Study On The Mechanism Of A1N Vacuum Thermal Decomposition Reaction

Comparing to the existing Hall-Heroult process,which has the disadvantages of long process flows,complex devices,high energy consumption,greenhouse gases and perfluorocarbons(PFCs)environmental pollution.Combined with the current Al production methods such as the direct carbothermal reduction process,the indirect carbothermal reduction process(carbochlorination route,carbonitridation route),blast furnace aluminum smelting process and ion liquid electrolysis process and so on,in order to provide theoretical and technical basis for the new process of aluminum production,a novel method was proposed to extract Al by thermal decomposition of aluminum nitride under vacuum,with advantages over conventional techniques,including short process,few environmental pollution,low production costs,simple operation and small occupation space.Firstly,the thermodynamic calculation of the possible reaction formula of thermal decomposition of aluminum nitride under vacuum is carried out,and the?G-T curve is drawn.The calculated results indicate that under1873K?2073K,30 and 60Pa,the thermal decomposition of aluminum nitride under vacuum can be performed,and the dissociation temperature calculated is 1900K at 30 Pa,1920K at 60Pa,respectively.Secondly,According to the thermodynamic calculation results,10ps dynamic simulation is carried out by using the program package Cambridge Sequential Total Energy Package(CASTEP)in the Materials Studio software for the vacuum thermal decomposition of W-AlN and Z-AlN under the conditions of 1873K?2073K,30Pa and 60Pa;1973K,30Pa and 60Pa,respectively.Compared with the crystal structure,partial density of states,Mulliken charge distribution and differential charge density map of W-AlN and Z-AlN before and after 10ps dynamic,it is concluded that the vacuum thermal decomposition of W-AlN under 30pa and 60pa is feasible,and W-AlN dynamics simulation has the most obvious changes on the condition of 30pa.Besides,the Al-N bonds between the first and second surface are broken,then the Al-N bonds of outermost level are broken,While Z-AlN dynamic simulation was not obvious changes under given constraint condition before and after 10ps dynamic simulation,indicating that Z-AlN was not easily decomposed.Finally,combined with thermodynamic calculation and molecular dynamics simulation results,the vacuum thermal decomposition of Analytical grade of wurtzite AIN grains experiments were carried out in vacuum distillation furnace under pressure of 7.5?70Pa and temperature of 1600?1700? The experimental results showed that aluminum nitride was decomposed and the product was mainly metallic aluminum.According to the results of XRD,the metal of aluminum,which is collected from 1nd and 2nd stage is a cubic structure and consistent with the standard JCPDS aluminum(Card No.85-1327)is collected on the primary and secondary condensing disks.And the maximum purity is 95.826 wt%and a conversion of metallic aluminum is 98.83%.