According to the different chemical mineral compositions, refractory materials are mainly divided into the following categories:
(1) Silica refractories. This is a refractory material with SiO2 as the main component. The main varieties are various silica bricks and quartz glass products.
(2) Aluminosilicate refractories. This is a refractory material with Al2O3 and SiO2 as the basic chemical composition. According to the content of Al2O3 and SiO2 in the product, it is divided into three categories: semi-silica refractories, clay refractories and high-alumina refractories.
(3) Magnesia refractories. This is a refractory material with MgO as the main component and periclase as the main mineral. According to its secondary chemical composition and mineral composition, there are the following varieties: magnesia bricks, magnesia-alumina bricks, magnesia-silica bricks, magnesia-calcium bricks, magnesia-chrome bricks, magnesia-carbon bricks and iron dolomite bricks. In addition, there is metallurgical magnesia sand.
(4) Dolomite refractories. This is a type of refractory material with CaO (40%~60%) and magnesium oxide (30%~42%) as the main components. Its main varieties are: tar dolomite bricks, fired oil-impregnated dolomite bricks, fired oil-impregnated semi-stable dolomite bricks, fired stable dolomite bricks, lightly fired oil-impregnated dolomite bricks and metallurgical dolomite bricks.
(5) Olivine refractory material. This is a refractory material containing MgO35-62%, MgO/SiO2 mass ratio fluctuates between 0.95-2.0, and composed of forsterite as the main mineral.
(6) Spinel refractory material. This is a type of refractory material mainly composed of spinel. The main varieties are chromium products composed of chrome spinel [(Cr03)≥30%], chrome-magnesium products composed of chrome spinel and periclase [(Cr2O3)18%~30%, (Mg0)25%~5%] and products composed of magnesium-aluminum spinel.
(7) Carbonaceous refractory materials. These materials contain a certain amount of carbon or carbide. The main types include carbon bricks or carbon blocks composed of amorphous carbon; graphite products composed of graphite; silicon carbide products composed of silicon carbide; carbon fiber and carbon fiber composites with resin or other carbon materials.
(8) Zirconium-containing refractory materials. These materials contain a certain amount of zirconium oxide. Commonly used types include zircon products with zircon as the main component; zirconium corundum and zirconium mullite products composed of zirconium oxide and corundum or mullite, and pure zirconium oxide products with zirconium oxide as the main component.
(9) Special refractory materials. This is a type of refractory material composed of relatively pure refractory oxides, carbides, silicides and borides and metal ceramics.
Basic requirements for refractory materials
High-temperature working departments require refractory materials to have the ability to resist high-temperature heat loads. However, due to different working departments, even in different parts of the same furnace, the working conditions are not the same. Therefore, the requirements for refractory materials are also different. Based on the general working conditions of ordinary industrial furnaces, the following requirements are generally put forward for the performance of refractory materials:
(1) Resist high temperature heat load, do not soften, do not melt. Refractory materials are required to have a fairly high refractoriness.
(2) Resist high temperature heat load, do not shrink in volume, only slightly expand evenly. The material is required to have high volume stability, small residual shrinkage and residual expansion, no crystal transformation and serious volume effect.
(3) Resist high temperature heat load and heavy load, do not lose strength, do not creep and collapse. The material is required to have a fairly high room temperature strength and high temperature hot strength, high load softening temperature, and high creep resistance.
(4) Resist rapid temperature changes or uneven heating, do not crack or peel off. The material is required to have good thermal shock resistance.
(5) Resist chemical erosion by molten liquid, dust and gas, do not deteriorate or corrode. The material is required to have good slag resistance.
(6) Resist the scouring, impact and wear of flames, furnace charge and dust, and do not lose the surface. The material is required to have a fairly high density and wear resistance at room temperature and high temperature.
(7) Resist the influence of high-temperature vacuum operation and atmosphere changes, and do not volatilize or damage. The material is required to have low vapor pressure and high chemical stability.
In addition, in order to ensure the overall quality of the structure or lining built by block refractory materials, the refractory materials are required to have good slag resistance and airtightness, and be easy to construct. The material is also required to have a neat appearance, accurate size, certain tolerances, and no defects that are allowed. In order to withstand impact during transportation and possible mechanical vibration and extrusion, the material must have a fairly high strength at room temperature. For some special requirements, its thermal conductivity and electrical conductivity must sometimes be considered.
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