ENVIRONMENTAL DURABILITY OF STRUCTURAL CERAMICS IN HIGH-PRESSURE AND HIGH-TEMPERATURE WATER VAPOR

研究了结构陶瓷在高温高压水蒸气中与高温高压水共存时的腐蚀行为和强度退化。本研究以硅酸盐玻璃和碳化硅陶瓷为试件，在300ﾟC的饱和水蒸气中进行了1~10d的水热腐蚀试验。腐蚀前后的重量变化、腐蚀后表面的X射线衍射分析、电感耦合等离子体原子发射光谱的溶液分析、扫描电子显微镜观察和X射线能谱分析，结果表明：(1)石英玻璃和碳化硅陶瓷在300ﾟC的饱和水蒸气中的腐蚀速率高于在水中的腐蚀速率；(2)碳化硅陶瓷的晶间腐蚀是以晶界优先侵蚀的方式进行的；(3)随着腐蚀时间的延长，石英玻璃的断裂强度随着腐蚀时间的延长而提高，这是由于水的渗透降低了石英玻璃的粘度。碳化硅陶瓷腐蚀后的断裂强度约为初始强度的80%。

The corrosion behavior and strength degradation of structural ceramics in high-temperature and high-pressure water vapor, which coexists with the high-temprtature and high-pressure water, have been studied. The porpose of this study is to clarify the corrosion reaction and the forms of corrosion for typical non-oxide and oxide ceramics in such environments, to evaluate the corrosion resistance and the environmental strength for these ceramics, and to present the suggestions for the material design and the material improvement.Silica glass and silicon carbide ceramics were used as the test samples.Corrosion tests were conducted hydrothermally in saturated water vapor at 300ﾟC for 1-10 d. The weight change before and after corrosion of the sample, XRD analysis of the surface for the corroded sample, the solution analysis by ICP-AES,SEM observation and EDX analysis of the corroded sample, and the fracture strength of the sample before and after corrosion by 3-point bending test, were measured.The following results were obtained.(1) Corrosion rates of silica glass and sic ceramics in saturated water vapor at 300ﾟC is higher than those in water.(2) Intergranular corrosion proceeded in the SiC ceramics by preferential attack at the grain boundaries.(3) The fracture strength of silica glass agter corrosion rised up with increasing duration time, because the viscosity of silica glass was reduced due to the permeation of water. The fracture strength of SiC ceramics after corrosion was reduced by about 80% of the initial strength.