TC4钛合金表面阳极氧化制备TiO_2多孔膜的实验研究

以硫酸为电解液,钛合金(TC4)为阳极,不锈钢片为阴极,采用恒压的氧化方式在钛合金表面获得TiO2多孔膜。通过扫描电镜(SEM)观察了多孔膜的微观形貌并用X射线衍射(XRD)对覆在钛合金基体上的氧化膜进行了物相分析,研究了氧化工艺参数电压、阳极氧化时间和硫酸浓度对TiO2多孔膜相组成的影响。结果表明:TC4钛合金阳极氧化获得的氧化膜为非均一平面的TiO2多孔膜,且膜的孔径分布在90~240nm,XRD分析表明在不同的氧化工艺参数下氧化膜均由锐钛相和金红石相双相晶型组成。在0.5mol/L硫酸溶液中,电压高于100V或氧化时间长于5min即出现锐钛相和金红石相TiO2,随着电压的升高和时间的增长金红石相TiO2的含量逐渐增加;在恒压120V时,硫酸溶液浓度为0.3mol/L即出现锐钛相和金红石相TiO2,随着硫酸浓度的提高金红石相TiO2的含量先增加后减少。     

Structure of nanotubular titanium oxide templates prepared by electrochemical anodization in H2SO4/HF solutions

The electrochemical formation of nanotubular titanium oxide films was investigated in 1 M H₂SO₄ and 0.05-0.4 wt.% HF electrolytes. Depending on anodization condition, i.e. cell voltage, anodization time, HF concentration, TiO₂ porous films having different thickness (from 350 to 500 nm) and pore diameter (from 40 to 150 nm) were obtained. By varying the cell voltage from 10 V to 40 V it was possible to gradually change the crystal structure of titanium oxide from anatase to rutile. The effect of annealing temperature and duration on crystal structure was also considered.     

Effect of substrate type, dopant and thermal treatment on physicochemical properties of TiO2–SnO2 sol–gel films

Thin nanocrystalline TiO₂–SnO₂ films (0–50 mol% SnO₂) were prepared on quartz and stainless steel substrates by sol–gel coating method. The obtained films were investigated by XRD, Raman spectroscopy and XPS. The size of the nanocrystallites was determined by XRD–LB measurements. We ascertained that the increase of treatment temperature and concentration of SnO₂ in the films favour the crystallization of rutile phase. The substrate type influences more substantially the phase composition of the TiO₂–SnO₂ films. It was established that a penetration of elements took place from the substrate into the films. TiO₂ films deposited on quartz substrate include a Si which stabilizes anatase phase up to 600 °C. The films which are deposited on stainless steel substrate and treated at 700 °C show the presence of significant quantity of rutile phase. This phenomenon could be explained by the combined effect of Sn dopant as well as Fe and Cr, which also are penetrated in the films from the steel substrate. The titania films doped up to 10 mol% SnO₂ on stainless steel possess only 12–17 nm anatase crystallites, whereas the TiO₂–(10–50 mol%) SnO₂ films contain very fine grain rutile phase (4 nm).     

Titanium oxide films produced on commercially pure titanium by anodic oxidation with different voltages

Titanium oxide films produced on commercially pure Ti by anodic oxidation with different voltages were analyzed. Anodic oxidation was carried out at room temperature using 1.4 M H₃PO₄ electrolyte and a platinum counter-electrode, in potentiostatic mode under the following conditions: 50 V, 100 V, 150 V, 200 V and 250 V. It was observed that porous titanium layers were formed at all voltage values but morphological differences were observed. Initially, the film was thin but with increasing voltage it broke down locally and porous regions became evident due to the dielectric breakdown. The porosity and the pore size increased with the increasing voltage. The surface morphology in samples formed with 200 V had substantially different porous structures than those formed with other voltage values. The anodic film surface displayed pores and craters formed on the relatively flat ground oxide surface. AFM images showed that higher voltages produced thicker titanium oxide films.     

Composition and mechanical properties of hard ceramic coating containing α-Al2O3 produced by microarc oxidation on Ti–6Al–4V alloy

Ceramic coatings with 1100–1600 HK_{50 g} hardness were deposited on Ti–6Al–4V alloy substrates using a microarc oxidation (MAO) technique, based on a dielectric barrier discharge created during anodic oxidation in an aqueous electrolyte. The influences of electrolyte concentration, deposition time and the cathodic to anodic current ratio Ic/Ia on phase composition and mechanical properties of the coatings have been studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis methods (EPMA), as well as microhardness measurement, direct pull-off and impact tests. The results show α-Al₂O₃ phase, which greatly improved the hardness of the coatings, can be obtained at high concentration of NaAlO₂ and its relative content increases with decreasing Ic/Ia ratio. The direct pull-off test and impact test results indicate that the films have the excellent adhesion with the substrate.     

Influence of substrate temperature and bias voltage on the optical transmittance of TiN films

Titanium nitride (TiN) thin films were prepared by means of reactive DC sputtering on quartz and sapphire substrates. Structural, electrical and optical effects of deposition parameters such as thickness, substrate temperature, substrate bias voltage were studied. The effect of substrate temperature variations in the 100-300°C range and substrate bias voltage variations in the 0-200 V DC range for 45-180 nm thick TiN films were investigated. Temperature-dependent electrical resistivity in the 100-350 K range and optical transmission in the 300-1500 nm range were measured for the samples. In addition, structural and morphological properties were studied by means of XRD and STM techniques.The smoothest surface and the lowest electrical resistivity was recorded for the optimal samples that were biased at about V_s=−120 V DC. Unbiased films exhibited a narrow optical transmission window between 300 and 600 nm. However, the transmission became much greater with increasing bias voltage for the same substrate temperature. Furthermore, it was found that lower substrate temperatures produced optically more transparent films.Application of single layers of MgF₂ antireflecting coating on optimally prepared TiN films helped increase the optical transmission in the visible region to more than 40% for 45 nm thick samples.     

Nanoscale characterization of anodic oxide films on Ti-6Al-4V alloy

The paper analyses, at nanoscale levels, the chemical composition and mechanical properties of the anodic oxide films formed on Ti-6Al-4V alloy by galvanostatic polarization at maximum final voltages of 12-100 V. For the investigations Auger Electron Spectroscopy, Photoelectron Spectroscopy and nanoindentation measurements have been used. The results have shown that anodizing the Ti-6Al-4V alloy produces an oxide film whose thickness depends on the final voltage. The chemical composition is not significantly dependent on the thickness, the film consists of TiO₂ and Al₂O₃. However, the best insulating properties of the films, determined from the growth parameter nm/V, are achieved with a final voltage between 30 and 65 V. Nanohardness and Young's modulus measurements have shown that the anodic films formed by different voltages exhibit similar mechanical properties which is consistent with the results of the surface analysis.     

Electrochemical characteristics of LiNiO2 films prepared for charge storable electrode application

In this paper, electrochemical investigation of LiNiO₂ films prepared by molten salt synthesis (MSS) method was performed to develop a storage electrode of solar cell energy. The preferred orientation constantly indicates (111), (012), (110) and (113). The microstructures confirmed the size of the LiNiO₂ particles in a narrow range of ~ 200 nm. Cyclic voltammogram (CV) profiles have broad cathodic peak at 3.7 V and three anodic peaks at 3.4, 3.1 and 1.9 V. For the charge and discharge range of 2.5-4.4 V, the discharge capacity was 159 mAh/g at first, and slowly decreased to 148 mAh/g during the 30th cycles.     

Influence of Nd dopant amount on microstructure and photoluminescence of TiO2:Nd thin films

TiO₂ and TiO₂:Nd thin films were deposited using reactive magnetron sputtering process from mosaic Ti–Nd targets with various Nd concentration. The thin films were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and spectroscopic techniques. Photoluminescence (PL) in the near infrared obtained upon 514.5 nm excitation was also examined. The relationship between the Nd concentration, structural, optical and photoluminescence properties of prepared thin films was investigated and discussed. XRD and TEM measurements showed that an increase in the Nd concentration in the thin films hinders the crystal growth in the deposited coatings. Depending on the Nd amount in the thin films, TiO₂ with the rutile, mixed rutile–amorphous or amorphous phase was obtained. Transmittance measurements revealed that addition of Nd dopant to titania matrix did not deteriorate optical transparency of the coatings, however it influenced on the position of the fundamental absorption edge and therefore on the width of optical band gap energy. All TiO₂:Nd thin films exhibited PL emission that occurred at ca. 0.91, 1.09 and 1.38 μm. Finally, results obtained for deposited coatings showed that titania with the rutile structure and 1.0 at.% of Nd was the most efficient in VIS to NIR photon conversion.     

Auger and A–C impedance studies of the R–F sputter deposited Fe2O3 films

Thin iron oxide films were prepared by r–f sputtering techniques. X-ray diffraction and Auger electron spectoscopic techniques were used to determine the structure of the films. The results showed that the film prepared with such techniques has an α-Fe₂O₃ structure. A–C impedance techniques were also applied to determine the electrochemical properties of the films. It was found that the flim exhibited semiconducting properties in the borate buffer solution at the anodic potentials below 0.73 V vs. R.H.E.     

Crystallinity and photocatalytic activity of TiO2 films deposited by reactive sputtering with radio frequency substrate bias

TiO₂ films with thicknesses of 400-460 nm were deposited on the unheated non-alkali glass by radio frequency (rf) reactive magnetron sputtering using a Ti metal target. Depositions were carried out using a 3-in. 1000 G magnetron cathode with various rf substrate bias voltages (V_sb, dc component of self bias) of 10-80 V under total gas pressure of 1.0 or 3.0 Pa. The oxygen flow ratio [O₂/(O₂ + Ar)] and rf sputtering power were kept constant at 60% and 200 W, respectively. Photocatalytic activity on photoinduced oxidative decomposition of acetaldehyde (CH₃CHO) of the TiO₂ films showed a clear tendency to decrease with the increase in the V_sb during the deposition. Most of the films consisted of the mixture of anatase and rutile polycrystalline portions. It was confirmed that the rutile phase content increased and anatase phase content decreased markedly with increasing V_sb, where the crystallinity of anatase phase was much higher than that of rutile phase.     

Electrochemical characteristics of surface of titanium formed by electrolytic polishing and anodizing

A clear surface was polished using electrolytic polishing (EP). The mean roughness (Rz) of the polished surface was 1.966 nm, as measured by atomic force microscopy (AFM) over a 2 × 2 um² scan area. The various directions of the grains could be observed clearly following EP. The multiple beam interference effect generated various colors of the grains after anodic treatment at constant anodic voltage. A template with ordered nanochannel-array of anodic titanium oxide (ATO) was formed at 20 V. The template formed by self-assembly. The long-range ordered nanochannel had a thickness of 170 nm film, a pore size of 100 nm, an inter-pore distance of 120 nm, pore walls with a thickness of 25 nm, a pore density of 8× 10⁹ pores/cm², and a porosity of 68.2%, after anodizing for 90 s. When the applied voltage exceeded the breakdown voltage (90 V) of titania, the corrosion rate increased and the color of the titanium became as measured electrochemically by Tafel polarization and AC impedance methods, and observed by optical microscopy.     

Effect of porosity on the Seebeck coefficient of mesoporous TiO2 thin films

Mesoporous TiO₂ films were prepared by using titanium tetraisopropoxide as the titania precursor and triblock copolymer as the structure directing agent. The synthesized mesoporous TiO₂ film was confirmed to have the ordered pore structure with rutile phase by small angle and wide angle X-ray diffraction analyses. The mesoporous TiO₂ film has the porosity range from 21.6 to 35.6%, and its Seebeck coefficient was changed according to its porosity, up to −88.6 μV/K. From the obtained Seebeck coefficient, the ordered mesoporous TiO₂ film was found to be a good candidate of thermal sensing layer of thin film thermal sensor.     

Synthesis of SiOF nanoporous ultra low-k thin film

In this work, we have investigated the effect of annealing temperature on physical, chemical and electrical properties of Fluorine (F) incorporated porous SiO₂ xerogel low-k films. The SiO₂ xerogel thin films were prepared by sol–gel spin-on method using tetraethylorthosilicate as a source of Si. The hydrofluoric acid was used as a catalyst for the incorporation of F ion in the film matrix. The thickness and refractive index (RI) of the films were observed to be decreasing with increase in annealing temperature with minimum value 156 nm and 1.31 respectively for film annealed at 400 °C. Based on measured RI value, the 34 % porosity and 1.53 gm/cm³ density of the film annealed at 400 °C have been determined. The roughness of the films as a function of annealing temperature measured through AFM was found to be increased from 0.9 to 1.95 nm. The Electrical properties such as dielectric constant and leakage current density were evaluated with capacitance–voltage (C–V) and leakage current density–voltage (J–V) measurements of fabricated Al/SiO₂ xerogel/P–Si metal–insulator-semiconductor (MIS) structure. Film annealed at 400 °C, was observed to be with the lowest dielectric constant value (k = 2) and with the lowest leakage current (3.4 × 10^?8 A/cm²) with high dielectric breakdown.     

Effect of bias voltage on microstructure and mechanical properties of arc evaporated (Ti, Al)N hard coatings

In the present study, authors report on the effect that substrate bias voltage has on the microstructure and mechanical properties of (Ti, Al)N hard coatings deposited with cathodic arc evaporation (CAE) technique. The coatings were deposited from a Ti _{0· 5}Al _{0· 5} powder metallurgical target in a reactive nitrogen atmosphere at three different bias voltages: U _B ?=??? 25, ?50 and ?100 V. The coatings were characterized in terms of compositional, microstructural and mechanical properties. Microstructure of the coatings was investigated with the aid of X-ray diffraction in glancing angle mode, which revealed information on phase composition, crystallite size, stress-free lattice parameter and residual stress. Mechanical properties were deduced from nano-indentation measurements. The residual stress in all the coatings was compressive and increased with increasing bias voltage in a manner similar to that reported in literature for Ti–Al–N coatings deposited with CAE. The bias voltage was also found to significantly influence the phase composition and crystallite size. At ?25 V bias voltage the coating was found in single phase fcc-(Ti, Al)N and with relatively large crystallites of ~ 9 nm. At higher bias voltages (?50 and ?100 V), the coatings were found in dual phase fcc-(Ti, Al)N and fcc-AlN and the size of crystallites reduced to approximately 5 nm. The reduction of crystallite size and the increase of compressive residual stress with increasing bias voltage both contributed to an increase in hardness of the coatings.     

Nanostructured layer formed on CP-Ti by plasma electrolysis (effect of voltage and duty cycle of cathodic/anodic direction)

The present work reports the usage of nanocrystalline plasma electrolytic saturation (PES) by applying pulsed current in an organic electrolyte based on Glycerol. Response surface methodology was applied to optimize the operating conditions for small nanocrystallite sizes of coatings. The levels studied were peak of applied cathodic voltage range between 500 and 700 V, peak of applied anodic voltage between 200 and 400 V and the ratio of duty cycle of cathodic direction to duty cycle of anodic direction at 0.25–0.35. The usage of high applied cathodic voltages and low anodic voltages and also low ratio of duty cycle of cathodic direction to duty cycle of anodic direction is more suitable for achieving lower sizes of complex nanocrystallites. The samples with high height to width ratio of distribution curves of nanocrystallites have simultaneously, smaller average sizes and lower length to diameter ratio of nanocrystallites.     

Growth and characterization of LiNiVO4 thin film cathode by pulsed laser deposition

Crystallized LiNiVO₄ thin films have been prepared by pulsed laser deposition and their physical and electrochemical properties have been studied. With the increase of deposition temperatures and oxygen pressures, the crystallization became better, but accompanied with large sizes of grains. The initial discharge capacity of the film deposited at 873 K and 40 Pa of oxygen was just around 7.2 μA h/cm² μm when it was cycled between 3.0 and 4.8 V with a current density of 10 μA h/cm². Cyclic voltammetry at a sweep rate of 0.1 mV/s showed a main anodic peak at 4.20 V, a weak anodic peak at 4.59 V and a cathodic peak located at 3.73 V. Based on the linear relationship between the peak currents of cathodic peaks and the square roots of scan rates, the diffusion coefficient was estimated to be about 2.3 × 10^− 15 cm²/s. Electrochemical impedance spectra revealed high charge-transfer resistance of Li-ion, such as about 9000 Ω at 4.0 V. The extremely slow Li-ion diffusion and high charge-transfer resistance indicate that the electrochemical reaction in LiNiVO₄ thin films is sluggish.     

Sol–gel deposited ceria thin films as gate dielectric for CMOS technology

In this work, cerium oxide thin films were prepared using cerium chloride heptahydrate, ethanol and citric acid as an additive by sol–gel spin-coating technique and further characterized to study the various properties. Chemical composition of deposited films has been analysed by FTIR which shows existence of CeO₂. The samples have been optically characterized using ellipsometry to find refractive index of 2·18 and physical thickness which is measured to be 5·56 nm. MOS capacitors were fabricated by depositing aluminum (Al) metal using the thermal evaporation technique on the top of CeO₂ thin films. Capacitance–voltage measurement was carried out to calculate the dielectric constant, flat-band voltage shift of 18·92, 0·3–0·5 V, respectively and conductance–voltage study was carried out to determine the D_it of 1·40 × 10¹³ eV^???1 cm^???2 at 1 MHz.     

The effect of Nb substitution on synthesis and photo-response of TiO2 thin films prepared by direct current magnetron sputtering

TiO₂ has a limited photoefficiency for solar energy harvesting and conversion due to its large bandgap. Nb substitution into the TiO₂ lattice was investigated to red-shift its photoresponse by introducing defect energy levels in the host bandgap. Ti_1−xNb_yO₂ thin films (0 ≥ y ≤ 0.52) were prepared by direct current reactive magnetron sputtering. The effect of Nb concentration on crystal phase formation and subsequent change in optical and electronic properties were determined. Films had an increasing rutile proportion as Nb concentration increased, and all films prepared for y > 0.25 were pure rutile. Nb substituted as Nb(V) or a mixture of Nb(IV)/(V) while Ti remained Ti(IV). Therefore, in these materials cation vacancies formed to electronically compensate for group V doping. Nb-doped rutile films showed no red-shift in optical response while Nb-doped anatase/rutile composites were strongly red-shifted. Photocurrent measurements were made to determine if the enhanced visible light absorption generated mobile electron-hole pairs or was due to localized excitations at color centers. At low Nb concentrations (~ 2 at.%), visible light absorption generated mobile charge carriers, while at higher concentrations ( > 9 at.%), no mobile charge carriers were created. At higher Nb concentrations, the formation of mobile charge carriers was hindered by charge recombination at cation vacancies.     

Synthesis of Mixed-Phase TiO2 Powders in Salt Matrix and Their Photocatalytic Activity

Three mixed-phase TiO₂ powders, containing ～80 volume % anatase and ～20 volume % rutile, were prepared from amorphous titanium hydroxide and three different salt matrices—pure sodium chloride, pure Na₂CO₃, and pure disodium hydrogen phosphate (DSP). Amorphous titanium hydroxide and salt mixtures were heat treated at 875°C in a rapid thermal annealing system for different times, according to the time–temperature phase transformation graphs. Time-dependent UV degradation of aqueous solutions of methylene blue dye (15 ppm) in the presence of mixed-phase powders was used to monitor the activity of the catalysts. Microstructural study of the powders by scanning electron microscope and transmission electron microscope combined with phase analysis by XRD and optical absorbance by UV-absorption spectroscopy indicated that the higher photocatalytic activity of the powder obtained from pure DSP salt could be explained by its smaller rutile particle size and anatase–rutile interparticle bonding.