High-temperature corrosion of a silicon-infiltrated silicon carbide material in combustion atmospheres

Abstract

High-temperature corrosion of a silicon-infiltrated alpha silicon carbide material was investigated, using an atmospheric pressure low-velocity Burner Rig to simulate gas turbine atmospheres with a range of SO 3 partial pressures and sodium concentrations. Experiments were carried out at temperatures above the dew point of sodium sulphate in the range 1250 to 1350 °C. Sample weight was monitored for corrosion assessment on a 20 h cyclic basis. Corrosion followed a parabolic rate law under all conditions studied and the activation energy was found to be 140 kJ mol −1. It was found that at constant sodium contaminant flux rates P SO 3 had a greater effect on corrosion than sodium concentration in the atmosphere. The corrosion rate increased as sulphur trioxide partial pressure decreased. There appeared to be a strong correlation between sodium content of the oxide scale and the rate of corrosion. This is explained by considering oxidation in the presence of sodium to occur by ionic diffusion of oxygen in the glassy scale. The mechanism of oxidation is discussed, and it is demonstrated that the metallic silicon in the ceramic must oxidise in advance of the silicon carbide in order for the reaction to proceed but it is also shown that the distance separating the two reaction fronts would not be observable in the present circumstances.