M. S. El-Basiouny

Kinetic studies of the dissolution behaviour of anodic oxide films on Zr in H2SO4

Abstract The dissolution behaviour of anodic oxide films on Zr in H2SO4 was investigated as a function of acid concentration, formation voltage and temperature, using the results of impedance measurements. In general, the oxide dissolution was found to follow the empirical relation Cm−1=α−βt1/2. The dissolution process suffered a change in its rate as indicated by the change in the value of β. This behaviour indicated that the oxide was of a duplex nature in which the outer layer undergoes dissolution more freely than the inner one. The dissolution process was found to follow a zero-order mechanism.

A mechanism for the corrodability of hafnium and the anodic oxide film thereon in HCl solutions

Abstract A study is made to account for the corrodability of each of the naturally developed and anodically formed oxide films on hafnium in HCl solutions. The behaviour of these oxide films was investigated by capacitance and potential measurements. The naturally developed oxide film grows spontaneously according to a direct logarithmic law. In diluted HCl (

Corrosion Inhibition of Zinc in HCl Solution by Several Pyrazole Derivatives

Abstract The corrosion inhibition of zinc in HCl solutions by several pyrazole derivatives—namely, 3(5) amino, 5(3) phenylpyrazole; 3(5) amino, 5(3) [4′—methylphenyl] pyrazole; 3(5) amino, 5(3) [4′...

Kinetic studies on the dissolution of the anodic oxide film on titanium in phosphoric acid solutions

Capacitance and potential measurements vs time show a two stage dissolution process in H3PO4 for the anodic oxide films formed galvanostatically on titanium. The dissolution mechanism of this duplex nature oxide film follows a zero order rate equation: the rate of film thinning, −d(1/Cm)/dt is independent of film thickness, which corresponds to 1/Cm. The oxide film formed at 15 V, which has a thickness larger than the others, is the most stable oxide film in H3PO4 solution and has the highest electrochemical insulating properties. The average rate constant for dissolution of the entire oxide film K (cm2 μF−1 min−1), is found to increase with increasing acid concentration. The effect of anion type of the formation medium on the value of K is also studied. In 0.1 N solutions of different inorganic acids K increases as the formation rate increases, and the order is H2SO4 (low) < HCl < HNO3 < HCLO4 < H3PO4 (high). The results indicate that the oxide film formed in H2SO4 is the most protective one with the lowest structural disorder.

Nature of the Corrosion Reaction at the Anodic Oxide Film on Titanium in HCl Solutions

Abstract The corrosion of the anodically formed oxide film on titanium has been studied in HCl solutions after the flow of the forming current ceases. Reciprocal capacitance, resistance, and the op...

Influence of Formation and Dissolution Environment on Dissolution Kinetics of Anodic Oxide Films on Antimony

Abstract The currentless dissolution behavior of the anodic oxide films formed on antimony in 0.1N H3PO4 was studied as a function of formation voltages and formation current densities. The dissolution rate of the oxide film was examined as a function of the electrolyte composition of the formation medium. Kinetics curves for the dissolution of the oxide film in most media show a two stage process that seems to be related to the dual nature of the oxide film. The validity of the first order mechanism for the dissolution process is illustrated with the kinetics curves of dissolution following the equation: This equation is used for each of the two stages of the dissolution process, with two different values of K. The rate of the dissolution process was found to be a function of electrolyte composition of the formation medium, while no effect was observed for the initial current density of the oxide formation. The role of anion type on the dissolution rate was more pronounced in acidic solutions than in neu...

Influence of Chloride Concentration on Surface Oxide Films on Niobium

Abstract A study by potential measurements of a niobium electrode in chloride solutions shows that the corrosion potential is a function of Cl− ion concentration and decreases with the increase of ...

Profiles of defects in anodic oxide films deduced from dissolution studies

Abstract From studies of the chemical dissolution of anodic oxide films on several valve metals, the relative concentration profiles of atomic defects across the films have been deduced. Oxides that are characterized by low energies of defect formation contain relatively high concentrations of defects, this concentration increasing as the oxide grows. Films that are characterized by intermediate energies of defect formation contain lower concentrations of defects, which decrease as the oxide grows, while those oxides that are characterized by high energies of defect formation contain low concentrations of defects, which decrease only insignificantly as the oxide grows. Respective examples of each type are tungsten oxide, titanium oxide, and hafnium oxide.

Zinc Passivation in Oxalate Solution

Abstract The passivation behavior of zinc in oxalic/oxalate solutions was studied using impedance and polarization measurements. A passive layer containing zinc oxalate is formed in these oxalate m...

Impedance Properties of the Passive Layer on a Titanium Electrode in a Phosphoric Acid Electrolyte

Abstract The change of the impedance components during passivation of titanium in H3PO4 solutions was investigated at frequencies ranging from 200 to 15,000 Hertz (Hz). Variation in the values of the resistance and capacitance components of the impedance for the system of passive Ti/electrolyte solution were recorded by using Wiens bridge and assuming a series combination between resistance and capacitance. Analyses of the results obtained from the dependence of Cs and Rs on frequency reveal deviation from (1) Youngs theory and from (2) the modification presented by Bardina and Lukovtsev. This is explained by the assumption that the layer on Ti does not represent an ideal dielectric, but is electrically unhomogeneous.