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Nanocrystalline diamonds can be synthesized by direct conversion of graphite or carbon black mixed with low amount of boron (0.1%-10%) at 8-10 GPa, according to US patent No.20120255236.

If some scientists decided to make very large monolithic diamonds (tens of cm size) to make for example large diamond anvil cells with a centimeter sample size, would it be practical to use large pressure vessels with very thick steel walls to reach such very high hydrostatic pressures for such a large volume?

How to calculate the required material thickness to withstand such high pressures?

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  • $\begingroup$ See, how well looks your question after my edit. $\endgroup$ – peterh Jun 27 '17 at 5:52
  • $\begingroup$ Just takes lots of money and massive containers. But why bother when there are simpler (chemical) methods? $\endgroup$ – Carl Witthoft Jun 27 '17 at 13:35
  • $\begingroup$ Carl Witthoft , what is the simpler method to make 10 cm size diamond ? I didn’t hear about something similar $\endgroup$ – anameen Jun 28 '17 at 5:19
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Such a pressure vessel is not technically achievable with current technology. See this question.

There are two main methods of making synthetic diamonds. HPHT (High pressure, high temperature), which uses something like a Diamond Anvil Cell to achieve pressures in the Gigapascal range and temperatures over 1400 $^o$C. The largest diamonds produced this way seem to be in the 1-2 cm range but it is difficult to get reliable information on this.

The other main method is CVD (Chemical Vapor Deposition) which doesn't require high pressures. A research team at the Carnegie Institute of Washington has developed a method to produce larger diamonds using CVD. See article in New Scientist. Apparently diamonds in the inch range are possible using their method. They also believe that larger sizes will be achievable in the future.

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