DIAMOND SYNTHESIS VIA A LOW-PRESSURE SOLID-STATE-SOURCE PROCESS

We describe herein a process which, also operating below one atmospher e pressure, transforms virtually any form of finely divided solid carb on into crystalline diamond in the reaction chamber. The key to the pr ocess is the creation of a two (or more) phase micro (or nano) composi te of the carbon solid form (graphite, carbon black, charcoal, etc.) w ith a few percent of very fine (typically in the micrometer range) dia mond (or SiC or Si or BN, etc.). The mixed powders as pastes or gels a re shaped into various morphologies and reacted in a pure H-2 microwav e plasma or in a tungsten filament assisted reactor at temperatures of 500-degrees-1000-degrees-C. No carbon is introduced externally via an y gaseous species. The mixtures are transformed wholly into a mass of diamond crystals often 5-10mum in size at rates, of several microns an hour. The conversion is total in smaller and partial in larger shapes depending on the density of the starting material. Raman, scanning el ectron microscopy (SEM), and x-ray diffraction (XRD) evidence confirm the essentially complete transformation irrespective of other variable s such as substrate materials, form of carbon, or second phase. The me chanism of conversion has not been studied and may well involve mass t ransfer over nanometer and micrometer distances via the vapor phase.