Silicon Mullite Brick

Silica brick

Silica-mullite brick, a new type of wear-resistant refractory brick, has a wear resistance coefficient more than five times higher than that of phosphate-bonded high-alumina brick. In terms of its physical composition, it should be a silicon carbide-mullite product, referred to as silica-mullite brick. This title is mostly popular in the building materials industry, and other industries generally call it high-alumina silicon carbide brick or aluminum oxide-silicon carbide brick.

Silica-mullite brick is an A1203-Si02-SiC refractory material made of high-alumina bauxite clinker and silicon carbide as the main raw materials. Its load softening temperature, thermal shock resistance, wear resistance and erosion resistance are better than high-alumina bricks, and even better than spinel bricks. At present, silica-mullite bricks are used in almost all parts of domestic cement rotary kilns except the firing zone.

 

The density of silica-mullite bricks is very important. Products with high density can inhibit the oxidation of SiC and improve the comprehensive technical performance of silica-mullite bricks. The particle grading of the mud has a direct impact on the density of the product. In order to obtain high-density products, the volume percentage of various particle sizes is calculated according to the Dinger-Funk formula. Then, the percentage of particle size composition is calculated based on the raw material density, and appropriate adjustments are made through experiments to obtain the particle grading required for production.

Phosphoric acid-bonded products not only have a dense structure and high strength, but also have a high refractoriness under load and good wear resistance.

The production of silicon carbide mullite from silicon carbide and high-alumina bauxite clinker is in line with the technological development of refractory brick products. Since silicon carbide is oxidized to produce silicon dioxide, it reacts with aluminum oxide to form mullite (3A12032Si02), which can improve the density and strength of the product and form a protective film on the surface of the product to prevent further oxidation of silicon carbide, so that silicon carbide can maintain a certain content in high-alumina silicon carbide refractory bricks, thereby improving the thermal shock stability, wear resistance and corrosion resistance of the product. The service life of high-strength and dense silicon-molybdenum bricks on the cement rotary kiln cylinder except the firing zone is 3 to 4 times longer than that of high-alumina bricks.

The large-scale application of silicon-molybdenum refractory bricks in cement rotary kilns, especially the emergence and large-scale of new dry kilns, has greatly increased the rotation speed of the kiln and the thermal stress intensity in the kiln, which has put forward new and higher requirements for the material and physical and chemical properties of refractory materials. Therefore, except for the firing zone of the cement rotary kiln, which is still using magnesia-chrome bricks under the protection of the kiln skin, the secondary firing zone, transition zone and cooling zone are converted to silica-molybdenum bricks, and the effect is obviously better than magnesia-chrome bricks.

(1) The product has a dense structure and good wear resistance.

The main crystal phase of silicon-molded refractory bricks is composed of the high-hardness mineral corundum (Mohs hardness 9.0-9.2), silicon carbide (Mohs hardness 9.0-9.5), and mullite (Mohs hardness 7.0-7.5). The structure of the product is highly dense, with a bulk density generally between 2.7 and 3.0 g/cm3. Find the refractory material network and refer to the information. The normal temperature wear resistance of refractory materials depends on its strength and structural density. Materials with high strength and density have better wear resistance. The lining of cement rotary kiln is subject to rolling friction of materials for a long time, and wear is one of the main reasons for the damage of refractory lining. The density, strength and wear resistance of silicon-molded refractory bricks are significantly better than those of anti-flaking high-alumina bricks and magnesia-alumina spinel bricks. Silica-molded refractory bricks are used effectively in cement rotary kiln secondary firing belts, filter belts and other parts. It can be said that good wear resistance plays a very important role.

(2) High load softening temperature and good high temperature performance.

The load softening temperature of silica-molybdenum bricks is above 1450℃, and the highest is above 1650℃. There are certain differences in the load softening temperature of products of different brands. The refractory brick surface temperature of different parts of the cement rotary kiln lining is different. The temperature of the secondary firing zone and the front transition zone is about 1400℃, which is higher than the refractory brick surface temperature of the firing zone (because the firing zone is protected by the kiln skin, the refractory brick surface temperature is 900-1000℃). The load softening temperature index of these bricks also exceeds the commonly used anti-stripping high-alumina bricks and phosphate high-alumina refractory bricks (load softening temperature is 1300-1520℃).

Compared with the firing zone, the transition zone is easily affected by the reducing atmosphere and heat load because it has no kiln skin protection. Its service life has always been a bottleneck problem for cement rotary kilns. Therefore, some cement plants use magnesium-alumina spinel products in the transition zone. According to the research on magnesium-aluminum spinel bricks used in the transition zone of a 5000 t/d large cement rotary kiln in a certain factory, it is concluded that magnesium-aluminum spinel refractory bricks used in the front transition zone are basically free of corrosion, but due to the deposition of alkali in the open pores, the structure is densified, resulting in different sections of the same refractory brick, which causes the hot surface of the refractory brick to peel off and crack, causing damage to the lining. However, due to the dense structure of the silicon-molybdenum refractory bricks, especially the continuous SiO2 dense layer formed on the surface of the refractory bricks, it prevents the penetration of molten materials. In addition, the chemical properties of A1203, Sic, and SiO2 are stable, and they do not react violently with gases such as S02, O2, and CO2 generated in the kiln, and do not react chemically with cement materials, so they have strong corrosion resistance. Secondly, silicon-molybdenum bricks have good thermal shock stability. Since silica-molybdenum bricks contain a certain amount of SiC, it is well known that SiC has high thermal conductivity and relatively small thermal expansion coefficient, which significantly improves the thermal shock stability of the product. The 1100℃ water cooling test is more than 10 times, and the highest is 46 times. Therefore, silica-molybdenum bricks used in cement rotary kilns do not peel off or break, which can significantly improve their service life.

Reduce kiln temperature and have good thermal insulation performance. The thermal conductivity of silica-molybdenum bricks [2.3-2.5 W/(m•K)] is lower than that of alkaline products [2.69-2.74 W/(m•K)], so silica-molybdenum bricks have better thermal insulation effect. Silica-molybdenum bricks are used in the secondary firing zone, transition zone, preheating zone, kiln tail, tertiary air duct, decomposition furnace and other parts of large rotary kilns. Compared with alkaline bricks, the surface temperature of the cylinder is reduced by more than 100°C.

The temperature of thermal expansion rate can be agreed upon by both parties.

Note: The technical requirements of special products shall be agreed upon by both parties.

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