What are the raw materials of refractories?

Refractory raw materials refer to the materials necessary for the production of refractory products. It is the basis of refractory production. Refractory raw materials are mostly natural minerals (such as refractory clay, bauxite, silica, chromite, magnesite, dolomite, forsterite, zircon, kyanite, sillimanite, andalusite, etc.). With the continuous improvement of the comprehensive performance requirements of refractory materials, industrial raw materials and synthetic raw materials (such as industrial alumina, synthetic mullite, artificial refractory fibers, artificial refractory hollow spheres, etc.). ).) is increasingly used to produce refractories. The quality and cost of refractory products largely depend on the correct selection and reasonable use of raw materials. Refractories can be divided into acid refractories, basic refractory refractories and neutral refractories according to their chemical properties. According to the source, it can be divided into natural mineral raw materials and synthetic raw materials; People usually divide the raw materials for producing refractories into main raw materials and auxiliary raw materials. The raw materials used to produce refractory products, whether natural mineral raw materials or synthetic raw materials, must have high enough fire resistance from the mineralogical point of view; From a technical point of view, it should be able to meet the basic requirements of technology; From the performance point of view, the products made of it should be able to meet the requirements of product performance, especially the high temperature performance. General refractories are divided into alumina-silica refractories (silica, clay, high alumina, etc. ), basic refractory, heat insulation refractories and other refractories. 1. Siliceous raw materials Due to the volume effect of time-varying materials, silica bricks are also directly made of silicon dioxide, which is the general term for gangue, quartzite, flint and sandstone. The main component of silicon dioxide is silicon dioxide, and the rest is impurities. Silica raw materials for refractories include crystalline macadam and cemented silica. Table 1 Classification and characteristics of silica for refractories. Clay raw material Refractory clay is the main raw material for producing aluminosilicate refractories. All kinds of hard clay, soft (semi-soft) clay and clayey shale with fire-resistant temperature higher than 1580℃ are collectively called fire-resistant clay. Natural refractory clay is usually a mixture of clay minerals, mainly composed of kaolinite (Al _ 2O _ 32 SiO _ 22 H _ 2O), namely hydrated silicate, mixed with free time, pyrite, rutile and organic matter. Most of this non-single mineral is a dispersion composed of particles with a diameter less than 1.2 μ m, which can be divided into primary clay and secondary clay according to the different conditions of clay formation. Primary clay refers to the clay formed by weathering of parent rock (such as feldspar), which still remains in place today. Secondary clay, also known as residual clay, is a clay that is transferred from primary clay to other places and then deposited under natural dynamic conditions. It has fine particles, large dispersibility and strong plasticity. Refractory clay used in refractory industry is mainly divided into the following two categories. ① Hard clay is characterized by compact structure, high hardness, extremely fine particles, difficult dispersion in water and low plasticity. The appearance of this clay is usually light gray, grayish white or gray. Shell-like cracks, some of which are greasy on the surface and easy to weather and break. (2) Soft (semi-soft) clay is usually a clod with soft tissue and good plasticity. Due to the different kinds and contents of impurities, the color of this clay varies greatly. From gray, dark gray to black; Some are purple, red or white. Three. Bauxite with high alumina content (1) is the main raw material for producing brown corundum, and high alumina clinker with Al2O3 content of 88%~90% is the main raw material for producing sub-white corundum. Alumina is the raw material for producing white corundum and dense corundum. Bauxite is also called bauxite or bauxite, and the main minerals are diaspore (al2o3 3H2O) and gibbsite (al2o3 3H2O). Bauxite reserves in China are extremely rich: the origin ranges from Shanxi, Hebei and Shandong to the north of the Yellow River, passing through Henan and Guangxi in the middle, and reaching Guizhou and Yunnan in the southwest. At present, the main producing areas of bauxite clinker are Shanxi, Henan and Guizhou. There are also some small coal mines under development in Hunan. The main minerals of bauxite in China are boehmite, boehmite, kaolinite and pyrophyllite, which can be divided into three types according to their mineral composition: boehmite-kaolinite type (DK); Boehmite-kaolinite type (BK); Diaspore-pyrophyllite type (DP). At present, DK bauxite is the most widely used. According to its Al2O3 content, DK bauxite clinker can be divided into S, _, _A, _B, _ and so on. (2) Sintered corundum and fused corundum are used to synthesize corundum, which is made by melting industrial alumina or high-alumina bauxite as the main raw materials in an electric arc furnace. In addition, corundum tabular alumina can be prepared by sintering. This method is still made of industrial alumina powder as the main raw material through calcination, fine grinding, pelletizing and firing. This method is technically difficult to produce, but the product has high strength, strong corrosion resistance and good thermal shock stability. The so-called "sub-white corundum" is actually a dense fused corundum with high alumina content of more than 98% and apparent porosity of less than 4%. It is made of bauxite by electric melting under reducing atmosphere and controlled conditions. Corundum crystal is granular, generally1~15 mm; The main impurities are rutile, aluminum titanate and their solid solutions. (3) Mullite Mullite is a refractory raw material with 3al2o3 2SiO2 crystal phase as the main component. Mullite is divided into natural mullite and synthetic mullite. Natural mullite is rare and generally synthetic. Mullite is chemically stable and insoluble in hydrofluoric acid. It has good mechanical and thermal properties at high temperature. Therefore, the synthesized mullite and its products have the advantages of high density, high purity, high structural strength at high temperature, low creep rate at high temperature, small thermal expansion coefficient, strong chemical corrosion resistance and thermal shock resistance. (4) Sillimanite minerals Sillimanite minerals include kyanite, andalusite and sillimanite, commonly known as "three stones". The three kinds of stones have the same chemical composition, but different crystal structures, belonging to isomorphism. When heated to high temperature, they are all transformed into mullite, forming a small amount of molten SiO2, accompanied by volume expansion. Because of the different thermal expansion of the three kinds of stones, their direct utilization degree is also different. Because of the small volume change of andalusite, it is directly used as raw material, whether it is used for making bricks or as an additive. Sillimanite and kyanite are often added to the ingredients in the form of expansion agents, especially amorphous refractories. To make bricks, it is necessary to calcine clinker, especially kyanite. Four. Alkaline refractory raw material 4. 1 magnesium raw material (1) magnesite There are mainly two kinds of magnesite in China: crystalline magnesite and amorphous magnesite. Magnesite in China is mainly distributed in Liaoning and Shandong provinces. The main impurity of magnesite is talc, and the CaO content of some magnesite is higher, followed by dolomite. Magnesite in China can be divided into five grades according to chemical composition: S, _, _, _, and only S and I are used to calcine magnesia for brick making. High purity magnesium oxide was prepared by two-step flotation and two-step calcination. Using the high-purity magnesium oxide prepared by this method as raw material, various high-performance refractory products can be developed. (2) The main mineral components of forsterite products in other magnesium-containing mineral magnesia refractories are forsterite (2MgOSiO2) and periclase (MgO). The product is characterized by strong resistance to molten iron oxide and better thermal shock stability than ordinary magnesia brick. The main raw materials for producing this product are peridotite and serpentine. 4.2 Dolomite raw material Dolomite is a kind of refractory raw material, and its main components are magnesium carbonate (MgCO3) and calcium carbonate (CaCO3). Its chemical formula is CaMg(CO3)2 or MgCO3CaCO3, and its theoretical composition is CaO30.4 1%, MgO2 1.87% and CO247. 72%.CaO/MgO= 1.39, hardness 3.54. China's dolomite is rich in raw materials, widely distributed and relatively high in purity. Liaoning Dashiqiao area is rich in reserves. Shandong, Hubei, Shaanxi, Guangxi, Gansu, Jiangxi, Anhui, Sichuan, Yunnan and Hunan provinces are rich in mineral resources. Ore bodies often coexist with limestone and magnesite. 5. Zirconium products raw material (1) Zirconium zircon (ZrO2SiO2 or ZrSiO4) is the main raw material for producing zirconium products and zirconium products. China zircon is produced in Hainan Province. Guangdong Province, Guangxi Zhuang Autonomous Region, Shandong Province, Fujian Province and Taiwan Province Province are all distributed. The theoretical composition of zircon is ZrO267. 0 1% and silica 32. 99%. It usually contains trace amounts of rare earth oxides, such as TiCfe. Because of these elements, it has different degrees of radioactivity. Therefore, when using this raw material to produce products, necessary protective measures should be taken. The thermal conductivity of zircon is very low, which is 3.72W/(m.K) at 20 1000℃. Compared with other crystal phases, the expansion coefficient of zircon is also lower, which is 4.6× 1000℃. The expansion coefficient of its single crystal is very different in the vertical direction and parallel direction of the main axis (C axis). Zirconite is chemically inert and difficult to react with acids. It hardly reacts with glass melt and is often used as a refractory in metallurgy and glass industry. (2) baddeleyite natural baddeleyite (ZrO2) is usually irregular and black, brown, yellow or colorless. There are few natural baddeleyite ore bodies in China. ZrO2 _ 2 _ 2 used in industry is a chemical raw material, which is a white or yellowish powder made of zircon by chemical method. From low temperature to high temperature, there are three crystal forms of pure ZrO2 _ 2 at atmospheric pressure: monoclinic phase, tetragonal phase and cubic phase. According to the degree of stability, stable ZrO2 can be divided into partially stable ZrO2 and completely stable ZrO2. Due to the large thermal expansion coefficient, completely stable ZrO _ 2 is not as good as partially stable ZrO _ 2 in thermal shock stability, so the latter is often used as toughening material for ceramics and refractories. (3) Desilicated Zirconium In foreign countries, except zircon concentrate, a certain amount of "Desilicated Zirconium" raw materials are mostly added in the production of fused zirconia corundum (AZS) refractories. The purpose is to adjust and stabilize the formula; The second is to improve and optimize product performance. (4) Zirconium corundum mullite raw materials are industrial alumina, kaolin and zircon, which are finely ground and evenly mixed, pressed into balls by semi-dry method, and calcined at 300 1700℃ to obtain the material. The results show that increasing the content of zircon will increase the sintering temperature, reduce the total shrinkage and increase the closed porosity. These reactions make the sintered zirconia corundum mullite have higher density, strength and better thermal shock resistance. Chromite or chromite, the raw material of intransitive verb chromium products, is one of the main raw materials for producing chromium (chrome brick, chrome-magnesium brick, magnesia-chrome brick) refractories. Chromite is a mixture of many minerals, and its chemical composition and physical properties are quite different because of its large fluctuation in mineral composition. It is usually composed of gangue minerals containing chromium particles. These gangue minerals are usually magnesium silicate such as serpentine, forsterite and olivine. Besides Cr2O3, chromite also contains Al2O3, Fe2O3 and MgO. Generally speaking, chromite is usually expressed as (Mg, Fe)Cr2O3 due to the existence of magnesium and iron.