Alumina carbothermal reduction

Keywords Alumina Carbothermic reduction Carbothermic-chlonnation Abstract... 

A fourth ahoy separation technique is fractional crystallization. If shica is co-reduced with alumina, nearly pure shicon and an aluminum shicon eutectic can be obtained by fractional crystallization. Tin can be removed to low levels in aluminum by fractional crystallization and a carbothermic reduction process using tin to ahoy the aluminum produced, fohowed by fractional crystallization and sodium treatment to obtain pure aluminum, has been developed (25). This method looked very promising in the laboratory, but has not been tested on an industrial scale. 

Also, the metal can be obtained by nonelectrolytic reduction processes. In carbothermic process, alumina is heated with carbon in a furnace at 2000 to 2500°C. Similarly, in Subhalide process, an A1 alloy, Al-Fe-Si-, (obtained by carbothermic reduction of bauxite) is heated at 1250°C with AlCl vapor. This forms the subchloride (AlCl), the vapor of which decomposes when cooled to 800°C. 

Aluminum nitride UFPs have been synthesized by thermal decomposition from many kinds of precursor such as polyminoalanef l/ ) AIH(NR)] (50), aluminum polynuclear complexes of basic aluminum chloride (BAC) or basic aluminum lactate (BAL) (51), and (hydroxo)(succinato) aluminum(lll) complex, A1(0H)(C4H404) jfLO (52). These precursors were calcined under N2 or NH, gas flow. The calcination temperatures, which depend on the individual precursor, can be lower by 600-200°C than the 1700°C in ihe conventional carbothermal reduction method. The XRD measurements at intermediate stages of the calcination process showed the phase change from an amorphous state to a trace of y-alumina with very fine grains and finally to wurtzite-type AIN (51,52). Lowering the calcination... 

Direct oxygen determination in MF-AIF3-AI2O3 (M = Li, Na, K) melts in dependence on the cryolite ratio and the alumina content was performed using the method of carbothermal reduction by Danek et al. (2000b). The MF-AIF3 melts with alumina, successively added in 5-7 steps from 0 mole % and beyond the solubility limit, were heated at... 

In order to synthesize boron carbide nanostructures, several techniques have been developed which include CNT template-mediated growth [149-152], CVD, and plasma-enhanced CVD (PECVD) [147,153,154], carbothermal reductions of boron oxides [155-159], a porous alumina templating technique [160], and electrostatic... 

Aluminum nitride powder is obtained by the carbothermal reduction of alumina, the decomposition of aluminum chloride and ammonia, and the reaction of aluminum powder with ammonia or nitrogen. 

When AIN was introduced for electronic packaging applications in 1985 it was considered inconsistent in properties. This inconsistency was due to problems with the AIN powders used to make sintered products. The powders were made by either of two methods direct nitridation of aluminum metal in a nitrogen gas atmosphere or carbothermal reduction of alumina, which involves the decomposition of the reaction product of aluminum trichloride with ammonia. The first process was cheaper, but the resultant powders were not especially well suited to materials for electronic applications. The carbothermal process produces powders of greater uniformity and purity, with greater control over size and shape, than the nitridation process, and is the more widely used process today." ... 

Comparative study on the metal aluminum produced from alumina by carbothermic reduction and carbothermic-chlorination... 

Experiment of carbothermic reduction of alumina with carbon in normal pressure was carried out at 2100 C. The product in the crucible was shown in Fig. 1. Loose granular substance was left. 

M. Halmann, A. Frei, and A. Steinfeld, Carbothermal reduction of alumina Thermochemical equilibrium calculations and experimental investigation, Energy, 32(2007), 2420-2427. 

Excess carbon must be removed after the carbothermal reduction. This process is normally carried out at around 700°C in dried air and residual carbon becomes less than 0.1 mass %. Carbothermal powder typically contains about 1 mass % of oxygen which stays as a surface oxide layer of AIN powder derived from the carbon removal process. Other impurities are mainly driven by the alumina powder source. The morphology of the AIN powder tends to conform to that of starting aluminum oxide powder. In most cases, carbothermal powders are fine, have... 

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