In June 20tons refractory silica bricks are packed for delivering to customer in UAE. High quality and best price refractory fire bricks in Topower Refractory.
Silica brick is the most common silica refractory material. It has excellent properties such as high high temperature strength and load softening temperature, good high temperature creep resistance and strong acid slag erosion resistance, which can meet the use requirements of coke ovens in harsh environments such as high temperature, heavy load and corrosion.
There are generally three crystal phases in silica refractory bricks, namely tridymite, cristobalite and a small amount of residual quartz, and the true density increases in turn. Generally speaking, true density, thermal expansion coefficient, tridymite and residual quartz content are the most critical performance indicators for characterizing silica bricks. The greater the degree of quartz conversion into volume-stable tridymite and cristobalite with excellent high temperature performance during the firing process, the less residual quartz content, the smaller the true density of silica fire bricks, the better the high temperature volume stability, and the smaller the re-expansion during use.
The silica suitable for refractory materials is mainly quartzite, which can be divided into crystalline silica and cemented silica according to its organizational structure. Generally speaking, crystalline silica has a higher purity, a higher raw material density, larger quartz crystal particles, and a slower transformation speed when heated; cemented silica often contains a small amount of impurities, and has a relatively low purity. In addition, the quartz particles in cemented silica are smaller in crystallization, have a higher content of cementing materials, and transform faster when heated. Therefore, a reasonable production process should be formulated according to the characteristics of silica raw materials to produce silica firebricks suitable for different purposes.
In the production process of silica bricks, a certain amount of mineralizer is often introduced. Its main function is to use the mineralizer and SiO2 or other impurities to form a low-melting-point high-temperature liquid phase, which promotes the conversion of quartz into tridymite and cristobalite during the firing process. At the same time, it can buffer the rapid expansion of volume caused by the phase change during the firing process, which leads to the loosening and cracking of the product.
The widely used mineralizers are lime and iron scale. Lime is usually added in the form of lime milk, which can not only increase the strength of the brick after molding, but also react with SiO2 in the low-temperature stage of firing to increase the strength of the brick. The pseudo-wollastonite generated after 1100°C can form a liquid phase with other mineralizers to convert quartz into tridymite. Iron scale is often added together with lime as a mineralizer, which can significantly reduce the temperature and viscosity of the liquid phase and reduce cracks in the product. In order to make the iron scale evenly distributed in the batch to achieve a good mineralization effect, the mass fraction of the particle size ≤0.088mm is required to be greater than 80%. In addition to lime and iron scale, fluorite and feldspar composite, MnO2, and C3S have also been shown to have a positive effect in promoting the formation of tridymite.
Adding SiC to silica bricks can promote the formation of tridymite, reduce the thermal expansion rate and creep rate of silica refractory bricks, and improve the thermal conductivity and high-temperature flexural strength of silica fire bricks; adding Si3N4 can improve the thermal shock stability of silica firebricks, and when the addition amount is 5%, it has a higher tridymite content and a dense microstructure; metals and their oxides as additives such as TiO2 added to siliceous refractory materials can reduce the apparent porosity of the material, increase the bulk density, reduce the residual quartz content, increase the tridymite content, and optimize the material strength and refractory properties.
