What are the six major types of raw materials commonly used in refractory materials?

Refractory raw materials are materials necessary for the production of refractory products. It is the basis for the production of refractory materials. Most of the refractory raw materials are natural minerals (such as refractory clay, bauxite, silica, chrome ore, magnesite, dolomite, forsterite, zircon, kyanite, sillimanite, andalusite, etc.). With the continuous improvement of the requirements for the comprehensive performance of refractory materials, industrial raw materials and synthetic raw materials (such as industrial alumina, synthetic mullite, man-made refractory fiber, man-made refractory hollow ball, etc.) are increasingly used in the production of refractory. The quality and cost of refractory products depend to a large extent on the correct selection and rational use of raw materials.

Refractory raw materials according to chemical properties can be divided into acidic refractory raw materials, alkaline refractory raw materials and neutral refractory raw materials; according to the source can be divided into natural mineral raw materials and synthetic raw materials; under normal circumstances, people put the production of refractory raw materials into the main raw materials, auxiliary raw materials.

The raw materials used for the production of refractory products, whether natural mineral raw materials or synthetic raw materials, from the mineralogical point of view, must have a sufficiently high refractoriness of the production products; from the technological point of view, it must be able to meet the basic requirements of the process; from the performance of the products made by it, it should be able to meet the performance of the products, especially the requirements of high temperature performance.

Refractory raw materials are usually divided into aluminum and silicon refractory raw materials (siliceous, clay, high alumina, etc.), alkaline refractory raw materials, heat insulation refractory raw materials and other refractory raw materials.

1. siliceous raw materials

Due to the volume effect of quartz variants, silica bricks are also directly made of silica, which is a general term for vein quartz, quartzite, flint and sandstone. The main component in silica is SiO2, and the others are impurities. The siliceous raw materials for refractory materials are crystalline gravel and cemented silica.

2. clayey raw materials

Refractory clay is the main raw material for the production of aluminosilicate refractories, and its refractoriness is required to be higher than 1580 ℃ of all kinds of hard clay, soft (semi-soft) clay and clay shale, people collectively referred to as refractory clay.

Natural refractory clay, usually clay minerals are mainly kaolinite (Al2O3 • 2SiO2 • 2H2O) as its main component, that is, water-containing silicate as the main body, and mixed with free quartz, yellow iron stone, rutile and a mixture of organic matter. This non-single mineral is mostly a dispersion of particles with a diameter of less than 1.2 μm.

According to the different generation of clay, it can be divided into: primary clay and secondary clay. Primary clay refers to the parent rock (such as feldspar) after weathering to form clay, still remaining in place. Secondary clay, also known as drift clay, is a clay that is transferred from primary clay to other places under natural dynamic conditions and then deposited, with small particle size, large dispersion and high plasticity.

The application of refractory clay in refractory industry mainly includes the following two categories.

① Hard clay is characterized by dense organization, high hardness, extremely fine particles, difficult to disperse in water, and low plasticity. Such clays are often light gray, off-white or gray in appearance. Shell-shaped fracture, some of the surface has a smooth feeling, easy to weather broken into pieces.

② Soft (semi-soft) clay is often in the form of soil block, with soft tissue and good plasticity. The color of this clay varies greatly due to the type and content of impurities. From gray, dark gray, until black; some are purple, light red or white.

3. high alumina raw materials

(1) Bauxite

Bauxite is the main raw material for the production of brown corundum, and high-alumina clinker with Al2O3 content of 88% ~ 90% is the main raw material for sub-white corundum; alumina is used as raw material for the production of white corundum and dense corundum. Bauxite is also called high bauxite or bauxite, the main minerals are bauxite (Al2O3 · H2O) and gibbsite (Al2O3 · 3H2O).

China's reserves of high bauxite are extremely rich: the origin is from Shanxi, Hebei and Shandong in the north of the Yellow River, through Henan and Guangxi in the middle, and until Guizhou and Yunnan in the southwest. At present, the main producing areas of high bauxite clinker are Shanxi, Henan and Guizhou. There are also some smaller mines under development in Hunan. The main minerals of high bauxite in China are diaspore, boehmite, kaolinite and pyrophyllite, which can be divided into three types according to their mineral composition: diaspore-kaolinite type (DK); boehmite-kaolinite type (BK); diaspore-pyrophyllite type (DP). At present, DK type high bauxite is widely used. DK type high bauxite clinker is divided into S, Ⅰ, ⅡA, ⅡB, Ⅲ and so on according to its Al2O3 content.

(2) Sintered corundum and fused corundum

Artificial production of corundum is the use of industrial alumina or high bauxite as the main raw material, in the electric arc furnace melting system. In addition, corundum plate-like alumina can also be obtained by sintering. This method is still based on industrial alumina powder as the main raw material, through calcination, fine grinding, into a ball and firing system. This method is 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 based on high bauxite, with Al2O3 content greater than 98% and apparent porosity less than 4%. It is made of high bauxite by electric melting under reducing atmosphere and controlled conditions. Corundum crystal is granular, generally 1~15mm; the main impurities are rutile, aluminum titanate and its solid solution.

(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 two categories. Natural mullite is rarely, generally synthetic. Mullite is chemically stable and insoluble in hydrofluoric acid. It has good high-temperature mechanical and high-temperature thermal properties, therefore, synthetic mullite and its products have the advantages of high density and purity, high-temperature structural strength, low high-temperature creep rate, small thermal expansion rate, strong resistance to chemical erosion, and thermal shock resistance.

(4) Sillimanite group minerals

Sillimanite minerals are kyanite, andalusite, sillimanite, commonly known as "three stone". The chemical composition of the three stones is the same, but the crystal structure is different, belonging to the homogeneous crystal. Heating to high temperature, are converted to mullite, generating a small amount of molten SiO2, accompanied by volume expansion.

Due to the different size of the heating expansion of the three stones, the degree of direct utilization is also different. Due to the small volume change of andalusite, whether it is used to make bricks or as additives, it is directly used raw materials. And sillimanite, kyanite is often added to the ingredients in the form of expansion agent, especially more for unshaped refractory materials. And used to make bricks to calcine clinker, especially kyanite must be calcined mature material.

4. alkaline refractory raw materials

4.1 magnesium raw materials

(1) Magnesite

There are two main types 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 some magnesite contains high CaO. The second mineral is dolomite. Magnesite in China can be classified into five grades according to chemical composition: S, I, II, III and IV. Only S and I grades are used for calcining brickmagnesia.

Using two-step flotation and two-step calcination to prepare high-purity magnesia, the high-purity magnesia prepared by this method can be used as raw materials to develop a variety of high-performance refractory products.

(2) Other magnesium-containing minerals

The main mineral composition of forsterite products in magnesia refractories is forsterite (2MgO · SiO2) and periclase (MgO). This product is characterized by strong resistance to molten iron oxide, thermal shock stability is better than ordinary magnesia brick. The main raw materials for the production of such products are peridotite and serpentinite.

4.2 dolomitic raw materials

Dolomite is magnesium carbonate (MgCO3) and calcium carbonate (CaCO3) double salt as the main component of refractory raw materials, its chemical formula is CaMg(CO3)2 or MgCO3 · CaCO3, its theoretical composition is CaO3 0.41%, MgO2 1.87%, CO2 47. 72%. CaO/MgO = 1.39, hardness of 3.5 to 4.

China's dolomite is rich in raw materials, widely distributed, and relatively pure. Liaoning Dashiqiao area is very rich in reserves. Shandong, Hubei, Shaanxi, Guangxi, Gansu, Jiangxi, Anhui, Sichuan, Yunnan, Hunan and other provinces are rich in mineral resources. This ore body is often associated with limestone and magnesite.

Raw materials for 5. zirconium products

(1) Zircon

Zircon (ZrO2-SiO2 or ZrSiO4) is the main raw material for the production of zircon products and zircon products, China's zircon origin is Hainan Province. It is distributed in Guangdong Province, Guangxi Zhuang Autonomous Region, Shandong Province, Fujian Province and Taiwan Province.

The theoretical composition of zircon is ZrO2 67. 01% and SiO2 32. 99%. It often contains TiCfe and other trace rare earth oxides, which are made radioactive to varying degrees due to the presence of these elements. Therefore, when using this raw material to produce products, there should be necessary protective measures.

The thermal conductivity of zircon is low, 3.72W/(m · K) between 20 and 1000 ℃. The expansion coefficient of zircon is also lower than that of other crystal phases, 4.6X10-6 ℃ at 1000 ℃, and the expansion coefficients of its single crystal in the two directions of vertical and parallel principal axes (C axis) are quite different. Zircon is chemically inert and difficult to react with acid. Reactions with the glass melt to a lesser extent, it is commonly used in refractories for metallurgy and the glass industry.

(2) oblique zircon

Natural oblique zircon (ZrO2) is often irregular, black, brown, yellow or colorless. There are few natural oblique zircon ore bodies in China. Industrial use of ZrO2, is a chemical raw material, is made of zircon (ZrO2 · SiO2) by chemical methods of white or yellowish powder.

Pure ZrO2 has three crystal forms under atmospheric pressure: from low temperature to high temperature, it is monoclinic phase, tetragonal phase and cubic phase.

Stable ZrO2, depending on the degree of stability, is divided into partially stable ZrO2 and fully stable ZrO2. Due to the large thermal expansion coefficient of fully stable ZrO2, its thermal shock stability is not as good as partially stable, so the latter is commonly used as toughening materials for ceramics and refractories.

(3) Desiliconized zirconium

Abroad in the manufacture of fused-cast zirconium corundum (AZS) refractories, in addition to the use of zircon concentrate, most of the addition of a certain number of "desiliconized zirconium" raw materials, its purpose: one is to adjust and stabilize the formula; the second is to improve and optimize product performance.

(4) Zirconium corundum mullite

The original raw materials are industrial alumina, kaolin and zircon, which are finely ground and mixed evenly, pressed by semi-dry method and calcined at 300~1700 ℃ to obtain this material. The research shows that increasing the content of zircon will lead to increasing the sintering temperature, reducing the total shrinkage and increasing the number of closed pores. These reactions make the sintered zircon corundum mullite have higher density and strength and better thermal shock resistance.

Raw materials for 6. chromium products

One of the main raw materials for the production of chrome (chrome brick, chrome-magnesium brick, magnesia-chrome brick) refractories is chrome ore or chromite. Chromite is a mixture of many minerals, because its mineral composition fluctuates greatly, and its chemical composition and physical properties also change greatly. It is usually composed of gangue minerals with chromium grains. These gangue minerals are usually magnesium silicates, such as serpentine, forsterite and olivine. In addition to Cr2O3 in chromite, there are also Al2O3, Fe2O3 and MgO, etc., the general chromite, due to the presence of magnesium and iron, often expressed as (Mg, Fe) Cr2O3.

The above are commonly used refractory raw materials. With the innovation of refractory technology, the types of raw materials are also more diverse. Especially in recent years, because of a series of reasons such as environmental protection and raw ore resources, we have continuously developed synthetic materials with better performance and more environmentally friendly resources. Renewable raw materials (such as ferrosilicon nitride, Sialon, etc.).