Matrix microstructure optimization of alumina-spinel castables and its effect on high temperature properties

摘要

In this paper, submicron spinel-containing calcium aluminate (SP-CA) cements were prepared at temperatures of 1200 degrees C (RA12), 1300 degrees C (RA13), and 1450 degrees C (RA14) using reactive alumina, magnesium hydroxide, and calcium carbonate as raw materials. The microstructural characteristics and high temperature properties of refractory castables bonded by SP-CA cement were investigated. The results indicated that the mineralogical compositions of SP-CA were spinel (MgAl2O4, MA) and CaAl2O4 (CA). The spinel phases presented no definite borders or shapes, with average size ranging from 0.1 pm to 1.2 mu m at different sintering temperatures. After heating alumina-spinel castables, the submicron spinel particles bonded with corundum and hibonite (CA(6)) grains could strengthen the castable body. However, the large sized ( < 88 mu m) spinel did not form links between spinel and alumina in the castable with added preformed spinel (castable AS). Submicron spinel can decrease the pore sizes of refractory castables from 2 mu m to 0.5 mu m. Extended finite element method (XFEM) calculations showed that smaller pores prevent stress concentration and result in increased deformation with limited crack propagation. Hence, large numbers of 0.5 mu m pores can act as crack-stoppers to improve the thermal shock resistance of castables with added SP-CA cements. Thermal shock resistance tests showed that R"" of castable RA12 was 39.7 m, which is significantly higher than that of castable AS (19.8 m). The corrosion rate of castable RA12 was 5 mm(2)/min, which is significantly lower than that of castable AS (7.4 mm(2)/min). Small pore size and submicron spinel played relevant roles in corrosion behavior.