Electrochemical behaviour of phenylethanolamine at gold in aqueous solution

The electrooxidation of phenylethanolamine (2-amino-1-phenylethanol) at a gold electrode in alkaline electrolyte has been studied. Measurement of the differential capacitance of the electric double layer versus the electrode potential has shown that the adsorption of phenylethanolamine at the gold-solution interface plays a significant role in the oxidation mechanism. The effect of amine concentration, electrolyte pH and potential scan rate on the electrooxidation is analysed.     

Electrodissolution of iron in sodium sulfate and sodium bicarbonate solutions at pH8

The effect of sulfate ions on the electrochemical behaviour of iron electrodes in the presence of bicarbonate ions has been investigated. In solutions containing sulfate ions only, iron electrodes experience uniform corrosion and sulfate ions are aggressive. In the presence of bicarbonate ions, the sulfate ions become less aggressive and a pitting–repassivation process is observed. The differences in electrochemical behaviour have been compared and explained by examining the formation of probable products and their physicochemical properties during electrochemical polarization.     

Electrodissolution of iron in sodium sulfate and sodium bicarbonate solutions at pH8

The effect of sulfate ions on the electrochemical behaviour of iron electrodes in the presence of bicarbonate ions has been investigated. In solutions containing sulfate ions only, iron electrodes experience uniform corrosion and sulfate ions are aggressive. In the presence of bicarbonate ions, the sulfate ions become less aggressive and a pitting–repassivation process is observed. The differences in electrochemical behaviour have been compared and explained by examining the formation of probable products and their physicochemical properties during electrochemical polarization.     

Electrochemical behaviour of cadmium in NaOH solution

The electrochemical behaviour of cadmium in 1 M NaOH solution was studied. Different electrochemical methods such as potentiodynamic measurements, polarization techniques and electrochemical impedance spectroscopy (EIS) were used. During the course of polarization, several characteristic features were observed, including prepassivation and a relatively wide passive range extending over 1.4 V. Equivalent circuit models for the electrode–electrolyte interface under different applied potentials were proposed. The impedance data measured at steady state were fitted to calculated data according to proposed equivalent circuits. The relevance of the proposed equivalent circuits to the different phenomena occurring at the electrode–solution interface was discussed. The passive film formed on Cd is composed of two layers: a barrier layer in contact with metal and a deposit on the barrier layer. The barrier layer appears to form directly from the metal through a solid state reaction, rather than by a dissolution–precipitation mechanism. For an applied potential >+0.7 V the relative passive film thickness and resistance decrease to lower values indicating transpassive dissolution at this potential.     

Electrochemical behaviour of 1024 mild steel in slightly alkaline bicarbonate solutions

The electrochemical behaviour of 1024 mild steel electrodes is investigated in the presence of 0.05–0.5 M sodium bicarbonate in aqueous solution at pH 8.9 and 25°C. Voltammograms are obtained with a rotating gold ring-mild steel electrode and the effect of the NaHCO3 concentration, the potential limits and the rotation speed of the disc electrode is considered. The voltammograms display an oxidation peak current at low potentials, a passivity region and a transpassive region at high potentials for the potential sweep in the anodic direction. The oxidation current in the passivity region is practically independent of the applied potential and the NaHCO3 concentration. The rate-determining step of the oxidation reaction in both the oxidation peak current region and the transpassive region is determined.     

Influence of temperature on the electro-dissolution of tin in NaCl aqueous solution at pH4

The influence of temperature in the range 25 to 80°C on the dissolution of tin was investigated in an acidic solution at pH4 containing 0.1 to 1m NaCl. The corrosion current is slightly dependent on both the temperature and the Cl^– ion concentration. The main dissolution characteristics of tin are

Electrochemical behaviour of cobalt in aqueous solutions of different pH

A systematic study of the corrosion and passivation behaviour of cobalt in aqueous solutions of different pH was carried out. Open circuit potential measurements, polarization experiments and electrochemical spectroscopic (EIS) investigations were employed. The experimental results show that the metal surface is always covered by a native passive film which consists of CoO. The formation of the oxide film obeys a two-electron charge transfer process. The dissolution of the barrier film is controlled by the pH of the solution. In neutral and basic solutions the barrier film is stable. In these media a barrier film thickening with the formation of secondary layer is considered. In acidic solutions, the passive film is unstable and dissolves via a pure chemical process. The mechanism of the corrosion and passivation processes taking place at the electrode/electrolyte interface in the different solutions is discussed. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to confirm the electrochemical measurements and the suggested mechanisms.     

Electrooxidation of stainless steel AISI 304 in carbonate aqueous solution at pH 8

The electrochemical behaviour of stainless steel AISI 304 (SS304) has been investigated in deaerated 0.1–1 m NaHCO₃ solutions at pH 8 using a rotating disc electrode. The polarization curves are characterized by a broad range of passivity at low potentials (–0.8 to 0.3 V), a depassivation region at 0.4 V vs SCE and, at high potentials (0.5 to 0.85 V), a passive region before oxygen evolution. In the low potential range, the SS304 electrode behaves like a Cr-rich metallic phase, and the dissolution of Fe²⁺ ions into the solution is hindered by the formation of a Cr₂O₃ layer. As the potential reaches 0.4V, the oxidation-dissolution of Cr(iii) oxide/hydroxide to CrO₄ ² ions occurs, with the participation of bicarbonate/carbonate as a catalyst in the dissolution reaction. Since the chromium oxide/hydroxide dissolution and subsequent surface enrichment of iron oxides occur, the applied potential, exposure time and oxidation charge have a considerable effect on the passive film properties. At high potentials, the presence of a passive film of iron oxides/hydroxides or oxyhydroxides plays a key role in the SS304 passivity with the presence of Fe(vi) species incorporated or adsorbed into the passive films. Colouration of the SS304 surface is observed in the second passive region. A film of a uniform gold colour formed on SS304, mild steel 1024 and iron in carbonate and borate solutions at pH 8. The colour of the electrode surfaces remain unchanged in air and in solutions at positive potential but it disappears at open-circuit potential or is easily reduced in the first negative-going potential scan.     

Electrochemical behaviour and electrowinning of rhodium in acidic chloride solution

The electrochemical behaviour and recovery of rhodium in an acidic solution were investigated using a rotating disc electrode system and a modified electrochemical cyclone cell, respectively. The electrochemical polarization data indicated that the Rh³⁺ ions were reduced to metallic Rh below ?0.1 V, and the limiting current density for rhodium deposition was observed at around ?0.3 V (vs. SCE) with a diffusion coefficient of 6.3 × 10^?6 cm² s^?1 using the Levich equation. The effects of the applied voltage and the initial concentration of rhodium were examined using the modified cyclone cell, and more than 91 % of the rhodium in solution was recovered within 2 h under the optimal conditions.     

Electrochemical behaviour of copper in aqueous solution containing potassium ethylxanthate

The electrochemical behaviour of copper in aqueous potassium ethylxanthate (KEX) is studied by using potentiodynamic techniques at different sweep rates, complemented with SEM and EDAX. In NaCl solutions a cuprous xanthate film is formed at low potentials, the initial stage of this reaction being the electroadsorption of KEX on copper competing with the adsorption of chloride ions and water. At low surface coverages for electroadsorbed KEX the electrodissolution of copper is partially inhibited as compared to plain NaCl solutions. As the KEX monolayer is completed, a tri-dimensional cuprous xanthate film grows in the electrode surface. On subsequent increase of the applied potential a complex anodic layer is formed leading to copper passivity. Passivity breakdown promoted by either chloride ions or electro-oxidation of the organic film can be observed when the potential exceeds a certain critical value.Facultad de Ciencias Exactas, Universidad Nacional de La Plata.     

Electrochemical studies of the pitting corrosion of tin in citric acid solution containing Cl

The electrochemical behavior of a tin electrode in citric acid solutions of different concentrations was studied by electrochemical techniques. The E/I curves showed that the anodic behavior of tin exhibits active/passive transition. Passivation is due to the formation of Sn(OH)₄ and/or SnO₂ film on the electrode surface. Addition of NaCl to citric acid solution, enhances the active dissolution of tin and tends to breakdown the passivity at a certain breakdown potential. Cyclic voltammetry and galvanostatic measurements allow the pitting potential (E_pit) and the repassivation potential (E_rp) to be determined. Potentiostatic measurements showed that the overall anodic processes can be described by three stages. The first stage corresponds to the nucleation and growth of a passive oxide layer. The second stages involve pit nucleation and growth and third stage involve repassivation. The impedance spectrum of pure Sn is found to consist of three intersecting capacitive semicircles at the high and medium frequencies with an inductive loop at low frequencies. The capacitive semicircles occurring at the high and medium frequency are due to the dielectric properties of surface oxide film and dissolution of underlying metal, respectively. The inductive loop at low frequencies results from Cl⁻ adsorption at the pitting region. By increasing the potential the pitting corrosion and the fractal dimension of surface due to pitting increase.     

Electrochemical study of the chromium electrode behaviour in borate buffer solution

The electrochemical behaviour of the chromium electrode in borate buffer solution (pH 9.3) was studied by cyclic voltammetry and electrochemical impedance spectroscopy. Chromium passivity was observed over a broad potential region, from –1.0 to 0.5 V vs SCE. The passivation process took place in two steps: formation of a chromium oxide monolayer and transition of chromium to a higher valence state. The anodic film exhibited the properties of a p-type semiconductor. Transpassive dissolution of chromium occurred at 0.5 V vs SCE, with two reaction intermediates present, Cr_Cr ^III and Cr_ad ⁴⁺.     

基于碳酸氢钠溶液的304与316L不锈钢电化学试验研究

采用电化学噪声、动电位极化和电容测量方法研究了304、316L不锈钢在不同NaHCO3溶液中的电化学行为及生成钝化膜的半导体性质。在NaHCO3溶液中,304、316L不锈钢存在明显相近的钝化区间;点蚀电位、零电流电位随着NaHCO3浓度的增大而减小。在0.5V电位形成钝化膜的Mott-Schottky曲线表明,304、316L不锈钢在NaHCO3溶液中生成的钝化膜为双层结构,具有相近的成膜特性。但随着NaHCO3溶液浓度变化所生成钝化膜的性质也不同,304不锈钢形成的表面膜稳定性稍好于316L。     

Electrochemical behaviour of some 3-methylthio-1,2-dithiolium cations in dimethylformamide solution

Substituted 3-methylthio-1,2-dithiolium cations were prepared by alkylation of the corresponding 1,2-dithiole-3-thiones. These compounds were easily reduced in DMF at a mercury electrode, following two one-electron waves. Electrolysis, carried out at a mercury pool electrode and followed by an alkylation or an acylation, provided the corresponding alkyl (or acyl) dithioesters and by-products. At a platinum or glassy carbon electrode the reduction was an irreversible process, which was dependent upon the cathode nature. Whatever the electrode, the reduction was a combination of two reactions, a two-electron reduction and a one-electron one involving a dimerization. The electrochemical behaviour of 3-methylthio-1,2-dithiolium cations exhibited many analogies with the cathodic behaviour of the corresponding 1,2-dithiole-3-thiones. Moreover, identical intermediates were implicated in the reduction of 3-methylthio-1,2-dithiolium cations and in the reductive alkylation of 1,2-dithiole-3-thiones.     

Electrochemical behaviour of copper/LDPE composites in the simulated uterine solution

Two metal/insulator composites, copper/low-density polyethylene (LDPE) microcomposites and copper/LDPE nanocomposites, were prepared in a uniform metal mass fraction. The corrosion characteristics of the two composites in the simulated uterine solution have been studied by cyclic voltammetry, potentiodynamic polarization measurement and electrochemical impedance spectroscopy. Results obtained during this study show that there are obvious differences on the corrosive rates and mechanisms between the two materials. The nanocomposites have stable corrosive reaction, hardly passivation, low corrosion rate and high transformation ratio of copper to soluble cupric ions compared with microcomposites, which indicate that the nanocomposites are perfect to be the novel material for intrauterine device. The corrosion behaviour of the microcomposites was controlled by both the processes of the pervasion of Cu²⁺ and the transfer of the charge, while that of the nanocomposites was only controlled by the transfer of the charge. This paper also compared the corrosion behaviours of the composites and bulk copper in the simulated uterine solution, there were more insoluble subproducts in the corrosion process of bulk copper than the composites. Further, the electrochemical method in this study is proved to be useful to characterize the corrosion behaviour of high electrical resistivity materials.     

Effect of some polymeric materials on the corrosion behaviour of tin in succinic acid solution

The anodic behaviour and corrosion of tin in various concentrations (0.05–0.7M) of succinic acid were studied using cyclic voltammetry. The potentiodynamic anodic polarization curves exhibit active/passive transition. The active dissolution of tin involves one anodic peak. The cathodic curve exhibits one cathodic peak corresponding to the reduction of the passive layer. The ratio of the anodic charge/cathodic charge is more than unity indicating that the passive layer is very thin and the dissolution products are mainly soluble species. Additions of some polyethylene glycols to the succinic acid solution decrease the anodic peak current and shift the peak potential in the negative direction. These changes depend on the concentration and molecular weight of the polyethylene glycol added. The effect of the inhibitors decreases in the following order: (PEG)₆₀₀₀ > (PEG)₄₀₀₀ > (PEG)₁₂₀₀. The inhibition efficiency decreases with increase in temperature, suggesting physical adsorption.     

Dissolution of tin in the presence of Cl− ions at pH 4

The anodic dissolution of tin, investigated in an acidic solution at pH 4 containing 0.1–1 M NaCl at 25°C, displays Tafel behavior as long as the electrode surface is bare (E–0.5 V vs SCE). The main characteristics can be derived from the proposed dissolution mechanism, i.e and . The mechanism involves two consecutive steps, each corresponding to the transfer of one electron, the second step being rate determining. ForE values anodic to –0.5V vs SCE partial coverage of the surface by a corrosion product is observed and the behavior is no longer Tafelian. From 0.4 to 1V vs SCE, a plateau current is observed on logi vsE curves and the anode is completely covdered by a corrosion product. Results obtained with a rotating disc electrode suggest that the rate-determining step of the dissolution process in this region of potential is the diffusion of an ionic species into the solution.     

Electrochemical behaviour of iron and copper in a culture solution for Spirulina platensis

Cyclic voltammograms of iron and copper electrodes were run in sodium hydroxide, carbonate–bicarbonate buffer and culture media for Spirulina platensis at 30°C. Potentiostatic steady state polarisation curves for both electrode surfaces in these electrolytes were performed in the presence and the absence of S. platensis at fixed temperature. Corrosion potential and corrosion current density values of iron and copper were obtained graphically from these curves. In all cases, the largest corrosion current density corresponded to the maximum biogenerated-oxygen concentrations, that is, illuminated culture media containing S. platensis. Corrosion potentials of iron electrodes shifted to positive values for increasing corrosion rates, whereas constant corrosion potentials were obtained for copper electrodes independently of the electrolyte.     

Endwise degradation of hydrocellulose in bicarbonate solution

Determinations of individual terminal carboxylic acid endgroups and terminal reducing sugar moieties together with analysis of spent liquor revealed that the same reactions occur during treatment of hydrocellulose with hot sodium bicarbonate as with sodium hydroxide solution. Some fragmentation reactions, of little importance in the presence of sodium hydroxide, are favored in bicarbonate medium while benzilic acid rearrangements are less favored. Hence, the formation of 2-dieoxyerythropentonic acid endgroups is more important. Among the soluble reaction products, 3,4-dideoxypentonic acid formed via 3-deoxypentulose and cyclic compounds formed via the same precursor are much more abundant in bicarbonate medium while 3-deoxy-2-hydroxymethylpentonic (isosaccharinic) acids are less abundant.     

Electrochemical behaviour of aluminium in sodiumpolysulphide melts at 330°C

An experimental set-up was developed which allows the investigation of electrodes in pure sodiumpolysulphide melts. It could be shown that aluminium forms a passivating layer of aluminiumsulphide at an anodic potential of about 1 V vs a sodium reference electrode. Below this value, aluminium is active. With a copper containing aluminium alloy the passivating potential is increased to about 1.2 V. Pitting corrosion was observed after operating the aluminium electrode at current densities of several hundred mA cm^?2. Reaction mechanisms which could explain the active, passive and transpassive regions observed, are discussed.