Application of high temperature refractory

The definition of refractories now does not just depend on whether the refractoriness is above 1580 ℃. Wholesale of magnesia carbon bricks at present, refractories generally refer to inorganic non-metallic materials used in the lining of metallurgical, petrochemical, cement, ceramics and other production equipment.

Acid refractories are mainly composed of silica (SiO₂) and commonly used silica bricks and clay bricks. Silica brick is a siliceous product containing more than 93% SiO₂. The raw materials used include silica, waste silica brick, etc. 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, or even slightly expand, but its thermal shock resistance stability is poor. Silica bricks are mainly used for thermal equipment such as coke oven, glass furnace and acid steel-making furnace. Silica bricks can be divided into several grades according to different SiO₂ content and physical and chemical indexes, mainly including silica bricks for glass furnace and silica bricks for coke oven. Clay silica brick is mainly made of refractory clay or charstone clinker, containing 30%-46% alumina, with a fire resistance of 1580-1770 ℃. It is a weakly acidic refractory material with good thermal vibration resistance and corrosion resistance to acid slag. It is widely used. The clay brick made of refractory clay is called ordinary clay brick, and the acid brick made of charstone clinker with an apparent porosity of less than 17% is called low porosity clay brick. The two kinds of clay bricks are divided into several grades according to their physical and chemical indexes. The price difference between ordinary clay brick and low porosity clay brick is large.

Neutral refractories are mainly composed of alumina, chromium oxide, silicon carbide or carbon. The main products of neutral refractories are: corundum brick, high aluminum brick, silica mullite brick, mullite brick, aluminum chrome brick, aluminum carbon brick, graphite or carbon brick, etc. The main crystalline 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 kind of high-quality refractory with wide application. Chromium brick with chromium oxide as the main component has good corrosion resistance to steel slag, but poor thermal shock resistance and low load softening degree. High alumina bricks are widely used because of their excellent indicators and good cost performance. However, because they are made of bauxite and silicon carbide as the main raw materials, they are mainly used in the transition zone of cement rotary kiln.

Carbonaceous refractories include silica bricks, graphite products and silicon carbide products. Carbonaceous 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 brick, graphite products and silicon carbide products. Carbon brick is made of high-grade petroleum coke as raw material, tar and asphalt as binder, and fired at 1300 ℃ under the condition of air isolation. Graphite products (except natural graphite) are made of carbon materials by graphitization at 2500-2800 ℃ in an electric furnace. Silicon carbide products are made of silicon carbide, clay, silicon oxide and other binders and fired at 1350-1400 ℃. Silicon nitride silicon carbide products can also be made by adding silicon carbide powder in the nitrogen atmosphere of the electric furnace. Carbon products have low coefficient of thermal expansion, high thermal conductivity, good heat shock resistance and high temperature strength.

It will not soften under high temperature for long-term use, and will not be eroded by any acid and alkali. It has good salt resistance and will not be 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 easy to oxidize at high temperature, so it is not suitable for use in oxidizing atmosphere. Carbon products are widely used in high temperature furnace lining (furnace bottom, hearth and lower part of furnace body, etc.) and lining of smelting nonferrous metal furnace. Graphite products can also be made into crucibles for smelting copper alloys and light alloys. The main component of carbon brick and graphite products is carbon (c), which has low coefficient of thermal expansion, high thermal conductivity, good heat shock resistance, high temperature strength, resistance to acid, alkali and salt erosion, especially weak acid and alkali has good resistance, is not wetted by metal and slag, and is light in weight. It is generally used in iron and steel smelting industry, and also used as autoclave lining in petroleum and chemical industry. Silicon carbide is an excellent refractory with good corrosion resistance, but it is easy to oxidize at high temperature (higher than 1400 ℃), so it is not suitable for use in oxidizing atmosphere.

Basic refractories are mainly composed of magnesium oxide and calcium oxide. The main products are magnesium brick, magnesium chromium brick, magnesium zirconium brick, magnesium aluminum brick, magnesium aluminum spinel brick, magnesium calcium brick, dolomite brick and the latest developed magnesium iron spinel brick, etc. Refractory bricks containing more than 80% of magnesium oxide (MgO) are called magnesia bricks, which can be divided into many grades and brands according to the indicators. Magnesia bricks have good resistance to alkaline slag and iron slag, and have higher fire resistance than clay bricks and silica bricks. They are mainly used in open hearth furnace, oxygen blowing converter, electric furnace non-ferrous metal smelting equipment, glass industry and some high-temperature equipment. Magnesia chrome bricks have stronger resistance to alkaline slag, and have much higher thermal shock temperature resistance than magnesia bricks, Therefore, it is more widely used. Magnesia chrome bricks have almost replaced magnesia bricks in the steel smelting and non-ferrous metal smelting industries. Due to the continuous diffusion of chromium oxide (Cr₂O₃) contained therein, magnesia chrome bricks can be easily adhered to the kiln skin. Therefore, in the past 30 years, it has been used as a refractory for the firing zone of cement kiln. The Cr₂O₃ in magnesia chrome bricks will react with water, and trivalent chromium will become a carcinogenic hexavalent, which will pollute the water, It is facing the trend of gradually withdrawing from the cement industry market. Magnesia alumina brick uses magnesia and alumina as raw materials. Compared with magnesia brick, its thermal shock stability and high-temperature creep performance are better, and the use position is almost the same as that of magnesia brick.

The properties of dolomite brick and magnesia calcium brick are almost the same. Dolomite brick is made of dolomite and magnesia calcium brick is made of synthetic magnesia calcium sand. The content of calcium oxide is generally 15-30%, and the rest is mainly magnesium oxide, which has the function of purifying molten steel. Generally, it is only used in the smelting of special steel. The production process of magnesia calcium brick is relatively complex. It is easy to hydrate and decompose in the presence of water and steam, and it is not easy to store and transport. Precautions must be taken in the process of use. Magnesia iron spinel brick is a new product, which is mainly used in the firing zone and transition zone of cement rotary kiln. It will be the main product to replace magnesia chrome brick in the cement industry.

The properties of dolomite brick and magnesia calcium brick are almost the same. Dolomite brick is made of dolomite and magnesia calcium brick is made of synthetic magnesia calcium sand. The content of calcium oxide is generally 15-30%, and the rest is mainly magnesium oxide, which has the function of purifying molten steel. Generally, it is only used in the smelting of special steel. The production process of magnesia calcium brick is relatively complex. It is easy to hydrate and decompose in the presence of water and steam, and it is not easy to store and transport. Precautions must be taken in the process of use. Magnesia iron spinel brick is a new product, which is mainly used in the firing zone and transition zone of cement rotary kiln. It will be the main product to replace magnesia chrome brick in the cement industry.

The special materials often used are AZS (i.e. zirconium corundum brick), corundum brick, directly bonded magnesium chromium brick, silicon carbide brick, silicon nitride bonded silicon carbide brick, nitride, silicide, sulfide, boride, carbide and other non oxide refractory materials; Calcium oxide, chromium oxide, alumina, magnesium oxide, beryllium oxide and other refractories. The frequently used insulating and refractory materials include diatomite products, asbestos products, thermal insulation boards, etc. The frequently used unshaped refractory materials include refractory castables, refractory slurries, refractory ramming materials, refractory plastics, furnace repair materials, refractory gunning materials, refractory projectiles, refractory coatings, lightweight refractory castables, gun slurries, etc.