Abstract

Refractories used in the aluminium industry undergo severe corrosion due to reaction with molten aluminium. The high wettability by aluminium melt is suspected to be a key factor for degradation and infiltration, hence anti-wetting additives such as BaSO4, CaF2 or AlPO4 are added to the refractory to limit the contamination of the melt. The conditions as well as the mechanisms of the improved corrosion resistance are not yet well understood. In particular the behaviour of phosphor at the interface between refractory and aluminium melt is subject of current research. The present work is aims at improving the corrosion resistance against molten aluminium of an alumina based no cement castable with addition of AlPO4. It has been shown that for an anti-wetting effect a high amount of 10 wt% AlPO4 is needed. Furthermore the use of additives leads to worsening of the refractory microstructure especially when sintered at high temperatures, presumably due to rheological issues. Nevertheless, an improved corrosion resistance was obtained even at fewer addition of AlPO4 around 6 wt%. This study intends to examine the impact of varying AlPO4 addition to an alumina no cement castable to the MA-spinel formation at the interface between aluminium alloy Al 7075 and the refractory castable. The applied methods include a first characterization of the material with open porosity, density and permeability measurements, examination of spinel formation mechanisms by SEM and XRD as well as a study of the reactivity with aluminium melt during a dynamic laboratory finger test according to standard CEN/TS 15418. The efficiency of the addition and its impact on the microstructure including Young’s Modulus as well as the possible improvement of the infiltration resistance are discussed.