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

该工程陶瓷、硅镍基和多聚体的腐蚀行为，在300 ℃ C和8.6兆帕的时间内研究了自动手套方法。结果按以下顺序汇总：1。硅基氮基陶瓷的腐蚀行为：带有附加物（Y_2O_3-Al_2O_3和MgO）的压力无关的Si_3N_4粉末在高温和压力下被严重腐蚀。在腐蚀产品层的重量损失和形成中的结果。去除腐蚀产品后，在Si_3N_4表面上发现了大约100微米的直径。在这些sintered Si_3 N_4中存在不同的氧化物添加剂; Si_3 N_4与Y_2 O_3-Al_2 O_3 forms深度坑，与MgO forms浅坑具有thick non-protective corrosion product layer。这一结果对较早的腐蚀抵抗力更强。多聚陶瓷的腐蚀行为：多聚陶瓷发生在反应上的多聚陶瓷的异常， 3Al_2O_3·2SiO_2+3H_2O -> 6AlOOH+2SiO_2，由于SiO_2的分解和Boehmite（AIOOH）重建层的形成。这种抗腐蚀性的程度在很大程度上依赖于粉末制备方法和化学成分。Seventy Four wt %Al_2O_3-mullite Prepared from a alkoxide-derived powder展示了最高的腐蚀抵抗力。已发现具有高腐蚀抗性的Mullite Ceramics可通过同源混合SiO_2和Al_2O_3在烷氧基ide-derived或coprecipitation powder.3。《陶瓷学的腐蚀性强度退化：用于硅氮基和多聚陶瓷的腐蚀性物质的弯曲强度在腐蚀早期阶段减少了2/3的原始价值，然后保留了大约10天。

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.