Corrosion and dissolution behaviors of Al
2O
3 ceramics prepared by the pressureless sintering method in demineralized water at 275°C were studied using the small once-through type experimental loop. Experiments were carried out for two specimens with different Al
2O
3 contents of 92% and 99.5%, respectively. The weight loss of exposed specimen with 92% Al
2O
3 content was large and reached to 3.48mg/cm
2 for 100h exposure. The surface of specimen was corroded deeply, of which corrosion depth was 150μm and changed to porous one. The release levels of the minor constituents of Al
2O
3 ceramics, Si, Ca, Na and K, were relatively high compared with that of Al, and the level of Al was about one forth of Si. On the other hand, the weight loss of exposed specimen with 99.5% Al
2O
3 content was very small and was 0.145mg/cm
2 including particles released from the corroded layer by ultrasonic cleaning. In addition, γ-AlOOH crystals were formed on corroded surface. These results suggested that the corrosion resistance of Al
2O
3 ceramics in high temperature water was dependent strongly on Al
2O
3 content, and then that the corrosion resistance of AO
2O
3 grain was very high, and on the hand, grain boundary itself was eluted selectively into the solution.
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