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Sunday, October 30, 2011

Amorphous diamond?

Yu Lin and Wendy Mao of Stanford University have succeeded in making what they call ‘an amorphous diamond’.  You may be wondering, as I was, what an amorphous diamond is and why it isn’t a non sequitur.

As you may already know, in addition to being the hardest naturally occurring material, diamonds are a crystalline, or highly ordered, form of pure carbon.  In contrast, amorphous substances have no repeating patterns.  They are by definition non-crystalline. It already doesn’t look good for ‘amorphous diamonds’.

To make their new material, the researchers took tiny beads of amorphous carbon and smashed them with over 400,000 atmospheres of pressure.  As a result, the bonds within the carbon beads shifted, making the resulting material as hard as diamonds (based on further pressure tests).  Yet, the beads did not become crystalline but stayed amorphous. 

The ‘amorphous diamond’ could turn out to be a very useful product.  Like oobleck, it’s only hard under extreme pressure. Once the pressure is released, the material returns to a softer state.  This means that the material may be tunable, responding to the amount of hardness required.  Not a bad feature in a structural component.

That said, in my opinion, ‘amorphous diamond’ is a non sequitur.  I think the authors are using the name ‘diamond’ as shorthand for ‘substance that is harder than anything else on Earth—I mean, this thing is really hard!  You won’t believe how hard it is!’.