybenzene (C99%,Sigma-Aldrich),dichloromethane(C99.5%, Merck),sodium hydroxide(C99%,Merck),hydrochloric acid(C37%,Riedel-de Haen),and deionized water were used.2.2Determination of the distribution coefficients Distribution coefficients K p were determined for QX,tet-rabutylammonium4-t-butylphenolate(QY),and sodium 4-t-butylphenolate(MY).Different concentrations of QX (4.35,3.25,2.18and1.09mmol/L)and MY(100,75,50 and25mmol/L)in1M aqueous sodium hydroxide solu-tion were prepared,whereas QY was prepared in situ by dissolving known amounts of QX and MY in the same solvent and stirred to form different concentrations of QY (4.34,3.25,2.17,and1.09mmol/L).The same volume of dichloromethane was added and stirred vigorously at a constant temperature(thermostated water bath)for about 1h to allow the reagents to distribute between both phases. At thefinal equilibrium state,a sample of the organic phase was taken and analyzed by1HNMR.2.3Reaction in organic phaseTo perform the organic phase reaction,QY was prepared first.Known amounts of MY and QX were dissolved in 1M aqueous sodium hydroxide solution and stirred at room temperature to form the complex QY.The same volume of dichloromethane was added,shaken vigorously for a few minutes,and then allowed to stand until the separation of the organic and aqueous phase was obtained. The concentration of QY in the organic phase was analyzed by1HNMR.The organic chemical reaction of QY and RX was car-ried out in a poly-etheretherketone(PEEK)microtube reactor(Vici AG,Schenkon,Switzerland)with an internal diameter of130l m connected to high performance syringe pumps(Harvard Apparatus,Holliston,USA)with perflu-oroalkoxy(PFA)tubes(with an internal diameter of 0.75mm).Thefirst feed consisted of QY dissolved indichloromethane(12.5and25mmol/L)prepared as described above,and another feed consisted of different concentrations of RX(12.5,25and50mmol/L)in the same solvent.A known amount of1,3,5-trimethoxyben-zene was used as the standard for1H NMR analysis.The mixing of both solutions was done in a PEEK T-mixer (Vici AG,Schenkon,Switzerland)with an internal diam-eter of250l m.Reactants’residence time(0.25–2s)was determined by the length of the microtube reactor(from60 to120mm)and the overallflow rate which varied from 47.8to191l L/min.Experiments were performed at dif-ferent temperatures and different amounts of both reac-tants.At the exit of the microtube reactor,the reaction was quenched with1M aqueous hydrochloric acid solution. The resulting mixture was separated and the aqueous phase was extracted with dichloromethane.The combined organic layers were evaporated and analyzed by1H NMR.2.4Two-phase PTC esterificationTwo-phase PTC esterification was carried out in the glass microreactor(Micronit Microfluidics B.V.,Enschede,The Netherlands)with Y-shaped inflow and outflow channels and the main channel with dimensions of220-l m width, 50-l m height,and332-mm length.The microchip was connected with PFA tubes(internal diameter of0.75mm) to high performance syringe pumps which insured highly controllableflow rates.The organic phase consisted of RX (25mmol/L)and1,3,5-trimethoxybenzene dissolved in dichloromethane.1,3,5-trimethoxybenzene was used as a standard for1H NMR analysis.The aqueous phase con-sisted of MY(100mmol/L)and QX(2.17and4.34mmol/ L)dissolved in1M aqueous sodium hydroxide solution.It must be mentioned that the concentrations of QX,which express characteristics of surface-active compounds,were always below the critical micelle concentration(Linden-baum and Boyd1964).The aqueous and organic phase reactants were fed at differentflow rates through two separate inlets.Two-phase PTC reaction was carried out at parallelflow conditions.The two streams were stable with a well-defined interface in between.Experiments were performed at different temperatures,different amounts of QX,and at a different aqueous-to-organic(AO)volumetric flow ratio.At the exit of the microreactor,the reaction was quenched with1M aqueous hydrochloric acid solution. The resulting mixture was separated and the aqueous phase was extracted with dichloromethane.The combined organic layers were evaporated and analyzed by1H NMR. Reactants’residence time(2.5–20s)was determined by the overallflow rate which varied from10.9to87.1l L/ min.At overallflow rates lower than10and22l L/min at AO volumetricflow ratio0.25and0.5,respectively, unstable parallelflow forming slugs were observed.2.5AnalysisThe conversion of RX in samples was evaluated by1H NMR spectroscopy(Bruker Avance III500MHz NMR). Different proton chemical shift of RX aromatic ring pro-tons(at8.08ppm—1H NMR spectra of the commercial compound),RY aromatic ring protons(at8.15ppm—1H NMR spectra of the product),and standards MeO-sub-stituent’s(at3.77—1H NMR spectra of the commercial compound)may be observed.The conversion of RX was determined by the surface area ratio between reactant RX aromatic ring protons and standard MeO-substituent’s signal.Results were compared and confirmed by determi-nation of the surface area ratio between reactant RX and product RY aromatic ring protons.The position of the interface between the organic and aqueous phase was determined by microscopicflow imaging. 3Results and discussion3.1Distribution coefficientThe distribution of a chemical compound between two immiscible phases usually depends on the chemical struc-ture of the solute,solvent,and solute concentration(Wang and Yang1991).The model presented in this work is subject to the assumption that distribution coefficients are not affected by the changes and interactions of other compounds in the phase composition.The distribution coefficient was defined as the concentration of QX,QY,or MY in the organic phase divided by the concentration of the same solute in the aqueous phase:K pi¼c i;orgc i;aqð1Þwhere i represents the chemical species.In Figs.1and2,the distribution coefficients of QX and MY are shown at different temperatures in dichlorometh-ane—1M aqueous sodium hydroxide solution two-phase system.It may be seen that the distribution coefficient of both solutes is a function of temperature,besides which the increasing of the distribution coefficient of QX with increasing concentration may be observed.The distribution coefficient of QX as a function of QX concentration in aqueous phase at20and35°C may be represented by the following two regression equations:K pQX¼0:0478Âc QX;aqþ0:1343ðT¼20 CÞK pQX¼0:0644Âc QX;aqþ0:1316ðT¼35 CÞð2Þwhere c QX,aq is a QX concentration in aqueous phase (mmol/L).The concentration dependency of the partitioning coef-ficient is negligible in the case of MY and an average value of K p at 20and 35°C is equal to 0.077and 0.117,respectively.As shown in Fig.3,the whole amount of the QY formed in the aqueous phase was transferred from the aqueous to the organic phase at all examined temperatures (from 10to 35°C).It is obvious that the addition of the lipophilic part of the molecule MY will make the quaternary ammonium cation move and transfer Y into the organic phase where the organic phase reaction may proceed.It was noticed that the reactant RX and product RY are insoluble in the aqueous phase.3.2Prediction of diffusion coefficientTo estimate molecular diffusion coefficients D AB of MY,MX,QX,QY,RX,and RY in the aqueous and organic phase,the Wilke–Chang empirical correlation was used.It is an empirical modification of the Stokes–Einstein relation and is one of the most widely used correlations for esti-mating diffusion coefficients:D AB ¼7:4Â10À8ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiw B MW B p Tg B "V 0:6A ð3Þwhere A and B denote solute and solvent,respectively,"V A (mL/mol)is the molar volume of the solute,MW B is the molecular weight of the solvent (g/mol),g B is solvent viscosity (cP),T is temperature in K,and w B is a constant which accounts for solvent/solvent interactions (1for nonassociated solvents,2.6for water)(Li and Carr 1997).3.3Reaction in the aqueous and organic phaseIn the aqueous phase reactant,MY reacts with the PTC QX to form the active complex QY.Because no electron-pair bonds need to be broken,the ion exchange reaction in the aqueous phase is very fast and limited only by the rate of ion diffusion.For this reason,it was impossible to deter-mine the reaction kinetics experimentally.It was also impossible to specify the reversibility of aqueous phase QY formation.Because QY is a lipophilic compound and is much more soluble in the organic than the aqueous phase,what was observed by analyzing the distribution coeffi-cients,all QY formed in the aqueous phase transfers into the organic phase,and reversibility may be neglected (Yang 1998).After the transfer of QY into the organic phase,the organic reaction with RX may occur,which may be described by the power-law kineticexpression:Fig.1The distribution coefficient of QX as a function of the concentration of QX in the aqueous phase at different temperatures [dichloromethane—1M aqueous sodium hydroxide solution two-phase system,T =10°C (filled triangle ),T =20°C (filled dia-mond ),T =30°C (filled square ),T =35°C (filled circle)]Fig.2The distribution coefficient of MY as a function of the concentration of MY in the aqueous phase at different temperatures [dichloromethane—1M aqueous sodium hydroxide solution two-phase system,T =10°C (filled triangle ),T =20°C (filled dia-mond ),T =30°C (filled square ),T =35°C (filled square)]Fig.3The concentration of QY in the organic phase as a function of the initial concentration of QY formed in the aqueous phaseÀd c RX ðt Þd t¼k org c a RX ðt Þc bQY ðt Þð4Þwhere k org is the intrinsic reaction rate constant in theorganic phase and c RX and c QY are concentrations of RX and QY in the organic phase,respectively.Exponents a and b identify the order of the reaction with respect to c RX and c QY ,respectively.The initial conditions of c RX and c QY at t =0are defined as:c RX ð0Þ¼c RX ;0c QY ð0Þ¼c QY ;0Integration of Eq.4for a =b =1gives the following:ln c RX c QY ;0c QY c RX ;0¼ðc RX ;0Àc QY ;0Þk org t ð5ÞA linear relationship in Fig.4obtained by plotting ln(c RX /c QY )versus time from experimental data describes the second order reaction.Based on experimental results at different initial con-centrations of c RX and c QY ,organic reaction parameters were defined and further confirmed with mathematical model simulations.As seen in Fig.5,experimental results are in good agreement with model simulation where the organic reaction was assumed to be of the first-order with respect to c RX and c QY (a =b =1),and the intrinsic reaction rate constant at 20°C is equal to 5.09102L/mol s.At higher reaction temperatures,almost complete conversion (from 97to 99%according to limiting reac-tant)was achieved in less than 0.5s.For this reason,it was impossible to determine the reaction kinetics at higher temperatures experimentally.3.4A mathematical model of two-phase esterificationin a microchannel To analyze experimental data and to forecast microreactor performance,a 3D mathematical model containing convection in the flow (z )direction,diffusion in x ,y ,z directions,and reactions in the aqueous and organic phase was developed (Fig.6).It was proposed that (a)both RX and RY are insoluble in the aqueous phase,(b)the aqueous phase chemical reaction takes place only in the aqueous phase (confirmed with exper-iments),(c)the whole amount of QX in the aqueous phase irreversibly forms the complex QY with MY,(d)the flow was laminar because the highest Reynolds number calculated was below 40,which is well below the critical Reynolds number,and (e)mass transfer of QX and QY between both phases takes place at the interfacial area between parallel flows of the organic and aqueous phase.For steady-state conditions,con-sidering a developed velocity profile,isotropic diffusion,and constant physical properties,the partial differential equation for the aqueous phase is (Stojkovic et al.2011):v x ;y ðÞo c i x ;y ;z ðÞo z ¼D i ;aq o 2c i x ;y ;z ðÞo x þo 2c i x ;y ;z ðÞo y þo 2c i x ;y ;z ðÞo z þr ið6Þwith the following boundary conditions:c i ðx ;0\y \w 1;0Þ¼c i 0o c i ð0;0\y \w 1;z Þd x ¼o c i ðH ;0\y \w 1;z Þd x ¼o c i ðx ;0;z Þd y ¼o c i ðx ;0\y \w 1;L Þd z ¼0where r i is the reactionterm:Fig.4Plot of ln(c RX /c QY )versus time at two different c RX /c QY ratiosat 20°C,c RX,0:c QY,0=1.2:1(filled square ),c RX,0:c QY,0=2:1(filled diamond)Fig.5The mathematical model simulations and experimental data of the organic product concentration versus time at different initial c RX /c QY ratios at 20°C,c RX,0:c QY,0=1:2(filled square ),c RX,0:c QY,0=4:1(filled circle ),c RX,0:c QY,0=1.2:1(filled diamond ),c RX,0:c QY,0=2:1(filled triangle )r MY ¼Àk aq c MY c QX r QX ¼Àk aq c MY c QX r MX ¼k aq c MY c QXr QY ¼k aq c MY c QXr RX ¼r RY ¼0ð7ÞFor the organic phase:u x ;y ðÞo c i x ;y ;z ðÞo z ¼D i ;org o 2c i x ;y ;z ðÞo x þo 2c i x ;y ;z ðÞo y þo 2c i x ;y ;z ðÞo z þr ið8Þwith the following boundary conditions:c i ðx ;w 1\y \W ;0Þ¼c i 0o c i ð0;w 1\y \W ;z Þd x ¼o c i ðH ;w 1\y \W ;z Þd x¼o c i ðx ;W ;z Þd y ¼o c i ðx ;w 1\y \W ;L Þd z¼0where r i is the reaction term:r QX ¼k org c RX c QY r RY ¼k org c RX c QY r QY ¼Àk org c RX c QY r RX ¼Àk org c RX c QY r MY ¼r MX ¼0ð9ÞAt the interphase:c i ;org x ;w 1;z ðÞ¼c i ;aq x ;w 1;z ðÞK p D i ;aqo c i ;aq x ;w 1;z ðÞo y ¼D i ;orgo c i ;org x ;w 1;z ðÞo ywhere c represents concentration,D is the moleculardiffusion coefficient,K p is the distribution coefficient,and v ,u are the z -direction velocities of the aqueous and organic phase,respectively.Subscripts ‘‘org,’’‘‘aq,’’and ‘‘0’’denote organic phase,aqueous phase,and initialcondition,respectively.H is the microchannel depth,W is the width,L is the length,and w 1is the location of the interfacial area.The fully developed Poiseuille-type flow of the aqueous and organic phase in steady-state conditions neglecting compressibility and the gravitational force inside the microchannel is calculated from (Znidarsic-Plazl and Plazl 2007)0¼Àd P d z þg aq d 2v ðx ;y Þd x 2þd 2v ðx ;y Þd y 2!0¼Àd P d z þg org d 2u ðx ;y Þd x þd 2u ðx ;y Þd y !ð10Þwith the associated boundary conditions:v ðx ;0Þ¼v ð0;y Þ¼v ðH ;y Þ¼0u ðx ;W Þ¼u ð0;y Þ¼u ðH ;y Þ¼0g aq d v ðx ;w 1Þd y ¼g orgd u ðx ;w 1Þd ywhere g aq and g org are the dynamic viscosities of the aqueous and organic phase,respectively,and P is the pressure.The velocity profile in the hydrodynamic devel-oping region was not considered due to the very long mi-crochannel (332mm).The experimental results of liquid–liquid two-phase esterification under PTC conditions at different concen-trations of catalyst compared with results of the 3D mathematical model simulation using Eqs.6–10with associated boundary conditions are shown in Fig.7.It may be seen that the overall reaction rate of experimental data is much higher than the values of the mathematical model calculation.It was observed that the mathematical model simulated reaction cannot be enhanced by increasing the aqueous reaction kinetic constant,which is the parameter in the mathematical model that could not be determined experimentally.The value of aqueous intrinsic reaction rate constant k aq was varied from 200to 16,000L/mol s and did not substantially affect the solution of the model.The reaction in aqueous phase is fast and is not rate-limiting step.Similarly,increasing the organic reaction kinetic constant did not enhance the overall reaction rate.We found out that only the increase of the diffusion coefficients of QX and QY in both phases resulted in a higher overall reaction rate,which means that the overall reaction rate was limited by the mass transfer.It may also be seen from Figs.7that the actual mass transfer rate between both phases is much higher than the one predicted by the 3D mathematical model.Similar unexpected high mass transfer coefficients between two phases were observed in the literature and were explained by the Marangoni convection at the inter-face,which occurs by the transfer of a solute between two liquid phases (Sherwood and Wei 1957;SternlingandFig.6Scheme of the main channel (W =220l m,H =50l m,L =332mm)Scriven 1959;Bakker et al.1967;Chao and Meldrum 2009;Pursell et al.2009;Agble and Mendes-Tatsis 2000).Sherwood and Wei (1957)reported the spontaneous interfacial activity that influenced the rate of mass transfer between two liquids.The influence of two-phase properties on interfacial turbulence and hydrodynamic instability was studied by Sternling and Scriven (1959).Bakker et al.(1967)investigated the increasing of ratio F of the mea-sured extraction rate and the predicted extraction rate due to interfacial movement on the microscale.Chao and Meldrum (2009)presented a singular oscillatoryinteraction between two droplets of different liquids driven by the Marangoni effect.The influence of added surface-active compounds on interfacial stability,interfacial con-vection,and on mass transfer rates was also studied (Pur-sell et al.2009).Agble and Mendes-Tatsis (2000)reported that the presence of an ionic surfactant in the aqueous phase could either initiate or increase the Marangoni con-vection and enhance the measured molar flux up to seven times.It may be assumed that similar effects appear in our experiments where QX,with the characteristics of a sur-face-active compound,was used as the PTC.The mass transfer of QX and QY between both phases causes rip-pling and erratic pulsation at the interface which then leads to increased mass transfer rates.In thisrespect,Fig.7The mathematical model simulations (without the mass transfer enhancement coefficient E )and experimental data of RX concentration versus time at different concentrations of QX,temperatures,and AO ratios;filled circle :c QX,0=2.17mmol/L,AO =0.25,T =20°C;filled square :c QX,0=4.34mmol/L,AO =0.25,T =20°C;filled diamond :c QX,0=4.34mmol/L,AO =0.25,T =35°C;filled trian-gle :c QX,0=4.34mmol/L,AO =0.5,T =35°C;straight line :model,c QX,0=2.17mmol/L,AO =0.25,T =20°C;big dashed line :model,c QX,0=4.34mmol/L,AO =0.25,T =20°C;small dashed line :model,c QX,0=4.34mmol/L,AO =0.25,T =35°C;dotted line :model,c QX,0=4.34mmol/L,AO =0.5,T =35°CFig.8The proposed mass transfer enhancement coefficient as a function of the cumulative flow rate (Eq.11)plotted for RU l.s.p.=Fig.9The mathematical model simulations (with the mass transfer enhancement coefficient E )and experimental data of RX concentration versus time at different concentrations of QX,temperatures,and AO ratios (RU l.s.p.=10l L/min and RU l.s.p.=22l L/min for AO ratio 0.25and 0.5,respectively);filled circle :c QX,0=2.17mmol/L,AO =0.25,T =20°C;filled square :c QX,0=4.34mmol/L,AO =0.25,T =20°C;filled diamond :c QX,0=4.34mmol/L,AO =0.25,T =35°C;filled triangle :c QX,0=4.34mmol/L,AO =0.5,T =35°C;straight line :model,c QX,0=2.17mmol/L,AO =0.25,T =20°C;big dashed line :model,c QX,0=4.34mmol/L,AO =0.25,T =20°C;small dashed line :model,c QX,0=4.34mmol/L,AO =0.25,T =35°C;dotted line :model,c QX,0=4.34mmol/L,AO =0.5,T =35°CTable 1The calculated values of the diffusion coefficientsD aq (m 2/s)aD org (m 2/s)a D aq (m 2/s)b D org (m 2/s)b MY 7.10910-10 2.18910-99.10910-10 2.41910-9QX 5.13910-10 1.45910-9 6.77910-10 1.80910-9MX 1.94910-9 5.52910-9 2.51910-9 6.67910-9QY 4.48910-10 1.27910-9 5.80910-10 1.54910-9RY 5.77910-10 1.64910-97.47910-10 1.98910-9RX7.39910-102.50910-91.11910-102.96910-9a At 20°C bAt 35°Cmicrofluidic systems themselves appear to be very pow-erful tools for the study of surfactant dynamics at the time-and length-scale relevant to the corresponding microfluidic application (Baret 2012).To take into account the Marangoni effect and conse-quently higher mass transfer coefficients,the mass transfer enhancement coefficient (E )was introduced.The optimal correlation for E was found as the best fit of all the experimental data:E ¼6:5Âexp ÀX U ÀXU l :s :p =20 þ1ð11Þwhere RU is the cumulative flow rate and RU l.s.p.is the lowest cumulative flow rate of stable parallel flow (Fig.8).Since the flow regime inside microchannels is influenced by the net result of interactions among surface tension,liquid inertia,and liquid viscous forces,along with wall adhesion effects (contact angle and surface roughness),the flow rates at which the stable parallel flow is formed vary considerably between different systems (Pohar et al.2012).The mass transfer enhancement coefficient was found to be the highest just before the breaking of stable parallel flow into slug flow,when the interfacial turbulence is the strongest.With a proposed correlation for mass transfer enhancement due to interfacial convection,all the experi-mental data were successfully predicted by the model (Fig.9).The values of the diffusion coefficients used for the simulations are presented in Table 1.The calculated concentration profiles at 20°C and c QX,0=4.34mmol/L are shown in Fig.10.MY (0.1M)and QX (0.00435M)already react in the syringe where all of QX is transformed into QY.As soon as QY is pumped into the central channel,where it comes in contact with the organic phase,it starts to migrate across the interphase.In the organic phase,it reacts with RX,which causes the formation of the product RY.QX is formed in the organic phase and migrates again across the interphase into the aqueous phase,where it transforms back into QY,which can be seen as a plateau on the QY graph.When all of MY is consumed,QY cannot be formed anymore.The rest of QY in the organic phase is transformed with the remaining RX into QX that migrates and,in the end,remains in the aqueous phase.The overall reaction can be observed through the depletion of MY and RX and the formation of MX and RY.4ConclusionsIn the present study,liquid–liquid two-phase PTC esteri-fication in a microreactor under parallel laminar flow conditions was studied.To predict the overall reaction rate and to forecast reactor performance,a 3D mathematical model considering convection in the flow direction (z ),diffusion in x ,y ,z directions,and reactions in the organic and aqueous phases was developed.To define the order of the reaction and the intrinsic reaction rate constant,first,the reaction kinetics in the organic phase wereinvestigated.Fig.10The depth-averaged concentration profiles of the reactants and products at 1l L/min flow rate of the aqueous phase and 4l L/min flow rate of the organic phase at 20°C.The aqueous phase occupied 30%of the microchannel (on the left )。
线性体合成反应性氨基硅油的工艺研究
0.0 0.5 1.0 1.5 2.0 2.5 3.0 NaOH 质量分数 / %
图 3 催化剂用量对氨基硅油黏度的影响 Fig.3 Effect of catalyst dosage on aminosilicone viscosity
CH3O
CH3 CH3
Si OCH3 C3H6NHC2H4NH2
NaOH
CH3
CH3
CH3 CH3
R Si-O
Si-O x
CH3
Si-O Si R忆 y
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（其中 R，R忆为 OH 或 CH3O）
1.3 性能测试与表征 （1）氨值测定：称取 1耀2 g 氨基硅油，加入 10 mL
摘 要：采用线性体（WC62M）、N-茁-氨乙基-酌-氨丙基甲基二甲氧基硅烷为原料，在碱催化下通过共缩聚反应合成
反应性氨基硅油.考察了反应温度、反应时间、偶联剂用量、催化剂用量等因素对氨基硅油氨值和黏度的影
响，并用红外、核磁共振氢谱对产物结构进行了表征. 结果表明：氨基硅油的氨值随着偶联剂用量的增大而
第2期
张志立袁等院 线性体合成反应性氨基硅油的工艺研究
— 71 —
聚链增长反应进行竞争.YDH-602 用量越多，延缓了 链增长，导致氨基硅油黏度降低. 2.2.2 催化剂用量对产物黏度的影响
适用于氨基硅油制备反应的催化剂主要有：甲醇 钠、四甲基氢氧化胺和碱金属氢氧化物如 NaOH、KOH 等.从价格因素考虑，本实验采用 NaOH 为催化剂.催 化剂用量对氨基硅油相对分子质量的影响较大 [7]，其 对黏度的影响如图 3 所示.
2 结果与讨论
国外期刊英文论文
Influence of Deformation
Li CL, Chen Mater. Sci. & 2002, 325: SCI a
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Effect of Fe-Mn-Si-Cr-Ni Alloy
Wang TJ
Comparison between fatigue
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Int. J. Fatigue 2002, 24(5): SCI a
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behavior of some ceramics: a new concept of intrinsic stress-corrosion
Wang HJ, Jin ZH
Ding HF, Jin
258-264
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The interfacial stability of the
Tang WM,
Mater. Chem. 2002, 77:
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Zheng ZX,
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Effects of crystalline morphology Xu T, Yu J, Jin Mater.
2014同等学力英语作文
2014同等学力英语作文英文回答：In the tapestry of human experience, the influence of nature's artistry upon our emotions, thoughts, and behaviors is an intricate and profound thread. From the soaring mountains that dwarf us to the crashing waves that invigorate us, nature possesses an unyielding power to shape our inner lives.Throughout history, poets and philosophers have eloquently extolled the virtues of nature. In the Romantic era, William Wordsworth and Samuel Taylor Coleridge celebrated the transformative power of nature on the human psyche, envisioning it as a sanctuary of tranquility and inspiration. Henry David Thoreau, an ardent naturalist and advocate for the preservation of wilderness, embarked on an extraordinary experiment at Walden Pond, seeking to reconnect with the primordial rhythms of nature and explore its profound impact on his soul.Modern science has lent empirical support to the long-held belief in nature's therapeutic effects. Studies have shown that exposure to natural environments can reduce stress levels, improve cognitive function, and promote overall well-being. The mere sight and sounds of nature have been found to have a calming effect on the mind, slowing the heart rate and reducing blood pressure.The emotional connection we forge with nature is often rooted in our childhood experiences. As children, we are drawn to the wonders of the natural world, exploring its nooks and crannies with a sense of unbridled curiosity and awe. These early experiences lay the foundation for a lifelong appreciation of nature's beauty and power.As we traverse the complexities of adulthood, the demands of daily life can often separate us from the restorative embrace of nature. However, it is crucial that we make a conscious effort to reconnect with our natural surroundings, whether it be through a leisurely walk in thepark, a weekend hike in the mountains, or a solitary moment spent by a babbling brook. These moments of immersion in nature offer a much-needed respite from the relentless pace of modern life, allowing us to recharge our batteries and rediscover our inner tranquility.中文回答：在大千世界的人类经历中，大自然鬼斧神工的影响力在我们的情绪、思想和行为中留下了错综复杂且深远的印记。
英语学术论文 lecture 2 练习部分答案
英语学术论文lecture 2 练习部分答案2.5 Reflection and Practice （Exercise）1.Please comment on the following titles or keywords and revise them ifnecessary.(1) A Research on the Artificial Neural Network (ANN) Applied in the Analysis of Structural MechanicsKey: Application of the Artificial Neural Network (ANN) in the Analysis of Structural Mechanics(2) Developing Computer Internet and Spread of Culture and InformationKey: Developing Computer Internet and Spreading of Culture and Information(3) Studies on Monoclonal Antibodies in Nuclear MedicineKey: Monoclonal Antibodies in Nuclear Medicine(4) An Investigation of Mechanisms of Retinal Damage from Chronic Laser RadiationKey: Mechanisms of Retinal Damage：Chronic Laser Radiation(5) Toward Commercialization of the Natural Gas VehiclesKey: Commercialization of the Natural Gas Vehicles(6) Can the Rate of Wash Load Be Predicted from the Bed Load Function?Key: Prediction of Wash Load Ratefrom the Bed Load Function?(7) Phase Equilibria between Fluorothene and Orange (a good title)(8)On Learning Foreign Languages and Cultural Background TeachingKey: Foreign Languages Learning and Cultural Background Teaching(9)Keywords: English, V ocabulary, Tendency(10)Keywords: Collocation Context ConnotationKey: Keywords: Collocation Context Connotation （单词间隔要大点) (Using larger space between words)2.The following title, affiliation, and are abridged from a journal article. Pleaselist the keywords for the paper based on the title and abstract.bine each of the groups of sentences below into a sound sentencecontaining one absolute.(1)Air resistance is neglected.The acceleration of gravity continually increases as the body approaches the earth.(答案：The acceleration of gravity continually increases as the body approaches the earth, air resistance being neglected. )(2)Almost all metals are good conductors.Silver is the best.(答案：Almost all metals are good conductors, silver being the best.)(3)In Group 1, we have hydrogen and the alkali(碱) metals.All of them have low density.(答案：In Group 1, we have hydrogen and the alkali metals,all of low density.)(4)There are many reasons for this.One of the reasons is that simulation allows the assessment of the potentialperformance before a newly designed system is operable.(答案：There are many reasons for this, among them the fact that simulation allows the assessment of the potential performance before a newly designed system is operable.)(5)Laser’s creation is thought to be one of today’s wonders.Laser’s nothing more than a light that differs from ordinary lights.(答案：Laser, its creation being thoug ht to be one of today’s wonders, i s nothing more than a light that differs from ordinary lights.)。
a study focusing on the
a study focusing on theA study focusing on the correlation between sleep quality and academic performance among college students has attracted widespread attention in recent years. This study aims to explore the impact of sleep quality on college students' academic performance and to provide practical suggestions for improving sleep quality.Sleep is an essential physiological process that plays a crucial role in maintaining physical and mental health. For college students, good sleep quality is not only beneficial for physical and mental development but also closely related to academic performance. Previous studies have suggested that sleep deprivation or poor sleep quality may negatively affect memory, concentration, and cognitive function, thereby impairing academic performance.To conduct this study, researchers adopted a questionnaire survey method to collect data from a sample of college students. The questionnaire included questions about sleep quality, sleep duration, sleep patterns, and academic performance. Additionally, participants were asked to provide information about their academic grades, study habits, and lifestyle factors that may affect sleep.The study found that there was a significant positive correlation between sleep quality and academic performance among college students. Students with better sleep quality tended to achieve higher grades and demonstrate better cognitive abilities. Furthermore, the study revealed that sleep duration, regularity, and the absence of sleep disturbances were important predictors of academic performance.Based on these findings, the researchers suggested that college students should pay attention to and improve their sleep quality. Some practical strategies include establishing a regular sleep schedule, creating a comfortable sleep environment, reducing the use of electronic devices before bed, engaging in regular exercise, and managing stress effectively. Additionally, educational institutions and parents can provide support and guidance to help students develop good sleep habits.In conclusion, this study emphasizes the significance of sleep quality for college students' academic performance. By raising awareness of the importance of sleep and providing practical suggestions for improving sleep quality, we hope to help college students achieve better academic outcomes while maintaining good physical and mental health. Further research is needed to explore the underlying mechanisms and develop more effective interventions strategies to optimize sleep and academic performance among college students.。
循环伏安法英文
循环伏安法英文Cyclic Voltammetry (CV) is an electrochemical technique used to study the redox behavior of materials in a solution. It involves applying a voltage potential to an electrode and measuring the resulting current response. This method is widely used in electrochemistry research to investigate reaction kinetics, electron transfer processes, and the stability of electroactive species.The experimental setup for CV consists of a working electrode, a reference electrode, and a counter electrode, all immersed in the electrolyte solution. The working electrode is the material of interest, where the redox reaction takes place. The reference electrode provides a fixed voltage reference, and the counter electrode completes the circuit. The potential difference between the working and reference electrode is varied in a triangular wave or staircase pattern, while the resulting current is measured.The CV technique provides several important parameters that can be extracted from the obtained voltammogram. The most fundamental parameter is the peak current (Ip), which represents the maximum current response during the forward or reverse scan of the potential. The peak potential (Ep) corresponds to the potential at which the peak current occurs. The peak current and potential can provide information on the ease of the redox reaction, the redox potential, and the kinetics of the electron transfer process. Another important parameter is the scan rate (v), which is the speed at which the potential is varied. By varying the scan rate, the rate of the electrochemical reaction and the stability of the electroactive species can be determined. The more stable thespecies, the less the current response will change with the scan rate. The diffusion coefficient (D) can also be determined from the CV experiment using the Randles-Sevcik equation, which relates the peak current to the scan rate and the concentration of the electroactive species.CV can also be used to study the adsorption and desorption processes occurring at an electrode surface. Adsorption/desorption peaks can be observed in the voltammogram, and their shape and position provide information about the adsorption kinetics, surface coverage, and stability of the adsorbed species. This information is valuable for understanding interfacial processes and designing surface modifications for applications such as sensors and catalysts. In summary, Cyclic Voltammetry is a powerful electrochemical technique for studying redox reactions, electron transfer kinetics, and adsorption processes. It provides valuable information about the electroactive species and their behavior in solution. By analyzing the obtained voltammogram and extracting parameters such as peak current, peak potential, scan rate, and diffusion coefficient, researchers can gain insights into the electrochemical properties and the stability of materials in various applications.。
215497098_Study_of_Native_Culture_Aphasia_and_Comp
Sino-US English Teaching, April 2023, Vol. 20, No. 4, 119-122doi:10.17265/1539-8072/2023.04.001 Study of Native Culture Aphasia and CompensationStrategies in English EducationLI SuzhenChina University of Petroleum (Beijing), Beijing, ChinaEnglish teaching in China has attached too much importance to the input of the target language culture, while neglectingour native culture. As a result, students cannot express Chinese culture in English, completely separating Chineseculture from English learning, leading to the serious native culture aphasia. This paper not only analyzes the reasonsfor this phenomenon from the aspects of curriculum setting, learning motivation, and teachers ’ quality, but alsoexplains the necessity of integrating Chinese native culture in English teaching. On this basis, effective solutions areput forward from the perspective of classroom teaching, textbook compilation, curriculum arrangement, and so on.Keywords: mother tongue aphasia, native culture, compensation strategies, communicative approachesIntroductionSince the popularization of English learning in China, English teaching has undergone rapid changes, the most prominent feature of which is the continuous improvement of teaching methods. Translation teaching method, in the early stage of English education, focused on the acquisition and training of pronunciation, grammar, and sentence patterns. In recent years, the communicative teaching method has been widely employed. English teaching is no longer limited to the form of language, but takes the cultivation of students ’ communicative ability as the key element in teaching. It emphasizes the function of inputting foreign language cultures —to provide background knowledge for language learning and stimulate students ’ interest in learning.In addition to affirming the achievements of English teaching, there arises a cause for concern —English teaching has a serious problem in terms of cultural input. All the input in teaching is British and American cultures, while there is no trace of any Chinese culture. Some students ’ English pronunciation and intonation are extremely standard, while the content of their talk seems empty. In the process of communication, they seldom take the initiative to express content related to Chinese culture, because their stock of Chinese culture is poor. Such “mother tongue cultural aphasia ” has attracted much attention in academic field in recent years.Professor Cong Cong (2000) pointed out that English teaching in our country has only strengthened the introduction of the material culture, institutional custom culture, and spiritual culture from the English-speaking Project source: China University of Petroleum (Beijing) Undergraduate Education Reform Project: Research on Compensation Strategies for Undergraduates ’ Lack of Mother Tongue Culture in Terms of Curricula of Integrated Ideology and Politics.LI Suzhen, M.A., associate professor, master tutor, School of Foreign Languages, China University of Petroleum (Beijing), Beijing, China.DA VID PUBLISHINGDSTUDY OF NATIVE CULTURE APHASIA AND COMPENSATION STRATEGIES120world, while the cultural background of communication—How to express Chinese culture in English—is absolutely ignored. Therefore, how to enable students to master the foreign language and understand British and American cultures while improving their abilities to express their native culture in English has become an important issue to be solved in China.Reasons for Mother Tongue Cultural AphasiaThe input of target language culture cannot be ignored in English teaching, because language and culture are inseparable. Language is the carrier of culture, and it is impossible to truly learn this language without understanding its culture. However, the input of target language culture in English teaching is not to make learners more and more “westernized”, but to provide them with background knowledge of cross-cultural communication so that they can achieve effective interaction between Chinese and foreign cultures. As far as college English teaching is concerned, the main reasons for this problem are as follows.Ignoring Chinese Culture in Curriculum ArrangementSome educators believe that mother tongue will inevitably encumber foreign language acquisition, so foreign language teaching should be deviate from the mother tongue as far as possible. This opinion has its theoretical basis, but inputting target language culture does not mean completely rejecting learners’ native language culture.English Departments in some universities apply the above teaching theory when setting courses, and offer courses with overlapping content centering on British and American culture. In the list of elective courses, there are only a handful courses related to Chinese culture. Such curriculum arrangement deprives students of the opportunity to learn Chinese culture in depth and comprehensively.Utilitarian Practice in English TestsMany students learn English just to deal with various exams. From elementary school to university, students have taken dozens of English tests: Cambridge Children’s English, PETS, IELTS, TOEFL, GRE, and participated in various English competitions. The purpose of taking these exams is obvious, that is, for further education, graduation, employment, and going abroad. And these exams basically do not involve Chinese culture. Thus, students naturally lose the motivation to learn Chinese culture.The Necessity of Emphasizing Mother Tongue Culture in English Teaching Larry A. Samovar, Richard E. Porter, Edwin R. McDaniel, and Carolyn Sexton Roy (2000, p. 253) point out that “Learners should know themselves and their own culture”, which is very important for successful cultural communication. Native language culture is an indispensable part of English education, and it plays an important role in improving students’ cognitive level and spreading Chinese culture. Therefore, Chinese culture cannot be ignored in English education in China.Increasing China’s Influence and Voice on the World StageIn the international community, the role of cultural soft power is becoming more and more significant. Zhu Lijia (2013) pointed out that strengthening China’s cultural soft power is of great importance to enhance China’s right to voice its opinion, and maintain and enhance national interests.STUDY OF NATIVE CULTURE APHASIA AND COMPENSATION STRATEGIES121With a long history, Chinese civilization has played an important role in the process of human development, and made indelible contributions to the advancement of world civilization. Chinese people have the responsibility to express their distinctive mother tongue culture and expand their influence in the world. To achieve this goal, it is necessary to strengthen the input and understanding of mother tongue culture.The Positive Transferring Effect of Mother Tongue on English LearningThe “distinction between basic interpersonal skills and language cognitive ability” and the “interdependence hypothesis between mother tongue and target language” proposed by linguistics professor Jim Cummins (1981) state that at a deep level, mother tongue and foreign language abilities are interdependent, and the relationship between language capacity sharing can be achieved. Therefore, on the whole, the positive impact of the mother tongue far exceeds the negative impact on foreign languages, and the improvement of the mother tongue level can help improve the foreign language learning effect. Cummins’ research shows that English learners’ cognition of their mother tongue can become the cognitive basis for their English acquisition and will play a positive role in the construction of the English language system (Wu & Wen, 2005).Professor Butzkamm (1993, p. 22), who studies English teaching methods in Germany, once discussed the role of the mother tongue in foreign language teaching, and made such an analogy: Mother tongue is not a coat that learners can take off and discard before they step into the foreign language classroom. It is impossible for learners to completely get rid of the influence of their mother tongue in the whole process of learning a foreign language, but they behave in different ways at each stage. The input hypothesis proposed by Krashen overemphasizes the importance of foreign language input, and believes that more input of foreign language can eliminate the negative transfer of native language. However, Guo Minghua (2002, pp. 24-27) has different opinion: “Especially in the environment where the native language is acquired, I am afraid that this is not just wishful thinking. It is very likely that the bath water was not thrown away, but the child was thrown out!”Native Language Culture Promoting Understanding of Foreign Language CultureIn terms of the relationship between culture and foreign language learning, Gao Yihong (1994) summarized three theories and expressed them with simple formulas: subtractive learning (1 - 1 = 0), additive learning (1 + 1 = 1), and productive learning (1 + 1 > 2). Subtractive learning means that learners should abandon their mother tongue culture while accepting foreign language culture in the process of learning a foreign language. Additive learning means that students separate the culture of the target language from the culture of their mother tongue when acquiring a foreign language. Productive learning is a complementary process, which means learners will combine the two languages and their cultural value systems in a reasonable way.Compensation Strategies for Mother Tongue Culture Aphasia in English Teaching Adding Chinese Culture Courses to the CurriculumChinese students learn their own culture systematically mainly in elementary and middle schools, and it basically comes to an end when they graduate from high school. At universities, most students no longer study courses related to Chinese culture, and these courses are severely marginalized. Insufficient investment ofSTUDY OF NATIVE CULTURE APHASIA AND COMPENSATION STRATEGIES122students in this area and lack of mother tongue knowledge ultimately affect the advancement of quality education. In order to change this situation, it is necessary to reform the structural arrangement of the curriculum at university to make it more rational and to give the Chinese culture curriculum its due status.Enhancing English Teachers’ Mother Tongue Cultural AwarenessThe cultural literacy of English teachers’ mother tongue will have a direct impact on students. Therefore, in addition to having a solid language foundation, English teachers also need to have dual cultural accomplishments, understand foreign cultures and be proficient in Chinese culture, and take on the important task of spreading Chinese culture. Apart from teaching students the language skills to express Chinese culture in the target language, English teachers should also provide students with materials related to Chinese culture as much as possible. Supplementing Teaching Materials With Mother Tongue CultureSupplementary materials related to Chinese culture should be appropriately added to English textbooks, for example, articles reflecting Chinese excellent culture, introduction about Chinese ethics and distinctive ideological traditions, and so on. In audio-visual teaching materials, English programs broadcast by CCTV that introduce Chinese culture can be applied as examples for Chinese students to express their own culture in English. Chinese students are more familiar with the content and relevant background knowledge in these programs, and they will be more willing to enjoy them.ConclusionMother tongue is not only a communication tool of a nation, but also a carrier of a nation’s traditional culture, moral concepts, and thinking patterns. Chinese students’ understanding of English vocabulary and culture cannot be completely separated from their mother tongue culture. It cannot make students fully assimilate to foreign cultures, nor can it make students simply pile up foreign culture and Chinese culture in cultural cognition. Identity, national self-esteem, and self-confidence, all these integrate the essence of mother tongue culture and foreign culture, and gradually cultivate cultural creativity.ReferencesButzkamm, W. (1993). Psycholinguistik des Fremdsprachenunterrichts. Tübingen: Francke.Cong, C. (Oct. 19th, 2000). “Chinese cultural aphasia”: The deficiency of English teaching in our country. Guangming Daily. Cummins, J. (1981). Empirical theoretical understandings of bilingual education. Journal of Education, 163(1), 16-29.Gao, Y. H. (1994). Study of productive bilingualism. Foreign Language Teaching and Research, 38(1), 59-64.Guo, M. H. (2002). On the role of mother tongue in foreign language classes. Foreign Languages and Their Teaching, 24(4), 24-27.Samovar, L. A., Porter, R. E., McDaniel, E. R., & Roy, C. S. (2000). Communication between cultures. Beijing: Foreign Language Teaching and Research Press.Wu, Z., & Wen, W. P. (2005). On the ECUP model for FLT. Shandong Foreign Language Teaching, 26(1), 70-74.Zhu, L. J. (2013). Understanding Chinese discourse by the world. People’s Tribune, 22(13), 64-65.。
多酸修饰的CuBi2O4
物 理 化 学 学 报Acta Phys. -Chim. Sin. 2024, 40 (2), 2304006 (1 of 2)Received: April 3, 2023; Revised: May 19, 2023; Accepted: May 22, 2023; Published online: June 2, 2023.*Correspondingauthors.Emails:*****************.cn(H.F.);*****************.cn(Q.L.)This work was supported by the National Key Research and Development Program of China (2021YFF0500700), National Natural Science Foundation of China (51976090, 52006101, 52006103), Scientific and Technological Innovation Project of Carbon Emission Peak and Carbon Neutrality of Jiangsu Province, China (BE2022024), and Natural Science Foundation of Jiangsu Province, China (BK20200491).国家重点研发计划(2021YFF0500700), 国家自然科学基金(51976090, 52006101, 52006103), 江苏省碳达峰碳中和科技创新项目(BE2022024)及江苏省自然科学基金(BK20200491)资助 © Editorial office of Acta Physico-Chimica Sinica[Article] doi: 10.3866/PKU.WHXB202304006 Improved Photoelectrochemical Performance by Polyoxometalate- Modified CuBi 2O 4/Mg-CuBi 2O 4 Homojunction PhotocathodeWencheng Fang, Dong Liu, Ying Zhang, Hao Feng *, Qiang Li *MIIT Key Laboratory of Thermal Control of Electronic Equipment, School of Energy and Power Engineering, Nanjing University of Science and Technology, Nanjing 210094, China.Abstract: Photoelectrochemical water splitting using semiconductormaterials is one of the most promising methods for converting solarenergy into chemical energy. Among the commonly usedsemiconductors, p-type CuBi 2O 4 is considered one of the most suitablephotocathode materials and can allow a theoretical photocurrent densityof about 20 mA ·cm −2 for photoelectrochemical water splitting. However,due to severe charge carrier recombination, the obtained photocurrentdensity is much lower than the theoretical value. Highly efficientphotoelectrochemical performance relies on fast charge carrierseparation and transport, and prompt reaction kinetics. In this study, wereport the development of a polyoxometalate-modified CuBi 2O 4/Mg-CuBi 2O 4 homojunction photocathode to improve both the bulk and interfacial charge carrier transport in the photocathode. For the bulk of the photocathode, the built-in electric field originating from the CuBi 2O 4/Mg-CuBi 2O 4 homojunction promotes the migration of photo-excited electrons on the conduction band from pure CuBi 2O 4 to Mg-doped CuBi 2O 4. Additionally, the electric field facilitates the transfer of holes from the valence band of Mg-doped CuBi 2O 4 to pure CuBi 2O 4. This directional transfer of both photo-excited electrons and holes plays a significant role in promoting separation and suppressing the recombination of the charge carriers. On the surface of the photocathode, the reduced polyoxometalate co-catalyst Ag 6[P 2W 18O 62] (AgP 2W 18) was used as a proton sponge to accelerate surface reaction kinetics and suppress carrier recombination. These synergistic effects improved the photo-generated charge carrier transfer and reaction kinetics. As a result, the novel photocathode displayed excellent photoelectrochemical properties, and the photocurrent density was observed to be −0.64 mA ·cm −2 at 0.3 V vs. RHE, which is better than that of −0.39 mA ·cm −2 for a pure photocathode. Furthermore, the novel photocathode had an applied bias photon-to-current efficiency (ABPE) higher than 0.19% at 0.3 V vs. RHE. In contrast, the pure photocathode had an ABPE of ~0.12% under the same conditions. Additionally, when H 2O 2 was used as an electron scavenger, the photocurrent density was −3 mA ·cm −2 at 0.3 V vs . RHE, which is an improvement of approximately 1.5 times compared to the pure photocathode. Furthermore, the charge separation and charge injection efficiency of the novel photocathode were significantly improved compared with the pure photocathode. The experimental results conclusively indicate that the formation of the CuBi 2O 4/Mg-CuBi 2O 4 homojunction and AgP 2W 18 modification played a significant role in the improved performance of the CuBi 2O 4 photocathode. The performance of the novel photocathode was comparable with the results reported in previous studies, demonstrating its promising potential in real applications. Key Words: CuBi 2O 4; Mg-doping; Photocathode; Polyoxometalate co-catalyst; Photoelectrochemistry物理化学学报 Acta Phys. -Chim. Sin.2024,40 (2), 2304006 (2 of 2)多酸修饰的CuBi2O4/Mg-CuBi2O4同质结光阴极用于高效光电化学转化方文诚，刘东，张莹，冯浩*，李强*南京理工大学，能源与动力工程学院，电子设备热控制工信部重点实验室，南京 210094摘要：CuBi2O4作为最有前景的光阴极材料之一，其理论光电流密度可达20 mA∙cm−2。
昆明“PEP”2024年11版小学六年级下册T卷英语第2单元暑期作业
昆明“PEP”2024年11版小学六年级下册英语第2单元暑期作业考试时间：80分钟（总分:110）B卷考试人：_________题号一二三四五总分得分一、综合题(共计100题)1、听力题：The Great Wall of China can be seen from ______ space.2、听力题：A ______ is a geographical feature that can act as a barrier.3、填空题：The __________ (大树) took many years to mature.4、What is the name of the fairy tale character with long hair?A. CinderellaB. Snow WhiteC. RapunzelD. Little Red Riding Hood5、填空题：My sister likes __________ games. (桌面)6、听力题：The phone is ringing ___. (loudly)7、听力题：The process of filtering separates solids from ______.8、听力题：The teacher is _____ the lesson. (starting)9、填空题：The writing system of ancient Egypt was called _____.My sister likes to keep a ____ (diary) every day.11、What do you call a young eagle?A. ChickB. EyassC. EagletD. Calf答案:C12、填空题：My neighbor has a ______ (宠物) snake that is very long.13、填空题：I like to _______ (听音乐) while studying.14、填空题：My mom is a __________ (护理人员).15、Which instrument has keys and is played by pressing them?A. GuitarB. ViolinC. PianoD. Drum答案:C16、填空题：Planting a variety of flowers can create a more interesting ______. (种植多样的花卉可以创造出更有趣的景观。
科技文章
Internet inequality:The relationship between high school students ’Internet use in different locations and their Internet self-ef ficacyLing Zhao a ,Yaobin Lu a ,*,Wayne Huang b ,1,Qiuhong Wang a ,2a School of Management,Huazhong University of Science and Technology,Wuhan 430074,China bCollege of Business,Ohio University,Athens,OH 45701,USAa r t i c l e i n f oArticle history:Received 10August 2009Received in revised form 9April 2010Accepted 13May 2010Keywords:Country-speci fic developmentsDistance education and telelearning Public spaces and computing Secondary educationa b s t r a c tThis research study utilized the framework of digital inequality proposed by DiMaggio and Hargittai (2001)to examine the relationships among the subdimensions of Internet inequality and their outcomes.We firstly investigated the relationships between constructs of technical apparatus,autonomy of use,availability of social support,variation of use at different locations of Internet access (school,home,Internet cafe,and combinations of these locations)and Internet self-ef ficacy (ISE).Then the relationships between ISE and high school students'exploratory behavior and academic were also investigated.The survey was developed from reliable instruments used in previous research to measure the following variables:Internet Self-Ef ficacy,Internet accessibility at home and school,exploratory behaviors,academic performance,study use,leisure use,parents in fluence,superior in fluence,and training support.Internet access at the Internet café,gender,and self-reported academic achievement were added to the student survey.Bivariate correlation and regression statistical analyses were conducted to find signi ficant relationships among these variables.ANOVA statistical analysis was used to find signi ficant differences among groups.Signi ficant findings indicated that digital inequality in Internet existed in school,home and Internet caféand students with Internet access at home had the highest level of ISE.Our study also showed that different dimension of Internet inequality had different relationships with ISE.Home Internet accessibility positively related to ISE.Availability of social support from school had a greater effect than that from home as parents in fluence did not associate with ISE.And last,the variation of use was also related to ISE.Leisure use at Internet café,leisure use at home and study use at home positively associated with ISE.In addition,at home and Internet café,the relationship between leisure use and ISE was stronger than that between study use and ISE.As to the outcome of ISE,high levels of ISE were positively related to exploratory behaviors,and for those students who used the Internet at school and home,higher ISE related to better academic performance.Ó2010Elsevier Ltd.All rights reserved.1.IntroductionThe phenomenon called ‘digital divide ’in Internet,however,is still severe in China and impedes fair Internet use by people.For example,the Internet penetration rate in China is lower than the average level of the world which was 21.1%(CNNIC,2008);in the middle of 2007,the Web users in the rural of China were only 29.9%of those in the urban regions,and the penetration rate in the rural was 5.1%that was relatively low (CNNIC,2007c ).Adolescent students,as a great portion of whole web users in China,should be given more attention,especially those high school students aged from 12to 18.More than 50%of the adolescent students which account for 35.8%of the web users in China are high school students (CNNIC,2007a ).It is reported that there are 21.11million senior high school students (36.4%)and 15.41million junior high school students (26.6%)which make part of the whole adolescent student web users (CNNIC,2007a ).Those adolescent students are usually described as the future of the nation in reports of the government,thus,examining the in fluences of digital divide in Internet on the next generation would be helpful to understand the actuality and the results would be referential for policies making.*Corresponding author.Tel.:þ862787558100.E-mail addresses:lingzhao@ (L.Zhao),luyb@ (Y.Lu),huangw@ (W.Huang),qhwang@ (Q.Wang).1Tel.:þ7405931801.2Tel.:þ86189********.Contents lists available at ScienceDirectComputers &Educationjournal homepage:/locate/compedu0360-1315/$–see front matter Ó2010Elsevier Ltd.All rights reserved.doi:10.1016/pedu.2010.05.010Computers &Education 55(2010)1405–1423The existing literature on digital divide at individual-level mainly focused on ICT (Information Communicate Technology)adoption.Some of the research addressed the social factors and demographic characteristics that are related to the adoption of ICT,e.g.,income,education,race,age,and gender etc.(Hoffman &Novak,1998;Bimber,2000;Katz &Rice,2002;Lenhart et al.,2003;Rice &Katz,2003).Some investigated the intention to use ICT from a cognitive prospective,e.g.,examining how Internet self-ef ficacy in fluence Internet use intention (Lam &Lee,2005),or using the Theory of Planned Behavior to investigate the continued Internet use intention (Eastin &LaRose,2000;Hsieh,Rai,&Keil,2008).Others examined the effects of government efforts (Hsieh et al.,2008;Jaeger,2004),and social support or training (Lam &Lee,2005)on bridging the digital gap.These studies contribute to our understanding of digital divide,however,they are subject to limitations.First,few of the studies on digital divide examine the relationship between IT usage and its outcomes.Digital divide may lead to various outcomes.For instance,Fairlie (2005)found that home computer ownership increased the likelihood of school enrollment for those teenagers who had not graduated from high school,which implies that digital divide could impact educational outcomes.Digital divide was also found to affect the self-directed learning of secondary schools students (Wei,Teo,Chan,&Tan,2009).Thus,as DiMaggio and Hargittai (2001)suggested,instead of documenting the digital divide,an urgent issue is to address “the relationship between the use of these technologies and valued individual-level outcomes ”.Second,some important dimensions of digital divide are missing.According to the framework of digital divide proposed by DiMaggio and Hargittai (2001),digital divide contained five dimensions in terms of access and quality of access,autonomy of use,social support,usage and skill.But most of the existing studies examined only one or two dimensions of Internet inequality at the same time (Shaw &Gant,2002;Novak,Hoffman,&Venkatesh,1998).Measuring the digital divide from different dimensions may facilitate a holistic understanding on its driving forces and outcomes.Thirdly,the differences as results from the locations where individuals access ICT are generally ignored in the existing studies.While Researchers have examined the in fluences of different locations on use of IT applications (Levine &Donitsa-Schmidt,1998),the studies on Internet use were limited to the locations of school and home (Abrams,1997;Sax,Astin,Korn,&Mahoney,1998;Service,1997),with less concern on other sites.Hoffman and Novak (1999)suggested that it was necessary to under-stand Internet use outside the home particularly for those without home access to the Internet.As school,home and Internet caféare main locations for high school students to use the Internet,digital inequality may exist in these locations.In urban areas,students can use the Internet either at home or at school,but students in rural areas may have to use the Internet at Internet cafédue to insuf ficient facilities at school or unaffordable expenses for Internet access at home.Even in the same area,Internet usage of the students may differ in the level of infrastructure or training that their schools provide.Hence,locations provide different accessibility and quality,which may affect the Internet digital inequality re flected at different locations.As the Internet becomes an integral part of our daily life and the critical infrastructure for business and economy,it calls for a cross-sectional view of the Internet inequality along various dimensions.With the cooperation of Xiangfan Bureau of Education,we conducted a project lasted from January to July 2008which attempted to get a better understanding of high school students ’Internet using in city of Xiangfan.In particular,we address the following research questions in this paper:1.How is the Internet inequality re flected at home,school or Internet caféassociated with the Internet self-ef ficacy for high school students?2.How does Internet inequality associate with high school students ’exploratory behavior of Internet use and their academic performance?This study contributes to the literature of digital divide as following.Firstly,we studied the effects of Internet inequality at different locations including home,school and Internet café,while the Internet use at Internet caféwas seldom researched in previous studies.In some developing countries like China,Internet caféis considered as one important location to use the Internet and a place where high school students most often visit.According to the report of CNNIC (2008),about 57.3%of the student web users in senior high school and 39.3%in junior high school use the Internet at Internet café,and the proportion is even higher in rural areas.In China,Internet caféappeared in the 1990s,and have developed greatly in the past two decades.Internet caféplays an important role in narrowing the digital gap as it provides chances for many people to know the Internet for the first time when they can ’t afford a computer at home (Hong &Huang,2005).However,problems rise along with the development of Internet café.For example,in some rural areas,even minors are allowed to go to the Internet caféwithout their guardians ’permission and against the forbiddance by law.Without effective management and supervision by teachers and parents,adolescent students may be immersed in online gaming,chatting or other online entertainment,and even become addicted (Hille,2009).Meanwhile,adolescent students are exposed to pornographic and violent contents flooding the Internet.As these problems are not particular to China,conducting research in the context of Internet caféis necessary and important.The further comparison across the three locations would provide clearer comprehension on the status quo of each location and their impacts on high school students.Secondly,we quantitatively examined related dimensions of Internet inequality.Previous research on Internet inequality usually focused on describing the extent of digital divide and summarized findings or derived implications based on atheoretical analysis (DiMaggio,Hargittai,Neuman,&Robinson,2001;Haan,2004).Thus,our study could be a helpful attempt to understand the “how and why ”parts of this phenomenon,as suggested by Hsieh et al.(2008).Thirdly,we examined the outcomes caused by digital inequality,such as academic performance and high school students ’online exploratory behaviors which refers to the extended Internet usage primarily stimulated by intrinsic reasons (Baumgartner &Steenkamp,1996).Surveys on the Internet development from CNNIC every year provide information on conditions of Internet infrastructure and web users ’characteristics,etc,but do not investigate the relationships between digital divide and its outcomes (CNNIC,2007a;CNNIC,2008).Just as we mentioned before,most research on digital divide also focused on the description or causes of this phenomenon,but not its effects (Wang &Li,2006;Xie,2008).The remaining sections of the paper are organized as follows.Section 2presents the review of the related literature.In Section 3,we propose the research framework and research model with detailed explanation about the hypotheses.In Section 4,we discuss the research methodology including the processes of instrument development,data collection,and analysis,followed by the discussion of results in Section 5.Finally,we conclude this paper with discussion on the limitations,implications in Section 6.L.Zhao et al./Computers &Education 55(2010)1405–14231406L.Zhao et al./Computers&Education55(2010)1405–14231407 2.Literature review2.1.From digital divide to digital inequalityThe Internet has existed for several decades and gets great development since the second part of1990s.By the end of March2008,there are more than14billions Internet users in the world with a growth rate of290%between2000and2008,and the world Internet penetration has reached21.1%(Stats,2008).Undoubtedly,as technologies usually develop with the rising of social problems,the Internet would not be an exception given its rapid growth.Among the emerging problems,digital divide in the Internet is regarded as one of the most important issue,and has attracted great attention from governments,world organizations and academia(Andrés,Cuberes,Diouf,&Serebrisky,2007; Cuervo&Menéndez,2006;Gore,1998).Digital divide is also called digital gap,or digital division.Though the origin is uncertain and ambiguous,a consensus on this term that it wasfirst formally defined by the US Department of Commerce’s National Telecommunications and Information Administration(NTIA)forms among researchers.It was defined as“the divide between those with access to new technologies and those without”(NTIA,1999).In the early period of Internet diffusion,people hardly got accesses to Internet because of low income or weak telecommunication infrastructure investment.Even nowadays,access limited by disadvantaged positions,such as low income,low educational level or minority would obstruct those people to use the Internet.As more and more people get the chance to use these technologies with the development of ICT, the inequality in access seems to be inadequate to describe the content of‘digital divide’(DiMaggio&Hargittai,2001;Gunkel,2003). Though access availability indeed affects the usage,the problem seems not to be resolved easily through introducing technology to disadvantaged communities.Besides inequality in access between those haves and have-nots,researchers realize that gaps of other dimensions,such as skills and training,should also exist among those people who already have access to the technology(Hargittai,2002). Thus,Internet access is no longer the only measure of the inclusion of digital divide.Attewell(2001)proposed that digital divide comprised two dimensions,thefirst dimension referred to access to ICT,and the second one related to the ways people used ICT.From a research on the digital divide in Canadian schools,differences in use patterns of information technology were found among high school students with accesses to computers(Looker&Thiessen,2003).In other studies,skill was considered as the second level of digital divide(Dewan&Riggins,2005;Hargittai,2002).The Organization for Economic Cooperation and Development(OECD,2001)also defined digital divide as“the gap between individuals,households,businesses and geographic areas at different socioeconomic levels with regard both to their opportunities to access information and communication technologies and to their use of the Internet for a wide variety of activities”.DiMaggio and Hargittai(2001)proposed the concept of digital inequality,which“refers not just to differences in access”,but also to “inequality among the Internet users in the extent to which they are able to reap benefits from their use of the technology”.In current study, we adopted their framework that containedfive dimensions:1)Inequality in technical apparatus refers to the availability of suitable equipments used to access the Web,such as high-speed computers,and necessary hardware,software and connections.2)Inequality in autonomy of use refers to the control people exercised over their use of the Internet.This dimension reflects the limitationspeople would face when they are using the Web at different locations,such as theflexibility to use the Internet,or the permission of use at school or work places.3)Inequality in skill refers to the diversity in“Internet competence”,which is defined as“the capacity to respond pragmatically andintuitively to challenges and opportunities in a manner that exploits the Internet’s potential”(DiMaggio and Hargittai,2001).4)Inequality in the availability of social support refers to the technical assistance and emotional support from others,including colleagues,teachers,family members,friends and so on.5)Variation in use refers to the different use patterns,such as the purposes and main activities when using the Internet.2.2.Internet self-efficacyThe concept of self-efficacy,which comes from the Social Cognitive Theory,refers to the belief that one has the capability to perform a task(Bandura,1977).Bandura(1986)defined it as“people’s judgment of their capabilities to organize and execute courses of action required to attain designated types of performances”.It should be pointed out that self-efficacy reflects the perception of one’s capability, not the actual skills one has(Bandura,1986).As self-efficacy is considered as the predictor of actual behaviors(Bandura,1982),this cognitive component is widely applied in research on the use of ICTs.For example,previous research studied the effects of computer self-efficacy(CSE)on computer use,which was defined as an individual assessment of his ability to use a computer(Compeau&Higgins,1995).With the development of the Internet,Internet self-efficacy (ISE)was then used to describe individual judgment of his capability to use the Internet(Torkzadeh&Dyke,2001).Internet self-efficacy is an important concept in the research of ICT,and it is usually used to represent the skill dimension as actual skill which is comparatively difficult to measure.Internet self-efficacy was used to investigate the effects of training(Torkzadeh&Dyke,2002;Torkzadeh,Chang,&Demirhan,2006), the new technology or new service adoption(Hsu&Chiu,2004;Lam&Lee,2005),and Internet use(Eastin&LaRose,2000).In the research of Hsu and Chiu(2004),they distinguished two kinds of ISE:general Internet self-efficacy(GISE)and Web-specific self-efficacy(WSE).The former was trait-oriented efficacy which referred to“an individual’s judgment of efficacy across multiple Internet application domains”,whereas the latter was state-oriented efficacy which referred to“an individual’s perception of efficacy in using a specific WWW application within the domain of general Internet computing”(Hsu&Chiu,2004).For example,“I can use the Internet to get information I need”refers to the GISE,however,“I can buy a book from the successfully”refers to the WSE.Internet self-efficacy in our study refers to the general Internet self-efficacy(GISE)as one of our research aims is to investigate the students’general judgments of their ability to perform some encompassing tasks by using the Internet rather than the ability to use a specific application or service on the Web.Though researchers have developed instruments to measure the Internet self-ef ficacy,there are still limitations in these scales.In the widely cited paper by Eastin and LaRose (2000),the items they used to measure ISE did not represent the activities involved in Web use.Torkzadeh and Dyke (2001)used 17items to measure ISE in terms of sur fing/browsing,encryption/decryption and system manipulation.However,this scale also has limitations,for example,some items of their scale,such as “I feel con fident encrypting/decrypting e-mail messages ”,are not among the general activities when using the ter,Hsu and Chiu (2004)adapted this instrument and developed a 19-item scale to measure GISE in terms of browsing/search,message exchange and computer manipulations,which might well re flect the content of ISE.Thus we adapted the scale of GISE from Hsu and Chiu (2004)in our study.3.Research framework and hypothesesFig.1presents our research framework based upon the research of DiMaggio and Hargittai (2001).In this framework,we propose that four dimensions of digital inequality,including technical apparatus,autonomy of use,availability of social support and variation of use,associate with the skill dimension,and the digital inequality would further result in different level of academic performance and exploratory behavior in Internet use.According to the de finitions of the five dimensions,we propose the representative variables that measure each dimension and summarize them in Table 1.Applying this framework in our study,we further present the research model with control variables in Fig.2.The details would be explained in the following content.3.1.Technical apparatus and Internet self-ef ficacyTechnical apparatus refers to the possession and quality of equipment.The level of skills may differ in students with or without the access availability to the Internet.Students with access to the Internet have the chance to learn how to use it and gain experience.Although both the possession and quality of equipment are the measurements of the technical apparatus,we only consider the “haves and have-nots ”aspect.This is because with the advancement in information technology,connection to the Internet is just a basic requirement for most of the computers and thus there is much less difference in quality.Theoretically,enactive mastery,or performance accomplishments is considered one of the most in fluential sources of self-ef ficacy (Bandura,1982).There are also evidences from empirical studies indicating that experience is signi ficantly related to skills.For example,knowledge of computers was signi ficantly related to the access to home computer and the usage of computer (Geissler &Horridge,1993).In the research on computer self-ef ficacy,prior computer experience was found as a predictor of computer self-ef ficacy in different IT applications (Agarwal,Sambamurthy,&Stair,2000).Wei et al.(2009)proved that the availability of school resources signi ficantly affected computer self-ef ficacy of secondary schools students.In the research of Eastin &LaRose (2000),previous experience was also proved to be the strongest predictor of Internet self-ef ficacy.(Eastin &LaRose,2000).High school students with the chance to use the Internet at more locations,they may get more familiar with the Internet and become more skilled at the manipulation of the Internet.Thus we hypothesize that:H1a :The more sources to access the Internet,the higher is the Internet self-ef ficacy.Regional development level is another important cause of digital divide,as it greatly impacts the regional development of tele-communication infrastructures for the Internet,the household income and education level.Areas with higher development levels may have better infrastructures for accessing the Internet than those with lower levels.According to the report from CNNIC,provinces with higher levels of development usually occupy more basic resources of the Internet than other ones,such as the computers connected to Internet,IP addresses,bandwidth and so on (CNNIC,2008).In addition,households in developed areas are more likely with higher income and to afford the Internet access at home.In previous studies,income was always signi ficantly and positively related to the ownership of computers and the Internet access (Hargittai,2003;Wasserman &Richmond-Abbott,2005).Coley,Cradler,and Engel (1997)also found that education level and income are strongly correlated to the Internet access.Parents with higher education are more likely to realize the importance of the Internet,and they may use the Internet at home for the purposes of work or entertainment.Then we have:H1b :The higher the level of development in the area,the more sources students would have to access the Internet,and the higher is their Internet self-ef ficacy.H1c :The higher the education level of parents,the more likely the family owns access to the Internet.Fig.1.Research Framework (Adapted from DiMaggio and Hargittai [17]).L.Zhao et al./Computers &Education 55(2010)1405–142314083.2.Autonomy of use and internet self-ef ficacyInternet accessibility refers to the autonomy of using the Internet at different locations.For high school students in China,there are many constraints to use the Internet freely at school or home.The main reason probably is the intensive competition for high school students to enter senior schools or universities.Because of this pressure,teachers or parents may not support students using the Internet and even consider it harmful to their schoolwork.Based upon our observation and interviews with teachers and students in high school,we found that computer-or Internet-related courses at school were not compulsory,and sometimes these courses were even canceled or replaced by other courses,such as Chinese or mathematics for those graduating students both in junior and senior schools.Constraints to access the Internet may be also due to the insuf ficient resources.The statistics of the Internet infrastructure in the surveyed schools shows that the average number of computers per capita for these schools is as low as 0.24.However,among those high schools,some are authorized as “the model of high school ”which refers to the high school with reputation on various aspects and higher education quality.Those models of high schools may get more support from the ministry of education including the resources to access the Internet.Meanwhile,as the adminis-tration and operation in these schools are more normative,students would less likely to be deprived of using the Internet when they ought to.To compare the difference between model and non-model schools,we propose that:H2:Internet accessibility at the models of high schools would be higher than those non-model high schools.Generally speaking,high Internet accessibility provides a convenient environment for the students to learn how to use the Internet.Higher Internet accessibility implies that students are more likely to use the Internet as they wish,whereas lower Internet accessibility implies Internet use may be inhibited by many factors.As exposure to computer-related devices was found to determine one ’s attitude toward computers (Brown,Brown,&Baack,1988),we might believe that more exposure to the Internet will indicate more practice on Internet use,and further enhance the familiarity of the students with the Internet.It has to be pointed out that the Internet accessibility at Internet caféis different from at home or school.As students are rarely intervened by others at the Internet café,thus we consider that the extent to which students could access to the Internet easily at this location is re flected by whether minors are forbidden to use the Internet at Internet café.We hypothesize that Internet accessibility would positively promote the skills to use the Internet.H3a :Internet accessibility at school would be positively related to Internet self-ef ficacy of high school students.H3b :Internet accessibility at home would be positively related to Internet self-ef ficacy of high school students.H3c :Internet accessibility at Internet caféwould be positively related to Internet self-ef ficacy of high school students.3.3.Availability of social support and internet self-ef ficacySocial support includes technical supports and mental encouragements for Internet use.At school,social support refers to the training courses and the encouragement from teachers on the use of Internet.Training is important to improve skills.The report from CNNIC reveales that,the lower penetration rate in these rural regions is due to the lack of equipments and training (CNNIC,2007a ).In the research on computer and Internet use,training was proved as an importance approach to improve computer self-ef ficacy (Compeau &Higgins,1995;Table 1Source:DiMaggio and Hargittai [17].Fig.2.Research Model.L.Zhao et al./Computers &Education 55(2010)1405–14231409。
学术端正英语作文
学术端正英语作文Certainly, here's a brief academic English essay following your guidelines:---。
In contemporary society, the intersection of technology and culture is undeniable. From the proliferation of social media to the advent of artificial intelligence, our lives are increasingly intertwined with digital innovation. Yet, amidst this rapid transformation, questions about the ethical implications persist.Consider the phenomenon of online privacy. With each click and keystroke, individuals generate vast amounts of data, often without full awareness of how it is collected and utilized. This raises concerns about surveillance capitalism and the commodification of personal information.Moving beyond the digital realm, let us examine therole of language in shaping our perceptions of reality. Language is not merely a tool for communication but a lens through which we interpret the world. The nuances of linguistic expression reflect cultural values, power dynamics, and societal norms.In the realm of education, the concept of "lifelong learning" has gained traction in recent years. This paradigm shift acknowledges that learning is not confined to formal institutions but is a continuous process that occurs throughout one's life. Embracing this philosophy empowers individuals to adapt to an ever-changing world.Shifting gears, let us explore the relationship between art and politics. Throughout history, artists have used their craft to challenge authority, provoke thought, and inspire social change. Whether through paintings, literature, or music, art has the power to transcend boundaries and ignite movements.Turning our attention to environmental sustainability, it is clear that urgent action is needed to address climatechange. The exploitation of natural resources and the proliferation of pollution threaten the delicate balance of ecosystems worldwide. Solutions must be interdisciplinary, involving science, policy, and grassroots activism.In conclusion, the complex interplay of technology, culture, and ethics underscores the need for critical inquiry and thoughtful engagement. By interrogating assumptions, embracing diversity, and advocating for positive change, we can navigate the challenges of the 21st century with resilience and integrity.。
西安2024年10版小学三年级上册第3次英语第四单元测验试卷
西安2024年10版小学三年级上册英语第四单元测验试卷考试时间：80分钟（总分:120）A卷考试人：_________题号一二三四五总分得分一、综合题(共计100题)1、小鲸鱼) swims in the deep ocean. 填空题：The ___2、填空题：My __________ (玩具名) can __________ (动词) if I shake it.3、What is the largest moon of Saturn called?A. TitanB. GanymedeC. CallistoD. Europa4、听力题：I have _____ friends at school. (many/few/one)5、听力题：In a chemical reaction, the substances that are produced are called _____.6、填空题：The __________ was a period of exploration and colonization. (大航海时代)7、听力题：The cat is _______ (sleeping) on the couch.8、What is the name of the ancient Greek philosopher who proposed the heliocentric model?A. PtolemyB. AristotleC. CopernicusD. Galileo9、Which planet is known for having a very thick atmosphere?A. MercuryB. VenusC. EarthD. Mars10、填空题：A __________ (气泡) forms when gas is released during a reaction.11、What is the name of the famous fictional detective created by Sir Arthur Conan Doyle?A. Hercule PoirotB. Sherlock HolmesC. Sam SpadeD. Philip Marlowe答案: B12、Which body part is used for hearing?A. EyesB. EarsC. NoseD. Mouth答案:B13、What is the national animal of the United States?a. Eagleb. Bearc. Liond. Wolf答案:a14、What is the main purpose of a refrigerator?A. To cook foodB. To freeze foodC. To cool foodD. To heat food答案: C15、听力题：My favorite season is ______ (winter).16、听力填空题：I admire people who follow their passions. They inspire me to pursue my own interests and dreams. I hope to find my passion in __________.17、What is the capital of Germany?A. BerlinB. MunichC. FrankfurtD. Hamburg18、填空题：I enjoy learning new languages because it helps me communicate with ________ (不同的人).19、What is the opposite of "fast"?A. QuickB. SlowC. RapidD. Speedy答案: B20、填空题：I love to watch ______ movies with my family.21、听力题：You can find _______ in the desert.22、填空题：My cousin has a _________ (玩具恐龙) that roars loudly.23、听力题：The clock says it is ________ o'clock.24、填空题：A starfish has five ______ (手臂).25、填空题：My grandma gave me a _________ (手工制作的玩具) that is very special.26、听力题：The ______ is wearing a blue dress.27、填空题：The invention of the telephone revolutionized ________ (沟通).28、听力题：The ________ (lizard) is sunbathing on the rock.29、What is the largest mammal?A. ElephantB. Blue WhaleC. GiraffeD. Hippo30、What do you call the frozen form of water?A. SteamB. LiquidC. IceD. Vapor答案：C31、填空题：I like to go ______ (滑冰) at the rink with my friends.32、听力题：She is reading a ________ story.33、填空题：The rabbit has a cute ______ (鼻子).34、What do you call a person who writes books?A. ArtistB. AuthorC. MusicianD. Chef答案:B35、填空题：The discovery of ________ has had a profound impact on environmental science.36、听力题：The capital of Timor-Leste is _______.37、填空题：My cousin is very __________. (有趣)38、填空题：I like to visit ______ during spring break.39、How many sides does a pentagon have?A. 4B. 5C. 6D. 7答案:B40、听力题：The ____ has a thick, warm coat for cold climates.41、What is the name of the famous animal in the story of "The Tortoise and the Hare"?A. RabbitB. TortoiseC. FoxD. Lion答案:A42、听力题：A substance that changes color when pH changes is called an ______.43、选择题：What do we call a story that is told through pictures?A. ComicB. Graphic NovelC. Picture BookD. All of the above44、听力填空题：My favorite season is __________ because __________. I love doing activities like __________ during this time. It makes me feel __________.45、填空题：I received a big ____ for my birthday. (玩具名称)46、What is the capital of Spain?A. BarcelonaB. ValenciaC. MadridD. Seville答案:C. Madrid47、What is the name of the famous wizard in J.K. Rowling's books?A. GandalfB. DumbledoreC. MerlinD. Harry Potter答案: D48、What do we call a book that tells a true story?A. FictionB. NovelC. BiographyD. Fantasy49、What do you call the process of making bread?A. BakingB. BoilingC. FryingD. Grilling50、填空题：The tortoise is slower than the ________________ (兔子).51、填空题：The ______ (生态恢复) can take many forms.52、听力题：The _______ provides shelter and food for wildlife.53、填空题：The ________ (植物种类) offers variety.54、听力题：We like to _____ (travel/study) during summer.55、填空题：The ______ (种族) of plants varies worldwide.56、What is the capital of the United Kingdom?A. LondonB. EdinburghC. DublinD. Cardiff答案:A57、What do we call the animal that lives in a hive?A. AntB. BeeC. WaspD. Fly答案:B58、What do you call an animal that eats plants?A. CarnivoreB. HerbivoreC. OmnivoreD. Scavenger59、听力题：The kitten is very ______ (curious).60、What do you call the part of a tree that grows above the ground?A. RootsB. TrunkC. LeavesD. Branches答案: B61、填空题：I have a toy ________ that I built.62、填空题：He likes to _______ (draw/paint) pictures.63、What is the capital of Italy?A. VeniceB. FlorenceC. RomeD. Naples答案:C64、听力题：Leaves change color in _______.65、听力题：A magnet can attract ______ (metal) objects.66、填空题：We will have a ________ (聚会) for the holidays.67、听力填空题：At school, I have many friends. We often play __________ together during recess. My best friend is __________. We enjoy __________ and __________ after school.68、听力题：The chemical symbol for technetium is _______.69、听力题：The chemical formula for magnesium sulfate is _____.70、What is the primary reason we need to drink water?A. To feel fullB. To stay hydratedC. To wash our handsD. To eat food答案:B71、填空题：The eagle is a _______ (伟大的) hunter.72、填空题：My grandmother makes the best __________. (蛋糕)73、填空题：The __________ (大航海时代) changed global trade routes.74、听力题：A telescope helps us see distant ______.75、听力题：Oxygen is necessary for ______.76、听力题：The boy plays the ________.77、What is the name of the fairy tale character who lived in a shoe?a. Jackb. Jillc. Old Mother Hubbardd. Old Woman Who Lived in a Shoe答案:D78、plate tectonics) explain how continents move. 填空题：The ____79、填空题：The ________ was a significant treaty that ended a major conflict.80、选择题：What is the name of the famous explorer who sailed around the world?A. Ferdinand MagellanB. Christopher ColumbusC. Marco PoloD. Vasco da Gama81、听力题：A _____ can be millions of light-years away from Earth.82、填空题：The _______ (小狼) howls at the moon during the night.83、Which bird is known for its colorful feathers?A. PenguinB. SparrowC. PeacockD. Pigeon答案:C84、听力题：A dog loves to chase a _____.85、 to play with her toy _____ (车). 填空题：She love86、听力题：The chemical formula for silicate is ______.87、填空题：The frog's skin helps it breathe through ______ (皮肤).88、What color are bananas when they are ripe?A. GreenB. YellowC. RedD. Blue89、填空题：The _______ (猫) is known for its curious nature.90、填空题：I have a big collection of _____ (乐高).91、填空题：The ancient Egyptians used hieroglyphics for ______ (书写).92、How many hearts does an octopus have?A. OneB. TwoC. ThreeD. Four93、听力题：__________ are found in the center of an atom.94、听力题：I want to ___ (learn/teach) English.95、填空题：A hamster's cheeks can hold a lot of ______ (食物).96、What is the name of the superhero who wears a cape and can fly?A. Spider-ManB. BatmanC. SupermanD. Iron Man答案:C97、What is the term for a baby rabbit?A. KittenB. BunnyC. PupD. Foal答案: B. Bunny98、听力题：The sun is _____ (shining/raining) today.99、选择题：What is the opposite of sweet?A. SourB. BitterC. SaltyD. Spicy100、听力题：The _____ (moon/sun) is bright.。
襄阳“PEP”2024年11版小学4年级上册第四次英语第三单元综合卷[有答案]
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襄阳“PEP”2024年11版小学4年级上册英语第三单元综合卷[有答案]考试时间：100分钟（总分:120）B卷考试人：_________题号一二三四五总分得分一、综合题(共计100题)1、听力题：The chemical formula for calcium phosphate is __________.2、听力题：My uncle is a ______. He enjoys traveling abroad.3、填空题：I like to make crafts with ________.4、填空题：A ______ (猴子) loves bananas and climbing trees.5、填空题：The _______ (鸭子) waddles around.6、听力题：In a chemical reaction, substances are called ________.7、听力题：The flowers smell very ___ (sweet).8、填空题：My favorite animal is a _______ (猫), and I think they are very _______ (可爱).9、听力题：The _______ can be a source of inspiration for your artwork.10、听力题：My cousin plays the ____ (clarinet) in the band.A mouse can fit through very _______ (小) spaces.12、听力题：The park has ______ (many) fun swings.13、填空题：The capital city of Sri Lanka is ________ (斯里兰卡的首都城市是________).14、trial Revolution began in the late ________ (18世纪). 填空题：The Indu15、What is the main gas that plants take in?A. OxygenB. Carbon DioxideC. NitrogenD. Hydrogen16、填空题：My uncle gave me a rare _________ (玩具) from his collection.17、What is the capital of Kazakhstan?a. Almatyb. Nur-Sultanc. Shymkentd. Aktobe答案:b18、填空题：The _______ (Impeachment) is a process used to remove a president from office.19、What is the capital of Nigeria?A. AbujaB. LagosC. KanoD. Port Harcourt答案:A20、听力题：A __________ is a small area of land surrounded by water.21、填空题：The _____ (carnivorous) plants trap insects for nutrients.22、填空题：My favorite hobby is ______.The ______ is high in the sky. (moon)24、填空题：A garden can have both ______ (花卉) and vegetables.25、听力题：A chemical reaction can produce gases, solids, or ______.26、填空题：I like to explore the ______ (城市) and discover new places.27、ts have ______ (刺). 填空题：Some pla28、填空题：A ______ (蜗牛) carries its home on its back.29、听力题：The chemical formula for carbon dioxide is __________.30、听力题：The teacher tells a ______ (story).31、What is the capital of El Salvador?A. San SalvadorB. TegucigalpaC. ManaguaD. Guatemala City答案: A. San Salvador32、Which instrument has strings and is played by plucking?A. HarpB. FluteC. TrumpetD. Trombone答案: A33、What is 20 + 30?A. 50B. 60C. 70D. 80答案:A34、What is the main ingredient in bread?A. SugarB. FlourC. SaltD. Water35、选择题：What do we call the time of year when plants bloom?A. WinterB. SpringC. SummerD. Fall36、What do we call a story about someone's life?A. AutobiographyB. BiographyC. NovelD. Fiction答案:B37、听力题：The study of ancient geological formations is known as ______.38、填空题：My cousin is studying to be a __________ (医生).39、听力题：The main gas produced during photosynthesis is ______.40、选择题：What do we call a person who studies the past?A. HistorianB. ArchaeologistC. AnthropologistD. Sociologist41、What is the name of the famous artist known for his work on the Sistine Chapel?A. MichelangeloB. Leonardo da VinciC. RaphaelD. Caravaggio答案: A42、Which is not a primary color?A. RedB. BlueC. YellowD. Green43、What do you call a person who travels in space?A. AstronautB. PilotC. ScientistD. Explorer答案: A44、听力题：Elements in the same column of the periodic table have similar _______.45、填空题：The __________ (历史的演讲) can inspire movements.46、D. WaterWhich shape has three sides?A. SquareB. TriangleC. Circle47、What is the primary ingredient in salsa?A. TomatoB. OnionC. PepperD. Cilantro48、填空题：A _____ (植物保护组织) works towards conservation goals.49、选择题：What is the name of the animal that can live both in water and on land?A. FishB. FrogC. LizardD. Turtle50、听力题：The puppy is ______ in the sun. (sleeping)51、What is the smallest unit of life?A. OrganB. CellC. TissueD. Organism答案: B52、canyon) can be formed by river erosion. 填空题：The ____53、听力题：The process of combustion requires __________ and fuel.54、听力题：My dad _____ a new car last week. (bought)55、填空题：He is my _____ (好友) from childhood.56、填空题：A _____ (小鸭) loves to swim with its family.57、填空题：I want to visit ________ (纽约) someday.58、听力题：A ______ is a type of reaction that occurs when energy is absorbed.59、填空题：My _____ (玩具枪) is for playtime.60、填空题：My ___ (小狗) enjoys going for walks.61、Which of these is a vegetable?A. BananaB. TomatoC. GrapeD. Mango答案: B62、填空题：My dad, ______ (我爸爸), loves to tell stories about his childhood.63、What is the common name for a feline pet?A. DogB. CatC. RabbitD. Guinea Pig答案: B64、What do we call a person who studies geography?A. GeographerB. HistorianC. BiologistD. Anthropologist答案: A65、听力题：The chemical symbol for neodymium is _______.66、填空题：We celebrate New Year in ______.67、What is the name of the holiday celebrated on July 4th in the USA?A. Memorial DayB. Independence DayC. Labor DayD. Thanksgiving68、What do you call the place where you go to see movies?A. LibraryB. TheaterC. MallD. Park答案:B69、填空题：Did you know that a _______ (小海豚) is very intelligent?70、填空题：The artist creates beautiful _____ (壁画).71、What do you call the place where you buy books?A. LibraryB. BookstoreC. SchoolD. Office答案:B72、填空题：A lizard can shed its tail to escape ______ (捕食者).73、听力题：An endothermic reaction absorbs ______.74、填空题：A cow gives us ________________ (牛奶).75、听力题：The atomic structure of an element is determined by its ______.76、听力题：A chemical reaction that occurs in the presence of oxygen is called a ______ reaction.77、选择题：What is the name of the famous dinosaur known for its short arms?A. T-RexB. VelociraptorC. StegosaurusD. Brachiosaurus78、What do flowers need to grow?A. WaterB. SandC. MetalD. Plastic79、What is the term for a large body of saltwater?A. LakeB. OceanC. RiverD. Pond答案：B80、What is the capital of Saint Lucia?a. Castriesb. Vieux Fortc. Soufrièred. Gros Islet答案:a81、听力题：My sister loves to create ____ (art projects).82、What is the name of the famous ancient city located in Jordan?A. PetraB. BabylonC. AthensD. Rome答案：A83、听力题：The man is very ________.84、听力题：It is _____ to play outside. (fun/quick/small)85、填空题：My uncle teaches me about ____.86、听力题：She is _____ (teaching) a lesson.87、填空题：My favorite place is the ______.88、听力题：Hydrochloric acid is a strong _____.89、What is the opposite of "hot"?A. ColdB. WarmC. CoolD. Spicy90、听力题：A __________ is an area of land that is surrounded by water on three sides.91、听力题：I want to visit ______ (Paris) someday.92、听力题：The Great Wall is located in __________.93、填空题：I want to learn about science because it explains how the _______ (世界) works.94、What is the main purpose of a refrigerator?A. To cook foodB. To keep food coldC. To wash dishesD. To store clothes95、填空题：The _____ (花卉展) showcases different types of flowers.96、填空题：I like to ______ (参与) in student council meetings.97、Which planet is known as the Red Planet?A. VenusB. MarsC. JupiterD. Saturn答案:B98、填空题：I have a toy _______ that can walk and talk.99、听力题：An atom consists of protons, neutrons, and ______.100、听力题：She has a _____ (dog/cat) in her bag.。
了解通信和环境的英语作文
As a high school student with a keen interest in technology and the environment, Ive always been fascinated by the intersection of communication and environmental science. This essay is a reflection on how communication technologies are shaping our understanding and approach to environmental issues.Growing up in the digital age, Ive witnessed the rapid evolution of communication tools, from the early days of dialup internet to the current era of smartphones and social media. These advancements have not only transformed the way we interact with each other but also how we engage with the environment.One of the most significant impacts of communication technology on environmental awareness is the ease of access to information. With just a few taps on a screen, I can learn about the latest climate change reports, endangered species, and environmental policies. This instant access to knowledge has empowered me and my peers to become more informed and proactive about environmental issues.Moreover, social media platforms have become powerful tools for environmental advocacy. Influencers and organizations use these platforms to share images, videos, and stories that highlight the beauty and fragility of our planet. These visual narratives are incredibly impactful, often evoking an emotional response that motivates people to take action. For instance, the viral campaign against singleuse plastics has led to a significant reduction in their use, demonstrating the power of communication in driving environmental change.However, the relationship between communication and the environment is not without its challenges. The digital footprint of our communication technologies is substantial, contributing to electronic waste and energy consumption. As a student who is environmentally conscious, I am aware of the need to balance the benefits of these technologies with their environmental impact.To address this, I have started to explore and advocate for more sustainable communication practices. This includes promoting the use of energyefficient devices, recycling ewaste, and supporting companies that prioritize environmental responsibility. I also encourage my peers to be mindful of their digital consumption, such as reducing screen time and using adblockers to decrease the energy used by online advertisements.Furthermore, I believe that education plays a crucial role in bridging the gap between communication and environmental responsibility. Schools should integrate environmental education into their curricula, teaching students about the environmental implications of their digital habits and how they can contribute to a more sustainable future.In conclusion, the relationship between communication and the environment is multifaceted and complex. While communication technologies have undoubtedly increased our awareness and engagement with environmental issues, they also present new challenges that we must address. As a high school student, I am committed to using my understanding of this relationship to advocate for more sustainablepractices and educate others about the importance of environmental responsibility in the digital age. By doing so, I hope to contribute to a future where communication technologies and environmental conservation can coexist harmoniously.。
海口“PEP”2024年小学3年级下册A卷英语第5单元真题试卷[有答案]
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海口“PEP”2024年小学3年级下册英语第5单元真题试卷[有答案]考试时间：80分钟（总分:140）A卷考试人：_________题号一二三四五总分得分一、综合题(共计100题)1、填空题：I have a __________ (拼图) of animals that I love to complete.2、听力题：My ______ loves to organize events.3、填空题：My mom is a dedicated __________ (教育者).4、听力题：She has a _____ (funny) face.5、填空题：The _____ (温带雨林) hosts a variety of plant species.6、填空题：A _____ (leaf) changes color in autumn.7、听力题：A chemical reaction that occurs spontaneously is known as a ________ reaction.8、What do you call the process of learning and gaining knowledge?A. EducationB. RecreationC. VacationD. Celebration答案:A9、What is the name of the famous ancient city in Ethiopia?A. AxumB. LalibelaC. GondarD. All of the above10、听力题：The girl loves to ________.11、填空题：I often invite my friends over for a toy ________ (名词) party. We share our favorites and play together.12、What is the smallest continent?A. AsiaB. AfricaC. AustraliaD. Europe答案:C13、填空题：The spider spins a _________. (网)14、填空题：The _____ (大树) provides shade.15、What do we call a scientist who studies the weather?A. MeteorologistB. ChemistC. BiologistD. Physicist16、What do we call the process of a seed growing into a plant?A. GerminationB. PollinationC. FertilizationD. Photosynthesis答案: A17、What type of tree produces acorns?A. PineB. OakC. MapleD. Birch答案:B18、填空题：The __________ (文明的发展) is a reflection of human ingenuity._____ (根茎) store nutrients for the plant.20、填空题：The sunflowers in the field are very ______ (高大). They follow the ______ (阳光).21、What do you call a collection of stories?A. AnthologyB. NovelC. CompilationD. Collection答案:A22、填空题：I call my friend’s dad __________. (叔叔)23、填空题：The __________ (历史的启发性) promotes innovation.24、填空题：The alligator has a powerful ________________ (下颚).25、听力题：The chemical formula for isopropanol is ______.26、听力题：The __________ is the layer of rock that lies beneath the soil.27、Which one is a vegetable?A. TomatoB. BananaC. StrawberryD. Orange答案: A28、What do we call the process of taking in and using nutrients?A. DigestionB. MetabolismC. AbsorptionD. Assimilation答案: B. Metabolism29、填空题：The ________ was a famous rebellion against British rule in India.I have a beautiful _____ (花瓶) that holds fresh flowers.我有一个漂亮的花瓶，里边插着新鲜的花。
广州“PEP”24年小学四年级T卷英语第6单元测验试卷
广州“PEP”24年小学四年级英语第6单元测验试卷考试时间：80分钟（总分:140）B卷考试人：_________题号一二三四五总分得分一、综合题(共计100题)1、Where do penguins live?A. DesertB. ArcticC. AntarcticD. Rainforest答案:C2、填空题：What do you wear when it’s ______ (凉爽)?3、填空题：_____ (drought) can affect plant growth.4、选择题：What is the name of the famous mountain range in Asia?A. HimalayasB. RockiesC. AndesD. Alps5、填空题：The ________ was a key figure in the environmental sustainability movement.6、听力题：Chemical reactions can be influenced by temperature and _____.7、What do you call a large body of salt water?A. LakeB. RiverC. OceanD. Pond答案:C8、What is the name of the famous ancient city in Italy?A. PompeiiB. RomeC. VeniceD. All of the above9、选择题：What do we celebrate on our birthday?A. New YearB. ChristmasC. Our birthD. Thanksgiving10、填空题：Tropical plants thrive in ______ (潮湿) climates.11、What do you call the leader of a country?A. PresidentB. GovernorC. MayorD. Senator答案: A12、填空题：My mom loves to read __________ (书籍) in the evenings.13、听力题：A ______ is an animal that is known for its sharp eyesight.14、填空题：I enjoy playing with my ________ (车模) and racing them.15、听力题：The Bronze Age followed the ________ age.16、听力题：Gases have no definite ______.17、选择题：What do we call a book that tells us how to do something?A. NovelB. ManualC. GuidebookD. Recipe book18、听力题：Saltwater is an example of a ______.19、填空题：The ancient Greeks produced many famous ______ (哲学家).20、听力题：The _____ (sky/ground) is cloudy.21、填空题：I love to play games with my __________. (弟弟)22、听力题：The chemical formula for magnesium oxide is ______.23、听力题：The __________ of water is degrees Celsius.24、填空题：I found a _______ (小青蛙) near the pond.25、填空题：The _______ (小乌鸦) caws loudly in the tree.26、What is the value of 6 2 × 2?A. 2B. 4C. 6D. 8答案:B27、What is the main language spoken in the USA?A. SpanishB. EnglishC. FrenchD. German28、What do you call the area in which people live and work?A. CommunityB. NeighborhoodC. ZoneD. District答案: B29、选择题：What do we call a person who studies marine life?A. Marine BiologistB. OceanographerC. Aquatic ScientistD. All of the above30、填空题：__________ (化石燃料) are natural sources of energy made from ancient plants and animals.31、选择题：What do you call the place where you go to watch movies?A. CinemaB. TheaterC. MuseumD. Library32、听力题：The chemical symbol for tantalum is __________.33、听力题：We plan to ________ (implement) changes.34、What do you call a young lion?A. CubB. KitC. PupD. Fawn答案:A35、填空题：The _____ (大象) is a magnificent creature.36、填空题：The _____ (猴子) swings from tree to tree.37、填空题：The __________ (历史的传承) shapes our identity.38、填空题：A ________ (湿地) is a valuable ecosystem.39、What is the opposite of "light"?A. BrightB. HeavyC. SoftD. Hard答案: B. Heavy40、听力题：The chemical formula for water is ______.41、What is 7 x 6?A. 40B. 42C. 44D. 46答案:B42、填空题：The kitten loves to chase a ______.43、填空题：My dog enjoys going for _______ (散步) with me.44、填空题：He is very _____ (认真) about his studies.45、听力题：A ______ can jump very high.46、What is the sum of 5 + 5?A. 12B. 10C. 8D. 11答案：B47、填空题：I made a treasure map for my _________ (寻宝游戏) with my _________ (玩具).48、听力题：I can _____ my shoes by myself. (put on)49、What do you call a person who studies animals?A. ZoologistB. BiologistC. EcologistD. Anthropologist答案:A50、听力题：I go to the library to _____ (read/study).51、听力题：I enjoy ___ (reading) about dinosaurs.52、What is the name of the ancient civilization that built the Machu Picchu?A. AztecsB. IncasC. MayansD. Egyptians答案:B53、听力题：The cake has ______ (berries) on top.54、选择题：What do we call a small, round vegetable that is usually green?A. PeaB. BeanC. LentilD. Chickpea55、Which of these is a vegetable?A. BananaB. PotatoC. AppleD. Grape答案:B56、填空题：Butterflies go through _______ (变形) stages.57、听力题：A ____ is a playful animal that loves to jump and run.58、What do we call the time when the sun sets?A. DawnB. DuskC. NoonD. Midnight59、How many players are there in a soccer team?A. 9B. 10C. 11D. 12答案:C60、填空题：The doll has a pretty ________.61、What is the name of the famous wizarding school in Harry Potter?A. Xaverius AcademyB. HogwartsC. DurmstrangD. Beauxbatons答案：B62、填空题：The ______ (花期) is the time when flowers bloom.63、What is the smallest planet in our solar system?A. EarthB. MarsC. MercuryD. Venus答案:C64、Which part of a plant absorbs water?a. Leafb. Stemc. Rootd. Flower答案:c65、听力题：The weather is _____ (sunny/cloudy) today.66、听力题：A solution that can no longer dissolve more solute is called _______.67、填空题：The ______ (植物的栖息地) must be preserved.68、填空题：The _____ (citrus) fruits are refreshing in summer.69、填空题：The cat caught a small _____.The _____ (向日葵) turns to face the sun.71、How many players are on a baseball team?A. NineB. TenC. ElevenD. Twelve72、填空题：The fish swims in the ______.73、听力题：A __________ is a large area of grassland.74、填空题：The __________ (历史的艺术) often reflects societal values.75、听力题：I see a __ in the garden. (bee)76、听力题：The __________ is the largest continent on Earth.77、What do you call a young wolf?A. PupB. CubC. KitD. Fawn答案:A78、填空题：I love to help my mom ________ (清理) the house.79、填空题：A __________ (气体) can diffuse quickly through space.80、填空题：In which country is the Eiffel Tower located? __________. (法国)81、填空题：在中国历史上，________ (silk) 是一种珍贵的商品。
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A study on the interfacial reaction and dielectric properties of Ba 0.88(Nd 1.40Bi 0.42La 0.30)Ti 4O 12/alkali-borosilicate glass compositesKuan-Hong Lin a ,*,Chang-Lun Liao b ,Shun-Tian Lin baDepartment of Mechanical Engineering,Tungnan University,Taipei 222,Taiwan,ROCbDepartment of Mechanical Engineering,National Taiwan University of Science and Technology,Taipei 106,Taiwan,ROCReceived 11March 2010;received in revised form 3April 2010;accepted 14June 2010Available online 3August 2010AbstractThis study investigated the effects of sintering parameters and the addition of alkali-borosilicate glass into the Ba 0.88(Nd 1.40Bi 0.42La 0.30)Ti 4O 12B(NBL)T ceramic.The microstructure evolution,ionic exchange phenomenon at phase interfaces and the dielectric properties variation of composites were examined by XRD,EPMA,TEM,RF impedance analyzer and network analyzer,respectively.XRD patterns revealed that interactions between B(NBL)T ceramic and glass during sintering could have caused the change in the preferred orientation as well as the shifting of the crystals’diffraction angles.EPMA mapping showed that the concentrations of Ba,and Bi decreased along the edge of the B(NBL)T ceramic that is closest to the glass phase,while the opposite trend was seen for Na and Ca.TEM and EDS analyses confirm that an ionic exchange took place during sintering with the glass phase wetting the B(NBL)T ceramic and was responsible for the change in the crystal plane and the variation in lattice parameters.The ionic exchange that occurred between the B(NBL)T ceramic and the glass phase resulted in a decrease in the electrical resistivity of the glass phase,which in turn reduced the dielectric loss.#2010Elsevier Ltd and Techna Group S.r.l.All rights reserved.Keywords:A.Sintering;posites;B.Microstructure-final;C.Dielectric properties1.IntroductionMost well-known commercial microwave dielectric materi-als exhibit a high dielectric constant (e r ),a high quality factor (Q ),and very low temperature coefficients of the resonant frequency (t f )[1–4].For these classical microwave dielectric materials to reach superior dielectric properties,a very high sintering temperature,ranging from about 12008C to 14008C,is required [5,6].However,if these dielectric materials are to be co-fired with silver conductors,the sintering temperature of the dielectric materials must be lower than the melting point of silver (9618C).The most common approach to reducing the sintering temperature of a microwave dielectric ceramic is to add sintering aids or glass with low melting temperatures [2,6,7].For example,BaO(Nd 0.8Bi 0.2)2O 34TiO 2added with 10wt.%Li 2O–B 2O 3–SiO 2–Al 2O 3–CaO glass could be sintered at 9008C,yielding a composite structure having a quality factor(Q Âf)of 2200GHz,an e r of 68,and a t f of 55ppm/8C [5].Similar trends were observed in the BaNd 2Ti 4O 12microwave ceramic,in which B 2O 3–Bi 2O 3–SiO 2–ZnO or La 2O 3–B 2O 3–TiO 2glass was added to reduce the sintering temperature [8,9].It was also shown that alumina and silica based glasses were more effective in improving the dielectric properties of Ca 5Nb 2TiO 12ceramics,whereas borate glasses are preferred for lowering the sintering temperature.On the other hand,although a glass phase additive could reduce the sintering temperature,it was shown that a larger amount of glass added to Ca 5Nb 2TiO 12caused increased porosity,resulting in reduced dielectric properties [10].Researchers have also reported that La 4Ti 9O 24ceramics added with 20vol.%PbO–B 2O 3–SiO 2and ZnO–B 2O 3–SiO 2glass could be sintered at 10008C,yielding a composite structure having a 95%theoretical density.The interaction between PbO–B 2O 3–SiO 2and La 4Ti 9O 24results in the formation of a secondary phase La 2/3TiO 3,which strongly influences the dielectric properties of La 4Ti 9O 24ceramics [11].Jung et al.[9]indicated that the BaNd 2Ti 4O 12(BNT)ceramic added with La 2O 3–B 2O 3–TiO 2(LBT)glass could be sintered at 8508C,/locate/ceramintAvailable online at Ceramics International 36(2010)2365–2374*Corresponding author.Tel.:+886286625917;fax:+886286625919.E-mail address:khlin@.tw (K.-H.Lin).0272-8842/$36.00#2010Elsevier Ltd and Techna Group S.r.l.All rights reserved.doi:10.1016/j.ceramint.2010.07.021yielding a dielectric constant of20,a quality factor(QÂf)of 8000GHz,and a low temperature coefficient of resonant frequency(t f=76.8ppm/8C)at frequencies ranging from 6GHz to7GHz.The most significant sintering result was the formation of HT-LaBO3(high temperature forming)and TiO2 due to the reaction between the BNT ceramic and LBT glass. The reaction products played positively in improving the microwave dielectric properties of BNT ceramics.Lee et al.[12]added B2O3to BaTi4O9ceramics and observed active dissolution of Ba and Ti atoms from BaTi4O9into B2O3liquid, leading to the formation of many secondary phases,such as Ba2Ti9O20,BaTi(BO3)2,TiO2,and,many large pores were formed by B2O3.These results deteriorated the dielectric characteristics of BaTi4O9.Chang et al.[13]added Al2O3-doped silica glass to the BaO–Nd2O3–Sm2O3–TiO2microwave materials and observed that glass additives enhance the growth in the longitudinal direction of the columnar crystal and had a preferred(002)orientation.The high QÂf value of dielectric ceramics is attributed to an increase in composite density when glass is added.Some researchers[14]have also reported that the incorporation of B2O3into the Ba(Nd2Àx Sm x)Ti4O12crystal changes the lattice constants of the crystal as a result of the diffusion of B atoms to the interstitial sites.Although the above-mentioned studies have examined the changes that occur when glass and dielectric ceramic are sintered,and noted the effect of secondary phase on the dielectric properties,not much research has been focused on understanding the effect that the ion interdiffusion between alkali-borosilicate glass and Ba0.88(Nd1.40Bi0.42La0.30)Ti4O12 ceramic has on the crystal structure and dielectric properties.In this study,an alkali-borosilicate glass of low softening temperature was added to Ba0.88(Nd1.40Bi0.42La0.30)Ti4O12 dielectric ceramic to investigate the effect of glass additives on the microstructure and dielectric properties of ceramics.An XRD,EPMA,DSC,and TEM with an attached energy dispersive X-ray spectrometer,were used to perform more accurate analysis to address the above-mentioned questions.2.Experimental proceduresThe materials used in this study were Ba0.88(Nd1.40Bi0.42-La0.30)Ti4O12ceramic(abbreviated as B(NBL)T,Prosperity Dielectric,NPO-110)and alkali-borosilicate glass powder (SiO2–B2O3–Al2O3–CaO–Na2O–K2O–BaO,China Glaze,CS-9609).The average particle sizes of B(NBL)T ceramic and glass powder were3.2m m and4.6m m,respectively.The physical propertiesandcompositionsofthesematerialsarelistedin Table1.B(NBL)T ceramic and glass powders of various volumetric ratios(50/50,45/55,and40/60)were ball-milled in an isopropyl alcohol(IPA)solvent containing zirconia balls3mm in diameter for24h in a polyethylene bottle.A solution composed of an acrylic resin(Elvacite,2046)and IPAwas then mixed with the milled powder and spray-dried into spherical granules.Granules with a mean particle size of around70m m were obtained through sieving and uniaxially pressed into pellets that were15mm in diameter and either4mm or8mm in thickness at a pressure of90MPa.Sintering was then carried out in air.The thermal profile included heating at a rate of28C/ min to3508C,held for30min,followed by heating at a rate of 28C/min to5008C,held for30min,andfinally heating at a rate of38C/min to a sintering temperature ranging between 7508C and9508C and held for a period ranging from30min to 120min.The crystal structure of the sintered composites were analyzed using an X-ray diffractometer(XRD,REGAKU,DMAX-VB)at 40kVand100mA,using Cu K a(l=0.15418nm)radiation.In a scanning range(2u)of108–508,the scanning rate was38/min and the scanning interval was0.058.Back-scattered electron images(BEI)of the polished specimens were examined along with electron probe microanalysis(EPMA),using a scanning electron microscope(JEOL,JXA-8900R)operated at an accelerating voltage of20kV.The interfacial reaction between B(NBL)T ceramic and glass was examined using EPMA.The specimen used was prepared byfiring a piece of green glass compact on top of a densified B(NBL)T substrate at a heating rate of58C/min from room temperature to9508C in air.A transmission electron microscope(AEM,JEOL-2010) with an energy dispersive X-ray spectrometer(EDS,OXFORD, ISIS-300)attached was operated at an accelerating voltage of 200kV.Selected area diffraction(SAD)patterns were recorded at a camera length of100cm and an aperture of150nm.The electron beam size of this EDS analysis was7nm and the analyzed area was approximately50nm in diameter.Quanti-tative composition analysis of the selected area was carried out using the Cliff-Lorimer Ratio of Thin Section,using copper as the calibration standard.The absorption correction and fluorescence correction were neglected and only the atomic number correction was carried out using the attached software.A TEM analysis of a silicon specimen(Si,a=0.5431nm, JCPDS27-1402)was used for calibration from which the SAD pattern of Si[110]was obtained and the lattice parameter calculated to be0.552nm.As this value exceeded the standard value of Si by approximately1.7%,this instrumentation error (1.7%)was deducted directly from the results of subsequent experiments.Table1Physical properties and compositions of B(NBL)T ceramic powder and alkali-borosilicate glass powder. Material Density(g/cm3)Mean particlesize(m m)Composition(wt.%)B(NBL)T 5.64 3.2TiO237.6Nd2O328.4BaO16.2Bi2O311.9La2O35.9Glass 2.45 4.6SiO238.1Al2O317.3B2O316.9CaO12.1K2O6.8Na2O4.7BaO4.1K.-H.Lin et al./Ceramics International36(2010)2365–2374 2366Glass transition temperatures(T g)were investigated using a thermal analyzer(SETARAM,SETSYS-TGA,TG/DSC)at a heating rate of108C/min from room temperature to11008C in air.The dielectric properties were measured using an RF impedance analyzer(HP4291B)set to a frequency of1GHz, while the resonant frequencies were measured via a parallel plate dielectric resonator on a network analyzer(AGILENT 8722ES)using Hakki and Coleman’s method.The diameter-to-height ratio of specimens was maintained between1.8and2.3.3.Results and discussion3.1.X-ray diffraction analysisThe X-ray diffraction patterns of samples sintered under various conditions are shown in Fig.1(a).Note that the X-ray diffraction patterns of the original B(NBL)T powder and those sintered for1h at12608C,13608C,and14608C are almost identical with all exhibiting an orthorhombic crystalline structure.These results are consistent with those reported by Silva et al.[15]for BaNd2Ti4O12.Fig.1(b)–(d)shows the X-ray diffraction patterns of B(NBL)T/glass composites with 50vol.%,55vol.%,and60vol.%glass additions,respectively, sintered at various temperatures for2h.It can been seen that as the sintering temperature increased,the peak intensity of the (320)plane of B(NBL)T increased,whereas a decrease was observed for the(401)plane.Such a development could be attributed to a change in the preferred orientation of the B(NBL)T crystals,due to wetting by the glass phase and possibly a phase reaction at the sintering temperature[16].Similar observations were also reported for aluminosilicate glass addition to BaO–Nd2O3–Sm2O3–TiO2,which promoted development of colum-nar grains of(002)preferred orientation[17].In addition to a change in intensity,it can also be observed that as the sintering temperature increased,the diffraction angle of (320)plane decreased.This indicates that when B(NBL)T is sintered in the presence of the glass phase,not only does a change in preferred orientation but also a change in lattice parameters. The diffraction angles of the(320),(401),and(303)planes of the B(NBL)T/glass45/55vol.%composite sintered at9508C for 2h were32.808,31.558,and29.058,respectively.A least square regression of the three equations yielded lattice constants of a=1.154nm,b=0.776nm,and c=pared with the JCPDS data of BaNd2Ti4O12ceramics(No.35-0331, a=1.147nm,b=0.769nm,c=1.552nm),the lattice constants were larger by0.6%in the a-axis and0.9%in the b-axis but smaller by1.0%in the c-axis.From previous studies,it was found of the addition of B2O3 into a Ba(Nd2Àx Sm x)Ti4O12crystal would result in changes in the crystal’s lattice constants due to the diffusion of B atomsFig.1.X-ray diffraction patterns at various sintering temperatures of(a)B(NBL)T ceramic,(b)B(NBL)T/glass50/50vol.%,(c)B(NBL)T/glass45/55vol.%,(d) B(NBL)T/glass40/60vol.%.K.-H.Lin et al./Ceramics International36(2010)2365–23742367into the interstitial sites [14].Similarly,interaction between the B(NBL)T ceramic and the glass phase could have caused a change in the preferred orientation,as well as a shift in the diffraction angles of the XRD patterns.Fig.2shows the relationship between the sintering temperature and ratio of the peak intensity of (320)to that of (401),I (320)/I (401),for B(NBL)T/glass composites with 50vol.%,55vol.%,and 60vol.%glass additions,respectively.It can be observed that not only an increase in sintering temperature but also anincrease in the volume percentage of glass phase significantincrease the I (320)/I (401)ratio.3.2.EPMA analysisFig.3shows the BEI photograph and corresponding mappings of Ba,Na,and Ca in a B(NBL)T/glass 45/55vol.%composite,sintered at 7508C for 30min.Based on the color contrasts in the EPMA mappings,it can be seen that the concentration of Ba within the ceramic is higher than that in the glass phase,whereas the concentration of Na and Ca in the glass phase is higher than that within the ceramic.Similar results were also observed in the B(NBL)T/glass 50/50vol.%,and B(NBL)T/glass 40/60vol.%composites.The interdiffu-sion of Ba,Na,and Ca between the B(NBL)T ceramic and the glass phase is not apparent most likely due to a low sintering temperature and insufficient held time.The BEI photograph and corresponding mappings of Ba,Na,and Ca in a B(NBL)T/glass 45/55vol.%composite,sintered at 9508C for 2h are shown in Fig.4.It can be observed that the concentration of Ba was reduced slightly around the edge of the ceramic,as a result of dissolution of Ba into the glass phase.Na and Ca,on the other hand,diffused into the ceramic and therefore a slight increase in the concentration of these two elements was found near the edge of the ceramic.Similar results were also observed in the B(NBL)T/glass 50/50vol.%,and B(NBL)T/glass 40/60vol.%composites.Due to the resolution of the sintered composite BEI photograph was insufficient to examine the interface between the B(NBL)T ceramic and the glass phase after sintering,aFig.2.Intensity ratio I (320)/I (401)as a function of sintering temperature for B(NBL)T/glass composites with 50vol.%,55vol.%,and 60vol.%glass sin-tered for 2h in air.Fig.3.BEI photograph and EPMA mappings of,Ba,Na,and Ca of a B(NBL)T/glass 45/55vol.%composite,sintered at 7508C for 30min.The B(NBL)T ceramics (bright domain),and the glass phase (dark domain).K.-H.Lin et al./Ceramics International 36(2010)2365–23742368reaction couple was designed.Fig.5shows the BEI photograph of a B(NBL)T/glass reaction couple,sintered at9508C for2h. Based on the BEI photograph it is evident that an interface of approximately2m m in thickness exists between the two original phases.Previous research have reported interdiffusion coeffi-cients between Ba2+and Na+,and Ba2+and K+to be approximately10À8cm2/s at9508C[18].Based on thisfinding to apply Fick’s second law,the interdiffusion distance after2h is estimated to be100m m.Therefore,the interfacial reaction might have controlled the growth of this interfacial reaction zone.The BEI image and corresponding element mappings of Ba, Nd,Bi,La,Ti,Al,Na,Ca,and K in the B(NBL)T/glass interface are shown in Fig.6.It can be observed that the concentrations of Ba and Bi decreased along the edges of the B(NBL)T ceramic, whereas the opposite trend was observed for Na,Ca,and K. However,Nd,La,Ti,Al,and Si did not show significant changes.3.3.TEM analysisDue to the inadequate resolution of EPMA mappings in the interfacial area,a TEM was used to examine the interface between the B(NBL)T and the glass,and an EDS was performed to measure the composition variation between the ceramic and the glass phase.Fig.7(a)displays the TEM bright field image of the B(NBL)T/glass45/55vol.%composite sintered at8008C for2h.Fig.7(b)–(d)shows results from EDS analysis.Taking the average of4points along the edge of the B(NBL)T ceramic,the composition at the edge of the B(NBL)T ceramic was estimated to be Ba(7.1at.%),Nd(8.3at.%),Bi(1.7at.%),La(2.6at.%),Ti(21.3at.%),Al(0.3at.%),Na(2.5at.%),Ca(0.2at.%),and Si(1.3at.%).By taking the average of three different points along the edge of the glass,the average composition along the edge of the glass was determined to be Ba(0.5at.%),Nd(0.2at.%),Bi(0.1at.%), La(0.2at.%),Ti(0.7at.%),Al(6.4at.%),Na(0.6at.%),Ca (0.2at.%),and Si(29.5at.%).Fig.4.BEI photograph and EPMA mappings of Ba,Na,and Ca in a B(NBL)T/glass45/55vol.%composite,sintered at9508C for2h.The B(NBL)T ceramics (bright domain),and the glass phase(gray domain).Fig.5.A BEI photograph of a reaction couple for B(NBL)T and glass,sinteredat9508C for2h.K.-H.Lin et al./Ceramics International36(2010)2365–23742369Fig.6.BEI photographs and EPMA mappings of (a)Ba,Nd,Bi,(b)La,Ti,Al,(c)Na,Ca,K of a B(NBL)T and glass reaction couple,sintered at 9508C for 2h.K.-H.Lin et al./Ceramics International 36(2010)2365–23742370Fig.8(a)displays the TEM brightfield image of a B(NBL)T/ glass45/55vol.%composite sintered at9508C for2h.It can be seen that the B(NBL)T phase is rectangular in shape, implying that interfacial reaction might have influenced the growth of the B(NBL)T crystal,which is consistent with conclusions drawn from previous research[16].Fig.8(b)–(d)shows the EDS analysis results of the B(NBL)T/glass composite.The average concentration along the edge of the B(NBL)T ceramic for Ba,Nd,Bi,and Ti were 2.8at.%, 7.3at.%,0.4at.%,and18.0at.%,respectively;both were lower than that of the specimen sintered at8008C(4.3at.%,1.0at.%, 1.3at.%,and3.3at.%,respectively).La(2.2at.%),and AlFig.7.B(NBL)T/glass45/55vol.%composite sintered at8008C for2h:(a)TEM brightfield image,(b)–(d)EDS composition analysis.Fig.8.B(NBL)T/glass45/55vol.%composite sintered at9508C for2h:(a)TEM brightfield image,(b)–(d)EDS composition analysis.K.-H.Lin et al./Ceramics International36(2010)2365–23742371(0.4at.%)did not show significant differences as compared with that of the specimen sintered at8008C.The average concentrations of Na(6.8at.%),Ca(1.3at.%),and Si(2.1at.%) were higher than that of the specimen sintered at8008C (4.3at.%,1.1at.%and0.8at.%,respectively).The average concentrations of Ba(0.8at.%),Nd(0.3at.%),Bi (0.2at.%),and La(0.3at.%)near the edge of glass were higher than that of the8008C specimen(0.3at.%,0.1at.%,0.1at.%, and0.1at.%,respectively).For Ti(0.7at.%),Al(6.1at.%),Na (0.6at.%),Ca(0.3at.%),and Si(30.8at.%),no significant changes occurred.It is evident that during sintering an ionic exchange took place with the glass phase wetting the B(NBL)T, resulting in a change of the preferred crystal plane from(401)to (320)and the variation in lattice parameters as shown through XRD analysis.The relationships that exist between the composition,microstructure,and dielectric properties of a B(NBL)T/glass composite will be discussed in the next section.Fig.9(a)and(b)shows the select area diffraction(SAD) patterns of the B(NBL)T phase along the zone axis of[101] and[010].From the diffraction patterns,it can been seen that the B(NBL)T phase had an orthorhombic crystalline structure with lattice parameters of a=1.156nm,b=0.772nm,and c=pared with the JCPDS data of the BaNd2Ti4O12ceramic,the lattice parameters of the B(NBL)T phase were larger by0.8%in the a-axis and0.4%in the b-axis but smaller by0.6%in the c-axis.The small difference in the lattice parameters between the two ceramics is likely caused by the interdiffusion of Ba2+,Bi3Àions of the B(NBL)T ceramic with the Na+,Ca2+and K+ions of glass.However,as the crystal structure of B(NBL)T phase is extremely complex,it is difficult to determine the affect of ion exchanges on lattice parameters using the rule of mixtures.On the other hand,Fig.9(c)shows the SAD pattern of the glass,which reveals an amorphous structure.3.4.Dielectric propertiesFig.10shows the differential scanning calorimetry(DSC) patterns of the glass powder,a B(NBL)T/glass40/60vol.% composite,and a B(NBL)T/glass50/50vol.%composite.The transition temperature of the glass phase(T g)showed two discrete temperatures,5488C(T g1)and6568C(T g2):a result possibly caused by the phase separation of glass during heating. When the sintering temperature increases above the glassFig.9.SAD pattern of a B(NBL)T/glass45/55vol.%composite sintered at9508C for2h,B(NBL)T phase zone axis:(a)[101],(b)[010],and(c)SAD pattern of glass.Fig.10.DSC patterns of the glass powder,the B(NBL)T/glass40/60vol.% composite,and the B(NBL)T/glass50/50vol.%composite.Fig.11.Dielectric properties as a function of sintering temperature for a B(NBL)T/glass45/55vol.%composite,sintered in air for2h.K.-H.Lin et al./Ceramics International36(2010)2365–2374 2372transition temperature,thermal activation occurs and the glass phase is softened.For the glass powder,the commencing softening temperature (T s )was 7768C.For the B(NBL)T/glass 40/60vol.%composite,the glass transition temperatures T g 1and T g 2were around 5708C and 8698C and the commencing softening temperature was 10308C.For the B(NBL)T/glass 50/50vol.%composite,both the two discrete glass transition temperatures and the softening temperature increased.The glass transition temperatures increased to about 5728C (T g 1)and 8758C (T g 2),and the commencing softening temperature increased to 10708C.Such increases in glass transition temperatures (T g )and softening temperature (T s )were not completely attributed by the volume percentage of glass.It is believed that the exchange of Na +,Ca 2+,and K +ions with Ba 2+and Bi 3Àions caused the dissolution of larger Ba 2+and Bi 3Àions into the glass phase and the loss of smaller Na +,Ca 2+,and K +ions from the glass phase,resulting in increases in glass transition temperatures and softening temperatures.Fig.11shows the relationship between the dielectric properties and the sintering temperature for the B(NBL)T/glass 45/55vol.%composite,sintered in air for 2h.As the sintering temperature increased,the dielectric constant increased,but the loss tangent decreased.Normally,an increase in the sintered density results only in an increase of the dielectric constant and not in a decrease of the dielectric loss.Thus,a decrease in the dielectric loss with an increase in the sintering temperature must have been caused by the phase reaction between the B(NBL)T ceramic and the glass phase,resulting in an ionic exchange between Na +,Ca 2+,K +ions and Ba 2+,Bi 3Àions in the composite.This would cause a decrease in the electrical resistivity of the glass phase,which in turn would yield a decrease in dielectric loss [19].Similar observations were reported elsewhere,where an increase in the concentration of sodium and potassium ions always resulted in an increase of the loss tangent for many low temperature co-firable dielectric and glass composites [20].Table 2shows the sintered densities and dielectric properties of glass,B(NBL)T ceramic,and B(NBL)T/glass composites,processed under various conditions.The B(NBL)T/glass composite with 55vol.%glass addition had the optimal set of dielectric properties.The lower dielectric constant of the B(NBL)T/glass composite with 50vol.%glass addition as compared to the one with 55vol.%is attributed to a lower glass content,which translates to a lower sintered density.On the other hand,the existence of an excessive amount of the glass phase with a lower dielectric constant but a larger dielectric lossthan those of the B(NBL)T ceramic,was responsible for the lower dielectric constant and higher dielectric loss of the B(NBL)T/glass composite with 60vol.%glass addition.The B(NBL)T/glass composites do not achieve dielectric constant values estimated from the rule of mixtures,but rather exhibits higher dielectric losses,which arise from the motion of the alkali ions (Na +and K +)in the glass phase [21].The substantial deviation of the measured dielectric constant from that estimated by the rule of mixtures is a percolation phenomenon and is believed to arise from the high threshold volume percentage of the B(NBL)T phase that is required to induce a dielectric response in the composite structure [22].Consequently,in order to further increase the dielectric constant of the composites,a higher volume percentage of B(NBL)T and a better sintering aid are required.4.ConclusionsFrom the XRD pattern,it can be seen that the peak intensity ratio I (320)/I (401)of B(NBL)T not only increased with an increase in sintering temperature,but also with an increase in the volume percentage of the glass phase.This is attributed to interactions between the B(NBL)T ceramic and the glass phase,which caused a change in the preferred orientation,as well as lattice parameters,of the crystal.EPMA mapping and TEM analysis reveal that the concentrations of Ba and Bi decreased along the edge of the B(NBL)T ceramic close to the glass phase,while the opposite trend can be seen for Na,Ca,and K.This is evidence that an ionic exchange took place during sintering with the glass phase wetting the B(NBL)T ceramic,resulting in the change in the crystal plane from (401)to (320),the change in lattice parameters,the decrease in dielectric loss,as well as the increase in glass transition and softening temperatures.A relatively low sintered density in addition to an excessive amount of the glass phase was responsible for the low dielectric constants of B(NBL)T/glass composites.When sintered at 9508C for 2h,the composite with 55vol.%glass yielded the highest dielectric constant (e r =23.2),the lowest dielectric loss (loss tangent =4.1Â10À3),and a high Q Âf value (1620GHz,Q =1/tan d ,f =6.67GHz).References[1]Y.C.Zhang,Z.X.Yue,Z.L.Gui,L.T.Li,Effects of CaF 2addition on themicrostructure and microwave dielectric properties of ZnNb 2O 6cera-mics,Ceram.Int.29(2003)555–559.Table 2Sintered density and dielectric properties of glass,B(NBL)T,and B(NBL)T/glass composites under various sintering conditions.Specimensr (g/cm 3)e r tan df (GHz)Q Âf (GHz)Glass at 7008C (at 1GHz) 2.45 6.8a 2Â10À3a–a –a B(NBL)T at 12608C 5.5190.32 1.3Â10À3 3.462586B(NBL)T at 13608C 5.6194.30 1.2Â10À3 3.422855B(NBL)T at 14608C5.4088.42 1.9Â10À3 3.501878B(NBL)T/glass 50/50vol.%at 9508C 2.9820.5 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