Characterization of native and anodic oxide films formed on commercial pure titanium using electrochemical properties and morphology techniques

Potentiostatically anodized oxide films on the surface of commercial pure titanium (cp-Ti) formed in sulfuric (0.5 M H₂SO₄) and in phosphoric (1.4 M H₃PO₄) acid solutions under variables anodizing voltages were investigated and compared with the native oxide film. Potentiodynamic polarization and electrochemical impedance spectroscopy, EIS, were used to predicate the different in corrosion behavior of the oxide film samples. Scanning electron microscope, SEM, and electron diffraction X-ray analysis, EDX, were used to investigate the difference in the morphology between different types of oxide films. The electrochemical characteristics were examined in phosphate saline buffer solution, PSB (pH 7.4) at 25 °C. Results have been shown that the nature of the native oxide film is thin and amorphous, while the process of anodization of Ti in both acid solutions plays an important role in changing the properties of passive oxide films. Significant increase in the corrosion resistance of the anodized surface film was recorded after 3 h of electrode immersion in PSB. On the other side, the coverage (θ) of film formed on cp-Ti was differed by changing the anodized acid solution. Impedance results showed that both the native film and anodized film formed on cp-Ti consist of two layers. The resistance of the anodized film has reached to the highest value by anodization of cp-Ti in H₃PO₄ and the inner layer in the anodized film formed in both acid solutions is also porous.     

Improvement of corrosion resistance of NiTi sputtered thin films by anodization

Anodization of sputtered NiTi thin films has been studied in 1 M acetic acid at 23 °C for different voltages from 2 to 10 V. The morphology and cross-sectional structures of the untreated and anodized surfaces were investigated by field emission scanning electron microscopy (FE-SEM). The results show that increasing anodization voltage leads to film surface roughening and unevenness. It can be seen that the thickness of the anodized layer formed on the NiTi surface is in the nanometer range. The corrosion resistance of anodized thin films was studied by potentiodynamic scan (PDS) and impedance spectroscopy (EIS) techniques in Hank's solution at 310 K (37 °C). It was shown that the corrosion resistance of the anodized film surface improved with increasing voltage to 6 V. Anodization of austenitic sputtered NiTi thin films has also been studied, in the same anodizing conditions, at 4 V. Comparison of anodized sputtered NiTi thin films with anodized austenitic shape memory films illustrate that the former are more corrosion resistant than the latter after 1 h immersion in Hank's solution, which is attributed to the higher grain boundary density to quickly form a stable and protective passive ?lm.     

Effects of hydrogen and oxygen on the electrochemical corrosion and wear-corrosion behavior of diamond films deposited by hot filament chemical vapor deposition

A diamond film was deposited on silicon substrate using hot filament chemical vapor deposition (HFCVD), and H₂ and O₂ gases were added to the deposition process for comparison. This work evaluates how adding H₂ and O₂ affects the corrosion and wear-corrosion resistance characteristics of diamond films deposited on silicon substrate. The type of atomic bonding, structure, and surface morphologies of various diamond films were analyzed by Raman spectrometry, X-ray diffraction (XRD) and atomic force microscopy (AFM). Additionally, the mechanical characteristics of diamond films were studied using a precision nano-indentation test instrument. The corrosion and wear-corrosion resistance of diamond films were studied in 1 M H₂SO₄ + 1 M NaCl solution by electrochemical polarization. The experimental results show that the diamond film with added H₂ had a denser surface and a more obvious diamond phase with sp³ bonding than the as-deposited HFCVD diamond film, effectively increasing the hardness, improving the surface structure and thereby improving corrosion and wear-corrosion resistance properties. However, the diamond film with added O₂ had more sp² and fewer sp³ bonds than the as-deposited HFCVD diamond film, corresponding to reduced corrosion and wear-corrosion resistance.     

Effects of half-wave and full-wave power source on the anodic oxidation process on AZ91D magnesium alloy

Anodic films have been prepared on the AZ91D magnesium alloys in 1 mol/L Na₂SiO₃ with 10 vol.% silica sol addition under the constant voltage of 60 V at room temperature by half-wave and full-wave power sources. The weight of the anodic films has been scaled by analytical balance, and the thickness has been measured by eddy current instrument. The surface morphologies, chemical composition and structure of the anodic films have been characterized by scanning electron microscopy (SEM), energy dispersion spectrometry (EDS), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the thickness and weight of the anodic films formed by the two power sources both increase with the anodizing time, and the films anodized by full-wave power source grow faster than that by half-wave one. Furthermore, we have fitted polynomial to the scattered data of the weight and thickness in a least-squares sense with MATLAB, which could express the growth process of the anodic films sufficiently. The full-wave power source is inclined to accelerate the growth of the anodic films, and the half-wave one is mainly contributed to the uniformity and fineness of the films. The anodic film consists of crystalline Mg₂SiO₄ and amorphous SiO₂.     

Compositional and structural characterization of nanoporous films produced by iron anodizing in ethylene glycol solution

We report on the composition and morphology of as-grown anodic oxide films onto the iron surface in an ethylene glycol solution containing some NH₄F and H₂O by anodizing under direct current bias. Decrease in the content of NH₄F and the temperature of electrolyte allow us to form either nanochannel or nanotubular films over a larger potential window, ca. from 30 to 100 V. By this way, the films in thickness of up to10 μm have been formed. Mössbauer spectra recorded at room to cryogenic temperatures under conversion electron and transmission modes revealed the formation of lepidocrocite (γ-FeOOH) film containing some Fe(OH)₂ and/or FeF₂·4H₂O. An increase in anodizing voltage results in fabrication of more porous and less Fe(II) compounds containing films.     

Electrochemical, SEM/EDS and quantum chemical study of phthalocyanines as corrosion inhibitors for mild steel in 1 mol/l HCl

The inhibition effect of metal-free phthalocyanine (H₂Pc), copper phthalocyanine (CuPc) and copper phthalocyanine tetrasulfuric tetrasodium salt (CuPc·S₄·Na₄) on mild steel in 1 mol/l HCl in the concentration range of 1.0 × 10⁻⁵ to 1.0 × 10⁻³ mol/l was investigated by electrochemical test, scanning electron microscope with energy dispersive spectrometer (SEM/EDS) and quantum chemical method. The potentiodynamic polarization curves of mild steel in hydrochloric acid containing these compounds showed both cathodic and anodic processes of steel corrosion were suppressed, and the Nyquist plots of impedance expressed mainly as a capacitive loop with different compounds and concentrations. For all these phthalocyanines, the inhibition efficiency increased with the increase in inhibitor concentration, while the inhibition efficiencies for these three phthalocyanines with the same concentration decreased in the order of CuPc·S₄·Na₄ > CuPc > H₂Pc according to the electrochemical measurement results. The SEM/EDS analysis indicated that there are more lightly corroded and oxidative steel surface for the specimens after immersion in acid solution containing 1.0 × 10⁻³ mol/l phthalocyanines than that in blank. The quantum chemical calculation results showed that the inhibition efficiency of these phthalocyanines increased with decrease in molecule's LUMO energy, which was different from the micro-cyclic compounds.     

The corrosion behavior of intermetallic compounds Ni3(Si,Ti) and Ni3(Si,Ti) + 2Mo in acidic solutions

The corrosion behavior of the intermetallic compounds homogenized, Ni₃(Si,Ti) (L1₂: single phase) and Ni₃(Si,Ti) + 2Mo (L1₂ and (L1₂ + Ni_ss) mixture region), has been investigated using an immersion test, electrochemical method and surface analytical method (SEM; scanning electron microscope and EPMA: electron probe microanalysis) in 0.5 kmol/m³ H₂SO₄ and 0.5 kmol/m³ HCl solutions at 303 K. In addition, the corrosion behavior of a solution annealed austenitic stainless steel type 304 was studied under the same experimental conditions as a reference. It was found that the intergranular attack was observed for Ni₃(Si,Ti) at an initial stage of the immersion test, but not Ni₃(Si,Ti) + 2Mo, while Ni₃(Si,Ti) + 2Mo had the preferential dissolution of L1₂ with a lower Mo concentration compared to (L1₂ + Ni_ss) mixture region. From the immersion test and polarization curves, Ni₃(Si,Ti) + 2Mo showed the lowest corrosion resistance in both solutions and Ni₃(Si,Ti) had the highest corrosion resistance in the HCl solution, but not in the H₂SO₄ solution. For instance, it was found that unlike type 304 stainless steel, these intermetallic compounds were difficult to form a stable passive film in the H₂SO₄ solution. The results obtained were explained in terms of boron segregation at grain boundaries, Mo enrichment and film stability (or strength).     

Sol-gel derived 6SrO·6BaO·7Al2O3 thin films using metal alkoxides

A novel 6SrO·6BaO·7Al₂O₃ (S6B6A7) thin film has been deposited onto soda lime float glass via sol-gel dip coating technique. The optical and electrical properties of S6B6A7 films annealed in air and H₂ atmosphere have been investigated. The structural and compositional properties of the S6B6A7 thin films have been investigated using Fourier transferred infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The S6B6A7 films prepared using 5 (wt.%) sol and annealed at 450 °C in air and H₂ atmosphere exhibit an average transmittance of over ∼91% in wide visible range. The electrical properties of the S6B6A7 films affect film thickness as revealed by sheet resistance measurements. The sheet resistance of the 150 nm S6B6A7 films was 67.85 and 6.06 kilo ohms per square for air and H₂ annealed, respectively.     

Adsorption orientation of sodium of polyaspartic acid effect on anodic films formed on magnesium alloy

We previously reported organic addition agent in improving the performance of anodic film formed on magnesium alloy. Here we report that the environment-friendly electrolyte with sodium of polyaspartic acid (PASP) affects the anodizing process including the microstructure, phase constituents and corrosion performance. We have used SEM, XRD, XPS and polarization curve to study in detail the electrolyte impact. Our results show that the anodic film in electrolyte with 19.2-28.8 g/L PASP is compact, smooth and high corrosion resistant. And also, increasing the PASP concentration ranging from 9.6 to 28.8 g/L results in enhancing the cell voltage, thickness and the content of compound including MgO and Mg₂SiO₄ in anodic film. Interestingly, the anodic film is non-stoichiometric oxide. Comparing with Tafel curves of the anodic film to the addition of PASP or not to, the corrosion current density is 1-2 magnitudes less than the later. Furthermore, a plausible model we propose that the anodizing process is regulated by two main plausible adsorption orientations of PASP at the surface anode. With the increasing of PASP content, the adsorption orientation may transit from “end-on” to “flat-on”. This research using organic addition agent PASP may further broaden applications of organic additive in the anti-corrosion engineering and electrochemical surface treatment of magnesium alloy.     

Theoretical rate coefficients for the reaction of methyl radical with hydroperoxyl radical and for methylhydroperoxide decomposition

The kinetics of the CH₃ + HO₂ bimolecular reaction and the thermal decomposition of CH₃OOH are studied theoretically. Direct variable reaction coordinate transition state theory (VRC-TST), coupled with high level multireference electronic structure calculations, is used to compute capture rates for the CH₃ + HO₂ reaction and to characterize the transition state of the barrierless CH₃O + OH product channel. The CH₂O + H₂O product channel and the CH₃ + HO₂ → CH₄ + O₂ reaction are treated using variational transition state theory and the harmonic oscillator and rigid rotor approximations. Pressure dependence and product branching in the bimolecular and decomposition reactions are modeled using master equation simulations. The predicted rate coefficients for the major products channels of the bimolecular reaction, CH₃O + OH and CH₄ + O₂, are found to be in excellent agreement with values obtained in two recent modeling studies. The present calculations are also used to obtain rate coefficients for the CH₃O + OH association/decomposition reaction.     

Sodium self-diffusion coefficient in sodium silicate glass by quasielastic neutron scattering

Using pulsed neutrons of 19.8 Å wavelength a quasielastic line broadening as low as 0.03 eV (FWHM) has been observed due to Na⁺ diffusion in the glass Na₂O·2SiO₂. From the linewidths a Na⁺ self-diffusion coefficient of 3.1·10^–8 cm²/s at 420°C was obtained in excellent agreement with the diffusion coefficient determined for the same sample batch using²²Na radioactive tracers. The experimental Q dependence of the quasielasic linewidths gives a hint for deviations from a purely random walk in an ionic glass.     

Properties of NiO thin films deposited by chemical spray pyrolysis using different precursor solutions

NiO thin films have been deposited by chemical spray pyrolysis using a perfume atomizer to grow the aerosol. The influence of the precursor, nickel chloride hexahydrate (NiCl₂·6H₂O), nickel nitrate hexahydrate (Ni(NO₃)₂·6H₂O), nickel hydroxide hexahydrate (Ni(OH)₂·6H₂O), nickel sulfate tetrahydrate (NiSO₄·4H₂O), on the thin films properties has been studied. In the experimental conditions used (substrate temperature 350 °C, precursor concentration 0.2-0.3 M, etc.), pure NiO thin films crystallized in the cubic phase can be achieved only with NiCl₂ and Ni(NO₃)₂ precursors. These films have been post-annealed at 425 °C for 3 h either in room atmosphere or under vacuum. If all the films are p-type, it is shown that the NiO films conductivity and optical transmittance depend on annealing process. The properties of the NiO thin films annealed under room atmosphere are not significantly modified, which is attributed to the fact that the temperature and the environment of this annealing is not very different from the experimental conditions during spray deposition. The annealing under vacuum is more efficient. This annealing being proceeded in a vacuum no better than 10⁻² Pa, it is supposed that the modifications of the NiO thin film properties, mainly the conductivity and optical transmission, are related to some interaction between residual oxygen and the films.     

Effect of different dopant elements (Al,Mg and Ni) on microstructural,optical and electrochemical properties of ZnO thin films deposited by spray pyrolysis (SP)

In the present work we studied the influence of the dopant elements and concentration on the microstructural and electrochemical properties of ZnO thin films deposited by spray pyrolysis. Transparent conductive thin films of zinc oxide (ZnO) were prepared by the spray pyrolysis process using an aqueous solution of zinc acetate dehydrate [Zn(CH₃COO)₂·2H₂O] on soda glass substrate heated at 400 ± 5 °C. AlCl₃, MgCl₂ and NiCl₂ were used as dopant. The effect of doping percentage (2–4%) has been investigated. Afterwards the samples were thermally annealed in an ambient air during one hour at 500 °C. X-ray diffraction showed that films have a wurtzite structure with a preferential orientation along the (0 0 2) direction for doped ZnO. The lattice parameters a and c are estimated to be 3.24 and 5.20 ?, respectively. Transmission allowed to estimate the band gaps of ZnO layers. The electrochemical studies revealed that the corrosion resistance of the films depended on the concentration of dopants.     

Investigation of heat-treatment and pre-treatment on microstructure and electrochemical properties of cerium nano-oxide films on AA7020-T6 by sol-gel methods

In this paper cerium nano-oxide films were applied on AA7020-T6 alloy by sol-gel method. Potentiodynamic polarization and EIS studies have been used to study the corrosion behavior of cerium oxide nano films in 3.5% NaCl. Microstructural and phase properties of cerium oxide were investigated by SEM and XRD. The results showed that heat-treatment temperature and pre-treatment have an important effect on microstructure and electrochemical properties of cerium nano-oxide films. It can be seen from the results that with increasing heat-treatment temperature from 150 to 300 °C, the corrosion resistance of the films increased. It is related to increase the condensation of the films with adding temperature. Also, it can be seen that with adding temperature from 300 to 400 °C, the corrosion resistance of the films decrease. This is an important case related to crystallization of the cerium oxide films between 300 and 400 °C which showed that crystallized ceria films illustrate less corrosion resistance with respect to an amorphous film. Although with applying cerium oxide films the corrosion resistance of the films increased but still the passive region of the ceria films was tiny. So that in this research especially pre-treatment (etching in NaOH solution for 1 min, washing with deionized water for 5 min, etching with acid solution which contained several acids (H₂SO₄, HF, HCl, H₃PO₄), washing with deionized water for 5 min and after that following the samples in boiling deionized water for 1 h) was applied on samples before ceria treatment. The results showed that after applying this pre-treatment the passive region of the films increased extremely. It is related to formation of the thick and porous alumina films after applying pre-treatment which are similar to millepore.     

The influence of H2/(H2 + Ar) ratio on microstructure and optoelectronic properties of microcrystalline silicon films deposited by plasma-enhanced CVD

Hydrogenated microcrystalline silicon films were deposited by glow discharge decomposition of SiH₄ diluted in mixed gas of Ar and H₂. By investigating the dependence of the film crystallinity on the flow rates of Ar and H₂, we showed that the addition of Ar in diluted gas markedly improves the crystallinity due to an enhanced dissociation of SiH₄. The infrared-absorption spectrum reveals that the fraction of SiH bonding increases with increasing the rate ratio of H₂/(H₂ + Ar). The surface roughness of the films increases with increasing the flow rate ratio of H₂/(H₂ + Ar), which is attributed to the decrease of massive bombardment of Ar ions in the plasma. Refractive index and absorption coefficient of the films were obtained by simulating the optical transmission spectra using a modified envelope method. Electrical measurements of the films show that the dark conductivity increases and the activation energy decreases with the ratio of H₂/(H₂ + Ar). A reasonable explanation is presented for the dependence of the microstructure and optoelectronic properties on the flow rate ratio of H₂/(H₂ + Ar).     

The reaction of allyl radicals with oxygen atoms—rate coefficient and product branching

The primary product formation of the C₃H₅ + O reaction in the gas phase has been studied at room temperature. Allyl radicals (C₃H₅) and O atoms were generated by laser flash photolysis at λ = 193 nm of the precursors C₃H₅Cl, C₃H₅Br, C₆H₁₀ (1,5-hexadiene), and SO₂, respectively. The educts and the products were detected by using quantitative FTIR spectroscopy. The combined product analysis of the experiments with the different precursors leads to the following relative branching fractions: C₃H₅ + O → C₃H₄O + H (47%), C₂H₄ + H + CO (41%), H₂CO + C₂H₂ + H (7%), CH₃CCH + OH and CH₂CCH₂ + OH (<5%). The rate of reaction has been studied relative to CH₃OCH₂ + O and C₂H₅ + O in the temperature range from 300 to 623 K. Here, the radicals were produced via the fast reactions of propene, dimethyl ether, and ethane, respectively, with atomic fluorine. Laser-induced multiphoton ionization combined with TOF mass spectrometry and molecular beam sampling from a flow reactor was used for the specific and sensitive detection of the C₃H₅, C₂H₅, and CH₃COCH₂ radicals. The rate coefficient of the reaction C₃H₅ + O was derived with reference to the reaction C₂H₅ + O leading to k(C₃H₅ + O) = (1.11 ± 0.2) × 10¹⁴ cm³/(mol s) in the temperature range 300-623 K. The C₃H₅ + O rate and channel branching, when incorporated in a suitable detailed reaction mechanism, have a large influence on benzene and allyl concentration profiles in fuel-rich propene flames, on the propene flame speed, and on propene ignition delay times.     

Study on the anodizing of AZ31 magnesium alloys in alkaline borate solutions

A kind of environmentally friendly anodizing route for magnesium alloys, based on a new kind of organic additive (AA) contained traditional alkaline borate solution and 50 Hz civil ac current, has been studied. It is found that the formation of the anodic films is always coupled with the additive depended sparking and oxygen evolution, and the optimized ivory-white smooth anodic film possesses high corrosion resistance and excellent binding strength to AZ31 substrate. Meanwhile, The results also show that the structure, the corrosion resistance and the morphology of the anodic films are mainly dependent on the anodizing voltage, time and additives.     

Role of reactive gas in atmospheric plasma for cell attachment and proliferation on biocompatible poly ?-caprolactone film

This paper reports the surface modification of a biocompatible poly ?-caprolactone (PCL) film treated by atmospheric cold plasma (ACP) with reactive gases. The change in wettability and surface morphology of the PCL film after the plasma treatment with the reactive gases (Ar, H₂, N₂ and O₂) were determined using contact angle and surface roughness measurements. The chemical bonding states and molecular vibration modes of the activated organic groups on the polymer surface were examined by X-ray photoelectron spectroscopy and Fourier-transformation infrared techniques. The surface of the ACP-treated PCL films was also examined for their in vitro cell attachment and proliferation using human prostate epithelial cells (HPECs). The increase in the hydrophobicity of the Ar + H₂ plasma-treated PCL film resulted in a lower cell loading in the initial step of cell culture as well as a decrease in the level of cell attachment and proliferation compared with the pristine film. However, the hydrophilic properties of the Ar + N₂, Ar and Ar + O₂ plasma-treated PCL film improved the adhesion properties. Therefore, the Ar + N₂, Ar and Ar + O₂ plasma-treated PCL films showed a better cell distribution and growth than that of the pristine PCL film. The ACP-treated PCL film is potentially useful as a suitable scaffold in biophysics and bio-medical engineering applications.     

Structure and hardness of a-C:H films prepared by middle frequency plasma chemical vapor deposition

a-C:H films were prepared by middle frequency plasma chemical vapor deposition (MF-PCVD) on silicon substrates from two hydrocarbon source gases, CH₄ and a mixture of C₂H₂ + H₂, at varying bias voltage amplitudes. Raman spectroscopy shows that the structure of the a-C:H films deposited from these two precursors is different. For the films deposited from CH₄, the G peak position around 1520 cm⁻¹ and the small intensity ratio of D peak to G peak (I(D)/I(G)) indicate that the C-C sp³ fraction in this film is about 20 at.%. These films are diamond-like a-C:H films. For the films deposited from C₂H₂ + H₂, the Raman results indicate that their structure is close to graphite-like amorphous carbon. The hardness and elastic modulus of the films deposited from CH₄ increase with increasing bias voltage, while a decrease of hardness and elastic modulus of the films deposited from a mixture of C₂H₂ + H₂ with increasing bias voltage is observed.     

The role of oxygen and hydrogen partial pressures on structural and optical properties of ITO films deposited by reactive rf-magnetron sputtering

Sn doped In₂O₃ films are deposited by rf-magnetron sputtering at 300 °C under Ar, Ar + O₂ and Ar + H₂ gas ambients. For the film prepared under argon ambient, electrical resistivity 6.5 × 10⁻⁴ Ω cm and 95% optical transmission in the visible region have been achieved optimizing the power and chamber pressure during the film deposition. X-ray diffraction spectra of the ITO film reveal (2 2 2) and (4 0 0) crystallographic planes of In₂O₃. With the introduction of 1.33% oxygen in argon, (2 2 2) peak of In₂O₃ decreases and resistivity increases for the deposited film. With further increase of oxygen in the sputtering gas mixture crystallinity in the film deteriorates and both the peaks disappeared. On the other hand, when 1.33% hydrogen is mixed with argon, the resistivity of the deposited film decreases to 5.5 × 10⁻⁴ Ω cm and the crystallinity remains almost unchanged. In case of reactive sputtering, the deposition rate is lower compared to that in case of non-reactive sputtering. HRTEM and first Fourier patterns show the highly crystalline structure of the samples deposited under Ar and Ar + H₂ ambients. Crystallinity of the film becomes lower with the introduction of oxygen in argon but refractive index increases from 1.86 to 1.9. The surface morphology of the ITO films have been studied by high resolution scanning electron microscopy.