Effects of Oxidation and Hot Corrosion on the Erosion of Silicon Nitride

Abstract

The effect of oxidation and hot corrosion on the solid particle erosion was investigated for hot-pressed silicon nitride using as-polished, pre-oxidized and pre-corroded specimens by molten sodium sulfates. Erosion tests were performed at 22, 500 and 900 ℃ using angular silicon carbide particles of mean diameter 100 ㎛. Experimental results show that solid particle erosion rate of silicon nitride increases with increasing temperature for as-polished or pre-oxidized specimens in consistent with the prediction of a theoretical model. Erosion rate of pre-oxidized specimens is lower than that of as-polished specimens at 22 ℃, but it is higher at 900 ℃. Lower erosion rate at 22 ℃ in the pre-oxidized specimens is attributed due to the blunting of surface flaws, and the higher erosion rate at 900 ℃ is due to brittle lateral cracking. Erosion rate of pre-corroded specimens decreases with increasing temperature. Less erosion at 900 ℃ than at 22 ℃ is associated with the liquid corrosion products sealing off pores at 900 ℃ and the absence of inter-granular crack propagation observed at 22 ℃.