FORMATION OF HEXA-ALUMINATE SOLID SOLUTION PHASES IN SPINEL CONTAINING CASTABLES - MINERALOGICAL INVESTIGATIONS IN THE SYSTEM CaO-Al2O3-MgO

MgAl2O4 spinel has been used in the refractory industry for many years and is well known to improve the thermal stability of alumina based refractory materials. Refractory products in demanding application conditions such as purging plugs or impact pads show increased thermo-mechanical stability and high erosion resistance when spinel is included. This research describes the formation of ternary hexa-aluminate phases CAM I (C2M2A14) and CAM II (CM2A8) at elevated temperatures between 1400°C and 1700°C. Mineralogical investigations of refractory castables prove CAM phases grow into sintered alumina grains resulting in an interlocking of matrix and aggregate compounds. The resulting microstructure contributes to improved hot strength properties, especially thermo-mechanical resistance. Further on, white fused alumina aggregates show a weaker reaction with the surrounding matrix which leads to less potential for interlocking