Refractory raw materials refer to 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, high alumina bauxite, silica, chromite, magnesite, dolomite, forsterite, zircon, kyanite, sillimanite, andalusite, etc.), With the continuous improvement of the requirements for the comprehensive performance of refractory materials, more and more industrial raw materials and artificial synthetic materials are used in the production of refractory materials (such as industrial alumina, synthetic mullite, artificial refractory fibers, artificial refractory hollow balls, etc.) . 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 can be divided into acidic refractory raw materials, alkaline refractory raw materials and neutral refractory raw materials according to their chemical properties; according to their sources, they can be divided into natural mineral raw materials and synthetic raw materials; under normal circumstances, people divide the raw materials for producing refractory materials into main raw materials , Auxiliary materials, etc.
The raw materials used to produce refractory products, whether they are natural mineral raw materials or artificial synthetic raw materials, must have a sufficiently high refractoriness to be achieved from the perspective of mineralogy; from the perspective of technology, they must meet the basic requirements of the process Requirements: From the performance of products made with it, it should be able to meet the requirements of product performance, especially high temperature performance.
Refractory raw materials are usually divided into aluminum-silicon refractory raw materials (siliceous, clay, high aluminum, etc.), alkaline refractory raw materials, insulating refractory raw materials and other refractory raw materials.
1. Silica raw materials
Due to the volume effect of quartz variants, silica bricks are also directly made of silica bricks. Silica is a collective term for vein quartz, quartzite, flint and sandstone. The main component in silica is SiO2, and the others are impurities. The siliceous raw materials used in refractories are divided into two categories: crystalline crushed stone and cemented silica.
2. Clay material
Refractory clay is the main raw material for the production of aluminum silicate refractory materials. Various hard clays, soft (semi-soft) clays and clay shale whose refractoriness requirements are higher than 1580 ℃ are collectively called refractory clays.
Natural refractory clay is usually made of clay minerals mainly kaolinite (Al2O3 • 2SiO2 • 2H2O) as its main component, that is, water-containing silicate as the main body, and mixed with free quartz, pyrite, rutile and organic matter, etc. Composition of the mixture. Most of these non-single minerals are dispersions composed of particles less than 1.2μm in diameter.
According to the different formation of clay, it can be divided into: primary clay and secondary clay. Native clay refers to the clay formed after weathering of the parent rock (such as feldspar), which remains in place. Secondary clay is also called drift clay. It is the clay that is transferred from the original clay to other places and deposited under natural dynamic conditions. It has fine grain size, large dispersion and high plasticity.
The refractory clays used in the refractory industry mainly fall into the following two categories.
① Hard clay is characterized by dense structure, high hardness, extremely fine particles, difficult to disperse in water, and low plasticity. The appearance of this kind of clay is often light gray, off-white or gray. Conchoidal fractures, some have a slippery surface, and are easily weathered and broken into pieces.
② Soft (semi-soft) clay is often in the form of soil masses, 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, to black; some are purple, light red or white.
Three, high-aluminum raw materials
(1) Bauxite
Bauxite is the main raw material for the production of brown corundum, and high-aluminum clinker with an Al2O3 content of 88% to 90% is the main raw material for subwhite corundum; alumina is used as raw material for the production of white corundum and dense corundum. Bauxite is also called high alumina bauxite or bauxite. The main minerals are diaspore (Al2O3•H2O) and gibbsite (Al2O3•3H2O).
The reserves of high bauxite in our country are extremely rich: the origin ranges from Shanxi, Hebei and Shandong north of the Yellow River, through Henan and Guangxi in the middle, to Guizhou and Yunnan in the southwest. At present, the main producing areas of high-bauxite clinker are in Shanxi, Henan and Guizhou. There are also some smaller mines under development in Hunan. The main minerals of high alumina bauxite in my country are diaspore, boehmite, kaolinite and pyrophyllite, which can be divided into three types according to their mineral composition: diaspore-kaolinite (DK); boehmite -Kaolinite type (BK); diaspore-pyrophyllite type (DP). At present, DK type high alumina bauxite is the most widely used. DK type high alumina bauxite clinker is divided into S, Ⅰ, ⅡA, ⅡB, and Ⅲ according to its Al2O3 content.
(2) Sintered corundum and fused corundum
Artificial corundum is made by melting industrial alumina or high alumina bauxite as the main raw material in an electric arc furnace. In addition, sintering method can also be used to prepare corundum tabular alumina. This method still uses industrial alumina powder as the main raw material, and is prepared by calcination, fine grinding, ball formation and firing. This method is difficult to produce, but the product has high strength, strong erosion resistance and good thermal shock stability. The so-called "subwhite corundum" is actually a dense fused corundum based on high alumina bauxite, with Al2O3 content greater than 98% and apparent porosity less than 4%; it is made of high alumina bauxite by fusion under reducing atmosphere and controlled conditions of. Corundum crystals are granular, generally 1~15mm; the main impurities are rutile, aluminum titanate and their solid solutions.
(3) Mullite
Mullite is a refractory material with 3Al2O3•2SiO2 crystal phase as the main component. Mullite is divided into two types: natural mullite and synthetic mullite. There is very little natural mullite, and it is generally synthesized artificially. 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 high density and purity, high high-temperature structural strength, low high-temperature creep rate, low thermal expansion rate, strong chemical resistance, and thermal shock resistance Etc.
(4) Sillimanite group minerals
Sillimanite group minerals include kyanite, andalusite, and sillimanite, commonly known as "three stones". The chemical composition of the three stones is the same, but the crystal structure is different. When heated to a high temperature, all are converted into mullite, and a small amount of molten SiO2 is generated, accompanied by volume expansion.
Due to the different sizes of Sanshi's thermal expansion, the degree of direct utilization is also different. Due to the small volume change of andalusite, raw materials are used directly whether it is used to make bricks or as an additive. Sillimanite and kyanite are often added to the ingredients in the form of expansion agents, especially for monolithic refractories. The clinker must be calcined to make bricks, 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 my country: crystalline magnesite and amorphous magnesite. my country's magnesite is mainly distributed in Liaoning and Shandong provinces. The main impurity of magnesite is talc. There are also some magnesites that contain high CaO. The second mineral is dolomite. According to the chemical composition, my country's magnesite can be classified as S, There are five grades of Ⅰ, Ⅱ, Ⅲ, and Ⅳ. Only grade S and grade I are used for calcining brick magnesia.
The two-step flotation method and the two-step calcination method are used to prepare high-purity magnesia. The high-purity magnesia prepared by this method is used as a raw material to develop a variety of high-performance refractory products.
(2) Other magnesium-containing minerals
Forsterite products in magnesia refractories, its main mineral composition is forsterite (2MgO·SiO2) and periclase (MgO). This product is characterized by strong resistance to molten iron oxide, and its thermal shock stability is better than ordinary magnesia bricks. The main raw materials for producing such products are peridotite and serpentinite.
4.2 Dolomite raw materials
Dolomite is a refractory raw material whose main components are the double salt of magnesium carbonate (MgCO3) and calcium carbonate (CaCO3). 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.
my country'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 have abundant mineral resources. This ore body often coexists with limestone and magnesite.
5. Raw materials for zirconium products
(1) Zircon
Zircon (ZrO2 · SiO2 or ZrSiO4) is the main raw material for the production of zirconium products and zircon products. The origin of zircon in my country 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 trace rare earth oxides. Due to the existence of these elements, it has different degrees of radioactivity. 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°C. The expansion coefficient of zircon is also low compared with other crystal phases, 4.6X10-6°C at 1000°C, and the expansion coefficient of its single crystal in the two directions perpendicular and parallel to the main axis (C axis) is quite different. . Zircon has high chemical inertness and is difficult to react with acids. Reacts with glass melt to a lesser extent. It is often used in refractories for metallurgy and glass industries.
(2) Oblique zircon
Natural oblique zircon (ZrO2) is often irregular, black, brown, yellow or colorless. There are very few natural plagioclase ore bodies in my country. ZrO2 used in industry is a chemical raw material and is a white or slightly yellow powder made from zircon (ZrO2·SiO2) chemically.
There are three crystal forms of pure ZrO2 under normal pressure: from low temperature to high temperature, they are monoclinic phase, tetragonal phase and cubic phase.
Stable ZrO2 can be divided into partially stable ZrO2 and fully stable ZrO2 according to its degree of stability. Since fully stable ZrO2 has a larger thermal expansion coefficient, its thermal shock stability is not as good as that of partially stable ZrO2. It is commonly used as toughening material for ceramics and refractory materials.
(3) Desiliconized zirconium
In the manufacture of fused cast zirconium corundum (
AZS) refractories, in addition to zircon concentrate, most of them add a certain amount of "desiliconized zirconium" raw materials, the purpose of which is to adjust and stabilize the formula; the other 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 uniformly, pressed in a semi-dry method and calcined at 300-1700°C to prepare this material. Studies have shown that increasing the zircon content will increase the sintering temperature, reduce the total shrinkage, and increase the number of closed pores. These reactions make the sintered zirconium corundum mullite have higher density and strength and better thermal shock resistance.
6. Raw materials for chrome products
One of the main raw materials for the production of chrome (chrome brick, chrome magnesia brick, magnesia chrome brick) refractories is chrome ore or chromite. Chromite is a mixture of multiple minerals. Because of its large fluctuations in its mineral composition, its chemical composition and physical properties also vary greatly. It is usually composed of gangue minerals with chromium grains. These gangue minerals are usually magnesia silicates, such as serpentine, forsterite and olivine. In addition to Cr2O3, there are Al2O3, Fe2O3 and MgO in chromite. General chromite, due to the presence of magnesium and iron, is often expressed as (Mg, Fe) Cr2O3.
The above are commonly used refractory raw materials. With the development of refractory technology, there are more types of raw materials. Especially in recent years, due to a series of reasons such as environmental protection and raw ore resources, artificial synthetic materials with better performance and More environmentally friendly renewable raw materials (such as ferrosilicon nitride, Sialon, etc.).
