Alumina magnesia castable include corundum, spinel and corundum - magnesia castable, after high temperature treatment in the process of or use six calcium aluminate (CA6), magnesium aluminate spinel and corundum phase three high melting point, good combination between three phase, the castable has good slag resistance and thermal shock resistance, is widely used in ladle lining, breathable element and nozzle, etc.

　　Study of alumina magnesia castable performance improvement from the perspective of the optimization of matrix system normally, such as change the spinel type (add the synthesis or in situ generated spinel), regulation of spinel or generation, adjustment for the amount of magnesium oxide powder particle size, change the kinds of binder and adding trace amounts of SiO2 powder (spinel with the volume expansion of in situ reduction), etc., but aggregate of alumina magnesia castable performance improvement research is relatively small, with the literature change aggregate types (white corundum, corundum, tabular corundum and rich aluminum spinel) can control the slag resistance. Castable was slag erosion processes, intrusion into matrix system, and then penetrate the aggregate. Usually castable in aggregate particles are difficult to slag erosion damage. Therefore, appropriate to reduce the aggregate density, the lightweight microporous aggregate can reduce resource consumption, reduce the energy consumption of refractory material and and not obviously reduce the slag resistance of materials.

　　Bo knight (Bonite, Wallace aluminum) as a kind of dense six calcium aluminate aggregate, has the six-party plate microstructure and more micropore (shown in figure 1), its high refractoriness, thermal shock, resistance to basic slag and reducing atmosphere resistance is strong, low thermal conductivity (1.7 w. k. m - 1-1), at the same time of liquid metal and slag has no wettability. Relative to tabular corundum aggregate (density: 3.63 g · cm - 3), Bonite aggregate with lower bulk density (density: 3.0 g · cm - 3), higher porosity show porosity (8.5%), and the smaller pore size, the material is introduced into the corundum, spinel castable, can significantly affect the castable of porosity, pore size, thermal conductivity, slag resistance and thermal shock resistance, etc.

　　Figure 1

　　Literature reported that the introduction of 40% Bonite aggregate preparation of knight - corundum - spinel quantitative castable, light and not introduce Bonite compared to aggregate corundum, spinel castable, the castable has more porous structure after burn, showed a low thermal conductivity, good thermal shock resistance and slag resistance, and high temperature flexural performance without significant reduction. Lightweight castable fracture SEM photos as shown in figure 2. (chong zhang for high temperature; the experimental data of: the Ceram. Int., 42 (2016) 4941)

　　Figure 2