Silica brick is the most common silica refractory material. Because of its high high temperature strength and load softening temperature, good resistance to high temperature creep and strong resistance to acid slag erosion, it is widely used in industrial production and application.
There are generally three crystal phases in silicon bricks, namely tridymite, cristobalite and a small amount of residual quartz, and the true density increases sequentially. Generally speaking, true density, thermal expansion coefficient, tridymite and residual quartz content are the most critical performance indicators for characterizing silica bricks. During the firing process, the greater the degree of conversion of quartz into tridymite with stable volume and cristobalite with excellent high-temperature performance, the less residual quartz content and the lower the true density of the silica brick, the better the high-temperature volume stability. During use The further expansion is also smaller.
The Choice of Mineralizer
In the production process of silica bricks, a certain amount of mineralizer is often introduced. Its function is mainly to use the mineralizer and SiO2 or other impurities to form a low-melting high-temperature liquid phase, which promotes the conversion of quartz into tridymite and square quartz during the firing process. Quartz can also buffer the rapid expansion of the volume caused by the rapid phase change during the firing process, resulting in loosening and cracking of the product. At present, the widely used mineralizers are lime and iron scale. Lime is usually added in the form of lime milk. It can not only increase the strength of the brick after forming, but also can react with SiO2 in the low-temperature firing stage (600~700℃) to increase the strength of the brick. Wollastonite can form a liquid phase with other mineralizers to convert quartz to tridymite. Iron scale is often added as a mineralizer at the same time as lime, which can significantly reduce the temperature and viscosity of the liquid phase and reduce product cracks.
In order to make the scales evenly distributed in the ingredients to achieve a good mineralization effect, the mass fraction of particle size ≤0.088mm is required to be >80%. In addition to lime and iron scales, fluorite and feldspar composite, MnO2, and C3S have also been shown to have a positive effect in promoting the formation of tridymite. In addition to the type of mineralizer, the particle size of the mineralizer is also more important. The finer the particle size of the mineralizer, the more evenly distributed it is in the siliceous raw material, and the better its effect. Nano-scale mineralizers have good dispersibility and higher mineralization efficiency, which makes the internal particles of siliceous products and the volume expansion and contraction between the particles in the process of crystal transformation better synchronization, reducing the volume stress caused by Crack pores, while improving the physical and mechanical properties of silica bricks, reducing the true density of siliceous products, and reducing the content of residual quartz in the products.
Introduction of Additivesb
For different purposes, certain properties of silica bricks, such as thermal conductivity, abrasion resistance and thermal shock resistance, need to be further strengthened. At this time, in addition to the rational selection of silica raw materials and the addition of appropriate mineralizers, a certain amount of additives need to be introduced to achieve the desired effect. Adding SiC to silicon bricks can promote the formation of tridymite, reduce the thermal expansion rate and creep rate of silicon bricks, and increase the thermal conductivity and high-temperature flexural strength of silicon bricks; adding Si3N4 can improve the thermal shock stability of silicon bricks. When the addition amount is 5%, it has a higher content of tridymite and a dense microstructure; the addition of metal and its oxides as additives such as TiO2 into siliceous refractories can reduce the apparent porosity of the material, increase the volume density, and reduce the residual quartz content , Increase tridymite content, optimize material strength and fire resistance.
Silica Brick for Coke Oven
Silica brick is the main material of coke oven masonry, which is mainly used to build the combustion chamber, carbonization chamber, chute, regenerator wall and furnace roof of coke oven, accounting for 60~70% of the total refractory bricks used in coke oven . The silica bricks for coke oven use tridymite as the main crystal phase. Because of the need to withstand the dynamic load of the coal loading cart on the roof of the furnace at high temperatures during use, and the coking coal needs to be heated by the thermal conduction of the partition wall of the coking chamber and the combustion chamber, the coke oven cycle Charging coal and coking out will cause the temperature of the silica bricks on both sides of the combustion chamber to change drastically. Therefore, the coke oven silica bricks require high load softening temperature, high thermal conductivity, good thermal shock resistance and high temperature volume stability. In order to improve the production capacity of modern large coke ovens, silica bricks for coke ovens require less residual quartz, higher density, thermal conductivity, high temperature strength and thermal shock resistance, and further development and application of high-density, high-purity silica bricks and high thermal conductivity Silica brick is the direction to meet the needs of different parts of the coke oven.
Silica Brick for Glass Kiln
Because silica bricks have the advantages of low cost, high chemical purity, high load softening point, no pollution to glass, and good resistance to a small amount of R2O gas phase and acid gas corrosion, they are widely used in glass kilns on ceilings and suspended walls. The upper part and the front and back walls. The use environment of the glass kiln requires the control of the non-SiO2 content in the silica bricks, and the silica bricks are required to use cristobalite as the main crystal phase. For large glass furnaces and full-oxygen combustion glass furnaces, high-purity, creep-resistant, and corrosion-resistant siliceous refractory materials are required.
Silica Brick for Hot Blast Stove
Silica bricks are widely used in large-scale blast furnace hot-blast stoves. The high temperature area of the hot blast stove includes the vault and the upper part of the checker bricks, mainly the fuel combustion space and the surrounding area. The temperature in this area is always stable at the high temperature section with small fluctuations, and is mainly composed of silica bricks. The silica bricks used in the high temperature part of the blast furnace hot blast stove mainly use tridymite as the main crystal phase, and have the following characteristics: ①Under the condition of long-term high temperature and load, the volume is stable, the high temperature creep rate is low, and one or even two blast furnaces can be used continuously Furnace activity; ②It has good thermal shock resistance above 600℃, adapts to the variability of hot blast stove temperature, so that the bricks and masonry remain intact; ③The chemical resistance is better than
clay fire bricks and general high alumina bricks, and the gas and smoke dust The erosion of silica bricks by alkaline substances is limited to the formation of a layer of glass on the surface, and no peeling occurs; ④The thermal conductivity is larger than that of clay bricks and high alumina bricks, which is conducive to storing and releasing heat in a shorter time.
