Impact of a Subsonic Dissociated Air Flow on the Surface of HfB2-30 vol % SiC UHTC Produced by the Sol-Gel Method

A new method, which included the sol-gel synthesis of a HfB2-(SiO2-C) reactive composite powder and its subsequent consolidation by hot pressing (1700 degrees C, 30 MPa, 15 min) with simultaneous carbothermic synthesis of nanocrystalline silicon carbide, was used to produce HfB2-SiC ultra-high-temperature ceramic material promising for using in an air atmosphere at temperatures above 2000 degrees C. Its elemental and phase compositions, as well as its microstructure were investigated. The density and calculated porosity were 7.6 g/cm(3) and 13.5%, respectively. The behavior of a cylindrical sample of the material was studied on long-term (40 min) exposure to a subsonic dissociated air flow in a high-frequency induction plasmatron. The change in the temperature of the surface of the material was examined in the context of its relationship with the HfB2 and SiC oxidation and the evaporation of the oxidation products. The phase composition and microstructure were determined in regions of the oxidized surface of a HfB2-SiC sample containing 30 vol % SiC that were heated on exposure to high-enthalpy flows to 2600-2700 degrees C and in regions the temperature of which was 1850-1950 degrees C. By scanning electron microscopy, the thickness, microstructure, and composition of the oxidized layer were found.