【雙語閱讀】通過裂紋解決問題.

　　Science and Technology Materials science Cracking a problem

　　Another use for a fashionable, new material

　　LIKE all other human activities, science is subject to fads. One of the latest is for graphene. This wonder material—a form of carbon that comes in films a single atomic layer thick—won Andre Geim and Konstantin Novoselov the Nobel prize for physics last year. Because of its unusual electrical properties it has been touted as a way of making everything from touch screens to solar cells. Now a humbler use is being proposed. Another of graphene&aposs qualities is that it is strong. That, suggests Erica Corral of the University of Arizona, makes it ideal for reinforcing ceramics.

　　Engineers like ceramics because they can be heated without melting. Unlike metals and plastics, though, they are brittle. Because they crack easily, using them in places that are exposed to a lot of physical punishment is difficult. But a paper just published in the American Chemical Society&aposs journal, Nano, by Dr Corral and her colleagues, suggests a sprinkling of graphene may deal with that.

　　The ceramic they experimented with was silicon nitride, a material much admired in the aerospace industry. Components are made by sintering it in powder form in a mould, at 1,000oC, for several hours. Unfortunately, graphene disintegrates above 600oC, so the team had to think of a clever way of mixing the two materials. Their solution was to take advantage of graphene&aposs electrical conductivity, by running a current through the mixture. This generated a temperature of 1,650oC—more than enough to sinter the silicon nitride. The graphene, however, did not break down. Why, is not entirely clear. But rapid electrical heating did not seem to affect it in the way that slower oven heating would. The result was a composite that was able to withstand twice as much pressure as unalloyed silicon nitride.

　　When the team examined what they had done under a microscope, they found that the graphene had wrapped itself around the silicon-nitride grains, forming continuous walls. When they looked at samples that they had whacked hard enough to come close to cracking, they found that these walls were encouraging the cracks to spread in three dimensions—in contrast with the two-dimensional pattern usually seen in silicon nitride. Dr Corral suspects that extending cracking into the third dimension dissipates the energy faster and stops the fault spreading. A cracking idea, as it were.

　　【中文對照翻譯】

　　科技 材料科學(xué) 通過裂紋解決問題

　　一種流行新材料的新用途

　　像其它人類活動一樣，科學(xué)是一個時尚主題。 最新的話題是關(guān)于石墨烯的。 作為碳的一種形式，這種源自膠帶操作的奇妙材料只有單原子層厚度，發(fā)明者安德烈·杰姆和克斯特亞·諾沃塞洛夫為此獲得了去年的諾貝爾物理學(xué)獎。 由于石墨烯非同尋常的電特性，它被吹噓為制造一切產(chǎn)品的新途徑--從觸摸屏到太陽能電池。 如今石墨烯的一種低層次應(yīng)用被提出來。 它的另一特性是機械強度高， 因而被亞利桑那大學(xué)的埃里卡·科拉爾視為加強陶瓷材料硬度的一種理想材料。

　　工程師喜歡陶瓷材料，因為它們加熱時不會融化， 這點不像金屬和塑料，盡管它們是脆的。 因為陶瓷材料易碎，因此將其用于高物理強度的場合非常困難。 但在美國化學(xué)協(xié)會雜志剛發(fā)表的一篇論文《納米》中，科拉爾博士和她的同事們認為，加入少許石墨烯也許就能解決這個問題。

　　她們測試的陶瓷材料是氮化硅--一種在太空工業(yè)中飽受贊譽的材料。 這些部件是將氮化硅粉末置于模具中，處于1000攝氏度高溫下燒制數(shù)小時而成。 不幸的是，溫度高于600攝氏度，石墨烯就碎裂，因此研究團隊必須想出一種巧妙辦法將兩種材料融合在一起。 解決辦法就是利用石墨烯的導(dǎo)電特性，將電流通過混合物， 產(chǎn)生的1650攝氏度的高溫足以燒結(jié)氮化硅， 而石墨烯也沒有碎裂。 其原理尚未完全弄清楚。 但與通過熔爐緩慢加熱不同，快速電加熱對石墨烯看起來沒有什么影響。 和純氮化硅相比，其合成物能經(jīng)受的壓力強度翻倍。

　　當(dāng)研究團隊在顯微鏡下觀察合成物時，他們發(fā)現(xiàn)石墨烯包裹在氮化硅顆粒周圍，形成了連續(xù)的"壁"。 當(dāng)檢查這些不斷敲擊而近乎開裂的樣品時， 他們發(fā)現(xiàn)這些"壁"有助于裂紋向三個維度上延伸，和通常在氮化硅上觀察到的"二維裂解模式"形成了對比。 科拉爾博士推測，那種裂紋擴展為三個維度使能量擴散的更快，同時制止了缺陷的擴展。 通過三維裂紋來增強陶瓷材料強度，真是一個絕妙的點子!

　　Science and Technology Materials science Cracking a problem

　　Another use for a fashionable, new material

　　LIKE all other human activities, science is subject to fads. One of the latest is for graphene. This wonder material—a form of carbon that comes in films a single atomic layer thick—won Andre Geim and Konstantin Novoselov the Nobel prize for physics last year. Because of its unusual electrical properties it has been touted as a way of making everything from touch screens to solar cells. Now a humbler use is being proposed. Another of graphene&aposs qualities is that it is strong. That, suggests Erica Corral of the University of Arizona, makes it ideal for reinforcing ceramics.

　　Engineers like ceramics because they can be heated without melting. Unlike metals and plastics, though, they are brittle. Because they crack easily, using them in places that are exposed to a lot of physical punishment is difficult. But a paper just published in the American Chemical Society&aposs journal, Nano, by Dr Corral and her colleagues, suggests a sprinkling of graphene may deal with that.

　　The ceramic they experimented with was silicon nitride, a material much admired in the aerospace industry. Components are made by sintering it in powder form in a mould, at 1,000oC, for several hours. Unfortunately, graphene disintegrates above 600oC, so the team had to think of a clever way of mixing the two materials. Their solution was to take advantage of graphene&aposs electrical conductivity, by running a current through the mixture. This generated a temperature of 1,650oC—more than enough to sinter the silicon nitride. The graphene, however, did not break down. Why, is not entirely clear. But rapid electrical heating did not seem to affect it in the way that slower oven heating would. The result was a composite that was able to withstand twice as much pressure as unalloyed silicon nitride.

　　When the team examined what they had done under a microscope, they found that the graphene had wrapped itself around the silicon-nitride grains, forming continuous walls. When they looked at samples that they had whacked hard enough to come close to cracking, they found that these walls were encouraging the cracks to spread in three dimensions—in contrast with the two-dimensional pattern usually seen in silicon nitride. Dr Corral suspects that extending cracking into the third dimension dissipates the energy faster and stops the fault spreading. A cracking idea, as it were.

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