Preparation Of Al-Sc Alloy By Staging Reverse-flowing Thermal Reduction

In this dissertation,the preparation methods of Al-Sc alloys in both laboratories and industries,i.e.,direct mixing method,molten salt electrolytic one,and metallothermic reduction one,are introduced.By comparative analysis,it is found that the aluminothermic reduction?ATR?method of Sc₂O₃should have better application prospects in the preparation of Al-Sc alloys.However,the Sc recovery rate needs further improvement.Based on thermodynamic calculation and parameters fitted from the experimental data in literature,the relationship between Sc concentration and Sc recovery rate at 1223 K for the preparation of Al-Sc alloys with ATR method is derived with a thermodynamic model.The results show that the Sc recovery rate decreases with the increase of Sc concentration of Al-Sc alloys.In addition,the Sc recovery rate does not exceed 50%for Al-Sc alloys with Sc concentration of 1.21at.%.Hence,two methods?adding Ca O to the reaction system and staging reverse-flowing thermal reduction,SRFTR?are proposed to increase the Sc recovery rate.Theoretical analyses show that SRFTR method should be more effective to increase the Sc recovery rate.Based on the thermodynamic model of thermal reduced Sc₂O₃,models corresponding to each thermal reduction stage?three stages in all?at1223 K are established.The theoretical Sc recovery rate corresponding to different Sc concentration alloys for both ATR and SRFTR methods are calculated with specific parameters.Comparing to lower Sc recovery rate and Sc concentration obtained by ATR method,a higher Sc recovery rate and Sc concentration of Al-Sc alloys can be obtained by SRFTR method with thermodynamic regulating the reaction process in each stage.According to the derived thermodynamic model,Al-Sc alloys were prepared by ATR and SRFTR method,respectively.The results show that the experimental results of ATR method are in well agreement with the prediction of the model.The Al-Sc alloy with Sc of about 1.21at.%was prepared by SRFTR method.The comprehensive Sc recovery rate reached about 90%,which is apparently higher than that?less than50%?of ATR method.The experimental results also suggests that the SRFTR method should be an effective method to improve the Sc recovery rate and increase the Sc concentration.The analyzing methods of Sc concentration in Al-Sc alloy,and the content of both Al₂O₃and Sc₂O₃in reaction slag of alloys are developed.It shows that Sc concentration in alloys and Sc₂O₃concentration in reaction slag can be analyzed by the EDTA complexiometric titration method,and the analysis error is within±2%for Sc concentration while it is smaller than±1%after correction for Sc₂O₃concentration.The Al₂O₃concentration in reaction slag can be analyzed by replacement titration.However,the analysis results of replacement titration should be the sum of Sc₂O₃and Al₂O₃.Hence,the actual Al₂O₃concentration can be obtained by subtracting the analysis results of replacement titration with Sc₂O₃concentration obtained by EDTA complexiometric titration method.For this method,the analysis error of Al₂O₃concentration is less than±2%,which is within the allowable range.