Showing papers on "Titanium published in 1999"

Structure and physicochemistry of anodic oxide films on titanium and TA6V alloy

Abstract: Anodization of titanium and its alloys is an important surface treatment, especially for adhesion applications, but is not as well studied as for aluminium alloys. This paper deals with the morphological, structural and physicochemical characterization of anodic oxide films grown on titanium and Ti–6Al–4V (TA6V) in chromic acid solution without (CA) or with (CA/HF) hydrofluoric acid addition. Several investigations methods are used: high-resolution scanning electron microscopy (HR-SEM), reflection high-energy electron diffraction (RHEED), x-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), nuclear reaction analysis (NRA) and wetting angle measurements. The occurrence and morphology of the nanoporous structure for CA/HF anodization are described. The compact films grown in CA solution are amorphous and the porous films grown in the CA/HF solution are partially crystalline. The thickness and morphology of the films are described and discussed as a function of the anodizing conditions and of the composition of the underlying substrate. The composition of the film appears to be TiO2+Al2O3 (with Ti/Al atomic ratio ∽5), with incorporation of fluorine from the solution in the porous films and of small quantities of vanadium in the films that are grown. The specific role played by the Cr(VI) and F species on the film growth-and-dissolution formation process is discussed and a growth mechanism is proposed. Copyright © 1999 John Wiley & Sons, Ltd.

Nanostructuring Titania: Control over Nanocrystal Structure, Size, Shape, and Organization

Abstract: Control over crystal structure, size, shape, and organization of TiO2 nanocrystals has been achieved by means of wet chemistry. Hydrolysis and polycondensation of titanium alkoxide [Ti(OR)4] has been performed in the presence of tetramethylammonium hydroxide (Me4NOH). This base both catalyzes the reaction and provides an organic cation that stabilizes the anatase polyanionic cores formed in this medium. These anatase clusters are organized so as to favour self-assembly into intermediate nanocrystals, which, in turn, self-assemble into superlattices. This self-assembling process has been exploited for the processing of highly structured titania films. Furthermore, larger anatase TiO2 nanocrystals of different sizes and shapes have been obtained by adjusting the relative concentrations of titanium alkoxide and Me4NOH, the reaction temperature, and the pressure. HRTEM, XRD, and EXAFS have been used to characterize the various samples and to elucidate the growth of titania anatase. Our observations are in accordance with theoretically predicted condensation and growth pathways. The formation of mesoscopic structures through a self-assembling process of the multiply charged polytitanate anions in the presence of Me4N+ is also discussed.

Mechanical surface treatments on titanium, aluminum and magnesium alloys

Abstract: Generally, mechanical surface treatments induce high dislocation densities in near-surface regions. Due to the local plastic deformation, residual stresses are developed and the surface topography is changed. These changes can have contradictory influences on the fatigue strength. Results on the influence of mechanical surface treatments on magnesium are presented in relation to the relatively well-studied titanium and aluminum alloys.

Incorporation of Titanium into Mesoporous Silica Molecular Sieve SBA-15

Abstract: Mesoporous silica molecular sieve SBA-15 has been synthesized and incorporated with variable amounts of titanium via incipient-wetness impregnation with titanium isopropoxide in ethanol followed by calcination. Characterization by powder X-ray diffraction, nitrogen adsorption, X-ray photoelectron, Raman, and diffuse reflectance ultraviolet spectroscopies has been carried out to understand the chemical nature of the titanium. The results suggest that titanium is present in two distinct chemical forms and that their relative amounts depend on the titanium loading. At low titanium loading of 1 atom % relative to silicon, the titanium ions are monatomically dispersed and the pore size of SBA-15 is not altered. This isolated titanium species reaches a maximum concentration around 6 atom % relative to silicon. At higher titanium loading, titanium dioxide (anatase) is also formed. The materials with significant titanium dioxide formation have reduced pore diameters, which suggests that the titanium dioxide exist...

Machining titanium and its alloys

Abstract: Titanium and its alloys are attractive materials due to their unique high strength-weight ratio that is maintained at elevated temperatures and their exceptional corrosion resistance. The major application of titanium has been in the aerospace industry. However, the focus shift of market trends from military to commercial and aerospace to industry has also been reported. On the Other hand, titanium and its alloys are notorious for their poor thermal properties and are classified as difficult-to-machine materials. These properties limit the use of these materials especially in the commercial markets where cost is much more of a factor than in aerospace. Machining is an important manufacturing process because it is almost always involved if precision is required and is the most cost effective process for small volume production. This paper reviews the machining of titanium and its alloys and proposes potential research issues.

Graded surface structure of bioactive titanium prepared by chemical treatment.

Abstract: An NaOH treatment of pure titanium (Ti) forms a sodium titanate hydrogel surface layer with a smooth graded interface structure to the Ti metal substrate. Subsequent heat treatment at 600 degrees C of the NaOH-treated Ti forms an amorphous sodium titanate surface layer with a smooth graded interface structure similar to the Ti metal substrate. These treated Ti metals both form an apatite surface layer with a smooth graded interface structure to the Ti metal substrates in simulated body fluid (SBF). The smooth graded interface structures give a tight bond of the apatite layer to the substrates. Heat treatment at 800 degrees C of the NaOH-treated Ti forms crystalline sodium titanate and a rutile surface layer with a graded interface structure to the Ti metal substrate, which is intervened by a thick titanium oxide. This substrate forms an apatite layer with a graded interface structure to the Ti metal substrate, which is intervened by a thick titanium oxide in SBF. This irregular graded structure gives a less tight bond of the apatite layer to the substrate.

Effect of Fluoride Concentration and pH on Corrosion Behavior of Titanium for Dental Use

Abstract: Titanium is used as a metal for biocompatible materials such as dental implants or restorations because of its excellent chemical stability. However, the corrosion of Ti in the prophylactic fluoride-containing environment can become problematic. To clarify the effects of fluoride concentration and pH on the corrosion behavior of Ti, we conducted anodic polarization and immersion tests in NaF solution of various concentrations and pH values. The concentrations of dissolved Ti in the test solutions were analyzed by inductively coupled plasma mass spectroscopy. There were obvious limits of fluoride concentration and the pH value at which the corrosion behavior of Ti changed. The corrosion of Ti in the solution containing fluoride depended on the concentration of hydrofluoric acid (HF). When the HF concentration in the solution was higher than about 30 ppm, the passivation film of the Ti was destroyed. The results of this study revealed a relation between the fluoride concentrations and pH values at which Ti corrosion occurred and provided data on such corrosion in environments where the fluoride concentration and pH value are known.

Theoretical study of the effects of alloying elements on the strength and modulus of β-type bio-titanium alloys

Abstract: Titanium alloys are favorable implant materials for orthopedic applications, due to their desirable mechanical properties and biochemical compatibility (or bio-inertness). However, current bio-titanium alloys still possess too high an elastic modulus compared with that of the bone, which can lead to premature failure of the implant. Here, a theoretical methodology for the design and development of low modulus Ti alloys and/or structures is provided by means of electronic structural calculations using the discrete variational cluster method (DVM). The preliminary study concentrated on two β-Ti atomic clusters consisting of 15, and 27 atoms, respectively. The binding energies between titanium and various alloying atoms within the clusters were first calculated, from which strength and modulus were then estimated. The results of the calculation suggested that Nb, Mo, Zr and Ta were suitable alloying elements for β-type titanium alloys, capable of enhancing the strength and reducing the modulus of the materials.

In vivo metallic biomaterials and surface modification

Abstract: The chemical properties of metallic biomaterials used for artificial joints, bone plates, and dental implants in vivo are discussed based on empirical data, focusing on the maturation of surface oxide film on titanium and the film’s destruction and regeneration in body fluids. It is reviewed the behavior of metallic materials in vivo and how to modify the surface of biomaterials to improve corrosion and wear resistance and bone conductivity. Effect of calcium ion implantation into titanium for improvement of its bone conductivity is given as an example.

Bioactivation of Metal Oxide Surfaces. 1. Surface Characterization and Cell Response

Abstract: Silicon and titanium oxide surfaces (SiO2/Si and TiO2/Ti) were covalently modified with bioactive molecules (e.g., peptides) in a simple three-step procedure. Bioactive surfaces were synthesized by first immobilizing N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane (EDS) to either polished quartz disks, polished silicon wafers, or sputter-deposited titanium films. Subsequently, a maleimide-activated surface amenable to tethering molecules with a free thiol (e.g., cysteine) was created by coupling sulfosuccinimidyl 4-(N-maleimidomethyl) cyclohexane-1-carboxylate (sulfo-SMCC) to the terminal amine on EDS. In particular, Cys-Gly-Gly-Asn-Gly-Glu-Pro-Arg-Gly-Asp-Thr-Tyr-Arg-Ala-Tyr (-RGD-) and Cys-Gly-Gly-Phe-His-Arg-Arg-Ile-Lys-Ala (-FHRRIKA-) peptides with terminal cysteine residues were immobilized on maleimide-activated oxides. X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry were used to assess the chemistry, thickness, and surface density of the grafted layers. EDS deposited from anhy...

Terabit-per-square-inch data storage with the atomic force microscope

Abstract: An areal density of 1.6 Tbits/in.2 has been achieved by anodically oxidizing titanium with the atomic force microscope (AFM). This density was made possible by (1) single-wall carbon nanotubes selectively grown on an AFM cantilever, (2) atomically flat titanium surfaces on α-Al2O3 (1012), and (3) atomic scale force and position control with the tapping-mode AFM. By combining these elements, 8 nm bits on 20 nm pitch are written at a rate of 5 kbit/s at room temperature in air.

Metal-organic atomic-layer deposition of titanium-silicon-nitride films

Abstract: Titanium–silicon–nitride films were grown by metal–organic atomic-layer deposition at 180 °C. When silane was supplied separately in the sequence of a tetrakis(dimethylamido) titanium pulse, silane pulse, and ammonia pulse, the Si content in the deposited films and the deposition thickness per cycle remained almost constant at 18 at. % and 0.22 nm/cycle, even though the silane partial pressure varied from 0.27 to 13.3 Pa. Especially, the Si content dependence is strikingly different from the conventional chemical-vapor deposition. The capacitance–voltage measurement revealed that the Ti–Si–N film prevents the diffusion of Cu up to 800 °C for 60 min. Step coverage was approximately 100% even on the 0.3 μm diam hole with slightly negative slope and 10:1 aspect ratio.

Titanium is a highly thrombogenic biomaterial: possible implications for osteogenesis.

Abstract: Titanium has superior osteointegrating properties compared to other biomaterials. The mechanism for this is unknown. During the initial phase of bone implantation the biomaterial comes into direct contact with whole blood. In this study we use a newly developed in vitro chamber model to compare different commonly used biomaterials in contact with whole blood. These materials were selected with respect to their different osteointegrating properties in order to correlate these properties with the response to whole blood. In the presence of 3 IU/ml of heparin only titanium induced macroscopic clotting. This was reflected by the generation of thrombin-antithrombin which was much increased in blood in contact with titanium compared with steel and PVC. The coagulation activation caused by titanium was triggered by the intrinsic pathway because the generation of FXIIa-AT/C1 esterase inhibitor paralleled that of thrombin-antithrombin, and both thrombin-antithrombin complex and FXIIa-AT/C1 esterase inhibitor generation were abrogated by corn trypsin inhibitor, which is a specific inhibitor of FXIIa. The binding of platelets was increased on the titanium surface compared to the other biomaterial surfaces and the state of platelet activation was much more pronounced as reflected by the levels of beta-thromboglobulin and PDGF. This study indicates that titanium is unsuitable as a biomaterial in devices which are in direct contact with blood for a prolonged period. Furthermore, PDGF and other alpha-granule proteins e.g. TGF-beta, are known to be potent promotors of osteogenesis which suggests that the pronounced thrombogenic properties of titanium might contribute to the good osteointegrating properties.

Dental implant materials: commercially pure titanium and titanium alloys.

Abstract: Manufacturers use six different titanium-based biomaterials to fabricate dental implants. Each of these materials, including four grades of commercially pure titanium and two titanium alloys, has distinct mechanical and physical properties. Clinicians should recognize these differences for optimal treatment planning and patient care.

Characterization of anodic spark-converted titanium surfaces for biomedical applications.

Abstract: The aim of the present study was to characterize the surface morphology, microstructure and the chemical composition of anodic spark-converted titanium surfaces. The coatings were prepared in an electrochemical cell by the anodic spark deposition technique in an aqueous solution of Ca(H2PO4)2. The coatings were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and X-ray diffraction (XRD). The properties of the coatings are described in terms of morphology.

Corrosion wear fracture of new β type biomedical titanium alloys

Abstract: Metallic materials such as stainless steel, Co–Cr alloy, pure titanium and titanium alloys have been used for surgical implant materials. The α+β type titanium alloy such as Ti-6Al-4V ELI has been most widely used as an implant material for artificial hip joint and dental implant because of its high strength and excellent corrosion resistance. Toxicity of alloying elements in conventional biomedical titanium alloys like Al and V, and the high modulus of elasticity of these alloy as compared to that of bone have been, however, pointed out [1] , [2] . New β type titanium alloys composed of non-toxic elements like Nb, Ta, Zr, Mo and Sn with lower moduli of elasticity, greater strength and greater corrosion resistance were, therefore, designed in this study. The friction wear properties of titanium alloys are, however, low as compared to those of other conventional metallic implant materials such as stainless steels and Co–Cr alloy. Tensile tests and friction wear tests in Ringer’s solution were conducted in order to investigate the mechanical properties of designed alloys. The friction wear characteristics of designed alloys and typical conventional biomedical titanium alloys were evaluated using a pin-on-disk type friction wear testing system and measuring the weight loss and width of groove of the specimen.

New Bis(salicylaldiminato) Titanium Complexes for Ethylene Polymerization

Abstract: New bis(salicylaldiminato) titanium complexes were synthesized and investigated as ethylene polymerization catalysts. These complexes, when activated with methylalumoxane, exhibited one of the highest activities displayed by group 4 transition metal complexes having no cyclopentadienyl ligand(s).

Two step barrier process

Abstract: A process for forming a tungsten plug structure, in a narrow diameter contact hole, has been developed. The process features the use of a composite layer, comprised on an underlying titanium layer, and an overlying, first titanium nitride barrier layer, on the walls, and at the bottom, of the narrow diameter contact hole. After an RTA procedure, used to create a titanium silicide layer, at the bottom of the narrow diameter contact hole, a second titanium nitride layer is deposited, to fill possible defects in the underlying first titanium nitride, that may have been created during the RTA procedure. The tungsten plug structure is then formed, embedded by dual titanium nitride barrier layers.

Does Chemistry Really Matter in the Chemical Vapor Deposition of Titanium Dioxide? Precursor and Kinetic Effects on the Microstructure of Polycrystalline Films

Abstract: A side-by-side comparison of the TiO2 deposition kinetics and the corresponding microstructures was studied. The two precursors were titanium(IV) isopropoxide and anhydrous titanium(IV) nitrate, and all depositions were conducted at low pressures (<10-4 Torr) in an ultrahigh vacuum chemical vapor deposition reactor. For both precursors deposition kinetics were qualitatively similar and exhibited three distinct regimes as a function of temperature. At the lowest temperatures, growth was limited by the rate of precursor reaction on the substrate surface. At intermediate temperatures flux-limited growth was obtained, and at the highest temperatures the growth rates decreased with increasing temperatures. The overall behavior was modeled quantitatively for each precursor using a two-step mechanism involving reversible adsorption followed by irreversible reaction. Titanium(IV) nitrate exhibited a lower activation energy of reaction (Er = 98 kJ/mol) which allowed deposition at lower temperatures compared to tit...

Electrochemical water disinfection Part I: Hypochlorite production from very dilute chloride solutions

Abstract: Electrolytic production of hypochlorite in very dilute chloride solutions is investigated using platinum and iridium oxide coated titanium expanded metal electrodes as anodes. The dependence of the hypochlorite production rate on temperature, chloride concentration and current density was determined. It was found that the hypochlorite production rate is consistently higher on iridium oxide coated titanium compared to platinum coated titanium electrodes.