Electrochemical behavior of CoCrMo implant in Ringer's solution

CoCrMo has been successfully employed as an orthopedic and orthodontic material because of its excellent corrosion resistant and suitable biocompatibility. The purpose of this research was to investigate the susceptibility of CoCrMo in Ringer's solution at three different temperatures: 22 °C, 37 °C, and 60 °C. The corrosion behavior of CoCrMo was carried out by using common electrochemical methods such as open circuit potential, potentiodynamic measurement, electrochemical impedance spectroscopy (EIS), and Mott–Schottky measurements. CoCrMo was passivated by the air, forming a passive film, which was not destroyed during the immersion in electrolytes under different temperatures. Results from potentiodynamic tests showed that at high anodic potentials, the passive film did not demonstrate significant localized corrosion and rather exhibited overall passive film degradation corresponding to the general corrosion of the alloy in Ringer's solution at the three temperatures. EIS measurements showed the presence of the stable passive film on the alloy surface when tested at open circuit potential. Mott–Schottky test indicated that the preformed passive film is an n‐type semiconductor due to the presence of a donor species. This is implied by the existence of oxygen vacancies and interstitial metallic cations. As the potential increased, the Cr³⁺ oxidized and produced soluble Cr⁴⁺ species. This resulted in the film changing to a p‐type semiconductor owing to the dissolution and creation of cation vacancies (acceptor species). The passive film rupture was not due to p‐type characteristics but rather was a result of the considerable oxidative dissolution of the film at high anodic potential. Copyright © 2013 John Wiley & Sons, Ltd.     

Multiple plasmonic effect on photocurrent generation of metal‐loaded titanium dioxide composite/dye films on gold grating surface

We demonstrate the multiple plasmonic effect on the photocurrent properties of photoanodes containing Ag or Au nanoparticles (NPs) loaded onto titanium dioxide film (Ag–TiO₂ or Au–TiO₂) on Au grating surfaces. Ag–TiO₂ or Au–TiO₂ nanocomposite particles are prepared by a flame spray pyrolysis route. The structures and morphologies of the prepared products are characterized by high‐resolution transmission electron microscopy. The Ag–TiO₂ or Au–TiO₂ composite NPs are deposited by spin coating onto the Au grating surfaces. The photoanode electrode is a layered structure of blu‐ray disc‐recordable grating substrate/Au/Ag (or Au)–TiO₂/dye/electrolyte/indium‐tin oxide. The plasmonic effect is induced when Ag or Au NPs are located within the propagating surface plasmon (SP) field on the Au grating surface. The short‐circuit photocurrent is increased by exciting the grating‐coupled propagating SP on the Au gratings and is further enhanced by positioning the Ag or Au NPs within the grating‐coupled SP field. Copyright © 2014 John Wiley & Sons, Ltd.     

Influence d'une reduction cathodique prealable sur le comportement electrochimique du titane et des alliages TiAu et TiPt en solution H2SO4 10N

The study of the behaviour of Titanium and its alloys containing “cathodic” elements shown that the electrolytically formed hydride film is unable to modify their corrosion resistance in a 10N H₂SO₄ solution.This fact disagrees with the generally accepted hypothesis that the corrosion inhibition of titanium and its alloys is exherted by a hydride film in a 10N H₂SO₄ solution; it stresses the rôle played by noble elements which enhance the trend toward passivation of titanium in acid media; it finally clarifies the influence of side reactions, which may sometimes occur at the counterelectrode and modify the behaviour of the working electrode.     

Development of CeO<Subscript>2</Subscript>- and TiO<Subscript>2</Subscript>-incorporated aluminium metal-composite matrix with high resistance to corrosion and biofouling

Cerium oxide (CeO₂) is a potential corrosion inhibitor for aluminium, and titanium oxide (TiO₂) is an efficient anti-fouling agent in the marine environment. The present study explored the possibility of incorporating CeO₂ and TiO₂ in aluminium to prepare a metal matrix composite that could have high corrosion and biofouling resistance under marine conditions. Such incorporation of CeO₂ and TiO₂ in pure aluminium offered high resistance to corrosion and biogrowth under marine conditions as evidenced during different tests. The specimens exhibited more anodic and stable open circuit potential throughout the period of the study. The optimum concentration of CeO₂ and TiO₂ was found to be 0.2 and 0.1%, respectively. The present results lay emphasis on the potential scope of the use of CeO₂- and TiO₂-incorporated aluminium in marine environments.     

The surface characterization and corrosion resistance of 11 % Cr ferritic/martensitic and 9–15 % Cr ODS steels for nuclear fuel reprocessing application

In spent fuel nuclear reprocessing plant, nitric acid is the main medium used in PUREX method. The passive film compositions and corrosion resistance of 11 % Cr ferritic/martensitic and 9–15 % Cr oxide dispersion strengthened steels in different nitric acid concentrations were studied. The open circuit potential is shifted toward more noble potential as the concentrations increased from 1 M HNO₃ to 9 M HNO₃ in all the investigated alloy steels. The results of the potentiodynamic polarization plots also exhibited a shift in corrosion potential as the concentrations increased from 1 M to 9 M HNO_3. This shift is undesirable because of risk of overshooting the potential beyond passive region and may result into transpassive corrosion. The X-ray photoelectron spectroscopy results of the passive film analysis are composed mostly of Fe₂O₃, Cr₂O₃, and Y₂O₃, and the depth profile of Fe and Cr concentrations vary depending upon the nitric acid concentration. The surface morphology after the corrosion test does not show intergranular corrosion attack at the nitric acid concentrations studied. It is desirable that materials for use in nitric acid service are resistant to such corrosion induced degradation.     

Highly Active Nickel Nanoparticles Supported on TiO2 Nanotube Electrodes for Methanol Electrooxidation

Nickel nanoparticles/TiO₂ nanotubes/Ti electrodes were prepared by galvanic deposition of nickel nanoparticles on the TiO₂ nanotubes layer on titanium substrates. Titanium oxide nanotubes were fabricated by anodizing titanium foil in a DMSO fluoride‐containing electrolyte. The morphology and surface characteristics of titanium dioxide nanotubes and Ni/TiO₂/Ti electrodes were investigated using scanning electron microscopy and energy‐dispersive X‐ray spectroscopy, respectively. The results indicated that nickel nanoparticles were homogeneously deposited on the surface of TiO₂ nanotubes. The electrocatalytic behaviour of nickel nanoparticles/TiO₂/Ti electrodes for the methanol electrooxidation was studied by electrochemical impedance spectroscopy, cyclic voltammetry, differential pulse voltammetry and chronoamperometry methods. The results showed that Ni/TiO₂/Ti electrodes exhibit a considerably higher electrocatalytic activity toward the oxidation of methanol.     

Silver‐Doped TiO2‐Coated Cotton Fabric as an Effective Photocatalytic System for Dye Decolorization in UV and Visible Light

In this study, titanium tetra‐isopropoxide was used as a precursor of TiO₂ for in situ coating on cotton fabric by sol–gel method. Subsequently, silver nitrate was used as doping agent to prepare silver‐doped TiO₂‐coated cotton fabric during hydrothermal treatment. The treated samples were characterized through field‐emission scanning electron microscopy, energy‐dispersive X‐ray analysis, inductively coupled plasma‐mass spectroscopy and UV–visible absorption spectroscopy to study morphology, composition of deposited elements and light absorption behavior of treated samples. X‐ray photoelectron spectroscopy was carried out to analyze the electronic state of silver in TiO₂‐coated fabric after hydrothermal treatment. Doping of silver on TiO₂‐coated fabric and subsequent hydrothermal treatment was found to enhance dye decolorization rate of rhodamine B dye solution in both UV and visible light radiations with respect to undoped TiO₂. The study shows that an optimal level of silver‐doped TiO₂‐coated fabric can be used repeatedly for dye decolorization without significant loss in its photocatalytic activity. The self‐cleaning properties of samples were also studied using methylene blue as a staining agent. It was observed that the presence of 1.8% silver on the weight of titanium in doped samples provides almost 82% of stain degradation.     

Scanning electrochemical microscopy investigation of the rate of formation of a passivating TiO2 layer on a Ti G4 dental implant

Titanium and alloys with titanium as the major component are widely used for making biomedical implants, such as artificial dental roots. In our laboratory, we have studied the kinetics of the self-healing reaction of the TiO₂ film that forms on the surface of such an implant. Amperometric SECM approach curves were recorded over the surface of a grade 4 titanium (Ti G4) dental implant sample at specific times after the metal surface had been exposed to an air-saturated buffer solution. A ferrocene methanol redox mediator and a platinum microelectrode tip (r = 12.5 μm) were used in the experiments. The effective rate coefficient (k_eff) values for the mediator regenerating surface reaction were estimated using Wittstock's method from the approach curves recorded at different time points. Decreasing values of k_eff over time indicated an increasing rate of formation of the passivating TiO₂ film.     

Self‐Organization of Honeycomb‐like Porous TiO2 Films by means of the Breath‐Figure Method for Surface Modification of Titanium Implants

This study describes a facile breath‐figure method for the preparation of honeycomb‐like porous TiO₂ films with an organometallic small‐molecule precursor. Multiple characterization techniques have been used to investigate the porous films and a mechanism for the formation process of porous TiO₂ films through the breath‐figure method is proposed. The pore size of the TiO₂ films could be modulated by varying the experimental parameters, such as the concentration of titanium n‐butoxide (TBT) solution, the content of cosolvent, and the air flow rate. In vitro cell‐culture experiments indicate that NIH 3T3 fibroblast cells seeded on the honeycomb‐like porous TiO₂ films show good adhesion, spreading, and proliferation behaviors, which suggests that honeycomb‐like porous TiO₂ films are an attractive biomaterial for surface modification of titanium and its alloys implants in tissue engineering to enhance their biocompatibility and bioactivity.     

Influence of hydrothermal exposure on surface characteristics and corrosion behaviors of anodized titanium

Titanium surface was modified by anodization in phosphoric acid solution at the voltages of 100 and 250 V, respectively. Surface characteristics and corrosion behaviors of anodized titanium were investigated before and after hydrothermal exposure in 3.5 wt.% NaCl solution at 160 °C for 24 h. It was found that anodization at 100 and 250 V resulted in the formation of a dense and a porous TiO₂ layer, respectively. The existence of anatase in the oxide layers of the 250‐V samples was confirmed by X‐ray diffraction analysis but not in the oxide layers of the 100‐V samples. After the hydrothermal exposure, the surface morphology of the 100‐V sample changed significantly, and discrete nanorods were formed on the surface. In contrast, the 250‐V sample basically preserved their original surface structures after the exposure except that numerous closely packed nanoparticles emerged on the surface. X‐ray diffraction analysis indicated that the exposure transformed the amorphous oxides into crystalline anatase. The corrosion behavior investigation of anodized titanium showed that the hydrothermal exposure had slight influence on the corrosion resistance of the 100‐V samples but decreased the corrosion resistance of the 250‐V samples significantly. Copyright © 2014 John Wiley & Sons, Ltd.     

Photoelectrochemical Study of Anodic Oxide Films on Titanium–Cobalt Alloys

Properties of anodic oxide films as a function of the composition of Ti _x –Co (x= 0, 10, 20, 30, 50, 67, 75 at. %) alloys in solutions of a borate buffer and sodium sulfate are studied by the voltammetric technique combined with photocurrent measurements. The oxide film on the alloys is shown to contain TiO₂and Co₂O₃. In a borate buffer, the oxide film presumably comprises two layers: an outer layer of cobalt oxides and an inner layer of a mixture of cobalt and titanium oxides.     

Synthesis of zirconia‐incorporated titania layer by microarc oxidation for biomedical applications

The structural features, biocompatibility, and mechanical performance of a titania (TiO₂) layer with incorporated zirconia (ZrO₂) formed by microarc oxidation on commercially pure titanium have been examined in the present study. In comparison to the ZrO₂‐free TiO₂ layer, the ZrO₂‐incorporated oxide layer was dense and contained ZrTiO₄ as a new oxide as well as ZrO₂ particles. Associated changes in the microstructure enhanced the mechanical durability of TiO₂ layer. Owing to the incorporation of identical biocompatible compounds and almost similar surface roughness, no remarkable difference in bioactivities of the ZrO₂‐free and ZrO₂‐incorporated oxide layers was detected after simulated body fluid tests. Copyright © 2015 John Wiley & Sons, Ltd.     

钌配合物敏化La3+掺杂纳米多孔TiO2电极的光电性能研究

在染料敏化太阳能电池中,TiO2膜和敏化剂决定着电池的总体效率和机械性能。本文以4-甲基吡啶为原料,经过偶联、氧化、配位和配体交换反应合成了cis-RuL2(SCN)2, (L=2,2’-联吡啶-4,4’-二羧酸),通过溶胶-凝胶法制备了TiO2膜。为了提高TiO2膜的光电性能,将不同浓度的La(NO3)3 (0.1%、0.3%、0.5%和0.7%) 加入到溶胶中,采用cis-RuL2(SCN)2将掺杂前后的TiO2膜进行敏化。利用X射线衍射仪、原子力显微镜和X射线光电子能谱对所得薄膜进行结构表征。结果表明,当La离子的浓度为0.5%时,太阳能电池的效率最高,短路电流和开路电压比未掺杂的分别提高了0.54 mA/cm2和30.41 mV。     

The electrochemical behavior and characterization of the anodic oxide film formed on titanium in NaOH solutions

Titanium dissolution and passivation were studied in NaOH aqueous solution using open-circuit potential, potentiodynamic and potentiostatic techniques. Potentiodynamic data showed that the active-passive transition involves active metal dissolution followed by formation of a poorly conducting passive oxide film that passivates the electrode. The critical current density varied with pH as d log<I> j</I><SUB>m</SUB>/d pH=-0.098 in the pH range 11.00–14.00, while the passivation potential is changed according to the following two features: at pH 10.55–13.00, d<I>E</I><SUB>m</SUB>/d pH=-0.06 V; and at pH 13.50–14.00, d<I>E</I><SUB>m</SUB>/d pH=-0.40 V. The apparent activation energy, E*, was calculated from the slope of the Arrhenius plot and was found to be 12.6 kJ mol^–1. Current-time transients showed that the growth of titanium oxide passive film is a diffusion-controlled process. XPS measurements indicated that the passive oxide film consists mainly of TiO₂ and a mixture of suboxides of Ti₂O₃ and TiO. Electronic Publication     

Anti-Reflective Coatings for CRTs by Sol-Gel Process

Two types of anti-reflective coatings composed of nano-particles were developed for cathode ray tubes (CRTs). The anti-reflective and anti-static coating is composed of two layers. An outer SiO₂ layer is formed over a porous inner layer composed of titanium oxynitride (TiO _x N_y), antimony-doped tin oxide (ATO) and SiO₂. To control the reflection of the film, a porous structure is formed using a mixed sol composed of TiO _x N _y -ATO particles and hydrolyzed-polymerized tetraethoxy-silane (TEOS). The resulting double layered coating is shown to consist in a nanocomposite pseudo three-layer structure. The antireflective electromagnetic-wave-shielding coating is also composed of two layers. An outer SiO₂ layer is formed over an electric-conductive inner layer composed of silver colloids, TiO _x N _y nano particles. Silver colloids are used to obtain a film having low surface resistivity and TiO _x N _y nano-particles contained in the inner layer enhance the durability of the film. To reduce the plasma-resonance absorption caused by silver colloids, silver ions are added to the outer layer solution. The silver ions diffuse into the inner layer from the outer layer when the film is cured, touch to the surface of silver colloids, suppress the silver colloid growth and reduce the specific absorption of the film. These coatings are successfully applied to the panel glass for CRTs on an industrial scale.     

Enhancing the Performance of Dye‐Sensitized Solar Cells with a Gold‐Nanoflowers Box

To improve the electron collection, electron lifetime, and light‐harvesting efficiency of dye‐sensitized solar cells simultaneously, Au nanoflowers were prepared and used to cover the entire TiO₂ film. Deposition of Au nanoflowers around the TiO₂ film formed a light‐scattering “box” that covered the entire TiO₂ film. Compared with a light‐scattering layer that only covers the top surface of TiO₂, the Au‐nanoflowers box exhibited better light‐harvesting efficiency due to omnidirectional light scattering, faster electron transport (attributed to the formation of electron channels between the metallic Au nanoflowers and the electron‐collection electrode), and slower charge recombination. As a consequence, the short‐circuit photocurrent and open‐circuit photovoltage were both enhanced significantly, which improved the power conversion efficiency from 8.12 to 10.91 % (34 %) when an Au‐nanoflowers box was wrapped around the photoanode.     

Impedance spectroscopy study of passive layers on the surface of lead-tin and lead-tin-calcium alloys anodically oxidized in 4.8 M sulfuric acid solution

The nature of passive films, which were formed at various potentials in 4.8 M H₂SO₄ solution on the lead-tin and lead-tin-calcium alloys, is studied by the method of impedance spectroscopy. At the potentials of 1.3 and 1.7 V, the electrode impedance is presented by the equivalent circuit, which corresponds to the formation of a bilayer film consisting of lead(II) sulfate and oxide on the electrode surface. Lead(II) oxide, which forms under the layer of lead sulfate, determines a high resistance of passive layer on the electrodes of lead alloys under investigation. An introduction of tin into the lead alloys significantly decreases the resistance of passive layers. An addition of calcium to the lead-tin alloy raises the impedance of the system. At a potential of 2.05 V, a single-layer compact passive film forms on the electrodes of the test lead alloys. It consists predominantly of lead oxides PbO _x (1 < x ≤ 2), which exhibit a higher electron conductivity. An introduction of tin into the lead alloys decreases the resistance of formed films; calcium has almost no effect on the resistance of passive film under these conditions.     

Effect of heat treatment on the properties and structure of TiO2 nanotubes: phase composition and chemical composition

Titanium oxide (TiO₂) nanotubes prepared by electrolytic anodisation of a titanium electrode have been systematically heat treated to control the conversion of the as‐prepared amorphous structure to nanocrystalline anatase and rutile. Raman spectroscopy revealed that the temperature of calcination is critical in determining the structure and crystallinity of the titania. X‐ray Photoelectron Spectroscopy analysis shows the as‐prepared film to consist mainly of oxide, although a small amount of fluoride contamination remains from the electrolyte. Organic components from post‐anodising cleaning treatments were also present. Fluorine ions are gradually ejected from the anodic layer during annealing and the fluorine concentration is negligible in samples that are heat treated above 400 °C. Choosing the appropriate annealing temperature allows the structure to be made up of defined proportions of anatase and rutile with a reduced contamination of species from the electrolyte or organic solvents. Copyright © 2010 John Wiley & Sons, Ltd.     

Physicochemical and electrorheological properties of titanium dioxide modified with metal oxides

The properties of electrorheological fluids containing dispersed phase of titanium dioxide nanoparticles prepared via the sol-gel method and modified with metal oxides have been studied. Titanium dioxide has the anatase structure with crystallite sizes of 8–10 nm and a specific surface area of 90–140 m²/g. It has been found that the magnitude of the electrorheological response of the filler is determined by the specific surface area and the content of a modifying component. The strongest electrorheological response has been revealed for titanium dioxide modified with aluminum oxide at an Al content of 6.5–7.0 mol % relative to TiO₂.     

Effect of TiO2–Ti and TiO2–TiN composite coatings on corrosion behavior of NiTi alloy

Two kinds of biocompatible coatings were produced in order to improve the corrosion resistance of nickel titanium (NiTi) alloy. A titanium oxide–titanium (TiO₂–Ti) composite was coated on NiTi alloy using electrophoretic method. After the coating process, the samples were heat‐treated at 1000 °C in two tube furnaces, the first one in argon atmosphere and the second one in nitrogen atmosphere at 1000 °C. The morphology and phase analysis of coatings were investigated using scanning electron microscopy and X‐ray diffraction analysis, respectively. The electrochemical behavior of the NiTi and coated samples was examined using polarization and electrochemical impedance spectroscopy tests. Electrochemical tests in simulated body fluid demonstrated a considerable increase in corrosion resistance of composite‐coated NiTi specimens compared to the non‐coated one. The heat‐treated composite coating sample in nitrogen atmosphere had a higher level of corrosion resistance compared to the heat‐treated sample in argon atmosphere, which is mainly due to having nitride phases. Copyright © 2014 John Wiley & Sons, Ltd.