Diamonds of new alkaline carbonate-graphite HP syntheses: SEM morphology, CCL-SEM and CL spectroscopy studies

Colorless octahedral diamonds up to 150 mu m in size were spontaneously cry stallized from carbon solutions in alkaline-carbonate melts in the Na2Mg(CO 3)(2)-graphite and NaKMg(CO3)(2)-graphite systems at pressures of 8-10 GPa and temperatures of 1700-1800 degrees C, Seeded growth of carbonate-carbon (CC) diamond layers was realized on both octahedral {111} and cubic {100} f aces of natural and synthetic "metal-carbon" (MC) diamond single crystals 0 .5-0.7 mm in size. Scanning electron microscopy (SEM) morphology studies cl early demonstrate that a preferable mechanism of diamond growth from alkali ne CC melts is the deposition of newly formed layers in parallel with octah edral faces, in much the same way as in the case of natural diamonds. A col or cathodoluminescence (CL) SEM study shows that the specific feature of th e CC diamonds is the lack of surface color CL as for natural diamonds of ty pe II with lower nitrogen concentration. The CL spectra of the CC diamonds consist of three-band system H3, 575 nm, and a weak blue A-band. The struct ure of the H3 band closely resembles that of natural diamonds of type IIa. (C) 1999 Elsevier Science S.A. All rights reserved.