Showing papers on "Titanium published in 2003"
TL;DR: In this paper, the stability of titanium oxide nanotube arrays at elevated temperatures was studied in dry oxygen as well as dry and humid argon environments, and it was found that the nanotubes architecture was stable up to approximately 580 °C, above which oxidation and grain growth in the titanium support disrupted the overlying nanotub array.
Abstract: The stability of titanium oxide nanotube arrays at elevated temperatures was studied in dry oxygen as well as dry and humid argon environments. The tubes crystallized in the anatase phase at a temperature of about 280 °C irrespective of the ambient. Anatase crystallites formed inside the tube walls and transformed completely to rutile at about 620 °C in dry environments and 570 °C in humid argon. No discernible changes in the dimensions of the tubes were found when the heat treatment was performed in oxygen. However, variations of 10% and 20% in average inner diameter and wall thickness, respectively, were observed when annealing in a dry argon atmosphere at 580 °C for 3 h. Pore shrinkage was even more pronounced in humid argon environments. In all cases the nanotube architecture was found to be stable up to approximately 580 °C, above which oxidation and grain growth in the titanium support disrupted the overlying nanotube array.
668 citations
TL;DR: The use of titanium alloys in the aerospace sector will be highlighted including airframe, engine, helicopter, and space applications as discussed by the authors, which is probably no other material more closely related to aerospace than titanium and its alloys.
Abstract: There is probably no other material more closely related to aerospace than titanium and its alloys. With a density of 4.5 g/cm{sup 3}, titanium alloys are only about half as heavy as steel or Ni-based superalloys, yielding an excellent strength-to-weight ratio. Furthermore, they have exceptional corrosion resistance. The use of titanium alloys in the aerospace sector will be highlighted including airframe, engine, helicopter, and space applications. (Abstract Copyright [2003], Wiley Periodicals, Inc.)
589 citations
TL;DR: Porous Ti compacts for biomedical applications are successfully fabricated in the porosity range from 50 to 371 vol% by controlling sintering conditions and Ti powder sizes as discussed by the authors, where Young's modulus and bending strength at the porosa of around 30 vol% are found to be similar to those of human cortical bone.
519 citations
TL;DR: The formation of porous on titanium was investigated in electrolytes containing low concentrations of HF (0.05-0.4 wt %) under optimized electrolyte conditions and extended polarization as mentioned in this paper.
Abstract: The formation of porous on titanium was investigated in electrolytes containing low concentrations of HF (0.05-0.4 wt %). Under optimized electrolyte conditions and extended polarization, highly ordered porous is obtained that consists of pore arrays with single pore diameter of 140 nm and a pore spacing of 150 nm. During the formation process, significant current oscillations are observed with an amplitude which depends strongly on the HF content of the electrolyte. Electrochemical, scanning electron microscope and X-ray photoelectron spectroscopy investigations show that the porous layer forms under a competition of formation and oxide dissolution up to a limiting thickness of and that the time scale for complete self-ordering for the investigated systems is in the order of several hours. © 2003 The Electrochemical Society. All rights reserved.
499 citations
TL;DR: Localized corrosion sensitivity of the Ti6Al4V alloy has been correlated to the dissolution of vanadium at the surface film/electrolyte interface coupled with generation of cation vacancies and their diffusion through the film as a part of the solid-state diffusion process.
381 citations
TL;DR: The properties of thin blocking layers of titanium dioxide used to improve the performance of dye-sensitized nanocrystalline solar cells have been studied in this article, showing that the ability of the blocking layer to prevent the back reaction of electrons with tri-iodide ions in the electrolyte is excellent under short circuit conditions, but is limited under open circuit conditions by electron accumulation at the surfa...
Abstract: The properties of thin blocking layers of titanium dioxide used to improve the performance of dye-sensitized nanocrystalline solar cells have been studied. TiO2 blocking layers prepared on fluorine-doped tin oxide-coated glass by spray pyrolysis have been characterized by electrochemical impedance spectroscopy, spectroscopic ellipsometry, and voltammetry. The impedance data reveal the presence of a distribution of surface states at the titanium dioxide−electrolyte interface that is similar to the one seen in the case of nanocrystalline TiO2 films. The influence of the blocking layers on the back transfer of electrons to tri-iodide ions in electrolyte-based dye-sensitized nanocrystalline cells has been studied by open circuit photovoltage decay. The results show that the ability of the blocking layer to prevent the back reaction of electrons with tri-iodide ions in the electrolyte is excellent under short circuit conditions, but is limited under open circuit conditions by electron accumulation at the surfa...
372 citations
TL;DR: In this article, a numerical simulation of the heat flow equation has been performed and compared with experimentally obtained titanium plates, which allowed to obtain a process map of the sintering process.
332 citations
TL;DR: In this article, the growth kinetics of TiO2 nanoparticles synthesized from aqueous solution using titanium(IV) isopropoxide as precursor were reported, and the radius of primary particles was found to be between 1.5 and 8 nm.
Abstract: We report on the growth kinetics of TiO2 nanoparticles synthesized from aqueous solution using titanium(IV) isopropoxide as precursor. The radius of primary particles was found to be between 1.5 and 8 nm, and the average particle radius cubed is shown to increase linearly with time in agreement with the Lifshitz-Slyozov-Wagner model for coarsening. The rate constant for coarsening increases with temperature due to the temperature dependence of the viscosity of the solution and the equilibrium solubility of TiO2. At longer times and higher temperatures, secondary particles formed by epitaxial self-assembly of primary particles were observed with high-resolution transmission electron microscopy. The number of primary particles per secondary particle increases with time, and the percentage of primary particles present in the colloid decreases with increasing temperature.
330 citations
TL;DR: The greater surface roughness, higher surface energy and more surface hydroxyl groups resulted in greater numbers of adhered osteoblasts and higher cell activity, suggesting that the interactions between the cells and the titanium involved chemical reactions.
327 citations
TL;DR: In this article, a review of the issues in depth and examines emerging directions for improving the performance of orthopaedic devices is presented, including bulk alloying with titanium and nitrogen, surface alloying by ion implantation of stainless steels and titanium and its alloys, and surface modification of stainless steel with bioceramic coatings.
Abstract: Chemical stability, mechanical behaviour and biocompatibility in body fluids and tissues are the basic requirements for successful application of implant materials in bone fractures and replacements. Corrosion is one of the major processes affecting the life and service of orthopaedic devices made of metals and alloys used as implants in the body. Among the metals and alloys known, stainless steels (SS), Co-Cr alloys and titanium and its alloys are the most widely used for the making of biodevices for extended life in human body. Incidences of failure of stainless steel implant devices reveal the occurrence of significant localised corroding viz., pitting and crevice corrosion. Titanium forms a stable TiO2 film which can release titanium particles under wear into the body environment. To reduce corrosion and achieve better biocompatibility, bulk alloying of stainless steels with titanium and nitrogen, surface alloying by ion implantation of stainless steels and titanium and its alloys, and surface modification of stainless steel with bioceramic coatings are considered potential methods for improving the performance of orthopaedic devices. This review discusses these issues in depth and examines emerging directions.
TL;DR: In this paper, a 7-nm-sized TiO2 nanoparticles were synthesized by hydrothermal reaction of titanium alkoxide stabilized in an acidic ethanol/water solution and the sizes of particles were controlled to the range of 7−25 nm by adjusting the concentration of Ti precursor and the composition of the solvent system.
Abstract: TiO2 nanoparticles were prepared by hydrothermal reaction of titanium alkoxide stabilized in acidic ethanol/water solution. The sizes of particles have been controlled to the range of 7−25 nm by adjusting the concentration of Ti precursor and the composition of the solvent system. The TiO2 samples synthesized under this acidic ethanol/water environment were mainly primary particles in anatase phase without secondary structure. The suspension of as-prepared 7-nm-sized TiO2 nanoparticles demonstrates long-term stability, and has been applied successfully for the fabrication of ultra-transparent particulate TiO2 films. The photocatalytic efficiency of TiO2 films prepared from the 7-nm-sized nanoparticles was 1.6 times of that of films derived from Degussa P25 in decomposing gaseous 2-propanol.
TL;DR: In this article, the authors studied the tensile behavior of titanium at room temperature in the as-processed condition (using severe plastic deformation by high pressure torsion) and also in various annealed states and found that controlled annealing could lead to enhancement of both strength and ductility of this material.
TL;DR: In this paper, the morphology, elemental composition and phase components of the titania-based films were investigated as a function of the electrolytes composition and the applied voltage (in the range of 200-500 V).
Abstract: Titania-based films on titanium were formed by micro-arc oxidation in electrolytic solutions containing sodium carbonate, sodium phosphate, acetate monohydrate and β-glycerophosphate disodium salt pentahydrate using a pulse power supply. The morphology, elemental composition and phase components of the films were investigated as a function of the electrolytes composition and the applied voltage (in the range of 200–500 V). In vitro bioactivity of the films was evaluated in a most commonly used simulated body fluid as proposed by Kokubo et al. The results showed that the films were porous with 1–8 μm pores and nano-crystallized, without apparent interface to the titanium substrates. The phase components of the films could be anatase, rutile, CaTiO 3 , β-Ca 2 P 2 O 7 and α-Ca 3 (PO 4 ) 2 , strongly depending on the electrolytes composition and the applied voltage. The pore size and the content of Ca and P tended to increase with the applied voltage. Among the prepared titania-based films, only the film containing CaTiO 3 , β-Ca 2 P 2 O 7 and α-Ca 3 (PO 4 ) 2 could induce an apatite layer on its surface, exhibiting bioactivity. The bioactive response of the micro-arc oxidized films to the structural factors and the apatite-induced mechanism were discussed.
TL;DR: In this paper, thin films of titanium dioxide (TiO2) were deposited on a variety of substrates by a simple sol-gel dip coating technique, where the substrates were coated with titanium peroxide precursor solution of controlled viscosity at a constant pulling rate of 1mm s−1, air-dried and further heated at 400°C to obtain uniform films with good adhesion to the substrate.
TL;DR: In this paper, anatase nanoparticles with mean size in the range 5-10 nm were prepared by precipitation of TiCl4 in aqueous medium in a range 2 ≤ pH ≤ 6.
Abstract: Nanoparticles of anatase with mean size in the range 5–10 nm were prepared by precipitation of TiCl4 in aqueous medium in the range 2 ≤ pH ≤ 6. Hydroxylation of TiCl4 at room temperature leads instantaneously to an amorphous titanium oxyhydroxide phase which crystallizes as anatase upon aging at 60 °C in suspension. Small amounts of brookite or rutile are concurrently obtained depending on the acidity. The size of anatase particles was characterized by X-ray diffraction, electron microscopy and Raman spectroscopy. The latter was also used to determine the particle size and to characterize the crystallinity of particles through the phonon confinement effect. The particle size, dependent on the acidity, is closely related to the electrostatic surface charge density of particles. The size variation was interpreted as resulting from a lowering of the interfacial tension due to the protonation of particle surface groups. Composite materials were synthesized by polymerisation of silica in aqueous sols of anatase. The dispersed anatase nanoparticles are stable against the transformation to rutile up to 1000 °C.
TL;DR: In this article, the authors examined the crystallization of amorphous anodic films grown at constant current density on sputtering-deposited titanium and Ti-Si alloys, in ammonium pentaborate electrolyte, by transmission electron microscopy.
TL;DR: In this article, a simple sol−gel route was developed for the preparation of mesoporous and nanocrystalline anatase thin layers, and an anatase hydrosol was first synthesized at room temperature from acidic hydrolysis of titanium isopropoxide.
Abstract: A simple sol−gel route has been developed for the preparation of mesoporous and nanocrystalline anatase thin layers. An anatase hydrosol was first synthesized at room temperature from acidic hydrolysis of titanium isopropoxide. The optimization of the synthesis parameters, including titanium concentration, HCl/Ti and H2O/Ti ratios, temperature, and aging time, enabled us to produce a clear sol with a very low HCl/Ti ratio (equal to 1). As a function of the further thermal treatment conditions, it was then possible to control the size of the anatase crystallites (from 5 to >10 nm) and the O/Ti stoichiometry (from 1.9 to 2.0). Ordered mesoporosity was obtained by using a triblock copolymer as the templating agent. Preliminary experiments evidenced the photocatalytic activity of the prepared layers.
TL;DR: Silicatein, an enzymatic biocatalyst purified from the glassy skeletal elements of a marine sponge, is shown to be capable of catalyzing and templating the hydrolysis and subsequent polycondensation of a water-stable alkoxide-like conjugate of titanium to form titanium dioxide as discussed by the authors.
Abstract: Silicatein, an enzymatic biocatalyst purified from the glassy skeletal elements of a marine sponge, and previously shown capable of catalyzing and structurally directing the hydrolysis and polycondensation of silicon alkoxides to yield silica and silsesquioxanes at low temperature and pressure and neutral pH, is shown to be capable of catalyzing and templating the hydrolysis and subsequent polycondensation of a water-stable alkoxide-like conjugate of titanium to form titanium dioxide. The structure and behavior of the TiO2 formed through this biocatalytic route, including thermally induced crystal grain growth and phase transformation from anatase to rutile, differ from those of TiO2 formed from the same precursor via alkali catalysis or thermal pyrolysis. This enzymatic route affords a path to templated synthesis that avoids the high temperatures and extremes of pH typically required for synthesis of metallo-oxanes from the corresponding alkoxide-like precursors, and thus provides access to a new and pot...
TL;DR: In this paper, the molar amounts of defective sites (Md) in several titanium(IV) oxide (TiO2) powders were determined using photoinduced reactions of electron accumulation in deaerated aqueous solutions containing sacrificial hole scavengers and subsequent reduction of methylviologen to its cation radical.
Abstract: The molar amounts of defective sites (Md) in several titanium(IV) oxide (TiO2) powders were determined using photoinduced reactions of electron accumulation in deaerated aqueous solutions containing sacrificial hole scavengers and subsequent reduction of methylviologen to its cation radical. Measurements of pH dependence of typical anatase and rutile TiO2 powders showed that these defective sites were of electronic energy just below the conduction band edge of TiO2 in ranges of 0–0.35 V for anatase and 0–0.25 V for rutile. A linear relation of Md with the rate constant of electron-hole recombination determined by femtosecond pump-probe diffuse reflection spectroscopy revealed that Md could be a quantitative parameter of recombination between a photoexcited electron and a positive hole. The fact that there was no linear relation between Md and the specific surface area suggests that the surface area was not directly reflected on Md. A reciprocal correlation between photocatalytic activity for water oxidation in aqueous silver sulfate solution and Md revealed that the rate of recombination is one of the predominant physical properties governing the activities of TiO2 powders in this reaction system.
TL;DR: The high degree of resistance of the PEGylated surface to non-specific adsorption makes peptide-modified PLL-g-PEG a useful candidate for the surface modification of biomedical devices such as implants that are capable of eliciting specific interactions with integrin-type cell receptors even in the presence of full blood plasma.
01 Jun 2003-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this paper, a concept for direct reduction of titanium dioxide in molten CaCl2 is proposed and experimentally tested, where both the thermochemical reaction of the calciothermic reduction and the electrochemical reaction for recovery of the reducing agent, Ca, coexist in the same molten caCl2 bath.
Abstract: A concept for calciothermic direct reduction of titanium dioxide in molten CaCl2 is proposed and experimentally tested. This production process consists of a single cell, where both the thermochemical reaction of the calciothermic reduction and the electrochemical reaction for recovery of the reducing agent, Ca, coexist in the same molten CaCl2 bath. A few molar percentages of Ca dissolve in the melt, which gives the media a strong reducing power. Using a carbon anode and a Ti basket-type cathode in which anatase-type TiO2 powder was filled, a metallic titanium sponge containing 2000 ppm oxygen was produced after 10.8 ks at 1173 K in the CaCl2 bath. The optimum concentration of CaO in the molten CaCl2 was 0.5 to 1 mol pct, to shorten the operating time and to achieve a lower oxygen content in Ti.
Patent•
04 Aug 2003TL;DR: A phase change material may be processed to reduce its micro-crystalline grain size and may also be processed in order to increase the crystallization or set programming speed of the material as mentioned in this paper.
Abstract: A phase change material may be processed to reduce its microcrystalline grain size and may also be processed to increase the crystallization or set programming speed of the material. For example, material doped with nitrogen to reduce grain size may be doped with titanium to reduce crystallization time.
TL;DR: In this paper, a thin bone-like apatite layer was coated onto titanium (Ti) metals via an alkali pre-treatment, followed by immersion in a simulated body fluid.
Abstract: Biomimetic processes have attracted huge attention in recent years due to their significant applications in biomedical areas such as bone tissue engineering. In the present study, a biomimetic process was employed to form a nanocrystallite apatite coating on metal. A thin bone-like apatite layer was coated onto titanium (Ti) metals via an alkali pre-treatment. This was followed by immersion in a simulated body fluid. Analysis of the coating by thin film x-ray diffraction and scanning electron microscope has shown that the apatite layer grown in this way exhibits nanostructure and has similar stoichiometry to that of natural bone. It is observed that the thickness of the apatite layer increases as the immersion period increases. The growth kinetics and mechanism are also discussed. A cross-sectional study has also shown that a uniform coating of carbonate-containing apatite (hydroxyapatite) is firmly adhered on the Ti metal. The adhesion of the apatite layer on the Ti substrate was further confirmed by a shear test, which has shown an average value of 9.5 MPa. The bioactivity of the coating was finally examined by cell culturing experiments. The results have shown that the nanocomposite prepared using the present method possesses good mechanical properties and bioactivity.
TL;DR: In this paper, two types of titanium dioxide electrode have been used for photoelectrocatalytic and photocatalytic disinfection of E. coli suspensions by titanium dioxide in a sparged photo-electrochemical reactor.
Abstract: This paper reports studies of the photoelectrocatalytic and photocatalytic disinfection of E. coli suspensions by titanium dioxide in a sparged photoelectrochemical reactor. Two types of titanium dioxide electrode have been used. ‘Thermal’ electrodes were made by oxidation of titanium metal mesh; ‘sol–gel’ electrodes were made by depositing and then heating a layer of titania gel on titanium mesh. Cyclic voltammetry was used to carry out an initial characterisation and optimisation of both electrode types. The best ‘thermal electrodes’— i.e. those with the highest photocurrents—were prepared by heating titanium mesh at ∼700 ◦ C in air. For sol–gel derived electrodes, optimum performance was obtained by heating at ∼600 ◦ C. These electrodes were then used, in a gas sparged reactor, to disinfect E. coli suspensions with an initial concentration of 10 7 colony forming units (cfu) ml −1 . Films prepared by the oxidation of titanium metal were shown to be superior to sol–gel derived films. Direct experimental comparison demonstrates that the photoelectrochemical system is more efficient than photocatalytic disinfection effected by slurries of Degussa P25 titanium dioxide. Since in practical systems the TiO2 would be exposed to a variety of species additional to those that are targeted, we also examined the effects of H2PO4 − and HCO3 − ions on the measured disinfection rates. Phosphate addition poisons both the electrode and particulate-slurry systems and is only partially reversible. By contrast, although bicarbonate addition affects all three systems, the effects are reversible. © 2002 Elsevier Science B.V. All rights reserved.
15 Sep 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effect of particle size on the de-hydrogenation of fine titanium hydride is studied, using thermal analysis along with structural investigations, and a two-step process is proposed, where 07
Abstract: Hydrogen is a unique alloying element for titanium because it can be introduced into the metal to form solid solutions or stoichiometric compounds by exposure to the gas at elevated temperatures and removed by vacuum annealing Studies on dehydrogenation of fine titanium hydride are important for several applications such as thermohydrogen processing of Ti and Ti based alloy components, hydrogen storage materials and bonding of metals and ceramics using TiH2 Effect of particle size on dehydrogenation of TiH2 is studied here, using thermal analysis along with structural investigations Dehydrogenation of nanocrystalline hydride powder differs considerably from the micron size starting powder A two step dehydrogenation process, (TiH2 → TiHx → α-Ti) where 07
TL;DR: In this article, the effect of alkali and heat treatments on titanium rods in an intramedullary rabbit femur model, in regard to the cementless hip stem was examined.
Abstract: In cementless fixation systems, surface character is an important factor. Alkali and heat treatments of titanium metal have been shown to produce strong bonding to bone and a higher ongrowth rate. In this study we examined the effect of alkali and heat treatments on titanium rods in an intramedullary rabbit femur model, in regard to the cementless hip stem. The implant rods were 5 mm in diameter and 25 mm in length. Half of the implants were immersed in 5 mol/L sodium hydroxide solution and heated at 600 degrees C for 1 h (AH implants), and the other half were untreated (CL implants). The rods were implanted into the distal femur of the rabbits; AH implants into the left femur and CL implants into the right. The bone-implant interfaces were evaluated at 3, 6, and 12 weeks after implantation. Pull-out tests showed that the AH implants had a significantly higher bonding strength to bone than the CL implants at each time point. As postoperative time elapsed, histological examination revealed that new bone formed on the surface of both types of implants, but significantly more bone made direct contact with the surface of the AH implants. At 12 weeks, approximately 56% of the whole surface of the AH implants was covered with the bone. In conclusion, alkali- and heat-treated titanium offers strong bone bonding and a high affinity to bone as opposed to a conventional mechanical interlocking mechanism. Alkali and heat treatments of titanium may be suitable surface treatments for cementless joint replacement implants.
TL;DR: In this article, the authors studied the plasma induced at the surface of a titanium target following irradiation with femtosecond and nanosecond laser pulses, and they could discriminate between three different velocity populations in the plasma expansion.
Abstract: We have studied the plasma induced at the surface of a titanium target following irradiation with femtosecond and nanosecond laser pulses. Time-resolved imaging and spectroscopic measurements allowed us to evidence some features specific to the femtosecond-laser-induced plasma. In this ultrashort interaction regime, we could discriminate between three different velocity populations in the plasma expansion. Coulomb explosion firstly creates highly energetic Ti+ ions, which are followed by atomic neutral titanium and lastly by nanoscale titanium oxide clusters.