Characteristics and Application of Silicon Brick Refractory Products
Silica brick refers to refractory products with SiO2 content above 93%. The silica brick of Kerry kiln is made of silica stone with SiO2 content no less than 96% as raw material, adding mineralizing agent (such as iron scale, lime milk) and binder (such as waste liquid of sulfite pulp) through mixing, forming, drying and firing processes. The higher the SiO2 content in silica material, the higher the refractoriness of the product. Impurities such as K2O and Na2O are harmful and will seriously reduce the refractoriness of refractory products. Fe2O3, CaO, MgO and other impurities play the role of flux. The raw materials of advanced silicon brick need special treatment to remove impurities.
The mineral composition of the silica brick is the multiphase structure of squamous quartz, cristobalite, a small amount of residual quartz and vitreous formed at high temperature. The mineral composition of silica brick fluctuates greatly according to the production process and the nature of raw materials used.
Silica brick is an acid refractory material with strong resistance to acid slag or acid melt erosion, but poor resistance to alkaline material erosion, easy to be destroyed by Al2O3, K2O, Na2O and other oxides, and has good resistance to CaO, FeO, Fe2O3 and other oxides.
The high softening temperature under load is the excellent characteristic of silica brick, which is generally 1640-1680 ℃, close to the melting point of squamous quartz (1670℃) and cristobalite (1713℃). The volume of silica brick is stable between 300℃ and melting point (squamous quartz or cristobalite). When heated to 1450℃, the volume expansion of silica brick is about 1.5% ~ 2.2%, which is beneficial to ensure the structural strength and air tightness of masonry.
The biggest disadvantage of silicon brick is poor thermal shock resistance (water cooling cycles are generally 1 ~ 4 times), followed by low refractoriness (generally 1690 ~ 1730℃), its application scope is greatly limited.
The properties and process of silica brick are closely related to the crystal transformation of SiO2, and the true density of silica brick is one of the important indicators to judge the degree of crystal transformation. Therefore, true density is an important quality index of silicon brick. The general requirements are below 2.38/cm3, and the high quality silica brick should be below 2.35g /cm3. Kerry kiln believes that the low true density reflects the high quantity of squamous quartz and chrysoquartz in the brick. The amount of residual quartz is small, so the residual expansion is small, and the strength drop is small in use.
Silica brick is mainly used for laying coking chamber, combustion chamber and partition wall of coke oven (about 73% of refractory material used in a coke oven is silica brick), glass pool kiln and kiln roof, pool wall, high temperature bearing part of hot blast furnace, carbon baking furnace and other thermal kiln. In order to improve the production capacity of modern large coke oven, it is necessary to thin coke oven carbonization chamber, combustion chamber and partition wall, so high density and high thermal conductivity silicon brick is required. There are many kinds of silica bricks, which can be divided into silica bricks for coke oven, silica bricks for hot blast stove, silica bricks for electric furnace, silica bricks for glass kiln, etc. According to the complex degree of brick, cent is standard brick, general brick, different brick and special brick.