Waheed A. Badawy

Electrochemical behaviour and corrosion inhibition of Al, Al-6061 and Al-Cu in neutral aqueous solutions

Abstract The electrochemical behaviour of Al and two of its widely used alloys, Al-6061 and Al–Cu, was investigated in neutral solutions at pH 7. The corrosion inhibition of these materials was studied in neutral solutions using sulphates, molybdates and dichromates as passivators. The effectiveness of dichromates as passivators for Al and its alloys in these solutions was discussed. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to explain the role of the passivating anion in the corrosion inhibition process. It was found that Cr and Mo are incorporated in the barrier film on Al or its alloys after immersion in neutral solutions containing these anions. Sulphate ions are adsorbed on the barrier film surface or present in the film in a very low concentration compared to dichromates and molybdates. The inhibition efficiency increases as the concentration of the passivating anion in the solution increases. Scanning electron microscopy (SEM) has shown that the Al–Cu alloy has remarkable flawed regions which are due to the presence of Cu on the alloy surface, as was confirmed by XPS. The flawed regions completely disappear after immersion in solutions containing dichromates and partially disappear after immersion in solutions containing molybdates.

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.

Electrochemical and XPS investigations of cobalt in KOH solutions

The electrochemical behaviour of cobalt in KOH solutions of different concentrations was studied. The effects of applied potential, temperature and the presence of aggressive Cl− ions were investigated. Different electrochemical methods such as open-circuit potential measurements, polarisation techniques and electrochemical impedance spectroscopy (EIS) were used. The electrochemical behaviour of cobalt in naturally aerated KOH solutions is characterized by three different regions according to the alkali concentration. Corrosion behaviour was observed at high concentrations (0.3–1.0 M); passivation at lower concentrations (0.01–0.05 M), and at intermediate concentrations (0.1–0.2 M) corrosion followed by passivation was recorded. The corrosion parameters (icorr, Ecorr, and Rcorr) under various conditions were calculated. Equivalent-circuit models for the electrode–electrolyte interface under different conditions were proposed. The experimental impedance data were fitted to theoretical data according to the proposed models. The relevance of the proposed models to the corrosion–passivation phenomena occurring at the electrode–solution interface was discussed. The electrochemical experimental results and discussions were supported by surface analytical techniques.

Optical and Photovoltaic Characteristics of In‐Modified SnO2 Thin Films

thin films were prepared conveniently and reproducibly using the spray‐pyrolysis technique. This method enables the incorporation of foreign materials like indium in the matrix. The effect of In incorporation on the conductivity and optical properties of the prepared films was studied. The presence of In in the bulk of the film increases its conductivity and does not affect the optical properties to a significant extent. The energy gap of the prepared films was calculated for different layer thickness of pure and In‐incorporated films. Heterojunction solar cells were prepared and investigated using a standard potentiostatic technique. The power characteristics of the prepared photovoltaic cells were analyzed and compared with those of pure solar cells.

A review on solar cells from Si-single crystals to porous materials and quantum dots.

Graphical abstract

The Photocurrent‐Voltage Characteristics of the Heterojunction Combination n ‐ Si / SnO2 / Redox ‐ Electrolyte

A model for Schottky barrier-like heterojunction photoelectrodes is presented. This model allows the calculation of the current-voltage curves for such electrodes under different conditions of illumination and electrochemical charge transfer. SnO2-coated n-type Si electrodes in contact with the redox systems K3/K4 Fe (CN)6 and Cl2Cl(-) show experimental photocurrent-voltage curves with the behavior predicted by the model. The effect of the charge transfer overvoltage and the expected current limitation due to photon control and/or redox ion diffusion are demonstrated. The feasibility of solar energy conversion through photoelectrolysis, by means of cells based on heterojunction photoelectrodes, is discussed.

Electrochemical behaviour of vanadium in aqueous solutions of different pH

Abstract he electrochemical behaviour of vanadium in aqueous solutions of pH covering the range 1–13 in oxygen saturated, oxygen free and naturally aerated solutions was investigated. The behaviour of the vanadium electrode in alkaline solutions ( pH > 8) is different from that in acid or neutral solutions (pH 1–8). The equilibrium electrode potential is a linear function of the solution pH. The slope of the linear relation changes from −0.039 V/decade for solution of pH ≤ 8 to −0.058 V/decade for solutions of pH > 8. EIS investigations have shown that the metal undergoes active dissolution in aqueous solutions. In solutions of pH > 8 the corrosion behaviour of vanadium can be simulated to a Randles equivalent circuit model. In oxygen saturated solutions the electrode surface is covered with an oxide film. The interaction of this film with the H + and OH − in solutions with different pH was discussed. Polarization measurements have shown that the rate of corrosion in acid solutions is not affected by the prevailing gas. In alkaline solutions, removal of oxygen or air from the solution leads to a decrease in the corrosion rate of the metal.

Impedance studies of corrosion resistance of aluminium in chloride media

Abstract The electrochemical behaviour of aluminium in chloride solutions has been studied. Open-circuit impedance measurements reveal that in both acidic and neutral media the dissolution of the oxide formed on aluminium is governed by an empirical relation of the form C m -1 = a − Bt 1 2 where a and B are constants. The rate of the oxide film dissolution in the chloride-containing solutions is found to be markedly lower than that in other halide media, especially in fluoride solutions. The behaviour of the oxide is determined by the pH of the dissolution medium rather than its chloride ion content. Complex plane analysis of the anodic oxide film formed on aluminium indicates that the corrosion resistance is very high in neutral chloride solutions in comparison with acid solutions containing the same amount of chloride ions. Both the charge transfer resistance θ and the Warburg impedance caused by diffusional mass transfer attain markedly higher values in the neutral media which reflect the high passivation properties of the oxide film. It is suggested that many constructions could be coated with aluminium oxide films to protect them from corrosion, especially in marine media.

“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...