Monday, September 03, 2007

An elemental glass

It's a good day indeed when you see two of your friends featured in a news story on a recent discovery that was reported in Nature. The two friends are Srikanth Sastry (at Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore) who is among the authors of that paper, and U. Ramamurty (Ram, my colleague whose office is just next door to mine) who has commented on its findings.

As The Telegraph's T.V. Jayan puts it, a myth was indeed shattered when a pure substance -- germanium in this case -- was coaxed into a glassy form for the first time. The story focuses on Srikanth, whose theoretical and computational work provided vital clues for achieving this feat. Jayan also has quotes Ram on the importance and implications of this research.

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What good are metallic glasses? It turns out that they are fantastic in one key property: springiness (resilience), which should make some of them suitable for things such as golf clubs. In fact, the opening paragraph in the Telegraph story features Tiger Woods, Maria Sharapova and Srikanth Sastry!

[Take a look at this video for a neat demonstration of a high-resilience material in comparison with normal materials such as a stainless steel.]

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Alloys with two or more elements have been prepared in a glassy or amorphous state in which the atoms are not arranged in a regular three dimensional grid like they normally are in a crystalline state [Check out this Discover article or this Wikipedia entry]. The first metallic glasses were prepared using ultrafast cooling of molten liquid alloys; the cooling needed to be fast enough to suppress crystallization. Techniques based on fast cooling could produce glasses only in the form of thin sheets with thicknesses less than half a millimeter.

Subsequent research led to techniques for making metallic glasses in thicker blocks which can be used in a wider variety of applications. Centimeter-wide samples can now be made; they are called bulk metallic glasses (BMGs), and they enable a more precise and detailed study of their properties. Ram is an expert in the mechanical behaviour of these BMGs (and many other classes of materials, too).

Let me just end with a curious thing about the field of BMGs: it is unique in elevating 'Confusion' to the status of a 'Principle'! Since suppression of crystallization is important for coaxing an alloy into a glassy form, one of the strategies that scientists have hit upon is called the Confusion Principle according to which, very crudely, liquids with many elements -- with many different sizes and chemical properties -- are easier to turn into glass because the atoms in such a liquid are 'too confused' to form a regular crystalline arrangement on cooling.


  1. truti said...

    Metallurgy is back in a sort of way! I was getting tired of hearing all those paeans sung to carbon fiber and polymers!

    Germanium based polymers too have some interesting properties, right?

    Can these 'metallic glass' blocks be doped?

  2. Pratik . said...

    Nice to hear the news. How did they go about characterizing the glass?

    Back in 2004 there was a paper, also in Nature, on the synthesis of elemental zirconium in glassy form. The paper, though, was subsequently retracted by the authors, citing newer observations using an angular-dispersive method and imaging-plate detector, together with X-ray-transparent anvils.

    The original paper was: Nature 430, 332-335 (15 July 2004). The retraction was in 2005: Nature 437, 1057 (13 October 2005)