Sub-stoichiometric Titanium Oxide Research Articles

Activity and Stability of Sub-Stoichiometric Titanium Oxide Supported Pt Nano-Particles

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Comparing Biocompatibility of Nanocrystalline Titanium and Titanium-Oxide with Microcrystalline Titanium

ABSTRACTTitanium (Ti) is the material of choice for orthopaedic applications because it is biocompatible and encourages osteoblast ingrowth. It was shown that the biocompatibility of Ti metal is due to the presence of a thin native sub-stoichiometric titanium oxide layer which enhances the adsorption of mediating proteins on the surface [1]. The present studies were devised to evaluate the adhesion, survival, and growth of cells on the surface of new engineered nano-crystal films of titanium and titanium oxides and compare them with orthopaedic-grade titanium with microcrystals. The engineered nano-crystal films with hydrophilic properties are produced by employing an ion beam assisted deposition (IBAD) technique. IBAD combines physical vapor deposition with concurrent ion beam bombardment in a high vacuum environment to produce films (with 3 to 70 nm grain size) with superior properties. These films are “stitched” to the artificial orthopaedic implant materials with characteristics that affect the wettability and mechanical properties of the coatings.To characterize the biocompatibility of these nano-engineered surfaces, we have studied osteoblast function including cell adhesion, growth, and differentiation on different nanostructured samples. Cell responses to surfaces were examined using SAOS-2 osteoblast-like cells. We also studied a correlation between the surface nanostructures and the cell growth by characterizing the SAOS-2 cells with immunofluorescence and measuring the amount alizarin red concentration produced after 7 and 14 days. The number of adherent cells was determined by means of nuclei quantification on the nanocrystalline Ti, TiO2, and microcrystalline Ti and analysis was performed with Image J. Our experimental results indicated that nanocrystalline TiO2 is superior to both nano and microcrystalline Ti in supporting growth, adhesion, and proliferation. Improving the quality of surface oxide, i.e. fabricating stoichiometric oxides as well as nanoengineering the surface topology, is crucial for increasing the biocompatibility of Ti implant materials.

Nanostructurally Designed Ultra-hydrophilic Hard Ceramic Oxide Coatings for Orthopaedic Application

ABSTRACTThis paper addresses the application of engineered nanocrystalline ultrahydrophilic titanium oxide films to artificial orthopaedic implants. Titanium (Ti) is the material of choice for orthopaedic applications and has been used for over fifty years because of its known bio-compatibility. Recently it was shown that biocompatibility of Ti metal is due to the presence of a thin native sub-stoichiometric titanium oxide layer [1] which enhances the adsorption of mediating proteins on the surface thus enhancing cell adhesion and growth [2,3,4]. Improving the quality of surface oxide, i.e. fabricating stoichiometric oxides as well as nanoengineering the surface topology that matches the dimensions of adhesive proteins, is crucial for the increase of protein adsorption [2] and, as a result, the biocompatibility of Ti implant materials. We have fabricated ultrahydrophilic nano-crystalline transparent films of anatase phase of titania (TiO2) by ion beam assisted deposition (IBAD) processes in an ultrahigh vacuum system. Source material was 99.9% pure rutile TiO2. Various ion beam conditions were used to produce these coatings with different grain sizes (4 to 70 nm) that affect the wettability, roughness, and the mechanical and optical properties of the coating [5]. Our biological experiments have shown that biocompatibility of these ultrahydrophilic nanoengineered TiO2 coatings are superior to commonly used orthopaedic titanium and even hydroxyapatite.

Fabrication of titania coatings on stainless steel via laser-induced deposition of colloidal titanium oxide from sol–gel suspension

A novel processing route that exploits the application of laser energy to induce deposition of colloidal titania (TiO2) from sol–gel suspension was developed to produce titania coatings onto stainless steel (AISI316) substrate. Various laser parameters were investigated in order to establish the feasibility and to work out the key factors and optimal conditions for effectively fabricating these coatings on the substrate. The SEM, EDS, ATR-FTIR, XRD, and contact angle measurement were employed to analyse surface morphology, phase composition, crystalline structure, and the surface properties of the deposited titania coatings. Results show that the laser energy density plays a key role in controlling the deposition process and the deposited coating's properties, whilst traverse speed is also an effective factor. Higher laser energy density delivered to the specific area leads to thicker coatings and higher crystalline phases in the deposited coatings. At lowest energy density of 4.4 J mm−2 tested in this work, the deposited coating is mainly amorphous, although a small amount of anatase phase is detectable. More crystalline phases are formed including anatase, rutile, substoichiometric titanium oxides, ilmenite and hematite when the laser energy density is increased to 8.7–17.4 J mm−2. Further increases in laser energy density to 21.7 J mm−2 results in an increase in the amount of rutile phase and the disappearance of substoichiometric titanium oxide phase. The coated surfaces show an elemental composition very close to the theoretical atomic ratio of TiO2 which is significantly different from that of the as-dried coating from the same sol. Laser irradiation over a control solution, which has the same composition as the titania sol, but without the titania precursor, was also carried out and the result showed that no change on the solution composition was detected under all laser conditions, but slight oxidation of the substrate was observed at the higher laser energy density.

Platinum–titanium alloy catalysts on a Magnéli-phase titanium oxide support for improved durability in Polymer Electrolyte Fuel Cells

The robustness of the cathode catalysts used in polymer electrolyte fuel cells (PEFCs) is one of the major factors that determines their durability. In this work, a new class of corrosion-resistant catalyst, Pt–Ti alloy nanoparticles deposited on nano-sized sub-stoichiometric titanium oxide (TiOx), was prepared, and the durability of a Pt–Ti/TiOx cathode under conditions of fuel cell operation was evaluated. Cell performance under a constant current density for >900 h was examined to demonstrate the practical stability of the Pt–Ti/TiOx MEA under PEFC operating conditions. To investigate the effect of high potentials on cathode catalyst activity, a potential cycling test between 1.0 V and 1.5 V vs. a hydrogen anode was applied to the MEA. The results indicated that the electrochemical surface area (ECA) of the Pt–Ti/TiOx MEA is much more stable than that of a conventional Pt/XC72 MEA, and there is almost no loss of ECA even after 10,000 potential cycles. In addition, there was almost no change in the internal resistance of the MEA. TEM analyses of the potential-cycled MEA clearly revealed the excellent stability of Pt nanoparticles supported on TiOx particles.

TiOx Films Deposited by Plasma Enhanced Chemical Vapour Deposition Method in Atmospheric Dielectric Barrier Discharge Plasma

The plasma enhanced chemical vapour deposition method applying atmospheric dielectric barrier discharge (ADBD) plasma was used for TiOx thin films deposition employing titanium (IV) isopropoxide and oxygen as reactants, and argon as a working gas. ADBD was operated in the filamentary mode. The films were deposited on glass. The films′ chemical composition, surface topography, wettability and aging were analysed, particularly the dependence between precursor and reactant concentration in the discharge atmosphere and its impact on TiOx films properties. Titanium in films near the surface area was oxidized, the dominating species being TiO2 and substoichiometric titanium oxides. The films exhibited contamination with carbon, as a result of atmospheric oxygen and carbon dioxide reactions with radicals in films. No relevant difference of the film surface due to oxygen concentration inside the reactor was determined. The films were hydrophilic immediately after deposition, afterwards their wettability diminished, due to chemical reactions of the film surface and chemical groups involved in the atmosphere.

Corrosion-Resistant PEFC Cathode Catalysts Based on Sub-Stoichiometric Titanium Oxide Supports

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Excellent Durability of Substoichiometric Titanium Oxide As a Catalyst Support for Pd in Alkaline Direct Ethanol Fuel Cells

In this study, substoichiometric titanium oxide, TinO2n–1, was compared with carbon black and TiO2 in the role of catalyst supports for Pd in alkaline direct ethanol fuel cell. 10%Pd/C, 10% Pd/commercial TiO2 and 10%Pd/TinO2n–1 catalysts were successfully prepared by a polyol method. The supports and electrocatalysts were characterized by X-ray diffraction (XRD), nitrogen adsorption, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), linear sweep voltammetry (LSV), and chronoamperometry (CA) techniques. Excellent durability was found for TinO2n–1 with holding potential and multiscan tests in N2-purged 1 M KOH solution. Among the three catalysts, Pd/TinO2n–1 showed the best activity and stability for ethanol electrooxidation in alkaline media.

Facile General Route toward Tunable Magnéli Nanostructures and Their Use As Thermoelectric Metal Oxide/Carbon Nanocomposites

Engineering nanoscale interfaces is a requisite for harnessing electrical and thermal transports within nanostructured materials, especially those destined for thermoelectric applications requiring an unusual combination of low thermal conductivity and electrical resistivity. Nanocomposites open up possibilities in this area, but are still bound to a very narrow range of materials. Here, we report a new approach combining the sol-gel process toward hybrid materials with spark plasma sintering (SPS) to yield functional nanocomposites based on substoichiometric titanium oxides Ti(n)O(2n-1), so-called Magnéli phases. The potential of this new approach is demonstrated by three results. First, multiple Ti(n)O(2n-1) compounds (n = 3, 4, 5, 6, 8) are obtained for the first time as sole nano-Magnéli crystalline phases with controlled specific surface areas from 55 to 300 m(2)·g(-1), classified as potential thermoelectric n-type metal oxides and paving the way toward advanced systems for energy-harvesting devices and optoelectronics. Second, this work combines the use of sol-gel and SPS processes to yield percolated nanocomposites based on metal oxide nanoparticles embedded in a carbon matrix with low electrical resistivity (2 × 10(-4) Ω·m for a Ti(4)O(7) compound) and reduced thermal conductivity (1 W·m(-1)·K(-1)) with respect to bulk phases. Finally, the discovered materials are reliable with thermoelectric figures of merit (ZT = 0.08) relatively high for n-type Ti-O-based systems and metal oxides. Thereby this study represents a proof of concept for the development of promising, cheaper, and more efficient thermoelectric conversion devices.

Substoichiometric TiO2 Thin Films as a Support Catalyst for Hydrogen Fuel Cells

Substoichiometric titanium oxide films as thin as 25nm were grown using atomic layer deposition (ALD) and determined by x-ray diffraction (XRD) to consist of Magneli phase Ti4O7. These films were synthesized at temperatures as low as 125°C, significantly lower than traditional methods. The films possess high electrical conductivity, making them attractive as potential fuel cells support materials. Titanium oxide nanotubes 70 nm in diameter and 2-3 um long were formed when the deposition was performed over sacrificial porous aluminum substrates.

Corrosion-Resistant PEMFC Cathode Catalysts Based on a Magnéli-Phase Titanium Oxide Support Synthesized by Pulsed UV Laser Irradiation

Nano-sized sub-stoichiometric titanium oxide (TiOx), synthesized by pulsed UV laser irradiation of TiO2, was used as a catalyst support material for a PEMFC cathode, and its catalytic activity for the oxygen reduction reaction (ORR) and stability against high potentials >1.0 V were examined by comparison to a conventional Pt/C catalyst. The catalyst structure and composition were determined by XRD, TEM and EDX, and the results showed that Pt particles deposited on a TiOx support are alloyed with titanium to form an ordered Pt3Ti phase. The catalytic activity for ORR was evaluated using the rotating disk electrode (RDE) technique in 0.1M HClO4 at 25°C, and the results showed that Ti-alloyed Pt/TiOx catalysts exhibited 2-fold higher specific activity than conventional Pt/XC72. This enhanced activity of Pt/TiOx catalysts is believed to be due to the formation of Pt-Ti alloy. Catalyst stability at high potentials was examined by potential cycling between 1.0 and 1.5 V vs RHE in 0.1M HClO4 at 60°C. While Pt/TiOx catalysts retained their initial electrochemical active area (ECA) after 10000 voltage cycles, Pt/XC72 lost 30–50% of its initial ECA after 10 000 cycles, which indicates that Pt/TiOx catalysts are highly stable under high potential conditions.

Formation of electro-conductive titanium oxide fine particles by pulsed UV laser irradiation

Nano-submicron particles of sub-stoichiometric titanium oxide (TiOx) were synthesized by irradiation of TiO(2) particles dispersed in liquid with a Nd:YAG pulsed UV laser, and their physicochemical and electrochemical properties were examined. After laser irradiation for 1 h, spherical oxide particles of up to ca. 300 nm in diameter were formed regardless of the liquid used, however the reduction of TiO(2) largely depended on the liquid: acetonitrile most strongly promoted the reduction of TiO(2) by UV laser irradiation. The mean valence of titanium in TiOx synthesized in acetonitrile was ca. 3.5, which is comparable to that of the most-reduced Magnéli phase, Ti(4)O(7). While the electrical conductivity of as-washed TiOx was significantly low, annealing at 900 degrees C in hydrogen dramatically improved conductivity. The oxidation resistance of TiOx was examined by cyclic voltammetry to a high potential (1.5 V) using a MEA under PEMFC operating conditions. TiOx showed a much lower anodic corrosion current at >1.0 V than XC-72R carbon, which suggests that TiOx may exhibit superior oxidation resistance as a catalyst support material at high potentials.

Kinetic study of the hydrogen oxidation reaction on sub-stoichiometric titanium oxide-supported platinum electrocatalyst in acid solution

Abstract The kinetics and mechanism of the hydrogen oxidation reaction were studied in 0.5 mol dm −3 HClO 4 solution on an electrode based on titanium oxide with Magneli phase structure-supported platinum electrocatalyst applied on rotation Au disk electrode. Pt catalyst was prepared by impregnation method from 2-propanol solution of Pt(NH 3 ) 2 (NO 2 ) 2 and sub-stoichiometric titanium oxide powder. Sub-stiochiometric titanium oxide support was characterized by X-ray diffraction and BET techniques. The synthesized catalyst was analyzed by TEM technique. Based on Tafel–Heyrovsky–Volmer mechanism the corresponding kinetic equations were derived to describe the hydrogen oxidation current–potential behavior on RDE over the entire potential region. The polarization RDE curves were fitted with derived polarization equations according to proposed model. The fitting shows that the HOR on Pt proceeds most likely via the Tafel–Volmer (TV) pathway in the lower potential region, while the Heyrovsky–Volmer (HV) pathway is operative in the higher potential region. It is pointed out that Tafel equation that has been frequently used for the kinetics analysis in the HOR, can not reproduce the polarization curves measured with high mass-transport rates. Polarization measurements on RDE revealed that the Pt catalyst deposited on titanium suboxide support showed equal specific activity for the HOR compared to conventional carbon-supported Pt fuel cell catalyst.

Stability of Corrosion-Resistant Magnéli-Phase Ti4O7-Supported PEMFC Catalysts at High Potentials

Substoichiometric titanium oxide -supported Pt catalysts were prepared and their electrochemical properties, particularly the effects of high-potential conditions on the activity and stability of catalysts, were compared to those of catalyst. Polarization measurements using membrane electrode assemblies revealed that the cathode shows a similar activity for the oxygen reduction reaction as catalyst at . A high-potential holding test ( holding at vs anode) demonstrated that the catalyst is quite stable against high potential up to . A single cell using a cathode was operated at , and voltage stability for with was also demonstrated.

Stability of Corrosion-Resistant Magnéli-Phase Ti4O7-Supported PEMFC Catalysts

Sub-stoichiometric titanium oxide (Ti4O7)-supported Pt catalysts were prepared and their electrochemical properties, particularly the effects of high potential conditions on the activity and stability of Pt/Ti4O7 catalysts, were examined in comparison to those of Pt/C catalyst. Polarization measurements using MEAs revealed that the Pt/Ti4O7 cathode shows similar activity for the oxygen reduction reaction as Pt/C catalyst at 80oC. A high-potential holding test (1 hour holding at 1.0 - 1.5 V vs. anode) demonstrated that the Pt/Ti4O7 catalyst is quite stable against high potential up to 1.5 V. Similar results were obtained in potential step tests (0.9 V-30 sec./1.3 V-30 sec.). A single cell using a Pt/Ti4O7 cathode was operated at 80oC, and voltage stability for >350 hours with H2/O2 was also demonstrated.

Sub-Stoichiometric Titanium Oxides as Platinum Support for PEM Fuel Cells

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Sub-stoichiometric titanium oxide-supported platinum electrocatalyst for polymer electrolyte fuel cells

Sub-stoichiometric titanium oxide, Ti 4O 7-supported Pt electrocatalysts for polymer electrolyte fuel cells (PEFCs) were prepared, and the electrochemical properties under PEFC operating conditions were examined. Platinum nanoparticles were deposited by a conventional impregnation method, and the applicability as an electrocatalyst was confirmed by cyclic voltammetry (CV). The onset potential of the corrosion current during the positive direction sweep of CV was much higher for Ti 4O 7 than for the Vulcan XC-72 carbon support, which indicates that Ti 4O 7 would be quite oxidation resistant under the actual PEFC operating conditions. Polarization measurements during single cell operation revealed that the Pt catalyst particles deposited on Ti 4O 7 showed equal specific activity for both the hydrogen oxidation reaction and the oxygen reduction reaction compared to a conventional carbon-supported Pt fuel cell catalyst.

Neutron reflection studies of titanium segregation to metal–ceramic interfaces

Titanium is an extremely reactive element which is known to promote the wetting of ceramics by liquid metals. The wetting process is believed to be controlled by the segregation of a very thin layer of Ti to the metal/ceramic interface where it undergoes a localised redox reaction with the ceramic. This hypothesis is consistent with cross-sectional microanalysis studies of metal–ceramic interfaces where thin layers of substoichiometric titanium oxides have been identified. The study of titanium segregation is ideally suited to neutron reflection because of the negative scattering length of the dominant isotope. In this study we have characterised the chemical composition of three interfaces between metals and a sapphire (Al 2O 3) single crystal using specular neutron reflection. The interfaces are: Sn/sapphire, Sn/sapphire containing a thin (≈20 nm) Ti interlayer introduced by physical vapour deposition (PVD), and an interface between sapphire and a commercial Ag-Cu-Ti alloy used to braze ceramics. We have evaluated the neutron reflection data collected from the CRISP reflectometer at the ISIS facility using a multilayer model of the interface. The results indicate that the 20 nm evaporated layer cannot be distinguished from interface roughness while the interface between sapphire and the commercial braze alloy contains a thin (≈70 nm) titanium suboxide layer.

Sub-stoichiometric titanium oxides as ceramic electrodes for oxygen evolution—structural aspects of the voltammetric behaviour of Ti nO 2 n−1

Oxygen evolution by electrolysis of aqueous solutions has been studied on metallic conducting oxides, known as Magnéli phases. The Ti n O 2 n−1 ceramic electrodes have been prepared by reduction of TiO 2 compacts with hydrogen. The voltammetric behaviour before and after the electrode reaction was investigated and the response of the oxide surface to the anodic polarization was observed. The influence of porosity of the ceramic electrodes on the electrochemical reaction was examined using electrodes of different pore size distributions. The roughness factors of the electrodes were estimated utilizing cyclic voltammetry.