Naked Science Forum
On the Lighter Side => That CAN'T be true! => Topic started by: Kryptid on 09/12/2003 05:14:28
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Believe it or not, mankind has synthesized substances that are harder than diamond. Two of them, in fact.
1) Ultrahard fullerite, which is roughly twice as hard as diamond, is a network solid containing buckyballs that are interconnected with one another. Like diamond, it is made of pure carbon. I believe it was created a few years ago. I wonder why I didn't learn about it earlier?
2) Another new form of carbon was created last october which also exceeds diamond in hardness. It was created by exposing graphite to extremely highy pressures. The structure of the graphite changed, causing some of the pi bonds to break and form sigma bonds between the graphite layers, forming a much sturdier structure. It cracked the diamond anvil that it was being compressed on.
I am not sure which of these substances is the hardest, but we know now that diamond is not the hardest substance anymore!
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Between this and finding out 2 different labs have exceeded the speed of light, I'm at a loss for words today.
I don't suppose you know the name of the 2nd compound you mention?
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find a diagram of the structure and post it, please?
Am I dead? Am I alive? I'm both!
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I don't think that the second material has a name yet. The source just calls it "superhard graphite", but it really isn't graphite anymore.
I have searched for websites that show the structure of these materials, but have come up empty. I did read, however, that half of the pi bonds in the graphite were transformed into sigma bonds during the compression. These new single bonds link the sheets of graphite together, keeping them from sliding around.
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So where do the extra electrons go when these pi bonds are are shifted to sigma bonds on another carbon? The carbon it's moving to must already have a full valence shell too, so the electrons need to go somewhere...
What's graphite's crystalline structure look like anyway? I've taken so much organic chem now that it's hard to think of a carbon molecule that doesn't have hydrogens, nitrogen, and/or oxygen on it.
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Graphite is flat sheets of carbon in a hexagonal array with sheets stacked vertically and held together by van der Waals forces.
chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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So are the carbons all double bonded to each other then since they're in clusters of 6?
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Carbon forms 4 bond, in the case of graphite each carbon is bonded to 3 other carbon with covalent bonds in a layer. Because they are held together by Van der Waals forces it can be easily broken hence the softness. Diamond is hard because it forms 4 covalent bonds to all 4 other carbon(gives it a different structure - tetrahedral), the electrons are held together tightly and very hard to move or break the bonds. So to produce a stong graphite that cracks diamond which is originally "n" times as hard is pretty shocking.[:0]
Tom
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quote:
Originally posted by cannabinoid
So are the carbons all double bonded to each other then since they're in clusters of 6?
Not quite. Draw a hexagon with a carbon atom at each of the apices. Now draw more hexagons touching each of the sides. Each carbon (at each of the apices) thus participates in 4 hexagons and hence makes 4 bonds.
Graphite contains no double bonds.
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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Ah, I understand. Thanks.
That being the case, there would be no pi bonds in the structure, so I'm a little confused now about how this "super graphite" is made.
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In diamond each carbon is tetrahedrally surrounded by other carbon atoms, whilst in graphite the sheets form a planar structure meaning that they can slide over each other which is why graphite is soft. Perhaps some of the carbons can be induced to form bonds to carbons of sheets vertically above and below, thus preventing the sheets froms slipping across each other and producing something that is half way to diamond ?
Chris
"I never forget a face, but in your case I'll make an exception"
- Groucho Marx
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Oh..yeah glad you point that out Chris, forgot to answer cannabinoid's question, it doesn't contain double bond. I wasn't specific enough.
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A little diagram to go with the explaination
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Tom
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Well, I found a picture of Ultrahard Fullerite's structure. The picture is 2-D and hard to understand though. Here's the web address:
http://www.if.ufrgs.br/~perott/PRBc60.pdf
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That's really cool, thanks Supercryptid.
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One more thing...maybe you didn't notice, but they say in the first paragraph of the abstract that diamond is still harder than the ultra-fullerite.
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There are several different varieties of fullerite, one of them is called superhard fullerite. Perhaps the one that the paper refers to is a different kind? I have read from other sources that ultrahard fullerite has been used in a scratch test with diamond. It scratched diamond, but the diamond couldn't scratch the fullerite.