Molten-Salt Corrosion of Silicon Nitride: I, Sodium Carbonate

Corrosion of Si3N4 under thin films of Na2CO3 was investigated at 1000°C. Pure Si3N4 and Si3N4 with various additives were examined. Thermogravimetric analysis and morphology observations lead to the following detailed reaction mechanism: (I) decomposition of Na2CO3 and formation of Na2SiO3, (II) rapid oxidation, and (III) formation of a protective silica layer below the silicate and a slowing of the reaction. For Si3N4 with Y2O3 additions, preferential attack of the grain‐boundary phase occurred. The corrosion of pure Si and SiC was also studied for comparison to Si3N4. The corrosion mechanism generally applies to all three materials. Silicon reacted substantially faster than Si3N4 and SiC.