The diamond growth from Li2CO3, Na2CO3, K2CO3 and Cs2CO3 solvent-catalysts at P=7 GPa and T=1700–1750°C

Abstract

Abstract In the series of experiments at P =7 GPa and T =1700–1750°C with their duration from 10 min to 18.5 h the processes of diamond spontaneous nucleation and growth on a seeds in the systems Li 2 CO 3 –C, Na 2 CO 3 –C, K 2 CO 3 –C and Cs 2 CO 3 –C were studied using the ‘split-sphere’ type of apparatus (BARS). Diamond formation in such conditions requires more time than in metal–graphite systems. The essential dependence of diamond morphology and nucleation peculiarities on the composition of crystallization medium was established. It is shown that the catalytic activity of alkaline carbonates is determined by the sequence Li 2 CO 3 ≫Na 2 CO 3 >K 2 CO 3 >Cs 2 CO 3 , while the morphology of diamond crystals, synthesized in the carbonates of the sequence, changes regularly from cuboctahedron to octahedron. The maximum size of synthesized crystals reaches 600–700 μm, while the maximum layer, grown on a seed is 400–500 μm. The rate of synthesis reaction and the number of diamond nuclei decrease regularly with the increase of cation radius in the sequence Li + →Na + →K + →Cs + , while the duration of the synthesis inductive period increases simultaneously.