General Property Of Refractory

Among common and special refractory materials, the common varieties are as follows:
acidic
Refractory abrasive
Silica brick and clay brick are widely used. Silica brick is a siliceous product containing more than 93% SiO2. The raw materials used include silica and waste silica brick. Silica brick has strong resistance to acid slag erosion, but is vulnerable to alkaline slag erosion. Its load softening temperature is very high, close to its fire resistance. After repeated calcination, its volume does not shrink, even slightly expands, but its thermal shock resistance is poor. Silica brick is mainly used in thermal equipment such as coke oven, glass furnace, acid steel furnace, etc. The clay brick contains 30%~46% alumina. It takes refractory clay as the main raw material, has a fire resistance of 1580~1770 ℃, and good thermal shock resistance. It belongs to weak acid refractory material, has corrosion resistance to acid slag, and is widely used. It is the largest class of refractory material in production.
neutral
The main crystalline phases in high-alumina products are mullite and corundum, and the content of corundum increases with the increase of alumina content. Corundum products containing more than 95% alumina are a high-quality refractory material with a wide range of uses. Chromium bricks are mainly made of chromite, and the main crystalline phase is chromite. It has good corrosion resistance to steel slag, but poor thermal shock resistance, and low high temperature load deformation temperature. Chromium-magnesium bricks made of chromite and magnesia in different proportions have good thermal shock resistance and are mainly used as basic open-hearth roof bricks.
Refractory abrasive
Carbon products are another kind of neutral refractory materials. According to the composition of carbonaceous raw materials and the mineral composition of products, they are divided into three categories: carbon bricks, graphite products and silicon carbide products. Carbon brick is made of high-grade petroleum coke as raw material, tar and asphalt as adhesive, and fired at 1300 ℃ to isolate the air. Graphite products (except natural graphite) are made of carbon materials by graphitizing at 2500~2800 ℃ in an electric furnace. Silicon carbide products are fired at 1350~1400 ℃ with silicon carbide as raw material and clay, silicon oxide and other binders. Silicon nitride and silicon carbide products can also be made from silicon carbide and silicon powder under nitrogen atmosphere in electric furnace. Carbon products have low thermal expansion coefficient, high thermal conductivity, good thermal shock resistance and high temperature strength. It will not soften after long-term use at high temperature, will not be eroded by any acid or alkali, has good salt resistance, and will not be wetted by metal and slag. It is light, and is a high-quality high-temperature resistant material. The disadvantage is that it is easy to oxidize at high temperature and is not suitable for use in oxidizing atmosphere. Carbon products are widely used in high-temperature furnace lining (furnace bottom, hearth, lower part of furnace body, etc.) and lining of smelting non-ferrous metal furnace. Graphite products can be used as reaction tank and autoclave lining of petrochemical industry. Silicon carbide and graphite products can also be made into crucibles for smelting copper, gold and light alloys.
alkalinity
Take magnesium products as the representative. It contains more than 80%~85% magnesium oxide and is mainly composed of periclase. The main raw materials for producing magnesia brick include magnesite, seawater magnesia, which is calcined from magnesium hydroxide extracted from seawater at high temperature), etc. It has good resistance to alkaline slag and iron slag. The melting point of pure magnesium oxide is as high as 2800 ℃, so the fire resistance of magnesia brick is higher than that of clay brick and silica brick. Since the mid-1950s, the production of basic refractories has increased gradually, while the production of clay bricks and silica bricks has decreased due to the adoption of oxygen blowing converter steelmaking and the use of basic open-hearth furnace top. Basic refractories are mainly used in open hearth furnaces, oxygen blowing converters, electric furnaces, non-ferrous metal smelting and some high-temperature thermal equipment.