The refractory bricks made of sintered or fused mullite as the main raw material can be all mullite, partly mullite and partly corundum. The former is called mullite refractory brick, and the latter is called corundum-mullite refractory brick or corundum mullite brick. The production process of mullite refractory bricks is the same as that of high alumina bricks. The ingredients are mixed, formed, dried and fired. The firing temperature is related to the composition of ingredients, the purity of raw materials and the performance requirements of refractory bricks, usually 1500-1700 °C.
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Mullite refractory bricks and corundum mullite bricks have the advantages of high softening temperature under load, low creep rate at high temperature, good thermal shock resistance, etc. They are widely used in blast furnace hot blast furnace, glass melting furnace, CDQ and heating furnace and other industries on the kiln. Mullite refractory bricks are easily corroded by alkaline refractory bricks at high temperatures. In addition, at high temperatures, mullite can be damaged by reacting with water vapor to form Al2O3.
Therefore, mullite refractory bricks are not suitable for long-term use in environments with high alkaline slag and high water vapor content.
In addition to mullite and its composite refractory bricks with corundum, mullite can also form refractory bricks with other materials to improve its performance, such as zirconium mullite refractory bricks, mullite-silicon carbide refractory bricks, etc. The so-called zirconium mullite refractory bricks are mullite-zirconia composite materials. However, due to the high price of zirconia, zirconium mullite clinker or refractory bricks are often prepared by reacting Al2O3 or bauxite with zircon in actual production.
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The manufacturing methods of such refractory bricks and raw materials include electrofusion method and sintering method. Aluminium-Zirconium-Silicon (AZS) refractory bricks made by fused casting have been discussed in fused zirconium corundum bricks. Zirconium mullite clinker is obtained by calcining Al2O3 and ZrSiO4 ingredients, and then crushed, mixed, shaped and fired to obtain zirconium mullite refractory bricks, namely sintered AZS bricks.
When using bauxite as raw material, it is most common to introduce ZrSiO4 into high-alumina bricks to improve the thermal shock resistance of high-alumina bricks, the so-called "anti-peeling high-alumina bricks". The ZrO2 produced by the reaction is dispersed in mullite and corundum. Due to the phase transition of ZrO2 during heating and cooling, microcracks are generated around the ZrO2 particles, thereby improving their thermal shock resistance.
Sintered AZS refractory bricks are commonly used in glass kilns.
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