The definition of refractories now depends not only on whether the refractoriness is above 1580℃. At present, refractory materials generally refer to inorganic non-metallic materials used in the lining of metallurgical, petrochemical, cement, ceramic and other production equipment.
The acid refractories use silicon oxide (Si02) as the main component, commonly used are silicon bricks and clay bricks. Silica brick is a silicon product containing more than 93% Si02. The raw materials used are silica and waste silica brick. Silica brick has strong resistance to acid slag erosion, but it is easily eroded by alkaline slag. Its load softening temperature is very high and close to Its refractoriness, the volume does not shrink after repeated calcination, and even slightly expands, but the thermal shock stability is poor. Silica brick is mainly used for thermal equipment such as coke oven, glass melting furnace, acid steel-making furnace, etc. Silica brick can be divided into several grades according to the difference of SiO2 content and physical and chemical indicators, mainly divided into silica brick for glass kiln and silicon for coke oven Two categories of bricks. Clay silica bricks are made of refractory clay or coke clinker as the main raw material, containing 30%-46% alumina, refractoriness 1580-1770 ℃, it is a weak acid refractory material, good thermal shock resistance, corrosion resistance to acid slag The clay brick is made of refractory clay as the main raw material. It is called ordinary clay brick, and the coke gem clinker is the main raw material. The acid brick with a porosity of less than 17% is called low porosity clay brick. The two kinds of clay bricks are divided into several grades according to the different physical and chemical indicators. The price difference between ordinary clay bricks and low porosity clay bricks is large.
Neutral refractories are mainly composed of alumina, chromium oxide, silicon carbide or carbon. The main products of neutral refractory materials are: corundum bricks, high alumina bricks, silicon-molybdenum bricks, mullite bricks, aluminum-chromium bricks, aluminum-carbon bricks, graphite or carbon bricks, etc. The main crystal phases of high-aluminum 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 wide range of high-quality refractory materials. Chrome bricks with chromium oxide as the main component have good corrosion resistance to steel slag, but poor thermal shock resistance and low load softening. The various indicators of high alumina bricks are relatively good and have good cost performance, so they are widely used, but because high alumina bricks are made of bauxite and silicon carbide as the main raw materials, they are mainly used in cement rotary kilns. Transition zone.
Carbon refractory materials include silicon bricks, graphite products and silicon carbide products. Carbon products are another kind of neutral refractories. According to the composition of carbon-containing raw materials and the mineral composition of products, they are divided into three categories: carbon bricks, graphite products and silicon carbide products. Carbon bricks are made from high-grade petroleum coke as raw materials, plus tar and asphalt as binders, and fired at 1300°C in an air-insulated condition. Graphite products (except natural graphite) are made of carbonaceous materials by graphitization in an electric furnace at 2500-2800℃. Silicon carbide products are made of silicon carbide as raw material, with clay, silicon oxide and other binders fired at 1350-1400 ℃. Silicon nitride-silicon carbide powder can also be made into silicon nitride-silicon carbide products under an electric furnace nitrogen atmosphere. Carbonaceous products have a low coefficient of thermal expansion, high thermal conductivity, good thermal shock resistance, and high temperature strength.
It is not softened for a long time under high temperature, is not eroded by any acid or alkali, has good salt resistance, and is not wetted by metals and slag. It is lightweight 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 an oxidizing atmosphere. Carbonaceous products are widely used in the lining of high-temperature furnace linings (bottom, bottom of hearth and furnace body, etc.) and 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 low coefficient of thermal expansion, high thermal conductivity, good thermal shock resistance, high temperature strength, resistance to acid and alkali and salt corrosion, especially weak acids and alkalis. The resistance is not affected by the wetting of metals and slag, and it is light in weight. It is generally used in the steel smelting industry and also used as the lining of autoclaves in the petroleum and chemical industries. Silicon carbide is an excellent refractory material with good corrosion resistance, but it is easily oxidized at high temperatures (above 1400 degrees) and is not suitable for use in an oxidizing atmosphere.
The basic refractory material is composed of magnesium oxide and calcium oxide. The main products are magnesium brick, magnesium chrome brick, magnesium zirconium brick, magnesium aluminum brick, magnesium aluminum spinel brick, magnesium calcium brick, dolomite brick, and the newly developed Magnesium iron spinel bricks and so on. Refractory bricks containing more than 80% of magnesium oxide (Mg0) are called magnesium bricks, and can be divided into many grades according to the indicators. Magnesium bricks have good resistance to alkaline slag and iron slag, and the refractory degree is higher than clay bricks and silica bricks. , Mainly used in open hearth furnace, oxygen blowing converter, electric furnace
In non-ferrous metal smelting equipment, glass industry, and some high-temperature equipment, magnesia-chromium bricks are more resistant to alkaline slag, and the thermal shock temperature resistance is also much higher than that of magnesia bricks, so they are more widely used. The iron and steel smelting and non-ferrous metal smelting industries have almost replaced magnesium bricks. Since the chromium oxide (Cr203) contained in them can be continuously diffused, the magnesium chromium bricks can be easily adhered to the kiln skin, so in the past 30 years, it has been fired by cement kilns As the first choice for refractory materials, Cr203 in magnesium-chromium bricks will react when it encounters water, and trivalent chromium becomes a carcinogenic six price, which will cause water pollution and is facing the trend of gradually withdrawing 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 performance, and the use parts are almost the same as magnesia bricks.
The properties of dolomite bricks and magnesia-calcium bricks are almost the same. Dolomite bricks are made of dolomite, and magnesia-calcium bricks are made of synthetic magnesia-calcium sand. The content of calcium oxide is generally 15-30%, and the remaining components are mainly magnesium oxide. It has the function of purifying molten steel. It is generally only used in the smelting of special steel. The production process of magnesia-calcium brick is relatively complicated. It is easy to be hydrated and decomposed when encountered with water and steam. It is not easy to save and transport. Precautions must be taken during use. Magnesia-iron spinel brick is a new product, mainly used in cement rotary kiln firing zone and transition zone, and will be the main product of cement industry to replace magnesia-chrome brick.
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 carbide, nitride, boride, silicide and sulfide 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.), boride (boron Zirconium, titanium boride, hafnium boride), silicide (aluminum disilicide) and sulfides (thorium sulfide, cerium sulfide, etc.). Their melting point is 2000-3887℃, among which the most refractory carbides, high-temperature composite materials such as cermets, high-temperature inorganic coatings and fiber-reinforced ceramics.
Frequently used special materials include AZS (zirconium corundum brick), corundum brick, directly bonded magnesia chrome brick, silicon carbide brick, silicon nitride bonded silicon carbide brick, nitride, silicide, sulfide, boride, carbide, etc. Non-oxide refractories; calcium oxide, chromium oxide, aluminum oxide, magnesium oxide, beryllium oxide and other refractories. Frequently used thermal insulation refractory materials include diatomaceous earth products, asbestos products, thermal insulation boards, etc. Frequently used indefinite refractory materials include refractory castables, refractory mud, refractory ramming materials, refractory plastics, furnace repair materials, refractory spray materials, refractory projectile materials, refractory coatings, lightweight refractory castables, and mortar.
