In the series of experiments at P=7GPa and T=1700-1750°C with their duration from 10min to 18.5h the processes of diamond spontaneous nucleation and growth on a seeds in the systems Li2CO3-C, Na2CO3-C, K2CO3-C and Cs2CO3-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 Li2CO3≫Na2CO3>K 2CO3>Cs2CO3, 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 600-700μm, while the maximum layer, grown on a seed is 400-500μm. 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.
|ジャーナル||Diamond and Related Materials|
|出版ステータス||Published - 1999 6月 6|
ASJC Scopus subject areas
- 化学 (全般)