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  • Steel and plastic.

  • These two materials are essential to so much of our infrastructure and technology,

  • and they have a complementary set of strengths and weaknesses.

  • Steel is strong and hard,

  • but difficult to shape intricately.

  • While plastic can take on just about any form,

  • it's weak and soft.

  • So wouldn't it be nice if there were one material

  • as strong as the strongest steel

  • and as shapeable as plastic?

  • Well, a lot of scientists and technologists

  • are getting excited about a relatively recent invention called metallic glass

  • with both of those properties, and more.

  • Metallic glasses look shiny and opaque, like metals,

  • and also like metals, they conduct heat and electricity.

  • But they're way stronger than most metals,

  • which means they can withstand a lot of force

  • without getting bent or dented,

  • making ultrasharp scalpels,

  • and ultrastrong electronics cases,

  • hinges,

  • screws;

  • the list goes on.

  • Metallic glasses also have an incredible ability

  • to store and release elastic energy,

  • which makes them perfect for sports equipment,

  • like tennis racquets,

  • golf clubs,

  • and skis.

  • They're resistant to corrosion,

  • and can be cast into complex shapes with mirror-like surfaces

  • in a single molding step.

  • Despite their strength at room temperature,

  • if you go up a few hundred degrees Celsius,

  • they soften significantly,

  • and can be deformed into any shape you like.

  • Cool them back down,

  • and they regain the strength.

  • So where do all of these wondrous attributes come from?

  • In essence, they have to do with metallic glass' unique atomic structure.

  • Most metals are crystalline as solids.

  • That means that if you zoomed in close enough to see the individual atoms,

  • they'd be neatly lined up in an orderly, repeating pattern

  • that extends throughout the whole material.

  • Ice is crystalline,

  • and so are diamonds,

  • and salt.

  • If you heat these materials up enough and melt them,

  • the atoms can jiggle freely and move randomly,

  • but when you cool them back down,

  • the atoms reorganize themselves,

  • reestablishing the crystal.

  • But what if you could cool a molten metal so fast

  • that the atoms couldn't find their places again,

  • so that the material was solid,

  • but with the chaotic, amorphous internal structure of a liquid?

  • That's metallic glass.

  • This structure has the added benefit of lacking the grain boundaries

  • that most metals have.

  • Those are weak spots where the material is more susceptible to scratches

  • or corrosion.

  • The first metallic glass was made in 1960 from gold and silicon.

  • It wasn't easy to make.

  • Because metal atoms crystallize so rapidly,

  • scientists had to cool the alloy down incredibly fast,

  • a million degrees Kelvin per second,

  • by shooting tiny droplets at cold copper plates,

  • or spinning ultrathin ribbons.

  • At that time, metallic glasses could only be tens or hundreds of microns thick,

  • which was too thin for most practical applications.

  • But since then, scientists have figured out

  • that if you blend several metals that mix with each other freely,

  • but can't easily crystallize together,

  • usually because they have very different atomic sizes,

  • the mixture crystallizes much more slowly.

  • That means you don't have to cool it down as fast,

  • so the material can be thicker,

  • centimeters instead of micrometers.

  • These materials are called bulk metallic glasses, or BMGs.

  • Now there are hundreds of different BMGs,

  • so why aren't all of our bridges and cars made out of them?

  • Many of the BMGs currently available are made from expensive metals,

  • like palladium and zirconium,

  • and they have to be really pure

  • because any impurities can cause crystallization.

  • So a BMG skyscraper or space shuttle would be astronomically expensive.

  • And despite their strength,

  • they're not yet tough enough for load-bearing applications.

  • When the stresses get high, they can fracture without warning,

  • which isn't ideal for, say, a bridge.

  • But when engineers figure out how to make BMGs from cheaper metals,

  • and how to make them even tougher,

  • for these super materials,

  • the sky's the limit.

Steel and plastic.

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B1 中級

TED-ED】メタリックガラスとは?- アシュウィニー・バラチュラ (【TED-Ed】What is metallic glass? - Ashwini Bharathula)

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    黃于珍 に公開 2021 年 01 月 14 日
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