Thermal expansion characteristics of alumina-magnesia and alumina-spinel castables in the temperature range 800 degrees-1650 degrees C

The thermal expansion of Al2O3-MgO castables containing 5.5 wt% MgO and 1.3 6 wt% CaO and Al2O3-spinel castables containing 20 wt% spinel having 95 wt% Al2O3 and 1.7 wt% CaO was measured in the temperature range of 800-1650 de greesC by dilatometry. A sharp increase in expansion from around 1425 degre es to 1525 degreesC, followed by a sharp decrease with further increasing t emperature, is characteristic of Al2O3-MgO castables. The sharp increase in expansion is believed to be caused by the bond linkage between the CA, and spinel grains in the bonding matrix, while the sharp decrease is apparentl y related to liquid-phase sintering. The sharp increase and decrease in exp ansion mere not observed in Al2O3-spinel castables because of the much lowe r MgO (around 1 wt% MgO) and impurity contents. The magnitude of thermal ex pansion of calcium aluminate bonded castables containing self-forming or pr eforming spinels or both is dictated by the MgO content of the castables.