Study On Preparation Of Titanium Silicon Alloy By Molten Salt Electrolysis Of High Titanium Slag

Ti₅Si₃ alloy owns high melting point?2130??,low density?4.32g/cm3?,capacity to maintain high strength at about 1200?,creep resistance and excellent oxidation,so it may be used as a high-temperature structural material.At present this alloy is prepared by self-propagating high-temperature synthesis?SHS?,mechanical alloy?MA?,and powder metallurgy.But these methods have many disadvantages,such as high energy-consumption,low efficient and repairing ultrapure Ti and Si as raw materials,at the same time the process of preparing Ti and Si involve pollution.Ti-enriched slag that the content of TiO₂ lower than 80wt%is easy to acidolysis and high concentration of Ca and Mg,therefore it is mainly used to prepare titanium dioxide by sulphate process,but a large number of waste acid will be producted by this process,it is bad for the environment.For those problems mentioned above,based on the FFC method,Ti₅Si₃ is prepared directly from Ti-enriched slag and SiO₂ mixed pellet via an electro-deoxidization process in both CaCl₂-NaCl and CaCl₂ molten salts in this paper.The effect of Electrolysis time,cell voltage,electrolysis temperature and CaO addition in molten salt on the reduction process and products were investigated.The research results show that:?1?Porous Ti₅Si₃ alloy with particle size of about 5?m was prepared directly from Ti-enriched slag/SiO₂ mixed pellet under the condition of 900?,8h and 3.2V in equal-molar CaCl₂-NaCl molten salt.The reduction process could be divided into three stages:in the initial period,TiO₂ and SiO₂ could be direcly redced to Ti₅Si₃;the intermediates CaTiO₃,CaSiO₃,Ti2O₃ formed with the electrolysis time goes by,and then they would be reduced with TiO₂ and SiO₂ to form Ti₅Si₃;Finally,the main reaction is the reductions of CaTiO₃ and CaSiO₃ to form Ti₅Si₃.The reduction process is roughly the same that in CaCl₂ molten salt.?2?In equal-molar CaCl₂-NaCl and CaCl₂ molten salts,the reaction rate was fast in the initial period,and then became slow in the late due to the formation of intermediates CaTiO₃ and CaSiO₃ is unavoidable.The reductions of CaTiO₃ and CaSiO₃ are the rate-controlling steps of the process.?3?Electrolysis temperature is an important condition in the electrolysis process.As the temperature increases,the rate of deoxidation in cathode and the rate of ion transfer could become faster,the result woud be better in the same electrolysis time.The temperatures at least higher than 900? are required for the preparation of Ti₅Si₃ from Ti-enriched slag/SiO₂ mixed pellet by electrolysis in CaCl₂-NaCl molten salt.?4?Cell voltage has great influence to electrolysis process no matter in equal-molar CaCl₂-NaCl molten salt or in pure CaCl₂ molten salt.The reaction rate was slow when a cell voltage of 2.6V was applied,there are still lots of intermediates in the products that were electrolyzed for 20h and 8h in equal-molar CaCl₂-NaCl and pure CaCl₂ molten salts respectively,indicating that the reactions have not been completed.The reaction rate became fast obviously in both tow kinds of molten salts when 2.8V was supplied,and the reactions could be completed in 20h and 8h,respectively.?5?The reduction rate of Ti-enriched slag/SiO₂ mixed pellet in CaCl₂ molten salt is far more quickly than that in equal-molar CaCl₂-NaCl molten salt.High purity Ti₅Si₃ cound be obtained in CaCl₂ molten salt when the electrolysis time is 14h,but 20h is necessary in equal-molar CaCl₂-NaCl molten salt.?6?The addition of CaO would not improve the total rate of electrolysis reduction.On the contraty,too much CaO would inhibit the electrolysis reduction.In addition,the addition of CaO plays an important role in morphology of the product.The results show that the electrolysis rate would become lower significantly when the addition of CaO is more than 3mol%;when the addition is 1mol%,the morphology of the products is porous large particles gathered by small particles with uniform size.