A Study On Reduction Of Magnesium Metal By A Coupled Electric And Thermal Field

Magnesium is the lightest metallic material for contemporary engineering field.In recent years,metallic magnesium has been increasing in its application scope and scale year by year,resulting in an increasing demand for primary magnesium.For a major country of magnesium production,traditional Pidgeon process is the main magnesium production method in China.This method requires extremely high temperature for long time to ensure its reduction effect,which causes waste of energy and environmental pollution.At the same time,high temperature conditions will also cause serious loss of the reduction tank and increase the cost of smelting magnesium.To address the mentioned problems,a new method for preparing metal magnesium should be exploited at low temperature.In recent years,current-assisted technology has made considerable progress in metal forming,ceramic sintering and so on.Compared with traditional single heating methods,the furnace temperature is greatly reduced for the obvious feature of this technology.In view of the advantages of current-assisted technology,it will be applied to the field of producing magnesium in this thesis.The high energy consumption and high pollution can be solved for using the coupled electro-thermal field to smelt magnesium.The main research work and result are as follows:For ferrosilicon as the reducing agent,the calcined dolomite was subjected to low-temperature vacuum reduction experiments by an electrothermal coupled field to obtain magnesium.The effects of reduction time,initial DC field strength(corresponding to equipment temperature),and ampere density on the reduction effect of Mg O were studied.The results revealed that when reduction time and ampere density were increased,initial DC field strength was diminished,the reduction effect of Mg O enlarged markedly.In order to reduce the temperature of reduction device,it was necessary to increase the initial DC field strength.When initial DC field strength was 950 V/cm,furnace temperature was 700°C,ampere density was1.18 A/cm~2 and reduction time was 150 min,the reduction rate was 88.35%.The analyses about XRD and EPMA displayed that 98.54 wt%of purity for magnesium could be got for this method.The Joule-heated effect could interpret the silicothermic mechanism of electrothermal coupled field.For cheap semi-coke as reducing agent instead of ferrosilicon,the calcined dolomite was subjected to low-temperature vacuum reduction experiments by an electrothermal coupled field to obtain magnesium.The results revealed that when reduction time and ampere density were increased,initial DC field strength was diminished,the reduction effect of Mg O enlarged markedly.When initial DC field strength was 510 V/cm,furnace temperature was 900°C,ampere density was 10.61 A/cm~2 and reduction time was 80 min,the reduction rate was 95.61%.At the same time,the analyses about XRD and EPMA displayed that 89.37 wt%of purity for magnesium could be got for this method.In addition,Joule-heated effect could interpret the carbothermic mechanism of electrothermal coupled field.With silicothermic reduction as a representative,the influence of electrode category used at both ends of the sample on the reduction of metal magnesium by a coupled electro-thermal field was further studied.The results showed that the use of ferrosilicon,graphite and silicon carbide electrodes could all reduce magnesium metal under the best process conditions,and the reduction effect was basically same.These electrodes were participated in the reduction,and there were varying degrees of mass changes before and after the reaction,showing the mass of positive was decreased and negative was gained,which might be caused by a puny chemical reaction.