Showing papers on "Titanium published in 1998"

Mechanical properties of biomedical titanium alloys

Abstract: Titanium alloys are expected to be much more widely used for implant materials in the medical and dental fields because of their superior biocompatibility, corrosion resistance and specific strength compared with other metallic implant materials. Pure titanium and Ti–6Al–4V, in particular, Ti–6Al–4V ELI have been, however, mainly used for implant materials among various titanium alloys to date. V free alloys like Ti–6Al–7Nb and Ti–5Al–2.5Fe have been recently developed for biomedical use. More recently V and Al free alloys have been developed. Titanium alloys composed of non-toxic elements like Nb, Ta, Zr and so on with lower modulus have been started to be developed mainly in the USA. The β type alloys are now the main target for medical materials. The mechanical properties of the titanium alloys developed for implant materials to date are described in this paper.

Design and mechanical properties of new β type titanium alloys for implant materials

Abstract: Pure titanium and Ti–6Al–4V alloy have been mainly used as implant materials. V-free titanium alloys like Ti–6Al–7Nb and Ti–5Al–2.5Fe have been then developed because toxicity of V has been pointed out. Al- and V-free titanium alloys as implant materials have been developed. Most of them are, however, α+β type alloys. β type titanium alloys with lower moduli of elasticity and greater strength have been developed recently. Design of new β type titanium alloys composed of non-toxic elements like Nb, Ta, Zr, Mo or Sn with lower moduli of elasticity and greater strength were, therefore, studied based on the d-electron alloy design method, and the basic mechanical properties of designed alloys of button ingots melted by tri-arc furnace in the laboratory were investigated in this study. β type alloys, Ti–Nb–Ta–Zr, Ti–Nb–Ta–Mo and Ti–Nb–Ta–Sn system alloys designed in this study are expected to have greater performance for implant materials. The Young's moduli of these alloys are lower compared with that of Ti–6Al–4V ELI which has been used as an implant material. The alloys on which some heat treatments have been conducted offer suitable tensile properties as implant materials. The tensile strength and elongation of designed alloys in this study are equivalent or greater than required values already reported.

Determination of the concentration of surface hydroxyl groups on metal oxide films by a quantitative XPS method

Abstract: Quantitative XPS has been used to determine the surface concentration of hydroxyl groups in native air-formed oxide films on metals having low surface areas. A mathematical expression has been derived to give the concentration of surface hydroxyl groups as a function of the intensity ratio of the OH to O2− contributions to the O 1s photopeak. This expression is based on modeling the oxide film on a metal to be a multilayer system consisting of an outermost layer of organic contamination, a layer of chemisorbed water, a surface hydroxylated region of the oxide film and the inner portion of the oxide film. The average values of the experimentally determined concentrations of surface hydroxyl groups are 15, 13, 11, 6 and 8 OH nm−2 for oxide-covered aluminum, chromium, titanium, tantalum and silicon, respectively. X-ray photoelectron spectroscopy depth profiles using argon ion sputtering and variable-angle XPS have been utilized in this work. Surface treatments have employed either ultrasonic cleaning with organic solvents or argon plasma treatment. © 1998 John Wiley & Sons, Ltd.

Electrodes based on Magnéli phase titanium oxides: the properties and applications of Ebonex® materials

Abstract: Magneli phases are a range of substoichiometric oxides of titanium of the general formula TinO2n−1, (where n is between 4 and 10) produced from high temperature reduction of titania in a hydrogen atmosphere These blue/black ceramic materials exhibit a conductivity comparable to that of graphite and can be produced in a number of forms, such as tiles, rods, fibres, foams and powders While these materials have been studied for many years, they have only recently received interest for use as ceramic electrode materials, commercially termed ‘Ebonex®’, and are beginning to challenge precious metal coated anodes for some applications in aggressive electrolytes Other uses for these materials include electrowinning, electroplating, battery materials, impressed current cathodic protection anodes, electrochemical soil remediation, oxidation of organic wastes, flexible cable materials and electrophoresis The scope of this review considers the structure and properties of Magneli phase titanium oxide materials, together with their electrochemical behaviour and applications

Wettability of carbon by aluminum and aluminum alloys

Abstract: Wetting (both equilibrium contact angle and spreading kinetics) of aluminum and aluminum alloys with silicon and titanium on carbon substrates is investigated as a function of temperature and carbon microstructure. Experiments are carried out by the sessile drop technique under high vacuum, in the range from 1023 to 1250 K. Three different types of carbon substrates are examined: vitreous carbon, pyrolytic carbon and graphite pseudo single crystals. It is shown that an increase in temperature and a decrease in the preferred orientation of the graphite basal planes with respect to the substrate surface greatly enhance the three-phase line reactivity and the spreading kinetics. From a practical point of view the results obtained in this study show that in processes involving short-time contact (up to a few minutes) between deoxidized molten Al (or Al–Si and Al–Ti alloys) and carbon at T

Structural and Electronic Properties of Sol−Gel Titanium Oxides Studied by X-ray Absorption Spectroscopy

Abstract: X-ray absorption spectroscopy (XAS) has been used to study the local Ti environment in titania xerogel samples containing nanoparticles of different sizes. The xerogels were prepared by hydrolysis of titanium isopropoxide followed by peptization with HNO3 and size control was achieved through calcination in air at different temperatures. An amorphous precipitate obtained by hydrolysis of titanium isopropoxide prior to peptization with HNO3 has also been studied. The X-ray absorption near edge structure (XANES) of the precipitate possesses a characteristic preedge that is dominated by a transition designated as A2 at 4970.7 eV, and assigned to five coordinate Ti. This A2 component is detected in all of the studied xerogels. Its intensity decreases as the surface-to-volume ratio of the titania particles decreases, suggesting that it is associated with surface layers of the anatase particles. Other changes observed in the XANES of the xerogels as a function of particle size include broadening of 1s → np tran...

Surface modification of titanium alloys for combined improvements in corrosion and wear resistance

Abstract: A simple and effective surface modification technique, namely palladium-treated thermal oxidation (PTO), has been developed in the present research. Comparative investigations on both corrosion and wear resistance have been carried out on surface-engineered titanium-based materials by conventional plasma nitriding (PN), thermal oxidation (TO), and the newly developed palladium-treated thermal oxidation (PTO). Both the TO- and PTO-treated materials have a significantly superior corrosion resistance in boiling HCl solutions compared to the PN-treated and untreated materials. The lifetime for the protective surface layer breakdown of the TO-treated titanium in boiling 20% HCl solution is about 13 times that of the PN-treated titanium, whereas the lifetime of the PTO-treated material has been increased further by a factor of 2.6 over the TO-treated material. The PTO-treated material has shown a better anti-scuffing capacity than the TO-treated material under oil-lubricated conditions. Characterisation of both the TO- and PTO-treated surface layers was performed using glow discharge spectrometry (GDS), X-ray diffraction (XRD) and scanning electron microscopy (SEM).

Hot workability of titanium and titanium aluminide alloys—an overview

Abstract: The hot workability of conventional titanium alloys and titanium aluminides is reviewed. For both alloy classes, the influence of hot working variables and microstructure on failure via fracture or flow-localization controlled processes is summarized. The occurrence of wedge cracking and cavitation during bulk forming of α / β alloys with Widmanstatten microstructures or γ titanium aluminides with lamellar or equiaxed structures, is examined. In particular, the effects of grain size, grain boundary second phases and process variables on failure are presented. Observations and models of flow localization and cavitation processes which lead to failure during low strain rate, superplastic, tensile-type deformation of titanium and titanium aluminide alloys with fine equiaxed structures, are also described. In the area of flow-localization-controlled failure during bulk forming, the occurrence of shear bands and other flow nonuniformities during both conventional and isothermal hot working processes is reviewed. The influence of material properties, such as flow softening rate and strain rate sensitivity and process variables, which lead to temperature and hence flow nonuniformities, is examined. The flow localization concepts are illustrated for several hot working processes.

Repassivation of titanium and surface oxide film regenerated in simulated bioliquid

Abstract: The change in potential during repassivation of titanium in artificial bioliquids was examined, and the regenerated surface oxide film on titanium was characterized using X-ray photoelectron spectroscopy and Auger electron spectroscopy to elucidate the repassivation reaction of titanium in a biological system. The repassivation rate in Hanks' solution was slower than that in saline and was not influenced by the pH of the solution. This indicates that more titanium ions dissolve in a biological system than hitherto was predicted when the surface film is destroyed. Phosphate ions are taken up preferentially in the surface film during regeneration, and the film consists of titanium oxide and titanium oxyhydroxide containing titanium phosphate. Calcium ions and phosphate ions are adsorbed by the film after regeneration, and calcium phosphate or calcium titanium phosphate is formed at the outermost surface. Ions constituting Hanks' solution other than calcium and phosphate were absent from the surface oxide.

Calcium phosphate induction by sol‐gel‐derived titania coatings on titanium substrates in vitro

Abstract: Titanium and its alloys are used widely in the manufacture of orthopedic and dental implants. Sol-gel-prepared titania is able to stimulate bone-like apatite formation in in vitro and in vivo cultures. These materials can be used, for example, as coatings on dental and orthopedic implants. However, the processes that lead to apatite formation are not fully understood. In this study different kinds of titania coatings on commercially pure titanium (c.p. Ti) were tested for apatite-forming ability. The rate of apatite formation is considered to be descriptive of a material's bioactive (bone-bonding) potential. Apatite-forming tests were done in simulated body fluid (SBF). Apatite-forming ability was highest with the addition of valeric acid to sol (600°C) or with sintering sol-gel coatings at 450°–550°C. At that temperature range calcium phosphate forms on the coatings in 1 week. Calcium phosphate forming is observed in 1 day on standard coatings sintered at 500°C. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 504–510, 1998.

Characterization of Titanium−Silicon Binary Oxide Catalysts Prepared by the Sol−Gel Method and Their Photocatalytic Reactivity for the Liquid-Phase Oxidation of 1-Octanol

Abstract: Titanium−silicon (Ti/Si) binary oxides having different Ti contents were prepared by the sol−gel method and used as photocatalysts. The photocatalytic reactivity of these catalysts was investigated as a function of the Ti content for the liquid-phase oxidation of 1-octanol to 1-octanal, and it was found to be dramatically enhanced in regions of lower Ti content. In situ photoluminescence, UV−vis reflectance, FT-IR, ESR, XAFS, XRD, and XPS spectroscopic investigations of these Ti/Si binary oxides indicated that the titanium oxide species are highly dispersed in the SiO2 matrixes and exist in a tetrahedral coordination exhibiting a characteristic photoluminescence spectrum due to the radiative decay from the charge-transfer excited state of the tetrahedrally coordinated titanium oxide species. The good parallel relationship between the yield of the photoluminescence and the specific photocatalytic reactivity of the Ti/Si binary oxides as a function of the Ti content clearly indicates that the high photocata...

Selective oxidation of propylene over gold deposited on titanium-based oxides

Abstract: Gold supported on titanium-based metal oxides can assist the selective partial oxidation of propylene at temperatures from 313 K to 573 K in a gas containing both H2 and O2 The preparation method was found to be crucial in controlling the selectivities In general, impregnation and chemical vapor deposition methods do not produce selective catalysts Only the deposition-precipitation method makes gold selective to propylene oxide or propanal, suggesting that a strong contact between the gold particles and the titanium ion sites on the support is important The effect of changing the support was also dramatic; the use of the anatase form of TiO2 and Ti-MCM-41 results in propylene oxide production, while the rutile structure of TiO2 caused complete oxidation to CO2 Microporous crystalline titanium silicates such as TS-1, TS-2, and Ti-β zeolite make gold relatively selective to propanal and of the three TS-1 gives the highest selectivity These results indicate that the oxidation of propylene in the copresence of H2 must involve the surface of the supports and that the reaction takes place at the interface perimeter around the gold particles

Variation of oxide films on titanium induced by osteoblast‐like cell culture and the influence of an H2O2 pretreatment

Abstract: Variations of titanium oxide films induced by osteoblast-like cells in a rat calvaria culture system and the influence of an H2O2 pretreatment have been investigated by using X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy For abraded titanium, the results revealed that phosphate and calcium ions may incorporate into the surface oxide film during the cell culture, forming a precipitate with a Ca/P ratio near that of hydroxyapatite Oxidized carbon also was found in the surface layer, most likely precipitated hydroxylcarbonated apatite (HCA) The H2O2 pretreatment of titanium in a phosphate-buffered saline solution results in a 10-fold thickened porous oxide film and large amounts of surface hydroxyl groups as well as a certain amount of phosphate ions inside the oxide film During the cell culture, the H2O2-treated titanium surface favors the ion incorporation and precipitation of the HCA-like compound, which probably is inlaid into the oxide film Osteoblast-like cells on the H2O2-treated titanium showed a more active morphology during the initial stage compared with cells on abraded titanium Moreover, bone-like nodule formation and mineralization appear to be related to the precipitation of the HCA-like compound on the surface The results are discussed with respect to corrosion resistance, ion incorporation and precipitation of the HCA-like compound on the surface, osseointegration, and bioactivity of titanium Implants © 1998 John Wiley & Sons, Inc J Biomed Mater Res, 40, 244–256, 1998

Quasi-biological apatite film induced by titanium in a simulated body fluid

Abstract: Commercially pure titanium (cpTi) is capable of inducing the formation of a carbonated apatite onto its surface in a simulated body fluid (SBF) comprised of calcium ions, phosphate ions, and other inorganic species present in the body fluid In addition to the incorporation of carbonate ions, such formed apatite has other important characteristics of the bone mineral phase, such as a small crystal size and ionic substitution by Mg2+ and Cl− Thus, we call this apatite a quasi-biological apatite The formation of the quasi-biological apatite is proposed to be related to TiOH groups that develop on the titanium surface through interaction with the SBF The results suggest that titanium implants may be activated such that they can form a strong bond with bone tissue through the in vivo formation of apatite Since the solution can reach any open space, the process discussed in this study is very suitable for coating porous titanium implants with a quasi-biological apatite film © 1998 John Wiley & Sons, Inc J Biomed Mater Res, 41, 341–348, 1998

In-situ hot pressing/solid-liquid reaction synthesis of dense titanium silicon carbide bulk ceramics

Abstract: An in-situ hot pressing/solid-liquid reaction process was developed for the synthesis of dense polycrystalline Ti3SiC2 ceramics using Ti, Si, and graphite powders as starting materials. The present work demonstrated that this process was one of the most effective and simple methods for the preparation of dense bulk Ti3SiC2 materials. Lattice constants of a=3.068 and c=17.645 are calculated for Ti3SiC2 made through this process. The synthesis temperature influenced the phase composition, microstructure and mechanical properties of Ti3SiC2 prepared at different temperatures. And bulk materials with flexural strength of 480 MPa and fracture toughness of 7.88 MPa.m1/2 were obtained at 1600°C. The high fracture toughness and strength are discussed based on microstructure analysis.

Carbon encapsulated nanoparticles of Ni, Co, Cu, and Ti

Abstract: Despite intensive research on the encapsulation of metal nanoparticles into carbon clusters deposited by arc discharge, the detailed pathways of the formation of these novel forms of materials remain unclear. The growth of a rich variety of morphologies is not well understood. Studies are reported here on the growth phenomena of different metals encapsulated into carbon cages that emphasize the effect of carbon and metal supply on the size of particles. Post-deposition annealing was introduced as a process that induces structural rearrangements, and thus enables changes in morphologies. A set of carbon encapsulated Ni, Co, Cu, and Ti particles were prepared by an arc discharge process modified in the geometry of the anode and flow pattern of helium or methane gas. The samples were then annealed under flowing argon gas. Three annealing temperatures were used (600, 900, and 1100 °C). Samples were characterized by transmission and scanning electron microscopy. Particles made under the same experimental conditions are of roughly the same size. When the supply of metal in the reactor space was increased by using a larger diameter of the metal pool, the average diameter of the particles is bigger than those of produced from the smaller metal pool. The thickness of the carbon cages of Ni and Co particles increased during the annealing. The carbon cages of Cu particles, however, did not change their thickness, while some carbon coatings of Ti particles disappeared under annealing. This suggests that the addition of layers for the Ni and Co cages results from a precipitation of carbon previously dissolved in the metal, while the much lower solubility of C in Cu prevents this possibility. The Ti of high reactivity, on the other hand, may further react with the available carbon under annealing to form TiC. It is suggested that annealing provides additional thermal energy that makes structural re-arrangement possible long after the initial deposition process was terminated. This may explain the rich variety of morphologies of deposit obtained at different locations of the reaction chamber.

Preparation of bioactive microporous titanium surface by a new two-step chemical treatment.

Abstract: Microporous oxide layers allowing fast deposition of calcium phosphate layers (CPLs) were formed on commercially pure titanium (c.p.Ti) after the application of a newly developed two-step chemical treatment. The micropores were of submicrometre size. The two-step treatment was carried out by etching c.p.Ti samples with HCl and H2SO4 first and then treating them in boiling 0.2 N NaOH solution at 140 °C for 5 h. Conformal CPLs, about 20 μm thick, were deposited on the two-step treated c.p.Ti surface by means of a two-day immersion in an in vitro supersaturated calcification solution. The CPL was characterized to be mainly composed of two sublayers, i.e. an outside loose octacalcium phosphate crystal sublayer and an inside dense carbonated apatite sublayer. A scratching test indicated that the apatite sublayer was strongly bonded to the c.p.Ti substrate. Moreover, it was observed that the untreated or single-step treated c.p.Ti surfaces are not only morphologically different from one another but significantly different from the two-step treated one, in that no precipitation was observed on them up to 14 d immersion in the same calcification solution. It is indicated that the two-step chemical treatment is a simple and easily controllable method to prepare bioactive titanium surfaces and subsequently to induce the rapid precipitation of conformal and adherent CPL from in vitro supersaturated calcification solutions. © 1998 Chapman & Hall

Preparation of calcium phosphate coatings on titanium implant materials by simple chemistry

Abstract: A two-step chemical treatment has been developed in our group to prepare commercially pure titanium (cpTi) surfaces that will allow calcium phosphate (Ca-P) precipitation during immersion in a supersaturated calcification solution (SCS) with ion concentrations of [Ca2+] = 3.10 mM and [HPO42−] = 1.86 mM. It was observed that a precalcification (Pre-Ca) procedure prior to immersion could significantly accelerate the Ca-P deposition process. In this work, the bioactivity of chemically treated cpTi and Ti6Al4V was further verified by applying commercially available Hanks' balanced salt solution (HBSS), an SCS with very low ion concentrations of [Ca2+] = 1.26 mM and [HPO42−] = 0.779 mM, as the immersion solution. It was found that a uniform and very dense apatite coating containing magnesium impurities was formed if the Pre-Ca procedure was performed before immersion, as compared with the loose Ca-P layer obtained from the abovementioned high concentration of SCS. The formation of a microporous titanium dioxide thin surface layer on cpTi or Ti6Al4V by the two-step chemical treatment could be the main reason for the induction of apatite nucleation and growth from HBSS. Variations of pH values, Ca and P concentrations, and immersion time in HBSS were investigated to reveal the detailed process of Ca-P deposition. The described treatments provide a simple chemical method to prepare Ca-P coatings on both cpTi and Ti6Al4V. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 41, 227–236, 1998.

CoNbTi as high resistivity SAL material for high-density MR

Abstract: A soft adjacent layer made from a ternary alloy material and a MR sensor utilizing this soft adjacent layer The ternary alloy material CoXY includes cobalt (Co), a first transition metal X and a second transition metal Y In a preferred embodiment, X is niobium (Nb) and Y is titanium (Ti) so that the resulting ternary alloy material is CoNbTi Alternatively, X and Y may be any transition metals such that the resulting ternary alloy material CoXY exhibits properties similar to CoNbTi The high-density MR sensor of the present invention includes a SAL made from the ternary alloy material, a MR layer and a non-magnetic spacer sandwiched between the SAL and MR layer

A quantitative comparison of machined commercially pure titanium and titanium-aluminum-vanadium implants in rabbit bone.

Abstract: Screw-shaped implants made from rods of commercially pure titanium (grade 1) and titanium-aluminum-vanadium (grade 5) were machined, and the implant surface structures were numerically described before being placed in rabbit tibiae for healing periods of 1 month, 6 months, and 12 months. Quantitative comparisons of the removal torque (Ncm) necessary to loosen the implants from the bone bed were performed. Short-term (1 month) observations revealed no significant differences between the two tested materials. However, after 6 and 12 months, the commercially pure titanium implants were significantly more stable in the bone bed, as compared to the alloy samples. After 6 months, the commercially pure titanium had a mean removal torque of 29 Ncm versus 23 for the alloy (P = .01), and after 12 months, the mean removal torque was 38 Ncm for commercially pure titanium as compared to 35 Ncm for the alloy (P = .01). Quantifications of the bone tissue response to the materials did not show any significant differences; however, the commercially pure titanium showed a tendency to have a higher percentage of bone in contact with the implant as compared to the alloy screws. Bone volumes in the threads were similar. The absence of any quantitative light microscopic difference after 1 month following placement may relate to the fact that there was a sparse amount of bone, since the tissue was in the organization/granulation phase. After 6 and 12 months of follow-up, substantial bone formation had occurred, resulting in significantly increased removal torques for the commercially pure titanium samples. (INT J ORAL MAXILLOFAC IMPLANTS 1998;13:315‐321)