White fused alumina

Alumina (non metallurgical grade) Australia (44,100), USA (5100), and Jamaica (3400) 50,000,000 calcined alumina (CA) 75-85 tabular alumina (TA) 435-580 white fused alumina (WFA) 600-900 brown fused alumina (BFA) 600-700... 

Some materials have characteristic microstructures that can be used for confirmation of their presence. For instance, fused magnesia, sintered magnesia, and seawater magnesia are structurally different. Similarly, calcined alumina, tabular alumina, and white fused and brown fused alumina all have very different characteristics. 

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. 

Alumina is traditionally formed via thermal dehydration of aluminum hydroxides [94,95]. The final size and crystallinity of the alumina abrasives largely depend on the temperature and time of the thermal treatment process. It has been reported that the total reaction conversion occurs at a temperature of 1500 K. Technical grades of calcined alumina are commonly used for smelting, ceramics, and abrasive particles. Other common forms of alumina produced are fused and white tabular alumina. Fused alumina is produced by melting calcined alumina at a high-temperature furnace for extended time periods. White tabular alumina is composed of large well-developed crystals of... 

White bauxites are chiefly used for the production of aluminium sulphate and the alums. Red bauxites form the raw material for the preparation of alumina, and therefore of aluminium. Intermediate or refractory bauxites, fused in an electric furnace, give artificial corundum. 

Alumen (j5r.)-AJ.XSO,) (NHJ,SO, -t- 24 Aq 74 + 432—is the compound now usually met with as ofum, both in thia country and in England, ft differs from potash alum in being more soluble in H,0 between 20°-30° (68°-30 F.), and less soluble at other temperatures and in the action of heat upon it At 92° (197°.6 F.) it fuses m its Aq at 205° (401° F.) it loses its ammonium sulphate, leaving a white, hygroscopic substauce, very slowly and incompletely soluble in H,0. More strongly heated, it leaves alumina... 

It crystallizes, with difficulty, in thin, flexible plates soluble in HaO very sparingly soluble in alcohol. Heated, it fuses in its Aq, which it gradually loses up to 200° (392° F.), when a white, amorphous powder, (Ala)(SO<)3, remains this is decomposed at a red heat, leaving a residue of pure alumina. 

The flame fusion technique (see Figure 7.20b) was originally devised in 1904 by Verneuil for the manufacture of artificial gemstones, such as corundum (white sapphire) and ruby. This method is now used for the mass production of jewels for watches and scientific instruments. A trickle of fine alumina powder plus traces of colouring oxides is fed at a controlled rate into an oxyhydrogen flame. Fusion occurs and the molten droplets fall on to a ceramic collecting rod. A seed crystal cemented to the rod is fused in the flame and the rod is lowered at a rate that allows the top of the growing crystal (known as a boule) to remain just molten. Renewed interest has recently been shown in this method for the production of rubies for lasers. 

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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