Study On Preparation Of Dy-Cu Alloy By Consumable Cathode Electrolysis In Fluoride Molten Salt System

In recent years,the rapid development of high-tech industries increased the demand for rare earth functional materials.Due to the extremely excellent magnetic properties of rare earth Dy-Cu master alloys,in high performance permanent magnet materials,magnetostrictive materials,magnetic refrigeration,and high strength alloys which the application prospects are considerable.Therefore,Dy-Cu master alloy has become a research hotspot in the field of new materials.The preparation of rare earth master alloy by consumable cathode electrolysis is the main method at present which has uniform composition and no added rare earth burned,low production cost and energy consumption,simple electrolysis process and short cycle,and can be mass mass-produced.It is easier and more effective to add the NdFeB permanent magnet in the form of an master alloy,so that the alloy composition is more uniform after the addition.In this thesis,LiD-DyF₃ was used as electrolyte,Dy₂O₃ was used as raw material,Dy-Cu master alloy was prepared by consumable cathodic electrolysis,and studied the reaction dissolution behavior,thermodynamic calculation and cyclic voltammetry electrochemical analysis of molten salt system and systematically studied the electrolytic preparation of the alloy process,and analyz the microstructure and composition of the alloy.In this paper studied the thermodynamic and electrochemical of LiF-DyF₃-Dy₂O₃molten salt system at first.It was found that LiF and DyF₃ reacted to form LiDyF₄compound.Dy₂O₃ dissolved in the system to form DyOF compound.Dy₂O₃ and graphite anode could not react spontaneously.The main gases generated by the electrolysis reaction are CO,CO₂ and a small amount of CF₄ and C₂F₆ gases.cyclic voltammetry electrochemical mechanism analysis shows that Dy³⁺reduces Dy atoms on Cu electrode rods and alloys them on electrode rods to form Dy-Cu master alloy.Study on the preparation of Dy-Cu alloy by consumable cathode molten salt electrolysis,and found when the electrolysis temperature was 950°C,the molten salt mass ratio DyF₃:LiF was 4:1 and the cathode current density was 2.7 A/cm²,the value of the electrolysis current efficiency reach maximum of 78.54%;When the electrolysis voltage was 4.5 V and the mass ratio was 9:1 the Dy content in the alloy reaches a maximum of 54.25%.So it is preferred to electroly prepare the Dy-Cu alloy under the condition that the molten salt mass ratio is 4:1,the current density is 2.7 A/cm²,or the mass ratio is 9:1 and the electrolysis voltage is 4.5 V.Adopt SEM,EDS,XRD,metallographic microscope etc to analysis of the Dy-Cu alloying process of the cathode Cu rod and the microstructure characterization and composition analysis of the alloy,it can be seen that the reduced Dy metal diffuses and penetrates from the edge of the Cu rod to the center.The process of alloying is from DyCu→DyCu₂→DyCu₅→DyCu₇ to the continuous phase transition process from the edge to the center.With the increase of electrolytic alloying degree,the Dy content increases continuously and the phase transition process from DyCu₇→DyCu₅→DyCu₂→DyCu.The prepared alloy by electrolysis the suitable temperature of 950°C,which has high electrolysis efficiency,and the alloy composition is stable alloys of DyCu₂ and DyCu.Finally,Dy was selectively leached by hydrochloric acid-oxalic acid precipitation gra vimetric method,and Cu was precipitated and precipitated to analyze the composition of Dy-Cu alloy.The method was highly efficient and accurate.