Neutral Borate Solution Research Articles

Benzotriazole as an inhibitor of the anodic dissolution of cadmium, bismuth, and their eutectic alloy in a neutral borate solution

The electrochemical behavior of an eutectic cadmium-bismuth alloy in borate buffer solution containing 1,2,3-benzotriazole (BTA) as an additive has been studied. The additive inhibits the cadmium and alloy dissolution to an appreciable extent. It has been shown that the experimental polarization curve of the alloy is similar to that calculated based on the additive scheme. However, the currents on the experimental curve are lower due to selective mode of cadmium dissolution from the alloy. The kinetics of passive film formation was also studied.

XPS study of 5-chloro-1,2,3-benzotriazole adsorption on nickel surface

Surface layers formed by adsorption of 5-chloro-1,2,3-benzotriazole (5-chloroBTA) on nickel and influence of pH of borate buffer solution and electrode potential on formation multicomponent oxidized films on nickel were studied by XPS. It was found that at concentration of 10 –4 mol/l in neutral borate solutions a 0.7 nm monomolecular layer of 5chloroBTA is formed. Using peak intensity angular dependence of XPS spectra the orientation of 5-chloroBTA close to vertical on nickel hydroxide formed on the nickel surface was shown. 5-ChloroBTA forms a chemical bond by lone pair of nitrogen and surface nickel cations.

Preparation and Characterization of (Ba0.8Sr0.2)TiO3–Al2O3 Composite Oxide for Thin Film Capacitor

Barium strontium titanate–alumina composites were fabricated using a sol–gel and anodizing process for high performance thin film capacitors and the properties of the films were studied. The (Ba0.8Sr0.2)TiO3 (BST) films were formed by spin coating and subsequent annealing at 150–550 °C. The respective annealed films were anodized in a neutral borate solution. The capacitance density increased with increasing annealing temperature up to 450 °C but decreased at 550 °C. The capacitance density was approximately 28.46% higher with the BST coating than without the BST layer.

XPES of 1,2,3-benzotriazole nanolayers formed on iron surface

The effect of 1,2,3-benzotriazole (BTA) on the electrochemical behavior of St3 steel in different environments, as well as the adsorption of BTA on the steel surface, is studied using the XPES technique. Based on the XPES data using the MultiQuant program, the thickness of the layers formed on the St3 steel surface are calculated. In neutral borate solutions, a thin protective layer of iron-BTA complex with a thickness of 0.7–1.5 nm, which completely suppresses the anodic process, but does not prevent the local depassivation in the presence of chlorides, is found to form on the surface of St3 steel. In alkaline solutions, BTA hardly chemisorbs at all, though adding BTA to the solutions and increasing its concentration results in the increase in the pit-formation potential. In sulfuric-acid solutions, a monomolecular layer is formed on the steel surface. Independently of the pH value, the interaction between BTA and iron cations is shown to result in the proton detachment from BTA molecules.

In-situ Raman Spectroscopy for the Passive Oxide Film on Iron in Neutral Borate Solution

In-situ Raman spectra of the passive oxide film in neutral borate solution at pH 8.4 was measured without any enhancement such as surface enhanced Raman scattering or resonance Raman scattering. To measure the Raman spectra of the surface thin film on the electrode, we introduced a confocal collection system to reject the scattering signal from the electrolytes surrounding the surface in front of the spectrometer. The background signal is still high, and it is more intensive by 100 times than the Raman signal from the passive film. The difference Raman signal between the surfaces of the passivated iron and the reduced bare iron reveals a peak at about 670 cm-1. When we measured the passivated iron surface soon after transfer from the electrolytes to air, we observed another broad and faint peak at 320 cm-1. From these peaks, we assume that the passive oxide film on iron is composed of Fe3O4 and γ-Fe2O3.

Electrochemical properties of iron silicocarbide and cementite in acidic and neutral environments

Voluminous specimens of individual Fe5SiC iron silicocarbide and Fe3C iron carbide phases were produced by mechanical alloying with subsequent pressing and considered as models of nonmetallic inclusions in carbon steels and siliceous cast irons. In an acidic sulfate solution, silicocarbide is highly active in hydrogen reduction and iron ionization in the active dissolution range. Therefore, the corrosion resistance of silicocarbide in acids is lower compared to iron and cementite, which is caused by the peculiarities of its crystal structure. In a neutral borate solution both on silicocarbide and cementite, two anodic peaks are observed that are caused by the dissolution of the corresponding phase and the additional oxidation of the passive film, which is characterized by the heightened defectiveness because of the carbon accumulation. Silicocarbide has lower dissolution currents compared to cementite and a higher resistance to the local activation and depassivation, which is caused by the presence of a superficial layer enriched in SiO2.

Photo-luminescence from passive oxide films on nickel and chromium by photo-excitation of UV light

Photo-luminescence emission was measured from the thin passive oxide film on nickel and chromium under the in-situ condition in 0.1 kmol m −3 (M) sulfuric acid solution at pH 0.9 and neutral buffer solution of borate-boric acid mixture at pH 8.4 in order to obtain the insight of the electronic properties in the passive oxide film as thin as a few nm. The photo-luminescence induced by UV laser beam at 325 nm wavelength from nickel oxidized in both pH 0.9 sulfuric acid and pH 8.4 borate buffer solutions exhibited a broad spectrum feature with a peak at 400–420 nm. The energy of the peak wavelength from 400 to 420 nm is 2.95–3.10 eV which may correspond to the band-gap energy of the semiconduncting NiO. The photo-luminescence spectra from chromium oxidized in the sulfuric acid and neutral borate solutions had a peak at 400 nm and about 440 nm, respectively. These photo-emission from nickel and chromium oxidized is assumed to correspond to luminescence accompanied by recombination between excess electrons produced by UV light illumination in the conduction band and positive holes in the valence band. The broad tailing of the luminescence at longer wavelength side may represent high density of localized states originated in an amorphous nature of the passive oxides.

In-situ Raman Spectroscopy for the Passive Oxide Film on Iron in Neutral Borate Solution

not Available.

Passivation oxide film on Nd–Fe–B permanent magnets in borate buffer solution by ellipsometry

The passivation of Nd–Fe–B permanent magnet was investigated in neutral borate solution at pH 8.4. The thickness of the passive oxide film on the magnets was measured by ellipsometry and the composition was estimated by glow discharge optical emission spectroscopy (GD-OES). The passivation of the magnets takes place in the potential range between −0.2 and 1.0 V vs. Ag/AgCl/Sat. KCl. In the potential range, current density decays to the lower than 10 −6 A cm −2 after potentiostatic oxidation for 1800 s. The passive oxide film growth is assumed to be optically simulated from a model with a homogeneous film with complex refractive index, N = 2.1 − j0.086. The thickness estimated from the refractive index linearly increases with potential from 3.6 nm at −0.2 V to 7.8 nm at 1.0 V. The passive film growth follows the ionic migration model under high electric field, i.e., the Cabrera–Mott growth model. The ionic conductivity estimated from the model is about κ = 1.7 × 10 −16 Ω −1 cm −1. The passive oxide film is preferentially composed of iron oxide/hydroxide. Boron and neodymium are, respectively, concentrated at the surface of the oxide film and at the inner layer in the oxide film.

The effect of chloride and sulfate anions on the iron dissolution rate in neutral and nearly neutral media

Analysis of results of steady-state potentiostatic measurements on iron in the neutral and nearly neutral borate solutions is complicated by the fact that the metal is in the state of active-passive transition near the free-corrosion potential. This difficulty is overcome using the method of neural network simulation. The study of the behavior of neural-network model shows that chloride and sulfate ions can promote or inhibit iron dissolution depending on their concentration and the pH value of solution. The ambiguous effect of anions is explained by the fact that, when they are adsorbed at the metal, they prevent its cations from passing to the solution, and, entering into the metal-water adsorption complexes, they assist the decomposition of complexes thus promoting the dissolution. Sulfate ions, compared with chloride ions, are, probably more adsorption-active with respect both to iron and to water adsorbed on it.

ゾル・ゲルコーティング／アノード酸化によるＡｌ‐Ｎｂ複合酸化物皮膜の形成

Aluminum specimens coated with niobium oxide by a sol-gel method were galvanostatically anodized in a neutral borate solution. The time-variations in anode potential during anodizing were monitored, and the structure and dielectric properties of the anodic oxide film were studied by TEM, EDX, RBS, and electrochemical impedance measurements.It was found that the anode potential increases linearly with time after a rapid increase in potential at the initial period of anodizing. During anodizing, an anodic oxide film, which consisted of an inner Al2O3 layer and an outer Al-Nb composite oxide layer, grew at the interface between the Nb2O5 layer and the aluminum substrate. The interface between the outer and inner layers became more vaguer as the potential rose, and the concentrations of aluminum and niobium ions in the composite oxide layer also changed. The capacitance of the specimen after the sol-gel coating and anodizing was 150% as large as that without the sol-gel coating. This is due to the high dielectric constant of the composite oxide layer.The mechanism of the anodic oxide film's growth on the specimen coated with Nb2O5 is discussed in terms of the pore distribution in the Nb2O5 layer and the transport of Nb-cations across the anodic oxide film during anodizing.

Anodizing of Aluminum Coated with Silicon Oxide by a Sol-Gel Method

Aluminum specimens were covered with film by a sol-gel coating and then anodized galvanostatically in a neutral borate solution. Time variations in the anode potential during anodizing were monitored, and the structure and dielectric properties of the anodic oxide films were examined by transmission electron microscopy, Rutherford backscattering spectroscopy, and electrochemical impedance measurements. It was found that anodizing of aluminum coated with films leads to the formation of anodic oxide films, which consist of an outer Al-Si composite oxide layer and an inner layer, at the interface between the film and the metal substrate. The capacitance of anodic oxide films formed on specimens with a coating was about 20% larger than without a coating. In the film formation mechanism, the conversion of to Al-Si composite oxide at the interface between the inner and outer layers is discussed in terms of inward transport of Si-bearing anions across the outer layer. © 2001 The Electrochemical Society. All rights reserved.

Formation of Al–Zr composite oxide films on aluminum by sol–gel coating and anodizing

Al specimens were covered with zirconium oxide film by sol–gel coating using zirconium alkoxide, and then anodized galvanostatically in a neutral borate solution. The time-variation in anode potential during anodizing was followed, and the structure and dielectric properties of the anodic oxide film were examined by TEM, EDX, RBS, and impedance measurements. It was found that the anode potential increases during anodizing, and that the slope of the potential–time curve becomes steeper with increasing number of dippings in sol–gel solution. An anodic oxide film was formed at the interface between zirconium oxide and the aluminum substrate during anodizing. This anodic oxide film was composed of an inner Al2O3 layer and an outer Al–Zr composite oxide layer. The capacitance of anodic oxide films formed after sol–gel Zr-oxide coating and anodizing was about 20% higher than without Zr-oxide coating.

Oxide Film Formation on a Microcrystalline Al Alloy at Various Temperatures in Neutral Borate Solution

FVS0812 is a rapidly solidified Al alloy consisting of an intermetallic (dispersoid) phase, containing Al, Fe, V, and Si, surrounded by a predominately Al matrix. The electrochemical behavior and the oxide film structure of FVS0812 were compared to that of its two phases, as well as pure Al, in neutral borate solution at a range of temperatures. While in acidic solution, FVS0812 is unable to form an adherent, thick, porous oxide film, in 60°C neutral solution, stable, although substantially thinner, porous oxides are formed on Al, FVS0812, and the matrix. In contrast to its dissolution in acidic medium, the dispersoid phase is retained within the porous film formed on the alloy in neutral solution. However, the dispersoid phase also causes the formation of a somewhat contorted porous oxide structure. Impedance measurements suggest that solution penetration into fine flaws in the barrier oxide at the barrier/porous oxide interface, a phenomenon exacerbated by increased temperature and time at applied potentials, is more prevalent for FVS0812 than for Al and the matrix.

Formation of Al/(Ti, Nb, Ta)‐Composite Oxide Films on Aluminum by Pore Filling

Aluminum specimens coated with porous anodic oxide films were dipped in solutions containing , or ions and heated in air mainly at 400°C to deposit Ti, Nb, or Ta oxide on the inner walls of pores. After 0 to 7 cycles of the dipping and heating process, the specimens were reanodized in a neutral borate solution to fill the pores with . The incorporation of Ti, Nb, or Ta oxide in the anodic oxide films was examined by transmission electron microscopy, Rutherford backscattering spectroscopy, and impedance measurements. Incorporation of Ti, Nb, or Ta oxide was found only in the outermost part of the anodic oxide film after reanodizing up to 400 V. The Al/Ti composite oxide films consisted of an outer Al/Ti‐composite oxide layer, an intermediate crystalline alumina layer, and an inner amorphous alumina layer, while the Al/Nb‐ and Al/Ta‐composite oxide films consisted of an outer composite oxide layer and an inner amorphous alumina layer. The parallel electric capacitance of Al/Ti‐composite oxide film was 40% higher than those of the other two due to its small thickness and high dielectric constant. The formation mechanisms of the composite oxide films during reanodizing are discussed in terms of the ion transport across the oxide film.

Oxide Film Formation at a Microcrystalline Al Alloy in Room Temperature Neutral Borate Solution

The differences in the electrochemical behavior of a rapidly solidified, two‐phase (matrix and dispersoid) microcrystalline Al‐based alloy containing Fe, V, and Si (FVS0812 alloy), the bulk forms of its phases, and polycrystalline Al were investigated in neutral borate buffer solution. FVS0812 shows higher activity than the matrix and pure Al while the dispersoid is the most active, due to oxygen evolution and dissolution, even in this benign solution. Barrier oxide films formed at FVS0812 appear to be generally uniform and similar in thickness to those formed at the matrix material At low anodizing voltage the dispersoid phase appears to form an oxide film, although some loss of Fe and V is inferred However, at higher voltages, evidence for the incomplete oxidation of the dispersoid phase and its incorporation and/or subsequent loss from some sites in the oxide film is seen, leading to a more flawed film of less uniform thickness The higher capacitance of the oxide film at FVS0812 compared to that of films formed under identical conditions at Al and the matrix is consistent with the penetration of solution, via flaws, into the oxide film and the development of regions of thinner oxide film at dispersoid containing sites.

チタン上に生成したアノード酸化皮膜の Breakdown 現象の解析

Voltammogram and impedance measurements were applied for analysing the change in electronic property of the anodic oxide film formed on titanium in neutral borate solution with the electrolytic breakdown at anodic potentials higher than the breakdown potential of 7.5V. Anodic current histerisys was observed between the potential sweeps toward negative and positive directions for the film after the breakdown. The histerisys disappeared when the electrode was held at potentials lower than the breakdown potential. From analysis of the current histrisys it is suggested that high valency oxide such as TiO3 or high valency state such as Ti5+ or Ti6+ are formed in the film at the breakdown. From the change of the Mott-Schottky plot with oxidation potential and period, it is estimated that the donor density in the oxide film increases after breakdown.

Raman Spectra of Passive Films of Iron in Neutral Borate Solution

The Raman spectra of the passive films formed on iron in a neutral borate solution at various potentials were measured for evaluating its composition without any enhancement technique. The ex-situ spectrum measured in air after removal from the aqueous solution corresponds to the composition of disordered Fe 3 O 4 , i.e., Fe 3-δ O 4 . The passive film in the aqueous solution, which could not be measured in this paper due to a large background scattering light intensity from surrounding water around the iron electrode, may be a compositional framework same as the ex-situ passive film, although it is expected to be hydrated under the in-situ condition. For the in-situ measurement of the passive film, it is speculated that much accumulation will be required to decrease the noise level of the background light scattering relative to the signal from the thin film.

Growth of a passive film on iron in a neutral borate solution by three-parameter ellipsometry

Abstract The growth of passive film on iron has been traced during potential sweep at various sweep rates in a neutral borate solution at pH 8.4. The transient thickness increase from a stationary state at 0.0 V (vs. AgAgCl) was measured by automated ellipsometry by which the ellipsometric parameters Ψ and Δ, and the reflectivity change ΔR/R, are simultaneously obtained. The transient thickness change and the complex refractive index, N = n − jk, of the film were calculated by the three parameters. The complex refractive index of the film during the transient growth is estimated to be N = 2.18 – 0.352j for light of 632.8 nm wave length. The linear potential increase initially causes an increase of the potential difference at the film/solution interface, where the film thickness remains constant and the observed current increases gradually. In the latter stage, where the interfacial potential difference reaches a constant value, steady growth of the film thickness takes place and the current reveals an almost constant value. The interfacial potential difference is a function of the potential sweep rate, and accordingly the current at the steady film growth stage is also a function of the sweep rate. From the transient change of the film thickness and current during the potential sweep at various sweep rates, the interfacial ionic transfer reactions and the mechanism of the film growth are discussed.

Electrochemical and microstructural study of oxide films formed electrochemically at microcrystalline Al-Fe-V-Si alloys.

A recent advance in metallurgical technology has been the application of rapid solidification techniques to Al alloy production. FVS0812 is the designation given to a microcrystalline Al-based alloy consisting of 8 wt% Fe, 1 wt% V and 2 wt% Si. It is a two-phase alloy, consisting of ca. 27 vol percent of approximately spherical Fe-V-Si-rich dispersoids in an essentially pure Al matrix. The high strength, low density properties of this advanced material, and other related alloys, have not yet been realized, however, due, in part, to the inability of the alloy to form a thick, adherent, abrasion-resistant outer surface oxide film, a feature readily achieved at conventional Al alloys by normal anodizing methods. The present research has involved an electro-chemical study of oxide film growth at the 812 alloy, with the specific goals being to seek an understanding of the origin of the oxide film growth problem and ultimately to propose alternative approaches to the formation of a thick, stable oxide film at this material. The techniques used in this research have included electrochemical methodologies such as cyclic voltammetry and electrochemical impedance spectroscopy. Crucial information has been obtained through transmission electron microscopy (TEM) of ultramicrotomed specimens. Experiments were carried out initially in neutral borate solutions to characterize the compact barrier oxide film formed in this environment and expected to be present beneath the porous oxide film formed in the normal sulfuric acid anodizing medium.(ABSTRACT TRUNCATED AT 250 WORDS)