Corrosion Behavior of Si₃N₄ Ceramics under High-Temperature and High-Pressure Water Condition

Abstract

Silicon nitride (Si3N4) ceramics have been considered for various components of nuclear power plants such as mechanical seal of reactor coolant pump (RCP), guide roller for control rod drive mechanism (CRDM), and seal support, etc. Corrosion behavior of Si3N4 ceramics in high-temperature and high-pressure water must be elucidated before they can be considered for components of nuclear power plants. In this study, the corrosion behaviors of Si3N4 ceramics at hydrothermal condition (300°C, 9.0 MPa) were investigated in pure water. The grain-boundary phase was preferentially corroded and the corrosion reaction was controlled by the diffusion of the reactive species and/or products through the corroded layer. Results of this study imply that the variation of sintering aids and/or the control (e.g., crystallization) of the grain-boundary phase are necessary to increase the corrosion resistance of Si3N4 ceramics in high-temperature water.

Comparison of hydrothermal corrosion behavior of SiC with Al2O3 and Al2O3 + Y2O3 sintering additives

“…According to the weight loss result of this study, it can be found that the weight loss rate of the AY‐SiC specimen was gradually decreasing after corrosion for 12 days, as shown in Figure , indicating that the protection of the deposited layer plays a dominant role for the higher corrosion resistance of the AY‐SiC specimen. Moreover, it should be noted that the Y 2 SiO 5 precipitate was not generated on the surface of the AY‐SiC specimen until corrosion for 12 days, as shown in Figures and , indicating that the corrosion resistance of Y 2 O 3 is better than that of Al 2 O 3 , in agreement with previous studies which reported that the increase in Y 2 O 3 content could increase the corrosion resistance of Y 2 O 3 /Al 2 O 3 ‐doped Si 3 N 4 ceramics . To this end, it seems possible that reducing the content of Al 2 O 3 or increasing the content of Y 2 O 3 , can improve the corrosion resistance of SiC.…”

“…During hydrothermal corrosion, some precipitates were formed on the surface due to the corrosion of the sintering additive Y 3 Al 5 O 12 , resulting in a protective layer on the surface after corrosion, which can effectively protect the AY‐SiC specimen from further corrosion, and thereby improving the corrosion resistance of the AY‐SiC specimen. In addition, the corrosion resistance of sintering additive (Y 3 Al 5 O 12 ) in the AY‐SiC specimen is better than that of sintering additive (Al 2 O 3 ) in the A‐SiC specimen, which is another reason for the higher corrosion resistance of the AY‐SiC specimen . According to the weight loss result of this study, it can be found that the weight loss rate of the AY‐SiC specimen was gradually decreasing after corrosion for 12 days, as shown in Figure , indicating that the protection of the deposited layer plays a dominant role for the higher corrosion resistance of the AY‐SiC specimen.…”

Effects of sintering aides on the hydrothermal oxidation of silicon nitride spherical rolling elements

“…Previous authors have attempted to isolate the effects of various sintering aides on the final microstructure of Si 3 N 4, and some authors have also studied the effects on the resulting corrosion behaviour. The corrosion behaviour has been studied at 473-573 K in air [7,8], moist air [9] and water [8,[10][11][12][13][14][15], as well as in acidic environments [10,16,17]. While general trends in corrosion have been established, each sintering aide has a discrete effect on the densification, mechanical and wear behaviour of the final product.…”