Fawzi H. Assaf

Cyclic voltammetric behaviour of – brass in alkaline media

Abstract The electrochemical behaviour of a brasses was studied in NaOH solutions using the cyclic voltammetric technique to establish the effect of such variables as alloy composition, reversal anodic potential, scan rate, NaOH concentration, and temperature. Compounds that formed on the surface during the anodic sweep were analysed using X-ray diffraction analysis (XRD). The data show that the voltammetric behaviour of – brass consists of two potential regions. The first or subcritical potential region was indicated by two anodic peaks designated A1 and A2. Within this potential region, selective dissolution of the less noble component, zinc, occurs (i.e. dezincification). The second potential region consists of three anodic peaks, designated A3, A4, and A5, where the two components of the alloy, namely copper and zinc, dissolve simultaneously. Alloying zinc with copper resulted in a decrease in the dissolution of zinc from the alloy. This behaviour could be explained on the basis that the dissolution is limited by the non-steady state diffusion of zinc atoms from the bulk of the alloy to the alloy solution interface, which implies that the rate determining step of dezincification is the diffusion of zinc atoms. The process of preferential dissolution of zinc leads to the formation of a layer rich in copper and depleted in zinc on the electrode surface.

Cyclic voltammetric behaviour of copper-nickel alloys in alkaline media

Abstract The electrochemical behaviour of two copper nickel alloys; cu-20 wt-%Ni and Cu-80 wt-%Ni, was studied in alkaline solution using the cyclic voltammetric technique. The voltammograms of the alloys were compared with those of the pure copper and pure nickel recorded under the same conditions. The influence of different variables such as switching potential Es, scan rate, NaOH concentration, solution temperature, and repetitive cycling was also studied. The forward sweep was characterised by the appearance of five anodic peaks: A1, A2, A3, A4, and A5, which are related to the formation of Ni(OH)2, Cu2O, Cu(OH)2, CuO, and Ni2O3, respectively. The activity of copper dissolution and, hence, the heights of the corresponding anodic peaks decreased as the nickel content in the alloy increased. X-ray diffraction analysis of the surface of the 80% nickel alloy after polarisation in the anodic direction confirmed the existence of only nickel corrosion compounds. Increasing the nickel content in the alloy retards the dissolution of copper via the formation of a very protective nickel hydroxide passive film. The addition of chloride ions, owing to their ease of adsorption, increases dissolution from the alloy. When the ratio of [Cl-]/[OH-] ex ceeds 1·5, the chloride ions initiate pitting attack. To examine the alloy surface for pit formation SEM was used.

Electrochemical behavior and corrosion resistance of electrodeposited nano-particles Zn-Co-Fe alloy

Purpose – The purpose of this study was to compare the electrodeposition behavior and corrosion resistance of ternary and binary alloys. Design/methodology/approach – Potentiodynamic polarization resistance measurement and anodic linear sweep voltammetry techniques were used for the corrosion study. The surface morphology and chemical composition of the deposits were examined using scanning electron microscopy and atomic absorption spectroscopy, respectively. The phase structure was characterized by X-ray diffraction analysis. Electrodeposition behavior was carried out using cyclic voltammetry and galvanostatic techniques. Findings – It was found that the obtained ternary alloy exhibited better corrosion resistance and a more-preferred surface appearance compared to the binary alloys that were electrodeposited under similar conditions. Research limitations/implications – The ternary alloy showed better anticorrosion properties compared to binary deposits that were electroplated successfully from the plati...

Electrodeposition Mechanism of Zn‒Ni‒Mn Alloy at Different Time Intervals

Mechanism of electrodeposition and stripping of Zn‒Ni‒Mn alloys deposited at different time intervals from aqueous sulfate media were investigated. The corrosion properties of coatings on steel substrate were studied by using different techniques. It might have been established that the attained Zn‒Ni‒Mn alloy exhibits a superior corrosion resistance at low plating times. Also, the ternary Zn‒Ni‒Mn alloy shows finer-grain size, more homogeneous, more uniformity, adherence, hardness, and compactness with respect to the alloy electrodeposited at high plating times. Alloys of the high content of Ni have been obtained at very low deposition times indicating that the initial layer of alloy plating is nickel, as the more noble metal than Zn or Mn, which deposits preferably during the first few seconds. As a result, the coatings obtained at low deposition times have more noble corrosion potentials than those obtained at high deposition times.

Fabrication of Zn-Ni-Mn alloy by electrodeposition and its characterization

Abstract Electrodeposition and stripping of Zn, Mn and Ni metals and their alloys were investigated in an aqueous sulfate solution. The effect of coating processes and its impact on the substrate were evaluated by investigating the prepared alloys with X-ray diffraction analysis, scanning electron microscopy and atomic absorption spectroscopy. The electrodeposition mechanism of the Zn-Ni-Mn alloy was found to be an anomalous type. The high corrosion resistance of the Zn-Ni-Mn alloy, as well as its preferable surface appearance, has been ascertained compared with the electrodeposited Zn-Ni alloy under homogeneous conditions. It was found that Mn can be codeposited with Ni or with Ni and Zn understudied conditions where it does not deposit in its pure form. During electrodeposition of manganese alone or manganese alloys, a dark brown deposit was formed on the counter platinum electrode surface as a result of oxidation to manganese dioxide.

Electrochemical behaviour of copper-nickel alloys in stagnant Na2CO3 solutions

Abstract The electrochemical behaviour of two copper-nickel alloys in solutions containing the carbonate ion has been investigated by cyclic voltammetric, potentiodynamic, and current/time transient techniques. Among the variables studied were alloy composition, stepwise increasing potential, scan rate, carbonate ion concentration and temperature. The composition of the compounds formed on the alloy surface during the anodic polarisation was characterised using X-ray diffraction analysis. The dissolution behaviour of the alloy consists of two potential regions separated by the critical potential Ecrit. The first potential region involves the selective dissolution of the more active constituent, nickel, and the appearance of one anodic peak A1 as a result of the formation of Ni(OH)2on the alloy surface. The second potential region relates to the simultaneous dissolution of copper and nickel. This region was characterised by the appearance of four anodic peaks A2, A3, A4, and A5, which are related to the formation of Cu2O, {CuO and Cu(OH)2}, CuCO3-Cu(OH)2 composite, and NiOOH, respectively. Potentiostatic current/time transients showed that the formation of Ni(OH)2, Cu2O, CuO, Cu(OH)2, CuCO3-Cu(OH)2 and NiOOH layers involves a nucleation and growth mechanism under diffusion control.