Corrosion and dissolution behaviors of hot-pressed Si
3N
4 ceramics at 88°C in lithiated and borated water that was prepared to simulate PWR primary coolant were studied using a small once-through type experimental loop. Experiments were carried out for two Si
3N
4 ceramics with different sintering aids composed of MgO and Y
2O
3/Al
2O
3, respectively, and also Al
2O
3 which is used as the component of the mechanical seals for PWR primary coolant pump. The weight loss of exposed Si
3N
4 specimen containing MgO was relatively large and reached to 2.1mg/cm
2 after 1, 000h exposure. Mg was dissolved selectively into the test solution, but dissolution of Si
3N
4 grain itself was estimated to be negligibly small. The surface was deeply corroded with the depth of 70μm, and changed to porous one. On the other hand, the weight loss of 1, 000h exposed specimen containing both Y
2O
3 and Al
2O
3 was very small at around 0.12mg/cm
2. This value was nearly equal to that of Al
2O
3 ceramics. Similar to the case of Si
3N
4 containing MgO, Y was dissolved selectively and the surface was changed to porous. The corrosion depth, however, was small, of the order of 2μm. It was thus estimated that the corrosion resistance of Si
3N
4 ceramics in hot water was largely dependent on the compositions of sintering aids.
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