Study On The Mechanism Of Carbothermal Products And AlN Chlorination Of Al ₂ 3

At present, considerable experimental effort has been made to study aluminum production by carbothermic reduction and chlorination reaction of alumina under vacuum. It is found that carbothermal products (Al4C3 and Al4CO4) are disadvantage in chlorination reaction and Al2O gas is difficult to recycle and easily disproportionate into alumina. Thereby, they reduce the conversion rate and purity of metal aluminum. Focusing on the two problems above, in this paper, chlorination mechanisms of carbothermal products of alumina and AlN are studied by the first principles calculation, which can assist in finding the solutions to the problems in order to provide corresponding theoretical basis and improved scheme for experimental research.Firstly, under 60Pa pressure,59 reactions which may occur during the chlorination process of carbothermal products of alumina have been studied by thermodynamics calculations to find the main reactions at 1760K,60Pa.Secondly, a systematic study is carried out by density functional theory (DFT) for Al2O-C-AlCl3 and Al2O-C-AlCl2 systems. The results show that after 0.7ps dynamic simulation, Al2O molecule adsorbed on C (001) surface has dissociated and this interaction are not beneficial to chlorination reaction. AlCl3 and AICl2 molecules adsorb on C (001) surface with the top and bridge sites of Al atom, respectively. After lps dynamic simulation, their structures have not dissociated. When AlCl3 and AlCl2 molecules simultaneously adsorb on C (001) surface, AlCl3 molecules rapidly form adsorbed AlCl2 molecules and ultimately generate adsorbed AlCl molecules in the condensation zone. Therefore, AlCl3 gas should be inputted to chlorination furnace on time in order to effectively avoid disproportionation of Al2O molecule and generation of Al4C3 and Al4CO4.Thirdly, a systematic study is performed by density functional theory (DFT) for Al4CO4-C-AICl3 systems. The results show that when adsorbed onto Al4CO4(100) surface, at a given conditions (1760K and 60Pa), carbon tends to bond with aluminum and carbon atoms, and does not bond with oxygen atom on the surface. Carbon interaction with AlCl3 molecule and Al4CO4 (100) surface, the free A1C1 molecules are very difficult to generate and the formation rate are restricted, resulting in low chlorination activity of Al4CO4.On the basis of chlorination mechanisms of carbothermal products of alumina, a novel A1 extraction method is proposed through AIN chlorination process. Firstly, under 1760K,60Pa, the feasibility of AIN chlorination reaction is carried out by thermodynamics calculations. Secondly, theoretical research of AIN chlorination mechanism is performed by density functional theory (DFT). After 1ps dynamic simulation, AICl3 molecule adsorbed on C (001) surface has dissociated, generating adsorbed A1C1 molecule. Thirdly, the products of AIN chlorination are confirmed to metallic aluminum of cubic structure by experiment.