Pyrolytic-Carbon Coatings on Ceramic Fuel Particles

The effects of varying deposition conditions on the properties, especially the structural features, of pyrolytic carbon deposited on ceramic fuel particles in a fluidized bed were systematically investigated. The carbon was formed by thermally decomposing methane on 200-µm-diam uranium carbide particles. Variables considered were deposition temperature, between 1300 and 2000°C, and methane flow rate, between 0.0167 and 2.53 cm³ / (min cm²). It was shown that these variables strongly influence microstructure, density, crystallite size, and preferred orientation of the pyrolytic-carbon coatings. The results are presented as contour maps for property dependence and as a montage of photomicrographs for microstructure dependence. The microhardness of coatings deposited at 1400°C increased with methane flow rate by a factor .of 3 over the range of flow rates employed.