Study On Preparation Of Mg-Ca Alloy By Vacuum Aluminothermy Reduction

Activity of magnesium and calcium is relatively high in the magnesium-calcium alloy prepared with traditional methods,making the burning cost serious during the process where the magnesium-doped calcium alloy is doped with Re melting.In this paper,magnesite and dolomite were used as raw materials,aluminum powder as a reductant.One-step preparation process to fabricate magnesium calcium alloy is developed using vacuum thermal reduction method.Since magnesite mixed with dolomite were used,exploring the process will contribute to the usage of low-grade magnesite and dolomite.In this paper,the reaction equation of Mg-Ca alloy,the factors influencing reaction progress,crystallizer shape,the crystal height selection and the mechanism of reduction reaction were studied.The main conclusions are as follows:(1)Calcium was prepared in condition that the molar ratio of Al2O3/(CaO+Al2O3)=0.25,0.37,0.5,0.67 and 0.85.However,the reduction rate was highest with the reaction equation of 33CaO+14Al=21Ca+12CaO·7Al2O3,reaching 86.34%;when MgO and CaO were used as raw materials,magnesium was prepared in condition that the molar ratio of MgO/(CaO+MgO)=0.64,0.75,0.86 and 0.95.The results show that magnesium has the highest reduction rate of 98.87%with the reaction equation of 12Cao+21 MgO+14 Al=21 Mg+12CaO·7 Al2O3.Therefore,the reaction formula of 12Ca0-7Al2O3 was applied to prepare Mg-Ca alloy.(2)The tests on the influence of different crystallization height on magnesium,calcium recovery rate and collected crystal state show the distance from metal evaporation surface to the mold cooling surface(H)is 370mm.(3)The optimized experimental conditions were as follows:the block pressure was 150MPa,the reaction temperature was 1250?,the holding time was 1h,and the aluminum excess coefficient was 10%.The reduction rate of magnesium and calcium were 95.48%and 78.15%respectively via the optimized test conditions,and MgO and CaO as raw materials;the reduction rate of magnesium and calcium were 88.63%and 49.74%with the raw materials of magnesite and dolomite.(4)Tests were conducted by mixing the raw mateirlas with calcixum content of 10%,15%and 20%and appling the aforementioned optimized test conditions,and the results show that the reduction rates of magnesium and calcium decrease gradually with the increase of calcium content.