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

研究了结构陶瓷在与高温高压水共存的高温高压水蒸气中的腐蚀行为和强度退化。本研究的目的是阐明典型的非氧化陶瓷和氧化陶瓷在这种环境下的腐蚀反应和腐蚀形式，评价这些陶瓷的耐蚀性和环境强度，并提出材料设计和改进的建议。以二氧化硅玻璃和碳化硅陶瓷为试样。采用水热法在300℃饱和水蒸气中进行1 ~ 10 d的腐蚀试验，测定腐蚀前后试样的重量变化、腐蚀试样表面的XRD分析、腐蚀试样的ICP-AES溶液分析、SEM观察和EDX分析以及腐蚀前后试样的三点弯曲断裂强度。得到了以下结果：(1)硅玻璃和碳化硅陶瓷在300℃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在晶界处优先发生的。(3)石英玻璃agter腐蚀的断裂强度随着持续时间的增加而上升，这是由于水的渗透降低了石英玻璃的粘度。腐蚀后SiC陶瓷的断裂强度降低了约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.