Preparation of High-Grade Titania Slag from Ilmenite-Bearing High Ca and Mg by Vacuum Smelting Method

Ilmenite produced from the Panxi area in China has high impurities such as Ca and Mg. High-grade titanium (Ti) slag can be obtained by the electric arc furnace process, a traditional method of treating ilmenite. Thus, Ti slag prepared from the Panxi ilmenite contains high CaO and MgO, exceeding 5 pct of the slag content. This high CaO and MgO content confers considerable difficulty in producing titania (TiO₂) white using fluidizing chlorination. In this study, a new process named vacuum separation was found to produce high-grade TiO₂ materials. The effects of separation temperature and time on the TiO₂ grade were studied. The high-grade TiO₂ slag, which has 93 pct TiO₂, <0.1 pct MgO, <1.2 pct SiO₂, and <0.5 pct CaO, can be produced at 1823 K (1550 °C) in 45 minutes through the proposed method.     

Green Electrochemical Process Solid-Oxide Oxygen-Ion-Conducting Membrane (SOM): Direct Extraction of Ti-Fe Alloys from Natural Ilmenite

The direct electrochemical extraction of Ti-Fe alloys from natural ilmenite (FeTiO₃) in molten CaCl₂ is reported in this article. The sintered porous pellet of natural ilmenite acted as the cathode of the electrochemical system, and the carbon-saturated liquid tin contained in a solid-oxide oxygen-ion-conducting membrane (SOM) tube served as the anode of the electrolytic cell. The electrochemical process was carried out at 3.8?V, under 1223?K and 1273?K (950?°C and 1000?°C). Oxygen was ionized continuously from the cathode and discharged at the anode; solid porous Ti-Fe alloys were obtained at the cathode. The electro-deoxidation procedure of the ilmenite was characterized by analyzing partially electro-deoxidized samples taken periodically throughout the electro-deoxidation process. The findings of this study are as follows: (1) The electro-deoxidation process followed these steps: Fe₂TiO₅????FeTiO₃????Fe₂TiO₄????Fe, Ti (and/or Ti-Fe alloys); and TiO₂????CaTiO₃????Ti; and (2) two types of particle growth pattern are observed in the experiments. The first pattern is characterized with particle fusion and second pattern is interconnection of particles to form porous structure. A microhole oxygen-ion-migration model is suggested based on the experimental evidence.     

The oxidation of llmenite and its relationship to the FeO-Fe2O3-TiO2 phase diagram at 1073 and 1140 K

The oxidation of synthetic ilmenite was investigated in the temperature range of 1048 to 1273 K using a continuous flow electrobalance, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). The phases observed and their relative distribution in partially oxidized samples were related to the FeO-Fe₂O₃-TiO₂ phase diagrams at 1073 and 1140 K. Initial stages of oxidation were characterized by the formation of rutile and ilmenite-hematite solutions containing up to 10 mole pct hematite at 1073 K and 7 mole pct at 1140 K. Final stages of oxidation included the formation of ferropseudobrookite-pseudobrookite solutions containing up to 56 mole pct ferropseudobrookite at 1073 K and up to 66 mole pct ferropseudobrookite at 1140 K. Although not all of the predicted phase fields were observed during oxidation, generally the expected oxidation sequences were followed.     

Surface tension of liquid Fe-Cr-O alloys at 1823 K

The surface tension of liquid Fe-Cr-O alloys has been determined by using the sessile drop method at 1823 K. It was found that the surface tension of liquid Fe-Cr-O alloy markedly decreases with oxygen content at constant chromium content, and the surface tension at a given oxygen content remains almost constant, regardless of the chromium content. When the surface tension of liquid Fe-Cr-O alloys is plotted as a function of oxygen activity, with an increase in the chromium content, the surface tension shows a much steeper decrease with respect to oxygen activity. The surface tension of liquid Fe-Cr-O alloys at 1823 K is given as follows: σ=1842-279 ln (1+K _O a _O). Here, assuming a Langmuir-type adsorption isotherm, the adsorption coefficient of oxygen, K _O(Fe-Cr), as a function of chromium content, was shown to be K _O=140+4.2 × [wt pct Cr]+1.14 × [wt pct Cr]².     

Upgrading Titanium Ore Through Selective Chlorination Using Calcium Chloride

To develop a simple and effective process for upgrading low-grade titanium ore (ilmenite, mainly FeTiO₃), a new selective chlorination process based on the use of calcium chloride (CaCl₂) as the chlorine source was investigated in this study. Titanium ore and a titanium ore/CaCl₂ mixture were placed in two separate crucibles inside a gas-tight quartz tube that was then positioned in a horizontal furnace. In the experiments, the titanium ore in the two crucibles reacted with either HCl produced from CaCl₂ or CaCl₂ itself at 1100 K (827 °C), leading to the selective removal of the iron present in the titanium ore as iron chlorides [FeCl _x (l,g) (x = 2, 3)]. Various kinds of titanium ores produced in different countries were used as feedstock, and the influence of the particle size and atmosphere on the selective chlorination was investigated. Under certain conditions, titanium dioxide (TiO₂) with purity of about 97 pct was directly obtained in a single step from titanium ore containing 51 pct TiO₂. Thus, selective chlorination is a feasible method for producing high purity titanium dioxide from low-grade titanium ore.     

Aluminum deoxidation equilibrium in liquid Fe-16 pct Cr alloy

For thermodynamic prediction, the deoxidation equilibrium of aluminum in liquid Fe-16 pct Cr alloy was studied by employing the electromagnetic levitation technique with a cold crucible in an Ar gas atmosphere at 1923 K. The interaction parameters were determined to be e _Al(Fe) ^Cr =0.0001 (0.19/T, 1823 K≤T<1923 K) and r _Al(Fe) ^O,Cr =−0.001. The calculated relationship between aluminum and oxygen contents in Fe-16 pct Cr alloy by thermodynamic data obtained in this study is in good accordance with the experimental results of the present study and other research.     

Preparation of titania from llmenite by selective H2S sulfidization

Experiments on preferential sulfidization of ilmenite in a static bed by hydrogen sulfide gas with a flow rate of about 20 cu cm per min were conducted at 800°, 900°, 1000°, and 1100°C for different periods. Sulfidization (conversion of about 95 pct of the iron to its sulfide) at 1000°C for 5 hr or at 1100°C for 4 hr was considered quite suitable. The sulfidized samples were leached with boiling dilute hydrochloric acid and the influence of the concentration, amount of the acid, and the duration of leaching was studied. Leaching was most effective by employing 20 pct excess 2 N boiling hydrochloric acid for 1/2 hr. By this treatment, about 95 pct of the iron in ilmenite could be removed and a residue containing about 91 pct TiO₂ has been obtained. X-ray analysis revealed that TiO₂ in the residue has rutile structure. The merits of the process for commercial utilization have been mentioned briefly.     

Thermodynamics on the formation of spinel (MgO·Al<Subscript>2</Subscript>O<Subscript>3</Subscript>) inclusion in liquid iron containing chromium

The stability diagram of MgO, spinel solid solution (MgO·(Al _X Cr_1−X )₂O₃), and sesquioxide solid solution ((Al _Y Cr_1−Y )₂O₃) as a function of Mg, Al, and O contents at a constant chromium content (18 mass pct) in liquid iron is drawn at 1873 K. The interaction parameters between Mg and other solutes (Al, Cr, Ni, Ti, Si, and C) are determined by the experimental method, which assures equilibrium between Mg vapor and liquid iron, were applied to calculate the diagram. Titanium deoxidation is not recommended for the prevention of spinel formation, because Ti accelerates Mg dissolution from refractory or slag due to its high affinity for Mg (e _Mg ^Ti = − 0.64). The standard Gibbs free energies of formation for the three inclusions (periclase, spinel, and sesquioxide solid solutions) and the tielines between two solid solutions were calculated with the aid of the regular solution model and the thermochemical F*A*C*T database computing system, respectively. The phase stability regions and oxygen content in steel for the current Fe-Mg-Al-Cr (18 mass pct)-O system are compared with those of the previous non-Cr system. Detailed information on the spinel composition according to Mg and Al contents is also available from the present stability diagram.     

Thermodynamics of TiO x in blast furnace-type slags

Equilibrium studies between CaO-SiO₂-10 pct MgO-Al₂O₃-TiO_1.5-TiO₂ slags, carbon-saturated iron, and a carbon monoxide atmosphere were performed at 1773 K to determine the activities of TiO_1.5 and TiO₂ in the slag. These thermodynamic parameters are required to predict the formation of titanium carbonitride in the blast furnace. In order to calculate the activity of titanium oxide, the activity coefficient of titanium in carbon-saturated iron-carbon-titanium alloys was determined by measuring the solubility of titanium in carbon-saturated iron in equilibrium with titanium carbide. The solubility and the activity coefficient of titanium obtained were 1.3 pct and 0.023 relative to 1 wt pct titanium in liquid iron or 0.0013 relative to pure solid titanium at 1773 K, respectively. Over the concentration range studied, the effect of the TiO _x content on its activity coefficient is small. In the slag system studied containing 35 to 50 pct CaO, 25 to 45 pct SiO₂, 7 to 22 pct Al₂O₃, and 10 pct MgO, the activity coefficients of TiO_1.5 and TiO₂ relative to pure solid standard states range from 2.3 to 8.8 and from 0.1 to 0.3, respectively. Using thermodynamic data obtained, the prediction of the formation of titanium carbonitride was made. Assuming hypothetical ‘TiO₂,’ i.e., total titanium in the slag expressed as TiO₂, and using the values of the activity coefficients of TiO_1.5 and TiO₂ determined, the equilibrium distribution of titanium between blast furnace-type slags and carbon-saturated iron was computed. The value of [pct Ti]/(pct ‘TiO₂’) ranges from 0.1 to 0.2.     

Investigation into the equilibrium of the wustite and spinel solutions in the Fe-Ge-O system

Equilibrium conditions of the wustite and spinel solutions in the Fe-Ge-O system in temperature range T = 1100–1300 K are investigated by measuring the emf of the galvanic element with solid electrolyte (the emf method). X-ray diffractometry and electron probe microanalysis were used to determine the phase composition. It is established that the iron magnetite and germanate are partially miscible in one another. The isothermal sections of the phase diagram of the Fe-Fe₃O₄-Fe₂GeO₄ system at T = 1273 K and 1173 K are constructed.     

High temperature chlorination kinetics of a niobium pyrochlore

The chlorination kinetics of a niobium (Cb) pyrochlore has been studied between 1873 and 2223 K, the chlorine concentration in helium varying between 0 and 20 pct. The pyrochlore was subjected to a preliminary thermal treatment at 1473 K in order to remove fluorine which escaped under the form of niobium oxyfluorides. This left NaNbO₃, CaNb₂O₆ and residual refractory oxides. The large chlorination reaction rate difference between NaNbO₃ and CaNb₂O₆ made possible the definition of distinct chlorination reaction rates for these constituents. It was found that the decomposition of CaNb₂O₆ is the controlling step in the chlorination of this constituent, while Nb₂O₅ (NbO₂ + NbO₂ at the prevailing temperatures) chlorination is very fast. The reaction is second order with respect to CaNb₂O₆ concentration and first order with respect to chlorine partial pressure between 1873 and 2023 K, a distinct reaction rate equation being obtained at 2223 K. Reaction rate constants have been calculated and vary between 3 and 10 moleJ.kg ·min for the temperature range considered. The NaNbO₃ reaction rate is first order with respect to total Nb₂O₅ concentration and 2.5 order with respect to chlorine partial pressure for the temperature range covered (1973 to 2223 K). Reaction rate constants are much higher than in the former case, being respectively 148 (1873 K), 214 (2023 K) and 518 (2223 K) mole/kg-min. Reaction orders may be affected by an error varying between 16 and 40 pct. The reaction rate constants are found accurate within 40 pct for CaNb₂O₆ and 25 pct for NaNbO₃.     

Effect of Mg on the evolution of non-metallic inclusions in Mn–Si–Ti deoxidised steel during solidification: experiments and thermodynamic calculations

Abstract

The effects of Mg on the evolution of non-metallic inclusions in Mn–Si–Ti deoxidised steels during solidification were investigated in a study based on experiments and thermodynamic calculations. The inclusions were composed of the MgO–MnO–Ti₂O₃–TiO₂ oxide, MnS, and TiN. With the increase of Mg concentration in steels, the phases of oxide inclusions were changed, in the order of pseudobrookite (Ti₃O₅–MnTi₂O₅), ilmenite (MgTiO₃–MnTiO₃–Ti₂O₃), spinel (Mg₂TiO₄–MgTi₂O₄–Mn₂TiO₄–MnTi₂O₄) and MgO. Thermodynamic calculations for inclusion evolutions were in good agreement with the experimental results.     

Index/Volume 11/1972

Abstract

Samples of Magpie titaniferous iron ore – deposits totalling one billion tons – are already known and have been systematically studied by chemical analysis, X-ray diffraction and electron microprobe. The main constituents of this ore, expressed as oxides, are: FeO 26.6%, Fe₂O₃ 36.4%, TiO₂ 12%. The main minerals are magnetite, ilmenite and a spinel; their composition has been determined with an electron microprobe. Results of magnetic concentration of the ore are presented and interpreted with the help of the electron microprobe data.

Résumé

Des échantillons du minerai de Magpie dont les gisements atteignent 1 milliard de tonnes ont été étudiés de façon systématique par analyse chimique, diffraction des rayons X et microsonde électronique. Les principaux constituants de cette magnétite titanifère, exprimés sous forme d'oxydes sont: FeO 26.6%, Fe₂O₃ 36.4%, TiO₂ 12%. Les principaux minéraux présents sont la magnétite, l'ilménite et un spinelle; leur composition a été déterminée par microsonde électronique. Les résultats des études de concentration magnétique du minerai sont également présentés et interprétés grace aux résultats de l'analyse par microsonde.     

Microstructure and ordering of L12 titanium trialuminides

The present article reports and discusses the results of the microstructural characterization of various modifications of Ll₂ trialuminides containing various titanium contents, including the first ever report on their degree of ordering. The Ll₂ trialuminide alloys Al₃Ti + X, where X = Cu, Fe, Cr, and Mn were studied. The as-cast structure contains a very low level of porosity, and the amount of second phase depends on the particular alloy. After homogenization, the second phase is reduced in almost all the alloys to the level less than 0.5 pct, except for the Mn-high Ti alloy in which it remains at about 20 pct and its composition is 67.9 ± 0.6 at. pct Al, 2.2 ± 0.6 at. pct Mn, and 29.9 ± 0.3 at. pct Ti. In almost all the alloys, porosity after homogenization increases about twofold, except in the Al₃Ti + Cr alloy in which it remains at almost the as-cast level. Limited transmission electron microscopic observations have revealed the existence of very fine (≈10 nm) unidentified precipitates in the homogenized Al₃Ti + Cu alloy. The homogenized Al₃Ti + Cr and Mn alloys have greater lattice parameters than the Al₃Ti + Fe and Cu alloys. It is also found that the long-range order parameterS of the ho- mogenized Ll₂ Al₃Ti + X alloys dramatically decreases with increasing titanium content.     

Evaluation of Isothermal Separating Perovskite Phase from CaO-TiO2-SiO2-Al2O3-MgO Melt by Super Gravity

Perovskite phase was successfully separated from CaO-TiO₂-SiO₂-Al₂O₃-MgO melt by super gravity. Under the hypothesis that the titanium exists in the slag in terms of TiO_2, with the gravity coefficient G = 600, time t = 5 minutes, and temperature T = 1563 K (1290 °C), the mass fraction of TiO₂ in the concentrate is up to 52.94 pct, while that of the tailing is just 5.88 pct. The recovery ratio of Ti in the concentrate is up to 81.28 pct by centrifugal separation.     

Nitrogen solubility and nitride formation in austenitic Fe-Ti alloys

The equilibrium nitrogen solubility and nitride formation in austenitic Fe and Fe-Ti alloys were measured in the temperature range from 1273 to 1563 K. Specimens 0.5 mm thick were equilibrated with four different nitrogen-argon gas mixtures containing 1 pct hydrogen. The nitrogen solubility in austenitic iron obeys Sieverts' law. The equilibrium nitrogen content was determined to be log (wt pct N)_γ-Fe, P_{N2=1 atm} = (539 ± 17)/T − (2.00 ± 0.01). The precipitated titanium nitride was identified as cubic TiN, and the solubility product was determined to be log(wt pct Ti) (wt pct N) = −14,400/T + 4.94.     

Role of Ti on Phase Evolution,Oxidation and Nitridation of Co–30Ni–10Al–8Cr–5Mo–2Nb–(0, 2 & 4) Ti Cobalt Base Superalloys at Elevated Temperature

Titanium is an important alloying addition to γ/γ′ cobalt-based superalloys that enhances the high temperature microstructural stability and make the alloys lighter. In this work, we probe the role of Ti composition on the phase stability and oxidation behavior of Co–30Ni–10Al–8Cr–5Mo–2Nb superalloys. With Ti addition, the γ′-solvus temperature is enhanced and the γ′-precipitate shape changes from spherical to rounded cuboids. Addition of 4 at. pct Ti to the alloy promotes topologically-close-packed (TCP) phase formation that are rich in Co, Cr, and Mo. During oxidation at 900 °C, Ti was found to facilitate the early formation of passivating oxide layers (spinel CoCr₂O₄/CoAl₂O₄) on the exposed surfaces, however, it was not effective in reducing the oxidation-induced mass gain. Microstructural analysis reveals that Ti delays the Al₂O₃ layer formation eventually leading to faster oxidation kinetics. Additionally, we also found formation of (Ti,Nb)N in the γ′ denuded zones near the alloy-oxide interface.

     

Structural Studies of Dispersoids in Fe–15 wt% Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–5 wt% Ti Model ODS Alloys During Milling and Subsequent Annealing

Oxide dispersion strengthened (ODS) steels have very high thermal stability and creep resistance due to reinforcement of hard and stable nano-sized ceramic dispersoids in metallic matrix which act as barriers to dislocation motion. This study established the role of Ti in the structural evolution of yttria during mechanical milling and subsequent annealing in a Fe–15 wt% Y₂O₃–5 wt% Ti model ODS alloy, using electron microscopy and XRD techniques. The alloy was synthesized in a high energy planetary ball mill in Ar atmosphere by varying the milling durations in the range of 0 (un-milled) to 60 h. The XRD result revealed amorphisation of Y₂O₃/Ti during milling and evolution of YTiO₃ complex oxide upon annealing at 1273 K for 1 h. The electron microscopy studies revealed the refinement of alloy powders from ~50  μm to few nanometers during milling. Electron diffraction analysis and high resolution transmission electron microscopy of 60 h milled as well as and annealed powder showed formation of different types of Y–Ti–O complex oxides such as Y₂Ti₂O₇, Y₂TiO₅ and YTiO₃.     

Novelty on reduction of raw and pre-oxidised titaniferous magnetite ore with boiler grade coal

Pre-oxidation of fines of magnetite containing materials is usually carried out to get better yield of metals. Titaniferous magnetite ore (TMO) is one kind of low-grade iron ore (around 45–50% of total Fe) with a significant amount of TiO₂ (23.23%) and V₂O₅ (0.403%). TMO fines have been pre-oxidised at 973?K (700°C) for 9?h under air atmosphere. The effect of reduction of raw TMO fines as well as the pre-oxidised TMO fines using boiler grade coal in the form of cylindrical briquettes has been studied in the temperature range of 1273?K (1000°C) to 1473?K (1200°C) for periods of 10, 20, 30, 40 and 60?min to estimate the relative yield of iron. The influence of temperature and time on reduction experiments has also been investigated with XRD, FESEM analyses along with chemical analysis of the reduced samples. The most novel result is that the yield of Fe by direct reduction of raw TMO (92.42%) is even marginally better than that of reduction of pre-oxidised TMO (90.89%) at 1473?K (1200°C) for 60?min. Thus the single-step reduction of raw TMO is techno-economically more viable than the pre-oxidation followed by reduction technique.     

Internal displacement reactions in multicomponent oxides: Part III. Solid solutions of ternary oxide compounds

In an internal displacement reaction between a reactive metal A and multicomponent oxide (B,C,D,…)O, the noble cation B in the oxide is selectively displaced by reactive metal A, without changing the crystal structure of the oxide. Concurrently, B is precipitated as an internal metal phase in the oxide matrix. The cations (C,D,…) are inert in terms of exchange reaction. The solid-state displacement reaction occurs by the counterdiffusion of A and B inside the reaction zone. The diffusion of “inert” cations and the concentration profile in the product oxide are dependent on the nature of the oxide: (1) “line” compound of narrow homogeneity range or (2) solid solution of wide composition range. These reactions were discussed in previous articles^[1,2] (Parts I and II) along with specific examples. This article is a continuation of studies in Parts I and II and involves the internal displacement reaction between a metal and a quaternary oxide, which is a solid solution of two ternary line compounds. As a model, the reaction between Fe and an ilmenite solid solution of NiTiO₃-MgTiO₃ was studied at 1273 K as a function of time: In ilmenite solid solution (Ni, Fe, Mg) occupy the same cation sublattice, which is different from the Ti sublattice. During the reaction, only Ni cation in the oxide is displaced Fe; Mg and Ti are “inert” in terms of cation exchange. The reaction products consist of internal “Ni” precipitates (Ni-Fe alloy) in a matrix of (Fe, Mg, Ni)TiO₃ solid solution. In particular, the study focuses on cation flux during the reaction and evolution of product oxide composition profile after time t. The three cations in the product oxide that occupy the same sublattice, (Ni, Fe, Mg), show concentration gradients across the reaction zone, even though Mg is inert for cation displacement. The counterdiffusion of Fe and Ni is consistent with their chemical potential gradients. The diffusion of Mg is in the same direction as that of Fe, indicating that, at constant NMgTiO3, the chemical potential for MgTiO₃ is higher in (Mg, Fe)TiO ₃ solid solution than in (Mg, Ni)TiO₃ solid solution. The concentration of Ti, which occupies a different sublattice, remains constant across the reaction zone (i.e., zero diffusional flux for Ti). The ratio, (Fe+Mg+Ni):Ti=1:1, is consistent with the ilmenite structure of the product oxide. The shape of the cation concentration profiles indicates that terms containing cross-coefficients in the general flux equations contribute significantly to cation diffusion during the reaction.