Some Physical Properties of Eight Refractory Oxides and Carbides

An investigation of eight hot‐pressed refractory oxides and carbides for possible gas‐turbine application was undertaken. The properties, short‐time tensile strength at elevated temperatures, thermal‐shock resistance, coefficient of linear expansion, and density, were determined. The compositions of the ceramics included beryllium oxide, magnesium oxide, stabilized zirconia, zircon, boron carbide, 85% silicon carbide plus 15% boron carbide, titanium carbide, and zirconium carbide. The short‐time tensile strengths of these ceramics were determined at 1800° and 2200°F. Resistance to thermal shock was determined by rapid cooling in air to room temperature from 1800°, 2000°, 2200°, and 2400°F. The thermal‐expansion characteristics of these materials were studied from room temperature to 1100°F. Zirconium carbide was the strongest material at 2200°F. with a maximum short‐time tensile strength of 15,850 lb. per sq. in.; however, it exhibited extremely poor resistance to oxidation. Boron carbide had a short‐time tensile strength of 22,550 lb. per sq. in. at 1800°F., and was the strongest material at this temperature. Boron carbide also had very poor resistance to oxidation and was among the worst compositions investigated in its ability to resist fracture by thermal shock. The evaluation of strength of boron carbide at 2200°F. was unsuccessful because it fluxed with the grips. Titanium carbide had the best resistance to thermal shock, and had strengths of 15,850 lb. per sq. in. at 1800°F. and 9400 lb. per sq. in. at 2200°F. It was the most promising of the eight compositions investigated. Hot‐pressing of these eight highly refractory bodies indicated that a density of at least 93% of theoretical density could be obtained by this fabrication method.