Fused corundum brick is the oxidation of bauxite and other raw material product cooling and solidification of melt in the furnace, it has the advantages of simple process, short process, low product cost. Because of the different varieties of fused alumina, can add different reductant in the process of the welding torch. Approaching corundum melting point (2100 ℃) of the structure of the alumina melt is similar to corundum brick, when this kind of melt on cooling, crystallization becomes corundum brick. When corundum brick melt, melt molar volume increased 23.5%, the heat of fusion is 109.2 KJ/mol, and with the increase of melt temperature, reducing its density.
Usually said "fusion alumina" generally refers to the fused white corundum. It is with industry oxidation name or calcined alumina oxide as raw materials, forming high temperature digital in electric arc furnace, and the Al2O3 content is generally over 98.5%, showed white, crystalline is huge , porous, apparent porosity is 6%~10%, the main crystal phase is a - Al2O3, crystal is long strip and the diamond, is the important raw materials to make high-grade refractory materials, is widely used in abrasive industry.
Although the content of industrial alumina Al2O3 is more than 98.5%, there is a small amount of Na2O, SiO2 and a trace of Fe2O3. Although fused process has a certain purification effect on preparation white corundum, can not completely ruled out these impurities. Among them, the Na2O and Al2O3 in molten state generating β Al2O3 melting point is low, density is small, therefore, when clinker cooling crystallization, in central part of the frit. Although through selected can eliminate, there are still a few remaining in corundum melt, seriously influence the refractory performance of corundum, therefore, Na2O of industrial alumina content must be strictly controlled。
In order to eliminate or reduce the harmfulness of Na2O, join the quartz sand or aluminum fluoride. The former makes the β Al2O3 become nepheline, the latter promotes the Na2O evaporate.
Dense fused alumina is with industrial alumina as raw materials, after joining admixture in electric arc furnace, melting and forming. Its appearance is gray, ash black or hoary, Al2O3 is not less than 98%, apparent porosity was lower than fused white corundum, generally not more than 4%, the volume density is not less than 3.8 g/cm. Dense fused cast alumina block is a new type of high-grade refractory material, volume stability under high temperature, acid-proof, alkali resistance, has the characteristics of the makings density, low porosity, etc.