The basic chemical component of lay brick and high aluminum brick used for furnace building is SiO2 and Al2O3.
In SiO2 and Al2O3, the brick containing 30-46% of A1203 is known as the clay refractory bricks, and the brick containing more than 48% of Al2O3 is called high aluminum refractory brick, and when containing 72% Al2O3, the brick will generate mullite crystal. When the brick is in the form of Al2O3, it is called corundum products.
(1) Clay brick: the main raw material of clay brick is refractory clay and kaolin. The product is made of soft clay (bond) and clinker, then it has to be burned in 1300-1300 ℃
temperature. The main chemical composition is: Al2O3 (30-46%) and SiO2(52-60%), and the rest of composition are small amount of metal oxide, such as Fe2O3, CaO, MgO, Na2O, K2O, etc.
In high temperature, the brick turns out to be weak acidic or neutral: it can suffer 20 times of heat and cool, higher than that of other refractories. Its heat capacity, thermal conductivity, coefficient of expansion is all lower than other refractory products. Load softening temperature is 1250 to 1350 ℃
, lower than that of the other refractory products. The highest using temperature is 1300 to 1400 ℃
; Products surface are often covered with yellow brown with black spots. This kind of brick is widely used in masonry wall, roof and furnace bottom. Due to its corrosion effect on iron chromium aluminum alloy, it is not suitable for the electric heating body, because it is vulnerable to furnace CO and H2 erosion.
(2) High aluminum brick: raw materials for manufacturing high aluminum brick are high bauxite, whose main mineral composition is kaolinite and water alumina ore. The brick containing 48 - 72% carbon is high aluminum brick. The brick containing more than 72% A1203 is corundum products, and the rest of the component is mainly SiO2 and small amounts of impurities. High aluminum refractory product shows neutral property at high temperature; Weight softening temperature and refractoriness all increase with the increase of Al2O3 content.
Usually, load softening temperature is 1420 to 1650 ℃ and refractoriness is 1750 to 1900 ℃. The highest temperature can reach 1650 to 1650 ℃. It has good resistance to thermal shock. This refractory product
can be used for high temperature furnace refractory lining.