South Korea customer order 2*40GP ceramic fiber blanket and silica bricks.
In the production of silica bricks, the particle composition is very important to ensure the density, especially the manufacture of high-density silica bricks.
02. The influence of firing conditions and other aspects
Since the silica raw material is very brittle, the particles will be broken during the mixing and molding process. During the firing process, the particles will expand and crack due to the phase change. Therefore, in addition to paying attention to the principle of the closest packing, the particle composition in the ingredients should also fully consider the influence of mixing process, molding pressure, firing conditions and other aspects in terms of production.
When the particle size of the raw material particles is larger, the adobe is easier to be crushed during the molding process. During firing, the volume expansion caused by the crystal form transformation of raw materials is large, and it is also very easy to crack. Therefore, the critical particle size of silica brick production cannot be greater than 3mm; when gangue is used as raw material, it is less than 2mm. When selecting the critical particle size, it is most suitable that the bricks do not loosen and crack during firing, and are dense and stable.
The mass ratio of 3~1mm is 35%~45%, the mass ratio of 1~0.088mm is 20%~25%, and the mass ratio of less than 0.088mm is 35%~40%. In addition, due to the interaction between fine particles and mineralizers, enhanced sinterability, and small volume expansion during transformation, it is conducive to volume stability during firing. Therefore, the amount of fine powder added can be appropriately increased. Mineralizers are some compounds containing iron, calcium, and manganese components. For example, 2% Ca0 and 2% M0 can be added to coke oven silica bricks, and 0.8% Fe0 and 0.2% Ca0 can be added to high silicon bricks. Ca0 and Fe0 are introduced in the form of lime milk and iron scale or iron filings respectively. Mineralizers can also be added dry, such as using limestone leftovers as calcium-containing mineralizers, and adding them in the form of pyrite slag. The binder can use industrial lignin sulfonate and milk of lime.
03. Sintering and relaxation are affected during the firing process
The nature and quantity of the two kinds of particles in the particle composition have a great influence on the sintering and loosening of the brick during the firing process. Coarse particles form the skeleton of the green body. However, the phase transformation of coarse particles lasts for a long time, and often occurs after the phase transformation of fine particles and the sintering of the green body, so the volume expansion caused by the phase transformation of coarse particles is an important reason why the green body tends to loosen and even crack.
The more coarse particles, the lower the temperature at which the adobe starts to expand violently, and the greater the tendency of the adobe to crack when fired. For the same raw material and different particle composition of silica bricks, when the true density is the same, the larger the particle size The green body swells during firing, contrary to the coarse particles, and the fine powder is mostly in the pores where the coarse particles accumulate. Due to the larger specific surface area of the fine powder, the greater the mineralization expansion, the greater the tendency to crack.
in conclusion
The fine powder smaller than 0.088mm is the part that promotes sintering activity. Since the appearance of the liquid phase can buffer the stress caused by part of the expansion, and because the fine powder is relatively easy to produce tridymite, there must be sufficient fine powder content in the adobe. The change of coarse particles in the green body during firing is: “transformation-expansion-cracking”; while the change of fine particles is “transformation-sintering-shrinkage”.
Therefore, the production of silica bricks must pay attention to the size control of particles.