The sintering of corundum mullite bricks mainly refers to the formation of mullite phase or the formation of a very small amount of glass phase to achieve the densification process.
In the corundum-mullite complex structure, mullite is generally columnar, rod-shaped crystals, corundum is generally granular, and corundum-like crystals are filled in the voids of the mullite columnar crystal network structure to form a continuous interlaced structure. Corundum phase crystals can play a role in strengthening and toughening; or mullite columnar crystals are filled in the voids of corundum phase crystals. The existence of columnar mullite crystals can play a role of strengthening and toughening similar to fibers and particles. The two filling states are very beneficial to improve the high temperature mechanical properties of corundum mullite bricks.
For corundum mullite bricks, on the one hand, due to the different thermal expansion coefficients of corundum and mullite, during the cooling process, micro-cracks will occur inside the composite ceramic, which will seriously affect its thermal shock resistance. On the other hand, the thermal expansion of corundum is higher, and that of mullite is lower. The gradation and particle size of the two have a great influence on the coefficient of thermal expansion of multiphase ceramics. And the total content of mullite includes the mullite raw material and the mullite formed during the firing process. The mullite formed by the reaction of the raw materials not only plays a binding role in the composite material, but also inevitably affects the mechanical properties of the composite material, thereby affecting the composite material’s comprehensive properties such as thermal shock resistance.
