Effects of AlPO₄ Addition on the Corrosion Resistance of Andalusite-Based Low-Cement Castables with Molten Al-Alloy

This paper investigates the effects of AlPO₄ addition on the corrosion resistance of andalusite LCC refractories. Corrosion tests using the Alcoa cup test (850 °C and 1160 °C for 150 h and 72 h, respectively) were conducted to determine the extent of penetration. The addition of AlPO₄ was shown to improve the corrosion resistance of the castables in contact with molten Al-alloy. SEM/EDS analyses of the interfacial reaction zone showed the formation of corundum in the interfacial layer, along with a significant decrease in the phosphorus content in the interface. Thermodynamic calculations revealed that reaction with the alloy leads to the formation of corundum as the reaction product along with gaseous products (phosphorus trioxide gas) and small amounts of aluminum phosphide. Corundum formation at the interface enhances the corrosion resistance of sample due to high stability of corundum against molten Al alloy, while the metal quality is enhanced due to absence of dissolved phosphorus in the metal.