Showing papers on "Titanium published in 2005"

Titanium and titanium alloys : fundamentals and applications

Abstract: Foreword.List of Contributors.1. Structure and Properties of Titanium and Titanium Alloys (M. Peters, et al.).2. Beta Titanium Alloys (G. Terlinde and G. Fischer).3. Orthorhombic Titanium Aluminides: Intermetallic with Improved Damage Tolerance (J. Kumpfert and C. Leyens).4. gamma-Titanium Aluminide Alloys: Alloy Design and Properties (F. Appel and M. Oehring).5. Fatigue of Titanium Alloys (L. Wagner and J.K. Bigoney).6. Oxidation and Protection of Titanium Alloys and Titanium Aluminides (C. Leyens).7. Titanium and Titanium Alloys - From Raw material to Semi-finished Products (H. Sibum).8. Fabrication of Titanium Alloys (M. Peters and C. Leyens).9. Investment Casting of Titanium (H.-P. Nicolai and Chr. Liesner).10. Superplastic Forming and Diffusion Bonding of Titanium and Titanium Alloys (W. Beck).11. Forging of Titanium (G. Terlinde, et al.).12. Continuous Fiber Reinforced Titanium matrix Composites: Fabrication, Properties and Applications (C. Leyens, et al.).13. Titanium Alloys for Aerospace Applications (M. Peters, et al.).14. Production, Processing and Application of gamma(TiAl)-Based Alloys (H. Kestler and H. Clemens).15. Non-Aerospace Applications of Titanium and Titanium Alloys (M. Peters and C. Leyens).16. Titanium and its Alloys for Medical Applications (J. Breme, et al.).17. Titanium in Dentistry (J. Lindigkeit).18. Titanium in Automotive Production (O. Schauerte).19. Offshore Applications for Titanium Alloys (L. Lunde and M. Seiersten).Subject Index.

High‐Aspect‐Ratio TiO2 Nanotubes by Anodization of Titanium

Abstract: Nanotubular material surfaces produced by the electrochemical formation of self-organized porous structures on materials such as aluminum and silicon have attracted significant interest in recent years. While scientific thrust is often directed towards the elucidation of the principles of the self-organization phenomena, technological efforts target applications based on the direct use of the high surface area, for example, for sensing 6] or controlled catalysis, exploit the optical properties in photonic crystals, waveguides, or in 3D arranged Bragg-stack type of reflectors. The highly organized structures may be used indirectly as templates for the deposition of other materials such as metals, semiconductors, or polymers. Over the past few years, nanoporous TiO2 structures have also been formed by electrochemical anodization of titanium. Although several applications have been proposed, a wider impact of these structures has been hampered by the fact that the layers could only been grown to a limiting thickness of a few hundreds of nanometers. Herein we demonstrate for the first time how high-aspectratio, self-organized, TiO2 films can be grown by tailoring the electrochemical conditions during titanium anodization. Figure 1 shows scanning electron microscope (SEM) images of self-organized porous titanium oxide formed to a thickness of approximately 2.5 mm in 1m (NH4)2SO4 electrolyte containing 0.5 wt.% NH4F. From the SEM images it is evident that the self-organized regular porous structure consists of pore arrays with a uniform pore diameter of approximately 100 nm and an average spacing of 150 nm. It is also clear that pore mouths are open on the top of the layer while on the bottom of the structure the tubes are closed by presence of an about 50-nm thick barrier layer of TiO2. The key to achieve high-aspect-ratio growth is to adjust the dissolution rate of TiO2 by localized acidification at the pore bottom while a protective environment is maintained along the pore walls and at the pore mouth. In our previous work in HF and NaF solutions it was established that the thickness of the porous layer is essentially the result of an equilibrium between electrochemical formation of TiO2 at the pore bottom and the chemical dissolution of this TiO2 in an F ion containing solution (Figure 2). The solubility of TiO2 in HF, forming [TiF6] 2 , is essential for pore formation, however, it is also the reason that previous attempts to form porous layers in HF electrolytes always resulted in layer thicknesses in the range of some 100 nm. We tackled the problem by controlling the self-induced acidification of the pore bottom that is caused by the electrochemical dissolution of the metal (Figure 2 a–c). Main reason for the localized acidification is the oxidation and hydrolysis of elemental titanium [Eq. (1), in Figure 2]. The chemical dissolution rate of TiO2 is highly dependent on the pH value (see Figure 2 d). Using a numerical simulation of the relevant ion fluxes we can construct the pH profile in the pore (such as in Figure 2b), in other words, the ideal ion flux for the desired pH profile can then be determined. Furthermore we can tune the dissolution rate by the dissolution current. In other words, using a buffered neutral solution as electrolyte and adjusting the anodic current flow to an ideal value, acid can be created where it is needed, that is, at the pore bottom, while higher pH values are established at the pore mouth as a result of migration and diffusion effects of the pH buffer species (NH4F, (NH4)2SO4). Assuming equilibrium, the flux of dissolving species (leading to acidification at the pore bottom) and the flux of buffering species are equal. The calculations show that for the experimental conditions given in Figure 1 the pH value at the pore bottom is around 2 and increase to about 5 at the pore mouth, this corresponds to a drop in the local chemical etch rate of about 20 times. We used a voltage-sweep technique to achieve a steadystate current and to establish the desired pH profile. The reason to use a voltage-sweep technique rather than a Figure 1. SEM images of porous titanium oxide nanotubes. The crosssectional (a), top (b), and bottom (c) views of a 2.5-mm thick selforganized porous layer. The titanium sample was anodized up to 20 V in 1m (NH4)2SO4 + 0.5 wt. % NH4F using a potential sweep from open-circuit potential to 20 V with sweep rate 0.1 Vs . The average pore diameter is approximately 100 nm and the average pore spacing is approximately 150 nm.

The Effect of Electrolyte Composition on the Fabrication of Self-Organized Titanium Oxide Nanotube Arrays by Anodic Oxidation

Abstract: We report on the fabrication of self-organized titanium oxide nanotube arrays of enhanced surface area prepared by anodic oxidation of a pure titanium sheet in electrolyte solutions containing potassium fluoride (KF) or sodium fluoride (NaF). The effects of electrolyte composition and concentration, solution pH, and the anodic potential on the formation of nanotubes and dimensions of the resulting nanotubes are detailed. Although nanotube arrays of length greater than 500 nm are not possible with hydrofluoric acid containing electrolytes [G.K. Mor, O.K. Varghese, M. Paulose, N. Mukherjee, C.A. Grimes, J. Mater. Res. 18, 2588 (2003)], by adjusting the pH of a KF containing electrolyte to 4.5 using additives such as sulfuric acid, sodium hydroxide, sodium hydrogen sulfate, and/or citric acid, we could increase the length of the nanotube-array to approximately 4.4 μm, an order of magnitude increase in length. The as-prepared nanotubes are composed of amorphous titanium oxide. Independent of the electrolyte composition, crystallization of the nanotubes to anatase phase occurred at temperatures ≥280 °C. Rutile formation occurred at the nanotube-Ti substrate interface at temperatures near 480 °C. It appears geometry constraints imposed by the nanotube walls inhibit anatase to rutile transformation. No disintegration of the nanotube array structure is observed at temperatures as high as 580 °C. The excellent structural and crystal phase stability of these nanotubes make them promising for both low- and high-temperature applications.

Enhancing the microstructure and properties of titanium alloys through nitriding and other surface engineering methods

Abstract: Over the last 40 years, the commercial production of titanium and its alloys has increased steadily. Whilst these materials have some very attractive properties, enabling applications in many industries, they are seldom used in mechanical engineering applications because of their poor tribological properties. This paper starts with an introduction to the titanium material and a review of the different types of surface treatment. The processes of nitriding, oxidation and carburizing are among the most popular thermochemical treatments aiming at improving the surface properties of Ti-alloys. Different kinds of nitriding are investigated like plasma nitriding, ion nitriding, and laser and gas nitriding. The kinetics of nitriding and the conditions for the formation of nitrided layers are studied. The influence of the main processing parameters such as temperature, time on the microstructure and the formation of new phases during the processes of nitriding is discussed. Also based on investigations presented in the literature, the effects of nitriding on the microhardness and the corrosion resistance of titanium and titanium alloys are analyzed. The improved mechanical properties, which arise from these thermochemical treatments, are discussed in relation to the potential for applying these alloys to different industries.

Transparent Highly Ordered TiO2 Nanotube Arrays via Anodization of Titanium Thin Films

Abstract: Titanium thin films, 400 nm to 1000 nm thick, fabricated by radio frequency (rf) sputter deposition are anodized in an electrolyte containing acetic acid and hydrofluoric acid to form optically transparent films of highly ordered titania nanotube arrays Real-time monitoring of the anodization current, at a fixed potential, is used to controllably eliminate the Ti layer underneath the titanium oxide nanotube array without disturbing the architecture Fabrication variables critical to achieving the transparent nanotube-array film include annealing temperature of the anodized, initially amorphous nanotube array and Ti-film sputter deposition variables, including rate, film thickness, and substrate temperature Structural investigations on the transparent nanotube arrays reveal only the presence of the anatase phase even after annealing at 500 °C In contrast, both rutile and anatase phases were observed in films with a metal layer underneath the nanotubes and annealed in an oxygen ambient above 430 °C Rutile growth occurs at the nanotube–metal interface as metal oxidation takes place during annealing The average refractive index of the transparent nanotube-array film is found to be 166 in the UV-vis range, with a calculated porosity of 67 %; the bandgap is determined as 334 eV, with a bandgap tail extending to 24 eV

Phase Transition between Nanostructures of Titanate and Titanium Dioxides via Simple Wet-Chemical Reactions

Abstract: Titanate nanofibers of various sizes and layered structure were prepared from inorganic titanium compounds by hydrothermal reactions. These fibers are different from "refractory" mineral substances because of their dimension, morphology, and significant large ratio of surface to volume, and, surprisingly, they are highly reactive. We found, for the first time, that phase transitions from the titanate nanostructures to TiO2 polymorphs take place readily in simple wet-chemical processes at temperatures close to ambient temperature. In acidic aqueous dispersions, the fibers transform to anatase and rutile nanoparticles, respectively, but via different mechanisms. The titanate fibers prepared at lower hydrothermal temperatures transform to TiO2 polymorphs at correspondingly lower temperatures because they are thinner, possess a larger surface area and more defects, and possess a less rigid crystal structure, resulting in lower stability. The transformations are reversible: in this case, the obtained TiO2 nanocrystals reacted with concentrate NaOH solution, yielding hollow titanate nanotubes. Consequently, there are reversible transformation pathways for transitions between the titanates and the titanium dioxide polymorphs, via wet-chemical reactions at moderate temperatures. The significance of these findings arises because such transitions can be engineered to produce numerous delicate nanostructures under moderate conditions. To demonstrate the commercial application potential of these processes, we also report titanate and TiO2 nanostructures synthesized directly from rutile minerals and industrial-grade rutiles by a new scheme of hydrometallurgical reactions.

Visible-light sensitization of TiO2 photocatalysts by wet-method N doping

Abstract: Titanium dioxide powders prepared by a wet method, i.e., the hydrolysis of titanium tetra-isopropoxide or titanium tetrachloride with an aqueous ammonia solution, followed by calcination at temperatures above 330 °C, exhibit photocatalytic activity in the visible-light region owing to N doping. The maximum absorption of visible light by the N-doped TiO 2 was about 50% at around 440 nm. Thermal analysis revealed that N doping occurs upon the oxidation of ammonia included in titanium hydroxide with lattice oxygen in TiO 2 . XPS analysis showed that the N doped in TiO 2 is less than 1.3 at.% and is not bound directly to Ti. The oxidation state of doped N was found close to that of NO. Quantum yield for the CO photooxidation on the N-doped TiO 2 in the visible region was less than that in UV region. These results show that the N doping by the wet method is similar to impurity doping such as metal ion doping.

Electrochemical lithium reactivity with nanotextured anatase-type TiO2

Abstract: Anatase TiO2 particles were synthesized by a two-step method consisting of the preparation of a solid precursor through hydrolysis of titanium alkoxide followed by heat treatment at different temperatures under ambient air. This simple method led to a highly porous material with a 200 nm homogenous particle size, while the BET specific surface area and crystallite sizes evolved between 49 m2 g−1 to 223 m2 g−1 and from 17.0 nm to 6.3 nm, respectively. Their electrochemical performances clearly revealed the beneficial influence of the divided texture of anatase-type TiO2 on the reactivity with lithium, namely in terms of reversibility. Furthermore, we showed that the TiO2 texture strongly affects the extent of the solid solution domain. Finally, through a simple chemical titration it was possible to clearly quantify the capacitive/faradaic contributions of the electrochemical reaction.

Chemical modification of titanium alkoxides for sol–gel processing

Abstract: The chemical modification of titanium alkoxides by alkoxy- and aminoalcohols, s-diketones, s-ketoesters, carboxylic and phosphonic acids, and related compounds, and the hydrolysis behavior of the organically modified precursors are reviewed Special focus is put on structural aspects and on the possibility to introduce functional organic groups Such precursors have a high potential for innovative materials syntheses because they permit control of the precursor reactivity in sol–gel processes and the preparation of titania-based inorganic–organic hybrid materials Coordination, solvation, aggregation and redistribution equilibria play an important role in the chemistry of the modified titanium alkoxides, and organic side reactions have to be taken into account

Initiation and Growth of Self-Organized TiO2 Nanotubes Anodically Formed in NH4F ∕ ( NH4 ) 2SO4 Electrolytes

Abstract: The anodic formation of self-organized porous TiO 2 on titanium was investigated in 1 M (NH 4 ) 2 SO 4 electrolytes containing 0.5 wt % NH 4 F by potential sweeps to 20 V S C E . By a combination of electrochemical, morphological, and compositional information we show that the sweep rate has a significant influence on the initiation and growth of the porous structures. In the first phase of the anodization process, a precursor barrier type of oxide film is formed; underneath this film pores then start growing first randomly and then self-organize. High-aspect-ratio TiO 2 nanostructures can be obtained under optimized electrochemical conditions. These nanotubular oxide layers have single-pore diameter ranging from 90 to 110 nm, average spacing of 150 nm, and porosity in the order of 37-42%. The current work indicates that the nature of the initial barrier-type layer has a strong influence on establishing optimized pore growth conditions.

Plasma treatment of hafnium-containing materials

Abstract: In one embodiment, a method for forming a dielectric material is provided which includes exposing a substrate sequentially to a metal-containing precursor and an oxidizing gas to form metal oxide (e.g., HfO x ) during an ALD process and subsequently exposing the substrate to an inert plasma process and a thermal annealing process. Generally, the metal oxide contains hafnium, tantalum, titanium, aluminum, zirconium, lanthanum or combinations thereof. In one example, the inert plasma process contains argon and is free of nitrogen, while the thermal annealing process contains oxygen. In another example, an ALD process to form a metal oxide includes exposing the substrate sequentially to a metal precursor and an oxidizing gas containing water vapor formed by a catalytic water vapor generator. In an alternative embodiment, a method for forming a dielectric material is provide which includes exposing a substrate to a deposition process to form a metal oxide layer and subsequently exposing the substrate to a nitridation plasma process and a thermal annealing process to form metal oxynitride (e.g., HfO x N y ).

Pyrogenic Iron(III)-Doped TiO2 Nanopowders Synthesized in RF Thermal Plasma: Phase Formation, Defect Structure, Band Gap, and Magnetic Properties

Abstract: Iron(III)-doped TiO(2) nanopowders, with controlled iron to titanium atomic ratios (R(Fe/Ti)) ranging from nominal 0 to 20%, were synthesized using oxidative pyrolysis of liquid-feed metallorganic precursors in a radiation-frequency (RF) thermal plasma. The valence of iron doped in the TiO(2), phase formation, defect structures, band gaps, and magnetic properties of the resultant nanopowders were systematically investigated using Mossbauer spectroscopy, XRD, Raman spectroscopy, TEM/HRTEM, UV-vis spectroscopy, and measurements of magnetic properties. The iron doped in TiO(2) was trivalent (3+) in a high-spin state as determined by the isomer shift and quadrupole splitting from the Mossbauer spectra. No other phases except anatase and rutile TiO(2) were identified in the resultant nanopowders. Interestingly, thermodynamically metastable anatase predominated in the undoped TiO(2) nanopowders, which can be explained from a kinetic point of view based on classical homogeneous nucleation theory. With iron doping, the formation of rutile was strongly promoted because rutile is more tolerant than anatase to the defects such as oxygen vacancies resulting from the substitution of Fe(3+) for Ti(4+) in TiO(2). The concentration of oxygen vacancies reached a maximum at R(Fe/Ti) = 2% above which excessive oxygen vacancies tended to concentrate. As a result of this concentration, an extended defect like crystallographic shear (CS) structure was established. With iron doping, red shift of the absorption edges occurred in addition to the d-d electron transition of iron in the visible light region. The as-prepared iron-doped TiO(2) nanopowders were paramagnetic in nature at room temperature.

Titanium Alloys: Russian Aircraft and Aerospace Applications

Abstract: Structure and Properties of Unalloyed Titanium Interaction Between Titanium and Alloying Elements Low and Middle Strength Alloys General Usage, Medium and High-Strength Martensitic Type Two Phase Alloys Heat Resistance Titanium Alloys Titanium Alloys for Castings Some Peculiarities of Titanium Alloys Production and Usage in Aero-Space Industries Fields and Efficiency of Application Titanium Alloys in Aero-Engines and Aircrafts

Self‐organized nanotubular oxide layers on Ti‐6Al‐7Nb and Ti‐6Al‐4V formed by anodization in NH4F solutions

Abstract: The present work reports the fabrication of self-organized porous oxide-nanotube layers on the biomedical titanium alloys Ti-6Al-7Nb and Ti-6Al-4V by a simple electrochemical treatment. These two-phase alloys were anodized in 1M (NH(4))(2)SO(4) electrolytes containing 0.5 wt % of NH(4)F. The results show that under specific anodization conditions self-organized porous oxide structures can be grown on the alloy surface. SEM images revealed that the porous layers consist of arrays of single nanotubes with a diameter of 100 nm and a spacing of 150 nm. For the V-containing alloy enhanced etching of the beta phase is observed, leading to selective dissolution and an inhomogeneous pore formation. For the Nb-containing alloy an almost ideal coverage of both phases is obtained. According to XPS measurements the tubes are a mixed oxide with an almost stoichiometric oxide composition, and can be grown to thicknesses of several hundreds of nanometers. These findings represent a simple surface treatment for Ti alloys that has high potential for biomedical applications.

Diffusion bonding of commercially pure titanium to 304 stainless steel using copper interlayer

Abstract: Diffusion bonding was carried out between commercially pure titanium (cpTi) and 304 stainless steel (304ss) using copper as interlayer in the temperature range of 850–950 ◦ C for 1.5 h under 3 MPa load in vacuum. The microstructures of the transition joints were revealed in optical and scanning electron microscopy (SEM). The study exhibits the presence of different reaction layers in the diffusion zone and their chemical compositions were determined by energy dispersive spectroscopy. The occurrence of different intermetallic compounds such as CuTi2, CuTi, Cu3Ti2 ,C u 4Ti3, FeTi, Fe2Ti, Cr2Ti, T2 (Ti40Cu60−xFex ;5

Defect-related optical behavior in surface-modified TiO2 nanostructures

Abstract: The surface modification of TiO2 nanostructures to incorporate nitrogen and form visible light absorbing titanium oxynitride centers is studied. Anatase TiO2 structures in the 5–20 nm range, formed by a wet chemical technique, were surface modified and the nitridation of the highly reactive TiO2 nanocolloid surface, as determined by X-ray photoelectron spectroscopy (XPS) studies, is achieved by a quick and simple treatment in alkyl ammonium compounds. The nitriding process was also simultaneously accompanied by metal seeding resulting in a metal coating layer on the TiO2 structures. The structure of the resultant titanium oxynitride nanostructures remains anatase. These freshly prepared samples exhibited a strong emission near 560 nm (2.21 eV), which red-shifted to 660 nm (1.88 eV) and dropped in intensity with aging in the atmosphere. This behavior was also evident in some of the combined nitrogen doped and metal seeded TiO2 nanocolloids. Electron spin resonance (ESR) performed on these samples identified a resonance at g = 2.0035, which increased significantly with nitridation. The resonance is attributed to an oxygen hole center created near the surface of the nanocolloid, which correlates well with the observed optical activity.

Characterization of Titanium Dioxide Nanoparticles Using Molecular Dynamics Simulations

Abstract: Molecular dynamics simulations of titanium dioxide nanoparticles in the three commonly occurring phases (anatase, brookite, and rutile) are reported. The structural properties inferred by simulated X-ray diffraction patterns of the nanoparticles were investigated. The titanium-oxygen bond length as a function of size, phase, and temperature was determined and was found to be dependent on the coordination environment of the titanium and independent of phase and size. The equilibrium Ti-O bond length is 1.86 A for a four-coordinated titanium ion, 1.92 A for a five-coordinated titanium ion, and 1.94 A for an octahedral titanium ion. Smaller nanoparticles are characterized by a higher fraction of titanium ions that are four and five coordinated, due to the larger surface area-to-volume ratios. The surface energies for anatase, rutile, and brookite particles were reported. The surface energy of the nanoparticle increases and approaches a constant value as the particle gets bigger. The surface energies of small rutile particles are higher than that for anatase particles of a similar size, consistent with anatase being the more stable phase of nanocrystalline titanium dioxide.

Optimum surface properties of oxidized implants for reinforcement of osseointegration: surface chemistry, oxide thickness, porosity, roughness, and crystal structure.

Abstract: PURPOSE: To investigate detailed surface characterization of oxidized implants in a newly invented electrolyte system and to determine optimal surface oxide properties to enhance the bone response in rabbits. MATERIALS AND METHODS: A total of 100 screw-type titanium implants were prepared and divided into 1 control group (machine-turned implants) and 4 test groups (magnesium ion-incorporated oxidized implants). Forty implants were used for surface analyses. A total of 60 implants, 12 implants from each group, were placed in the tibiae of 10 New Zealand white rabbits and measured with a removal torque test after a healing period of 6 weeks. RESULTS: For the test groups, the oxide thicknesses ranged from about 1,000 to 5,800 nm; for the control group, mean oxide thickness was about 17 nm. The surface morphology showed porous structures for test groups and nonporous barrier film for the control group. Pore diameter ranged from < or = 0.5 microm to < or = 3.0 microm. In regard to surface roughness, arithmetic average height deviation (Sa) values varied from 0.68 to 0.98 microm for test implants and 0.55 microm for control implants; developed surface ratio (Sdr) values ranged from 10.6% to 46% for the test groups and were about 10.6% for the control group. A mixture of anatase and rutile-type crystals were observed in the test groups; amorphous-type crystals were observed in the control group. After a healing period of 6 weeks, removal torque measurements in all 4 test groups demonstrated significantly greater implant integration as compared to machine-turned control implants (P < or = .033). DISCUSSION: Determinant oxide properties of oxidized implants are discussed in association with bone responses. Of all surface properties, RTVs were linearly increased as relative atomic concentrations of magnesium ion increase. CONCLUSIONS: Surface properties of the oxidized implants in the present study, especially surface chemistry, influenced bone responses. The surface chemistry of the optimal oxidized implant should be composed of approximately 9% magnesium at relative atomic concentration in titanium oxide matrix and have an oxide thickness of approximately 1,000 to 5,000 nm, a porosity of about 24%, and a surface roughness of about 0.8 microm in Sa and 27% to 46% in Sdr; its oxide crystal structure should be a mixture of anatase- and rutile-phase crystals.

Nonalloyed titanium as a bioinert metal--a review.

Abstract: Titanium is used for many dental applications and instruments, such as orthodontic wires, endodontic files, dental implants, and cast restorations. The popularity of titanium is primarily due to its good mechanical properties, its high corrosion resistance, and its excellent biocompatibility. A thorough review of the medical and dental literature reveals, however, that titanium can also cause chemical-biological interactions. Tissue discoloration and allergic reactions in patients who have come in contact with titanium have been reported. The biostability of titanium is becoming increasingly questioned. At the same time, new technologies and materials, such as high-performance ceramics, are emerging which could replace titanium in dentistry in the not-too-distant future.