Anodic Dissolution Mechanism 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.

The effect of antimony presence in anodic copper on kinetics and mechanism of anodic dissolution and cathodic deposition of copper

The influence of the presence of Sb atoms, as foreign metal atoms in anode copper, on kinetics, and, on the mechanism of anodic dissolution and cathodic deposition of copper in acidic sulfate solution has been investigated. The galvanostatic single-pulse method has been used. Results indicate that presence of Sb atoms in anode copper increase the exchange current density as determined from the Tafel analysis of the electrode reaction. It is attributed to the increase of the crystal lattice parameter determined from XRD analysis of the electrode material.

Susceptibility to Stress Corrosion Cracking of AZ31B Magnesium Alloy by Slow Strain-Rate Technique

Due to advantages such as high strength-to-weight ratios, specific castability and recycling efficiency, magnesium alloys are used in a wide variety of industrial applications. Stress corrosion cracking (SCC) tests of AZ31B magnesium alloy in distilled water and 2∼8wt% sodium chloride solutions at 298K were performed with slow strain-rate technique. In a distilled water, the SCC of the magnesium alloy occurs surely and its susceptibility increases with a decrease of strain-rate. This magnesium alloy in sodium chloride solutions is very susceptible to the SCC under open circuit condition, regardless of the strain-rate and solution concentration. The SCC in 4wt% sodium chloride solution under potential-controlled condition occurs near the corrosion potential, which lies to the potential range of hydrogen evolution. Furthermore, the fracture surface is characterized by transgranular quasi-cleavage appearance. The evidence introduced here supports a hydrogen embrittlement for the SCC of AZ31B magnesium alloy in sodium chloride solution, including an anodic dissolution mechanism by chloride ion.

Corrosion resistant low temperature carburized SS 316 as bipolar plate material for PEMFC application

One of the current challenges for application of PEM fuel cell is to find corrosion resistant, electrically conductive, light weight, cost competitive bipolar plate material. Low temperature carburization (LTC) of stainless steels is a novel, patented process by Swagelok Company. This paper addresses the corrosion resistance characteristics of LTC SS 316 for polymer electrolyte membrane fuel cell (PEMFC) bipolar plate applications. Corrosion properties of this material were studied using potentiodynamic and potentiostatic tests in simulated (1 M H 2SO 4 + 2 ppm HF, 0.5 M H 2SO 4, pH: 4.0, and 5% HCl + 5% Na 2SO 4) PEMFC conditions. LTC SS 316 showed excellent corrosion resistance in these conditions compared to SS 316. The mechanism of anodic dissolution and general corrosion of LTC SS 316 was observed to be similar to SS 316 however the extent of LTC SS 316 corrosion was less. LTC SS 316 showed corrosion currents well below 16 μA cm −2 in anodic and cathodic atmospheres under potentiostatic conditions. The potentiostatic current rapidly falls to ∼4.0 and ∼1.5 μA cm −2 under anodic and cathodic conditions, respectively. LTC SS 316 was observed to form a thinner oxide layer as compared to SS 316 after 24 h of potentiostatic testing. Moreover LTC SS 316 lowered the interfacial contact resistance by approximately 24% as compared to SS 316 after corrosion testing. Hence this study clearly states the performance advantage of using LTC SS 316 as bipolar plate material as compared to conventional materials.

Structure and formation mechanism of phosphate conversion coating on die-cast AZ91D magnesium alloy

Phosphate conversion coating, which is considered as an alternative to chromium conversion coating for improving the corrosion resistance of die-cast AZ91D magnesium alloy is studied. The structure and formation mechanism of the coating was investigated in details using ESEM/EDX, XRD, EPMA, ICP and electrochemical method. It was found that the conversion coating was composed of complex phosphate containing magnesium and aluminum and showed amorphous structure. The thickness of the coating was about 10 μm. A possible formation mechanism for phosphate conversion coating was proposed. Local pH rise due to the evolution of hydrogen in the vicinity of micro-cathode attributed to the movement of hydrolysis reaction balance for manganese dihydro phosphate in treating solution and resulted in the phosphate coating precipitated on metal surface. Initial depositing position was related to the microstructure of substrate. Galvanic effect between α phase and β phase caused the flower-like phosphate nuclei preferential depositing on β phase. Ball-like phosphate nuclei deposited mainly in α phase interior due to the micro-galvanic effect within α phase. The primary α phase was removed from the metal matrix due to the corrosion dissolution, which suggested the anodic dissolution mechanism during phosphate conversion coating growth. The inner stress in dried film resulted in random distribution of the network micro-cracks on film surface, the crack site did not correspond to β phase.

Anodic and Electroless Etching of Germanium in Alkaline Hexacyanoferrate Solutions

This paper presents results of a study on the electrochemical and etching behavior of Ge in alkaline hexacyanoferrate solutions. A detailed analysis of the current–potential behavior in these solutions allowed important conclusions to be drawn concerning the anodic dissolution mechanism of Ge. It was found that some oxidation steps involve mobile dissolution intermediates instead of, as generally accepted, free holes. Moreover, the electrochemical experiments indicate that hexacyanoferrate etches Ge according to an electroless mechanism, which was confirmed by etching experiments at open-circuit potential. Reproducible etch rates were obtained and only slight surface roughening after etching was observed.

Acoustic emission study of corrosion fatigue crack propagation mechanism for LY12CZ and 7075-T6 aluminum alloys

Acoustic emission signals were continuously monitored during fatigue crack propagation for LY12CZ and 7075-T6 aluminum alloys in laboratory air and 3.5% NaCl solution. The results showed that the acoustic emission count rate was as a linear function of crack propagation rate during fatigue and corrosion fatigue. The acoustic emission activity for LY12CZ was smaller in solution than that in air; but for 7075-T6, greater in solution than that in air. The acoustic emission waveform parameter, the frequency centroid ratio, was tried to use as a criterion to distinguish the corrosion fatigue crack propagation mechanism for anodic dissolution of LY12CZ and hydrogen embrittlement of 7075-T6.

Anodic behaviour of zinc in methanol solutions of lithium perchlorate

Anodic dissolution of poly- and single-crystals of zinc was performed in methanol solution of lithium perchlorate by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The mechanism of anodic dissolution of zinc in organic solvents occurs in two oxidation steps. It is the first step that Z n L + surface anodic product is created. Stability of the surface product is much better in anhydrous organic environments than in aqueous media; because the product is stable, a barrier layer composed of Z n L + is formed at low anodic overvoltage. The formation of the Z n L + layer is much stronger on the low index ( 1 1 2 ¯ 0 ) than on the high-index plane (0 0 0 1), where the adsorption of anodic product is more difficult.

水溶液中での銅のアノード溶解反応に及ぼす塩化物イオンと硫酸イオンの影響

The influences of chloride and sulfate ions in natural aqueous solution on the anodic dissolution of copper were investigated using electrochemical techniques. The anodic dissolution mechanisms of copper were proposed using determining the reaction parameters by the anodic polarization curves. The valencies of the copper ions were also determined using channel flow double electrode.The anodic dissolution mechanism changed depending on the concentrations of chloride and sulfate ions in fresh water : specifically, between (1) a concentration range with trace amounts of chloride and sulfate ions, and (2) a concentration range with more than about 100ppm of chloride and sulfate ions. The anodic polarization curve didn't show pH dependence in concentration range (2), but did show pH dependence in concentration range (1). The anodic dissolution mechanisms in concentration range (2) are proposed to be as follows.In the chloride medium :Cu+Cl−=CuCl+e−CuCl+Cl−→CuCl2−In the sulfate medium :Cu+SO42−=CuSO4−ads+e−Cu+CuSO4−ads+2SO42−→CuSO4−ads+Cu(SO4)22−+2e− Cu(SO4)22−=Cu2++2SO42−The influence of silica in fresh water on the anodic polarization curve was discussed.

酸性およびアルカリ性溶液中での亜鉛のアノード反応機構の解析

Anodic dissolution mechanisms of zinc in citric acid/sodium hydroxide buffer solutions (pH2-5) and sodium carbonate/sodium hydrogen carbonate buffer solutions (pH9-10) have been investigated using electrochemical techniques. The reaction parameters were obtained from the polarization curves of zinc, and the following dissolution mechanism was proposed. Zn+OH−=ZnOHads+e− Zn+ZnOHads+OH−→ZnOHads+ZnOH++2e− ZnOH+=Zn2++OH− An electrochemical quartz crystal microbalance (EQCM) was applied, and the mass change of zinc electrode was determined simultaneously with the measurement of polarization curve. Furthermore, the influences of chloride and sulfate ions on the anodic behavior of zinc were discussed.

Spectrophotometric study of the anodic corrosion of Ti/RuO 2 electrode in acid sulfate solution

Electrochemical properties of RuO 2-based electrode, particularly the oxygen evolution and anodic dissolution of RuO 2 have been investigated in 0.5 mol dm −3 H 2SO 4 solution by means of polarization measurements and product analysis. It has been demonstrated that it is possible to determine very low concentration of dissolved ruthenium species (8 × 10 −10 mol dm −3 Ru) by a sensitive spectrophotometric method based on the ruthenium-catalyzed ceric-arsenite reaction. Finally, the probable mechanism of anodic dissolution of RuO 2-based electrode, has been proposed.

Failure mechanisms of high strength steels in bicarbonate solutions under anodic polarization

High strength steels used in prestressing concrete structures are not exempt from the effects induced by corrosion on the normal concrete reinforcement. Carbonation of surrounding concrete or mortar is not unlikely for prestressing tendons and strands. Moreover, these steels undergo to brittle fracture as a consequence of stress corrosion cracking phenomena. To evaluate if concrete carbonation can promote this kind of failure, constant load tests in bicarbonate aqueous solutions under anodic polarization were carried out on high strength steel wires. Microscopic examination pointed out that the wires exhibited a brittle fracture mode, while its natural feature is ductile, as indicated by air testing. Failure mechanism was evaluated by a fracture mechanic approach. Cracks initiation was attributed to an anodic dissolution mechanism, while its propagation, interpreted by means of the surface mobility theory, was related to interaction between hydrogen atoms and magnetite at a crack tip.

A refined scheme of the mechanism of iron anodic dissolution in acidic sulfate solutions

A refined scheme of iron anodic dissolution in acidic sulfate solution, in which Fe0 is oxidized to Fe+ in stages, is proposed. The first stage consists in chemisorption of H2O molecules with participation of SO4 2– anions; the degree of the participation x ≈ 0.5 per a water molecule. This stage produces adsorbed OH groups (Fe(OH)ads), which, as a result of their interaction with sulfate anions, form an adsorption complex Fe((OH)SO4 2– ads. The schemes of oxidation of Fe+ to Fe2+ do not differ from conventional ones. The scheme put forward agrees with the literature data on the kinetics of iron dissolution under steady-state conditions.

等径角度付き押出し法により作製された超微細結晶銅の応力腐食き裂伝ぱ挙動

Stress corrosion crack (SCC) propagation tests have been carried out in 1kmol/m3 sodium nitrite aqueous solution to investigate SCC propagation behaviour of ultra-fine grained (UFG) copper produced by equal-channel angular pressing (ECAP) technique. SCC propagation tests have been performed on Compact Tension (CT) specimens under constant load. Phenomenon of SCC propagation was estimated from the crack propagation rate (da/dt) and the stress intensity factor (KI). Relationship between the da/dt and the KI in UFG copper could be divided into region I and II. The da/dt increased with the KI in region I. The da/dt was independent of the KI and showed constant value in region II. SCC in UFG copper had propagated along grain boundary. On the other hand, the transgranular SCC propagation was observed in polycrystalline copper. The anodic dissolution mechanism should be considered for the SCC of UFG and polycrystalline coppers. The SCC propagation in UFG copper could be understood from the film rupture and dissolution if the grain boundary sliding is considered as a dominant slip event.

The Effect of Nickel Presence in Anodic Copper on Kinetics and Mechanism of Anodic Dissolution and Cathodic Deposition of Copper

The influence of the presence of Ni atoms, as foreign metal atoms in anode copper, on kinetics, as foreign metal atoms in anode copper, and on the mechanism of anodic dissolution and cathodic deposition of copper in acidic sulfate system has been investigated. The galvanostatic single-pulse method has been used. Results indicate that presence of Ni atoms in anode copper, decreases the exchange current density as determined from the Tafel analysis of the electrode reaction. It is connected with the decrease of the crystal lattice parameter determined from XRD analysis of the electrode material. © 2001 The Electrochemical Society. All rights reserved.

A Mechanism of the Anodic Dissolution of Armco Iron and High-Strength Ferritic Cast Iron in an Oxalate Medium

The kinetics of the anodic dissolution of Armco iron and high-strength ferritic cast iron is investigated in an oxalic-acid medium at different pH values. It is shown that passivation occurs with the participation of secondary and electrochemical mechanisms and the formation of ferrous oxalate film. It is ascertained that hydro-oxalate ions participate in the electrode process with the reaction order equal to 0.5. The proposed mechanism of anodic dissolution of Armco iron and high-strength ferritic cast iron includes the stages of the formation of passivating film and Fe2+ions. The latter, accumulating in a near-electrode layer, promote the passivation of metal by the mechanism of secondary crystallization.

Progress in Modeling of Active Dissolution of Hydrophilic Metals

Progress in comprehending the effect of anions on the kinetics and mechanism of anodic dissolution of metals is analyzed over the period from the discovery of this phenomenon by Academician Yakov Kolotyrkin till nowadays. It is shown that new spectroscopic data on water adsorption at freshly formed iron and nickel surface open a novel approach to the mechanism of anodic dissolution of hydrophilic metals and allows eliminating a number of confusions accumulated in the literature.

弱アルカリ性炭酸塩水溶液中における銅のアノード溶解機構 -チャンネルフロー電極法による検討-

弱アルカリ性炭酸塩水溶液中における銅のアノード溶解機構 -チャンネルフロー電極法による検討-

Anodic behavior of Cu−Zn alloys in perchlorate media

The effects the pH and the zinc content exert on the anodic behavior of Cu−Zn alloys in 0.1 M NaClO4 (pH 2–9.5) are studied. A mechanism of anodic dissolution of brasses, which takes into account the changes in the solution’s pH, is put forward.

Physicochemical basis of uniform, pseudoselective, and selective dissolution of homogeneous alloys

Presently accepted mechanisms of anodic dissolution of homogeneous metal alloys—uniform dissolution, pseudoselective dissolution, and selective dissolution with phase conversion in the surface layer— have a unified physicochemical basis. The relative contribution of one or another mechanism depends, in particular, on the probability of the formation of new-phase nuclei on the surface of dissolving alloy and also on the kinetic parameters of ionization and back deposition of the noble component ions. The uniform dissolution tends to give way to the selective one, and the mechanism of pseudoselective dissolution can serve as the transition, connecting link.