Composition and Influence of Fused Zirconium Mullite Brick

The fused mullite brick is mainly composed of high alumina bauxite or industrial alumina, clay or silica. The refractory brick is melted in an electric arc furnace, and then cast and annealed. The main mineral component is mullite.

 

The composition of mullite is 3AI2O3·2SiO2——2A12O3·SiO2, and the melting temperature is between 1827 and -1890 °C, and the hardness is large. When the high-temperature melt cools and crystallizes, coarse and uneven crystallization tends to occur, which easily causes cracks in the fused mullite brick. When in the composition of the eutectic mixture, the melt after melting has good fluidity, and can form uniform fine crystals when mullite is crystallized, thereby reducing the possibility of cracks in the casting. Therefore, the composition of the fused mullite brick should be preferably when the mass ratio of Al2O3/SiO2 is 79/21. However, in the production, it is necessary to consider that there is a certain amount of impurity components in the raw materials, which react with AI2O3 and SiO2 at high temperature, and accordingly change the ratio of A12O3 and SiO2. Therefore, the actual ratio of AI2O3/SiO2 is slightly lower.

The main effects of impurities on fused mullite bricks are:

(1) The iron oxide, like TiO2, can partially enter the mullite solid solution, has little effect on the melting point of mullite, but increases the glass content, and dyes the glass phase of the casting into a dark color, reducing the product. Refractory brick properties.

(2) Alkali metal oxides have a serious influence on mullite crystals and melts, which can reduce the mullite content and produce more glass phases.

(3) Although the effect of calcium oxide is small, it also acts to hinder the crystallization of mullite.

The effect of magnesium oxide on the crystallization of mullite is second to that of calcium oxide. When present in a small amount, aluminum spinel, cordierite and corundum appear in the crystallization mixture, and the amount of mullite is correspondingly reduced.

(4) The addition of charcoal or coke reducing agent can remove Fe2O3 during the smelting reduction process, and the remaining impurities cannot be removed by reduction, mainly into the melt and present in the glass phase.

 

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