Investigation On Synthesis Via Selective Reduction And Doping Mechanism Of TiC_xO_1-x

This research focuses on the doping mechanism of both Ti and C/O sites in TiC_xO_1-x solid solution,as the anode material of USTB titanium electrolysis process,and corresponding effect on the structural and thermodynamic properties.Particularly,one of the doped solid solution,namely TiC_xN_yO_z,has already exhibited bright prospect of reducing the cost of USTB titanium electrolysis process as a substitution of current anode material TiC_xO_1-x.Moreover,the selective reduction between TiO₂ and SiO₂ during the preparation of TiC_xO_1-x solid solution from ilmenite has been investigated,providing theoretical support for the optimization of the novel process of ilmenite metallurgy and the efficient utilization of titanium ores.Details are summarized as below:A series of TiC_xN_yO_z solid solution with different compositions were synthesized through solid-state reaction of TiC,TiN and TiO,demonstrating the doping of C/O sites in TiC_xO_1-x solid solution by N atom.TiC_xN_yO_z solid solution is found to be a kind of continous solid solution according to XRD patterns.The lattice constant and correponding fitting formula over the whole concentration range were obtained through Rietveld refinement of XRD patterns.Structural properties of TiC_xN_yO_z solid solution were studied by first-principles calculations,and segragated vacancy is found in TiC_xN_yO_z solid solution according to the consistency of calculated lattice constant and experimental results.Moreover,the mixing enthalpy and correponding fitting formula over the whole concentration range were obtained through first-principles calculations,which have properly explained the reaction sequence of carbothermal reduction of TiO₂ in N₂ atmosphere,that TiC_xN_yO_z solid solution instead of Ti₂O₃ exists after the presence of Ti₃O₅.TiC_xN_yO_z solid solution have exhibited great potential for the cost-reducing of USTB titanium electrolysis process as a substitution of current anode material TiC_xO_1-x,since it has a much lower synthesizing temperature.Ti_1-zC_xO_1-x solid solution with a Ti-vacancy concentration of 15%was synthesized through reaction between TiC and TiO₂ at 900℃,demonstrating the doping of Ti sites in TiC_xO_1-x solid solution by vacancy.Based on assessment of weight loss and characterization of sintering product,the reaction between TiC and TiO₂ at 900℃ is found to be a two-part process:1)redox reaction,that TiO₂ is reduced into Ti_nO_2n-1 by TiC;2)solid-state reaction,forming Ti_1-zC_xO_1-x solid solution with constant concentration of Ti vacancy.The lattice constant of synthesized Ti_0.85C_0.7O_0.3 solid solution is 0.4328 nm according to Rietveld refinement of corresponding XRD patterns.Structural properties of Ti_1-zC_xO_1-x solid solution were studied by first-principles calculations,declaring that the formation of Ti-vacancy in O-rich area is much easier than in other fields.Thus,the lattice constant of Ti_0.85C_0.7O_0.3 solid solution was calculated on the basis of first-principles and was found to be consistent with experimental results.The investigation of the phenomenon that SiO₂ was partially reduced during the preparation of TiC_xO_1-x solid solution from ilmenite through selective reduction was performed through thermodynamic analysis and experiments.SiO₂ was found to be reducd into Si,dissolving in metallic Fe as Fe-Si alloy,during carbothermal selective reduction of titanium concentrate ore.while SiO₂ was supposed to stay in the form of oxide.According to selective reduction experiment between TiO₂ and SiO₂,the above-mentioned phenomenon is attributed to the decreasing activity of Si due to the presence of metallic Fe,which promotes the reduction of SiO₂,and also the decreasing activity of SiO₂ caused by the presence of oxides（CaO,MgO and Al₂O₃）,which suppresses the reduction of SiO₂.The equilibrium between Si dissolving in metallic Fe and SiO₂ existed in slag phase was studied through a series of thermodynamically equilibrium experiments.The calculated equilibrium concentration of Si in Fe-Si alloy is consistent with not only equilibrium experimental data but also results of selective reduction of titanium concentrate ore,which properly explains the phenomenon that SiO₂ was partially reduced during the preparation of TiC_xO_1-x solid solution from ilmenite through selective reduction,providing solid theoretical support for the optimization of the novel process of ilmenite metallurgy.