Khaled M. Ismail

Characterization of the Passive State on Zinc

Despite intensive investigations, the nature of the passive state is one of the most complex and unresolved subjects in the electrochemistry of zinc in alkaline solutions. In this paper, we explore the electrochemistry of the passive state on zinc in 0.1 M sodium borate/1 M sodium hydroxide solution of pH 10.5. During the course of passivation, several characteristic features in the anodic region are observed, including a wide passive range extending over >2 V and a secondary passivation phenomenon that occurs at high anodic potentials. The steady-state current in the passive state is found to be independent of the applied voltage, which is consistent with the barrier layer being an interstitial zinc conductor or an oxygen vacancy conductor (or both) with interstitial zinc being the most likely defect. This model is also consistent with the well-known n-type character of the passive film on zinc.

Effects of Zn and Pb as alloying elements on the electrochemical behaviour of brass in borate solutions

The electrochemical behaviour of brasses with various Zn content (5.5–38) and brass (Cu–38Zn) with different Pb content (1.3–3.3) in borate solution, pH 9.0, was investigated. The effects of applied potential and the presence of aggressive Cl− ions were also studied. Different electrochemical methods such as open-circuit potential measurements, polarization techniques and electrochemical impedence spectroscopy (EIS) were used. Increase in zinc content decreases the corrosion rate of brass in borate solution exponentially. Long immersion of leaded brasses and alloys with different Zn content improves their stability due to the formation of a passive film. The passive film formation under open-circuit and potentiostatic conditions proceeds via dissolution–precipitation mechanism. The addition of a low concentration of Cl− ion (0.01 M) to the borate solution increases the corrosion rate of Cu–38Zn due to dezincification. Increase in Cl− ion concentration (0.01–0.2 M) decreases the corrosion rate of the brass exponentially due to formation of insoluble CuCl. For Cl− ion concentrations >0.2 M the corrosion rate of the brass increases again due to the formation of the soluble CuCl2− complex.

“Stability of Sputter-Deposited Amorphous Mn-Ta Alloys in Chloride-Free and Chloride-Containing H2SO4 Solutions.”

Amorphous alloys were prepared in a wide composition range by the addition of tantalum to manganese by the sputter deposition method. The effect of alloying tantalum on the corrosion behavior and the stability of sputter-deposited amorphous Mn-Ta alloys was studied. Different techniques such as weight-loss measurements, electrochemical techniques, and X-ray photoelectron spectroscopy (XPS) analysis were used. The addition of Ta remarkably reduces the rate of dissolution of the alloy and Ta passivates spontaneously. No signs of pitting corrosion or transpassive dissolution of Mn were observed. The anodic current density decreases significantly with increasing the tantalum content. XPS studies show a preferential oxidation of Ta in the air-formed (native) oxide. The preferential oxidation was remarkable after immersion in 1 M H 2 SO 4 solution for 30 min. The thickness of the passive film formed on the sputter-deposited Mn-30Ta alloy increases linearly with the applied potential as that observed in valve metals. The formed passive film consists mainly of Ta 2 O 5 . At potentials higher than +0.7 V (standard calomel electrode) high oxidation states of Mn were found to he incorporated in the passive film.

Effect of Nickel Content on the Corrosion and Passivation of Copper-Nickel Alloys in Sodium Sulfate Solutions

Abstract The effect of Ni content on the corrosion and passivation behaviors of copper-nickel alloys with different Cu to Ni ratios was investigated in neutral sulfate solutions. The influence of working conditions (e.g., immersion time, sulfate ions concentration, and temperature) on the electrochemical behavior of the different alloys was also studied. In this respect, conventional electrochemical methods like open-circuit potential (OCP) measurements, polarization techniques, and electrochemical impedance spectroscopy (EIS) were used. It was found that the initial corrosion resistance is relatively low for alloys with high nickel content. An increase in the nickel content and long immersion time in the neutral sulfate solution increases the corrosion resistance of the alloy and improves its stability. The stability of the alloy was considered to be due to the formation of a stable passive film on its surface. The impedance data were fitted to theoretical data obtained according to an equivalent circuit...

Electrochemical preparation and characterization of poly(1-amino-9,10-anthraquinone) films

Abstract Poly(1-amino-9,10-anthraquinone), PAAQ, films were prepared by electrochemical oxidation of the monomer, AAQ, in acetonitrile using LiClO 4 as supporting electrolyte. The influence of scan repetition, scan rate and monomer concentration on the formation of polymer film was studied. The electrochemical behavior of the formed polymer films was investigated in both non-aqueous and aqueous media. The prepared films were found to be more stable in organic solvents than in aqueous solutions. The investigated organic solvents are methanol, ethanol, acetone, carbon tetrachloride, benzene, and chloroform. The polymer film shows electrochemical response in both non-aqueous and aqueous media. In non-aqueous solutions it has a wide potential range of electroactivity (from −1.5 to +1.3 V). In aqueous media the polymer film shows electrochemical response in the potential range between −0.3 and +1.3 V only. The presence of quinone units suggests potential applications in diverse areas such as electrocatalytic processes and lithium ion batteries.

Influence of Zinc and Lead on Brass Corrosion in Dilute Sulfuric Acid

Abstract The corrosion behavior of Cu-Zn alloys in sulfuric acid (H2SO4) solutions was investigated using open-circuit potential measurements, potentiodynamic techniques, and electrochemical impeda...

Electrochemical and XPS studies of sputter-deposited ternary Mn-Ta-Cr alloys in chloride-free and chloride-containing sulphuric acid solutions

Amorphous manganese-rich (67/80 at.%) Mn/Ta/Cr alloy films were prepared by DC magnetron sputtering method. The corrosion behavior and stability of the Mn/Ta/Cr alloy films were examined in chloride-free and -containing 1 M H2SO4. AC and DC electrochemical techniques in combination with XPS analysis were used. Mn/Ta/Cr alloys exhibited very high corrosion resistance and stability up to transpassive dissolution region of chromium. The high corrosion resistance of Mn/Ta/Cr sputtered films is based on the formation of double oxyhydroxide passive film composed mainly of chromium and tantalum. The partial substitution of tantalum with chromium improves the corrosion resistance of the sputter-deposited alloys via accelerating the preferential dissolution of manganese and stabilizing alloy/passive film interface. A change in the passive film structure was observed when the alloys were anodically polarized at potentials higher than 0.6 V (SCE). # 2002 Elsevier Science Ltd. All rights reserved.

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.

Electropolymerization of Aminoanthraquinone from H2SO4/Acetonitrile Mixed Solvent – Polymer Film Characterization and its Use as Analytical Sensor

Abstract Polyaminoanthraquinone, PAAQ, films were prepared potentiodynamically and potentiostatically from acetonitrile/sulfuric acid mixed solvent. Series of investigations have been carried out in which the mixed solvent ratio, type of substrate, electrochemical technique, potential scan range, scan rate and number of cycles were investigated in order to optimize the electropolymerization process. The potentiodynamic technique using glassy carbon, GC, substrates provides more stable films and useful information about the electropolymerization process from the mixed solvent. The suitable monomer concentration was 5.0 mM of 1-amino-9, 10-anthraquinone dissolved in 4.0 M H2SO4/ACN mixed solvent with a volume ratio 7:3. The most suitable potential scan range was from − 0.5 to + 1.4 V at a scan rate of 100 mV s–1. The effect of the scan repetition i. e. the thickness of the prepared polymer films on the electroanalytical performance of the modified electrode was investigated and discussed. The kinetics of electropolymerization process was investigated and the reaction was found to be first order with respect to the monomer concentration and of negative order with respect to sulfuric acid. The formed films were used successfully as analytical sensors for ascorbic acid, catechol, Ce III ions, dopamine, epinephrine, p-aminophenol and pyrogallol. The determination is based on the construction of a calibration curve for each analyte using the values of the oxidation peak currents in the cyclic voltammogram obtained by the PAAQ modified electrode in each case. The data were compared with the data obtained previously by the same films prepared in non-aqueous and aqueous media. The significance of the analytical performance of the formed films with respect to the state-of-the-art was investigated and discussed. The use of the mixed solvent, beside its effectiveness as analytical sensor, has limited the effect of hazardous organic solvent.