Deoxidization Of TiO₂ And The Formation Of Interphase During Electrolysis In Molten CaCl₂

Titanium and its alloys have excellent properties such as high specific strength,corrosion resistance and high and low temperature resistance.It is considered to be used in any field,but at present,titanium and its alloys are known only as"space metal","marine metal"and"future metal".The fundamental reason is the high cost of production and processing of titanium.And the cost of preparation is 30%of the total cost,that is,the current magnesiothermic reduction process process?Kroll Process?.This process has long process,high energy consumption and high pollution,which leads to high production cost of titanium and its alloys.The new process of preparing titanium by direct electrolysis of TiO₂ in molten salt?FFC process?,proposed by University of Cambridge in 2000.It is considered to be one of the new technologies to replace the Kroll process.Since the process has been proposed in the past 20 years,the problem of low current efficiency has not been fundamentally solved.There are different views on the mechanisms of the deoxidization of multivalent titanium oxide and the formation of the interphase of the cathode.In this thesis,the phase change of titanium oxide in different time periods during the electrolysis was studied by experiments,and the pathway of TiO₂ electrolysis deoxidation was deduced.On this basis,the formation mechanism of the main interphase?CaTiO₃?,the process of subsequent electrolysis deoxidization and decalcification are systematically studied,the time axis of phase transformation is established to provide a basis for defining the limiting step of process deoxidization.Based on the previous research,the exploratory research on improving the current efficiency of the electrolysis process was carried out,which provided a basis for further development of the process.The main conclusions of this thesis are as follows:?1?The experimental study of TiO₂ electrolysis in the molten salt CaCl₂ shows that the deoxidization process includes four main stages:partial TiO₂ is directly deoxidized by electrons,the removed O^2-is captured by Ca²⁺in the molten salt,and CaO is generated,and CaO will react with the remained TiO₂ to produce CaTiO₃;the electrolysis of titanium suboxides and the CaTiO₃ is continued,oxygen ions are released from titanium suboxides by formation of TiO?Ti₂O?;titanium suboxides?TiO or Ti₂O?continued to deoxidize by electrolysis;titanium oxide solid solution?Ti-O?slowly deoxidized.?2?During the electrolysis of TiO₂ in the molten salt CaCl₂,CaTiO₃ is an inevitable interphase,which is formed by the chemical reaction between the oxygen ions removed from TiO₂ and the molten salt calcium ion and the non deoxidizing TiO₂.The amount of CaTiO₃ formed from the hydrolysis of the molten salt CaCl₂ only accounts for 0.001%of the total volume of the sample.Based on that,it is more determined that the molten salt Ca²⁺is formed in CaTiO₃ and it is the main source of the formation of interphase CaTiO₃.The formation of CaTiO₃ and the disappearance of electrolysis account for about 44.5%of the total electrolytic time.?3?Through the comprehensive detection of the gas released from the anode during the whole electrolysis process,it is known that the anode gas is mainly chlorine in the first stage of electrolytic deoxidation.Under the condition that the electrolysis voltage does not reach the molten CaCl₂ decomposition voltage,the fundamental reason for the release of the anode is that the cathode generates a large number of CaTiO₃ in the early stage of the electrolysis and consumes a large number of Ca²⁺in the molten salt.In order to maintain the electrical neutrality of the molten salt,the Cl^-that is balanced with the consumption of Ca²⁺is forced to discharge in the anode and produce Cl₂,when the CaTiO₃ phase is no longer formed,then the anode gas is CO or CO₂,and the anode is obviously consumed.?4?Direct electrolysis of pure CaTiO₃ agent or CaO and TiO₂ sintered to prepare CaTiO₃ for the preparation of metal titanium,the electrolysis efficiency did not increase obviously,but the addition of CaO has a great influence on the structure of metal titanium in the sample,and the CaO:TiO₂ molar ratio is 1:2 can be used to prepare the titanium foam.Direct electrolysis of titanium suboxides can increase the efficiency of electrolysis,and CaTiO₃ will also form in the course of Ti₂O₃ electrolysis,while Ti₃O₅will be more efficient to electrolysis.?5?By changing the structure of the electrolytic cell,the side reaction of the cathode can be reduced and the current efficiency is improved to a certain extent.It is considered from the simple structure and the improvement of the current efficiency,the use of the alumina piece between the anode and cahode is better.