Effect of Diamond Powder Grain Size on the Formation of Polycrystals under High Pressure and High Temperature

At a pressure of 8 GPa and a temperature of 1700°C, diamond crystals were synthesized in the Mg–Zn–B–C system, the synthesis product was chemically purified, and the resulting diamond powder was classified by grain size. The grain size distribution of mixtures of coarse- and fine-dispersed diamond powders synthesized in the Mg–Zn–B–C system was examined before and after exposure to high pressure, the influence of the initial mixture composition on the degree of comminution under high pressure was evaluated, and its relationship with the kinetics and densification level of polycrystals formed from these mixtures during subsequent high-temperature treatment was established. Raising the average particle size of the initial powder from 5 to 30 μm increases the degree of comminution by a factor of 6, which leads to powder densification during the high-temperature sintering stage at a pressure of 8 GPa and a temperature of 1800°C to a level of 99%.