Fused alumina hardness

Corundum is an aluminum oxide that possesses a hexagonal crystal structure, The compound is extremely hard (2000 on the Knoop scale), sp gr 3.95, and is widely used in abrasives and refractories. Corundum is manufactured by fusing alumina or bauxite in an electric arc furnace operated at about SIOO C. 

SiC, a hard substance(Moh s hardness 9.17), which can be obcained by heating sand and coke. with some sawdust in an electric furnace at high temp. The name carborundum is also applied to other hard materials, such as fused alumina. These materials are used as abrasives for cutting, grinding or polishing(Refs 2,3,5,6 7). 

Abrasive. A hard material used in the form of a wheel or disk for cutting, or as a powder for polishing. The usual abrasives are silicon carbide and fused alumina. Abrasive wheels are commonly... 

Oxide Aluminum oxide, alumina AI1O3, white solid, insoluble, melting point 2020 C. formed by heating aluminum hydroxide to decomposition when bauxite is fused in the electric furnace and then cooled, there results a very hard glass ( alundum ), used as an abrasive (hardness 9 Mohs scale) and heat refractory material. Aluminum oxide is the only oxide that reacts both 111 H20 medium and at fusion temperature, 10 form salts with both acids and alkalis. 

Aluminium, which is also manufactured on a large scale, is produced from its ore, bauxite, from which pure alumina, the oxide, is first prepared. The alumina is dissolved in fused cryolite, a fluoride of aluminium and sodium of the formula Na3AlF6, deposits of which occur in Greenland. The aluminium sinks to the bottom of the crucible, and when a sufficient quantity accumulates it is tapped out. The flux, as the cryolite is termed, is again melted, and a further quantity of alumina is dissolved in it. The metal is fairly hard, white, susceptible of a high polish, ductile and malleable. It is also very light (about two and a half times as heavy as water), and not easily oxidised in air at the ordinary temperature, nor is it attacked by water. 

In this section, the effects of chemical strengthening using ion exchange by paste method on the hardness and fracture toughness of dental porcelains with different microstmctures are shown. Table 1 shows descriptions of five porcelain powders used in this study, two recommended to be used as veneering materials for alumina cores (V and Ob) and three recommended for porcelain fused-to-metal restorations (C, D, and B), containing wide variation of leucite fraction (0 to 22 vol%). 

The catalyst components are mixtures of oxides which have been fused in an electric arc furnace at temperatures of ca 2000 K. The resulting large blocks of black hard material are broken into lumps of usually ca 1 cm diameter. The visual homogeneity of these lumps is, in general, a good indicator for the quality of the final activated catalyst. Poor catalysts exhibit white spots of segregated promoter oxides and bubble holes caused by evaporation of impurities during the fusion process. Primary sources of iron can be iron ores, scrap metal, or iron oxides (oxyhydrates) from other industrial processes. Potassium is added as potassium carbonate, nitrate, or potassium hydroxide, aluminum as alumina and calcium as oxide or carbonate. 

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