The current definition of refractory materials no longer depends solely on whether the refractoriness is above 1580℃. Currently, refractory materials generally refer to inorganic non-metallic materials used in the lining of production equipment in metallurgy, petrochemical, cement, ceramics, and other industries.

Acidic refractory materials are mainly composed of silicon dioxide (Si02), and commonly used ones include silica bricks and clay bricks. Silica bricks are siliceous products containing more than 93% Si02. The raw materials used include silica stone and waste silica bricks. Silica bricks have strong resistance to acidic slag erosion but are susceptible to alkaline slag erosion. Their softening temperature under load is very high, close to their refractoriness. The volume does not shrink after repeated calcination, and even expands slightly, but the thermal shock stability is poor. Silica bricks are mainly used in thermal equipment such as coke ovens, glass melting furnaces, and acidic steelmaking furnaces. Silica bricks can be divided into several grades according to the Si02 content and physical and chemical indicators, mainly divided into two categories: silica bricks for glass kilns and silica bricks for coke ovens. Clay silica bricks use refractory clay or calcined chamotte as the main raw material, containing 30%-46% alumina, with a refractoriness of 1580-1770℃. They are weakly acidic refractory materials with good thermal shock resistance and resistance to acidic slag corrosion, and are widely used. Clay bricks made mainly from refractory clay are called ordinary clay bricks, while those made mainly from calcined chamotte with an apparent porosity of less than 17% are called low-porosity clay bricks. The two types of clay bricks are further divided into several grades according to their physical and chemical indicators, with a large price difference between ordinary clay bricks and low-porosity clay bricks.

Neutral refractory materials are mainly composed of alumina, chromium oxide, silicon carbide, or carbon. The main products among neutral refractory materials include: corundum bricks, high-alumina bricks, sillarite bricks, mullite bricks, alumina-chrome bricks, alumina-carbon bricks, graphite or carbon bricks, etc. The main crystal phases of high-alumina varieties are mullite and corundum. The content of corundum increases with the increase of alumina content. Corundum products containing more than 95% alumina are a widely used high-quality refractory material. Chrome bricks, with chromium oxide as the main component, have good resistance to steel slag erosion, but poor thermal shock resistance and low softening temperature under load. High-alumina bricks have excellent overall indicators and a good cost performance ratio, so they are widely used. However, high-alumina bricks are made from bauxite and silicon carbide as the main raw materials and are mainly used in the transition zone of cement rotary kilns.

Carbonaceous refractory materials include silica bricks, graphite products, and silicon carbide products. Carbonaceous products are another type of neutral refractory material, divided into carbon bricks, graphite products, and silicon carbide products according to the composition of the carbon-containing raw materials and the mineral composition of the products. Carbon bricks are made from high-grade petroleum coke as raw material, with tar and pitch as binders, and fired at 1300℃ in an air-isolated environment. Graphite products (except for natural graphite) are made from carbonaceous materials graphitized in an electric furnace at 2500-2800℃. Silicon carbide products are made from silicon carbide as raw material, with clay, silicon oxide, and other binders fired at 1350-1400℃. Silicon nitride-silicon carbide products can also be made by adding silicon powder to silicon carbide in an electric furnace under a nitrogen atmosphere. Carbonaceous products have a very low coefficient of thermal expansion, high thermal conductivity, good thermal shock resistance, and high high-temperature strength.

They do not soften after long-term use at high temperatures, are not subject to acid and alkali erosion, have good salt resistance, are not wetted by metals and slag, and are lightweight, making them high-quality high-temperature materials. The disadvantage is that they are easily oxidized at high temperatures and should not be used in oxidizing atmospheres. Carbonaceous products are widely used in high-temperature furnace linings (furnace bottom, hearth, lower part of the furnace body, etc.) and linings for smelting non-ferrous metal furnaces. Graphite products can also be made into crucibles for smelting copper alloys and light alloys. The main component of carbon bricks and graphite products is carbon (C), which has a very low coefficient of thermal expansion, high thermal conductivity, good thermal shock resistance, high high-temperature strength, resistance to acid, alkali, and salt erosion, especially good resistance to weak acids and alkalis, is not wetted by metals and slag, and is lightweight. They are generally used in the iron and steel smelting industry and also as linings for autoclaves in the petroleum and chemical industries. Silicon carbide is an excellent refractory material with good erosion resistance, but it is easily oxidized at high temperatures (above 1400 degrees) and is not suitable for use in oxidizing atmospheres.

Alkaline refractory materials are mainly composed of magnesium oxide and calcium oxide. The main products include magnesia bricks, magnesia-chrome bricks, magnesia-zirconia bricks, magnesia-alumina bricks, magnesia-alumina spinel bricks, magnesia-calcium bricks, dolomite bricks, and newly developed magnesia-ferrite spinel bricks, etc. Refractory bricks containing more than 80% magnesium oxide (Mg0) are called magnesia bricks, which can be divided into many grades according to indicators. Magnesia bricks have good resistance to alkaline slag and iron slag, and their refractoriness is higher than that of clay bricks and silica bricks. They are mainly used in open-hearth furnaces, oxygen converters, and electric furnaces.

They are also used in non-ferrous metal smelting equipment, the glass industry, and some high-temperature equipment. Magnesia-chrome bricks have stronger resistance to alkaline slag, and their thermal shock resistance is also much higher than that of magnesia bricks, so they are more widely used. Magnesia-chrome bricks have almost replaced magnesia bricks in the iron and steel smelting and non-ferrous metal smelting industries. Because the chromium oxide (Cr203) contained in them can continuously diffuse, making magnesia-chrome bricks easy to adhere to kiln skins, they have been the main choice for refractory materials used in the firing zone of cement kilns for nearly 30 years. The Cr203 in magnesia-chrome bricks will react with water, turning trivalent chromium into carcinogenic hexavalent chromium, which will pollute the water, and is facing a gradual withdrawal from the cement industry market. Magnesia-alumina bricks use magnesia and alumina as raw materials. Compared with magnesia bricks, they have better thermal shock stability and high-temperature creep resistance, and the parts used are almost the same as magnesia bricks.

Dolomite bricks and magnesia-calcium bricks have almost the same performance. Dolomite bricks are made from dolomite as raw material, and magnesia-calcium bricks are made from synthetic magnesia-calcium sand as raw material. The calcium oxide content is generally 15-30%, and the remaining components are mainly magnesium oxide, which has the effect of purifying molten steel. They are generally only used for smelting special steel. The production process of magnesia-calcium bricks is more complex, and they are easily hydrated and decomposed when exposed to water and steam, making them difficult to store and transport. Precautions must be taken during use. Magnesia-ferrite spinel bricks are a new product mainly used in the firing zone and transition zone of cement rotary kilns and will be the main product to replace magnesia-chrome bricks in the cement industry.

Refractory materials used in special occasions also include high-temperature oxide materials, such as aluminum oxide, lanthanum oxide, beryllium oxide, calcium oxide, zirconium oxide, etc.; refractory compound materials, such as carbides, nitrides, borides, silicides, and sulfides, etc., are special refractory materials with melting points above 2050-3050℃; refractory compound materials such as carbides (silicon carbide, titanium carbide, tantalum carbide, etc.), nitrides (boron nitride, silicon nitride, etc.), borides (zirconium boride, titanium boride, hafnium boride), silicides (aluminum disilicide), and sulfides (thorium sulfide, cerium sulfide, etc.). Their melting points range from 2000-3887℃, among which the more refractory carbides, high-temperature composite materials such as cermets, high-temperature inorganic coatings, and fiber-reinforced ceramics, etc.

Frequently used special materials include non-oxide refractory materials such as AZS (i.e., fused cast alumina-zirconia-silica), corundum bricks, direct-bonded magnesia-chrome bricks, silicon carbide bricks, silicon nitride-bonded silicon carbide bricks, nitrides, silicides, sulfides, borides, carbides, etc.; refractory materials such as calcium oxide, chromium oxide, aluminum oxide, magnesium oxide, beryllium oxide, etc. Commonly used thermal insulation refractory materials include diatomite products, asbestos products, insulation boards, etc. Commonly used unshaped refractory materials include refractory castables, refractory mud, refractory ramming mixes, refractory plastics, patching mixes, refractory gunning mixes, refractory shotcrete, refractory coatings, lightweight refractory castables, taphole clay, etc.