Study On Preparation Of Mg And Sr Using Vacuum Reduction

Mg alloys are the lightest structural materials with many advantages such as high specific strength, specific stiffness, damping capacity, machinability, heatconducting good magnetic screen and easier to recycle etc. Mg alloys are widely used in several industrial fields, such as aerospace, weapon, automotive, machinery electronics industries etc. The application of Mg alloys in automobile and 3C products develops quickly.The traditional preparation methods of Mg-Sr alloys are mixture method and melt-leaching-reduction process. The mixture method is used widely, but the metal Sr is easy to be oxidated and evaporated, the loss of Sr is serious, so the technology economy of the process is worse. Melt-leaching-reduction process is simple and low cost, but the extraction rate is low , the content of Sr in the alloys is low , so this process can not be used to prepare the alloys that contain much Sr composition. At the meantime, electroanalysis method to prepare Mg-Sr alloys has been attracted more attention. A new idea to prepare Mg-Sr alloys—vacuum reduction is proposed in the thesis. But the later two processes have not known well and a plenty of study have to be done.By thermodynamic analysis, the relationships among Gibbs free energy, temperature and pressure in the reaction formula of the reduction MgO, SrO by Si and the critical reaction temperature in specific conditions were found. The result shows that preparing metal in vacuum reduction could greatly reduce the temperature and improve the efficiency of reaction and the metal that has been reduced is not easy to be oxidated.The general rule of the metal vapor condensation is studied and the saturated vapor pressure of Mg, Sr at different temperatures is calculated. The condensation conditions of Mg, Sr vapour is: in order to condensate the metal, the true vapor pressure of the metal in the condenser must be greater than the saturated vapor pressure at the temperature of the condenser, that is, PT > PS .The theoretical analysis is verified through the experimental research. The vacuum reduction experiment of different composition samples at a certain condition has been done. The experimental results were analyzed using such testing methods as XRD and AAS, and the percent reduction of Mg and Sr were calculated.The main results are as follows:①MgO can be reduced by Si and CaO if the pressure is less than 1000Pa and the temperature is higher than 1077℃;②SrO can be reduced by Si if the pressure is less than 1000Pa and the temperature is higher than 927℃;③MgO and SrO can be reduced by Si and CaO if the pressure is less than 1000Pa and the temperature is higher than 1077℃;④Reduce the furnace pressure and increase the reaction temperature are benefit for the reduction of MgO, SrO;⑤The component of Mg and Sr in the product can be controlled by controlling the composition of MgO and SrO.