1: Reduce the pore size of high alumina bricks to prevent the infiltration of aluminum liquid-physical method
The average pore size of traditional high-alumina bricks is about 22μm. Aluminum liquid can easily penetrate into the interior of the brick through the pores and react with silicon oxide in the high-alumina bricks to increase the content of Si in the aluminum liquid. In order to inhibit the infiltration reaction, the pore size of the high-alumina brick must be reduced.
The penetration of liquid aluminum into high-alumina bricks is a capillary phenomenon. The depth of the melt penetration into the high-alumina brick can be calculated using the Kelvin formula: where d is the pore diameter, r is the surface tension of aluminum melt, θ is the wetting angle between the aluminum melt and the surface of the high-alumina brick, η is the viscosity of aluminum melt, and t is the melting time.
2: Select appropriate anti-wetting agents to inhibit wetting with aluminum liquid-chemical method
The main reason for aluminum liquid to corrode high-alumina bricks is that aluminum liquid easily penetrates into high-alumina bricks, causing the reduction of oxide components in high-alumina bricks. If the wetting angle is greater than 90 degrees, the wetting of high alumina refractory bricks and aluminum liquid will not occur. No chemical reaction will occur. Therefore, applying a layer of non-wetting component with aluminum on the working surface of high alumina bricks or adding anti-wetting agent during the production process of high aluminum bricks can improve the corrosion resistance of high alumina brick lining to aluminum liquid.
Except for carbides (silicon carbide), borides and nitrides, most oxides are easily reduced by aluminum to produce wettability. Table 1 lists the reaction free energy between refractory oxides and liquid aluminum.
Therefore, when producing high aluminum bricks, try to use materials that do not react or wet with aluminum, and add appropriate anti-wetting agents. The following compounds are common anti-wetting agents: BaSO4 (barium sulfate); CaF2 (calcium fluoride); AIF3 (aluminum fluoride); AL2O3·TiO2 (aluminum oxide titanium oxide). However, when the temperature is higher than 1100℃, the anti-wetting agent will lose its effect. Therefore, it is particularly important to develop anti-wetting agents that will not degenerate and will not melt at high temperatures to improve the wetting angle.
According to the improvement measures, there must be appropriate additives and binders as well as appropriate firing temperatures. Appropriate additives act as anti-wetting agents in high alumina bricks, which can prevent the penetration of aluminum liquid into the interior of high-alumina bricks and reduce the reaction between aluminum liquid and high-alumina bricks. Binders can improve the mechanical strength of products and form a tissue structure with good damage resistance during firing and use.
