Aluminum In Alkaline Solution Research Articles

Participation of Aluminum Hydride in the Anodic Dissolution of Aluminum in Alkaline Solutions

The mechanism of anodic alkaline dissolution of aluminum was investigated through the analysis of cyclic voltammetry (CV) and potential step experiments. Attention was focused on the role of aluminum hydride as a reaction intermediate, as suggested by the recent detection of formation during open-circuit dissolution. Potential step experiments at pH 11.75 revealed that the potential at the metal–surface film interface was close to the Nernst potential of oxidation. This finding suggested a reaction mechanism in which an interfacial layer is formed continuously by reaction of cathodically formed H with Al, and is then oxidized to the dissolution product, aluminate ions. However, potential step experiments at pH 11 did not indicate the presence of interfacial ; instead, the metal–film interface was close to the equilibrium potential of Al oxidation. Analysis of the CV indicated an abrupt transition in dissolution behavior between the two pH values, from a relatively rapid dissolution controlled by diffusion and film conduction in highly alkaline solutions, to a slow dissolution at a lower pH controlled by a highly resistive surface film. The formation of interfacial occurs readily at the higher pH, but is suppressed as the pH approaches neutrality.

Inhibition of aluminium corrosion in alkaline solutions using natural compound

Inhibition of aluminium corrosion in 2 M sodium hydroxide solution in the presence and absence of 0.5 M NaCl using damsissa ( Ambrosia maritime, L.) extract has been studied employing different chemical and electrochemical techniques. Chemical gasometry technique showed that addition of chloride ions or damsissa extract to sodium hydroxide solution decreases the volume of the hydrogen gas evolved. Potentiodynamic results manifested that chloride ion retard the anodic dissolution of aluminium, below the pitting potential, in sodium hydroxide solution. Damsissa extract, in presence or absence of chloride ion, influenced both the anodic dissolution of aluminium and the generated hydrogen gas at the cathode indicating that the extract behaved as mixed-type inhibitor. The decrease in the observed limiting current with increasing damsissa extract concentration indicated that the anodic process is controlled by diffusion. Nyquist plots present two capacitive semicircles at higher and lower frequencies separated by an inductive loop at intermediate frequencies. The inductive loops were clarified by the occurrence of adsorbed intermediates on the surface. A proposed equivalent circuit was used to analyze the impedance spectra for aluminium in alkaline solutions. The results showed that the damsissa extract could serve as an effective inhibitor for the corrosion of aluminium in alkaline solutions. The impedance measurements verified the remarkable stability of the extracts during storage up to 35 days. Damsissa extract was found more effective in presence of chloride ions than in its absence. Inhibition was found to increase with increasing concentration of the extract but decreases with increasing temperature. The associated activation parameters were determined and discussed.

Factors controlling the time evolution of the corrosion potential of aluminum in alkaline solutions

The mechanism of corrosion of 99.99% purity aluminum in alkaline solutions was investigated, through detailed examination of open-circuit potential transients. These transients displayed a characteristic time dependence, in which the potential first decreased over a few seconds to a minimum of −1.7 to −1.9 V vs. Ag/AgCl, and then slowly increased over a period of hours. The value of the minimum potential of electropolished foils, along with its dependence on pH and aluminate ( Al ( OH ) 4 - ) ion concentration, indicated that it was determined by the Nernst potential for the oxidation of surface aluminum hydride (AlH 3). This finding supports the direct role of hydride in the dissolution process. The increase of anodic polarization after the minimum potential occurred in two stages, the first correlated with the buildup of surface hydride, and the second with surface enrichment of Cu and Fe impurities.

Electrochemical noise analysis of corrosion of pure aluminium in alkaline solution in the presence of SO 42− ion, NO 3− ion and Na 2S additives

The electrochemical noises obtained from pure aluminium in an alkaline solution have been analysed as a function of sulphate, nitrate or sodium sulphide concentration. A stochastic theory has been applied to the experimentally obtained electrochemical noises based upon the Weibull distribution function. From the occurrence of two linear regions on one Weibull probability plot, the present analysis method permitted us to distinguish between the dissolution of Al and the stochastic process concerning the series of nucleation, growth and detachment of hydrogen bubbles in an engineering sense. Moreover, the conditional event generation rate and the average charge in each event were quantitatively determined for the stochastic process of hydrogen bubbles as well as the dissolution of Al. Effects of sulphate, nitrate and sodium sulphide additives on the corrosion of pure aluminium in an alkaline solution have been discussed in terms of the conditional event generation rate and the average charge in each event.

A model for galvanostatic anodising of Al in alkaline solutions

In this paper, the modelling of anodic oxide film growth on aluminium in alkaline solutions under galvanostatic conditions is discussed. The material balance of dissolved and adsorbed hydroxyl anion species at the substrate–electrolyte interface is considered, taking into account electrochemical processes of oxide film formation and dissolution via field-assisted and chemical mechanisms associated with evolution of aluminate anions. A differential equation describing the kinetics of oxide film growth under the influence of the above processes is derived and numerically solved. Simulation of the voltage behaviour during oxide film growth, depending on the main electrolysis conditions (such as current density, electrolyte concentration and agitation rate), is performed. Possible reasons for observed discrepancies with experimental data are discussed.

Characterisation of polypyrrole electrosynthesised on aluminium

Cyclic voltammetry has been used to investigate the role of the anions and the solution pH on the redox properties of polypyrrole electrosynthesised onto aluminium in alkaline solutions. The polymer film was characterised by SEM and IR spectroscopy. Moreover, the influence of the cathodic potential on the redox process was analysed for films formed in acid and alkaline solutions. The electrochemical response was compared with that obtained on vitreous carbon electrode. The differences in the shape and evolution of the voltammograms during cycling have been explained by a different participation of the ions. The best redox activity of the polymer is obtained in NO 3 − due to the fact that this anion could limit the anodic dissolution of Al. The other anions analysed cannot be incorporated into the polymer matrix. As a consequence, the transport of OH − occurs, which provokes a significative Al dissolution. It is expected that the Al 3+ ions generated during the electrodissolution are incorporated into the polymer in order to equilibrate the charge of the film.

Anodic processes in plasma electrolytic oxidation of aluminium in alkaline solutions

In this paper, basic electrochemical processes (such as oxide film growth, anodic dissolution and oxygen liberation) on an aluminium anode in a model alkaline solution are considered under conditions of galvanostatic DC plasma electrolytic oxidation (PEO). The experiments performed include: (i) recording and analysis of the main electrical characteristics of the process; (ii) determination of the oxide layer thickness; (iii) anodic gas collection and composition analysis and (iv) electrolyte analysis to determine dissolved aluminium. Four different stages of the PEO process have been identified, characterised by various rate proportions of the partial anodic processes. Overall current efficiency of the oxide film formation has been estimated to be in the 10–30% range. The film growth rate decreases significantly with increasing electrolyte concentration from 0.5 to 2 g l −1 KOH, since the rate of anodic dissolution increases. Oxygen evolution is shown to be the main electrochemical process at the potentials corresponding to the plasma stages of the electrolysis. The overall rate of oxygen liberation at the anode exceeds the Faraday yield, which is probably due to the radiolytic effect of the plasma discharge on the adjacent electrolyte volume.

Influence of alloying additives on corrosion and hydrogen permeation through commercial aluminium in alkaline solution

The influence of alloying additives on the extent of corrosion and hydrogen permeation through aluminium of different grades such as 2S, 3S, 26S and 57S, in 0.01 M NaOH has been investigated using weight loss measurements and electropermeation. It is found that the extent of self corrosion and hydrogen permeated through different grades of commercial aluminium follow the order: 3S > 2S > 26S > 57S. The influence of incorporating zinc and indium either alone or in combination on self corrosion and permeation current has also been studied. It is found that ternary alloys of both 26S and 57S containing zinc and indium give considerably lesser values of self corrosion rate and permeation current.

Corrosion mechanism of pure aluminium in aqueous alkaline solution

The corrosion of pure aluminium in alkaline solution has been explored using an open circuit potential transient, potentiodynamic polarization experiment and a.c. impedance spectroscopy. The steady-state value of the open circuit potential (E ocp ss ) of pure aluminium in alkaline solution was observed to decrease with increasing rotation rate of the specimen, which is ascribed to the enhanced anodic reaction. The extent of anodic polarization for the aluminium dissolution reaction on pure aluminium at E ocp ss was found to be greater than that of cathodic polarization for the water reduction reaction. This indicates that the rate of corrosion of pure aluminium is mainly determined by the anodic reaction in alkaline solution. Based upon the experimental results, a corrosion mechanism for pure aluminium has been proposed in the presence of the native surface oxide film in alkaline solution, involving consecutive oxide film formation and dissolution, and simultaneous water reduction.

Effects of Cl −, NO −3 and SO 2−4 ions on anodic dissolution of pure aluminum in alkaline solution

The effects of the anions Cl −, NO − 3 and SO 2− 4 on the anodic dissolution of pure aluminum have been investigated in 0.01 M NaOH solution by using potentiodynamic polarization experiments, a.c. impedance spectroscopy and potentiostatic current transients. It was found that the addition of Cl −, NO − 3 and SO 2− 4 ions in 0.01 M NaOH solution reduces the anodic dissolution rate of pure aluminium in the passive potential region on the polarization curves and potentiostatic current transients. Pitting was observed only in the presence of Cl − and NO − 3 ions. The reduced anodic dissolution rate by the addition of Cl − and NO − 3 ions below the pitting potential was traced back to the formation of resistive insoluble compounds. Above the pitting potential, resistive transitory compounds would be formed up to the induction time and then dissolved into the solution as complex anions, thus causing pitting. By contrast, the decreased anodic dissolution rate by the addition of SO 2− 4 ions was accounted for by the reduced reacting surface area, by competitive adsorption of SO 2− 4 ions with OH − ions. The adsorption of SO 2− 4 ions does not cause pitting in all the applied anodic potential ranges.

The formation and dissolution of anodic oxide films on pure aluminium in alkaline solution

The mechanisms of formation and dissolution of anodic oxide films on pure aluminium rotating disc specimens in alkaline solution have been investigated using galvanostatic anodizing, potentiostatic anodizing, potential drop experiments and impedance spectroscopy. It was found that in alkaline solution the strength of the applied electric field accelerates the formation of the anodic oxide film, while it retards its dissolution, indicating electrochemical formation of the film and a complete lack of its field-assisted dissolution. The rate of growth and the thickness of the anodic oxide film were observed to decrease with an increasing rate of specimen rotation as a result of accelerated chemical film dissolution due to rapid removal of aluminate ions from and fast supply of hydroxide ions towards the film/solution interface.

Cementation of Copper on Aluminum in Alkaline Solutions

Cementation of copper onto aluminum is a galvanic process resulting from the dissolution of aluminum metal in alkaline media. The kinetics of cementation of copper onto aluminum in alkaline solutions has been investigated using powder and flat substrates. The results show that this process follows a first‐order reaction rate. The rate of the reaction is found to increase with an increase in NaOH concentration. No significant differences are found between flat and powder substrates, however, the results suggest a strong influence of surface area on the reaction rate. X‐ray diffraction and x‐ray fluorescence methods show that the cemented product is pure copper. Scanning electron microscopy photographs show that the cemented Cu has a bulbous (botryoidal) type of structure.

Ni‐Al Powder Electrocatalyst for Hydrogen Evolution: Effect of Heat‐Treatment on Morphology, Composition, and Kinetics

Electrocatalytic activity toward the hydrogen evolution reaction in alkaline media was studied on three types of electrodes: (i) pressed powders; (ii) same as but heated at 400°C; (iii) same as but heated at 700°C; followed by leaching aluminum in alkaline solution. Steady‐state polarization and ac impedance spectroscopy were used to determine the electrode activities. A dramatic increase in activity occurs after heating powders above the Al melting point, which is connected with the diffusion of Al into Ni and formation of new phases. The hydrogen evolution reaction proceeds through the Volmer‐Heyrovsky mechanism and the main factor influencing the activity is the roughness factor.

Kinetics of hydrogen evolution on Ni-Al alloy electrodes

The kinetics of the hydrogen evolution reaction have been studied on Ni-Al alloy electrodes. The electrodes after leaching aluminium in alkaline solution, are very active despite their large Tafel slopes. The SEM studies show a formation of deep pores on the electrode surface. The kinetics were studied using an ac impedance technique. It was found that the impedance plots may be explained assuming a fractal model. The logarithm of the charge transfer resistance is a linear function of the overpotential. Using a nonlinear least square approximation it was found that the reaction proceeds through the Volmer-Heyrovsky mechanism and the kinetic parameters were estimated.

Corrosion of aluminium in alkaline solutions

AbstractThe corrosion of Al in NaOH solutions has been investigated using polarization method as well as weight loss method. The effect of various organic and inorganic compounds on the rate of corrosion was studied. The results indicated that the rate of Al corrosion is maximum at [NaOH] ∼4M. Various benzoic acid as well as other organic acids inhibit the corrosion but to different extents depending on the structure. The inhibition is due to adsorption of these acids and not due to neutralizing effect. Some sulpher containing compounds inhibit the corrosion but to lesser extent than acids. Aniline and its derivative are mostly activators for corrosion.

Corrosion inhibition of aluminum in alkaline medium. I: Influence of hard bases

The inhibition of corrosion of aluminum in alkaline solution is a difficult problem, according to Evans, possibly because of the specific adsorption of OH on the metal surface. The presence of hard bases, acting as anode inhibitors, revealed high % inhibition; Cr 2O 7 −− < HCO 3 − < B 4O 7 −−, of aluminum in 0.5 n KOH at 28°C. At constant inhibitor concentration (⩽ 5 mM) of these bases, the % inhibition is compared with time of exposure and potentodynamic measurements were corroborated in the discussion of these results.

アルカリ溶液中におけるAlの腐食速度に及ぼす冷間圧延の影響

アルカリ溶液中におけるAlの腐食速度に及ぼす冷間圧延の影響

ChemInform Abstract: Ellipsometry of the Growth and Dissolution of Anodic Oxide Films on Aluminum in Alkaline Solution.

AbstractDie ellipsometrische Untersuchung des Oxid?lmwachstums auf hochreinem Al in 0.1 ‐4 M NaOH erfolgt in situ bei einer konstanten Wellenlänge von 632.8 nm.

Ellipsometry of the Growth and Dissolution of Anodic Oxide Films on Aluminum in Alkaline Solution

Ellipsometry has been used to study the growth of anodic films on superpure aluminum in sodium hydroxide of concentration range 0.1–4M. The ellipsometer used was a self‐nulling type, and all experiments were performed in situ at a constant wavelength of 632.8 nm. The results are explained by the growth and dissolution of anodic films that are duplex in nature. During the dissolution process, at certain potentials, a highly reproducible transient effect in the optical signal is seen. This effect has been related to roughening of the underlying aluminum substrate, followed by subsequent smoothing upon completion of the dissolution process. The latter is indicated by the optical signal returning close to its initial value prior to film growth.

The influence of electrolyte additives on the anodic dissolution of aluminum in alkaline solutions

The anodic dissolution of aluminum in alkaline solutions is accelerated by the addition of small quantities of gallium or indium ions to the electrolyte. This process increases the possibilities for using commercially available aluminum and its alloys in high-rate batteries.