Composition of barrier type oxide films anodically formed on aluminium in a neutral borate solution

99.99% Al specimens were anodically oxidized in a boric acid-borate solution (pH = 7.4, 20°C) by applying a constant potential of 50 V(vs sce). The oxide films formed were compact and had a thickness of about 76 nm. The distributions of Al(III), O(II), and B(III) ions in the films were determined by X-ray photoelectron spectroscopy and chemical analysis combined with chemical sectioning of the films in a sulfuric acid solution. It was ascertained that the film consists of two parts: the average composition of the outer part is AlO_1.36(OH)_0.28(B₂O₃)_0.07, and that of the inner part is AlO_1.5(B₂O₃)_0.027. The outer part is slightly hydrated, and in sulfuric acid solutions it dissolves more rapidly than the inner part. Borate ions are distributed throughout the films with an average concentration of 5.8 wt% as B₂O₃.     

Electrodeposition of polypyrrole on aluminium in aqueous tartaric solution

The electrosynthesis of polypyrrole (PPy) has been achieved on aluminium in aqueous medium of tartaric acid by means of cyclic voltammetry, potentiostatic and galvanostatic techniques. Scanning electron microscopy (SEM) and X-ray microanalysis by energy spectroscopy dispersion (EDS) applying on surfaces show that the PPy coating is developed from the metal surface through the cracks of the initial Al₂O₃ layer.A mechanism involving the participation of the supporting electrolyte and the pyrrole (Py) in distinct active sites was proposed based on the linear sweep voltammetry. It is observed for all applied electrochemical techniques that the pyrrole concentration has to be higher than 0.1 M to allow the polypyrrole electrodeposition in acid medium.Scanning electron microscopy, secondary electrons (SE) and backscattering electrons (BE), shows that the PPy coating obtained in galvanostatic and potentiostatic modes starts with small islands at weak applied potentials or current densities. Moreover, EDS reveals a good homogeneity and compactness of the film achieved in galvanostatic method. The corrosion results in 3% NaCl medium show that the PPy coating decreases the corrosion behaviour of the aluminium. The bilayer Al₂O₃/PPy shows a capacitor with future applications.     

Adsorption of organic compounds at the aluminium oxide/aqueous solution interface during the aluminium anodizing process

The paper reports a systematic study concerning the role played by different organic compounds (glycolic acid, oxalic acid, glycerol) on the electrochemical oxidation process of aluminium in sulphuric acid solution. The result of the experiment as a whole provides a clear indication of the deep influence exerted by the three selected organic compounds on the aluminium oxide structure, leading to the formation of a more compact oxide layer. Electrochemical impedance spectroscopy results appear of particular interest; they are discussed in the light of a model proposed by Bojinov. The relevant parameters, half-jump distance a and cross-capture section S, are found consistently related to variations in the oxide structure (porosity). This gives a sounder basis to the physically correct nature of the assumptions underlying the Bojinov model, also suggesting that organic compounds are adsorbed at the aluminium oxide/aqueous solution interface.     

The effect of CVD-diamond film thickness on the electrochemical properties of synthetic diamond thin-film electrodes

The electrochemical behavior of polycrystalline diamond films of different thickness (0.5–7 μm), grown by hot-filament CVD method, was studied by electrochemical impedance spectroscopy and cyclic voltammetry. The differential capacitance, background current, and potential window were measured in supporting electrolyte solution; the electrochemical kinetics, in [Fe(CN)₆]^3−/4− model redox system. With the increasing of the films thickness, the crystallite size increased; both the differential capacitance and background current in the indifferent electrolyte, as well as the transfer coefficients in the redox system, decreased; thus, the diamond electrode becomes as if less reversible. The effect of the films’ thickness is reduced to that of nondiamond (amorphous) carbon contribution from intercrystalline boundaries on the electrochemical behavior of the polycrystalline diamond electrodes.     

Micro-patterning in anodic oxide film on aluminium by laser irradiation

Microstructures such as microchannels and microchambers were fabricated on anodic oxide film of aluminium with laser direct patterning technique. The aluminium substrate covered with porous type anodic oxide film was dyed with organic dyes followed by hydrothermal treatment. The coloured and pore sealed film shows much higher absorption then as-formed porous film, that makes possible to pattern various types of microstructures on the film by removing the upper part of the film surface by laser irradiation. Structure of the crystallized hydroxide layer on the surface of the anodic oxide film, formed during pore sealing, as well as the partial removal of anodic oxide film from the surface is described. Microstructures with depth lower than 1-27 μm were patterned successfully on 16 and 32 μm thick anodic oxide film surfaces, using various combinations of laser power and laser scanning speed. The affect of the laser scanning speed and laser power density on the shape of the microstructures is also explained.     

AC-impedance measurements on aluminium barrier type oxide films

AC-impedance measurements in the frequency range 5 × 10^?3 Hz ≤ f ≤ 10⁴ Hz were performed in the system polycrystalline pure aluminium/0.16 M NH₄-tartrate at pH 5–7, in the potential range ?900 mV ≤ E_H ≤ 400 mV. The impedance of the system is characterized by a high-frequency capacitive and a low-frequency inductive behaviour. The capacity is unequivocally related to the thickness and dielectric properties of the barrier oxide film. The faraday impedance corresponds to a metal dissolution process at the oxide film/electrolyte interphase and can be interpreted by a model previously proposed by Armstrong.     

Layer-by-layer assembly and electrochemical properties of sandwiched film of manganese oxide nanosheet and carbon nanotube

Sandwiched film of MnO₂ nanosheet (MONS) and multi-walled carbon nanotube (MWCNT) was assembled by using the layer-by-layer method, based on electrostatic interaction of positively-charged poly (diallyl dimethyl ammonium chloride) and negatively-charged MONS and MWCNT. Ultraviolet-visible spectroscopy is used to probe the dynamic growth of multilayer film, exhibiting progressive enhancement of optical absorption due to the assembly of MONS and MWCNT. Thus, the assembled sandwiched film was characterized using scanning electron microscopy and X-ray photoelectron spectra. The multilayer film electrode presents excellent electrochemical capacitance properties, which were also highly dependent upon the deposition sequence and the order of structural components in sandwiched film.     

Synthesis of CuO nanowalnuts and nanoribbons from aqueous solution and their catalytic and electrochemical properties

One dimensional copper hydroxide nanostrands, two dimensional Cu(2)(OH)(3)NO(3) nanoribbons and three dimensional CuO nanowalnuts were synthesized from the same diluted copper nitrate solution with ethanolamine at room temperature and 10 °C, respectively. The Cu(2)(OH)(3)NO(3) nanoribbons were formed by slowly hydrolyzing ethanolamine at low temperature. The CuO nanowalnuts were formed through dehydration of copper hydroxide nanostrands in aqueous solution at room temperature. Although their average size is about 500 nm, the specific surface area of the CuO nanowalnuts can be as large as 61.24 m(2) g(-1), due to their particular morphology with assembling of 8 nm grains. The Cu(2)(OH)(3)NO(3) nanoribbons were converted to CuO porous nanoribbons, keeping the shape. The catalytic performance of the CuO nanowalnuts for CO oxidation is 160 mL h(-1) g(cat)(-1) which is 23 times higher than those of the CuO porous nanoribbons and 40 nm commercial CuO nanoparticles, respectively. The electrochemical properties of the CuO nanowalnuts were also examined in a lithium-ion battery. After 30 cycles, the capacity of the as-prepared CuO nanowalnuts could sustain 67.1% (407 mA h g(-1)) of the second cycle (607 mA h g(-1)) at a rate of 0.1 C.     

Enhancing polymer/graphene oxide gas barrier film properties by introducing new crystals

A transparent, gas barrier film comprised of poly(vinyl alcohol) (PVA) and graphene oxide (GO) is synthesized through combined methods of solution blending and isothermal recrystallization. The recrystallized PVA/GO film with only 0.07 vol% GO gives an O₂ transmission rate <0.005 cc m⁻² day⁻¹ and an O₂ permeability <5.0 × 10⁻²⁰ cm³ cm cm⁻² Pa⁻¹ s⁻¹; hence, it is far superior to other blend polymer/inorganic composites. The excellent O₂ barrier properties are attributed to a unique hybrid of PVA crystals and GO sheets. PVA crystals form around the GO during isothermal recrystallization, indicating that a GO sheet can act as a nucleating agent. The newly formed PVA crystals fill in the spaces between the GO sheets, and together they become ultra-large impermeable regions, which can prevent the passage of O₂. The hybrid film has potential applications in flexible electronics, pharmaceuticals, and food packaging.     

Improved mechanical and barrier properties of starch film with reduced graphene oxide modified by SDBS

Starch is regarded as one of the most promising biopolymers to replace the fossil resources. However, due to the poor mechanical properties, high sensitivity to humidity, and low barrier property, the development of starch‐based materials has been limited. In this study, they improved the mechanical and barrier properties of starch film with reduced graphene oxide (RGO) modified by sodium dodecyl benzene sulfonate (SDBS). The hydrophilia of modified RGO (r‐RGO) was improved and result in a good dispersion in oxidized starch (OS) matrix. The tensile strength of the r‐RGO‐4/OS film increased to 58.5 MPa which was more than three times of the OS film (17.2 MPa). Besides, both the water vapor and oxygen barrier properties of r‐RGO/OS film were improved greatly compared with OS and GO/OS films. Moreover, the r‐RGO/OS film could protect against UV light effectively due to its lightproof performance. In conclusion, the r‐RGO/OS composite film has great potential applications in packaging industry. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44910.     

The anodic oxide film on iron in neutral solution

The composition of the anodic passive oxide film on iron in neutral solution has been investigated by cathodic reduction, chemical analysis and ellipsometry. The cathodic reduction using a borate solution of pH 6·35 containing arsenic trioxide as inhibitor estimates iron in the film to be all iron (III), indicating that no magnetite layer is present. Oxygen in the film is estimated from the ellipsometric thickness to be in excess of the stoichiometric ferric oxide, suggesting the presence of bound water. The average composition is represented as Fe₂O₃.0·4H₂O, in which hydrogen may be replaced partly with iron-ion vacancy. The anodic oxide film is composed of an inner anhydrous ferric oxide layer, which thickens with the potential and an outer layer of hydrous ferric oxide whose thickness depends on the condition of passivation and environment.     

Effects of surface structure on the electrochemical properties of Nimetal complex oxide film electrode

Effects of surface structure on the electrochemical properties of Ni—metal complex oxide film electrodes prepared by radio frequency magnetron sputtering method and by thermal decomposition method have been investigated. Rotating disc electrode technique was applied to evaluate the electron transfer rate of the redox system [Fe(CN)₆]^3?/[Fe(CN)₆]^4? in 0.1 M NaOH solution. Dynamic impedance method to detect the impedance change of electrode/electrolyte interface and X-ray photoelectron spectroscopy were also used. The NiMo complex oxide film electrode prepared by rf magnetron sputtering method was found to have good stability, good reproducibility and effective electrochemical properties in comparison with the oxide film electrodes prepared by thermal decomposition method. Then, of the electrodes prepared by thermal decomposition method, the NiMo complex oxide film and the NiRe complex oxide film were shown to have good electrochemical properties. It was found by XPS analysis that both Mo ion at a higher oxidation state and oxygen influenced from this Mo ion, which showed clear occurrence for the NiMo oxide film prepared by rf sputtering method and no occurrence by thermal decomposition method, played a very important role in the reaction.     

Effect of graphene oxide on the solution rheology and the film structure and properties of cellulose carbamate

Highly ordered, homogeneous and reinforced cellulose carbamate (CC)/graphene oxide (GO) composite films were prepared using an easy, aqueous and solution-mixing method. The dynamic rheology measurement showed that the addition of 2 wt.% GO decreased the complex viscosity of CC solution and significantly prolonged the valid spinning time of CC solution. X-ray diffraction characterization revealed that GO promoted the transition of crystalline structure of CC from cellulose I to II, and the addition of 2 wt.% GO improved the orientation and crystallinity of the CC molecules. Scanning electron microscope images indicated that the GO layers were aligned parallel to the surface of the composite films. The incorporation of GO also showed profound effects on the macroscopic properties of the CC film. Compared to the pure CC, the composite showed a 280% increase in Young’s modulus and 180% increase in tensile strength by the addition of 2 wt.% of GO. Moreover, the carbon yields of all the composite films were higher than that of pure CC film.     

Long-term electrochemical behaviors of manganese oxide aqueous electrochemical capacitor under reducing potentials

Long-term electrochemical behaviors of hydrated MnO₂ electrochemical capacitor (EC) electrode in alkali chloride (KCl_(aq)) electrolyte have been studied by using potential cycling for thousands of cycles within different potential windows spanning from 0.8 V (versus Ag/AgCl_(aq)) to varied lower-end potentials below the open-circuit potential. Three potential ranges resulting in different cycling behaviors of the oxide EC have been identified. Range I: cycling above 0.2 V results in no change in either microstructure or surface chemistry of the oxide electrode, and no capacitance reduction has been observed. Range II: cycling down to 0.0 V leads to extensive morphological reconstruction and limited reduction of surface Mn ions, while the electrode capacitance remains stable. Range III: cycling with lower-potential end below 0.0 V results in obvious capacitance reduction, along with different morphological reconstruction and Mn reduction from those in Range II. For each selected lower-end potential in Range III, the capacitance descends to a plateau within first thousand cycles, and the extent of the capacitance reduction increases as the lower-end potential decreases.     

Kinetics of anodic oxide film growth on indium in alkaline solution

Data are presented which describe the kinetics of repassivation of freshly generated indium surfaces of pH 14. The process is controlled by ion conduction through the growing oxide film under high electric field. The associated kinetic parameters are tabulated. At high potentials an excess anodic charge is observed; it is attributed to conversion of some of the barrier film into an non-barrier layer. Some kinetic data associated with this process are presented.     

Corrosion resistance of aluminum oxide film and electrolytically coloured film in sodium chloride solution

The main interest of this study is to compare the corrosion resistance of aluminum anodic oxide film anodized in sulfuric acid bath with that of preanodized and electrolytically coloured film.Examinations have been carried out referring to (1) potentiostatted polarization curves shown on the specimens in 0.5 M sodium chloride solution, (2) impedance diagrams of the specimens and barrier thickness by Hunter's method and (3) optical metallographical observations of the aspects of pitting corrosion which took place on these specimens, and dipping test in corrosive solution.The results obtained are summarized as follows: (1) Typical difference was observed in regard to the potentiostatted polarization curves (i-t curves) between the two types of specimens in 0.5 M sodium chloride solution. The corrosion current caused by pitting corrosion of the electrolytically coloured specimens was smaller than that of anodized ones on the measurement by i-t curves. (2) The survey through the interfacial impedance diagrams of the specimens made clear that the impedance of the electrolytically coloured film was larger than that of uncoloured anodic oxide film, especially this greater increasing part of impedance was achieved in 15 s. This tendency was similar for the measurement of barrier thickness by Hunter's method. (3) The optical metallographical observations have demonstrated that there were far more advanced pitting corrosion on the anodic oxide film than on the electrolytically coloured film. In the dipping test, uncoloured anodized aluminum showed high extent of pitting corrosion, while electrolytically coloured aluminum performed well during colouring. So the total result of above examinations reveals that electrolytically coloured films are definitely more resistive to corrosion than anodic oxide films and this is due to the thick barrier layer of the former films.     

Estimation of film thickness nonuniformity effects on coating optical properties

Film nonuniformities cause many problems for the coating scientist. One area of coating film performance that they impact directly is optical properties. Measurements and predictions of film optical performance are all made assuming uniform film thickness. Incomplete leveling and other film application problems often yield nonuniform films with significant film thickness fluctuations. These film thickness imperfections can be modeled by a sine wave thickness fluctuation, and this fluctuation can be used to estimate the effects of nonuniformity in thickness on optical properties. This has been done using both approximate equations for scattering, transmission, and reflectance in films (zero absorption) and for the Kubelka-Munk equations including absorption. the effects of average film thickness and amplitude of fluctuation on measured S, R, and T values are predicted numerically for several cases of [K, S] pairs consistent with wavelength independent situations (white or similar films) over black substrates, and then the calculations are used to consider colored films [considering δE(L*a*b*)] over black substrates. Film thickness fluctuations are shown to have considerable impact on film optical properties, especially in thin highly scattering films. Examples of the types of predictions that can be made are given; how the results depend on the coating optical parameters is also shown.     

Effect of decreasing film thickness on the electrochemical responses of cations adsorbed in clay-modified electrodes

Clay-modified electrodes ranging in thickness from 3.4 μm to 8 nm, as estimated from the clay loadings, were prepared using three different smectites by spin-coating, solvent evaporation or electrophoretic deposition. For all three clays, the voltammetic waves obtained for [Ru(bpy)₃]²⁺ or [Os(bpy)₃]²⁺ adsorbed in these CMEs were independent of the film thickness for all films thicker than 100 nm. Only in very thin films, ≤40 nm were significant decreases in the peak currents observed. However, when the contributions to the peak currents from the electroactive concentrations, C* and effective diffusion coefficients, D_eff were separated, the values of C* were found to increase with decreasing film thickness, while D_eff decreased by several orders of magnitude. This was attributed to increase contributions to the electrochemical responses from less mobile electrostatically bound cations in the thinner films. Similar variations in C* and D_eff were obtained in films prepared by solvent evaporation. However, C* obtained in 20 nm thick electrodeposited films were significantly lower than in 40 nm spin-coated films. For [Ru(NH₃)₆]³⁺, the peak currents increased rapidly with the film thickness. However, no significant changes in the values of C* and D_eff with film thickness were found for this ion. This is consistent with the greater mobility of [Ru(NH₃)₆]³⁺ in clays films that allows a larger fraction of the adsorbed ions to remain electroactive even in thicker films. Results obtained for [Fe(bpy)₃]²⁺ were intermediate. While, the peak currents were independent of film thickness, the values of C* or D_eff obtained for this ion were also independent of the clay loadings.