Classification and performance index of 4 kinds of common fused corundum
Fused corundum is made from forged alumina or bauxite, which is melted in a restored atmosphere by electric arc furnace, separated from metals and other impurities, and then condensed. Depending on the material used and the smelting process, the common types are: fused white corundum, fused brown corundum, fine fused fused corundum (low porosity corundum), bauxite-based fused corundum (commonly known as high aluminum corundum, sub-white corundum) and zirconium corundum.
When smelting brown corundum with bauxite as the material, generally only recovery smelting is carried out. Carbonaceous materials used as restorants are generally coke or anthracite. The requirements for anthracite are: fixed C≥80%, ash ≤10%, volatile content <7%, moisture <3%. The amount of coke or anthracite is considered according to the demand for recovering SiO2, Fe2O3 and TiO2 impurities. The participating material is necessary to be fully dry and roasted and dehydrated, the particle size of the charge is generally 10 to 40㎜, not too fine, the particle size of coke or anthracite is 1 to 5㎜.
The melting process is carried out in the three-phase electric arc furnace, and there are two types: void type (furnace cooling method) and tilting type (pouring into other ladle cooling method). The latter process is more reasonable and is being used by more and more factories. The melting temperature is about 2000℃.
1, electric fused white corundum
Now generally referred to as "molten alumina" generally refers to "fused white corundum". It is based on industrial alumina as the material, melting at high temperature in the arc furnace, its Al2O3 content is not less than 99%, white, block material, apparent porosity 6% ~ 10%, the main crystal phase is a-Al2O3, the crystal is long and diamond shape, and often skeletal crystals. Because the material is very pure, there is no chemical reaction in the operation of the electric furnace, but the temperature and cooling speed of the molten liquid have a great impact on the structure of the block material. In terms of homogenization, it is important to obtain as fine a block as possible. When the Na2O of the quality is condensed, it forms β-Al2O3, which is easy to gather in the center of the block material, which will adversely affect the fire resistance and grinding data, so it is necessary to pay attention to the content of Na2O of the quality. In addition, the block guess there is a small amount of nepheline, glass flat.
2, fine fused corundum
Fine fused fused corundum is made of industrial alumina, which is fused in an electric furnace by adding admixtures. When melting should be strictly operated to control the excessive formation of carbide. The appearance of fine fused fused corundum is gray, gray black or gray white, Al2O3 is greater than 98%, the apparent porosity is lower than fused white corundum, generally less than 4%, the bulk density is greater than 3.8g·cm3, the main crystalline phase is a-Al2O3, the subcrystalline phase is FeTiO3, CaAl12O9, Ca3Si8O9, TiN, Ti4O7, etc. There is also a small glass phase. The C content in fine corundum should be less than 0.14%, and the formation of β-Al2O3 should be reduced as much as possible to improve the strength and corrosion resistance of corundum particles. When fused corundum contains carbides (Al4C3, Al4O4C), the carbides can react with water at room temperature:
(Al4C3+12H2O→4Al(OH)3+3CH4↑
Resulting in the powder of fused corundum particles. When the amorphous refractory material is manufactured, the construction body can be loosened, bulging, and even severe cracking. Fine fused corundum is more aggregate in refractory products, and the use of amorphous refractory is expanding.
3, fused brown corundum
Brown corundum is made of natural bauxite, carbon (primarily coke) as a restorative agent, and iron filings as a settler (clarifying agent) to form ferrosilicon sinking in the bottom of the electric furnace.
Brown corundum is brown, generally Al2O3≥94.5%, SiO2≤3.5%, TiO2≤3.5%, Fe2O3≤1%. The mineral composition is mainly a-Al2O3, and the central part of the crystal shape is diamond-shaped, thick plate shape and cracked particles, and there are more silicon oxide and calcium oxide melt crystals around it, which are long plate shape, and the most coarse grain is skeletal lamellae. Because the impurities have not been completely removed, brown corundum also contains secondary crystal phases such as rutile and glass phases, ferroalloys and solid solutions. The hue of brown corundum is largely dependent on the titanium oxide that remains in the product.
Brown corundum is mainly used as an abrasive. In recent years, it has been used in large and medium blast furnace castable and iron anhydrous blast mud aggregate and the material for the manufacture of general corundum bricks (including high alumina silicon carbide bricks).
4, bauxite-based fused corundum
Also known as subwhite corundum or high aluminum corundum, it is actually a fine fused fused corundum based on bauxite. It is produced by melting super grade or first grade bauxite under the conditions of recovery atmosphere and control, and the melting agent is included in the restoration agent (carbon), settling agent (iron chips) and decarburizing agent (iron scale). TiO2 is recovered with excessive restorative agent in the early stage of exercise, and then participate in decarburizing agent or oxygen blowing to remove excess carbon in the late stage of exercise, and then obtain subwhite corundum. Its physical and chemical target is close to the fine fused corundum, the color is also close, the general Al2O3 content is greater than 97%, the apparent porosity is less than 4%; Corundum crystal is generally granular, scale 1 ~ 15㎜; The main impurity deposits are calcium hexaluminate (CA6), rutile, aluminum titanate and its solid solution. However, the mineral composition contains higher titanium compounds, and the coefficient of thermal expansion is higher than that of fine fused corundum. Used in amorphous refractory materials, hot blast furnace bricks and Al2O3-SiC-C bricks.
