mullite whiskers derived from coal fly ash
2024年6月大学英语六级考试真题和答案(第1套)
2024年6月大学英语六级考试真题和答案（第1套）Part I Writing (30 minutes)Directions: For this part, you are allowed 30 minutes to write an essay that begins with the sentence “There is a growing awareness of the importance of digital literacy and skills in today’s world.” You can make comments, cite examples or use your personal experiences to develop your essay. You should write at least 150 words but no more than 200 words. You should copy the sentence given in quotes at the beginning of your essay.Part Ⅱ Listening Comprehension (30 minutes)Section ADirections:In this section, you will hear two long conversations. At the end of each conversation, you will hear four questions. Both the conversation and the questions will be spoken only once. After you hear a question, you must choose the best answer from the four choices marked A), B), C) and D). Then mark the corresponding letter on Answer Sheet 1 with a single line through the centre.Questions 1 to 4 are based on the conversation you have just heard.1. A) Reply to the man’s last proposal within a short time.B) Sign the agreement if one small change is made to it.C) Make a sponsorship deal for her client at the meeting.D) Give the man some good news regarding the contract.2. A) They are becoming impatient.B) They are afraid time is running out.C) They are used to making alterations.D) They are concerned about the details.3. A) To prevent geographical discrimination.B) To tap the food and beverage market.C) To avoid any conflict of interest.D) To reduce unfair competition.4. A) It is a potential market for food and beverage.B) It is very attractive for real estate developers.C) It is a negligible market for his company.D) It is very different from other markets.Questions 5 to 8 are based on the conversation you have just heard.5. A) They are thrilled by a rare astronomic phenomenon.B) They are celebrating a big event on mountain tops.C) They are enthusiastic about big science-related stories.D) They are joined by astronomers all across North America.6. A) It will be the most formidable of its kind in over a century.B) It will come closest to Earth in more than one hundred years.C) It will eclipse many other such events in human history.D) It will be seen most clearly from Denver’s mountain tops.7. A) A blur.B) Stars.C) The edge of our galaxy.D) An ordinary flying object.8. A) Use professional equipment.B) Climb to the nearby heights.C) Fix their eyes due north.D) Make use of phone apps.Section BDirections: In this section, you will hear two passages. At the end of each passage, you will hear three or four questions. Both the passage and the questions will be spoken only once. After you hear a question, you must choose the best answer from the four choices marked A)，B)，C) and D). Then mark the corresponding letter on Answer Sheet 1 with a single line through the centre.Questions 9 to 11 are based on the passage you have just heard.9. A) Whether consumers should be warned against ultra-processed foods.B) Whether there is sufficient scientific consensus on dietary guidelines.C) Whether guidelines can form the basis for nutrition advice to consumers.D) Whether food scientists will agree on the concept of ultra-processed foods.10. A) By the labor cost for the final products.B) By the degree of industrial processing.C) By the extent of chemical alteration.D) By the convention of classification.11. A) Increased consumers’ expenses.B) Greater risk of chronic diseases.C) People’s misunderstanding of nutrition.D) Children’s dislike for unprocessed foods.Questions 12 to 15 are based on the passage you have just heard.12. A) They begin to think of the benefits of constraints.B) They try to seek solutions from creative people.C) They try hard to maximize their mental energy.D) They begin to see the world in a different way.13. A) It is characteristic of all creative people.B) It is essential to pushing society forward.C) It is a creative person’s response to limitation.D) It is an impetus to socio-economic development.14. A) Scarcity or abundance of resources has little impact on people’s creativity.B) Innovative people are not constrained in connecting unrelated concepts.C) People have no incentive to use available resources in new ways.D) Creative people tend to consume more available resources.15. A) It is key to a company’s survival.B) It shapes and focuses problems.C) It is essential to meeting challenges.D) It thrives best when constrained.Section CDirections: In this section, you will hear three recordings of lectures or talks followed by three or four questions. The recordings will be played only once. After you hear a question, you must choose the best answer from the four choices marked A), B), C) and D). Then mark the corresponding letter on Answer Sheet 1 with a single line through the centre.Questions 16 to 18 are based on the recording you have just heard.16. A) Because they are learned.B) Because they come naturally.C) Because they have to be properly personalized.D) Because there can be more effective strategies.17. A) The extent of difference and of similarity between the two sides.B) The knowledge of the specific expectation the other side holds.C) The importance of one’s goals and of the relationship.D) The approaches one adopts to conflict management.18. A) The fox.B) The owl.C) The shark.D) The turtle.Questions 19 to 21 are based on the recording you have just heard.19. A) Help save species from extinction and boost human health.B) Understand how plants and animals perished over the past.C) Help gather information publicly available to researchers.D) Find out the cause of extinction of Britain’s 66,000 species.20. A) It was once dominated by dinosaurs.B) It has entered the sixth mass extinction.C) Its prospects depend on future human behaviour.D) Its climate change is aggravated by humans.21. A) It dwarfs all other efforts to conserve, protect and restorebiodiversity on earth.B) It is costly to get started and requires the joint efforts of thousands of scientists.C) It can help to bring back the large numbers of plants and animals that have gone extinct.D) It is the most exciting, most relevant, most timely and most internationally inspirational.Questions 22 to 25 are based on the recording you have just heard.22. A) Cultural identity.B) Social evolution.C) The Copernican revolution.D) Human individuality.23. A) It is a delusion to be disposed of.B) It is prevalent even among academics.C) It is a myth spread by John Donne’s poem.D) It is rooted in the mindset of the 17th century.24. A) He believes in Copernican philosophical doctrines about the universe.B) He has gained ample scientific evidence at the University of Reading.C) He has found that our inner self and material self are interconnected.D) He contends most of our body cells can only live a few days or weeks.25. A) By coming to see how disruptive such problems have got to be.B) By realising that we all can do our own bit in such endeavours.C) By becoming aware that we are part of a bigger world.D) By making joint efforts resolutely and persistently.Part III Reading Comprehension (40 minutes)Section ADirections: In this section, there is a passage with ten blanks. You are required to select one word for each blank from a list of choices given in a word bank following the passage. Read the passage through carefully before making your choices. Each choice in the bank is identified by a letter. Please mark the corresponding letter for each item on Answer Sheet 2with a single line through the centre. You may not use any of the words in the bank more than once.It’s quite remarkable how different genres of music can spark unique feelings, emotions, and memories. Studies have shown that music can reduce stress and anxiety before surgeries and we are all attracted toward our own unique life soundtrack.If you’re looking to____26____stress, you might want to give classical music a try.The sounds of classical music produce a calming effectletting____27____pleasure-inducing dopamine (多巴胺) in the brain thathelps control attention, learning and emotional responses.It can also turn down the body’s stress response, resulting in an overall happier mood. It turns out a pleasant mood can lead to____28____in a person’s thinking.Although there are many great____29____of classical music like Bach, Beethoven and Handel, none of these artists’ music seems to have the same health effects as Mozart’s does. According to researchers, listening to Mozart can increase brain wave activity and improve____30____function. Another study found that the distinctive features of Mozart’s music trigger parts of the brain that are responsible for high-level mental functions. Even maternity____31____use Mozart to help newborn babies adapt to life outside of the mother’s belly.It has been found that listening to classical music____32____reduces a person’s blood pressure. Researchers believe that the calming sounds of classical music may help your heart____33____from stress. Classical music can also be a great tool to help people who have trouble sleeping. One study found that students who had trouble sleeping slept better while they were listening to classical music.Whether classical music is something that you listen to on a regular basis or not, it wouldn’t____34____to take time out of your day to listen to music that you find____35____. You will be surprised at how good it makes you feel and the potentially positive change in your health.A) alleviateB) clarityC) cognitiveD) composersE) hurtF) inhibitingG) interrogationH) intrinsicallyI) looseJ) majesticK) mandatoryL) recoverM) significantlyN) soothingO) wardsSection BDirections: In this section, you are going to read a passage with ten statements attached to it. Each statement contains information given in one of the paragraphs. Identify the paragraph from which the information is derived. You may choose a paragraph more than once. Each paragraph is marked with a letter. Answer the questions by marking the correspondingletter on Answer Sheet 2.The Curious Case of the Tree That Owns ItselfA) In the city of Athens, Georgia, there exists a rather curious local landmark—a large white oak that is almost universally stated to own itself. Because of this, it is considered one of the most famous trees in the world. So how did this tree come to own itself and the land around it?B) Sometime in the 19th century a Georgian called Colonel William Jackson reportedly took a liking to the said tree and endeavored to protect it from any danger. As to why he loved it so, the earliest documented account of this story is an anonymously written front page article in the Athens Weekly Banner published on August 12, 1890. It states, “Col. Jackson had watched the tree grow from his childhood, and grew to love it almost as he would a human. Its luxuriant leaves and sturdy limbs had often protected him from the heavy rains,and out of its highest branches he had many a time gotten the eggs of the feathered singers.He watched its growth, and when reaching a ripe old age he saw the tree standing in its magnificent proportions, he was pained to think that after his death it would fall into the hands of those who might destroy it.”C) Towards this end, Jackson transferred by means of a deed ownership of the tree and a little land around it to the tree itself. The deed read, “W. H. Jackson for and in consideration of the great affection which he bears the said tree, and his great desire to see it protected has conveyed unto the said oak tree entire possession of itself and of all land within eight feet of it on all sides.”D) In time, the tree came to be something of a tourist attraction, known as The Tree That Owns Itself. However, in the early 20th century, the tree started showing signs of its slow death,with little that could be done about it. Father time comes for us all eventually, even our often long lived, tall and leafy fellow custodians (看管者) of Earth. Finally, on October 9,1942, the over 30 meter tall and 200-400 year old tree fell, rumor has it, as a result of a severe windstorm and/or via having previously died and its roots rotted.E) About four years later, members of the Junior Ladies Garden Club (who’d tended to the tree before its unfortunate death) tracked down a small tree grown from a nut taken from the original tree. And so it was that on October 9, 1946, under the direction of Professor Roy Bowden of the College of Agriculture at the University of Georgia, this little tree was transplanted to the location of its ancestor. A couple of months later, an official ceremony was held featuring none other than the Mayor of Athens, Robert L McWhorter, to commemorate the occasion.F) This new tree became known as The Son of the Tree That Owns Itself and it was assumed that, as the original tree’s heir, it naturally inherited the land it stood on. Of course, there are many dozens of othertrees known to exist descending from the original, as people taking a nut from it to grow elsewhere was a certainty. Thatsaid, to date, none of the original tree’s other children have petitioned the courts for their share of the land, so it seems all good. In any event, The Son of the Tree That Owns Itself still stands today, though often referred to simply as The Tree That Owns Itself.G) This all brings us around to whether Jackson ever actually gave legal ownership of the tree to itself in the first place and whether such a deed is legally binding.H) Well, to begin with, it turns out Jackson only spent about three years of his life in Athens,starting at the age of 43 from 1829 to 1832, sort of dismissing the idea that he loved the tree from spending time under it as a child and watching it grow, and then worrying about what would happen to it after he died. Further, an extensive search of land ownership records in Athens does not seem to indicate Jackson ever owned the land the tree sits on.I) He did live on a lot of land directly next to it for those three years, but whether he owned that land or not isn’t clear. Whatever the case, in 1832 a four acre parcel, which included the land the tree was on and the neighboring land Jackson lived on, among others, was sold to University professor Malthus A Ward. In the transaction, Ward was required to pay Jackson a sum of $1,200 (about $31,000 today), either for the property itself or simply in compensation for improvements Jackson had made on the lot. In the end, whether he ever owned the neighboring lot or was simply allowed to use it while he allegedly worked at the University, he definitely never owned the lot the tree grew on, which is the most important bit for the topic at hand.J) After Professor Ward purchased the land, Jackson and his family purchased a 655 acre parcel a few miles away and moved there. Ten years later, in 1844, Jackson seemed to have come into financial difficulties and had his little plantation seized by the Clarke County Sheriff’s office and auctioned off to settle the mortgage. Thus, had he owned some land in Athens itself, including the land the tree sat on, presumably he would have sold it to raise funds or otherwise had it taken as well.K) And whatever the case there, Jackson would have known property taxes needed to be paid on the deeded land for the tree to be truly secure in its future. Yet no account or record indicates any trust or the like was set up to facilitate this.L) On top of all this, there is no hard evidence such a deed ever existed, despite the fact that deed records in Athens go back many decades before Jackson’s death in 1876 and that it was supposed to have existed in 1890 in the archives according to the original anonymous news reporter who claims to have seen it.M) As you might imagine from all of this, few give credit to this sideof the story. So how did all of this come about then?N) It is speculated to have been invented by the imagination of the said anonymous author at the Athens Weekly Banner in the aforementioned 1890 front page article titled “Deeded to Itself”, which by the way contained several elements that are much more easily proved to be false. As to why the author would do this, it’s speculated perhaps it was a 19th century version of a click-bait thought exercise on whether it would be legal for someone to deed such a non-conscious living thing to itself or not.O) Whatever the case, the next known instance of the Tree That Owns Itself being mentioned wasn’t until 1901 in the Centennial Edition of that same paper, the Athens Weekly Banner. This featured another account very clearly just copying the original article published about a decade before, only slightly reworded. The next account was in 1906, again in the Athens Weekly Banner, again very clearly copying the original account, only slightly reworded, the 19th century equivalent of re-posts when the audience has forgotten about the original.36. Jackson was said to have transferred his ownership of the oak tree to itself in order to protect it from being destroyed.37. No proof has been found from an extensive search that Jackson had ever owned the land where the oak tree grew.38. When it was raining heavily, Jackson often took shelter under a big tree that is said to own itself.39. There is no evidence that Jackson had made arrangements to pay property taxes for the land on which the oak tree sat.40. Professor Ward paid Jackson over one thousand dollars when purchasinga piece of land from him.41. It is said the tree that owned itself fell in a heavy windstorm.42. The story of the oak tree is suspected to have been invented as a thought exercise.43. Jackson’s little plantation was auctioned off to settle his debt in the mid-19th century.44. An official ceremony was held to celebrate the transplanting of a small tree to where its ancestor had stood.45. The story of the Tree That Owns Itself appeared in the local paper several times, with slight alterations in wording.Section CDirections:There are 2 passages in this section. Each passage is followed by some questions or unfinished statements. For each of them there are four choices marked A), B), C) and D). You should decide on the best choice and mark the corresponding letter on Answer Sheet 2 with a single line through the centre.Passage OneQuestions 46 to 50 are based on the following passage.It is irrefutable that employees know the difference between right and wrong. So why don’t more employees intervene when they see someone exhibiting at-risk behavior in the workplace?There are a number of factors that influence whether people intervene. First, they need to be able to see a risky situation beginning to unfold. Second, the company’s culture needs to make them feel safe to speak up. And third, they need to have the communication skills to say something effectively.This is not strictly a workplace problem; it’s a growing problem off the job too. Every day people witness things on the street and choose to stand idly by. This is known as the bystander effect—the more people who witness an event, the less likely anyone in that group is to help the victim. The psychology behind this is called diffusion of responsibility. Basically, the larger the crowd, the more people assume that someone else will take care of it—meaning no one effectively intervenes or acts in a moment of need.This crowd mentality is strong enough for people to evade their known responsibilities. But it’s not only frontline workers who don’t make safety interventions in the workplace. There are also instances where supervisors do not intervene either.When a group of employees sees unsafe behavior not being addressed at a leadership level it creates the precedent that this is how these situations should be addressed, thus defining the safety culture for everyone.Despite the fact that workers are encouraged to intervene when they observe unsafe operations, this happens less than half of the time. Fear is the ultimate factor in not intervening. There is a fear of penalty, a fear that they’ll have to do more work if they intervene. Unsuccessful attempts in the past are another strong contributing factor to why people don’t intervene—they tend to prefer to defer that action to someone else for all future situations.On many worksites, competent workers must be appointed. Part of their job is to intervene when workers perform a task without the proper equipment or if the conditions are unsafe. Competent workers are also required to stop work from continuing when there’s a danger.Supervisors also play a critical role. Even if a competent person isn’t required, supervisors need a broad set of skills to not only identify and alleviate workplace hazards but also build a safety climate within their team that supports intervening and open communication among them.Beyond competent workers and supervisors, it’s important to educate everyone within the organization that they are obliged to intervene ifthey witness a possible unsafe act, whether you’re a designated competent person, a supervisor or a frontline worker.46. What is one of the factors contributing to failure of intervention in face of risky behavior in the workplace?A) Slack supervision style.B) Unfavorable workplace culture.C) Unforeseeable risk.D) Blocked communication.47. What does the author mean by “diffusion of responsibility” (Line 4, Para. 3)?A) The more people are around, the more they need to worry about their personal safety.B) The more people who witness an event, the less likely anyone will venture to participate.C) The more people idling around on the street, the more likely they need taking care of.D) The more people are around, the less chance someone will step forward to intervene.48. What happens when unsafe behavior at the workplace is not addressed by the leaders?A) No one will intervene when they see similar behaviors.B) Everyone will see it as the easiest way to deal with crisis.C) Workers have to take extra caution executing their duties.D) Workers are left to take care of the emergency themselves.49. What is the ultimate reason workers won’t act when they see unsafe operations?A) Preference of deferring the action to others.B) Anticipation of leadership intervention.C) Fear of being isolated by coworkers.D) Fear of having to do more work.50. What is critical to ensuring workplace safety?A) Workers be trained to operate their equipment properly.B) Workers exhibiting at-risk behavior be strictly disciplined.C) Supervisors create a safety environment for timely intervention.D) Supervisors conduct effective communication with frontline workers.Passage TwoQuestions 51 to 55 are based on the following passage.The term “environmentalist” can mean different things. It used to refer to people trying to protect wildlife and natural ecosystems. In the 21st century, the term has evolved to capture the need to combat human-made climate change.The distinction between these two strands of environmentalism is thecause of a split within the scientific community about nuclear energy.On one side are purists who believe nuclear power isn’t worth the risk and the exclusive solution to the climate crisis is renewable energy. The opposing side agrees that renewables are crucial, but says society needs an amount of power available to meet consumers’ basic demands when the sun isn’t shining and the wind isn’t blowing. Nuclear energy, being far cleaner than oil, gas and coal, is a natural option, especially where hydroelectric capacity is limited.Leon Clarke, who helped author reports for the UN’s Intergovernmental Panel on Climate Change, isn’t an uncritical supporter of nuclear energy, but says it’s a valuable option to have if we’re serious about reaching carbon neutrality.“Core to all of this is the degree to which you think we can actually meet climate goals with 100% renewables,” he said. “If you don’t believe we can do it, and you care about the climate, you are forced to think about something like nuclear.”The achievability of universal 100% renewability is similarly contentious. Cities such as Burlington, Vermont, have been “100% renewable” for years. But these cities often have small populations, occasionally still rely on fossil fuel energy and have significant renewable resources at their immediate disposal. Meanwhile, countries that manage to run off renewables typically do so thanks to extraordinary hydroelectric capabilities.Germany stands as the best case study for a large, industrialized country pushing into green energy. Chancellor Angela Merkel in 2011 announced Energiewende, an energy transition that would phase out nuclear and coal while phasing in renewables. Wind and solar power generation has increased over 400% since 2010, and renewables provided 46% of the country’s electricity in 2019.But progress has halted in recent years. The instability of renewables doesn’t just mean energy is often not produced at night, but also that solar and wind can overwhelm the grid during the day, forcing utilities to pay customers to use their electricity. Lagging grid infrastructure struggles to transport this overabundance of green energy from Germany’s north to its industrial south, meaning many factories still run on coal and gas. The political limit has also been reached in some places, with citizens meeting the construction of new wind turbines with loud protests.The result is that Germany’s greenhouse gas emissions have fallen by around 11.5% since 2010—slower than the EU average of 13.5%.51. What accounts for the divide within the scientific community about nuclear energy?A) Attention to combating human-made climate change.B) Emphasis on protecting wildlife and natural ecosystems.C) Evolution of the term ‘green energy’ over the last century.D) Adherence to different interpretations of environmentalism.52. What is the solution to energy shortage proposed by purists’opponents?A) Relying on renewables firmly and exclusively.B) Using fossil fuel and green energy alternately.C) Opting for nuclear energy when necessary.D) Limiting people’s non-basic consumption.53. What point does the author want to make with cities like Burlington as an example?A) It is controversial whether the goal of the whole world’s exclusive dependence on renewables is attainable.B) It is contentious whether cities with large populations have renewable resources at their immediate disposal.C) It is arguable whether cities that manage to run off renewables have sustainable hydroelectric capabilities.D) It is debatable whether traditional fossil fuel energy can be done away with entirely throughout the world.54. What do we learn about Germany regarding renewable energy?A) It has increased its wind and solar power generation four times over the last two decades.B) It represents a good example of a major industrialized country promoting green energy.C) It relies on renewable energy to generate more than half of its electricity.D) It has succeeded in reaching the goal of energy transition set by Merkel.55. What may be one of the reasons for Germany’s progress having halted in recent years?A) Its grid infrastructure’s capacity has fallen behind its development of green energy.B) Its overabundance of green energy has forced power plants to suspend operation during daytime.C) Its industrial south is used to running factories on conventional energy supplies.D) Its renewable energy supplies are unstable both at night and during the day.Part IV Translation (30 minutes)Directions: For this part, you are allowed 30 minutes to translate a passage from Chinese into English. You should write your answer on Answer Sheet 2.中国的传统婚礼习俗历史悠久，从周朝开始就逐渐形成了一套完整的婚礼仪式，有些一直沿用至今。
非水解溶胶-凝胶法制备莫来石晶须
非水解溶胶-凝胶法制备莫来石晶须江伟辉;彭永烽;刘健敏;冯果;谭训彦;于云【摘要】以正硅酸乙酯和无水氯化铝为前驱体,乙醚为氧供体,采用非水解溶胶-凝胶法制备了直径为0.2～20μm,长径比高达60～70的莫来石晶须.借助XRD、SEM和TEM等测试手段研究了莫来石干凝胶粉的活性、矿化剂氟化铝引入方式及其用量、成型压力以及煅烧温度等工艺参数对合成莫来石晶须的影响.结果表明:采用恒压回流工艺制备的莫来石干凝胶粉,在12MPa压力下压制成片状,以外置方式引入3wt%的氟化铝,在1200℃保温1h可制备质量较好的莫来石晶须.【期刊名称】《无机材料学报》【年(卷),期】2010(025)005【总页数】5页(P532-536)【关键词】非水解溶胶-凝胶法;莫来石;晶须;长径比【作者】江伟辉;彭永烽;刘健敏;冯果;谭训彦;于云【作者单位】景德镇陶瓷学院材料科学与工程学院,景德镇,333001;中国科学院上海硅酸盐研究所特种无机涂层重点实验室,上海,200050;景德镇陶瓷学院材料科学与工程学院,景德镇,333001;景德镇陶瓷学院材料科学与工程学院,景德镇,333001;景德镇陶瓷学院材料科学与工程学院,景德镇,333001;景德镇陶瓷学院材料科学与工程学院,景德镇,333001;中国科学院上海硅酸盐研究所特种无机涂层重点实验室,上海,200050【正文语种】中文【中图分类】TQ174莫来石晶须不仅具有耐高温、耐磨损、抗氧化等优良性能,而且还具有高温强度大、高温蠕变小、热膨胀较小和抗热震性好等特点[1],因此,它是一种优异的复合材料增强体,可以大幅度提高金属、聚合物以及陶瓷基复合材料的综合性能.不仅如此,与非氧化物晶须相比,它还能够在更高的温度和更恶劣的氧化条件下使用.目前,国内外合成莫来石晶须的方法主要有矿物分解法、熔盐法以及传统水解溶胶-凝胶法等.矿物分解法[2]直接采用粘土等矿物为原料,经高温煅烧,莫来石晶须从熔体中析出;熔盐法[3]主要是在莫来石前驱体中加入各种熔盐如 K2SO4,莫来石晶须于熔盐中析出.为了制备纯度较高的莫来石晶须,两者都要经过滤、洗涤和烘干等操作,工艺颇为复杂.而传统水解溶胶-凝胶法一般以硅的醇盐、铝的醇盐或铝的无机盐为前驱体,在制备的莫来石溶胶或干凝胶中加入生长矿化剂氟化物,如HF、AlF3等,在密闭的容器中煅烧而合成莫来石晶须.如 Okada等[4]以正硅酸乙酯和硝酸铝为原料,在制备的 A12O3-SiO2干凝胶中加入一定量的 AlF3,经 1100～1600℃密闭煅烧合成了长径比为 10～25的莫来石晶须.Is mail等[5]用相同的方法,用 HF代替了AlF3,经1400℃合成了长径比为 10～20的莫来石晶须.传统水解溶胶-凝胶法的不足之处在于合成莫来石的温度通常在1200℃以上,此时莫来石样品开始产生烧结,莫来石晶粒生长受到阻碍,制备的莫来石晶须长径比较小,不易合成高质量的莫来石晶须.与传统水解溶胶-凝胶法相比,非水解溶胶-凝胶技术具有工艺简单、制备周期短、晶须制备温度低等优势,但其溶胶-凝胶制备过程必须在干燥的环境中进行,否则会由于吸附环境中的水份而影响非水解缩聚反应.本研究采用非水解溶胶-凝胶技术[6],在1200℃制备出长径比达到 60～70的高质量莫来石晶须.1 实验1.1 试样制备以无水三氯化铝(CP)、正硅酸乙酯(AR)为前驱体,乙醚(AR)为氧供体,二氯甲烷(AR)为溶剂,氟化铝(Tech)为晶须催化剂.化学试剂均由国药集团化学试剂有限公司生产. 根据莫来石的理论组成n(Al)∶n(O)∶n(Si)= 6∶13∶2,在通风橱中称取0.0537mol无水三氯化铝置于 100mL的干燥锥形瓶中,量取 0.0179mol正硅酸乙酯倒入其中,室温快速磁力搅拌 15min,得到土黄色前驱体混合物;添加 0.0448mol 乙醚,继续搅拌得到黑色前驱体混合物溶液;然后采取恒压和恒容两种工艺制备莫来石干凝胶粉.恒压工艺是将前驱体混合物溶液于110℃油浴中加热回流 24h,得到莫来石干凝胶;恒容工艺则是在前驱体混合溶液中加入一定量的二氯甲烷作溶剂,继续搅拌 15min后,置于120mL的反应容弹内,在 90～130℃烘箱中,利用前驱体溶液自身产生的压力反应 16～32h,将生成的固态凝胶在烘箱低温干燥,得到干凝胶,分别将这两种干凝胶研磨粉碎备用.按内加和外置两种方式引入0～6wt%的氟化铝.其中,内加方式是将氟化铝与干凝胶粉直接混合均匀,造粒后用粉末压片机在 0～24MPa 的压力下压制成试片,然后将其置于密闭坩埚中煅烧;外置法是将干凝胶粉造粒后压成试片,再将试片置于已装有所需氟化铝的密闭坩埚中煅烧.煅烧制度如下:以4℃/min加热到350℃;然后,再以10℃/min升至 1100～1260℃,保温 1h,即可制备出高质量的莫来石晶须.1.2 测试及表征使用德国D8AdvanceX-ray衍射仪分析干凝胶在热处理过程中的晶相组成(CuKα辐射,波长0.154nm);运用中科院科学仪器厂 KYKY-1000B扫描电子显微镜观察莫来石晶须的形貌;借助日本JS M-2010透射电镜观察样品的形貌,并通过选区电子衍射和高分辨象分析晶须的取向生长.2 实验结果与讨论2.1 干凝胶粉制备工艺对合成莫来石晶须的影响分别以恒压和恒容两种工艺制备的莫来石干凝胶粉为原料合成莫来石晶须,结果见图 1(a)、(b).其中,外置氟化铝的用量为 3wt%,成型压力为12MPa,煅烧温度为1200℃.从图 1可以看出采用恒压工艺制备出的莫来石干凝胶粉所得到的晶须长径比大、质量好;而由恒容工艺制备出的莫来石晶须尺寸短、长径比小.恒容工艺制备出的莫来石干凝胶粉,比表面积很大(259.4m2/g),在煅烧过程中容易烧结成块,使晶须的生长空间受限制,致使晶须短小.相比之下,恒压工艺制备的干凝胶粉活性适中(比表面积为 16.4m2/g),在煅烧时,粉料不易烧结成块,有利于 F2气氛的扩散,给晶须生长提供了较大的空间,从而得到了大长径比的晶须.在以下的讨论中,均以恒压工艺制得的莫来石凝胶粉为原料.2.2 氟化铝引入方式对合成莫来石晶须的影响图 1 采用恒压(a)和恒容(b)两种工艺制备的干凝胶粉合成的莫来石晶须Fig.1 SEM micrographs ofmullite whiskers synthesized from xerogels prepared at constant pressure(a)and constant volume(b)为了探讨氟化铝引入方式对合成莫来石晶须的影响,采取了内加和外置两种加料方式,其中氟化铝的用量为 3wt%,成型压力为 12MPa,煅烧温度为1200℃.从图 2(a)可以看出:采用内加方式,试样仅出现少量长径比小的棒状晶须,大多为颗粒状和絮状夹杂物;而采取外置方式 (见图 2(b)),可得到晶须产率高、长径比大且分布均匀的莫来石晶须,且其中夹杂物少.这主要是由于采取内加方式时,矿化剂在试样中产生液相,促进了试样的致密化,导致气相氟化物不易在致密粉体中渗透,从而影响气相反应,不利于晶须生长.相比之下,外置方式不会在试样中产生液相而导致试样致密化,气相氟化物与固体粉料之间的气-固反应不受影响,其产物组成及反应过程也较容易控制,且反应均匀.因此,氟化铝以外置方式引入效果好.2.3 氟化铝用量对制备莫来石晶须的影响图3给出了氟化铝用量为 0、3wt%和 6wt%时试样的 XRD图谱,其中氟化铝的加料方式为外置,成型压力为12MPa,煅烧温度为1200℃.从图3中可以看出,当不加氟化铝时,试样所产生的衍射峰均为莫来石的衍射峰,无任何杂峰;当添加量为3wt%时,试样中的主晶相为莫来石,并伴随少量的刚玉相;随着氟化铝含量增至 6wt%,试样中除了主晶相莫来石以外,还含有刚玉相.图 2 采取内加(a)和外置(b)两种方式引入AlF3所制得的晶须Fig.2 SEM micrographs of mullite whisker with the inner addition(a)and outside addition(b)ofAlF3图 3 不同氟化铝用量制备的莫来石晶须的 XRD图谱Fig.3 XRD patterns of mullite whisker prepared with various amountsofAlF3(a)withoutAlF3;(b)3wt%AlF3;(c)6wt%AlF3不同氟化铝用量制备的莫来石晶须的 SEM照片见图 4.从图 4(a)中可以看出:不加氟化铝的试样,主要是颗粒状和板状结构相混合的莫来石;当加入3wt%氟化铝时(见图 4(b)),颗粒状莫来石已消失,取而代之的是沿一维方向生长的莫来石晶须,其直径为 0.2～2.0μm、长径比高达 60～70;当氟化铝的量为 6wt%时,莫来石呈现沿二维方向生长、厚度为0.5～1.5μm的片状结构 (见图 4(c)).当氟化铝不加或用量极少时,试样中产生的气相浓度低,晶须生长及晶须合成量受到限制;当氟化铝过多时,所产生的气相反应物浓度过大,超过了晶须定向生长所需的量,从而引起晶须径向生长的二维成核[7],莫来石易形成片状结构.AlF3与试样的适当配比是制备莫来石晶须的关键之一,其最佳用量为 3wt%.为了确定合成莫来石晶须的生长方向,图 5给出晶须的 TEM照片、选区电子衍射花样图(SAED)和HR-TEM照片.从图 5(a)和(b)中可看出,此棒状莫来石为单晶结构.根据衍射花样标定的 d值,计算出莫来石的晶胞常数为a=0.757nm,b=0.769nm,c= 0.288nm,与莫来石 XRD标准衍射卡片 (PDF15-0776)一致.同时还可知莫来石晶须的晶带轴为[1-10],沿晶须轴向衍射斑点对应于[001],莫来石的生长方向平行于[001],即沿 c轴方向生长 (见图5(c)).这主要是由于莫来石晶体中的{110}面具有相对其它晶面更低的表面能[8].因此,当莫来石针状晶核形成以后,其沿着 c轴的方向(也即[001]方向)以{110}面为界形成晶须.2.4 成型压力对制备莫来石晶须的影响不同成型压力对制备莫来石晶须的影响见图 6,其中氟化铝的加料方式为外置,氟化铝的用量为3wt%,煅烧温度为1200℃.从图 6(b)中可以看出当成型压力为 12MPa 时,此时获得的莫来石晶须质量最高、长径比最佳;当成型压力为 0时 (见图 6(a)),没有晶须存在,都是等轴状的晶粒,且晶粒与晶粒之间较为疏松;而当压力增至 24MPa 时 (见图 6(c)),莫来石晶粒并未生成一维莫来石晶须,而呈现米粒状颗粒,颗粒与颗粒间产生明显的烧结现象.当其他条件不变时,适当的压力使坯体密度适中,这一方面有利于矿化剂气相的扩散反应,晶须生长空间大,晶核易定向生长;另一方面也有利于莫来石颗粒间的固相传质.因此,最终形成的晶须量多、长径比大且分布均匀;反之,成型压力过大则坯体颗粒之间过于致密,导致气相传质困难,晶须生长空间受限,容易导致莫来石颗粒间的固相烧结.当成型压力为 0时,尽管此时气相传质很快,但是莫来石晶粒间传质很困难,无法确保晶粒沿一维优先生长,只能得到等轴状莫来石晶粒.图 4 不同氟化铝用量制备的莫来石晶须的 SEM照片Fig.4 SEM micrographs ofmullite whisker prepared with various amounts ofAlF3(a)WithoutAlF3;(b)3wt%AlF3;(c)6wt%AlF3图 5 晶须试样的 TEM照片(a),SAED(b)和 HRTEM照片(c)Fig.5 TE Mimage(a),SAED pattern(b)and HRTEM micrograph(c)of the whisker图 6 不同成型压力下制备的莫来石晶须的 SEM照片Fig.6 SEM micrographs ofmullite whisker prepared under various forming pressures(a)W ithout pressure;(b)12MPa;(c)24MPa图 7 不同煅烧温度下制备的莫来石晶须的 SEM照片Fig.7 SEM micrographsofmullite whisker calcined at differenttemperatures(a)1100℃;(b)1200℃;(c)1260℃2.5 煅烧温度对制备莫来石晶须的影响不同煅烧温度对制备莫来石晶须的影响见图 7,其中氟化铝的加料方式为外置,氟化铝的用量为3wt%,成型压力为12MPa.从图7中可以看出:晶须的最佳煅烧温度为1200℃;温度为1100℃时,所制备的晶须长径比较短;温度为1260℃时,晶须已明显粗化,长径比减小.煅烧温度较低时的氟化物气相浓度很低,气相传质不足,莫来石颗粒一维发育不够,故制备出的莫来石晶须长径比较小;煅烧温度过高,晶体沿各个方向生长速度差别缩小,导致晶须粗化.3 结论1)以正硅酸乙酯、无水氯化铝为前驱体,乙醚为氧供体,二氯甲烷为溶剂,通过非水解溶胶-凝胶法,引入氟化铝为矿化剂,制备出直径为 0.2～2.0μm、长径比高达 60～70的莫来石晶须;2)制备莫来石晶须的优化工艺为:采用恒压回流工艺制备的莫来石干凝胶粉,在12MPa的压力下压制成型,通过外置方式引入 3wt%的氟化铝,最后在1200℃热处理,保温 1h.参考文献:【相关文献】[1]王洪彬,张玉军,张敏.莫来石晶须研究进展.山东轻工业学院学报,2005,19(4):94-97.[2]Park YM,Yoon S Y,Stevens R,et al.Mullite whiskers derived from coal fly ash.Mater.Sci.Eng.A,2007,454-455:518-522.[3]Hashimoto Shinobu,YamaguchiAkira.Synthesis of needlelike mullite particles using potassium sulfate flux.J.Eur.Ceram.Soc., 2000,20(4):397-402.[4]Okada K,Otsuka N.Synthesis of mullite whiskers by vapour-phasereaction.J.Mater.Sci.Lett.,1989,8(9):1052-1054.[5]IsmailM,Arai H,Nakai Z,et al.Mullite whiskers from precursor gelpowders.J.Am.Ceram.Soc.,1990,73(9):2736-2739.[6]Niederberger M,Garnweitner anic reaction pathways in the nonaqueous synthesis ofmetal oxide nanoparticles.Chem.Eur.J., 2006,12(28):7282-7302.[7]李武.无机晶须.北京:化学工业出版社,2005:4-5.[8]Hong S H,Messing G L.Anisotropic grain growth in diphasic gel derived titania-doped mullite.J.Am.Ceram.Soc.,1998,81(5): 1269-1277.。
高中英语冀教版选择性必修第二册Unit2Let'sTalkMusic!Section3UsingEn
一、完形填空文章大意：本文是一篇记叙文。
文中叙述了一个名叫Samuel Osmond的音乐天才。
他在不会读乐谱的情况下，能把听到的乐曲弹奏出来。
他的记忆力好，不仅能记住乐曲，听到的故事也能复述。
1. Samuel Osmond is a 19-year-old law student from Cornwall, England. He never studied the _______. However, he can play very difficult musical pieces by musicians such as Chopin and Beethoven just a few minutes after he hears them. Two years ago, he _______his first piece Moonlight Sonata (奏鸣曲) by Beethoven. He _______ everyone around him. Amazed that he remembered this long and difficult piece of music and played it _______ music teachers said his ability was very rare. Music teachers told him he should study music instead. Now, he _______law and music. Samuel can’t _______why everyone is so surprised. “I _______with music. My mother played the piano and my father played the guitar. About two years ago, I suddenly decided to start playing the piano, without being able to read music and without having any music _______. It comes easily to me — I hear the notes (音符) and can bear them in _______—each and every note.” says Samuel.Recently, Samuel performed a piece during a special event at his college. The_______were impressed by his amazing performance._______, Samuel’s ability to remember things doesn’t stop with music. His family says that even when he was a young boy, Samuel _______ someone read a story, and thenhe could retell the _______word for word.As a teenager, he doesn’t know what he wants to do in the _______. For now, he is just happy to play beautiful music and _______his studies.1.A．song B．piano C．guitar D．law2.A．played B．acted C．spotted D．enjoyed3.A．worried B．delighted C．attracted D．surprised4.A．perfectly B．roughly C．simply D．nearly5.A．studies B．likes C．appreciates D．knows6.A．wonder B．understand C．explain D．explore7.A．turned up B．brought up C．showed up D．grew up8.A．questions B．advantages C．lessons D．plans9.A．mind B．heart C．head D．soul10.A．lawyers B．singers C．musicians D．audiences11.A．Thus B．Therefore C．However D．Instead12.A．learned B．heard C．taught D．caught13.A．pieces B．note C．story D．text14.A．life B．career C．way D．future15.A．trust B．realize C．continue D．end二、阅读选择(阅读理解)文章大意：本文是一篇说明文。
VOA慢速英语听力原文-劳动者之歌
美国劳动之歌Most of the world observes Labor Day on May 1. Butthe United States has its workers holiday on the firstMonday in September. Steve Ember and BarbaraKlein have a few songs from the history of theAmerican labor movement.Labor songs are traditionally stories of struggle and pride, of timeless demands for respect and the hopefor a better life.Sometimes they represent old songs with new words. One example is "We Shall Not Be Moved."It uses the music and many of the same words of an old religious song.Here is folksinger Pete Seeger with "We Shall Not Be Moved."Many classic American labor songs came from workers in the coal mines of the South. Mineowners bitterly opposed unions. In some cases, there was open war between labor activistsand coal mine operators.Once, in Harlan County, Kentucky, company police searched for union leaders. They went to oneman's home but could not find him there. So they waited outside for several days.The coal miner's wife, Florence Reece, remained inside with her children. She wrote this song, "Which Side Are Y ou On?"Again, here is Pete Seeger.Probably the most famous labor songwriter in America was Joe Hill. He was born in Sweden andcame to the United States in the early 1900s. He worked as an unskilled laborer.Joe Hill joined the Industrial Workers of the World, known as the Wobblies. More than any otherunion, they used music in their campaigns, urging members to "sing and fight."One of Joe Hill's best-known songs is "Casey Jones." It uses the music from a song about atrain engineer. In the old song, Casey Jones is a hero. He bravely keeps his train running in verydifficult conditions.In Joe Hill's version, Casey Jones is no hero. His train is unsafe. Y et he stays on the job afterother workers have called a strike against the railroad company.Pete Seeger and the Song Swappers sing "Casey Jones (The Union Scab)."Another American labor song is called "Bread and Roses." That term was connected with thewomen's labor movement.The song was based on a poem called "Bread and Roses" by James Oppenheim. The poem waspublished in The American Magazine in December of 1911.The following month there was a famous strike by textile workers in Lawrence, Massachusetts.They won higher pay and better working conditions. Oppenheim's poem gained more attention.At that time, conditions in factories were already a national issue. In 1911, a fire at a clothingfactory in New Y ork had taken the lives of 146 people. The victims were mostlyimmigrantwomen.Here is Pat Humphries with "Bread and Roses."Union activists know that labor songs can unite and help people feel strong. This can be trueeven when the music has nothing to do with unions."De Colores" is a popular Spanish folksong. It talks about fields in the spring, little birds,rainbows and the great loves of many colors.This song is popular with supporters of the United Farm Workers union. We listen as BaldemarV elasquez leads the band Aguila Negra in "De Colores."For many years, folksinger Joe Glazer was a union activist with a guitar. He was also a laborhistorian. Labor's Troubadour was the name of a book he about his life. He believed in organized labor and preserving the musical history of the American labor movement. JoeGlazer died in 2006 at the age of 88.Here is Joe Glazer with "Solidarity Forever," written by Ralph Chaplin.From VOA Learning English, this is the Agriculture Report.这里是美国之音慢速英语农业报道。
Waste-to-resource preparation of a porous ceramic membrane
Available online at ScienceDirectJournal of the European Ceramic Society35(2015)711–721Waste-to-resource preparation of a porous ceramic membrane support featuring elongated mullite whiskers with enhanced porosity and permeance Li Zhu a,b,Yingchao Dong a,b,∗,Stuart Hampshire c,Sophie Cerneaux d,Louis Winnubst ea CAS Key Laboratory of Urban Pollutant Conversion,Institute of Urban Environment,Chinese Academy of Sciences,PR Chinab Ningbo Urban Environment Observation and Research Station—NUEORS,Chinese Academy of Sciences,PR Chinac Materials and Surface Science Institute(MSSI),University of Limerick(UL),Limerick,Irelandd Institut Europeen des Membranes,UMR5635,Place Eugene Bataillon,34095Montpellier Cedex5,Francee Inorganic Membranes,MESA+Institute for Nanotechnology,University of Twente,PO Box217,7500AE Enschede,The NetherlandsReceived16June2014;received in revised form1September2014;accepted9September2014Available online1October2014AbstractDifferent from traditional particle packing structure,a porous structure of ceramic membrane support was fabricated,featuring elongated mullite whiskers with enhanced porosity,permeance and sufficient mechanical strength.The effect of additives(MoO3and AlF3)and sintering procedure on open porosity,mechanical properties,pore size distribution,micro-structure,phase structure,and permeance of the membrane supports was characterized in detail.The introduction of MoO3and AlF3promoted formation of a porous whisker-interlocked structure,which effectively improved open porosity and permeance.A mullite membrane support containing5wt.%MoO3and4wt.%AlF3exhibited an open porosity as high as48.6±0.5%,a mechanical strength of81.2±3.2MPa at1200◦C,and the value of permeance was higher than the membrane without any additives.Such enhancements in porosity and permeance,with sufficient mechanical strength,were a result of tortuosity decrease due to a porous structure of interlocked mullite whiskers.©2014Elsevier Ltd.All rights reserved.Keywords:Ceramic membrane support;Porosity;Mechanical strength;Mullite whiskers;Permeance1.IntroductionPorous ceramic separation membranes are used in industrial fields due to their unique advantages,such as excellent tempera-ture stability,good pressure resistance,good chemical stability, long life and good antifouling properties.1However,commercial porous ceramic membranes still cannot fulfill increasing envi-ronmental requirements at a large scale such as separation in strong alkaline media and massive liquid waste treatment due to the limited types of membrane materials2(such as Al2O3,ZrO2, SiO2,TiO2and their composites).Besides,high cost,associated with starting materials and formation/sintering processes,makes extensive applications of ceramic membranes still limited.3,4As ∗Corresponding author at:CAS Key Laboratory of Urban Pollutant Conver-sion,Institute of Urban Environment,Chinese Academy of Sciences,Xiamen, PR China.Tel.:+8605926190790;fax:+8605926190790.E-mail addresses:ycdong@,dongyc9@(Y.Dong).a result,the preparation and potential applications of porous mineral-based ceramic membranes(kaolin,5bauxite,6sepiolite clay,7industrial solid waste coalfly ash,8etc)have attracted more attention due to the low cost of abundant raw materi-als available worldwide.For example coalfly ash emerges as a by-product from the combustion of raw coal in thermal power plants.9Without suitable treatment,fly ash may be a source of dust which adversely affects our environment.Therefore,it is necessary to utilize this waste not only to decrease environmen-tal pollution but to produce high added-value products from it. Especiallyfly ash containing Al2O3and SiO2is suitable for the fabrication of dense mullite-based ceramics,as has been proven in.10,11Recently a study has been made on the conversion of coal fly ash to mullite(3Al2O3·2SiO2)for the preparation porous ceramic membranes.12As a structural material,porous mineral-based mullite is expected to be a promising candidate for ceramic membrane supports especially because of its excellent high temperature resistance,good corrosion resistance,abundant natural Al and/10.1016/j.jeurceramsoc.2014.09.016 0955-2219/©2014Elsevier Ltd.All rights reserved.712L.Zhu et al./Journal of the European Ceramic Society35(2015)711–721Si-sources,low cost,and environment friendliness.13These properties are especially important for porous mullite,which is used asfilter membrane for treatment of great volumes of liquid/gas effluents,which requires the use of porous support with higher porosity and good mechanical strength in order to maintain a lower pressure drop across thefilter membrane and to withstand the pressure gradient imposed during practical separation applications.Traditionally,the open porosity of a ceramic membrane is limited by the intergranular packing effect of the starting pow-der or precursor,mainly depending on its morphology and particle size distribution.It is well known that porosity can be effectively controlled by varying sintering conditions such as sintering temperature and dwelling time.14High tempera-ture partial sintering is required to produce sintering necks, endowing porous ceramic membrane with sufficient strength, while degrading open porosity to some extent.Normally,an improvement in open porosity,which is required to endow a lowfluid resistance,is achieved with addition of pore-forming agents such as graphite powder or some organic compounds,15,16which burn out or decompose completely dur-ing heating.However,the pores produced in this way are usually believed to deteriorate the mechanical reliability.17It is usually hard and thus of great importance tofind a way to produce high porosity without alteration of mechanical strength of ceramic membrane supports,which are expected to withstand large pressure gradient imposed during prac-tical separation applications.Apart from high mechanical strength,a proper ceramic membrane support should have high permeability.18Recently,mullite whiskers have been widely investigated as candidates for reinforcement of ceramic-based composites due to their high aspect ratio and high strength.19Several approaches, such as addition of AlF311,19,20to starting material mixtures,are developed to produce mullite-whisker-reinforced composites.In order to further enhance mullite phase content at low tempera-tures,some sintering aids(such as V2O5,21MgO,22TiO212and WO323)are used during fabrication of low-cost porous mullite. However,there are few reports with MoO3as sintering addi-tive.Since Mo and W are in the same subgroup of the element periodic table,associated with the lower melting point of MoO3 (795◦C),it is expected that addition of MoO3accelerates the growth of mullite crystals and thus enhances mullite content at lower temperatures.Different from traditional particle packing structure processed by partial sintering,in this work,with MoO3and AlF3as additives,a highly porous structure of inter-locked mul-lite whiskers is realized in mullite membrane support made from waste coalfly ash and bauxite.The present study aims at elaborating a new type of porous structure for ceramic membrane support with enhanced porosity and permeance,but without significant degradation of mechanical property.The effect of additives and sintering parameters on the main prop-erties of porous mullite membrane supports is studied in detail, mainly including porosity,mechanical properties,pore size dis-tribution,micro-structure(SEM and phase compositions)and permeance.2.Experimental procedures2.1.Starting materials for membrane supportCoalfly ash(Ningbo,Zhejiang Province,China)and nature bauxite(Yangquan,Shanxi Province,China)were used as the starting materials.AlF3(98–102%,Guangfu Fine Chemical Reagent Ltd.,Tianjin,China)and MoO3(Sinopharm Chemi-cal Reagent Co.,Ltd)were used as crystallization catalyst and mineralizer,respectively.Based on mullite stoichiometric composition (3Al2O3·2SiO2),a series of MoO3–AlF3doped and undoped mullite membrane supports were prepared by adding various weight percents(wt.%)of AlF3(x wt.%)and MoO3(y wt.%) into the powder mixture offly ash and bauxite.All samples are labeled as A x M y.A stands for AlF3,M for MoO3,and the numbers following them represent their mass percentage in the samples(e.g.A0M0for the sample without addition of AlF3 and MoO3,A4M5for the sample with addition of4wt.%of AlF3and5wt.%of MoO3).2.2.Fabrication of membrane supportThe raw materials with different compositions were wet-ball-milled in distilled water for12h using a planetary ball-milling machine(SFM-1,Hefei Kejing Materials Technology Co.,Ltd) at a milling speed of400rpm.After complete drying,the milled powders were uniformly mixed with organic binder PV A-1750 (5.0wt.%solution)in an alumina mortar and then uniaxially pressed into cylindrical pellets(20mm in diameter and1–2mm in thickness)at a pressure of190MPa.The green disc-shape membrane supports were placed in a closed alumina crucible and sintered in an electrically heated muffle furnace in air atfinal temperatures ranging from1100◦C to1500◦C for 2h.2.3.Characterization and testParticular emphasis is placed on characterization of mem-brane properties of the supports:open porosity,pore size distribution,mechanical strength,gas and water permeances.A detailed microstructural analysis was performed to under-stand the formation process and the reinforcement of this mullite membrane support.The particle size distribution offly ash and bauxite was determined by a laser particle size analyzer(Mastersizer2000, Malvern Instruments Ltd.,UK).Chemical compositions of the raw materials(coalfly ash and natural bauxite)were exam-ined by X-rayfluorescence spectrometry(WDXRF,PANalytical Corporation,The Netherlands).Open porosity was determined by the Archimedes method24 with water as the liquid medium.Pore size distribution was measured by a pore size distribution analyzer(PSDA-20,Nan-jing Gaoqian function materials Co.Ltd.,China)based on a gas–liquid displacement method.The pore diameter can beL.Zhu et al./Journal of the European Ceramic Society35(2015)711–721713 calculated from the Washburn’s equation using the bubble-pointmethod22,25,26:d=4γcosθp(1)whereγis the surface tension coefficient of the liquid,θis the contact angle of the liquid on the pore wall and p is the applied pressure difference.In most cases,the shape of the pore tunnels is irregular,and the pore size is thus defined as the diameter of a circle which area is equal to the pore throat.25Biaxialflexural strength(BFS)was measured by a universal testing machine(AGS-X,Shimadzu Ltd.,Japan).BFS was cal-culated using the formula for maximum tensile stress given by Timoshenko and Woinowsky-Krieger27:BFS(MPa)=Nt2{(1+ν)[(0.485ln(a/t)+0.52]+0.48}(2)where N is the load(N),νis Poisson’s ratio(ν=0.26in this study),a is the radius of the support circle(m)and t is the thickness of the specimen(m).Weibull analysis was conducted on the results of biaxialflex-ural strength.The Weibull analysis curves28were made using lnσand lnln[1/(1−P f)]plot as X-axis and Y-axis,respectively, whereσis the biaxialflexural strength,P f is he fracture proba-bility.The latter P f is defined by the relation P f=i/(N+1),where i is the rank in biaxialflexural strength from smallest to largest and N denotes the total number of samples(here N=10in our study).The fracture energy was determined using the following equation:E a=Ni=1E iπa2t i×10−3N(3)where E a is the fracture energy per unit volume,E i is the fracture energy of sample i,a is the circumcircle radius of the three support balls(a=5mm in our study),N is the total number of test bodies(N=10in our study),t i is the average thickness of sample i.Microstructures of the sintered samples were analyzed by scanning electron microscopy(SEM,S-4800,Hitachi LTD., Japan).Phase analysis of the raw materials and sintered samples was determined by X-ray diffraction(XRD,D8advance,Bruker Corporation,Germany).XRD quantitative analysis based on the normalized reference intensity ratio(RIR)method,was adopted to calculate the mullite content in the sintered samples.292.4.Waterflux and permeance studyA home-made dead-endflow setup was used for water per-meance studies.The stainless-steel setup mainly consists of a top cylindrical water container and a base plate with a provi-sion to keep a support.The support is rested on a perforated disk(casing)and placed in the bottom compartment.The trans-membrane pressure for these experiments was in the range of 0.05–0.3MPa.The permeateflow rate was recorded at10min Fig.1.Open porosities of the sintered membrane supports with addition of 0–10%wt.%of MoO3and0–4%wt.%of AlF3as a function of sintering tem-perature.intervals for1h and the measurements were repeated for all the samples.2.5.N2flux and permeance studyN2permeance studies were performed at25◦C at differential pressures ranging from0.05to0.3MPa with0.05MPa intervals in a dead-end mode with the inlet pressure controlled by a pres-sure regulator and a digital pressure gauge.The gasflow across the membrane was measured with a bubbleflow meter on the exit gas stream of the membrane support.The samples were held at each pressure step until a steadyflow rate was achieved. 3.Results and discussion3.1.Characterization of membrane materialsThe chemical compositions of the coalfly ash and bauxite are given in Table1.The coalfly ash mainly consists of mullite (3Al2O3·2SiO2,PDF no.15-0776),belonging to primary mul-lite,which is formed from aluminosilicate clay minerals duringthe combustion process of raw coal.As to bauxite,the main crystalline phases detected are diaspore(AlO(OH),PDF no.87-0705)and kaolinite(Al2O3·2SiO2·2H2O,PDF no.78-2109). The average particle diameters of coalflyash and bauxite parti-cles are2.1m and1.2m,respectively.Most of the mixtures particle size after ball-milling center between1.1m(d10)and 4.3m(d90)in diameter.3.2.Open porosity and mechanical propertyFig.1indicates that the open porosity without additives (A0M0)shows a gradually-decreasing trend with sintering temperature.This result is similar to porous mullite,derived from the kaoline–alumina system,30but different from the trend of increasing porosity with increasing sintering temper-ature at certain range for thefly-ash–bauxite system involving714L.Zhu et al./Journal of the European Ceramic Society35(2015)711–721Table1Main chemical composition(wt.%)offly ash and natural bauxite measured by semi-quantitative XRF.Materials Chemical composition(%)Al2O3SiO2CaO Fe2O3TiO2SO3K2O Na2O Others Fly ash44.7644.17 4.57 3.02 1.920.440.40.220.49 Bauxite63.5310.410.477.08 2.980.180.280.150.52 The loss on ignition offly ash and bauxite is1.01and14.40wt.%,respectively.a sintering self-expansion,as reported in Ref.[6],which is possibly due to the difference in chemical compositions of raw materials.The samples with MoO3and AlF3(A4M5 and A4M10)have higher porosities at all temperatures as compared with A0M0.For A4M5,porosities as high as 46.9±0.4–48.6±0.5%are achieved at1100–1300◦C,then decreased to41.6±0.9–29.8±1.2%at1400–1500◦C due to the occurrence of a sintering densification.With addition of the same amount of AlF3(4wt.%),open porosity slightly increases with MoO3content(from5to10wt.%).These results indi-cate that co-addition of MoO3and AlF3is quite effective in enhancing open porosity of mullite membrane supports.When comparing A4M5with A0M0,it is interesting to note that the increase in porosity of the samples with addition of AlF3and MoO3is not followed by the degradation in mechanical strength at temperatures below1300◦C(see Fig.2a).The biaxial flexural strengths of the A4M5samples are at the same level with those of the samples without any additive from1100◦C to 1200◦C.Although the strengths of A4M5are lower than those of A0M0at1300–1500◦C,higher porosity enhancements are realized for A4M5when compared with A0M0.In particular, given the same level of biaxialflexural strength,A4M5always exhibits higher porosity than A0M0(Fig.2b).Fracture energy(Fig.2c)of A4M5and A0M0gradually increases with sintering temperature,which is consistent with the variation of biaxialflexural strength with sintering tem-perature(Fig.2a).At each temperature,A4M5exhibits higher fracture energy than A0M0.From1100to1400◦C,the fracture energy of A0M0increases from8.7±2.1to25.4±2.0kJ m−3. Upon MoO3and AlF3addition,the samples exhibit higher fracture energy(9.6±2.1to30.0±2.2kJ m−3).These improve-ments of fracture energy are ascribed to a new structure of a large quantity of compact interlocked needle-like mullite whiskers, which will be studied by SEM(Fig.7).This effect is similar to that reported by Li et al.,21where microstructural homogene-ity was improved and mechanical properties could be tuned by doping with V2O5.Fig.2d shows the Weibull analysis of the biaxialflexural strength results of A0M0and A4M5sintered at1200–1400◦C. Most of the points(lnσversus lnln[1/(1−P f)])center close to the correspondingfit lines,which proves a good reliability of the BFS results.In summary,with addition of MoO3and AlF3,open poros-ity is significantly improved without degradation of mechanical strength.At the same level of strength,A4M5always exhibits higher open porosity than A0M0.The A4M5membrane sup-port sintered at1200◦C possesses an enhanced open porosity as high as approximately48.6±0.5%,and an excellent strength of 81.2±3.2MPa.Forfiltration membrane application,pore size distribution,gas and water permeation properties are important and thus studied in the following subsections.3.3.Pore size distributionPore size distributions are closely related tofinal sintering temperatures.A0M0shows a unimodel distribution of pore size for all the sintering temperatures.The average pore sizes of A0M0(Fig.3a)are found to be0.32,0.33and0.37sintered at 1200◦C,1250◦C,and1300◦C,respectively.A gradual increase in average pore size is observed due to the sintering-induced growth of grains(which will be justified by the SEM results, Fig.6),leading to the formation of large pores and elimination of small pores at high temperature.These trends are similar with mullite membrane supports prepared in previous work.6 Compared with A0M0,the mean pore sizes of A4M5become smaller at all sintering temperatures.The average pore diameters at1200◦C,1250◦C and1300◦C are0.18,0.15and0.26,respec-tively(Fig.3b).The membranes supports show typical bimodal pore size distributions having maximum number of pores in two regions,56–70%of pores between0.20and0.45m and 30–44%of pores between0.08and0.20m.Based on the SEM images shown in Fig.7,the bimodal pore size distributions are probably due to the formation and growth of stiff skeleton needle-like mullite crystals,resulting in formation of somefiner pores among them.263.4.XRD analysisFig.4indicates that the two XRD patterns of A0M0and A4M5sintered at1100◦C are similar,consisting of mullite(PDF no.15-0776)characteristic peaks,weak characteristic peaks of cristobalite(PDF no.27-0605)and corundum(PDF no.10-0173).The dependence of mullite phase content on sintering temperature based on RIR analysis(Fig.5)shows the mullite content in A0M0(28%)is lower than that in A4M5(48%).In the A0M0sample,cristobalite is detected until1250◦C,which reacted with alumina,contributing to the formation of mullite phase.While in the A4M5sample,cristobalite is not detected when the sintering temperature increases up to1200◦C,where the mullite content is72%.This great increase in mullite content from48%to72%is due to the rapid formation of secondary mul-lite from1100◦C to1200◦C.The content of mullite does not significantly increase between1200◦C and1400◦C.By con-trast,the content of mullite in A0M0increases gradually from 32%to76%as the sintering temperature increases from1100◦C to1300◦C.L.Zhu et al./Journal of the European Ceramic Society35(2015)711–721715Fig.2.Biaxialflexural strength test results of the membrane supports with various compositions(a)biaxialflexural strength and open porosity versus sintering temperature,(b)biaxialflexural strength versus porosity,(c)fracture energy versus sintering temperature and(d)Weibull analysis.Standard deviations are not presented as they are very small.Fig.3.Pore size distributions of A0M0((a)and(A))and A4M5((b)and(B))sintered at different temperatures.716L.Zhu et al./Journal of the European Ceramic Society 35(2015)711–721Fig.4.XRD patterns of the A0M0(a)and A4M5(b)membrane supports sintered at various temperatures for 2h.Fig.5.Effect of sintering temperature on mullite content in the A4M5and A0M0membrane supports.During high-temperature sintering,Firstly,AlF 3reacted with O 2to form AlOF,and then AlOF reacted with the reaction prod-uct SiF 4to produce mullite at a lower temperature.The existence of MoO 3lowered the melting temperature of silica-rich glassy liquid and decreased the high-temperature viscosity of the liq-uid system,which was favorable to the formation of silica-rich liquid phase and thus promoted mass transportation during the reaction between Al 2O 3and SiO 2.The Al 2O 3dissolved into the glassy phase for second mullite formation.While the reaction between Al 2O 3and SiO 2went on,the mullite crystals grew up.The excess SiO 2in fly ash was thus consumed with the rapid for-mation of large crystals of secondary mullite at 1100–1300◦C.It is reasonable to assume that MoO 3acted as heterogeneous centers where mullite nucleation could be induced at lower tem-peratures,leading to lower mullitization temperature.This is similar with the positive effect of V 2O 5on sintering of mul-lite membrane supports.21With AlF 3and MoO 3addition,the temperature,at which mullite phase was formed,is lowered by 150◦C as compared with the samples prepared without any additives.3.5.Microstructural analysis of membrane supportThere is a great difference in microstructure evolution for A0M0and A4M5(Figs.6and 7).From Fig.6a,it is found that porous structure is formed by partial-sintering of mixture particles of fly ash and bauxite without morphological change (A0M0)at 1100◦C.From 1200to 1300◦C (Fig.6b and c),sin-tering is gradually enhanced with the presence of larger pores at 1300◦C,which is consistent with the pore size distribution results (see Fig.3a).With further increasing firing temperature up to 1400◦C,an obvious densification is observed,which cor-responds to the rapid decrease in open porosity as discussed above (see Fig.1).Comparing Fig.6a–d with Fig.7a–d,it is found that with the addition of the additives,a large amount of very fine mul-lite whiskers are observed to be distributed around some large particles in a porous structure at 1100◦C.With increasing tem-perature to 1200◦C,a uniform porous microstructure is formed,entirely composed of grown mullite whiskers (Fig.7b),which act as a skeleton of pore structure.With further increasing sin-tering temperature (1300◦C)(Fig.7c),mullite whiskers grow thicker and longer and interlocked with each other.A highly porous structure is observed for the sample sintered at 1300◦C.The formation of stiff skeleton needle-like mullite is very favor-able to increase the open porosity (consistent with the above results in Fig.2).The surface of A4M5-1300is more porous than that of A0M0-1300,indicating that the accelerated anisotropical growth of mullite whiskers induced by AlF 3and MoO 3favors the enhancement of open porosity (consistent with the above results in Fig.1).This type of grain morphology is quite essen-tial for developing highly porous filtration membrane with strong mechanical integrity.Fig.8shows the freshly fractured surface SEM images,after biaxial flexural strength tests,of A0M0and A4M5mem-brane supports sintered at 1200◦C and the proposed fracture mechanism schematic diagram.For A0M0sintered at 1200◦CL.Zhu et al./Journal of the European Ceramic Society35(2015)711–721717Fig.6.Fracture surface SEM images of the A0M0membrane supports sintered at various temperatures:(a)A0M0—1100◦C,(b)A0M0—1200◦C,(c) A0M0—1300◦C and(d)A0M0—1400◦C.(Fig.8a),most of the fractures upon failure occur from larger glassy phase regions between partially-sintered mullite crystals (as those indicated by red circles in the fracture mechanism schematic diagram made using CATIA software).The frac-ture is completely intergranular,which absorbs lower fracture energy during strength test because of lower intrinsic strength of glassy phase(see Fig.2c).Due to the addition of MoO3and AlF3,open porosity becomes higher,while there is also a sig-nificant change in the microstructure of the fabricated mullite membrane support,which is entirely composed ofinterlocked Fig.7.Fracture surface SEM images of the A4M5membrane supports sintered at various temperatures:(a)A4M5—1100◦C,(b)A4M5—1200◦C,(c) A4M5—1300◦C and(d)A4M5—1400◦C.718L.Zhu et al./Journal of the European Ceramic Society 35(2015)711–721Fig.8.Freshly fractured surface SEM images (left)and fracture mechanism schematic diagram (right)of the A0M0(a)and A4M5(b)membrane supports sintered at 1200◦C after biaxial flexural strength tests.mullite whiskers without the presence of glassy phase.The inter-grown rod-like mullite crystals (as those indicated by the circles in Fig.8b)could impart good mechanical strength and structure rigidity to the porous mullite support.These inter-locked mullite whiskers are expected to exhibit excellent mechanical properties such as high strength and high modulus since they absorb much higher fracture energies than partially-sintered glassy phase par-ticles (see Fig.2c),consequently resulting in an enhancement in mechanical strength.19,22Possible bridging crack and pull-out of bonded mullite whiskers in aligned way also contribute to this enhancement in strength,31as well indicated in Fig.8b.In summary,with addition of MoO 3and AlF 3,formation of more inter-locked mullite whiskers,which adsorb more energy during fracture,is responsible for the improvement in open porosity of A4M5and mechanical strength compared with A0M0sintered from 1100to 1400◦C.Besides,possible bridg-ing crack and pull-out of bonded mullite whiskers in aligned way also contribute to this strength enhancement.3.6.Water permeance across membrane supportsWater flux (Fig.9a)of A0M0and A4M5increases with trans-membrane pressure as well as sintering temperature.In all cases,the water flux increases linearly with transmembrane pressure,which indicates that pressure difference is the only driving force for the permeation of water.When the transport mechanism fol-lows the viscous flow model,the flux versus transmembrane pressure plot should be expressed as a straight line which coin-cides with the origin (Darcy’s law),32as indicated in this study.Similar trends were also reported for the other porous inor-ganic clay-based membranes.5In Fig.9b,an approximately linear relationship exists between water permeance and aver-age transmembrane pressure,indicating a preferential laminar flow mechanism in the mullite membrane supports.333.7.Nitrogen gas permeance across membrane supportsA pure,non-adsorbing gas flow through a homogeneous porous structure may be described by Knudsen diffusion,vis-cous flow,surface diffusion,dissolution diffusion,or some combination of these processes.The mechanism of gas transport through microporous membrane depends upon the pore size (r )of the membrane relative to the mean free path (λ)of the gas molecule.Knudsen diffusion occurs in small pores where colli-sions of the gas molecules with the pore walls have a significant effect on their movement.Viscous flow describes the situation where the pores are large enough so that the viscosity of the gas controls the flow rate through a porous body.In some cases,permeation may also be enhanced by the reaction of the gas with the pore wall surface,i.e.surface diffusion.When the membrane has pores comparable to the size to the mean free path of the gas molecule,the permeation flux through the membrane can be considered as a combination of Knudsen diffusion and viscous flow.So the permeation of the gas through the porous structure may be modelled by treating Knudsen diffusion and viscous flow as parallel processes,as shown in the following equation 34J =εr τk [2ν/3RTL ]P +εr 2τv [1/8RTLη]¯pP (5)where the flux J of a gas component is a function of:(i)gas properties,such as the gas mean molecular velocity νof the gas and the viscosity of the gas η,and the gas mean molecular velocity νis given byν= 8RT πM(6)where M is the gas molecular mass;(ii )the differential pressure across the membrane P ;(iii)the average pressure within the membrane ¯p ;(iv)the membrane thickness L ;and (v)the pore characteristics:open porosity ε,pore radius r and the tortuosity factor of the pores corresponding to either the Knudsen τk or vis-cous flow τv mechanisms.The tortuosity factors compensate for the pore structure features,which deviate from uniform straight pore structure.The gas permeance of a porous membrane,which is equal to the flux normalized by the pressure difference of the gas across the membrane (J /P ),is given byJ P =εr τk [2ν/3RTL ]+εr 2τv [1/8RTLη]¯p (7)Plotting the gas permeance vs.average pressure yields a straight line of the form:JP=a +b ¯p (8)。
高中英语冀教版选择性必修第二册Unit2Let'sTalkMusic!Section4Expandi
一、完形填空文章大意：本文是一篇记叙文。
文章主要讲述了“失落之声”是一个激励性的倡议，为具有挑战性的背景的青少年提供一个通过音乐表达自己的平台，帮助他们找到自己的声音并从创伤中治愈。
1. Music has universal power. It helps people from all walks of life find their creative_______. Lost Voices is an inspiring initiative that_______teenagers with challenging backgrounds with a platform to express themselves through music._______, it helps them find their voice and heal from trauma (创伤).Mike Ball, the founder of Lost Voices, first_______this population in 2005. Invited to speak about his_______career, he saw these kids. “They’re just like other children; they’re just in a different situation.” he said. He firmly believes that these young individuals are often overlooked and_______by the world. His mission is to change that by bringing their voices out.As a writer and music enthusiast, Ball recognized the potential of songwriting asa_______and creative outlet for these young individuals. Motivated by this_______, he called on local folk and blues musicians to join him. With a track record of impacting over 2,500 vulnerable (易受伤害的) youths, these initiatives havefacilitated_______therapeutic (治疗的) progress and many of the youths have benefited from the initiatives.Lost Voices conducts week-long programs, sending musicians into residential treatment facilities to________with the children in small groups. Through this process, the musicians guide and________the participants to craft their own songs, ultimately helping them find their unique voices.Through the________of individuals like Mike Ball and the________efforts of the musicians involved, Lost Voices serves as a signal of________for these often-forgotten young souls. It shows that their beautiful voices and great talents________to be heard by the world.1.A．gestures B．expressions C．thoughts D．talents2.A．rewards B．entertains C．provides D．challenges3.A．Meanwhile B．Otherwise C．Instead D．However4.A．greeted B．invited C．introduced D．encountered5.A．writing B．singing C．teaching D．recording6.A．misunderstood B．criticized C．changed D．unheard7.A．familiar B．positive C．loving D．humorous8.A．recommendation B．judgment C．realization D．creativity 9.A．frightening B．smooth C．plain D．significant10.A．engage B．play C．debate D．act11.A．watch B．assist C．forbid D．command12.A．experience B．devotion C．motivation D．adventure 13.A．challenging B．limited C．joint D．tiring14.A．wealth B．struggle C．hope D．peace15.A．want B．wait C．remain D．deserve二、阅读选择(阅读理解)文章大意：本文是一篇说明文。
鸟的英语介绍作文带翻译
Birds are a fascinating group of animals that have captivated humans for centuries with their beauty, diversity, and unique abilities. As a high school student with a keen interest in ornithology, I find myself constantly amazed by the world of birds.The first thing that strikes me about birds is their incredible variety. There are over 10,000 known bird species, ranging from the tiny hummingbird to the majestic eagle. Each species has its own unique characteristics, from the vibrant colors of a peacock to the haunting melodies of a nightingale.One of the most remarkable aspects of birds is their ability to fly. With their lightweight bones, strong muscles, and specially adapted feathers, birds are able to take to the skies and travel vast distances. This ability has allowed them to colonize almost every corner of the globe, from the Arctic tundra to the tropical rainforests.Birds also play a crucial role in the ecosystem. They are important pollinators, helping to spread seeds and fertilize plants. Many birds are also predators, controlling populations of insects and small mammals. In turn, birds themselves are a food source for larger animals, maintaining the delicate balance of nature.In addition to their ecological importance, birds have also held a special place in human culture. They have been revered as symbols of freedom, love, and spirituality. From the dove of peace to the phoenix of rebirth, birds have inspired countless works of art, literature, and music.However, despite their beauty and importance, birds are facing numerous threats in the modern world. Habitat loss, climate change, and pollutionare all taking a toll on bird populations. It is up to us to protect these incredible creatures and preserve their habitats for future generations.In conclusion, birds are truly a wonder of the natural world. Their diversity, adaptability, and ecological contributions make them an essential part of our planet. As we learn more about these fascinating creatures, we canonly deepen our appreciation for the role they play in our lives and the world around us.翻译：鸟类是一群迷人的动物，以其美丽、多样性和独特能力几个世纪以来一直吸引着人类。
Difference of Mullite Whiskers between Ytterbia-Doped Aluminum Hydroxide-Silica Gel and Mechanoc
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人教版(2019)必修第二册Unit 4 Reading for Writing课文中译英
美丽的爱尔兰及其传统
1.一直以来，爱尔兰的美丽乡村对当地的人民和传统产生着深远的影响。
2.爱尔兰有着孕育伟大作家和诗人的悠久传统。
3.美丽的乡村给人以激情和灵感，满足各种感官享受。
4.“绿宝石岛Emerald Isle”风光宁静秀美，郡县草木葱茏，青山连绵起伏，牛羊点缀其中，堪称一场名副其实的视觉盛宴。
5.海边波浪咆哮，海鸟鸣叫，奏响了海岸交响曲。
6.山里宁静的早晨，感受阳光洒落在你身上，呼吸着鲜花的芬芳，而鸟儿则用清晨的歌声迎接新的一天到来。
7.这般美景，自然造就了爱尔兰独特的民间传统，如音乐、舞蹈及菜肴等。
8.要想体验这一切，可以去一家乡村酒吧，喝一杯葡萄酒或本地的啤酒，放松身心。
9.更为美妙的是，可品尝美味的爱尔兰炖牛肉。
10.运气好的话，你还可以欣赏到传统的音乐和舞蹈。
11.向友善的当地人做个自我介绍，你定能亲身体验当地的文化和习俗。
哈姆雷特英文独白
哈姆雷特英文独白
以下是《哈姆雷特》中的英文独白，希望对你有所帮助：
To be, or not to be, that is the question: Whether 'tis nobler in the mind to suffer; The slings and arrows of outrageous fortune; Or to take arms against a sea of troubles, And by opposing, end them. To die, to sleep. No more; and by a sleep, to say we end The heart-ache, and the thousand natural shocks That flesh is heir to; 'Tis a consummation Devoutly to be wish'd. To die to sleep, To sleep, perchance to dream; Aye, there's the rub, For in that sleep of death, what dreams may come, When we have shuffled off this mortal coil Must give us pause. There's the respect That makes calamity of so long life.
这段独白出自莎士比亚的作品《哈姆雷特》，表达了主人公哈姆雷特在面对困境时的内心挣扎和思考。
哈姆雷特第二幕英语原文
哈姆雷特第二幕英语原文哈姆雷特第二幕英语原文HAMLET: I will tell you why; so shall my anticipation prevent your discovery, and your secrecy to the king and queen moult no feather. I have of late—but wherefore I know not —lost all my mirth, forgone all custom of exercises, and indeed it goes so heavily with my disposition that this goodly frame, the earth, seems to me a sterile promontory; this most excellent canopy, the air—look you, this brave o'erhanging firmament, this majestical roof fretted with golden fire—why, it appears no other thing to me than a foul and pestilent congregation of vapours. What a piece of work is a man! How noble in reason! how infinite in faculty! in form, in moving, how express and admirable! in action how like an angel! in apprehension how like a god! the beauty of the world! the paragon of animals! And yet, to me, what is this quintessence of dust? Man delights not no, nor woman neither, though by your smiling you seem to say so. ROSENCRANTZ: My lord, there was no such stuff in my thoughts.HAMLET: Why did you laugh then, when I said 'Man delights not me'?ROSENCRANTZ: To think, my lord, if you delight not in man,what lenten entertainment the players shall receive from you: we coted them on the way; and hither are they coming, to offer you service.HAMLET: He that plays the king shall be welcome; his majesty shall have tribute of me; the adventurous knight shall use his foil and target; the lover shall not sigh gratis; the humorous man shall end his part in peace; the clown shall make those laugh whose lungs are tickled o' the sere; and the lady shall say her mind freely, or the blank verse shall halt for't. What players are they?ROSENCRANTZ: Even those you were wont to take delight in, the tragedians of the city.HAMLET: How chances it they travel? their residence, both in reputation and profit, was better both ways.ROSENCRANTZ: I think their inhibition comes by the means of the late innovation.HAMLET: Do they hold the same estimation they did when I was in the city? are they so followed?ROSENCRANTZ: No, indeed, are they not.HAMLET: How comes it? Do they grow rusty?ROSENCRANTZ: Nay, their endeavour keeps in the wonted pace: but there is, sir, an aery of children, little eyases, that cryout on the top of question, and are most tyrannically clapped for't: these are now the fashion; and so berattle the common stages—so they call them—that many wearing rapiers are afraid of goose-quills and dare scarce come thither.HAMLET: What, are they children? Who maintains 'em? how are they escoted? Will they pursue the quality no longer than they can sing? will they not say afterwards, if they should grow themselves to common players—as it is most like, if their means are no better—their writers do them wrong to make them exclaim against their own succession?ROSENCRANTZ: Faith, there has been much to-do on both sides; and the nation holds it no sin to tarre them to controversy: there was, for a while, no money bid for argument, unless the poet and the player went to cuffs in the question.HAMLET: Is't possible?GUILDENSTERN: O, there has been much throwing about of brains.HAMLET: Do the boys carry it away?ROSENCRANTZ: Ay, that they do, my lord; Hercules and his load too.HAMLET: It is not very strange; for my uncle is king of Denmark, and those that would make mows at him while my fatherlived, give twenty, forty, fifty, a hundred ducats a-piece for his picture in little. 'Sblood, there is something in this more than natural, if philosophy could find it out.。
关于蚕桑的英语寓言作文
关于蚕桑的英语寓言作文英文回答：In the annals of wisdom and morality, fables have served as timeless vessels, conveying profound teachings through enchanting tales. Among these gems lies the enduring fable of the Silkworm and the Mulberry Tree, a poignant story that unveils the intricate bond between labor, sacrifice, and the creation of something truly extraordinary.Once upon a time, in a verdant land where nature's bounty unfolded, there lived a diminutive silkworm. This humble creature, endowed with an extraordinary gift, possessed the ability to spin silken threads of unparalleled strength and beauty. However, the silkworm's remarkable talent came at a profound cost.To produce its exquisite silk, the silkworm embarked on an arduous journey, consuming vast quantities of mulberryleaves. These leaves, the silkworm's sustenance, were essential for the production of the delicate filaments that would ultimately form the shimmering fabric of silk.As the silkworm tirelessly spun its silken masterpiece, it became oblivious to its surroundings, consumed by the demands of its task. Day and night, it relentlessly labored, driven by an unyielding determination to fulfill its purpose. In its unwavering pursuit of excellence, the silkworm surrendered its own body to the very fabric it created.In time, the silkworm completed its labor, leaving behind an opulent cocoon of delicate silk. This shimmering masterpiece, a testament to the silkworm's sacrifice and dedication, became a symbol of beauty and refinement throughout the ages.However, the tale of the silkworm and the mulberry tree offers more than just a captivating narrative. It embodiesa profound lesson about the relationship between effort and reward, and the sacrifices one must make to achieve truegreatness. Like the silkworm, we too must embrace the challenges that confront us, no matter how arduous or demanding they may seem.Through our unwavering efforts, we too can create something truly extraordinary—a legacy of our own making. And like the mulberry tree, we must provide nourishment and support to those who strive for excellence, enabling them to reach their full potential.The fable of the silkworm and the mulberry tree reminds us that the pursuit of greatness often requires sacrifice and dedication. By embracing this truth, we honor the legacy of the silkworm and ensure that its timeless wisdom continues to inspire generations to come.中文回答：蚕桑寓言是一个著名的故事，它讲述了一只勤劳的蚕和一棵茂盛的桑树之间的故事。
英语学习：看“肖申克的救赎”学英语
英语学习：看“肖申克的救赎”学英语英语学习：看“肖申克的救赎”台词学英语有种鸟是不应该被关在笼子里面的，他们羽毛太漂亮了。
安迪用19年的时间和耐心，用一柄比铅笔大不了多少的手锤，挖通了一条通往自由的道路。
这条路他的狱友瑞德认为600年才能挖通。
工具在不同的人手里作用是不一样的。
手锤在马家爵手里只是泄愤的东西。
安迪却用它开辟了一条自由之路。
安迪的忍辱负重有点儿像韩信。
人很难面对困难，对困难的惧怕甚至超过了对死亡的.........Andy Dufresne who crawled through a river of shit and came out clean on the other side.Andy Dufresne，爬过了那臭屎沟，然后干干净净的到另一边去了。
Andy Dufresne, headed for the Pacific.Andy Dufresne，向太平洋进发。
-Heywood: Hadley's got him by the throat, right? He says, I believe this boy's about to have himself an accident.throat: 喉咙Hadley抓住他的头，对吗？他说，我相信他将会发生意外。
-Red: Those of us who knew him best talk about him often. I swear ,the stuff he pulled.我们跟他熟的老是谈起Andy。
我发誓，他总是带来话题。
My friends could use a couple of beers. And he got it!我的朋友可以要两瓶啤酒。
他成功了。
Sometimes it makes me sad, though Andy being gone.有时那令我伤心，虽然Andy已经离开了。
夏威夷人反对莫纳克亚山望远镜站点修建考研英语（一）2017年Text2
夏威夷人反对莫纳克亚山望远镜站点修建考研英语（一）2017年Text22017年Text2主题：如何解决莫纳克亚山上的望远镜纷争题目：How to resolve the fight over telescopes on Mauna Kea如何解决莫纳克亚山上的望远镜纷争来源：Scientific American 《科学美国人》段落结构：共6段。
关键词：telescope 望远镜astronomy 天文学astronomical siteHawaiian 夏威夷Hawaiians 夏威夷人Mauna Kea 莫纳克亚山26.Queen Liliuokalani's remark in Paragraph 1 indicates _______.（细节题）第一段中利留卡拉妮女王的言论表明……the importance of astronomy in ancient Hawaiian society.天文学在古代夏威夷社会的重要性。
27.Mauna Kea is deemed as an ideal astronomical site due to ______.（细节题——问原因找原因）莫纳克亚山为视为理想的天文观测点是因为……its geographical features.其地理特征。
28.The construction of the TMT is opposed by some locals partly because _______.（细节题——问原因找原因）一些当地人反对建造TMT的部分原因是……it reminds them of a humiliating history.它让他们回想起屈辱的历史。
29.It can be inferred from Paragraph 5 that progress in today's astronomy _______.（推断题）从第5段可以推知，今天天文学所取得的进步……is fulfilliing the dreams of ancient Hawaiians.正在实现古代夏威夷人的梦想。
新视野大学英语读写教程2 unit6 课文翻译
Section A Door closer, are you?关门者，你是吗？1 下次你要在两个难于取舍的、主要的和次要的选择之间做决定时，不妨问自己这样一个问题：项羽会怎么做？2 项羽是公元前三世纪中国古代王朝的一位将军。
他带领他的部队横渡漳河，突袭进入了敌方的领地。
他下令砸锅烧船，令他的部队大为震惊。
3 他解释道，他强加给他们的是战胜对手的必要举措。
他所说的无疑十分鼓舞士气，但当他那许多忠诚的士兵眼睁睁地看着他们的船只在火焰中被焚毁时，他们并不赞成他的做法。
不过项羽将军的这种砸锅焚船的做法所显示出的天赋，在战场上和现代社会科学研究中都将得到肯定。
项羽将军是一个罕见的不墨守成规的人，他是一位经验丰富的领袖，由于他征战无数并达到了成功的顶峰，他深受尊敬。
4 丹·阿雷利极富启迪性的新书《可预见的非理性》对项羽作了专题介绍。
这本书对看似非理性的人类行为，譬如人类总想留住多项选择机会的倾向，进行了引人入胜的调查。
大多数人都不能整理自己的思路来做痛苦的选择，麻省理工学院上阿雷利博士行为经济学这门课的学生也不例外。
在调查作决策的一项实验中，几百名学生都不能忍受眼睁睁看着他们的选择机会消失，即使他们很清楚这样做对他们有利。
5 实验是围绕着一个游戏展开的，这个游戏排除了我们通常不肯放手的借口。
在现实世界里，我们总会说：“保留我们的选择机会是对的。
”想要一个好的例子吗？一个十多岁的女孩被足球、芭蕾舞、钢琴、中文课给累得筋疲力尽，但她的父母不会让她停止任何一项活动，理由是它们有一天可能会派上用场！6 在这个实验里，学生要玩一个电脑游戏: 在电脑屏幕上会显示三扇门，每扇门后都会提供一些现金。
该游戏的规则是每个人都只能点击100次，你点击获取的钱越多，你就玩得越好。
学生每点击一次打开一扇门，他们会用掉一个点击数，但却不会得到任何钱。
然而，随后接着在那扇门上的每次点击都会挣得数额不等的钱，三扇门显示的钱总有一扇比另外两扇多。
翻译理论——古诗词翻译
3.增加副词
The crowd melted away. 人群渐渐散开了. As he sat down and began talking, words poured out. 他一坐下来就讲开了,滔滔不绝地讲个没完.
He sank down with his face in his hands. 他双手蒙着脸,一下子坐了下去. He was fascinated by the political scenes --the wheeling and dealing of presidential politics, the manipulating, releasing and leaking of news, the public and private talks. 一幕幕政治花招真能使他看入迷了:总统竞选 活动中的勾心斗角,尔虞我诈;对新闻消息的 幕后操纵,公开发表和有意透露,以及公开和 秘密的谈话.
4.增加名词
a.在及物动词后面增加名词 在及物动词后面增加名词 to wash before meal 饭前洗手 First you borrow, then you beg. 头一遭借钱,下一遭讨饭. Day after day she came to her work --- sweeping, scrubbing, cleaning. 她每天都要干活——扫地,擦地板,收拾房间.
咏柳(贺知章) The Willow
碧玉妆成一树高,万条垂下绿丝绦. The slender tree is dressed in emerald all about, A thousand branches droop like fringes made of jade. 不知细叶谁裁出,二月春风似剪刀. But do you know by whom these slim leaves are cut out? The wind of early spring is sharp as scissor blade.
历代《使命召唤》名言
历代《使命召唤》名言In war, truth is the first casualty 战争中，第一个被扼杀的是真理。
Incoming fire has the right of way 飞来的子弹有优先通行权！Mankind must put an end to war, or war will put an end to mankind 人类必须结束战争，否则战争结束人类……War does not determine who is right - only who is left 战争没有谁对谁错，只有谁活下来……A ship without Marines is like a garment without buttons一艘船要是没有海军陆战队，就像衣服没有扣子……The press is our chief ideological weapon 媒体压力是我们思想的武器……Whether you like it or not, history is on our side. Wewill bury you不管是否喜欢，历史属于我们。
当然，我们会将你埋葬……If the enemy is in range, so are you 如果敌人在射程范围内，那么你也一样...................................Cost of a single Tomahawk cruise Missile: $900,000一枚战斧式巡航导弹耗资90万美子……Cost of a single F-22 Raptor: $135 million一架F-22猛禽式战斗机耗资1亿3千500万美子……Cost of a single AC-130U Gunship: $190 million一架AC-130U型重型攻击机（AC-130原本是运输机，传说中能在条件最为恶劣的机场起降的大力神，U型是用大力神机型改造的重击机，曾在变形金刚中出现过……）耗资1亿9千万美子……Cost of a single F-117A Nighthawk: $122 Million一架F-117夜鹰隐形攻击机耗资1亿2千200万美子……Cost of a single B-2 Bomber: $2.2 Billion一架B-2重型轰炸机耗资22亿美子……（这么多？不会吧？）So long as there are men, there will be wars 人类存在了多长时间，战争就存在了多长时间...........................Aim towards the Enemy 向敌人瞄准……I think the human race needs to think about killing. How much evil must we do to do good?我认为人类这个种族应该审视一下杀戮。
希腊神话之荷马史诗和奥德赛
《奥德赛》里的名句《奥德赛》
▪ 没有比漫无目的地徘徊更令人无法忍受的 了
▪ There is nothing worse than being always ways on the tramp.
希腊神话之荷马史诗和奥德赛
故事梗概展示:文字方式; 讲故事的方式; 短片; … …;
荷马史诗
Homeric Epic/Homer
--盲诗人荷马
希腊最早的一部史诗，产生于民间口头文学 《伊利亚特》the ILiad 《奥德赛》 the Odyssey
荷马史诗
▪ 荷马，生于公元前八世纪后半期的爱奥尼亚，是 古希腊最著名和最伟大的诗人。他是《荷马史诗》 （分《伊利亚特》和《奥德赛》两部分）的作者。 《荷马史诗》以扬抑格六音部写成，集古希腊口 述文学之大成。它是古希腊 最伟大的作品，也是 西方文学中最伟大的作品。 《伊利亚特》和《奥德赛》处理的主题分别是在 特洛伊战争中，阿基里斯与阿伽门农间的争端， 以及特洛伊沦陷后，奥德修斯返回绮色佳岛上的 王国，与皇后珀涅罗团聚的故事。
《奥德赛》
▪ 《奥德赛》叙述伊大卡国王奥德修斯在攻陷特洛 耶后归国途中十年漂泊的故事。它集中描写的只 是这十年中最后一年零几十天的事情。奥德修斯 受神明捉弄，归国途中在海上漂流了十年，到处 遭难，最后受诸神怜悯始得归家。当奥德修斯流 落异域时，伊大卡及邻国的贵族们欺其妻弱子幼。 向其妻皮涅罗普求婚，迫她改嫁，皮涅罗普用尽 了各种方法拖延。最后奥德修斯扮成乞丐归家， 与其子杀尽求婚者，恢复了他在伊大卡的权力。
荷马史诗里的谚语
▪ Helen of Troy 直译“特洛伊的海伦”，源自荷马 史诗《伊利亚特》中的希腊神话故事。
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Materials Science and Engineering A454–455 (2007) 518–522Mullite whiskers derived from coalfly ashY.M.Park a,T.Y.Yang a,S.Y.Yoon a,R.Stevens b,H.C.Park a,∗a Department of Materials Science and Engineering,Pusan National University,30Jangjeon-dong,Geumjeong-gu,Pusan609-735,South Koreab Department of Engineering and Applied Science,University of Bath,Bath BA27AY,UKReceived2August2006;received in revised form9November2006;accepted23November2006AbstractAlumina-deficient(Al2O3/SiO2=1.12,molar ratio),orthorhombic mullite whiskers with a diameter of0.6–1.8m(aspect ratio>30)have been manufactured byfiring compacts of coalfly ash and NH4Al(SO4)2·12H2O powders,with a small addition of NaH2PO4·2H2O,at1300◦C for10h. The manufacturing process,the morphology,and structure of the whiskers are described.© 2006 Elsevier B.V. All rights reserved.Keywords:Mullite whiskers;Coalfly ash1.IntroductionThe stable intermediate compound mullite(3Al2O3·2SiO2), which is formed in the Al2O3–SiO2system[1]is a potential candidate material for advanced structural applications because it has a high melting point,low coefficient of thermal expan-sion,excellent creep resistance,good chemical stability and high strength at high temperature.The stable crystal structure of mullite is orthorhombic with lattice constants a=7.545˚A, b=7.689˚A and c=2.884˚A(JCPDS Card#15-776),and it con-sists of edge-shared AlO6octahedral chains aligned in the c-direction and crosslinked by corner-shared(Si,Al)O4tetrahe-dra[2].Thus,the crystal growth may be faster in crystallographic direction parallel to the c-axis than in any other,resulting in a high degree of orientation.Whisker-shaped mullite has attracted attention because of its positive consideration as a reinforcement phase for use in high temperature composites.Various processing routes have been reported for the preparation of mullite whiskers.Hashimoto and Yamaguchi[3]synthesized mullite whiskers with a diameter of 0.5–2m(aspect ratio15–20),byfiring a powder mixture of Al2(SO4)3,amorphous SiO2,and Na2SO4in an alumina cru-cible at1000◦C for2h.Choi and Lee[4]obtained very large mullite whiskers(>15m in diameter,>300m in length)by heating a mixture of SiO2and silicon in an alumina tube reactor,∗Corresponding author.Tel.:+82515102392;fax:+82515120528.E-mail address:hcpark1@pusan.ac.kr(H.C.Park).under aflow of H2/CF4at1450◦C for3h.Li et al.[5]prepared mullite whiskers from commercial kaolin with the addition of foaming agents and discussed the effect of foaming agents on the development of mullite whiskers and the dissolution of the glass matrix in hydrofluoric acid.The recycling of industrial waste to produce valuable materi-als attracts a great deal interest from society and scientists alike. Resource recovery from the huge amounts offly ash generated by combustion of coal in a thermoelectric power plant is one of the important problems that require urgent attention.Coalfly ash consists offine inorganic particles having SiO2and Al2O3 as the main components,often in the form of cenospheres.The chemical composition allows the synthesis of high performance mullite whiskers from the coalfly ash and this is of commercial interest.The objective of the present work is to facilitate the recycling of coalfly ash and to produce mullite whiskers.2.Experimental procedureThe morphology and characteristics of the as-received coal fly ash are shown in Fig.1and Table1,respectively.The coalfly ash contained23.29wt%Al2O3and53.83wt%SiO2 (Al2O3/SiO2=0.25,molar ratio);it consisted mainly of silicate minerals,being a mixture offlake-like and nearly spherical-shaped particles,with a specific surface area of3.82m2/g and an agglomerate size of42.1m(<90%).The coalfly ash was calcined in air at600◦C for2h to remove the residual carbon and subsequently ball-milled for24h in ethanol.After rotary0921-5093/$–see front matter© 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2006.11.114Y.M.Park et al./Materials Science and Engineering A 454–455 (2007) 518–522519Table 1Characteristics of coal fly ash Chemical component (wt%)Crystalline phaseS BET (m 2/g)Agglomerate size distribution (m)<30%<50%<90%SiO 2(53.83),Al 2O 3(23.29),Fe 2O 3(5.96),MnO (0.10),CaO (7.87),MgO (0.83),K 2O (0.99),Na 2O (0.70),P 2O 5(0.65),TiO 2(0.85),Ig.loss (10.33)Mullite,sillimanite,quartz3.822.38.042.1vacuum evaporation,the dried powder was ground and passed through a 200mesh sieve.Ammonium aluminum sulfate hydrate (NH 4Al(SO 4)2·12H 2O,ammonium alum)used in this study was obtained from coal fly ash [6].The purity of the synthesized ammonium alum was >99.9%;it consisted of nearly spherically shaped particles (Fig.2)in the size range 100–200m.A measured amount of ammonium alum was added to the coal fly ash in order to increase the Al 2O 3/SiO 2molar ratio up to 0.32.In addition,2wt%of sodium dihydrogenphosphateFig.1.SEM micrograph of the as-received coal flyash.Fig.2.SEM micrograph of ammonium alum obtained from coal fly ash.(NaH 2PO 4·2H 2O,Junsei Chemical Co.,Tokyo,Japan)was added to the mixture of ammonium alum and coal fly ash.The batch powders were mixed and homogenized by ball milling in ethanol for 8h using a high density polyethylene bottle with alumina ball media.After drying,the mixed powders were crushed in an agate mortar and passed through a 200mesh sieve.Cylindrical (10mm diameter ×5mm)compacts were prepared by die pressing at 70MPa.The compacts were placed in an alumina crucible,and not covered.After heating in air at 1300◦C for 10h,the compacts were treated with 20wt%HF in water (Guaranteed Reagent,Junsei Chemical Co.,Tokyo,Japan);the product was filtered,washed with water,and finally dried.In this case,in order to effectively dissolve the glass matrix from the whiskers,the HF solution was heated to 50◦C for 5h using a microwave heating source.The resulting whiskers were characterized using X-ray diffractometry (XRD),scanning electron microscopy (SEM),energy dispersive spectroscopy (EDS),and transmission elec-tron microscopy (TEM).3.Results and discussionAfter chemically leaching the glass matrix with a 20wt%HF solution using microwave heating (50◦C,5h),the microstruc-ture of the product is shown in Fig.3using SEM.AmassFig. 3.SEM micrograph of whiskers obtained by firing compact (Al 2O 3/SiO 2=0.32,molar ratio)of coal fly ash and ammonium alum powders,with an addition of 2wt%NaH 2PO 4·2H 2O,at 1300◦C for 10h;etched with 20wt%HF solution at 50◦C for 5h using microwave heating source.520Y.M.Park et al./Materials Science and EngineeringA 454–455 (2007) 518–522Fig.4.XRD patterns of (a)JCPDS Card #15-776,mullite,and the products obtained by firing compact (Al 2O 3/SiO 2=0.32,molar ratio)of coal fly ash and ammonium alum powders,with an addition of (b)2wt%and (c)4wt%NaH 2PO 4·2H 2O,at 1300◦C for 10h.of relatively well-developed and interlocked whisker-shaped crystals having a high aspect ratio of >30(about 0.6–1.8m in diameter)was observed.The product generated XRD pat-terns consisting of the mullite characteristic peaks with Miller indices of 120,210,and 220(Fig.4);the XRD peak lines were not nearly shifted compared with JCPDS Card #15-776.As shown in Fig.5,the EDS spectrum of the whiskers con-firmed that they consisted of 65.29wt%Al 2O 3and 34.71wt%SiO 2(Al 2O 3/SiO 2=1.12,molar ratio),this result indicating an alumina deficient composition with respect to stoichiometric mullite (Al 2O 3/SiO 2=1.5,molar ratio).The crystal structure of the whiskers with a nanometer-sized diameter (<400nm)was shown by observation of TEM and microbeam diffraction (Fig.6),to be orthorhombic.The EDS analysis also takes in the background materials which could derive from material other than the whiskers.Such material would only be present in small amounts due to the HF leaching.With optimized additions of NH 4Al(SO 4)2·12H 2O and NaH 2PO 4·2H 2O,mullite whiskers were prepared by firing com-pacts of coal fly ash at 1300◦C for 10h.In the later stagesofFig. 5.EDS spectrum on mullite whiskers obtained by firing compact (Al 2O 3/SiO 2=0.32,molar ratio)of coal fly ash and ammonium alum powders,with an addition of 2wt%NaH 2PO 4·2H 2O,at 1300◦C for 10h;this showing ion concentration (wt%)of 39.36O,41.67Al and 18.97Si.Fig. 6.TEM micrograph and microbeam diffraction of mullite whiskers obtained by firing compact (Al 2O 3/SiO 2=0.32,molar ratio)of coal fly ash and ammonium alum powders,with an addition of 2wt%NaH 2PO 4·2H 2O,at 1300◦C for 10h.the reaction sintering (>1200◦C),the presence of a liquid phase allows sintering of low-Al 2O 3compositions and produces rel-atively large prismatic mullite crystals [7].On a similar basis,in this study,it was concluded that the mullite developed into whiskers in the presence a considerable amount of liquid phase with a low-Al 2O 3composition because of the relatively high iron oxide content (5.96wt%)of the precursor materials.Minor alkali impurities and/or other oxide components,which help for-mation of low melting point liquids during firing,are also present in the coal fly ash (Table 1).The presence of such impurities will lower the softening point of the glass and indeed enhance the volume fraction of glassy phase present at any given tempera-ture.Na 2O,K 2O and Li 2O are increasingly effective in reducing the melting point of silica binaries to below 800◦C.The ternary of Na 2O–K 2O–SiO 2has a lowest melting point of 540◦C and the introduction of iron oxide can further reduce this critical tem-perature [8].Thus,the richer the glass is in low melting point components,the lower will be its melting temperature and for any given temperature will lower the viscosity.This is accompa-nied by higher reaction rates with other phases at the glass solid phase boundary.The growth of the whiskers can be explained on the enhanced formation and lower melting point of a sec-ondary glass phase,allowing enhanced solution–precipitation in the glass.The microstructure of compact without an addition of NaH 2PO 4·2H 2O,fired at 1300◦C for 10h is shown in Fig.7.The mullite whiskers which grew at both the internal and exter-nal surfaces were observed.The whiskers existing at external surface were mainly embedded in the glassy phase and the internal whiskers generally were random and interlocked.The addition of 2wt%NaH 2PO 4·2H 2O (Fig.3)assisted the growth of whiskers and the dissolution of glass matrix compared withY.M.Park et al./Materials Science and Engineering A 454–455 (2007) 518–522521Fig.7.SEM micrograph of mullite whiskers obtained byfiring compact (Al2O3/SiO2=0.32,molar ratio)of coalfly ash and ammonium alum powders, with no addition of NaH2PO4·2H2O,at1300◦C for10h.no addition.Both sodium and phosphate,in this case,together with impurities such as iron oxide can lead to the presence of increasing amounts of liquid phase especially if the temperature is raised;this facilitating the growth of whisker-shaped grains. In such a situation the whiskers will develop by selective precip-itation on the larger needles in the presence of rich liquid phase, which will grow at the expense of thefiner needles and pow-der particle that are in turn preferentially dissolved.Thus the growth of whiskers orfibers is considered due to the conditions pertaining in the liquid glassy phase at thefiring temperature. Selective precipitation is occurring at the crystal faces at the tip of the whisker whilst the longer planar surfaces of the whisker grow at a slower rate.On the other hand,the nucleation of mullite can occur at the favorable particle surface sites by a solid-state reaction[9] and with increasingfiring temperature the mullite can possi-bly developfine whisker-shaped morphology by consuming the glassy melt.As shown in Fig.8,the initial reaction prod-uct obtained at1000◦C for10h exhibitedfine chrysanthemum flower shaped precipitates in a large volume of the particle sur-faces.At1200◦C,the appearance of whisker-shaped precipitates growing into the melt became evident(Fig.9).With further increasingfiring temperature(1300◦C),the whiskers continue to grow into the melts by a solution–precipitation until they impinge;in such case,the whiskers grow preferentially along the parallel direction to the c-axis,resulting in an orthorhombic structure.As shown in Fig.10,however,the addition of4wt% NaH2PO4·2H2O constrained the growth of mullite whiskers, making the crystals more“blocky”reducing their aspect ratio. The presence of an increased amount of glass melt could well induce crystal growth on the lateral crystal faces where the free energy difference is not so large.Li et al.[5]investi-gated the role of NaH2PO4·2H2O and Na2HPO4·2H2O added to aid the formation of mullitefibers from kaolin.On the basis of decreased mullite production,and increased Al2O3,Na2O, P2O5and decreased SiO2components in the glass matrix,with Fig.8.SEM micrograph of mullite whiskers obtained byfiring compact (Al2O3/SiO2=0.32,molar ratio)of coalfly ash and ammonium alum powders, with an addition of2wt%NaH2PO4·2H2O,at1000◦C for10h. increasing addition content of sodium phosphates,they stated that the introduction of Na2O caused more glass formation by dissolving mullite and P2O5enhanced the growth of mullite fibers.In such case,however,it is not clear that more glass for-mation is attributed to the dissolution of mullite phase or to the strongfluxing effect of Na2O;if the former cause is rea-sonable,the SiO2content in the glass matrix is presumably considered to increase with further addition of sodium phos-phates.On the other hand,Johnson and Pask[10]found that the addition of alkalis does not have a great influence on the growth rate of mullite in spite of their strongfluxing effect on Al2O3–SiO2mixtures.Fahrenholtz and Smith[11]reported that Na2O does not enhance the crystallization kinetics of mullite but increases the grain size and anisotropic growth.The presence of certain oxides in the glass phase can have a distinctive effect on the morphology of the mullite when formed.Kong et al.[12]investigated the effects of additions of MgO,CaO,SrO, Fig.9.SEM micrograph of mullite whiskers obtained byfiring compact (Al2O3/SiO2=0.32,molar ratio)of coalfly ash and ammonium alum powders, with an addition of2wt%NaH2PO4·2H2O,at1200◦C for10h.522Y.M.Park et al./Materials Science and EngineeringA 454–455 (2007) 518–522Fig.10.SEM micrograph of mullite whiskers obtained by firing compact (Al 2O 3/SiO 2=0.32,molar ratio)of coal fly ash and ammonium alum powders,with an addition of 4wt%NaH 2PO 4·2H 2O,at 1300◦C for 10h.and BaO on the reaction and morphology of the product.Only in the case of MgO addition well developed mullite whiskers formed,the other oxides aided the formation of more platelike grains.The authors explained their observation on the basis of a dissolution–precipitation mechanism.Synthesized mullite can have any composition between x =0(sillimanite)and x =1(alumina)in general formula Al 4+2x Si 2−2x O 10−x ,dependant on starting material and process-ing route [4,7,13].As a result of this study,the orthorhombic type mullite whiskers,which have a composition 47.11mol%SiO 2and 52.89mol%Al 2O 3were fabricated using SiO 2-rich starting composition (Al 2O 3/SiO 2=0.32,molar ratio).The reason is not obvious why the composition of the resulting mullite is restricted to a molar ratio of Al 2O 3/SiO 2=1.12,but could be due to limi-tations of the crystal chemistry,or possibly be due to amixtureFig.11.SEM micrograph of mullite whiskers obtained by firing compact (Al 2O 3/SiO 2=0.32,molar ratio)of coal fly ash and ammonium alum powders,with an addition of 2wt%NaH 2PO 4·2H 2O,at 1300◦C for 10h;chemically etched using a 20%HF solution,conventionally heated at 50◦C for 24h.of whiskers of different compositions,which would be averaged out in an EDS beam analysis in the SEM.Another possible rea-son could well be the low Al 2O 3content in the starting batch composition compared with 3/2-mullite,resulting in a SiO 2-rich,Al 2O 3deficient melt.de Souza et al.[13]prepared mullite whiskers by firing compacts of erbia-doped aluminum hydrox-ide and silica gel,at 1600◦C for 1–8h;the average molar ratio of Al 2O 3/SiO 2was 1.31,regardless of the Al 2O 3/SiO 2=1.5or 2,molar ratio of the starting composition;in this case a relatively high Al 2O 3/SiO 2ratio in the glass phase generated a low ratio value in the mullite grains.The free energies for the range of phases could well be dependent on the temperature and batch composition.The leaching of glass phase by 20wt%HF in water,as shown in Figs.3and 11,seemed to be more effective using microwave heating due to the inherent advantages of microwave [14],yielding further smooth surface of whiskers compared with leaching by conventional heating.Clearly the microwave radia-tion is aiding the dissolution process,a factor which could be due to microwave energy absorption at the water/ceramic interface increasing the local temperature and the rate of dissolution.4.ConclusionsWell developed mullite whiskers have been prepared by the firing of appropriate mixtures of coal fly ash and NH 4Al(SO 4)2·12H 2O with the addition of 2wt%NaH 2PO 4·2H 2O at 1300◦C for 10h.The resulting whiskers exhibited an aspect ratio of >30(0.6–1.8m in diameter),and had a composition of 47.11mol%SiO 2and 52.89mol%Al 2O 3,with an orthorhombic-type structure.The fabrication of high performance mullite whiskers by means of the recycling of coal 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