EFFECTS OF MgO, CeO2 AND SiO2 ADDITIONS ON THE CORROSION BEHAVIOUR OF Cr2O3 BASED CERAMICS IN HIGH TEMPERATURE SUPERCRITICAL WATER ENVIRONMENTS

摘要

This investigation is aimed at developing ceramic materials that can survive service in high temperature supercritical water (SCW), which is being considered as the coolant for one of the next generation nuclear energy reactors. Previous research in our group has found that Cr2O3, a primary protective film on all stainless steels, can be unstable due to the formation of soluble Cr6+ species, especially in an SCW environment with relatively high oxygen partial pressures. In this investigation, Cr2O3 ceramics with various amounts of other oxides such as MgO, CeO2 and SiO2 additives were prepared to enhance the stability of Cr2O3 in supercritical environments. These Cr2O3 based ceramics were exposed to an SCW environment at 650°C and 25 MPa for up to 600 hours. Gravimetric measurement, scanning electron microscope (SEM) analysis, X-ray diffraction (XRD) and mass spectrum analysis were conducted to determine the chemical and microstructural characteristics, and the corrosion behaviour of these Cr2O3 based ceramics before and after SCW exposure. The preliminary results obtained showed that adding a proper amount (≤ 5 wt. %) of CeO2 and MgO into Cr2O3 increased the corrosion resistance of Cr2O3 based ceramics in SCW environments, whereas large additions seem to deteriorate the stability of the Cr2O3 based ceramics. The beneficial effects can be attributed to the formation of diffusion barriers, which may block the diffusion of O at the grain boundaries.