Growth of TiO2-based nanotubes on Ti–6Al–4V alloy

The possibility of tailoring titania nanotube films on Ti–6Al–4V alloy is investigated using electrolytes based on NH₄H₂PO₄ with the addition of different concentrations of NH₄F. Several morphologies from high aspect ratio nanotubes to barrier layers are achieved by the control of the electrolyte composition, regarding its pH and fluoride concentrations. The morphology and composition of the anodic layers were evaluated by scanning and transmission electron microscopy, Rutherford backscattering spectroscopy (RBS) and Wavelength dispersive X-ray fluorescence spectroscopy.The formation efficiency and the fluoride ions content in the nanotubes depend on the F concentration in the electrolyte. The higher concentration of fluoride ions in the electrolyte promotes an increase of the F incorporated in the nanotubes, about 12 at.% but, reduces the nanotube formation efficiency. However, no significant presence of phosphorus was detected into the films by means of the above-mentioned analytical techniques.     

Fabrication of thick gel-like films by anodizing iron in a novel electrolyte based on dimethyl sulfoxide and H2SiF6

The thick bi-layered gel-like film has been grown by anodizing iron in a novel electrolyte composition based on dimethyl sulfoxide and silica hexafluoride acid (H₂SiF₆) and examined. The thickness of the anodic film composed of the inner orange-colored nanoporous layer and the outer cherry-colored gel-like layer increased at a constant rate up to 40–50 μm depending on the bath composition and anodizing conditions. Under drying and subsequently annealing, the gel layer shrinks and cracks producing hierarchical morphology of thick films mainly composed of hematite (a-Fe₂O₃). Scanning electron microscopy, Mössbauer, Raman and energy dispersive X-ray spectroscopies, and X-ray diffraction have been applied to reveal the composition and morphology of these novel films before and following various post-treatments.     

Formation of porous anodic titanium oxide films in hot phosphate/glycerol electrolyte

The present study reveals the formation of porous anodic films on titanium at an increased growth rate in hot phosphate/glycerol electrolyte by reducing the water content. A porous titanium oxide film of 12 μm thickness, with a relatively low content of phosphorus species, is developed after anodizing at 5 V for 3.6 ks in 0.6 mol dm⁻³ K₂HPO₄ + 0.2 mol dm⁻³ K₃PO₄/glycerol electrolyte containing only 0.04% water at 433 K. The growth efficiency is reduced by increasing the formation voltage to 20 V, due to formation of crystalline oxide, which induces gas generation during anodizing. The film formed at 20 V consists of two layers, with an increased concentration of phosphorus species in the inner layer. The outer layer, comprising approximately 25% of the film thickness, is developed at low formation voltages, of less than 10 V, during the initial anodizing at a constant current density of 250 A m⁻². The pore diameter is not significantly dependent upon the formation voltage, being ∼10 nm.     

Anodic oxidation of Mg-Cu and Mg-Zn alloys

Metastable, solid-solution Mg-0.8 at.% Cu and Mg-1.4 at.% Zn alloys have been anodized up to 250 V at 10 mA cm⁻² in an alkaline phosphate electrolyte at 293 K in order to investigate the enriching of alloying elements beneath the anodic films. Rutherford backscattering spectroscopy (RBS) revealed enrichments to about 4.1×10¹⁵ Cu atoms cm⁻² and 5.2×10¹⁵ Zn atoms cm⁻², which correlate with the higher standard Gibbs free energies per equivalent for formation of copper and zinc oxides relative to that for formation of MgO. The enriched layers were of thickness about 1.5-4.0 nm by medium energy ion scattering (MEIS). The anodic films, composed mainly of magnesium hydroxide, contained copper and zinc species throughout their thicknesses; the Cu:Mg and Zn:Mg atomic ratios were about 18 and 25% of those of the alloys, respectively. Phosphorus species were present in most of the film regions, with a P:Mg atomic ratio of about 0.16. The magnesium ions in the film account for about 30% of the charge passed during anodizing.     

One-step synthesis of Ni0.5Zn0.5Fe2O4 fine-patterned films via photosensitive sol–gel route

Ni_1−xZn_xFe₂O₄ (NZFO) (x=0.0–0.7) films were prepared by a photosensitive sol–gel route utilizing nickel acetate, zinc acetate and ferric nitrate as starting materials. The saturation magnetization of the NZFO film showed a parabolic tendency with Zn substitution. For Zn substitution of 0.5, the saturation magnetization reached the maximum value of 683 emu/cm³ with a relative low coercivity of 56 Oe at room temperature. The phase constituents and surface morphology of the films were characterized by X-ray diffractometer (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Through a direct patterning process, a fine-patterned Ni_0.5Zn_0.5Fe₂O₄ film was obtained by a photochemical reaction between the chelated complexes and UV light.     

The effects of growth conditions on the surface properties and photocatalytic activities of anatase TiO<Subscript>2</Subscript> films prepared via electrochemical anodizing and annealing methods

In the present work, nanostructured TiO₂ films were prepared by electrochemical anodization process of titanium in fluoride-containing electrolytes using an innovative approach. After anodization, the TiO₂ films were annealed at 480?°C for 2 h in air in order to acquire anatase phase transformation and increase its crystallinity. The effects of anodization voltage, electrolyte concentration and anodization time on the formation of TiO₂ films and the photocatalytic degradation of methylene blue (MB) were discussed in details. The phase structure and surface morphology of the samples characterized by means of X-ray diffraction and scanning electron microscope. The as-prepared nanostructured TiO₂ film anodized in 0.5% HF electrolyte at 15 V for 240 min showed excellent photocatalytic degradation of MB and is promising for environmental purification.     

Tribological behaviors of single and dual sol–gel ceramic films on Ti–6Al–4V

TiO₂, SiO₂, hydroxyapatite (HA), TiO₂–HA and SiO₂–HA thin films with good biocompatibility were grown on Ti–6Al–4V (coded as TC4) substrate by sol–gel and dip-coating processes from specially formulated sols, followed by annealing at 500 °C. The chemical states of some typical elements in the target films were detected by means of X-ray photoelectron spectroscopy (XPS). High-resolution scanning electron microscopy (SEM) is applied to characterize the surface and cross-sectional morphologies of obtained films. Various phases of the films were characterized by XRD. The tribological properties of thin films sliding against an AISI52100 steel ball were evaluated on a reciprocating friction and wear tester. As a result, the target films were obtained. Compared with the TC4 substrate, all the sol–gel ceramic films are superior in resisting wear. Among all, HA film shows the best resistance while SiO₂ film shows the worst wear resistance both under higher (3 N) and lower load (1 N). TiO₂ shows a good wear resistance under lower load but higher load. Compared with TiO₂, the wear resistance of the dual film TiO₂–HA can be improved under 3 N but deteriorated under 1 N. Compared with SiO₂, the wear resistance of SiO₂–HA is improved both under 3 N and 1 N. Compared with HA, the wear resistances of dual films are deteriorated both under 3 N and 1 N. Under 0.5 N, a very long wear life for TiO₂–HA is also obtained, illustrating that the lower wear resistance of dual films is closely related to the applied load. SEM observation of the morphologies of worn surfaces indicates that the wear of TC4 is characterized by abrasive wear. Differently, abrasion, plastic deformation and micro-crack dominate the wear of ceramic films. The superior friction reduction and wear resistance of HA films are greatly attributed to the slight plastic deformation of the film. Sol–gel is a potential method being applied to implant materials for wear protection according to proper process designs. The single HA film and the dual TiO₂–HA film is suggested for biomedical application from the point of view of wear protection.     

载银TiO2薄膜制备及其光催化灭菌性能

在硫酸电解液中,用阳极氧化法在纯钛表面制备了纳米多孔TiO₂薄膜,并通过光沉积法进行了载银修饰。采用XRD、SEM对薄膜的形貌与相结构进行了表征,并考察了电流密度、电压和电解液浓度等对生成的TiO₂薄膜光催化灭菌性能的影响。结果表明：TiO₂薄膜由锐钛矿型和金红石型组成。随电压升高,金红石型的含量逐渐增多,微孔孔径增大,在电流密度为150 mA&#8226;cm^-2时,分别由120 V时的19%和93 nm增加到180 V时的96%和283 nm。电流密度的适当增大和适量的载银修饰有助于提高TiO₂薄膜光催化灭菌性能。在1 mol&#8226;L^-1硫酸溶液中,140 V/150 mA&#8226;cm^-2条件下制备的TiO₂薄膜,经3 g&#8226;L^-1硝酸银溶液中载银修饰后灭菌效果最佳。     

Self-organized TiO2 nanotubes in mixed organic–inorganic electrolytes and their photoelectrochemical performance

The formation of self-organized TiO₂ nanotube array films by electrochemical anodizing titanium foils was investigated in a developed organic–inorganic mixed electrolyte. It was found that the structure and morphology of the TiO₂ nanotube layer were greatly dependent upon the electrolyte composition, anodizing potential and time. Under the optimized electrolyte composition and electrochemical conditions, a controllable, well-ordered TiO₂ nanotube array layer could be fabricated in a short time. The diameters of the as-prepared TiO₂ nanotubes could be adjusted from 20 to 150 nm, and the thickness could be adjusted from a few hundred nanometers to several micrometers. The photoresponse and the photocatalytic activity of the highly ordered TiO₂ nanotube array films were also examined. The nanotube array film with a thickness of about 2.5 μm had the highest incident photon to photocurrent conversion efficiency (IPCE) (34.3%) at the 350 nm wavelength, and had better charge transfer ability under UV light illumination. The photocatalytic experimental results indicated that the 450 °C annealing samples have the highest photodegradation efficiency for methyl orange pollutant.     

Li-intercalation behaviour of vanadium oxide thin film prepared by thermal oxidation of vanadium metal

In order to produce thin films of crystalline V₂O₅, vanadium metal was thermally oxidised at 500 °C under oxygen pressures between 250 and 1000 mbar for 1-5 min. The oxide films were characterised by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS). The lithium intercalation performance of the oxide films was investigated by cyclic voltammetry (CV), chronopotentiometry and electrochemical impedance spectroscopy (EIS). It was shown that the composition, the crystallinity and the related lithium intercalation properties of the thin oxide films were critically dependent on the oxidation conditions. The formation of crystalline V₂O₅ films was stimulated by higher oxygen pressure and longer oxidation time. Exposure for 5 min at 750 mbar O₂ at 500 °C resulted in a surface oxide film composed of V₂O_5, and consisting of crystallites up to 200 nm in lateral size. The thickness of the layer was about 100 nm. This V₂O₅ oxide film was found to have good cycling performance in a potential window between 3.8 and 2.8 V, with a stable capacity of 117 ± 10 mAh/g at an applied current density of 3.4 μA/cm². The diffusion coefficients corresponding to the two plateaus at 3.4 and 3.2 V were determined from the impedance measurements to (5.2 and 3.0) × 10⁻¹³ cm² s⁻¹, respectively. Beneath the V₂O₅ layer, lower oxides (mainly VO₂) were found close to the metal. At lower oxygen pressure and shorter exposure times, the oxide films were less crystalline and the amount of V⁴⁺ increased in the surface oxide film, as revealed by XPS. At intermediate oxygen pressures and exposure times a mixture of crystalline V₂O₅ and V₆O₁₃ was found in the oxide film.     

Film formation from PS/AL2O3 nanocomposites prepared by dip‐drawing method

In this study, steady state fluorescence (SSF) and UV–vis (UVV) techniques were used to examine film formation from pyrene (P) labeled polystyrene (PS) latex/Al₂O₃ (PS/Al₂O₃) composites prepared by the dip‐drawing method. The effects of dip‐drawing rates and dipping time in Al₂O₃ sol on film formation behavior and the morphology of PS/Al₂O₃ films were investigated. Films were prepared first by casting PS dispersion on clean glass substrates which creates a close‐packed array of PS sphere (203 nm) templates. These templates were then covered with Al₂O₃ utilizing the dip‐drawing method for various dip‐drawing rates and dipping times in Al₂O₃ sol. The film formation of these composites was studied by annealing them at a temperature range of 100°C to 270°C and monitoring the scattered light (I_sc), fluorescence (I_P), and transmitted light (I_tr) intensities after each annealing step. The structural properties of the composite films were analyzed with a scanning electron microscope (SEM). The results demonstrated that the film formation behavior and morphology of composites depended mainly on dipping time, and no dependence on the dip‐drawing rate was observed. The optical results indicated that PS/Al₂O₃ films undergo complete film formation independent of the dip‐drawing rate and dipping time. Additionally, the film formation stages were modeled and the corresponding activation energies were determined. After completion of film formation, PS polymers were extracted to obtain porous Al₂O₃ thin films. Highly ordered porous structures were observed for long dipping time in Al₂O₃ sol but no change was observed for different dip‐drawing rates, confirming the optical data. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

The effect of thickness on the composition of passive films on a Ti-50Zr at% alloy

Anodic films were grown potentiodynamically in different electrolytes (pH = 1-14) on a Ti-50Zr at% cast alloy, obtained by fusion in a voltaic arc under argon atmosphere. The thickness of the films was varied by changing formation potential from the open circuit potential up to about 9 V; growth was followed by 30 min stabilization at the forming potential. Films having different thicknesses were characterized by photocurrent spectroscopy (PCS) and electrochemical impedance spectroscopy (EIS). Moreover, film composition was analyzed by X-ray photoelectron spectroscopy (XPS).Regardless of the anodizing conditions, passive films on the Ti-50Zr at% alloy consist of a single layer mixed oxide phase containing both TiO₂ and ZrO₂ groups. However, an enrichment of Ti within the passive film, increasing with the film thickness, is detected both by PCS and XPS. This leads to concentration profiles of Ti⁴⁺ and Zr⁴⁺ ions along the thickness, and to different electronic properties of very thin films (more insulating) with respect to thicker films (more semiconducting), as revealed by the photocurrent-potential curves.     

Effect of electrolyte concentration on morphology,microstructure and electrochemical impedance of anodic oxide film on titanium alloy Ti-10V–2Fe–3Al

Anodic oxide films were fabricated on titanium alloy Ti-10V–2Fe–3Al in ammonium tartrate solutions at the concentrations: 1, 3, 5, 10 and 15 g L⁻¹. The morphological characteristics and microstructures of the films of the alloy were studied by optical microscopy (OM) and Raman spectroscopy (Raman), respectively. The electrochemical impedances of the films in 0.5 mol L⁻¹ H₂SO₄ solution were investigated by electrochemical impedance spectroscopy (EIS). It was showed that different electrolyte concentrations led to different change rates of anodizing forming voltage. The change rate significantly affected the morphology, microstructure and electrochemical impedance of anodic oxide film. When electrolyte concentration was 5 g L⁻¹, anodic oxide film was the most uniform, exhibited by the least and smallest breakpoints on the film. In addition, the amount of crystal phase of the film was the largest at 5 g L⁻¹, showed by the highest intensity of Raman peaks. Furthermore, the electrochemical impedance of the film of the alloy was the greatest at 5 g L⁻¹, demonstrated by the highest values of polarization resistances and lowest values of capacitances. These phenomenon were associated with the minimum value of the change rate of anodizing forming voltage at 5 g L⁻¹.     

Magnetite–graphene for the direct electrochemistry of hemoglobin and its biosensing application

Magnetite–graphene (Fe₃O₄–GE) was prepared via a simple effective chemical precipitation method, followed by the chemical reduction with hydrazine. Fe₃O₄–GE was characterized by Raman spectroscopy, transmission electron microscope, X-ray powder diffraction and electrochemical methods. A hydrogen peroxide (H₂O₂) biosensor was structured by immobilizing hemoglobin (Hb) into Fe₃O₄–GE for the first time. UV–vis and Fourier transform infrared spectra were employed to characterize Hb retained original structure in the resulting Hb–Fe₃O₄–GE membrane. Electrochemical investigation of the biosensor showed a pair of well-defined, quasi-reversible redox peaks with E_pa = −0.285 V and E_pc = −0.363 V (vs. SCE) in phosphate buffer solution (0.1 mol/L, pH 7.0) at the scan rate of 100 mV/s. The Hb–Fe₃O₄–GE showed a better synergistic electrochemical effect for the reduced process of H₂O₂. The biosensor displayed a fast response time (<3 s) and broad linear response to H₂O₂ in the range from 1.50 to 585 μmol/L with a relatively low detection limit of 0.5 μmol/L (S/N = 3). Moreover, the biosensor could be applied in practical analysis and exhibit good reproducibility and long-term stability.     

Film growth and relationship between microstructure and mechanical properties of a-C:H:F films deposited by PECVD

Results of a systematic investigation on the effects of some deposition parameters (partial pressure of CF₄ and self-bias voltage) on the microstructure, mechanical and tribological properties of a-C:H:F films are presented. The films were deposited by r.f.-PECVD using CH₄–CF₄ mixtures. The film composition was measured by ion beam analysis and, combining these results with the film thickness, the film density was determined. The structural arrangement was probed by Raman spectroscopy and the chemical bonding was investigated by infrared absorption and X-ray photoelectron spectroscopies. The hardness was measured by microindentation and the internal stress was determined by measuring the changing of the substrate curvature after the film deposition. The friction coefficient was measured by lateral force microscopy. The results indicate that the properties of a-C:H:F films are controlled by the ionic bombarding during the film growth. For a fixed self-bias, the increase of the CF₄ partial pressure leads to a transition from diamond-like to a polymer-like structure, to a higher fluorine incorporation and to a decrease of both hardness and internal stress. The friction coefficient decreases too. The fluorine incorporation also increases with the increase of the self-bias and was associated to higher plasma decomposition. Fluorine-poor polymer-like films were deposited at low self-bias (−50 V). In both situations, fluorine incorporation occurs at the expenses of the hydrogen content and the reduction of the energy of the bombarding species results in less dense and soft films with a polymer-like structure.     

Cyclic oxidation processes during anodizing of Al-Cu alloys

The influence of copper on the morphologies of porous anodic alumina has been investigated under current and voltage control using a sputtering-deposited Al-2.7 at.% Cu alloy and a commercial AA 2024-T3 aluminium alloy anodized in either sulphuric acid electrolyte or the same electrolyte but with addition of tartaric acid. The findings indicate that film development involves repeated formation of embryo cells of anodic alumina at the metal/film interface. During the initial stages of anodizing at constant voltage, cell formation is accompanied by current peaks in the current-time response. The porosity of the resultant films has a lateral aspect due to the layering of embryo cells. The thickness of individual layers is proportional to the formation voltage, with a ratio of the order 1 nm V⁻¹. The cell formation is accompanied by enrichment of copper in the alloy, incorporation of copper species into the anodic film, in low amounts relative to the alloy, and evolution of oxygen. These processes disrupt the formation of the classical pore morphology, characteristic of high purity aluminium, due to continuous formation of fresh embryo cells and re-direction of pores. The main effect of the tartaric acid addition to the sulphuric acid was to reduce the rate of anodizing of the alloys at constant voltage by about 10-20%.     

Plasma electrolytic ceramic-like aluminum oxide coatings on iron

The process characteristics of plasma-assisted electrochemical treatment of iron in aluminate electrolyte consisted of aqueous 0.1 M NaAlO₂ + 0.05 M NaOH have been studied. It has been shown that in the range of DC voltages from 260 to 340 V, it is possible to deposit dense ceramic-like coatings with the thickness increased from 0.3–0.5 μm after 1 min deposition time to 25–30 μm for 1 h of deposition. The coatings were examined by X-ray diffractometry, Fourier-transformed infrared, X-ray photoelectron spectroscopy, scanning electron microscopy, and an electrochemical potentiodynamic voltammetry. It is shown that in pre-spark conditions (100–200 V) and on the initial stages of micro-arc anodizing the forming films contain, along with amorphous aluminum oxide/hydroxide, a substantial amount of iron oxide/hydroxide. The coatings obtained by micro-arc anodizing at 260–360 V for 10–60 min represent amorphous aluminum oxide with inclusions of crystalline corundum phase. The films with a thickness of 4–15 μm deposited at the anodizing voltage of 320–360 V exhibited the uniformity and good corrosion protection properties after sealing with common agents.     

Mixed oxides Ca2Fe2O5 and Ca2Co2O5 as anode materials for Li-ion batteries

The electrochemical performance of mixed oxides, Ca₂Fe₂O₅ and Ca₂Co₂O₅ for use in Li-ion batteries was studied with Li as the counter electrode. The compounds were prepared and characterized by X-ray diffraction and SEM. Ca₂Fe₂O₅ showed a reversible capacity of 226 mAh/g at the 14th cycle and retained 183 mAh/g at the end of 50 cycles at 60 mA/g in the voltage window 0.005-2.5 V. A reversible capacity in the range, 365-380 mAh/g, which is stable up to 50 charge-discharge cycles is exhibited by Ca₂Co₂O₅ in the voltage window, 0.005-3.0 V and at 60 mA/g. This corresponds to recycleable moles of Li of 3.9±0.1 (theoretical: 4.0). Significant improvement in the cycling performance and attainable reversible capacity were noted for Ca₂Co₂O₅ on cycling to an upper cut-off voltage of 3.0 V as compared to 2.5 V. Coulombic efficiency for both compounds is >98%. Electrochemical impedance spectroscopy (EIS) data clearly indicate the reversible formation/decomposition of polymeric surface film on the electrode surface of Ca₂Co₂O₅ in the voltage window, 0.005-3.0 V. Cyclic voltammetry results compliment the galvanostatic cycling data.     

Formation of Al2O3–Nb2O5 composite oxide films on low-voltage etched aluminum foil by complexation–precipitation and anodizing

Niobium pentaoxide (Nb₂O₅) thin films were deposited on etched aluminum foils by complexation–precipitation followed by heat treatment. Then the Al₂O₃–Nb₂O₅ (Al–Nb) composite oxide films were formed by anodizing to increase the capacitance of anodized aluminum foils which are used in aluminum electrolytic capacitors. The composition and structure of niobium deposition layer were characterized by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), and the microstructures and dielectric properties of anodic oxide films were investigated by scanning electron microscope (SEM) and electrochemical impedance spectroscopy (EIS) respectively. The results show that the niobium deposition layer after heat treatment existed in the form of crystalline Nb₂O₅. The aluminum foil with Nb₂O₅ coating can be anodized with higher efficiency and energy saving. Compared with that of normal anodized aluminum foils, the effective area of the anodized aluminum foils with Al–Nb composite oxide films had no apparent change. The specimens with Al–Nb composite oxide films anodized at 30 V exhibited about 20% higher specific capacitance than that of those with pure aluminum oxide films. It suggests that the method of complexation–precipitation is an effective way to increase the specific capacitance of anodized aluminum foils used in aluminum electrolytic capacitors.     

Preparation and properties of core–shell nanosilica/poly(methyl methacrylate–butyl acrylate–2,2,2‐trifluoroethyl methacrylate) latex

A core–shell nanosilica (nano‐SiO₂)/fluorinated acrylic copolymer latex, where nano‐SiO₂ served as the core and a copolymer of butyl acrylate, methyl methacrylate, and 2,2,2‐trifluoroethyl methacrylate (TFEMA) served as the shell, was synthesized in this study by seed emulsion polymerization. The compatibility between the core and shell was enhanced by the introduction of vinyl trimethoxysilane on the surface of nano‐SiO₂. The morphology and particle size of the nano‐SiO₂/poly(methyl methacrylate–butyl acrylate–2,2,2‐trifluoroethyl methacrylate) [P(MMA–BA–TFEMA)] core–shell latex were characterized by transmission electron microscopy. The properties and surface energy of films formed by the nano‐SiO₂/P(MMA–BA–TFEMA) latex were analyzed by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy/energy‐dispersive X‐ray spectroscopy, and static contact angle measurement. The analyzed results indicate that the nano‐SiO₂/P(MMA–BA–TFEMA) latex presented uniform spherical core–shell particles about 45 nm in diameter. Favorable characteristics in the latex film and the lowest surface energy were obtained with 30 wt % TFEMA; this was due to the optimal migration of fluorine to the surface during film formation. The mechanical properties of the films were significantly improved by 1.0–1.5 wt % modified nano‐SiO₂. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011