Abdel-Rahman El-Sayed

Role of Ni content in improvement of corrosion resistance of Zn−Ni alloy in 3.5% NaCl solution. Part I: Polarization and impedance studies

Abstract Zn plays an important role in the protection of iron and steel from corrosion in sea water, and the alloying of Zn and Ni can improve its corrosion resistance. The corrosion behavior of Zn–Ni alloys in synthetic sea water (3.5% NaCl, mass fraction) was studied using Tafel plot and electrochemical impedance spectroscopy (EIS) techniques. The corrosion resistance of the investigated alloys with various Ni contents (0.5%–10%, mass fraction) was compared with that of Zn. The results show that the corrosion resistance of Zn–Ni alloys (except 0.5% Ni) is superior to that of Zn. The 10% Ni gives the highest corrosion resistance due to the formation of γ -Zn 3 Ni with γ -ZnNi phases in the alloy. In the case of alloy I (0.5% Ni), it exhibits a higher corrosion rate (less corrosion resistance) than Zn.

Effect of phosphoric acid concentration on conductivity of anodic passive film formed on surface of lead–indium alloy

The addition of phosphoric acid into sulfuric acid solution is mentioned to be helpful in the reduction of sulfation after deep discharge of lead-acid battery. The anodic behavior of Pb and Pb–In alloys was studied in pure phosphoric acid and sulfuric acid containing various concentrations of phosphoric. The electrochemical measurements were performed using potentiodynamic, potentiostatic and cyclic voltammetric techniques. The composition and morphology of passive layer formed on the surfaces of Pb and Pb–In alloys were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy analysis (EDX) and scanning electron microscopy (SEM). The potentiodynamic study shows that the passive current density increases with increasing the indium content in the alloy in the examined solutions. The addition of 0.1 mol/L H3PO4 into the electrolyte is more effective to decrease the thickness of passive film on the surface of alloys containing higher indium content (10% and 15%). The XRD, EDX and SEM data reveal that the formation of PbSO4 and PbO on the surface decreases with increasing the indium level in the alloy and is completely prevented at higher indium content (15%) in mixed acid.

Role of nickel alloying on anodic dissolution behavior of zinc in 3.5% NaCl solution. Part II: Potentiodynamic, potentiostatic and galvanostatic studies

Abstract Zinc is common metal used for steel protection from corrosion. The addition of further element, such as Ni, can modify the corrosion rate and maintain sacrificial protection. The anodic dissolution behavior of Zn, Ni and Zn–Ni alloys with different Ni contents (from 0.5% to 10%, mass fraction) in 3.5% NaCl solution was investigated using potentiodynamic, potentiostatic and galvanostatic techniques. The composition and microstructure of the corrosion layer on Zn, Ni and Zn–Ni alloys were characterized by energy-dispersive X-ray spectroscopy analysis (EDX) and scanning electron microscopy (SEM). The galvanostatic curves show that the anodic behavior of all investigated electrodes exhibits active/passive transition and the tendency of the alloys to passivity decreases with the increase in Ni content, except for 99.5Zn–0.5Ni alloy. While the potentiodynamic curves exhibit active passive transition only for pure Zn. Surface analysis reveals the presence of oxides, chlorides and metal hydroxide chloride in corrosion products, and very small cracks are observed for 90Zn–10Ni alloy compared with that of Zn.

Effect of nickel content on the anodic dissolution and passivation of zinc–nickel alloys in alkaline solutions by potentiodynamic and potentiostatic techniques

The effect of systematic increase of Ni on the anodic dissolution and passivation of Zn–Ni alloys in various concentrations of KOH solution (0.1–1 M) was investigated. The anodic dissolution and passivation behaviour for each pure Zn and Ni in the same studied solutions was also investigated, and the obtained data were compared. Potentiodynamic and potentiostatic methods were used, and the corrosion layer formed on each electrode surface was characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results of the anodic potentiodynamic measurements exhibited that the polarization curves showed active/passive transition in the case of Ni and active/pseudopassive in the case of both Zn and its alloys. The results showed that the increase in Ni content increases the activation energy (Ea) and decreases the dissolution rate of the alloys in KOH solution, and the lowest dissolution rate was obtained at 10% Ni. The results of both potentiodynamic and potentiostatic measurements exhibit sudden increase in current density which is observed at certain positive potential (+ 0.42 V vs. SCE) in the case of the investigated alloys. This indicates that the addition of Ni to Zn promotes the electrochemical reaction (in the passive region). However, the passivation potential shifted to more positive direction with the increase in Ni content in the alloy.

Role of Indium Alloying with Lead as a Means to Reduce the Passivation Phenomena in Lead/Acid Batteries

The influence of indium content on the anodic behaviour of Pb-In alloys in 4 M H2SO4 solution is investigated by potentiodynamic, potentiostatic, chronopotentiometric, and cyclic voltammetric techniques. The composition and microstructure of the corrosion layer on Pb-In alloys are characterized by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy analysis (EDX), and scanning electron microscopy (SEM). The potentiodynamic and chronopotentiometric curves show that the anodic behavior of all investigated electrodes exhibits active/passive transition. The active dissolution (except for alloy I) and passive currents increase with increasing both In content and temperature. This indicates that the conductivity of the anodic film on Pb-In alloy is enhanced. This study exhibits that indium catalyses the oxidation of Pb (II) to Pb (IV) and facilitates the formation of a more highly conductive corrosion layer on lead. Alloy I (0.5% In) exhibits that the corrosion rate is lower, while the passive current is higher than that of Pb. XRD, EDX, and SEM results reveal that the formation of both PbSO4 and PbO on the surface decreases gradually with increasing In level in the alloy and completely disappear at higher In content (15% In). Therefore, recharge of the battery will be improved due to indium addition to Pb.