Synthetic diamond is formed commercially using high-pressure, chemical-vapour-deposition and shock-wave processes, but these approaches have serious limitations owing to low production volumes and high costs. Recently suggested alternative methods of diamond growth include plasma activation, high pressures, exotic precursors or explosive mixtures, but they suffer from very low yield and are intrinsically limited to small volumes or thin films. Here we report the synthesis of nano- and micro-crystalline diamond-structured carbon, with cubic and hexagonal structure, by extracting silicon from silicon carbide in chlorine-containing gases at ambient pressure and temperatures not exceeding 1,000 degrees C. The presence of hydrogen 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 any depth, so that the whole silicon carbide sample can be converted to carbon. 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 applicable to large-scale production of crystalline diamond-structured carbon.
Highly disordered graphitic carbon layers were formed on various types of commercially available silicon carbide ͑SiC͒ ceramics by reaction with chlorine and chlorine-hydrogen gas mixtures at 1000°C. The carbon was produced ranging from only a few micrometers to hundreds of micrometers thick. When a platinum sample holder was employed ͑instead of fused silica͒, platinum was found dispersed in the carbon layer concentrated near the SiC/C interface. This process can be used for incorporating platinum in porous carbon films for catalytic and other applications. In addition, the platinum resulted in a smoother physical interface between the SiC and carbon sublayer. The morphology of the platinum dispersion, its effect on the carbon layer, and its proposed formation mechanism are presented in this paper.
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