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Just the quality of the jade refractory raw materials and its classification

   Corundum is polycrystalline alpha alumina materials. Alumina is one of the key components of the earth's crust, have the advantage of rich resources, relatively cheap easy. Corundum with high temperature resistance, high strength, high hardness, electrical insulation, corrosion resistance and other physical and chemical properties. Thus, corundum become extremely versatile refractory materials.

   Corundum as trigonal system mineral, its no = 1.768, ne = 1.760, ne - no = 0.008, relative density 4.02, hardness of 9. Corundum sometimes contain a small amount of impurities such as Fe, Mn, Cr, and Ti. Corundum these impurities can be dyed a different color.

   The melting point of corundum as high as 2050 ℃. High quality corundum products more than 1900 ℃, refractoriness under load softening starting temperature is about 1850 ℃, extreme temperature 1950 ℃, the long-term use of temperature 1800 ℃. However, the thermal expansion coefficient of corundum 8.6 x 10-6 ℃ - 1, belongs to the thermal shock resistance of below average. Corundum hardness of 9, it is only less than high hard mineral and a handful of synthetic diamond. Alumina products, has a high strength room temperature compressive strength of 2000 mpa; Normal temperature flexural strength can reach more than 250 mpa, 1000 ℃ when the flexural strength of 150 mpa. High density of alumina products can better withstand iron, aluminum, nickel, vanadium, the erosion of molten metal; Room temperature, free from corrosion of sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, but under high temperature, sodium fluoride, sulfuric acid on alumina have eroded. Alumina on the glass, slag erosion has certain resistance.

   According to different manufacturing methods corundum can be divided into two broad categories: first, taking bauxite as raw material to manufacture corundum material directly, such as brown fused alumina, alumina corundum; Secondly, extracting alumina from bauxite, then made corundum industrial alumina raw materials, such as dense white corundum, corundum, sintered corundum, etc. 

   All kinds of fused corundum performance comparison table:

All kinds of fused corundum performance comparison
PerformanceWhite fused aluminaDense aluminaHigh-alumina corundumBrown fused alumina
The raw materialIndustrial aluminaIndustrial aluminaBauxite, coal, ironBauxite, coal, iron
Bulk density/（g/cm33.553.813.83.8
True density/（g/cm33.893.993.83.96
The priceHighHighRelatively highMiddle

   By above knowable, from the viewpoint of purity and price, the highest white corundum, dense corundum second, again high-alumina corundum, corundum minimum. Dense white corundum, corundum is the industrial production of alumina. The purity of dense corundum below white corundum, but density is higher than white corundum. High-alumina corundum and corundum are all made of the alumina production. Brown fused alumina is lower than the high purity aluminum corundum, but true density higher than that of high-alumina corundum.

   Sintered corundum is industrial alumina as raw material, fine grinding, ball, then through about 1800 ℃ ultra high temperature sintering mixture refractory raw materials. High density of sintered corundum, low porosity, the bulk density of 3.50 g/cm3, or show porosity 4.5% or less. Therefore, sintered corundum with similar nature of fused corundum: high temperature has good volume stability, not affected by reducing atmosphere, erosion of metal and glass liquid is a certain resistance. The following table shows the performance of the sintered corundum:

The performance of the sintered corundum
OriginAl2O3/%R2O/%SiO2/%Fe2O3/%Bulk density/（g/cm3Show porosity/%