Research On The Physicochemical Properties And Structure Of High Titania Slag

Titanium is a kind of transition metal element with stable chemical properties,which enjoys the reputation of"space metal","ocean metal"and"future metal",and has extremely important practical value in the fields of aerospace,ocean engineering and biomedical.The preparation of titanium-based materials needs to go through the process of ilmenite enrichment of high titanium slag,so the preparation of high titanium slag is the first step in the production of titanium-based materials.The high temperature physicochemical properties of high titanium slag are closely related to the interface phenomena such as mass and heat transfer of slag,slag foaming,separation effect between the slag and liquid iron,heat distribution of molten pool and refractory furnace lining erosion,which affect the smelting cycle and smelting energy consumption of titanium slag,and ultimately determine the production efficiency and cost of the whole smelting process.Due to the characteristics of high melting point,high reactivity and strong corrosion of the high titanium slag,it is difficult to measure the physical and chemical properties of high titanium slag,which results in the systematic poor basic data of physical properties at high temperature.In addition,the macroscopic properties of high titanium slag are determined by its microstructure,but the research on high temperature microstructure of high titanium slag is relatively lacking.Therefore,it is of great significance to carry out the basic research on the structure and physicochemical properties of high titanium slag at high temperature for the production of electric furnace smelting titanium slag.Based on the composition of high calcium and magnesium type high titanium slag,effect of slag composition and temperature on the viscosity,electrical conductivity and high temperature oxygen potential of high titanium slag were systematically studied by means of the self-developed ultra high temperature melt physical property testing device.The high temperature structure of high titanium slag was simulated by using molecular dynamics.Based on the improved VFT equation,a effective viscosity prediction model was established for the high titanium slag.Based on the thermodynamic isothermal equation,the mathematical relationship between oxygen potential of high titanium slag and temperature and slag composition is established.Based on the electronic polarizability of slag oxides,the mathematical relationship between the electrical conductivity of high titanium slag and temperature and slag composition is established.The main work and conclusions of this paper are as follows:(1)The results show that the high titanium slag has good fluidity above the liquidus temperature and the viscosity value is about 0.6 d Pa·s,and the effect of temperature and composition on the viscosity is not significant.When the temperature is close to the turning point temperature,the viscosity of high titanium slag increases sharply with the decrease of temperature,showing an obvious characteristic of"short slag".The increase of FeO can significantly reduce the melting temperature of high titanium slag and the viscous activation energy of high titanium slag.The increase of TiO₂ and Ti₂O₃ can significantly increase the melting temperature and viscous activation energy of high titanium slag.When approaching the turning point temperature,the heterogeneous nucleation crystallization of rutile(TiO₂)and pseudoiron titanite(FeTi₂O₅)is the main reason for the rapid increase of the viscosity of high titanium slag.With the decrease of temperature,FeO and TiO₂ can form FeTi₂O₅ high crystallization properties of high temperature minerals,and the fully solidified high titanium slag is composed of most black titanite(M₃O₅)and a small amount of rutile(TiO₂).The mathematical relationship between liquidus temperature and composition of high titanium slag was established.(2)The results show that the high titanium slag has good electrical conductivity in the range of 43?141s.cm^-1,which is 1?2 orders of magnitude higher than that of silicate furnace slag.In the cooling process above the liquidus temperature,the conductivity decreases first,then increases suddenly and then decreases again.The increase of FeO can significantly reduce the conductivity of titanium slag,while the increase of TiO₂and Ti₂O₃ can significantly increase the conductivity.Conductive mechanism of high titanium slag and influenced by electronic-ionic mixed conductive patterns,at high temperature molten state,conductive mechanism can be explained with"electronic transition mechanism",in other words,the electrons with thermal excitation undergo energy level transition between Ti³⁺and Ti⁴⁺,making high titanium slag shows strong electron conduction characteristic,and with the decrease of temperature,the influence of electron conduction wane;When approaching the melting temperature,the precipitate of rutile(TiO₂)with semiconductor properties(hole conduction)is the reason for the sudden increase of electrical conductivity.The subsequent decrease of conductivity is due to the decrease of oxygen vacancy concentration in the TiO₂ lattice,the large amount of precipitation of M₃O₅ phase and the significant decrease of liquid slag content with the decrease of temperature.Based on the electronic polarizability of slag oxides,the mathematical relationship between the conductivity of high titanium slag and temperature and slag composition was established.(3)The results show that the oxygen potential of high titanium slag increases with the decrease of Ti³⁺/Ti⁴⁺mass ratio,and with the increase of FeO content.The oxygen potential of high titanium slag meets the following mathematical relationship with the composition and temperature,and the calculated values are in good agreement with the experimental values.Based on this model,the iso-oxygen potential diagram of high titanium slag was established.(4)Based on the modified VFT model,an accurate mathematical model was first set up to describe TiO₂-FeO-Ti₂O₃ slag and its sub-system within the scope of Newtonian fluid and parts of non-newtonian fluid viscous behavior.The current model can predict the viscosity of TiO₂-FeO-Ti₂O₃ system and its sub-systems in a wide range(TiO₂:0.598?0.890 mol%,FeO:0.027?0.954 mol%,Ti₂O₃:0.058?0.375 mol%)and in the temperature range of 1663 K to 2020 K,and the average relative error is 18.82%.Based on this model,the isoviscosity map of high titanium slag was established.(5)The high temperature structure of TiO₂-FeO system with different FeO content were simulated by molecular dynamics simulation,thus to master the electric furnace high titanium slag of three-dimensional network structure,the results show that the Ti-O,Fe-O ions pair bond length of 1.93?and 2.00?,respectively.The shorter the ion pair bond length,the more stable it is.The coordination number of Ti-O in the melt structure is 5.85,which indicates that the stable Ti-O bond structure in the high temperature melting state is mainly the[TiO₆]^8-octahedral network structure with six coordination.With the addition of FeO,part of the Ti-O bond was broken,the three-dimensional network structure composed of[TiO₆]^8-octahedron was gradually depolymerized by FeO,and the degree of polymerization of[TiO₆]^8-octahedron was greatly reduced,forming a large number of network structures with low degree of polymerization,and even[TiO₆]^8-octahedron monomer(Q⁰)structure.At the same time,part of the Ti-O-Ti coordination structure gradually evolved to the structure of Fe-O-2Ti(FeTi₂O₅)and2Fe-O-2Ti(FeTiO₃)with low melting point,macroscopic performance of high titanium slag fluidity significantly improved.The depolymerization of[TiO⁶]^8-octahedral structure by Fe²⁺shows the effect of network modifier,resulting in the formation of non-bridged oxygen structure Fe-O-Ti.Low FeO content,the O atoms around Ti atoms are mainly bonded to it in the form of 6 coordination,O atoms tend to bond with the three Ti atoms closest to each other,shows that high titanium slag melt on the short-range Ti-O bond structure has a structure similar to that of the rutile(TiO₂),high titanium slag molten into amorphous structure change has a"genetic effect",that is to say,the microstructure of melt is similar to the crystal structure,which is the main reason for the strong crystallinity of molten high titanium slag.