Research On Preparation Of Titanium By Electrolysis In NaF-AlF₃ Molten Salt

Titanium is a kind of structure and functional material with excellent properties.The Kroll process of preparing titanium whose procedure complicated,method is long,and can not be continuous production in industry.Since 2000,it has raised a hot wave of research on direct electrolysis of titanium dioxide powder to titanium in the world.But the current research are mainly focus on the chloride system,which has disadvantages of easy hygroscopic,high metal solubility,and chlorine evolution.Compared with chloride system,fluoride molten salt has advantages of not easy hygroscopic,low metal solubility,wide electrochemical window,high electric energy efficiency,small environmental pollution.In this study,taking metallic strontium advantage of suitable density and high reducibility,preparation of titanium by thermoelectric reduction in NaF-Na3AlF6 molten salt was studied.To prepare titanium by the direct electrolysis TiO2 powder in NaF-Na3AlF6 molten salt was studied at the same time.The ability of different components of LiF-AlF3、NaF-AlF3、KF-AlF3、NaF-KF molten salt to dissolve TiO2 were measured.The results show that NaF-Na3AlF6 eutectic molten salt has a strong ability to dissolve TiO2,and the solubility is 7.2%(mass fraction,same below)at 950℃.Related studies have shown that the dissolved TiO2 existed in the form of clathrate.Drawing part of pseudo binary phase diagram of NaF-Na3AlF6 eutectic molten salt with TiO2 verified the results the ability to dissolve.The dissolution rate of TiO2 in the molten salt is fast,which conducives to achieve continuous electrolysis.To prepare titanium in the NaF-Na3AlF6 molten salt was syudied by thermoelectric reduction TiO2 and strontium was used as the reducing agent.Electrolyser consisted of the graphite crucible with a molybdenum tube inside and molybdenum sheets bottom.Metallic titanium was produced after 5h electrolysis with 1%wtSrO(accounts for the total quality of the molten salt)and 2%wtTiO2 added to the 42%NaF-58%Na3AlF6(total quality 200g)bath.The SrO content in the molten salt determine the generation rate of reduction agent metal strontium.With the increasing of SrO content,the concentration of oxygen in the melt increases;deoxidization ability reduces;the electrolysis time should be extended to preparation metal titanium;better strontium oxide addition is 0.5～lwt%.The effect of the electrolytic cell’s structu +re on the electrolytic process and the product was studied.The electrolytic cell structure of the graphite anode with boron nitride tube and tin as the liquid cathode is better.With using liquid cathode and not adding SrO in the NaF-Na3AlF6 molten salt,the tin titanium alloy was produced by electrolytic after 5h at 1050℃ and 3.5V cell voltage.In the alloy,the majority of titanium extist in the form of elemental titanium,and the form of titanium tin segregation was present in the alloy,the current efficiency is 24.73%.Optimizing the structure of the electrolytic cell,collecting methods of the product,and expanding the scale of the reaction are expected to improve the current efficiency.