Improving hydration resistance of MgO–CaO ceramics by in situ synthesized CaZrO3 coatings prepared using a non-hydrolytic sol

Abstract As refractories, MgO–CaO materials exhibit excellent properties such as high refractoriness and good thermal shock resistance; however, their poor hydration resistance limits their practical applications. In this study, calcium zirconate (CaZrO3) coatings were deposited on CaO and MgO–CaO ceramics by dipping the ceramics in a non-hydrolytic sol. The optimised coating on the MgO–CaO ceramics was prepared by dipping the ceramics once in a 0.6 mol/L zirconia sol. The CaZrO3 coating was in situ synthesized after calcination. The multiphase ceramics with different CaO contents were characterised using scanning electron microscopy to determine the grain sizes of MgO and CaO and to analyse the distribution of CaO in the MgO matrix and the surface porosity of the samples. The microstructure and phase analysis results showed that most of the CaO on the surface transformed into CaZrO3 and was located at the grain boundaries. The MgO–CaO ceramics with the CaZrO3 coatings, especially the ceramics with 20 wt% CaO, showed significantly improved hydration resistance as compared to the untreated ceramics.