Thermal decomposition of glucose and diamond formation under diamond-stable high pressure-high temperature conditions

Thermal decomposition of glucose C6H12O6 was investigated under diamond-stable high pressure and high temperature (HP-HT) conditions at 7.7 GPa and 1500degreesC in a platinum sealed capsule. Glucose was first decomposed to amorphous carbon and a fluid mainly composed of H2O. In coexistence with the latter, the graphitization of the former proceeded very rapidly within 1 h followed by the recrystallization of graphite. A small amount of diamond was detected after a considerably long incubation time of 10 h. The yield of diamond increased almost linearly with the increase in the holding time and reached 100% after 33 h. The obtained diamond was found to be an aggregate, of several tens to approximately 100 mum in size composed of small octahedral diamond crystals a few micrometers in size. On the other hand, when a seed diamond crystal was present with glucose, diamond growth was observed within 1 h, suggesting that the incubation time was caused by the nucleation barrier of diamond crystallization from the fluid. (C) 2002 Elsevier Science B.V. All rights reserved.