Corrosion Behavior of Alumina Ceramics in Caustic Alkaline Solutions at High Temperatures |
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Authors: | Tsugio Sato Shigeki Sato Akitsugu Okuwaki Syun-ichiro Tanaka |
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Affiliation: | Department of Molecular Chemistry and Engineering, Faculty of Engineering, Tohoku University, Sendai 980, Japan;New Material Engineering Laboratory, Toshiba Corporation, Yokohama 235, Japan |
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Abstract: | The corrosion rate and changes in the microstructure and fracture strength of alumina ceramics (93.0% Al2O3 and 99.5% Al2O3) were studied in 0.1 m to 25 m NaOH solutions at 150°C to 200°C, where m = mol/(kg of H2O). The attack of the caustic alkaline solution started at the grain boundaries. Consequently, the corrosion resistance increased with decreasing SiO2 content in Al2O3 ceramics, and the corrosion resistance of 99.5% pure Al2O3 was similar to that of Si3N4 ceramics. Since large pits are formed by corrosion, the surface area increased first and the apparent corrosion rate increased with time in the initial stage of the corrosion. The corrosion rate of Al2O3 increased linearly with increasing NaOH concentration, and the activation energy was 102 kJ/mol. The fracture strength of corroded Al2O3 decreased monotonically as the degree of dissolution of alumina increased. |
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Keywords: | alumina silica corrosion resistance alkali resistance grain boundaries |
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