| Generally,titanium is mainly prepared using Kroll process.Nevertheless,the Kroll process is a batch-type process,which results to high processing cost and restricts the usage of titanium and its alloys.To address this issue,molten salt electrolysis is expected to replace the Kroll process due to the low energy consumption and cost of this process.Up to date,molten salt electrolysis has been widely used for titanium metallurgy and refining.Demonstrating the cathodic process of titanium ions in molten electrolyte is an essential fundamental research for advanced electrolysis process.However,the electro-deposition of titanium ions is more complex than alkali metal ions because there are many types of titanium ions in molten salt.To simplify the cathodic process of titanium ions,researchers studied the influence of electrolyte component for cathodic process.In addition,the depolarization of titanium ions at active cathode is an alternative method to simplify the cathodic process.However,only a few of literatures reported the depolarization of titanium ions at active iron and nickel cathodes over the past decades.In this work,we studied the cathodic process of titanium ions at active liquid metal electrodes in molten salt and even molten oxide electrolytes.Results are also helpful for the titanium extraction from Ti-bearing blast furnace slag.The specific results are shown as follows.(1)The electrochemical process of Ti3+ ion at solid molybdenium and liquid tin cathodes has been investigation using electro-analyses and chemical analyses in molten NaCl-KC1 eutectie salt with TiCl3.Result shows that depolarization of titanium ions on liquid tin cathode is more positive than that on solid tungsten cathode.Meanwhile,the cathodic process of Ti3+ ion on liquid tin cathode is a one-step reduction of Ti3+ 3e = Ti,which is a quasi-reversible process with diffusion-controlled mass transfer.The diffusion coefficient of Ti3+ ion is 1.05×10-5 cm2 s-1.In addition,galvanostatic electrolysis was carried out to investigate the effect of current density on cathodic deposition.The results indicate that the less of the current density,the greater of the depth at which the titanium will be diffused into the liquid tin cathode.(2)The influence of the addition of F' ion for electrochemical process of Ti3+ion has been disclosed on solid molybdenum,liquid tin and lead cathodes in molten NaCl-KC1-KF electrolyte.Cyclic voltammetric curve shows that the depolarization of Ti3+ ion shifts to negative direction on solid molybdenum cathode with the addition of F-ion.On liquid tin and lead cathodes,the Ti3+ ion is electro-reduced by one-step process and formed titanium alloys with substrates.The results of constant current electrolysis show that the well alloys with homogeneity distribution of titanium will be prepared at a cathodic current density of 0.1 Acm-2.(3)The cathodic process of TiF62-complex ion on liquid tin and bismuth electrodes has been investigated in molten LiF-NaF-KF electrolyte.Results show that,whether at liquid tin or lead cathode,the TiF62-is reduced firstly to TiF63-.However,within the electrochemical window,the electro-reduction of TiF63-is observed only at liquid tin cathode not liquid bismuth cathode.Those results mean that there are two reduction steps:Ti4++ e = Ti3+,Ti3++ 3e= Ti(Ti-Sn alloys)at the liquid tin electrode within the electrochemical windows of the melt.However,only one redox peak,which corresponds to the redox of the Ti4+/Ti3+,is appeared at liquid bismuth within the electrochemical windows of the melt.(4)The electrochemical process of titanium ions at liquid iron cathode has been investigated in molten CaO-MgO-Al2O3-TiO2 system at 1600?.The depolarization of titanium ions is appeared and the ferrotitanium alloy is observed on the surface of iron cathode.Based on above analyses,the Ti-Si-Fe and Ti-Si alloys have been prepared successfully by using constant current or constant potential on liquid iron and solid graphite in molten CaO-MgO-Al2O3-TiO2-SiO2 system. |
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