The mechanical strength and load deformation temperature of sintered mullite bricks are high, with a high density, low porosity, and a high content of crystalline phases. There are no abnormal phenomena on the thermal expansion curve. However, when these substances come into contact with a large amount of alkaline substances at high temperatures, mullite becomes unstable and easily decomposes, which to some extent reduces the stability of these refractory materials. In addition, the final properties of electric melted mullite bricks produced from different purity electric melted mullite raw materials will also vary; Even for the same chemical purity (such as high-purity) fused mullite, the performance of the resulting refractory bricks varies due to different melting processes.
Generally speaking, the high-temperature flexural strength of sintered mullite bricks is much higher than that of fused mullite bricks, due to the presence of some small but well-developed crystal networks in the structure of the former. The latter has good volume stability and excellent creep resistance due to its larger crystal size. Moreover, electric melted mullite bricks have better corrosion resistance than sintered mullite bricks with the same composition. This is because at high temperatures, when corroded by alkaline substances, mullite will form corundum and chalcedony liquid phases. Chalcedony liquid phase has low viscosity and is easily lost, causing damage to the brick body. Due to the relatively high porosity of sintered mullite, the above reaction can occur inside the brick, and the destructive force is much greater; However, due to its high density, the above reaction can only occur on the surface of refractory bricks, and the destructive power of electric melted mullite bricks is relatively weaker.
Although the price of mullite bricks is much higher than that of high alumina bricks, their superior performance determines their widespread use. The properties of mullite refractory bricks are mainly determined by the properties of mullite. It has high fire resistance, high load softening temperature, low high-temperature creep rate, excellent thermal vibration resistance, slag erosion resistance, high shear modulus, etc. Molonite refractory bricks have a wide range of applications, mainly used for high-temperature hot blast furnaces, large blast furnace hearths and bottoms, steelmaking electric furnace tops, ceramic industrial kiln linings, kiln equipment, as well as glass and cement kiln linings.
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