Showing papers on "Titanium published in 2008"

Phase-pure TiO 2 nanoparticles: anatase, brookite and rutile

Abstract: We report on the synthesis of phase-pure TiO2 nanoparticles in anatase, rutile and brookite structures, using amorphous titania as a common starting material. Phase formation was achieved by hydrothermal treatment at elevated temperatures with the appropriate reactants. Anatase nanoparticles were obtained using acetic acid, while phase-pure rutile and brookite nanoparticles were obtained with hydrochloric acid at a different concentration. The nanomaterials were characterized using x-ray diffraction, UV–visible reflectance spectroscopy, dynamic light scattering, and transmission electron microscopy. We propose that anatase formation is dominated by surface energy effects, and that rutile and brookite formation follows a dissolution–precipitation mechanism, where chains of sixfold-coordinated titanium complexes arrange into different crystal structures depending on the reactant chemistry. The particle growth kinetics under hydrothermal conditions are determined by coarsening and aggregation–recrystallization processes, allowing control over the average nanoparticle size.

Biomedical applications of titanium and its alloys

Abstract: Titanium alloys are considered to be the most attractive metallic materials for biomedical applications. Ti-6Al-4V has long been favored for biomedical applications. However, for permanent implant applications the alloy has a possible toxic effect resulting from released vanadium and aluminum. For this reason, vanadium-and aluminum-free alloys have been introduced for implant applications.

Corrosion and corrosion control : an introduction to corrosion science and engineering

Abstract: Definition and Importance. Electrochemical Mechanisms. Corrosion Tendency and Electrode Potentials. Polarization and Corrosion Rates. Passivity. Iron and Steel. Effect of Stress. Atmospheric Corrosion of Iron and Other Metals. Corrosion of Iron and Other Metals in Soil. Oxidation and Tarnish. Stray--Current Corrosion. Cathodic Protection. Metallic Coatings. Inorganic Coatings. Organic Coatings. Inhibitors and Passivators. Treatment of Water and Steam Systems. Alloying for Corrosion Resistance. Stainless Steels. Copper and Copper Alloys. Aluminum and Magnesium. Lead. Nickel and Nickel Alloys. Cobalt and Cobalt Alloys. Titanium, Zirconium, and Tantalum. Silicon--Iron and Silicon--Nickel Alloys. Problems. Appendix. Index.

Relationship between surface properties (roughness, wettability and morphology) of titanium and dental implant removal torque

Abstract: The biological properties of titanium depend on its surface oxide film. Several mechanical and chemical treatments have been used to modify the surface morphology and properties of titanium dental implants. One possible method of improving dental implant biocompatibility is to increase surface roughness and decrease the contact angle. In the present work, the biological properties of dental implants were investigated through in vivo and in vitro tests. The effects of surface roughness, contact angle and surface morphology on titanium dental implant removal torque were investigated. Machined dental implants and discs made with commercially pure titanium ASTM grade 4 were submitted to sandblasting treatments, acid etching and anodizing. The sample surface morphologies were characterized by SEM, the surface roughness parameters were quantified using a laser non-contact profilometer, and a contact angle measurement was taken. Dental implants were placed in the tibia of rabbits and removed 12 weeks after the surgery. It was found that: (i) acid etching homogenized the surface roughness parameters; (ii) the anodized surface presented the smallest contact angle; (iii) the in vivo test suggested that, in similar conditions, the surface treatment had a beneficial effect on the implant biocompatibility measured through removal torque; and (iv) the anodized dental implant presented the highest removal torque.

The Nature of Defects in Fluorine-Doped TiO2

Abstract: Fluorine-doped titanium dioxide was prepared via sol−gel synthesis and subsequent calcination in air. The presence of fluorine in the lattice induces the formation of reduced Ti3+ centers that localize the extra electron needed for charge compensation and are observed by electron paramagnetic resonance. Density functional theory calculations using hybrid functionals are in full agreement with such description. The extra electron is highly localized in a 3d orbital of titanium and lies a few tenths of an electron volt below the bottom of the conduction band. The preparation via sol−gel synthesis using aqueous solutions of fluorides also causes the formation of surface F− ions that substitute surface hydroxyl groups (OH−) without generating reduced centers.

Organic–Inorganic Surface Modifications for Titanium Implant Surfaces

Abstract: This paper reviews current physicochemical and biochemical coating techniques that are investigated to enhance bone regeneration at the interface of titanium implant materials. By applying coatings onto titanium surfaces that mimic the organic and inorganic components of living bone tissue, a physiological transition between the non-physiological titanium surface and surrounding bone tissue can be established. In this way, the coated titanium implants stimulate bone formation from the implant surface, thereby enhancing early and strong fixation of bone-substituting implants. As such, a continuous transition from bone tissue to implant surface is induced. This review presents an overview of various techniques that can be used to this end, and that are inspired by either inorganic (calcium phosphate) or organic (extracellular matrix components, growth factors, enzymes, etc.) components of natural bone tissue. The combination, however, of both organic and inorganic constituents is expected to result into truly bone-resembling coatings, and as such to a new generation of surface-modified titanium implants with improved functionality and biological efficacy.

Calcium phosphate-based coatings on titanium and its alloys

Abstract: Use of titanium as biomaterial is possible because of its very favorable biocompatibility with living tissue. Titanium implants having calcium phosphate coatings on their surface show good fixation to the bone. This review covers briefly the requirements of typical biomaterials and narrowly focuses on the works on titanium. Calcium phosphate ceramics for use in implants are introduced and various methods of producing calcium phosphate coating on titanium substrates are elaborated. Advantages and disadvantages of each type of coating from the view point of process simplicity, cost-effectiveness, stability of the coatings, coating integration with the bone, cell behavior, and so forth are highlighted. Taking into account all these factors, the efficient method(s) of producing these coatings are indicated finally.

Synthesis, crystallization mechanism, and catalytic properties of titanium-rich TS-1 free of extraframework titanium species.

Abstract: A new route to the synthesis of TS-1 has been developed using (NH4)2CO3 as a crystallization-mediating agent. In this way, the framework Ti content can be significantly increased without forming extraframework Ti species. The prepared catalyst had a Si/Ti ratio as low as 34 in contrast to the ratio of 58 achieved with the methods A and B established by the Enichem group (Clerici, M. G.; Bellussi, G.; Romano, U. J. Catal. 1991, 129, 159) and Thangaraj and Sivasanker (Thangaraj, A.; Sivasanker, S. J. Chem. Soc., Chem. Commun. 1992, 123), respectively. The material contained less defect sites than the samples synthesized by the other two methods. As a result, it showed much higher activity for the oxidation of various organic substrates, such as linear alkanes/alkenes and alcohols, styrene, and benzene. The crystallization mechanism of TS-1 in the presence of (NH4)2CO3 was studied by following the whole crystallization process with X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), thermogravimetry/differential thermal analysis (TG/DTA), inductively coupled plasma atomic emission spectrometry (ICP), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), diffuse reflectance UV-vis spectroscopy, and (29)Si MAS (magic-angle spinning) NMR spectroscopy techniques. It was shown that the presence of (NH4)2CO3 not only drastically lowered down pH, slowing down the crystallization process and making the incorporation of Ti into the framework match well with nucleation and crystal growth, but also modified the crystallization mechanism. It seems that the solid-phase transformation mechanism predominated in the crystallization process initiated by dissociation, reorganization, and recoalescence of the solidified gel although a small amount of nongelatinated Ti shifted to the solid during the crystal growth period. In contrast, a typical homogeneous nucleation mechanism occurred in the method A system. Thus, although in the method A system most of Ti cations was inserted into the lattice after the crystallization was nearly completed, the inclusion of Ti started at the earlier nucleation period in the presence of (NH4)2CO3. This is favorable for the incorporation of Ti into the framework, resulting in a more homogeneous distribution of Ti in the framework. Oxidation of 1-hexene and 2-hexanol over the samples collected during the whole crystallization process indicated that condensation of Ti-OH and Si-OH proceeded even after the crystallization was completed. This resulted in an increase in hydrophobicity and an overall improvement in microscopic character of Ti species and consequently a great increase in the catalytic activity with further progress of crystallization.

Effect of Carbon Doping on the Mesoporous Structure of Nanocrystalline Titanium Dioxide and Its Solar-Light-Driven Photocatalytic Degradation of NOx

Abstract: Effective mesoporous nanocrystalline C-doped TiO2 photocatalysts were synthesized through a direct solution-phase carbonization using titanium tetrachloride and diethanolamine as precursors. X-ray photoelectron spectroscopy (XPS) results revealed that oxygen sites in the TiO2 lattice were substituted by carbon atoms and formed a C−Ti−O−C structure. The absorption region of the as-prepared TiO2 was extended to the visible light region in view of the substitution for oxygen sites by carbon atoms. The photocatalytic activities of the as-prepared samples were tested in a flow system on the degradation of NO at typical indoor air levels under simulated solar-light irradiation. The samples showed a more effective removal efficiency than commercial photocatalyst (P25) on the degradation of the common indoor pollutant NO. The parameters significantly affecting the mesoporous structure and removal efficiency on indoor air were also investigated.

Osseointegration of zirconia implants compared with titanium: an in vivo study.

Abstract: Titanium and titanium alloys are widely used for fabrication of dental implants. Since the material composition and the surface topography of a biomaterial play a fundamental role in osseointegration, various chemical and physical surface modifications have been developed to improve osseous healing. Zirconia-based implants were introduced into dental implantology as an altenative to titanium implants. Zirconia seems to be a suitable implant material because of its tooth-like colour, its mechanical properties and its biocompatibility. As the osseointegration of zirconia implants has not been extensively investigated, the aim of this study was to compare the osseous healing of zirconia implants with titanium implants which have a roughened surface but otherwise similar implant geometries. Forty-eight zirconia and titanium implants were introduced into the tibia of 12 minipigs. After 1, 4 or 12 weeks, animals were sacrificed and specimens containing the implants were examined in terms of histological and ultrastructural techniques. Histological results showed direct bone contact on the zirconia and titanium surfaces. Bone implant contact as measured by histomorphometry was slightly better on titanium than on zirconia surfaces. However, a statistically significant difference between the two groups was not observed. The results demonstrated that zirconia implants with modified surfaces result in an osseointegration which is comparable with that of titanium implants.

Nanostructured titanium for biomedical applications

Abstract: Metallic materials, for example, stainless steel, titanium and its alloys, and tantalum, are widely used for medical implants in trauma surgery, orthopedic and oral medicine. Successful incorporation of these materials for design, fabrication and application of medical devices require that they meet several critical criteria. Paramount is their biocompatibility as expressed by their relative reactivity with human tissues. Another is their ability to provide sufficient mechanical strength, especially under cyclic loading conditions to ensure the durability of the medical devices made therefrom. Finally the material should be machinable and formable thereby enabling device fabrication at an affordable cost. In this paper we show that nanostructured commercial purity titanium produced by severe plastic deformation (SPD) opens new avenues and concepts for medical implants, providing benefits in all areas of medical device technology. Numerous clinical studies of medical devices fabricated from commercial purity (CP) titanium for trauma, orthopaedic and oral medicine has proven its excellent biocompatibility. However the mechanical strength of CP titanium is relatively low compared to other metals used in biomedical devices. Whereas the strength of this material can be increased by either alloying or secondary processing, for example rolling, drawing, etc., these enhancements normally come with some degradation in biometric response and fatigue behaviour. Recently it has been shown that nanostructuring of CP titanium by SPD processing can provide a new and promising alternative method for improving the mechanical properties of this material. This approach also has the benefit of enhancing the biological response of the CP titanium surface. This paper reports the results of the first developments and studies of nanostructured titanium (n-Ti), produced as long-sized rods with superior mechanical and biomedical properties and demonstrates its applicability for dental implants. The effort was conducted using commercially pure Grade 4 titanium [C – 0.052 %, O2 – 0.34 %, Fe – 0.3 %, N – 0.015 %, Ti-bal. (wt. pct.)]. Nanostructuring involved SPD processing by equal-channel angular pressing followed by thermo-mechanical treatment (TMT) using forging and drawing to produce 7 mm diameter bars with a 3 m length. This processing resulted in a large reduction in grain size, from the 25 lm equiaxed grain structure of the initial titanium rods to 150 nm after combined SPD and TMT processing, as shown in Figure 1. The selected area electron diffraction pattern, Figure 1(c), further suggests that the ultra fine grains contained predominantly high-angle non-equilibrium grain boundaries with increased grain-to-grain internal stresses. A similar structure for CP Ti can be produced in small discs using other SPD methods, for example – high pressure torsion (HPT) as studied in detail. In the present work it was essential to produce homogeneous ultrafine-grained structure throughout a three-meter length rod to enable the pilot production of implants and provide sufficient material for thorough testing of the mechanical and bio-medical properties of the nanostructured titanium. Table 1 illustrates mechanical property benefits attainable by nanostructuring of CP titanium, for example, the strength of the nanostructured titanium is nearly twice that of conventional CP titanium. Notably this improvement has been achieved without the drastic ductility reductions (to below C O M M U N IC A IO N S

Carbon Nanotubes Supported Mesoporous Mesocrystals of Anatase TiO2

Abstract: Carbon nanotubes (CNTs) and titanium dioxides (TiO2) are among the most studied functional materials in recent years. In this work, we have developed a one-pot chemical approach to prepare mesocrys...

Enhanced osteoblast functions on anodized titanium with nanotube‐like structures

Abstract: Previous studies have demonstrated increased osteoblast (bone-forming cells) adhesion on titanium and Ti-6Al-4V anodized to possess nanometer features compared with their unanodized counterparts. In this study, osteoblast long-term functions (specifically, synthesis of intracellular proteins, synthesis of intracellular collagen, alkaline phosphatase activity, and deposition of calcium-containing minerals) were determined on titanium anodized to possess either heterogeneous nanoparticles or ordered nanotubes. Titanium was anodized in dilute hydrofluoric acid at 20 V for 20 min to possess nanotubes, while titanium was anodized at 10 V for 20 min to possess nanoparticles. Most importantly, results showed that calcium deposition significantly increased on anodized titanium with nanotube-like structures compared with unanodized titanium and anodized titanium with nanoparticulate structures after 21 days of osteoblast culture. In this manner, the results of the present in vitro study indicated that anodization might be a promising quick and inexpensive method to modify the surface of titanium-based implants to induce better bone cell functions important for orthopedic applications.

Electric hot incremental forming: A novel technique

Abstract: In the current work, a new method is proposed for hot incremental forming. The method is based on simple tooling and is easy to employ. It makes use of electric current for heating hard-to-form sheet metals at the tool–sheet interface in order to fully utilize the formability of these materials. The potential effect of processing parameters, namely current, tool size, feed rate and step size, on the formability are investigated using AZ31 magnesium. In addition to this, the shape distortion of TiAl2Mn1.5 titanium workpiece after hot forming has also been addressed herein. Experimental results demonstrate that this technique is feasible and easy to control.

Switching redox site of photocatalytic reaction on titanium(IV) oxide particles modified with transition-metal ion controlled by irradiation wavelength

Abstract: Titanium(IV) oxide (TiO 2 ) particles were modified with several kinds of transition-metal ions (iron(III), copper(II), nickel(II) and chromium(III) ions) Photocatalytic activity for acetaldehyde decomposition over metal-ion-modified TiO 2 showed higher photocatalytic activity than bare TiO 2 under ultraviolet (UV) as well as visible-light irradiation The mechanism of photocatalytic reaction over metal-ion-modified TiO 2 was investigated by double-beam photoacoustic (DB-PA) spectroscopy, which enables observation of electron migration in the TiO 2 particles DB-PA measurements suggested that metal ions on TiO 2 surface acted differently depending on the wavelength of photoirradiation, ie, as electron acceptors under UV irradiation and as electron injectors under visible-light irradiation

Hydroxyapatite coating on titanium substrate by electrophoretic deposition method: Effects of titanium dioxide inner layer on adhesion strength and hydroxyapatite decomposition

Abstract: Nanosized hydroxyapatite (HA) powders were prepared by a chemical precipitation method and electrophoretically deposited on Ti6Al4V substrates. The powders were calcined before the deposition process in order to obtain crack-free coating surfaces. As an inner layer between Ti6Al4V substrate and HA coating, nanosized titanium dioxide (TiO 2 ) powders were deposited, using different coating voltages, in order to connect substrate and HA tightly. Moreover, this layer is considered to be acting as a diffusion barrier, reducing the HA decomposition due to ion migration from the metal substrate into the HA. After the sintering stage, adhesion strengths of coatings were measured by shear testing, phase changes were studied by X-ray diffraction, and coating morphology was analyzed through scanning electron microscopy observations. Results showed that usage of the TiO 2 inner layer prevented HA decomposition. Furthermore, decreasing the voltage used in TiO 2 deposition resulted in crack-free surfaces and increased adhesion strength of the overall coating.