Synthesis of gem grade diamond by temperature gradient method using high temperature sintered alumina ceramics

Gem diamond was synthesized by temperature gradient method under high temperature and high pressure. Alumina ceramics used as insulation chamber were prepared by sintering high purity alumina powder at different temperature. The results show that with the increase of sintering temperature, the density of alumina ceramics increases, the apparent porosity decreases, the corresponding crystal growth rate increases, and the inclusions in the crystal decrease. The relative density of alumina ceramics is 97% and the apparent porosity is 0.05% when sintered at 1 650 ℃ for 4h. The high-grade diamond without any inclusions, weighing 0.40 g (2 ct) and growing at a speed of 4.0 mg/h was prepared.