超细粉体表面包覆与改性

Results
• The pH value varied from 0.8 to 6.5 with incremental changes as a function of time during hydrochloric acid surface modification, and the pH value of acetic acid solution showed an almost linear increase from 2.6 to 3.1 for 0.6 ks at room temperature. After heating to 368 K, the pH rose to 4.2, as shown in Fig. 2.
• 具体：
• 超声波利用超声空化时产生的局部高温、 高压或强冲击波和微射流等，较大幅度地 弱化超微粒子间的超微作用能，有效地防 止超微粒子团聚而使之充分分散。
• 辐照技术将高能射线与物质相互作用时， 在极短的时间内即把自身的能量传递给介 质，使介质发生电离和激发等变化。
• 采用等离子体方法处理无机粉体，使表面 引入活性基团或使表面包覆聚合物，提高 与聚合物的黏合性、改善聚合物填充体系 的力学性能。
powder
K. Yanagimoto a,∗, K. Majimab, S. Sunada b, T. Sawadaa
a Sanyo Special Steel Co. Ltd., 672-8677 Himeji, Japan b Faculty of Engineering, Toyama University, 930-8555 Toyama, Japan
• 第三，采用高能电晕放电、紫外线照射或 等离子辐射等方法在颗粒表面形成不饱和 程度大的电子层或化学键，从而提高颗粒 表面活性以及与其他物质的界面结合程度。
改性方法
• 表面物理改性：超细粉体的表面物理改性 一般是指不用表面修饰剂而对超微粉体实 施表面改性的方法，包括电磁波、中子流 、α粒子、β粒子等的辐照处理、超声处理 、热处理、电化学处理、等离子体处理等 ，是很常用的超微粉体表面改性方法。
• The aim of this work is to clarify the surface structures of before/after acid treateቤተ መጻሕፍቲ ባይዱ MH powders prepared by gas atomization as well as discharge capacity change by surface modification.
• Surface modification was terminated when the solution pH reached 6.5 for hydrochloric acid or solution temperature exceeded 368K for acetic acid.
• A TEM specimen was prepared with FIB for thinning the area of interest of the MH powder particle and observed with FETEM. The surface layer of the particle was characterized by EDS analysis and electron diffraction.
• 偶联剂具有两性结构，其分子中的一部分 基团可与粉体表面的各种化学官能团反应 ，形成强有力的化学键。另一部分基团则 与有机高聚物发生某些反应或物理缠结， 从而将两种性质差异很大的材料牢固地结 合起来，使无机填料和有机高聚物之间产 生具有特殊功能的“分子桥”。
• 接枝聚合改性通过调节表面聚合改性单体 的配比，进行控制共聚物层及其无机粒子 界面层的结构和性质。
• 静电分散作用：通过表面改性使颗粒的荷 电量增大；通过表面改性改变颗粒表面性 质，消除液桥力的影响。
• 降低纳米粉体的团聚度、提高其流动性
合金粉末真空雾化设备
Effects of surface modification on surface structure and electrochemical properties of Mm(Ni,Co,Mn,Al)5.0 alloy
• The atomized powder was sieved to less than 180 μm and its average particle diameter was 59 μm.
• The sieved powder was then heat treated at 1073K for 36 ks under an Ar atmosphere. A SEM image of the atomized powder is shown in Fig. 1.
超细粉体表面包覆与改性
• 超细粉体表面是指表面的一个或几个原子 层，有时指厚度达几微米的表面层。表面 是体相结构的终止，表面向外的一侧没有 近邻原子，表面原子有一部分化学键形成 悬空键。
• 超微粉体内部的三维周期势场在表面中断 ，表面原子的电子状态也和体内不同，然 而表面不是体相结构的简单终止。由于超 微粉体表面有悬空键，因而有剩余成键能 力。为了使表面能降低，所有超微粉体的 表面原子都会离开它们原来在体相中应占 的位置而进入新的平衡位置，发生弛豫和 重构。因此导致颗粒表面有很高的活性。
Abstract
• The electrochemical properties of MmNi5type metal hydride powders produced by gas atomization were improved by acid surface modification. FIB specimen preparation followed by FE-TEM observation was used to analyze the surface structure before/after surface modification. The original oxide layer of the surface was removed and a nickel rich layer was formed by acid treatment.
• 表面化学改性：超微粉体的表面化学改性 是指在原来单一组分的基元物质表面上， 均匀地引入一种或者是多种其他组分的物 质，以改变原来基元的基本性质的方法。
• 常见的有：表面吸附包覆改性、化学反应 包覆改性、微乳液法、胶囊化改性和化学 镀法等。
表面改性目的
• 改变颗粒表面的晶体结构(表面无定形化)、 溶解性能、化学吸附和反应活性(增加表面 的活性点或活性基点)等。
超细粉体表面特性
• 超细粉体表面的润湿性 • 超细粉体的表面电性 （颗粒与其他介质接触时，表面会有电荷转
移，这种转移往往正负电荷数量不一致， 从而产生电势差。） • 超细粉体的表面能
超细粉体表面改性
• 表面改性是指采用物理或化学方法对固体 颗粒进行表面处理，即根据应用需要有目 的地改变颗粒表面物理化学性质与表面形 态结构工艺。
Introduction
• (Mm: La 33%, Ce 48%, Pr 5%, Nd 14%)
• MmNi5-type metal–hydride (MH) alloy powders are widely used for the negative electrodes of nickel/MH batteries. Much effort has been devoted to finding substitutes for Ni to improve basic electrode properties such as discharge capacity and cycle life. Modern alloy systems are primarily of the type Mm–Ni– Co–Mn–Al.
• 可以根据改性途径和赋予的改性产物功能 分为三个方面：
• 第一，有机改性剂在颗粒表面的覆盖，以 提高无机粉体在有机基体中的分散性和界 面结合强度；
• 第二，通过化学沉积或机械力化学作用将 固体小颗粒（子颗粒）或均一物质膜在较 大颗粒表面（母颗粒）均匀包覆形成复合 颗粒，从而赋予复合颗粒新的功能；
• Two acids, hydrochloric (0.27 mol/l) and acetic (3.4 mol/l), were used for surface modification. The weight ratio of powder to solution was held constant at 1:1, and the solution was magnetically stirred. The solution was kept at room temperature for hydrochloric acid treatment, while the acetic acid solution was reacted at room temperature for 0.6 ks and then heated to increase the speed of reaction.
• Table 1 shows the discharge capacity before/after hydrochloric acid and acetic acid surface treatment. Without surface treatment, the value of the standard conductivity electrode was 213 mAh/g, which is only 63% of the theoretical capacity (340 mAh/g). After acid treatment, the discharge capacity of the standard electrode increased, nearing the theoretical value for both acids.
• The structure of the nickel rich surface differed with the treatment conditions. For acetic acid treated powder prepared in heated solution, a nanocrystalline nickel layer was formed at the surface. In the absence of any auxiliary conductivity additives, discharge capacity of this powder was improved to 254 mAh/g versus 52 mAh/g for non-treated powder and 62 mAh/g for hydrochloric acid treated powder.
Experimental
• The MH alloy powder whose composition is Mm1.0Ni3.6Co0.6Mn0.6Al0.2 (Mm: La 33%, Ce 48%, Pr 5%, Nd 14%)was produced by Ar gas atomization after being melted in a 2 kg capacity induction furnace under an Ar atmosphere.