Effect of Compositional Variables on the Properties of Alumina-Magnesia Castables

摘要

The properties of Al_2O_3-MgO castables containing 5.5-7.5 mass-% MgO and 1.02-1.70 mass-% CaO, without addition of microsilica in general, were investigated. The magnesia was of 95 mass-% purity and the alumina cement contained 17.0 mass-% CaO and 0.1 mass-% SiO_2. Most aggregates were white fused alumina. Aggregates > 3 mm were a mix of white- and brown-fused aluminas. Fine aluminas were of the reactive and calcined types. The optimum chemical composition of castables is [mass-%]: 5.5 MgO, 1.36 CaO, and 0.75 microsilica. Hot Modulus of Rupture (HMOR) of the castables in the temperature range 1100-1500 ℃ generally increased up to 1000 ℃, reached a peak value at either 1100 or 1200 ℃ and then decreased with increasing temperature. HMOR at 1400 and 1500 ℃ decreased with increasing MgO content and temperature if CaO content remained constant, while another HMOR at 1400 and 1500 ℃ varied slightly with increasing CaO content and decreased with increasing temperature if MgO content maintained constant. Thermal subsidence under load (0.2 MPa) increased with increasing MgO or CaO content. The increasing subsidence is associated with increasing deficiency in fine alumina in the matrix for formation and growth of CA_6, as MgO or CaO content is increased. Addition of microsilica up to 1.5 mass-% beneficially raises the Al_2O_3 content of spinels in the castables and significantly enhances flowability of the castables. Wear resistance increases with addition of 0.50 or 0.75 mass-% microsilica, depending on the kind of cement used.