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Main varieties of refractory materials

Among ordinary and special refractories, the commonly used varieties are mainly as follows:

Acid refractory
Silica bricks and clay bricks are used in larger quantities. Silica bricks are siliceous products containing more than 93% SiO2, and the raw materials used are silica, waste silica bricks, etc. Silica brick has strong corrosion resistance to acid slag, but it is easily corroded by alkaline slag. Its load softening temperature is very high, which is close to its refractoriness. After repeated calcination, the volume does not shrink or even expands slightly.

Refractory Abrasives
Poor thermal shock resistance. Silica bricks are mainly used in thermal equipment such as coke ovens, glass melting furnaces, and acid steelmaking furnaces. Clay bricks contain 30% to 46% alumina. They use refractory clay as the main raw material, with a refractoriness of 1580 to 1770 °C and good thermal shock resistance. It is the largest type of refractory material currently produced.

Neutral refractory
The main crystal phases in high-alumina products are mullite and corundum. The content of corundum increases with the increase of alumina content. Corundum products containing more than 95% alumina are high-quality refractory materials with a wide range of uses. Chrome bricks are mainly made of chrome ore, and the main crystal phase is chromite. It has good corrosion resistance to steel slag, but poor thermal shock resistance and low deformation temperature under high temperature load. The chrome-magnesia bricks made of chrome ore and magnesia in different proportions have good thermal shock resistance and are mainly used as basic open-hearth furnace roof bricks.

Carbonaceous products are another type of neutral refractory materials. According to the composition of carbon-containing raw materials and the mineral composition of the products, they are divided into three categories: carbon bricks, graphite products and silicon carbide products. Carbon bricks are made of high-grade petroleum coke as raw materials, add tar and asphalt as binders, and are fired at 1300 ° C under the premise of isolating air. Graphite products (except natural graphite) are obtained by graphitizing carbon materials in an electric furnace at 2500-2800°C. Silicon carbide products use silicon carbide as raw material, add clay, silicon oxide and other binders and sinter at 1350-1400 ° C. Silicon carbide and silicon powder can also be made into silicon nitride-silicon carbide products in an electric furnace under nitrogen atmosphere.

Refractory Abrasives
Carbon products have low thermal expansion coefficient, high thermal conductivity, good thermal shock resistance and high high temperature strength. It will not soften after long-term use at high temperature, it is not corroded by any acid and alkali, has good salt resistance, and is not wetted by metal and slag. It is light in weight and is a high-quality high-temperature resistant material. The disadvantage is that it is easily oxidized at high temperature and should not be used in an oxidizing atmosphere. Carbonaceous products are widely used in high temperature furnace lining (furnace bottom, hearth, lower part of furnace shaft, etc.), lining of smelting non-ferrous metal furnaces. Graphite products can be used as linings for reaction tanks and petrochemical autoclaves. Silicon carbide and graphite products can also be made into crucibles for melting copper, gold and light alloys.

Alkaline refractory
Represented by magnesium products. It contains more than 80% to 85% of magnesium oxide, with periclase as the main crystal phase. The main raw materials for the production of magnesia bricks are magnesite and seawater magnesia, which are calcined at high temperature from magnesium hydroxide extracted from seawater. It has good resistance to alkaline slag and iron slag. The melting point of pure magnesia is as high as 2800 ℃, so the refractoriness of magnesia brick is higher than that of clay brick and silica brick. Since the mid-1950s, the production of basic refractories has gradually increased, while the production of clay bricks and silica bricks has decreased due to the use of oxygen-blown converters for steelmaking and the use of basic open-hearth furnace tops. Basic refractory materials are mainly used in open hearth furnaces, oxygen-blown converters, electric furnaces, non-ferrous metal smelting and some high-temperature thermal equipment.

oxide material
Such as alumina, lanthanum oxide, beryllium oxide, calcium oxide, zirconium oxide, uranium oxide, magnesium oxide, cerium oxide and thorium oxide, the melting point is 2050 ~ 3050 ℃.

refractory compound material
Such as carbides (silicon carbide, titanium carbide, tantalum carbide, etc.), nitrides (boron nitride, silicon nitride, etc.), borides (zirconium boride, titanium boride, hafnium boride, etc.), silicide (disilicide) molybdenum, etc.) and sulfides (thorium sulfide, cerium sulfide, etc.). Their melting point is 2000 ~ 3887 ℃, of which the most refractory is carbide.

High temperature composites
Such as cermets, high temperature inorganic coatings and fiber reinforced ceramics.

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