Aluminum oxide, production volume

Electrolytic aluminum production is the most important process in both volume and significance. World production is about 15 megatons per year, consuming about 240 billion kilowatthours of electrical energy. Aluminum oxide (alumina), AI2O3, is subjected to electrolysis at a temperature of 950°C to this end it is dissolved in molten cryolite NujAlFg, with which it forms a eutectic melting at about 940°C. Carbon anodes that are anodically oxidized to CO2 in the process are employed. The overall electrolysis reaction can be written as... 

This lower-ranking chemical, which has nowhere near the production volume of sulfuric and phosphoric acids, is consistently in the top 50 and is very important to some industries. Aluminum sulfate is manufactured from aluminum oxide (alumina, bauxite). The crude ore can be used. A mixture with sulfuric acid is heated at 105-110°C for 15-20 hr. Filtration of the water solution is followed by evaporation of the water to give the product, which is processed into a white powder. 

The product is poured into ice water, thoroughly extracted yith benzene, and the benzene solution washed with water. Benzene is then removed by distillation until a volume of 25-50 cc. is reached and the resulting deep-red solution is passed through a 12 by 2 cm. column of aluminum oxide. The column is developed with ordinary, undried benzene, and that portion of the eluate which runs through before the strawberry-red zone reaches the bottom of the tube is discarded. The solution that follows is collected, and a pale yellow crystalline mass is obtained upon removal of the solvent. Recrystallization from ethanol gives 1.24-1.37 g. (60-65%) of pale yellow crystals that sinter at 119° and melt at 122.7-123.2° (cor.). 

Dimethylaminophenyl 4-Fluorophenyl Tellnrinm Dichloride2 In a 250 ml flask fitted with a reflux condenser are placed 16.5 g (50 mmol) of 4-fluorophenyl tellurium trichloride, 19.0 g (50 mmol) of 4-dimcthylaminophenyl mercury acetate, and 100 ml of absolute dioxane. The mixture is heated under reflux for 8 h during which time it acquires a dark violet color. The mixture is allowed to cool to 20°, the precipitated mercury(II) chloride/dioxane adduct is filtered off, and activated charcoal is added to the filtrate which is then heated under reflux for 30 min. The mixture is allowed to cool and is then passed through a layer of aluminum oxide. The filtrate is concentrated to one-fourth of its original volume by distillation, the concentrate is diluted with 100 ml of hexane to precipitate the product which is filtered off, washed with hexane, dried, and recrystallized from propanol yield 7.2 g (35%) m.p. 145". 

The manufacture of molded articles is usually carried out with mixtures of aluminum oxides with different particle size distributions. This is particularly important when pore-free end-products are required, because this enables a higher volume concentration of aluminum oxide to be obtained than the 74% of ideally cubic close packed spheres by filling the gaps with smaller particles. The particle size distributions used in practice are usually determined using empirically determined approximate formulae (Andreasen or Fuller distribution curves) which take into account the morphology of the individual particles. 

RBAO involves a similar production route, but in this case the aluminum metal powder is a minor component in a powder mix that contains a substantial fraction of alumina. Oxidation of the aluminum metal by gas percolation yields a metastable oxide phase, which is replaced at higher temperatures by the stable corundum phase. Again, the large specific volume of the oxide product reduces the volume fraction of porosity, but in this case the thermal cycle actually sinters the product, and for the optimized powder formulation, expansion during oxidation of the metal at a moderate temperature is followed by the sintering contraction at a higher temperature to yield a dense alumina product whose final shape and volume is still very close to that of the green powder preform. 

A typical thermally conductive epoxy system used as an adhesive, as well as for other purposes, has a thermal conductivity of 0.0026 cal/cm/sec/°C and a volume resistivity of 1.5 x 10 ohm.cm (1.5 x 10 ohm.m). Fillers include alumina (aluminum oxide), beryllia (beryllium oxide), other unspecified inorganic oxides, boron nitride, and silica. Boron nitride is an excellent choice as a thermally conductive filler except that its content reaches a maximum at about 40% by weight in epoxy resins. The resultant products are always thixotropic pastes. BerylUa powder has excellent thermal conductivity by itself, but when mixed with a resin binder its conductivity drops drastically. It is also highly toxic and high in cost. Alumina is a commonly used filler to impart thermal conductivity in resins. ... 

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