Formation mechanism of synthetic carbonado type polycrystalline diamond

Carbonados are naturally occurring polycrystalline diamonds in which grain boundary contamination impairs the transparency and renders a dark color to the gemstone. A similar material known as type carbonado synthetic polycrystalline diamond, CSPD, can be synthesized by volume transformation in bulk graphite. In this work the mechanism associated with the formation of CSPD in the reaction chamber of an anvil with concavity high pressure device was studied. This study was based on computational simulation of the field of temperatures developed inside the reaction chamber at the moment of the graphite to diamond transformation. It was found that during the CSPD synthesis, nonsteady conditions of temperature take place resulting in changes in the thermodynamic equilibrium parameters. Experimental results on the microhardness profile of the CSPD were compared with the simulated field of temperature, disclosing a direct relationship. The study has also shown that this microhardness/temperature relationship indicates competing mechanisms occurring during the CSPD synthesis.