The AL2O3 content of the semi-silica brick is 15%-30%, and the SiO2 content is more than 65%. It is a semi-acid refractory brick. Semi-silica bricks generally use refractory clay containing quartz sand, pyrophyllite and refractory clay or kaolin tailings as raw materials. Semi-silica bricks have not too large expansion characteristics, this kind of micro expansion is beneficial to improve the integrity of masonry refractory bricks and reduce the erosive effect of slag on masonry; After the surface of the brick is in contact, a layer of glaze-like substance with high viscosity is produced on the surface of the refractory brick (the slag interacts with the product to form a melt with a high content of SiO2, with a thickness of 1~2mm), which blocks the pores and prevents the slag. Continue to penetrate into the refractory brick to form a protective layer, thereby improving the erosion resistance of the brick. The raw materials used in semi-silica bricks have large reserves and low prices. They can replace second and third-class clay bricks and have a wide range of applications. Because the semi-silica brick has good resistance to acid slag, and has high high temperature structural strength and relatively stable volume. It is mainly used for masonry coke ovens, acidizing iron furnaces, metallurgical furnace flues and ladle linings.
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The difference between silica brick and semi-silica brick
The most representative and commonly used semi-silica bricks are wax stone bricks, which are not much different from clay bricks in appearance, and are white or grayish white. The product is slightly expanded than the brick, and its expansion rate is about 0.7%~0.9%. The high temperature performance is similar to that of clay bricks, the refractoriness fluctuates from 1670°C to 1100°C, and the softening temperature under load is 1300°C to 1430°C (starting point).
Silica brick is made of quartzite as the main raw material, formed with a binder, and fired at a high temperature of 1350-1430 °C. It is a refractory brick product containing no less than 93% SiO2. Silica brick is an acid refractory material, which has good resistance to acid slag erosion. Its high softening point under load is close to its refractoriness, which is its advantage. During the firing process of silica bricks, most of the quartz with a larger specific gravity is transformed into cristobalite and tridymite with a smaller specific gravity, and the better the transformation is, the less the remaining quartz is, the smaller the true specific gravity of the silica brick is. The smaller the residual expansion during use, the better the body-length stability. Therefore, the true specific gravity of the silica brick is one of the important signs indicating the degree of quartz transformation. Silica bricks have more crystal transformations and larger volume changes below 600 °C. Above 600°C, there is no crystal transformation, the thermal expansion coefficient is small, and the volume change is small. Therefore, the furnace body built with silica bricks must pay attention to slowly heating up in the initial stage of the oven. There are two grades of silica bricks produced in my country, namely (GZ)-94 and (GZ)-93.
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The physical and chemical properties and operating temperature of silica bricks are described in the previous introduction. Silica bricks can be used to build lattice bricks in the high temperature section of heating furnaces, coke ovens and glass kilns, the middle section of the furnace wall of soaking furnaces and the upper part of the regenerator. Semi-silica brick is a kind of quartz clay brick, which is formed and fired from quartzite with clay as a binder. The semi-silica brick contains not less than 20% Al2O3, not less than 65% SiO2, its refractoriness is 1670°C, and its softening point under load is not less than 1250°C. The resistance to rapid cooling and rapid heating of semi-silica bricks is better than that of silica bricks, and the volume stability is better than that of clay bricks and silica bricks. When heated, the clay in the brick shrinks and the quartz expands, so that good volume stability can be obtained, which is the main advantage of semi-silica bricks. Semi-silica bricks can be used for the furnace body, preheater and flue of pit heating furnace.
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