Acid refractories mainly consist of silica and silica bricks and clay bricks commonly used by refractory manufacturers. Silicon brick is a kind of siliceous product containing more than 94% silicon oxide. The raw materials used are silica stone, waste silica brick, etc. It has strong resistance to acid slag erosion, high load softening temperature, no shrinkage or even slight expansion after repeated calcination, but it is vulnerable to alkaline slag erosion, poor thermal shock resistance. Silica bricks are mainly used in coke oven, glass furnace, acid steelmaking furnace and other thermal equipment. Clay brick is a kind of weak acidic refractory, which is mainly made of refractory clay and contains 30% ~ 46% aluminum oxide. It has good thermal vibration resistance and corrosion resistance to acidic slag and is widely used.

Neutral refractories are alumina, chromium oxide or carbon. Corundum products containing more than 95% alumina is a widely used high-quality refractory material. Chromium brick with chromium oxide as the main component has good corrosion resistance to steel slag, but its thermal shock resistance is poor, and the deformation temperature under high temperature load is low. Carbonaceous refractories include carbon bricks, graphite products and silicon carbide products. They have low coefficient of thermal expansion, high thermal conductivity, good thermal shock resistance, high temperature strength, resistance to acid, alkali and salt corrosion, especially weak acid and alkali, and are not wetted by metals and slags. Widely used as lining material for high temperature, and also used as autoclave for petroleum and chemical industry.

Alkaline refractories are mainly composed of Magnesium Oxide and calcium oxide, and commonly used magnesia bricks. Magnesium bricks containing more than 80% ~ 85% magnesia have good resistance to alkaline slag and iron slag, and have higher refractoriness than clay bricks and silica bricks. It is mainly used for open hearth, oxygen converter, electric furnace, non-ferrous metal smelting equipment and some high temperature equipment.

Refractories used in special occasions include high-temperature oxide materials, such as alumina, lanthanum oxide, beryllium oxide, calcium oxide, zirconia, refractory compounds, such as carbides, nitrides, borides, silicides and sulfides; high-temperature composite materials, mainly metal ceramics, high-temperature inorganic coatings and fiber reinforced ceramics. Porcelain and so on.

Frequently used refractories are AZS brick, corundum brick, directly bonded magnesia-chromium brick, silicon carbide brick, silicon nitride-bonded silicon carbide brick, nitride, silicide, sulfide, boride, carbide and other non-oxide refractories; calcium oxide, chromium oxide, alumina, magnesium oxide, beryllium oxide and other refractories.

Often used thermal insulation refractories include diatomite products, asbestos products, insulation panels, etc.

Often used amorphous refractories are remedial furnace charge, ramming material, castable, plastics, refractory cement, refractory gunning material, refractory projectile, refractory paint, light refractory castable, mud and so on.

Bulk refractories (amorphous refractories): An amorphous refractory is a refractory consisting of a reasonable gradation of granular and powdered materials and binders, which is directly used without molding and firing. Usually, the granular aggregate that constitutes this material is called aggregate, the powder is called admixture, and the binder is called binder. This kind of material has no fixed shape and can be made into slurry, mud and loose, so it is also known as bulk refractory. The refractories can be used as integral structures without joints, so they are also called monolithic refractories.

The basic composition of amorphous refractories is granular and powdery refractory materials. According to its requirements, it can be made of various materials. In order to combine these refractories as a whole, except for a few special cases, the appropriate variety and amount of binder are generally added. In order to improve its plasticity or reduce water consumption, a small amount of plasticizer and water reducer can be added. In order to meet other special requirements, a small amount of appropriate other additives can be added separately.

General nature

In common and special refractories, the main varieties are:

Acidic

Silica bricks and clay bricks are used in large quantities. Silica brick is a siliceous product containing more than 93% SiO2. The raw materials used include silica and waste silica bricks. Silicon brick has strong corrosion resistance to acid slag, but it is easy to be eroded by alkaline slag. Its load softening temperature is very high, close to its fireproof. After repeated calcination, the volume does not shrink, or even slightly expand, but its thermal shock resistance is poor. Silica bricks are mainly used in coke oven, glass furnace, acid steelmaking furnace and other thermal equipment. Clay brick contains 30% ~ 46% alumina. It is a kind of weak acid refractory with refractory clay as the main raw material, refractory degree 1580 ~ 1770 C, good thermal shock resistance, corrosion resistance to acid slag, wide range of uses, and is the largest production of refractories.

neutral

The main crystalline phases of 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 refractories with wide application. Chromium bricks are mainly made of chrome ore, and the main phase is chromite. Its corrosion resistance to steel slag is good, but its thermal shock resistance is poor, and the deformation temperature of high temperature load is low. Magnesium-chrome bricks made of chromite and magnesia in different proportions have good thermal shock resistance and are mainly used as basic open-hearth top bricks.

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 bricks, graphite products and silicon carbide products. Carbon brick is made of high-grade petroleum coke, tar and asphalt as binder, and fired at 1300 C under the condition of air insulation. Graphite products (except natural graphite) were treated with carbon materials in an electric furnace by 2500~2800 degree graphitization. Silicon carbide products are sintered with silicon carbide as raw material and clay and silicon oxide as binder at 1350~1400. Silicon carbide and silicon carbide can also be made into silicon nitride silicon carbide products under nitrogen atmosphere in an electric furnace.

Carbonaceous products have low thermal expansion coefficient, high thermal conductivity, good thermal shock resistance and high temperature strength. Long-term use at high temperature does not soften, is not eroded by any acid and alkali, has good salt resistance, and is not wetted by metal and slag, light weight, 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. Carbonaceous products are widely used in lining of high temperature furnace (bottom, hearth, bottom of furnace body, etc.) and smelting non-ferrous metal furnace. Graphite products can be used as reactor tanks and petrochemical autoclave lining. Silicon carbide and graphite products can also be used to make crucible for smelting copper with gold and light alloy.

alkalinity

The products are represented by magnesia products. It contains more than 80%~85% of Magnesium Oxide and the main crystal phase is calcite. The main raw materials for producing magnesia bricks are magnesite, magnesia extracted from seawater and calcined at high temperature. It has good resistance to alkaline slag and iron slag. The melting point of pure Magnesium Oxide is as high as 2800 degrees. Therefore, magnesia brick has higher refractories than clay bricks and silica bricks. Since the mid-1950s, the production of alkaline refractories has increased gradually, while the production of clay and silica bricks has decreased due to the use of oxygen blowing converter and alkaline open-hearth furnace roof. Basic refractories are mainly used in open hearth, oxygen converter, electric furnace, non-ferrous metal smelting and some high temperature.