Corrosion resistance of silicon nitride ceramics

Corrosion resistance of silicon nitride ceramics against various solutions were investigated. Two kinds of silicon nitrides were examined. One is standard material called TSN-03NH and the other is corrosion-resistant material called TSN-15NH. A test piece with a size of 3 x 4 x 40mm was set in each solution without stirring for 10 to 240h at 30 degreesC or for 10 to 100h at 80 degreesC. Low corrosion resistance of TSN-03NH was observed in sodium hydroxide solution at 80 degreesC, whereas that of TSN-15NE was relatively high. The corrosion resistance of both specimens in potassium hydroxide solution was high compared with that in sodium hydroxide solution. In 5wt% sulfuric acid solution at 30 degreesC, both specimens were found to be considerably corroded, whereas both specimens showed relatively strong corrosion resistance against 95wt% sulfuric acid. Corrosion was recognized even in such neutral solutions as sodium chloride and calcium chloride, although the weight loss was very small. The bend strength of the specimens after soaking at 80 degreesC was found to be inversely proportional to the weight loss except the result in sulfuric acid, indicating that the way of yielding flaws is almost the same in the solutions expect H2SO4.