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

We describe herein a process which, also operating below one atmosphere pressure, transforms virtually any form of finely divided solid carbon into crystalline diamond in the reaction chamber. The key to the process is the creation of a two (or more) phase micro (or nano) composite of the carbon solid form (graphite, carbon black, charcoal, etc.) with a few percent of very fine (typically in the micrometer range) diamond (or SiC or Si or BN, etc.). The mixed powders as pastes or gels are shaped into various morphologies and reacted in a pure H-2 microwave plasma or in a tungsten filament assisted reactor at temperatures of 500-degrees-1000-degrees-C. No carbon is introduced externally via any 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 electron microscopy (SEM), and x-ray diffraction (XRD) evidence confirm the essentially complete transformation irrespective of other variables such as substrate materials, form of carbon, or second phase. The mechanism of conversion has not been studied and may well involve mass transfer over nanometer and micrometer distances via the vapor phase.