Effect of BaSO₄ on the interfacial phenomena of high-alumina refractories with Al-alloy

The performance of high-alumina refractories used for aluminium casting significantly impacts the efficiency of metal production. The interfacial reactions with Al-alloys cause corundum and magnesium spinel deposition on the refractory surface, leading to refractory degradation. An experimental study was conducted to investigate the influence of varying barium sulphate (BaSO₄) concentrations in a high-alumina refractory on its interfacial reactions with molten Al-alloy in a horizontal tube furnace at 1523 K (1250 °C) under inert conditions. This study showed that the Al-alloy reactions with pure BaSO₄ would form barium aluminates at the interface. However, in the Al-alloy/refractory system, the interfacial behaviour was strongly influenced by the relative amount of BaSO₄, such that up to 5 wt%, the extent of alloy penetration into the refractory increased with increasing BaSO₄ contents. Electron-probe micro-analyser and X-ray diffraction studies indicated that the composition of the interface for these refractories was augmented with barium silicates and diminishing anorthite phases. In the presence of 10 wt% BaSO₄, the extent of metal penetration into the refractory decreased, whilst for 20% BaSO₄, the penetration was higher; these results were attributed to the interfacial presence of celsian (BaAl₂Si₂O₈) and unreacted barium sulphates, respectively. This study suggests that maximising the celsian formation at the interface is critical for optimising the BaSO₄ concentration for improving the refractory’s performance for Al-casting.