Ti-O Solid Solution Research Articles

Electro-deoxidation behavior of Ca4Ti3O10 in molten CaCl2-NaCl

Ca4Ti3O10 is one of the important minerals enriched by titanium-containing blast furnace slag. The electro-deoxidation behavior of Ca4Ti3O10 was investigated, and titanium metal was successfully prepared in molten CaCl2-NaCl by the FFC Cambridge process. Firstly, the band structure and state density of Ca4Ti3O10 were calculated by the first principle, and the bond-breaking trend was analyzed. Then, the reduction process of Ca4Ti3O10 and the preparation mechanism of titanium were carried out by electrochemical methods. Finally, constant voltage electrolysis experiments were conducted at 900 °C and a voltage of 3.2 V for different durations. The electrolytic products were characterized using XRD, SEM-EDS, and XPS. The results revealed that the reduction process of Ca4Ti3O10 proceeded as follows: Ti4+→Ti3+→Ti2+→Ti+→Ti. The deoxidation path of the product after constant voltage electrolysis was observed as Ca4Ti3O10 → TiO2 → CaTiO3→ TiO2→ Ti2O3 → TiO → Ti2O → Ti. The whole deoxidation process can be divided into three stages: (I) the Ti-Ca bond in Ca4Ti3O10 is broken to form CaTiO3 and TiO2; (II) CaTiO3 and TiO2 are reduced from the surface of the cathode sheet inward to form a Ti-O solid solution; (Ⅲ) Ti-O solid solution is further deoxidized to form Ti metal. This method provides a theoretical basis for the subsequent electrolysis of titanium-rich slag, thereby contributing to developing a more sustainable and efficient method for extracting titanium from enriched titanium slag.

The Deep Deoxygenation Behavior of Fine Hydrogenated Ti Alloy Powders

In this work, a novel thermochemical method was introduced to produce fine titanium alloy powders with low oxygen content by utilizing hydrogenated titanium alloy powders mixed with Ca and CaCl2 powders. The stability of Ti-O solid solution decreased when the hydrogen was released in situ during the thermochemical process. Hydrogen could increase the oxygen potentials of Ti-O solid solution alloys, and the average particle size could be mainly preserved at 35.23 μm after the heat treatment. Experimental results reveal that the oxygen content in final products could be remarkably decreased to 0.146 wt.% at low temperature of 680°C compared to the results of 0.67 wt.% when utilizing pre-dehydrogenated powders instead. Moreover, hydrogen can be easily reduced by heat treatment, and the experimental results show the remaining hydrogen concentration is 0.078 wt.%. This work is expected to provide a one-step solution by integrating the dehydrogenation with the deoxygenation process in to produce fine metal powders with low oxygen content.

Investigation of the electrochemical reduction of Na2Ti3O7 in CaCl2 molten salt

Sodium titanate (Na2Ti3O7), as an intermediate product for producing TiO2 through alkaline process, was used as precursor to prepare Ti metal successfully by FFC Cambridge Process. For the aim to gain insight into the electro-reduction mechanism, the sintered Na2Ti3O7 pellets(∼1.83 mm thinkness, open porosity ∼20%) were electrolysed using them as cathodes against graphite counter electrode in the molten CaCl2. The experiments were carried out at 900 °C and the applied voltage was 3.1V. Partially reduced samples were prepared by terminating the reduction process after different electrolysis times. The obtained samples were characterised by means of X-ray diffraction analysis, SEM and EDS. The results show that Na2Ti3O7 reacts easily with molten CaCl2 as 2Na2Ti3O7 + 2CaCl2 → Ca2Ti2O6 + 4TiO2 + 4NaCl and Ca2Ti2O6 → 2CaTiO3. The electrochemical reduction of sodium titanate proceeds via sequential formation of CaTiO3, titanium sub-oxides (such as Ti4O7, Ti3O5, Ti2O3 and TiO), CaTi2O4, Ti-O solid solution and Ti. The whole reduction can be divided into three stages: the first stage is that Ca2+ ions from electrolyte are inserted into Na2Ti3O7 particles leading to the formation of titanium sub-oxides and calcium titanates(CaTiO3 and CaTi2O4); the second stage is that calcium titanates are reduced into Ti-O solid solution from outside to inside of the pellets; the third stage is that the formed Ti-O solid solution is further deoxidised to form Ti metal.

Novel Method for Making Biomedical Segregation-Free Ti-30Ta Alloy Spherical Powder for Additive Manufacturing

Ti-Ta alloys offer a good combination of high strength and low modulus among Ti-based alloys, and are ideal for biomedical applications. However, making Ti-Ta alloys has always been challenging because they tend to suffer from compositional segregation during melting due to the large difference between the melting points of Ti and Ta. This article describes a novel process for making spherical Ti-30Ta alloy powder through a unique powder metallurgy technique, namely the granulation–sintering–deoxygenation process. The results indicate that the compositional segregation problem can be overcome using this process technology. Combined with use of a deoxygenation process, the critical interstitial element, oxygen, can be controlled to < 400 ppm for powder with particle size < 75 µm. The destabilization effect of Ta on Ti-O solid solutions, and the resulting improved deoxygenation process for Ti-Ta, are discussed, as well as the phase composition and microstructure of the powders.

Kinetically enhanced metallothermic redox of TiO2 by Mg in molten salt

Molten salt is used as a reaction medium in a number of thermochemical and electrochemical processes including a new method named “hydrogen assisted magnesiothermic reduction (HAMR)” for the production of Ti metal powder from TiO2. A key enabling element of the HAMR process is based on the thermodynamic effect of hydrogen on the relative stability of MgO versus that of Ti-O solid solutions. Another key of the process is the catalytic effect of molten salt, which is used as the reaction medium. Although the general positive effect of the molten salt in the HAMR has been recognized, the role and mechanisms of molten salt during the reaction are still not well understood. The focus of this work is thus placed on the effects of the molten salt on the kinetics of the redox of TiO2 by Mg, and the possible mechanisms by which the molten salt facilitates the reaction. Experiments were specifically designed to elucidate the role of molten salt when TiO2 is separated from the reducing agent Mg when Mg is in vapor, liquid, or solid states. The results show that the kinetic rate of the reduction can be significantly enhanced by increasing the amount of salt. Although the reduction can take place directly between vapor, liquid, or even solid Mg and TiO2, the ionization of Mg metal and the transport of Mg22+ through the molten salt play a major role in the reduction of TiO2 by Mg. The molten salt must be a Mg2+-bearing salt. A molten salt depleted of Mg2+ is not effective. The possible pathways by which the reaction species form and react with TiO2 are also discussed.

Elevated tensile properties of Ti-O alloy with a novel core-shell structure

Oxidized Ti powder was consolidated successfully by using spark plasma sintering into a fully dense bulk core-shell (CS) structured Ti alloy with isolated soft coarse-grained Ti cores and hard Ti-O solid solution shells. The temperature effect on the mechanical responses of CS Ti was assessed experimentally through tensile testing during 500–700°C at a constant strain rate of 0.0005s−1 and compared with those for its annealed counterpart and a pure Ti compact. All samples exhibit a decreased strength with the temperature. CS Ti exhibits a significantly enhanced tensile strength at all the testing temperatures compared with CP Ti. Contrary to the substantial brittleness of the annealed sample at 500°C and 600°C, CS Ti presents a much enhanced ductility at elevated temperatures, being 12% at 500°C and 77% at 600°C. At 700°C, all the samples show comparable elongation. The superior mechanical performances of CS Ti at elevated temperatures can be attributed to its novel heterogeneous microstructure along with high O content.

Hydrogen assisted magnesiothermic reduction of TiO2

Abstract The development of low cost titanium metal production processes has challenged the Ti research and industrial communities around the world for decades. The strong affinity of titanium to oxygen dictates that it is very difficult to produce low-oxygen Ti metal from TiO2 directly. In this paper, a hydrogen assisted magnesiothermic reduction (HAMR) process for producing Ti metal powder from TiO2 powder at relatively low temperatures (⩽750 °C) is established. The overall approach is based on the thermodynamic tuning of the relative stability of MgO versus that of Ti-O solid solutions by temporarily alloying the system with hydrogen. It is shown that Ti-H-O solid solutions are less stable than their corresponding Ti-O solid solutions, which changes the reaction of Mg with Ti-O from being thermodynamically unfavorable to being favorable. The key steps for producing pure Ti metal powder from TiO2 involve Mg reduction of TiO2 in a hydrogen atmosphere which produces porous TiH2, a heat treatment procedure to consolidate the powder and reduce specific surface area of the powder, and the final step to deoxygenate the powder using Mg in a hydrogen atmosphere to further reduce the oxygen content. This paper systematically examines the changes of oxygen content, phase transformations, and the evolution of the morphology of the particles during the entire process. The results show that this approach has great potential to be a viable method for the production of low-oxygen Ti metal powder from TiO2. In addition, the effect of hydrogen on the oxidation of Ti powder is analyzed using XPS, which reaffirms that titanium hydride is more impervious to surface oxidation than Ti metal, another crucial advantage of using hydrogen atmosphere.

Sodium Insertion/Extraction in Carbon-Coated Nanoscale Anatase TiO2

Rechargeable sodium batteries, as the replacement of rechargeable lithium batteries, are attracting much attention for large-scale applications such as electric vehicles and stationary energy storage due to the abundant resource of sodium compared to lithium. Up to now, there are only a few materials which have reasonable performances as negative electrodes of rechargeable sodium batteries, such as alloy materials [1], hard carbon [2], and sodium titanium oxides [3]. Recently, TiO2, an attractive alternative negative electrode material to graphite for rechargeable lithium batteries, was also investigated for rechargeable sodium batteries [4, 5]. However, the reported reversible capacities of TiO2 electrodes are less than 200 mAh g-1 and the Na insertion/extraction mechanism is still unclear. In the previous study, carbon-coated anatase TiO2 (TiO2/C) nanopowders were investigated as negative electrode material for rechargeable sodium battery with Na[FSA]-[C3C1pyrrr][FSA] (FSA = bis(fluorosulfonyl)amide; C3C1pyrr = N-methyl-N-propylpyrrolidinium) ionic liquid electrolyte [6]. In the present study, the electrochemical performance of TiO2/C electrode was further investigated in Na[FSA]-[C3C1pyrrr][FSA] ionic liquid electrolyte, and the Na insertion/extraction mechanism was explored. The TiO2/C electrode shows a high reversible discharge capacity of 275 mAh g-1 at 10 mA g-1 at 363 K. The observed capacity is higher than that reported for anatase TiO2 nanorods (193 mAh g-1 at 10 mA g-1) in organic electrolytes at room temperature [5]. Moreover, this capacity is comparable to that of a hard carbon negative electrode (260 mAh g-1) in Na[FSA]-[C3C1pyrrr][FSA] electrolyte [7]. Since the density of anatase TiO2 (ca. 3.9 g cm-3) is much higher than that of hard carbon (ca. 1.52 g cm-3), the TiO2/C nanopowder electrode is a promising negative electrode material for the rechargeable sodium batteries with high volumetric energy densities. The Na insertion/extraction mechanism was investigated by means of ex-situ X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) spectroscopy and electron diffraction. Ex-situ XRD analysis of the TiO2/C electrodes in the different charged/discharged states show that during the charge process, the anatase TiO2 crystal phase disappears and a new crystal phase is formed. During the discharge process, the newly formed crystal phase disappears and no anatase TiO2 phase appears again. According to the TEM, EDX and electron diffraction studies, the fully discharged TiO2/C electrode is suggested to consist of amorphous TiO2, amorphous Na2TiO3 and cubic TiO phases, and the crystal phase in the fully charged TiO2/C electrode is possibly a solid solution of cubic Na2TiO3 and cubic TiO phases. Thus, amorphous TiO2, amorphous Na2TiO3 and cubic TiO are regarded as active electrode materials, and reversibly react with Na ions to form Na2TiO3•TiO solid solution. The TiO2/C negative electrode also exhibits a high rate capability and good cycling performance. When the charge-discharge rate is increased, the shapes of the charge-discharge curves remain unchanged. The discharge capacities decrease gradually with an increase in the current rate. The TiO2/C electrode shows reversible discharge capacities of 174 and 93 mAh g-1 at current rates of 500 and 2000 mA g-1, respectively, corresponding to about 69 and 37% of the capacity at 20 mA g -1. The discharge capacity is 174 mAh g-1 after 400 cycles at a current rate of 200 mA g-1, exhibiting only 10% drop in capacity. After 1000 cycles, the capacity decreases by approximately 21%. Acknowledgements This study was partly supported by the Advanced Low Carbon Technology Research and Development Program (ALCA, No. 3428) of the Japan Science and Technology Agency (JST) and the “Elements Strategy Initiative to Form Core Research Center" program of the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT).

Thermodynamic Destabilization of Ti-O Solid Solution by H2 and Deoxygenation of Ti Using Mg.

Reactive metals including Ti, Zr, Hf, and V, among others, have a strong chemical affinity to oxygen, which makes them difficult to produce and costly to use. It is especially challenging to produce pure or metal alloy powders of these elements when extremely low oxygen content is required, because they have high solubility for oxygen, and the solid solution of these metals with oxygen is often more stable thermodynamically than their oxides. We report a novel thermochemical approach to destabilize Ti(O) solid solutions using hydrogen, thus enabling deoxygenation of Ti powder using Mg, which has not been possible before because of the thermodynamic stability of Ti(O) solid solutions relative to MgO. The work on Ti serves as an example for other reactive metals. Both analytical modeling and experimental results show that hydrogen can indeed increase the oxygen potential of Ti-O solid solution alloys; in other words, the stability of Ti-O solid solutions is effectively decreased, thus increasing the thermodynamic driving force for Mg to react with oxygen in Ti. Because hydrogen can be easily removed from Ti by a simple heat treatment, it is used only as a temporary alloying element to destabilize the Ti-O systems. The thermodynamic approach described here is a breakthrough and is applicable to a range of different materials. This work is expected to provide an enabling solution to overcome one of the key scientific and technological hurdles to the additive manufacturing of metals, which is emerging rapidly as the future of the manufacturing industry.

Chemical composition, crystallographic structure and impedance spectroscopy of titanium oxynitride TiN xO y thin films

Titanium oxynitride TiN xO y thin films have been deposited by DC-pulsed magnetron sputtering from Ti target in the Ar + N 2 + O 2 reactive atmosphere controlled by plasma emission spectroscopy. Correlation between chemical composition and crystallographic structure of thin films has been determined and presented in the form of the pseudo-equilibrium ternary phase diagram. The atomic N/Ti and O/Ti ratios have been derived from Rutherford backscattering (RBS) measurements. X-ray diffraction at grazing incidence has revealed formation of defective TiN–TiO solid solutions. The surface roughness estimated from atomic force microscopy (AFM) surface images decreases with increasing oxygen content in the films, in accordance with the progressive sample amorphisation. Impedance spectroscopy measurements indicate that the electrical conductivity changes its character from metallic to semiconducting with increasing oxygen content in TiN xO y thin films.

Phase diagram of the system Ca-Ti-O at 1200 K

Phase relations in the system Ca-Ti-O have been established by equilibration of several samples at 1200 K for prolonged periods and identification of phases in quenched samples by optical and scanning electron microscopy, XRD and EDS. Samples representing 20 compositions in the ternary system were analyzed. There was negligible solid solubility of Ca in the phases along the binary Ti-O, and of Ti in CaO. Four ternary oxides were identified: CaTiO3, Ca4Ti3O10 and Ca3Ti2O7 containing tetravalent titanium, and CaTi2O4 containing trivalent titanium. Tie-lines link calcium titanite (CaTi2O4) with the three calcium titanates (CaTiO3, Ca4Ti3O10 and Ca3Ti2O7), CaO, oxygen excess TiO1+δ and stoichiometric TiO. Tie-lines connect CaTiO3 with TiO2−x , Magneli phases Ti n O2n−1 (28 ≥ n ≥ 4), Ti3O5, Ti2O3 and TiO1+δ . CaO was found to coexist with TiO, and Ti-O solid solutions α and β. The phase diagram is useful for understanding the mechanisms and kinetics of direct calciothermic reduction of TiO2 to metal and electrochemical reduction of TiO2 using graphite anode and molten CaCl2 electrolyte.

Characterisation of the palladium-modified thermal oxidation-treated titanium

A novel and cost-effective surface modification technique, namely palladium-modified thermal oxidation (PTO), has recently been developed, which can dramatically enhance corrosion and wear resistance of titanium. The present paper reports characterisation of the surface engineered (thermal oxidation and palladium-modified thermal oxidation) titanium, using X-ray diffraction (XRD), glow discharge spectrometry (GDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). The surface case of the oxidised materials comprises a surface rutile TiO 2 layer and an underlying diffusion zone (Ti-O solid solution). It has been found that the palladium treatment can decrease the grain size of the surface oxide, improve the oxide layer adherence, and delay the stratification and spallation of the surface oxide.

Effects of a titanium interlayer on the formation of platinum silicides

Interfacial reactions of the Pt-Ti-Si structures were studied in this work. The role of the Ti interlayer is to react with native oxide on the Si substrate and form the Ti-O solid solution or titanium oxide depending on the Ti-layer thickness. A Ti-oxide layer between Pt and Si was found when the Ti-layer thickness was less than 5 nm. This layer acted as a diffusion barrier and inhibited the reactions between Pt and Si. For the Ti-layer thickness above 5 nm, the Ti-O solid solution was formed instead. Auger depth profiles showed that the Ti-O layer moved outward as the silicidation process proceeded. An improvement in the smoothness of the PtSi-Si interface was obtained.

Interfacial Reactions of the Pt/Ti/Si Structures

ABSTRACTA 15rm-thick Ti-layer incorporated between Pt and Si was found to be effective in improving the structures of PtSi/Si interface. The roles of Ti-layer were to react with native oxides on the Si substrate and to form Ti-O solid solutions instead of Ti oxides which act as diffusion barrier and inhibit the reactions between Pt and Si. Auger depth profiling gave evidence that Ti and O moved outward as platinum suicides were formed. A smooth PtSi/Si interface was revealed by the transmission electron microscope.

X-Ray Diffraction Study of Lattice Distortion in the Ti-O Solid Solution

X-Ray Diffraction Study of Lattice Distortion in the Ti-O Solid Solution