The effect of fine alumina type on composition of in situ spinel formation in alumina-magnesia castables

摘要

Three types of low cement castables (LCC) were prepared from 5% reactive alumina (R_5), 5% calcined alumina (A5) and equal proportions of 2.5% (AR). The nest of the composition was fine bauxite (0-1 mm, 57%), coarse bauxite (1-3 mm, 20%), calcined magnesia (5%), secar 71 refractory cemet (7%) and microsilica (1%). By the addition of 5% water, castables were moulded, aged, dried and fired to 1400°C for 2 h. XRD studies showed higher amount of in situ spinel formation in A_5. The lattice constants of spinels in A_5, AR and R_5 were, respectively, 8.0348, 8.0688 and 8.0847 ?. This accounted for respectively alumina rich, stochiometry and magnesia rich spinels. Since calcined alumina is cheaper, produce higher amounts of spinel with the aid of alumina from the aggregate of bauxite and the binder of cement, and alumina rich spinel has better corrosion resistance properties, use of calcined alumina is recommended in LCC.