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Corrosion Behavior of Engineering Ceramics in Water at High-Temperatures and Pressures

工程陶瓷在高温高压水中的腐蚀行为

基本信息

批准号：
02805094
负责人：
TETSUO Yoshio
金额：
$ 1.09万
依托单位：
Okayama University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1990
资助国家：
日本
起止时间：
1990 至 1991
项目状态：
已结题

项目摘要

The corrosion behaviors of the promising engineering ceramics, silicon nitrides and mullites, were studied by the autoclave method at 300ﾟC and 8.6MPa for times up to 10 days. The results are summarized as follows :1. Corrosion behavior of silicon nitride ceramics :Pressureless-sintered Si_3N_4 with additives(Y_2O_3-Al_2O_3 and MgO)prepared with imide decomposed Si_3N_4 powder was severely corroded in water at high-temperature and pressure. resulting in weight loss and formation of corrosion product layer. After removal of corrosion products, pits up to about 100 mu m in diameter were found distributed over the Si_3N_4 surface. Pit features in these sintered Si_3N_4 are different depending on the species of oxide additives ; Si_3N_4 with Y_2O_3-Al_2O_3 forms deep pits with a thin protective corrosion product layer and that with MgO forms shallow pits with a thick non-protective corrosion product layer. This result in higher corrosion resistance for the former than the latter.2. Corrosion behavior of mullite ceramics :The aqueous corrosion of mullite ceramics proceeded according to the reaction, 3Al_2O_3・2SiO_2+3H_2O -> 6AlOOH+2SiO_2, with weight loss by dissolution Of SiO_2 and formation of boehmite(AIOOH)residue layer. The extent of corrosion resistance was significantly dependent on the powder preparation method and chemical composition. Seventy four wt% Al_2O_3-mullite prepared from an alkoxide-derived powder showed the highest corrosion resistance. Mullite ceramics with highcorrosion resistance was found to be attained by homogeneous mixing SiO_2 with Al_2O_3 in an alkoxide-derived or coprecipitation powder.3. Corrosive strength degradation of the ceramics :The bending strength of the corroded specimens for both silicon nitride and mullite ceramics reduced to around 2/3 of the original values in the early stage of corrosion, and then remained almost constant up to 10 days.

采用高压釜法研究了氮化硅和莫来石这两种有前途的工程陶瓷在300 ℃、8.6MPa下长达10天的腐蚀行为。主要研究结果如下：1.氮化硅陶瓷的腐蚀行为：用酰亚胺分解的Si_3N_4粉末制备的添加剂（Y_2O_3-Al_2O_3和MgO）的无压烧结Si_3N_4陶瓷在高温高压条件下在水中腐蚀严重。导致重量损失和腐蚀产物层的形成。去除腐蚀产物后，发现Si_3N_4表面分布着直径约100 μ m的点蚀坑。不同氧化物添加剂的烧结Si_3N_4中的蚀坑特征不同，添加Y_2O_3-Al_2O_3的Si_3N_4形成深蚀坑，蚀坑内有较薄的保护性腐蚀产物层，而添加MgO的Si_3N_4形成浅蚀坑，蚀坑内有较厚的非保护性腐蚀产物层。这导致前者比后者具有更高的耐腐蚀性。莫来石陶瓷的腐蚀行为：莫来石陶瓷在水溶液中的腐蚀反应为3Al_2O_3·2SiO_2+3H_2O → 6AlOOH+2SiO_2，SiO_2溶解失重，形成薄水铝石（AlOOH）残留层。耐蚀性的程度显着依赖于粉末的制备方法和化学成分。74wt%Al_2O_3-莫来石粉末制备的醇盐具有最高的耐腐蚀性。采用SiO_2和Al_2O_3混合均匀的醇盐或共沉淀法制备了高耐蚀性莫来石陶瓷.陶瓷的抗弯强度退化：氮化硅和莫来石陶瓷的抗弯强度在腐蚀早期降低到原始值的2/3左右，然后几乎保持不变，直到10天。