TITANIUM: EXTRACTION, PROCESSING AND PROPERTIES FOR WIDE APPLICATIONS

Titanium alloys and intermetallics can be extensively used in variety of applications and industries if cheaper and more cost-effective methods of their production can be developed. A wide range of titanium-based materials comprising of titanium metal powder, gamma titanium aluminide intermetallic in powder and ingot forms and titanium aluminide-alumina nanocomposite powder have been successfully synthesised using TiO2 via a new simple and cheap combustion synthesis-based method. This paper deals with the production concept and characterization of these materials.

The paper is discussed the results of shock wave compaction of nano sized Al (<50nm) and coarse sized Ti (<10 micron) powders. Before preparation of experimental procedures the distribution of normal and tangential stress were theoretically investigated. Also stress deformed analysis was performed. The chasm of nano sized Al and coarse sized Ti were compacted near theoretical density by the shock-wave compaction technology. The explosives of industrial application on the base of emulsion and ammonium nitride were used for generating the shock waves. The reaction mixture on the base nano-sized Al and coarse-sized Ti powders was placed in special container and loaded by shock waves initiated in normal and cylindrical mode. Shock wave experiments were realized in the interval of 5-20 GPa intensity of loadings. The SEM and hardness measurements were carried out for study of phase composition and mechanical properties such as hardness and thermal conductivity. In this paper is given some results which describe the relationship and influence of particle size of initial composition and compacting regimes on the formation of materials with new characteristics.

Titanium is currently the most frequently used metal for manufacturing passive implantable medical devices, such as endosteal implants. It is an internationally recognized material of choice for medical applications. This applies, in particular, to the material specified by ASTM F67-06, purity Grade 1 to 4. For those fields of medicine where implantable metallic materials are used, bulk nanostructured titanium is available. It is manufactured by SPD techniques (Severe Plastic Deformation). This forming process leaves the chemical properties of the initial material unchanged but markedly improves its final mechanical properties, in particular the strength. Continuous extrusion of metals in Conform™-type equipment is a well-known process which has been used in industry for several decades as a technique for extrusion of soft metals (Al, Cu) and their alloys. Traditionally, it has been employed only to achieve the required shape of products. New developments in continuous extrusion of metals include its use for high-strength materials and a utilization of its beneficial side effect: The microstructure refinement. In this case, the extruded material has the same shape as the input stock, making it available for subsequent processing without reconfiguring the machine. Multiple repetitions of these steps lead to refinement of original grains down to the size between tens and hundreds of nanometres (80 – 300 nm). In this fashion, one can obtain nanostructured high-strength materials with unique properties. The company COMTES FHT a. S. Has been systematically engaged in development in this field. At the end of 2010, the company purchased Conform™ 315i machine, which is the standard choice for manufacturing products with required dimensions from rolled or cast stock from copper and aluminium alloys. Long-standing experience with research into the ECAP process and other technologies for preparing ultrafine structured materials inspired modifications to the design and material of the forming die. These changes allow repeated processing of high-strength alloys with strength above 1,000 MPa. This paper describes continuous extrusion of titanium at semi commercial scale. Process parameters along with the final microstructure and mechanical properties of processed titanium are given as well.

The titanium market has a long history of seeking a low cost titanium production route in combination with low cost direct consolidation or PM component production routes. Metalysis has developed a new generation, electrochemical cell for producing titanium and its alloys utilising the FFC Cambridge process principles. The new plant is at a scale that will provide titanium for comprehensive development programs into the production of low cost titanium parts. The pilot plant is also at a scale that is commercially viable for the production of tantalum. The current status of the development program will be discussed along with R&D developments in the use of the FFC Cambridge process for the production of CP-Ti and Ti-6Al-4V. This will include an overview of the new pilot plant design, future process equipment and recent results in terms of chemistry, structure and properties of powders.

Titanium and its alloys are used for biomedical applications because of their high mechanical properties and excellent biocompatibility. In the past two decades, in order to inhibit the stress shielding effect, many titanium alloys with low Young’s modulus has been newly developed in this field. Their Young’s modulus is attained down to 40-60 GPa. However, these Young’s modulus is still higher than that of bone (10-30 GPa). In this case, porous titanium (pTi) has an advantage to further decrease of Young’s modulus depending on its porosity. However, the mechanical strength of pTi deteriorates greatly with increasing porosity. On the other hand, certain medical polymers exhibit biofunctionalities, which are not possessed intrinsically by metallic materials. Therefore, a biodegradable medical polymer, poly-L-lactic acid (PLLA), was used to fill in the pTi pores using an in-situ polymerization technique developed by the authors. The mechanical and biodegradable properties of pTi filled with PLLA (pTi/PLLA) as fabricated by this technique were investigated in this study. The pTi pores are almost completely filled with PLLA. The PLLA filling improves the compressive 0.2% proof stress of pTi having any porosity and increases slightly the compressive Young’s modulus of pTi having relatively high porosity. The PLLA filled into the pTi pores degrades during immersion in Hanks’ solution at 310 K. The weight loss due to PLLA degradation increases with increasing immersion time. However, the rate of weight loss of pTi/PLLA during immersion decreases with increasing immersion time. Hydroxyapatite formation is also observed on the surface of pTi/PLLA after long immersion. The decrease in the weight-loss rate may be caused by weight gain due to hydroxyapatite formation and/or the decrease in contact area with Hanks’ solution caused by its formation on the surface of pTi/PLLA.

The electronic conductive CaxTiOy (x≥1,y≤3) compound were prepared by sintering the disc which was composed by TiO2, CaO, C in dry argon atmosphere. The CaxTiOy (x≥1,y≤3) compounds were used as cathode, the graphite as anode and the molten CaCl2-NaCl as electrolyte. The electrolysis was performed at 800℃ and constant-voltage 3.2V under dry argon atmosphere. The metallic Ti was obtained. Additive number of CaO and C were investigated to obtain the electronic conductive cathode. The results shown that the electrolytic rate could been significantly enhanced because of the additive CaO and C. The electrolysis time efficiently shorten than that of direct electrochemical reduction the insulating solid TiO2.

A study on the electro-deoxidation of vanadium trioxide precursors is reported. Experiments were performed with a two-terminal electrochemical cell, comprising a molten salt electrolyte of calcium chloride and sodium chloride with additions of calcium oxide, a cathode of compact vanadium trioxide and a graphite anode under the potential of 3.0 V at 1173 K. XRD and SEM were used to study the morphology and the composition of the samples. The results reveal that vanadium trioxide of 3 g can be converted to vanadium metal powder of 3000 ppm in mass within the processing time of 12 h. The kinetic pathway is investigated by analyzing the compositions of samples prepared at different reduction stages. It is found that CaV2O4 is the intermediate product in the reaction path and the presence of calcium oxide in the calcium chloride and sodium chloride accelerates the overall rate of the electro-deoxidation of vanadium trioxide.

In this paper LiF-NaF-KF-K2TiF6 melt was selected as a supporting electrolyte, and TiO2 as an active species, Ti ion reduction process was investigated on a tungsten electrode by cyclic voltammetry (CV) and square wave voltammetry (SWV) at the temperature 600-900 ℃. In addition, oxygen ion oxidation process was also studied on a spectroscopic graphite electrode by the same electrochemical method. The results showed that there existed three reduciton peaks and three corresponding oxidization peaks, which changed with TiO2 content in the melt, and the electron transfer number for each reduction was calculated according to the half-wave potential values. Moreover, oxygen ion oxidization was also determined by analyzing the oxidation potential recorded in CV. And the possibility of obtaining Ti from the fluoride melt with TiO2 was evaluated.

The effects of hydrogen processing on the microstructure and the tensile properties of welded joints of BT20 titanium alloy were investigated. The results show that some δ-hydrides are formed after hydrogenising at 600℃ and 700℃ for 3h, respectively. Complete α+H→β(H) transmission occurs during hydrogenizition at 800℃ for 30min. A lot of metastable β(H) and martensite α" are generated by water quenching. β(H) and α" gradually decompose to α and δ by eutectoid treatment. The decomposition effect becomes heavier by rising the eutectoid temperature. Hydrogen is removed and recrystallization occurs in the process of dehydrogenisng at 750℃ for 8h in vacuum. After dehydrogenising at 750℃ for 8h in vacuum, the refinement of large grains in the fusion area is very obvious, but the original large grain boundaries are observed vaguely. After annealing in vacuum, with the increasing of hydrogen content tensile strength and plasticity decreased when the temperature of hydrogenization was 650℃. Through hydrogenising at 800℃for 30min and quenching into water, then eutectoid at 300℃ for 8h, and dehydrogenising at 750℃ for 8h in vacuum, the ultimate strength decreases and the elongation increases a little in the joints by hydrogen treatment compared with those untreated.

Titanium alloys composed of no-toxic and allergy-free elements showing Young’s moduli being decreased as possible as low have developed or are being developed because of preventing stress shielding between the implant and the bone. They are mainly beta-type titanium alloys because their Young’s moduli are much lower than those of alpha- and (alpha + beta)-type titanium alloys due to the crystal structure of beta phase showing bcc structure, whose atomic density per a lattice is lower than that of alpha phase showing hcp structure. The lowest Young’s modulus of poly-crystal beta-type titanium alloy for biomedical applications seems to be around 40 GPa. The single crystal of a beta-type titanium alloy, TNTZ (Ti-29Nb-13Ta-4.6Zr), exhibits around 35 GPa, which is nearly equal to that of the bone (around 10-30 GPa), at <100> direction. The lowest Young’s modulus is generally obtained in solutionized conditions for beta-type titanium alloys. The strengths of beta-type titanium alloys are not sufficient for use in load bearing implants. The improvement of the strength of low Young’s modulus of beta-type titanium alloys is required. Young’s moduli of beta-type titanium alloys can be improved by precipitation hardening brought by thermomechanical treatments including aging treatment, while their Young’s moduli are increased. The improvement of their strength is required while maintaining Young’s modulus low. The short time aging after solution treatment or adding a very small amount of ceramic particles such as TiB and Y2O3 are effective for solving this problem. Especially, dispersing a small amount of such ceramic particles is effective to improve dynamic strength such as fatigue strength while maintaining Young’s modulus low. Nowadays, Young’s modulus changeable beta-type titanium alloys are required in order to satisfy demands from both patients and surgeons. They are low Young’s modulus for patients and high Young’s modulus for surgeons. Low Young’s modulus prevents stress shielding (prevent bone atrophy) and high Young’s modulus prevent spring back (maintain deformed shape). Bio-fuctionalization of beta-type titanium alloys for biomedical applications via surface modifications will be also discussed.

Titanium alloys can be classified in α, α + β and β-type. The beta titanium alloys also can be classified into three categories, stable β, metastable β and near β as function of the molybdenum equivalent [Mo eq]. If the [Mo eq] is lower than 11 wt. %, martensitic transformation may occur during quenching from temperatures above the β transus. The type of martensite phase formed (α’ or α’’) depend on the solute concentration in the titanium alloy. Besides, another metastable ω phase (hcp structure) also may precipitate in the β-Ti matrix during quenching. The objective of this work was to evaluate the correlation of phases precipitated in treated Ti-10Mo-xNb (x = 0, 3, 6, 9, 20 and 30) alloys with the mechanical properties (microhardness and Young modulus) The Ti-10Mo-xNb alloys, with Nb contents ranging from 0 to 30 wt. % were prepared from pure elements through arc melting under argon. The obtained ingots were solution treated at 950 ºC under argon atmosphere for 1 h and then quenched in water at room temperature. The microstructures were characterized by optical microscopy, X-ray diffraction and transmission electron microscopy and the mechanical characterization was carried out by Vickers microhardness test and Young’s modulus measurements. The resulted of microstructural characterization showed the presence of α’, ω and β phase for the Ti-10MoxNb (0, 3, 6 and 9) alloys and the presence of single β-phase for the Ti-10Mo-20Nb and Ti-10Mo-30Nb alloys. Among the six alloys, cp Ti and Ti-6Al-4V alloy, the Ti-10Mo-20Nb alloy [Mo eq = 15,6] showed the lower elastic modulus (~74 GPa) with a microstructure consisting of single β-phase.

The reduction of titanium concentrate by electrochemical method in molten calcium chlorice has been studied. An analysis of the experimental results showed that FeTi alloy can be obtained by electrolysis and the temperature has great effect on the final phase. FeTi can be obtained at 1173k and Fe2Ti can be obtained at 1123K. Fe and CaTiO3 are the main products at the electrolysis beginning. The intermediate compound CaTiO3 inhibite the electro-deoxidation process. FeTi alloy produced from Fe2Ti alloy and Ti metal. However, electrical conductivity is poor in the whole deoxidation process.

It has been found that during the electro-deoxidation of titanium dioxide in calcium chloride- calcium oxide melts that calcium titanate forms as a stable phase in the melt. Unfortunately, calcium titanate is an insulator and previous work has shown that doping has proved unsuccessful in substantially increasing the electronic conductivity. In this work calcium ruthenate, which is an excellent electronic conductor, was added to calcium titanate by two routes. The first method was to incorporate nanosized calcium ruthenate, as a second phase, into calcium titanate and it was found that the material retained its excellent electronic conductor down to XCaRuO3= 0.1 over a wide temperature range. In the second method, a solid solution of calcium ruthenate and calcium titanate was formed by sintering at 1673 K for extended times. When XCaRuO3= 0.1, the material was a semi-conductor and it was found that the conductivity varied from about 10-3 S cm-1 at room temperature to 10 S cm-1 at 1273 K. Both the two phase and solid solution materials were successfully used as inert anodes, without signs of degradation after more than 150 h of use, in calcium chloride-calcium oxide melts when oxygen ions were discharged at the anode. Furthermore, titanium and its alloys were prepared by electro-deoxidation in molten calcium chloride utilizing the as-prepared inert anode. The difference is the evolution of molecular oxygen on the inert anode instead of environmentally undesired CO2 greenhouse gases on the carbon anode.

Dye Sensitized Solar Cell (DSC) technology is often referred to as Artificial Photosynthesis by inventor Michael Graetzel, the recent 2010 Millennium Prize winner. DSC technology can best be described as a 3rd generations thin film technology using an electrolyte/ionic liquid, a layer of titania (a pigment used in white paints and tooth paste) and organo metallic based dyes/ruthenium and silver/other conductive materials, deposited on glass, metal or polymer substrates. Light striking the dye excites electrons which are absorbed by the titania to become an electric current many times stronger than that found in natural photosynthesis in plants. Compared to conventional silicon based photovoltaic technology, DSC technology utilizes lower cost and readily available materials and embodied energy in manufacture, produces electricity more efficiently in low light conditions and can be directly incorporated into buildings by replacing conventional glass panels or metal sheets in building envelopes. Dyesol is a global company and in August 2005 was listed on the Australian Stock Exchange (ASX Code ‘DYE’). Dyesol manufactures and supplies a range of dye solar cell products comprising equipment, chemicals, materials, components and related services to researchers and manufacturers of DSC. The Company is playing a key role in taking this third generation solar technology out of the laboratory and into the community. Dyesol is driving commercialization of DSC technology by partnering with large multi nationals with direct access to key markets such as Tata for DSC on steel and Pilkington for DSC on glass and with key material suppliers such as Merck (ionic liquids), Umicore (organometalic dyes) and others. Presenter: Marc Thomas, President & CEO of Dyesol Inc. Bio: Mr, Thomas was appointed President & CEO of Dyesol North America in 2009. Previously he held senior management roles in manufacturing, technical and business development positions at a number of hi-tech companies including Livescribe (smart pens, VP/Operations), The TECH Group (consulting/GM), Top Ecology (PV-powered portable desalination, VP Manufacturing) Alex & Wins (a technology transfer company, CTO), Ubiquity (consumer products, VP Operations) and Lectus, (robotic-based critical care beds, CTO, VP Mfg/Eng). He also held technical/marketing management and engineering positions at GE Plastics and Ford Motor Company. With over 25 years of experience in translating technologies into ongoing enterprise in start-ups and Fortune 100 companies, Mr. Thomas leverages his unique blend of operations, engineering, manufacturing, marketing and management experience to accelerate product development and sales cycles resulting in achieving significant strategic advantages. Mr. Thomas has a degree in Plastics Engineering from the University of Massachusetts Lowell, and holds 8 patents with others pending.

The properties of the native surface layer on titanium and its alloys can be enhanced and tailored to appropriate applications by changing parameters influencing the anodic oxidation process. Electrochemical oxidation in various electrolytes as well as different scan rates during the very first seconds of polarization used for anodization, may improve the properties of the oxide for effective implantation and biosensing. Enhanced bioactivity of barrier oxide TiO2 and self-organized TiO2 nanotube (NT) layers produced for biomedical applications is implemented by using phosphoric acid of higher concentration with or without fluoride ions. Formation of titanium oxide and oxide nanotube layers formed in 2 M phosphoric acid solutions on titanium and its alloys at various polarization conditions led to porous oxides covered by gel-like layers rich of phosphates. The oxide layers were characterized by tracing the open circuit potential (OCP) and capacitance values when immersed in simulated body fluid SBF. The morphological and structural properties were studied by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy revealing the presence of phosphate rich layer on the top of compact oxide and above nanotubes. Simultaneously, the increased amount of fluorine in the surface layer over nanotubes was observed. The presence of these two elements improves bioactivity of titanium implant materials in surgical applications. Electrochemical impedance investigation including Mott−Schottky analysis attests to a significant improvement of the interfacial electron-transfer kinetics together with a modification of the surface chemistry for the TiO2 nanotubes. For the system of semiconductor oxide nanotubes covering titanium foil, this observation offer the opportunity to use this nanotubular material as a platform for 3rd generation biosensors.

TiFe alloy is prepared directly from the ilmenite concentrate by electrolysis in molten salt at 1173K and 3.1 V. The process of electro-deoxidization of ilmenite concentrate is studied preliminarily through interrupted experiments at different time and the reduced samples are characterized by X-ray diffraction analysis and SEM analysis. The results show that the reducing process is divided into a series of stages in which iron is first reduced. Then perovskite and titanium suboxides which are intermediate products are produced to form TiFe2 and TiFe alloys. Finally, a mass-time curve during constant voltage electrolysis of the precursor is recorded to further verify above deoxidization process.

In recent years, one of the significant contributions made towards developing more cost-effective methods for extracting titanium metal from its oxide has been the invention of electro-deoxidation, also known as the FFC-Cambridge process. Using the application of a cathodic potential to a porous metal oxide precursor within a molten salt electrolyte, the oxide is reduced to the metallic state while oxide ions are transported to, and removed at, the anode. One of the interesting aspects of this process is that the metallic species basically remain in the solid state during their reduction. Changes from one phase to the next are by solid-state phase transformations. In consequence, the nature and rate of deoxidation depends not only on the thermodynamics of the reaction pathway and rates of ionic diffusion, but also on microstructural factors. This paper will reveal how the in-depth characterization of sample microstructures gives insights into the nature and rate-limiting steps of electro-deoxidation of titanium dioxide to titanium metal, identifying various microstructure-dependent kinetic factors. An overview of results on standard porous precursors will be given. This will lead to surprising results showing that, by manipulating precursor microstructure to have substantially lower porosity than usual, a new, more direct reaction pathway for electro-deoxidation is created. In contrast to the typically whole-body transformations of the standard porous precursors, deoxidation now proceeds by a moving transformation front. Together, the studies demonstrate the importance of understanding microstructural kinetics and controlling precursor design for process optimization.

The FFC Cambridge process for the metal extraction from its oxide was proposed by Fray et al. About decade ago, since then, the successful preparations of lots of metals and alloys via the process have been reported, indicating this environment friendly novel process of great potential to replace much traditional metallurgy for production of refractory metals and their functional alloys. Although the electrode process of solid oxide to metal has been long existed in aqueous electrochemistry, the FFC process makes the fundamental understanding of the electrochemical reduction of bulk oxide pellet become urgent to the industrial practice. For this purpose, however, a 3PIs model, namely, a dynamic metal/oxide/electrolyte three phase interlines model for the cathode process has been established and verified in this laboratory. In this report, the 3PIs model, together with the latest theoretical and practical achievements based on it are introduced by taking the electrolysis of various metals as examples. It is found, the application of the 3PIs theories would lead to optimized electrode design and electrolysis conditions for the FFC Cambridge processes.

Understanding the Electro-deoxidation of Titanium Dioxide to Titanium Metalvia the FFC-Cambridge ProcessCarsten SchwandtDepartment of Materials Science and Metallurgy, University of Cambridge, Cambridge, CB2 3QZ, United KingdomThe FFC-Cambridge process, invented at the Department of Materials Science and Metallurgy of the University of Cambridge approximately ten years ago, offers a novel and rather universal approach in the field of electro-winning of metals. In this process, metals and alloys may be produced directly from their oxides by polarising the oxide cathodically in a molten salt electrolyte based on calcium chloride. The winning of titanium metal from titanium dioxide has been the first and the main goal of the FFC-Cambridge process. This presentation summarises the key results of a series of in-depth studies performed at Cambridge with the aim of understanding the fundamentals that the process rests upon. Subjects of discussion are the pathway of electro-deoxidation in the cathode, the validation of a molten salt compatible pseudo-reference electrode, and the investigation of the reactions at the anode. A particular emphasis is on the importance of the composition of the electrolyte and its interplay with the other components of the electrolytic cell. The knowledge gained has enabled optimisation of the process and scale-up to pilot plant level.

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