Silica bricks have good high-temperature properties such as high refractoriness under load and low creep under high temperature. They also have good high-temperature corrosion resistance. Due to their mature production process and low price, they are widely used in glass kilns. As we all know, the mineral composition of silica bricks is composed of cristobalite, tridymite, residual quartz and a small amount of silicate liquid phase. When silica bricks are used, the transformation of various crystal phases is still in progress, and there is a large volume change during the crystal phase transformation process, resulting in poor thermal stability of silica bricks. When the temperature reaches 1470℃, the quartz in the silica brick will turn into cristobalite, which is the most stable crystal phase in silica bricks and will enhance the physical and chemical performance indicators of silica bricks. When some parts of the kiln are below 1470℃, the presence of tridymite will reduce the performance of silica bricks, especially the alkali dust or alkali vapor will corrode the calcium silicate (CaO·Si02) in the silica bricks, and the glass phase will begin to form in the silica bricks, and the glass phase will gradually melt the large particles of silicon oxide in the silica bricks, causing the silica bricks to dissolve and peel off, thus affecting the use effect of the silica bricks.
2. Alkaline bricks
Alkaline bricks have strong corrosion resistance to alkali dust, but in the high temperature area of the lattice body, magnesium bricks are easily corroded by Si02, V205 and Ca0, causing the volume of the lattice bricks to expand and peel off. In the lower middle part of the lattice body, that is, the condensation area of the lattice body, magnesium bricks are prone to sulfate corrosion. Directly bonded magnesia bricks are currently the best choice for the middle and lower lattice bodies, but the Cr203 in directly bonded magnesia bricks will pollute water resources. Some European and American countries have banned the use of magnesia-chrome bricks. I believe that my country will soon restrict the use of chromium-containing products.
Alkaline bricks have high thermal conductivity, large expansion coefficient and high creep rate. They deform when baking the kiln, which is not conducive to the sealing of the kiln body. Compared with mullite bricks, the heat dissipation of the wall increases, increasing the insulation cost of the kiln.
3. Fused zirconium corundum bricks
Fused zirconium corundum bricks have good resistance to erosion of the batch material. Under relatively stable temperature conditions, they can be used in almost all high-temperature zones of the glass kiln. The biggest disadvantage of fused zirconium corundum bricks is that they have poor thermal shock stability and are not suitable for use in areas with large temperature fluctuations. At the same time, fused zirconium corundum bricks have high thermal conductivity, resulting in large heat dissipation of the kiln body, which is not conducive to energy saving and improving the operating environment. Compared with other refractory materials used in glass kilns, fused zirconium corundum bricks are difficult to construct and expensive.
Mullite bricks are divided into two categories. One is sintered mullite bricks, which are made of natural mullite as the main raw material and pressed and sintered with additives. Due to the instability of the chemical composition and mineral composition of natural mullite raw materials, the physical and chemical performance indicators of sintered mullite bricks are less stable, and the high-temperature creep rate is higher. It seems that its high-temperature strength and hot-sand stability are higher, and it can be used in areas with lower melting furnace temperatures, such as the middle and lower parts of the regenerator.
The other is re-sintered mullite bricks, which are made of synthetic mullite as the main raw material and re-sintered with additives. Synthetic mullite comes from sintering and electric melting. Due to the controllability of the raw material properties, the physical and chemical properties of sintered mullite brick products are stable, the high-temperature physical properties are good, and the corrosion resistance is strong, especially the re-sintered electric melting mullite bricks. Because the mullite is more permeable, the products have stronger resistance to chemical corrosion of alkali dust and alkali vapor, and can be used in high-temperature areas, such as small furnaces and regenerator upper structures.
Analysis and research show that the alkali vapor in the flue gas has the strongest erosion on refractory materials, and the mullite phase in the mullite brick will react with the alkali vapor (NaOH) in the flue gas at above 1270℃ to form a stable corundum phase and a partial glass phase on the surface of the mullite brick, thereby effectively preventing the alkali vapor from further corroding the mullite brick and improving the mullite brick's ability to resist alkali vapor erosion.
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