Title: Deposition and characterization of pyrocarbon coatings produced by use of CO/sub 2/ dilution
Abstract: A Biso-coated fuel particle for the High-Temperature Gas-Cooled Reactor (HTGR) consists of a 500 ..mu..m ThO/sub 2/ kernel, an 85-..mu..m layer of low-density carbon, and a 75-..mu..m layer of high-density pyrocarbon. Coatings produced from mixtures of 50% propylene, 25% CO/sub 2/, and 25% Ar were found to be more gastight than were coatings produced from mixtures of propylene and argon, helium, or H/sub 2/. Higher concentrations of CO/sub 2/ in the gas mixture caused severe oxidation of graphite components within the coating furnace. The permeability of coatings deposited by use of CO/sub 2/ dilution was found to depend on the deposition temperature. Low deposition temperatures produced more gastight coatings. It was determined that CO/sub 2/ had little or no effect on coating anisotropy. 6 figures.