Conversion of silicon carbide to crystalline diamond-structured carbon at ambient pressure

Synthetic diamond is formed commercially using high-pressure(1), chemical-v apour-deposition(2) and shock-wave(3) processes, but these approaches have serious limitations owing to low production volumes and high costs. Recentl y suggested alternative methods of diamond growth include plasma activation (4), high pressures(5), exotic precursors(6,7) or explosive mixtures(8), bu t they suffer from very low yield and are intrinsically limited to small vo lumes or thin films. Here we report the synthesis of nano- and micro-crysta lline diamond-structured carbon, with cubic and hexagonal structure, by ext racting silicon from silicon carbide in chlorine-containing gases at ambien t pressure and temperatures not exceeding 1,000 degreesC. The presence of h ydrogen in the gas mixture leads to a stable conversion of silicon carbide to diamond-structured carbon with an average crystallite size ranging from 5 to 10 nanometres. The linear reaction kinetics allows transformation to a ny depth, so that the whole silicon carbide sample can be converted to carb on. Nanocrystalline coatings of diamond-structured carbon produced by this route show promising mechanical properties, with hardness values in excess of 50 GPa and Young's moduli up to 800 GPa. Our approach should be applicab le to large-scale production of crystalline diamond-structured carbon.