At present, the material of breathable brick is corundum, chrome corundum, high alumina and magnesium-chromium, etc.
1, Corundum-spinel system gas permeable brick
Single-phase corundum castables are not ideal in terms of slag resistance and thermal shock resistance, while spinel materials have good resistance to slag erosion. According to the principle of complex phase modification to improve the performance of refractory materials, high purity electrofused spinel is added to corundum castables to improve the performance of corundum castables. The raw material is made of plate corundum as granular material, electrofused white corundum, spinel, active α-Al2O3 micro powder as fine powder and calcium aluminate cement as binding agent. The advantage is that the thermal shock resistance and slag resistance are obviously improved; the disadvantage is that the volume change of spinel occurs during the high temperature treatment of breathable brick, resulting in poor volume stability of breathable brick, which is not easy to control during the production process.
2、Corundum-chromium oxide system gas permeable brick
In order to further improve the erosion resistance of air permeable brick, a certain amount of chromium oxide powder is added to the product. The main raw material of corundum is plate corundum as granular material, plate corundum fine powder, chromium oxide fine powder and calcium aluminate cement as binding agent. At high temperature chromium oxide, alumina to form high temperature solid solution, while with a small amount of magnesium oxide to form a partial solid solution MgO-Cr2O3-MgO-Al2O3. this solid solution to Fe2O3 or slag erosion and resistance is significantly enhanced, and the viscosity is very large, so that at high temperatures can effectively prevent the penetration and erosion of steel slag. At the same time, a small amount of Cr2O3 can also inhibit the excessive growth of Al2O3, which also reduces the stress within the crystal and improves the physical properties of the material. However, if too much is added, corundum grain growth is inhibited excessively, which will also generate internal stresses and thus reduce the physical properties of the material. In addition, the price of Cr2O3 is relatively high, adding too much will substantially increase the cost; in addition, Cr2O3 causes serious pollution to the environment.
3, Corundum - spinel system breathable seat brick
Corundum - spinel system breathable seat brick is the most widely used material, the main raw material to plate corundum, α-Al2O3 micro powder, spinel is the main, pure calcium aluminate cement combination. Its advantage is due to the spinel resistance to acid and alkali is relatively strong, and is a high melting point compounds, has good performance. Al-Mg spinel resistance to alkaline slag, the role of iron oxides is also more stable, at high temperatures and magnetite contact will react and form a solid solution, breathable seat brick high temperature erosion resistance can be improved; at the same time, solid solution MgO or Al2O3 spinel due to the difference in expansion coefficient between minerals, its thermal shock resistance is better. The disadvantage is that when MgO and Al2O3 form spinel according to the theoretical composition, it produces about 8% volume expansion, so it is difficult to densify when firing, and it is difficult to control the volume change of breathable seat brick.
4, Corundum - chromium oxide system breathable seat brick
Corundum-chromium oxide system is based on corundum-spinel system, in order to improve the high-temperature spalling resistance of breathable seat brick and produced. The main raw material is plate corundum, a-Al2O3 micronized powder, industrial chromium oxide, spinel as the main material, and pure calcium aluminate cement combined. The advantage is that on the basis of spinel to improve the performance of seat brick, the solid solution formed by Al2O3-Cr2O3 significantly increases the erosion resistance of iron oxide slag, adding less Cr2O3 can inhibit the excessive growth of alumina crystals, thus reducing the internal stress of the crystal and improving the thermal shock resistance, scouring resistance and erosion resistance of breathable seat brick. The disadvantage is that the addition of too much Cr2O3, corundum grain growth rate is seriously affected, thus reducing the physical properties of the material; in addition, Cr2O3 is a serious pollution of the environment, contrary to the requirements of national sustainable development.
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