Corrosion behavior of silicon nitride ceramics in aqueous solutions (Part 3). Corrosion behavior in hot sulfuric acid and microstructure of corroded layer

Corrosion behavior of gas pressure sintered silicon nitride ceramics was investigated in sulfuric acid solution with respect to the effect of solution temperature and to the microstructure of corroded layer. Weight loss of samples after corrosion test was severe in boiling solution as compared with in 90°C solution. Nevertheless strength degradation occurred similarly in each solution. The gradual growth of corrosion is considered to be controlled by the dissolution reaction of grain boundary phase of silicon nitride ceramics in sulfuric acid solution. The drastic strength degradation at initial stage is considered to be ascribed to the relaxation of the residual compressive stress during corrosion which was introduced on surfaces of specimens by machining.