Corrosion mechanism of polycrystalline corundum and calcium hexaluminate by calcium silicate slags

The chemical reactions involved in the corrosion of polycrystalline alumina (Al2O3) and calcium hexaluminate–hibonite (CaAl12O19) ceramics by two dicalcium silicate slags with additions of fluorspar (CaF2) were studied using a hot-stage microscopy (HSM) up to 1600 °C. The corrosion mechanism was investigated on post-mortem corroded samples and the phases formed at different stages of the dissolution process were characterised by reflected optical light microscopy (RLOM) and scanning electron microscopy (SEM) with energy dispersive X-ray spectrometry (EDS) microanalysis system.The attack of the fused slags on dense alumina substrates takes place through an interdiffusion mechanism producing successive layers of calcium aluminates. In porous hibonite samples chemical interactions were observed although only a layer of calcium dialuminate was formed. A sintering process in presence of liquid phase was also detected behind the reaction interphase.Thermodynamic calculations, based on the Al2O3–CaO–SiO2, Al2O3–CaO–SiO2–MgO, and Al2O3–CaO–SiO2–CaF2 phase equilibrium were used to further knowledge of the corrosion mechanism.