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I'm doing a science project, and we're wondering if it is possible to compress pure carbon (C) to the point where it becomes diamonds? What would the process have to be and how much energy would this take? Has this been done and is this feasible?

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  • $\begingroup$ i think process is posiblle and has been done in lab but it is not feasible also diamond formed were very small. $\endgroup$ Dec 14, 2015 at 16:19
  • $\begingroup$ but if a lot of carbon were to be used, the diamonds should be larger and more plentiful, right? $\endgroup$ Dec 14, 2015 at 16:30
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    $\begingroup$ @AnubhavGoel: synthetic diamonds are now being mass produced and on the market, their only problem is is they're better than natural stones! en.wikipedia.org/wiki/Synthetic_diamond $\endgroup$
    – Gert
    Dec 14, 2015 at 16:30

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The technique of using high pressures to make diamonds was pioneered by Francis Bundy of General Electric and others back in the 1960's using large volume presses, I believe. If you look at the carbon phase diagram, a pressure of at least 15 kbars (15,000 atmospheres) is required to turn carbon into diamond, but the transformation is very sluggish. Usually much higher pressures are used and also the carbon is heated to high temperature to accelerate the kinetics of the transformation. I believe that a catalyst like nickel is also often used. Currently, I think that Sumitomo of Japan does a lot of work in high-pressure synthesis of diamond for applications such as heat-spreaders for high-power electronics. They can actually grow rather large single crystals of a carat or so. Normally, their diamond crystals have a yellowish color, probably because of nitrogen impurities which they may be adding as a catalyst.

Nowadays, a popular method of growing synthetic diamond is not by using high pressures but by using a low pressure chemical vapor deposition (CVD) process in which diamond is grown from a methane and hydrogen plasma. In research which I perform with my colleagues, we actually use CVD diamond growth to encapsulate tiny electrical circuits inside diamond crystals to fabricate "Designer" diamond anvils for high pressure research.

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  • $\begingroup$ @Chris White - Thanks, I amended my answer to include a link to the nice and clear carbon phase diagram you suggested. $\endgroup$
    – user93237
    Dec 14, 2015 at 18:16
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This is not entirely serious, but if you're looking for a really great project, you can't do much better than this. Are you aware that you can make diamonds with high explosives? And since the starter mixture is not well-known, you might have to make multiple attempts.

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Theoretically yes but those diamonds would be industrial, not worth much and wouldn't have the exterior of natural diamonds. Like what was said in a previous answer, these diamonds can be made in an explosion too! I think there's a myth busters episode on it if I'm not wrong!

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  • $\begingroup$ Wrong, synthetic diamonds are still expensive, not as expensive as the natural ones, but still they are expensive. $\endgroup$
    – M D P
    Aug 6, 2018 at 5:19
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my profesor of structure of matter told us that is widely done in Russia, where there is a surplus of explosives and so the price is low.

The procedure consists in filling a container with graphite on the borders and with explosives in the center, and make the expolsive blow up.

This procedure will produce diamonds $100-200 \, \mu m$ thick, and not pure, so is suitable for industrial grade diamond production. So if you was wondering to create a huge diamond for a ring to give to your gf at the science fair you're better choose another method ;)

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    $\begingroup$ At one time the Russians were actually trying to market some of their nano-sized, explosively synthesized diamond as some sort of engine treatment. I remember my postdoc supervisor once showing me a Russian can of nano-sized diamond suspended in a liquid that they were trying to sell for this purpose. I forget what the logic behind adding nano-diamond to an engine was, though. It seems to me that adding an abrasive like small diamond crystals is the last thing that one would want to add to one's car engine. $\endgroup$
    – user93237
    Dec 14, 2015 at 18:05

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