Abstract

In this paper, we report on the influence of the H2O additive in the metal melt on the growth processes, morphology, and defect-and-impurity structure of diamond crystals. As a source of water, a mixture of Mg(OH)2 and SiO2 was used, which reacted under the experimental conditions following the reaction 2Mg(OH)2 + SiO2 = Mg2SiO4 + 2H2O. The main experiments were performed in the Ni0.7Fe0.3–C system at a pressure of 6 GPa, a temperature of 1370 °C, a duration of 15 h, and a H2O concentration (CH2O) ranging from 0 to 0.5 wt %. It is found that, as the H2O content increases from 0 to 0.2 wt %, the diamond morphology changes from bulky octahedra to {111} platelike crystals and then to {111} dendrites. Further increases in CH2O in the range of 0.22–0.4 wt % result in crystallization of bulky rhombic dodecahedra and then {110} dendrites. At a CH2O higher than approximately 0.43 wt %, nucleation and growth of diamond are completely terminated and only graphite crystallizes. The systematic changes in diamond growth and morphology are accompanied by a decrease in nitrogen impurity concentration in diamond from 220–230 to 40–50 ppm, an increase in the density of microinclusions, and the appearance in the IR spectra of a peak at 2840 cm–1, related to hydrocarbons.

Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call