Six Fundamental Base Materials in Refractory And Thermal Insulation Applications: From Raw Resources To Industrial Essentials

Refractory insulation raw material is the material necessary for the production of refractory insulation products. It is the basis for the production of refractory materials. Most of the refractory raw materials are natural minerals (such as refractory clay, high alumina bauxite, silica, chromite, magnesite, dolomite, magnesium peridotite, zircon, bluestone, silica, erythrite, etc.), with the continuous improvement of the comprehensive performance of refractory materials, refractory production is also more and more the use of industrial and synthetic raw materials (such as industrial alumina, synthetic mullite, man-made refractory fibers, artificial). Refractory hollow ball, etc.). The quality and cost of refractory products depends largely on the correct choice of raw materials and rational use.

Refractory raw materials can be divided into acidic refractory raw materials, alkaline refractory raw materials and neutral refractory raw materials according to chemical properties; according to the source can be divided into natural mineral raw materials and synthetic raw materials; in general, the production of refractory raw materials are divided into the main raw materials, auxiliary raw materials and so on.

Used to produce refractory insulation products raw materials, whether natural mineral raw materials or synthetic raw materials, from the mineralogical point of view, must have the production of products to achieve a sufficiently high degree of refractoriness; from the technological point of view, to be able to meet the basic requirements of the process; from the performance of the products made from it, should be able to meet the performance of the products, especially the high-temperature performance requirements.

Usually refractory raw materials are divided into aluminum-silicon refractory raw materials (silica, clay, high alumina, etc.), alkaline refractory raw materials, heat-insulating refractory raw materials and other refractory raw materials.

Due to the volume effect of quartz variants, silica bricks are also made directly from silica, which is a collective term for vein quartz, quartzite, flint and sandstone. The main component in silica is SiO2, and all others are impurity components. Refractory materials with siliceous raw materials have two categories of crystallized crushed stone and cemented silica.

Refractory clay is the main raw material for the production of aluminum silicate refractory materials, and its refractoriness is required to be higher than 1580 ° C. Various kinds of hard clay, soft (semi-soft) clay and clay shale, collectively known as refractory clay.

Natural refractory clay, usually clay minerals are mainly kaolinite (Al2O3 - 2SiO2 - 2H2O) as its main component, that is, the main body of the hydrous silicate, and interspersed with free quartz, pyrrhotite, rutile, and organic compositions of the mixture. This is not a single mineral, most of which are dispersions composed of particles with a diameter of less than 1.2 μm.

Depending on how the clay was generated, it can be categorized into: primary clay and secondary clay. Primary clay refers to the formation of clay after weathering of the parent rock (e.g. feldspar), which remains in situ. Secondary clay, also known as drift deposited clay, it is from the primary clay in the natural power conditions to transfer to other places and then deposited down the clay, its fine particle size, dispersion, high plasticity. Refractory clay used in the refractory materials industry is mainly of the following two categories.

① Hard clay is characterized by dense organization, hardness, very fine particles, not easily dispersed in contact with water, and very low plasticity. The appearance of such clay is often light gray, gray or gray. Shell-like fracture, some of the surface has a slippery feeling, easy to weathering broken into pieces.

② Soft (semi-soft) clay is often earthy, with loose tissue and good plasticity. The color of this clay, due to different types and content of impurities, vary greatly. From gray, dark gray, up to black; some are also purple, light red or white.

Bauxite

bauxite is the main raw material for the production of brown corundum, Al2O3 content of 88% ~ 90% of high-alumina clinker is the main raw material for sub white corundum; the production of white corundum, dense corundum, etc. with alumina as raw material. Bauxite is also known as high alumina bauxite or bauxite, the main minerals are hydrotalcite (Al2O3 - H2O) and trihydrate alumina (Al2O3 - 3H2O). China's high alumina bauxite reserves are extremely rich: origin from the Yellow River north of Shanxi, Hebei and Shandong, through the central Henan and Guangxi, until the southwest of Guizhou and Yunnan. At present the main production of high alumina bauxite clinker in Shanxi, Henan and Guizhou. There are also some smaller scale mines under development in Hunan. China's high alumina bauxite main minerals for hydrotalcite, boehmite, kaolinite and chlorite, according to its mineral composition, can be divided into three types: hydrotalcite - kaolinite type (DK); boehmite - kaolinite type (BK); hydrotalcite - chlorite type (DP). At present, DK-type high alumina bauxite is most widely used, and DK-type high alumina bauxite clinker is classified into S, Ⅰ, ⅡA, ⅡB, Ⅲ, etc. according to its Al2O3 content.

 Sintered corundum and electrofused corundum

Sintered corundum and electrofusion corundum artificial production of corundum is the use of industrial alumina or high alumina bauxite as the main raw material, in the electric arc furnace melting production. In addition, can also be sintered corundum plate alumina. This method is still to industrial alumina powder as the main raw material, by calcining, fine grinding, ball and sintering system. This method is technically difficult to produce, but the product has high strength, strong erosion resistance and good thermal shock stability. The so-called "sub white corundum" is actually high alumina bauxite based dense electrofusion corundum, Al2O3 content is greater than 98%, the apparent porosity is less than 4%; it is in the reducing atmosphere and control conditions electrofusion made of high alumina bauxite. Corundum crystallization is granular, generally 1 ~ 15mm; the main impurities for rutile, aluminum titanate and its solid solution.

Mullite Caucasus

Mullite mullite is 3Al2O3-2SiO2 crystalline phase as the main component of the refractory raw materials. Mullite is divided into natural mullite and synthetic mullite two categories. Natural mullite is rare, generally synthetic. Mullite is chemically stable, insoluble in hydrofluoric acid. It has good high-temperature mechanical and high-temperature thermal properties, so the synthetic mullite and its products have the advantages of higher density and purity, high-temperature structural strength, low high-temperature creep rate, low thermal expansion, strong resistance to chemical erosion, resistance to thermal shock and so on.

Silica minerals Silica minerals are bluestone, rhodochrosite, silica, commonly known as the "three stones". The chemical composition of the three stones is the same, but the crystal structure is different, is a homogeneous heterocrystal. Heated to high temperatures, are converted to mullite, generating a small amount of molten SiO2, accompanied by volume expansion. Due to the different size of the three stone heating expansion, the degree of its direct utilization is not the same. Due to the small change in the volume of rhodochrosite, whether it is used to make bricks, or as an additive, are directly with raw materials. And silica, blue crystal is often in the form of expansion agent added to the ingredients, especially more for the unshaped refractories. And used to make bricks should be calcined clinker, especially blue crystal must be calcined clinker.

4.1 Magnesium raw materials

(1) magnesite magnesite in China has two main types: crystalline magnesite and amorphous magnesite. China's magnesite is mainly distributed in Liaoning and Shandong provinces, magnesite main impurity is talc, there are some magnesite contains high CaO, followed by minerals for the dolomite, China's magnesite according to the chemical composition of magnesite can be graded as S, Ⅰ, Ⅱ, Ⅲ, Ⅳ five levels, only the S level and I level for calcination of magnesium sand for brick making. With two-step flotation method and two-step calcination method to prepare high-purity magnesia, high purity magnesia prepared in this way as raw materials, can develop a variety of high-performance refractory products.

(2) Other magnesium-containing minerals in magnesium refractories magnesium olivine products, the main mineral composition is magnesium olivine (2MgO-SiO2) and magnesite (MgO). This product is characterized by strong resistance to molten iron oxide, thermal shock stability is better than ordinary magnesium brick. The main raw materials for the production of such products are olivine and serpentine.

4.2 Dolomitic raw materials

Dolomite is a refractory raw material with magnesium carbonate (MgCO3) and calcium carbonate (CaCO3) complex salt as the main component, 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 is 3.5~4, China's dolomite raw materials are abundant, widely distributed, and relatively pure. Liaoning Dashiqiao area reserves are very rich. Shandong, Hubei, Shaanxi, Guangxi, Gansu, Jiangxi, Anhui, Sichuan, Yunnan, Hunan and other provinces are rich in ore sources. This ore body is often symbiotic with limestone and magnesite.

(1) Zircon

Zircon (ZrO2-SiO2 or ZrSiO4) is the main raw material for the production of zirconium products and zirconite products, and the origin of zircon in China 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%, SiO2 32. 99%. It often contains TiCfe and other traces of rare earth oxides, and the presence of these elements makes it radioactive to varying degrees. Therefore, when using this raw material to produce products, the necessary protective measures should be taken.

The thermal conductivity of zircon is low, 3.72 W/(m.K) between 20 and 1000°C. The coefficient of expansion of zircon is also low compared to other crystals. The coefficient of expansion of zircon is also low compared with other crystals, 4.6X10-6°C at 1000°C, and there is a large difference between the coefficients of expansion of its single crystals in the two directions, perpendicular and parallel to the major axis (C-axis). Zircon has high chemical inertness and is difficult to react with acids. Reacting with glass melts to a lesser extent, it is commonly used as a refractory material for the metallurgical and glass industries.

(2) Plagioclase zircon

Natural plagioclase zircon (ZrO2) is often irregularly massive, black, brown, yellow or colorless. There are few natural plagioclase zircon ore bodies in China. ZrO2 used in industry is a chemical raw material, which is a white or yellowish powder made from zircon (ZrO2-SiO2) by chemical method.

Pure ZrO2 has a total of three crystal types at atmospheric pressure: monoclinic, tetragonal and cubic phases in order from low to high temperatures.

Stabilized ZrO2, depending on the degree of stability, and partially stabilized ZrO2 and fully stabilized ZrO2, due to the thermal expansion coefficient of fully stabilized ZrO2 is larger, its thermal shock stability is not as good as partially stabilized, so the latter is often used to do ceramics and refractory toughening materials.

(3) Desilication of zirconium

Foreign fused zirconia corundum (AZS) refractories in the manufacture, in addition to the use of zircon concentrates, most of the addition of a certain amount of "desilicone zirconium" raw materials, the purpose of which: one is to adjust and stabilize the formula; the second is to improve and optimize the performance of the product.

(4)Zircon corundum mullite

The raw materials are industrial alumina, kaolin and zircon, which are finely ground and blended, semi-dry balled and calcined at 300 to 1700°C to produce this material. It has been shown that increasing the zircon content leads to higher sintering temperatures, less total shrinkage, and more closed pores, and that these reactions result in higher density and strength of the sintered zirconocorundum mullite, as well as better thermal shock stability.

One of the main raw materials for the production of chrome (chrome bricks, chrome-magnesium bricks, magnesium-chrome bricks) refractories is chrome ore or chromite. Chromite is a mixture of several minerals, which fluctuates greatly in its mineral composition and varies greatly in its chemical composition and physical properties. It usually consists of chrome-grained vein minerals. These vein minerals are usually magnesian silicates such as serpentine, magnesian olivine and olivine. In addition to Cr2O3, Al2O3, Fe2O3 and MgO are also present in chromite, which is usually expressed as (Mg, Fe) Cr2O3 due to the presence of magnesium and iron.

The above are commonly used refractory raw materials, with the refractory technology, the variety of raw materials is also more varied, especially in recent years, because of environmental issues and a series of reasons, such as raw mineral resources, and constantly developed better performance of synthetic materials and more environmentally friendly renewable raw materials (such as iron silica nitride, Seron, etc.).

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