S. A. Salih

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′...

Electrotransformations at some lead-antimony alloy/ sulphuric acid interfaces

The electrochemical behaviour of Pb-(0–8%) Sb alloys in H2SO4 solutions was studied using impedance and cyclic galvanostatic measurements. The experimental results indicated that the alloy containing 2.5% Sb is critical in many respects. The potential arrest corresponding to the formation of the sulphate layer was absent for the alloy containing 2.5% Sb while it was present for the other alloys. The efficiency of the charging was found to increase with decreasing anodizing current. The electrochemical transformations during cyclic galvanostatic polarization and self-discharge are discussed.

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...

Electrochemical behaviour of surface zirconium oxides in the presence of some electroactive species

The open circuit potential, capacitance and resistance techniques were used to investigate the behaviour of two types of surface zirconium oxides in pure 0.5 N H2SO4 and in the presence of additives of K2CrO4, KI, FeSO4 and HCOOH. The air-formed preimmersion oxide film grows in all solutions following a logarithmic rate law. Depending on the nature of the additive the oxide grows directly by oxidation of the surface by the oxidizing additive (K2CrO4) or indirectly by mediating the oxidation by atmospheric oxygen in the presence of reducing additives. Anodically formed zirconium oxide films dissolve in all solutions. The results of impedance measurements indicate that adsorption of HCOOH activates the oxide surface owing, possibly, to its hydrophilic nature while iodide adsorption diminishes the reactivity of active sites (probably oxygen vacanies) where the dissolution process is initiated.

Anodic Dissolution of Antimony in Phosphate Solutions

Abstract The anodic dissolution of antimony in alkaline phosphate solutions has been investigated by using a galvanostatic technique. The rate of anodic dissolution was found to depend on pH and showed a Tafel slope of 195 mV/decade. The reaction order with respect to OH− was found to approximately equal to one. The dissolution rate of antimony at constant pH value is increased with solution stirring and dissolution temperature. The activation energy ΔH* for the anodic dissolution process was found to be 20.3 kcal ·mol−1·°K− 1. The anion nature affected the anodic dissolution at pH 7.0, while at pH 12 the same anions have no effect. The dissolution rate of antimony is increased with increasing the phosphate ion concentration up to 1.0 N; higher concentration than this value decreased the dissolution.

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...

Effect of Phosphoric Acid on the Electronic and Diffusion Properties of the Anodic Passive Layer Formed on Pb-1.7%Sb Grid of Lead-acid Batteries

Potentiostatic oxidation of Pb-1.7%Sb alloy used in the manufacture of grids of lead-acid batteries over the potential range from -1.0V to 2.3V in 5M in the absence and the presence of 0.4M and the self-discharge characteristics of the oxide layer formed is studied by electrochemical impedance spectroscopy (EIS). Depending on the potential value, sharp variations in resistance and capacitance of the alloy are recorded during the oxidation and they can be used for identification of the various substances involved in passive layer. Addition of is found to deteriorate the insulating properties of the passive layer by the retardation of the formation of . completely inhibits the current and impedance fluctuations recorded in -free solutions in the potential range 0.5 V-1.7 V. These fluctuations are attributed to the occurrence of competitive redox processes that involve the formation of , , PbO and and the repeated formation and breakdown of the passive layer. Self-discharge experiments indicate that the amount of formed in the presence of is lesser than in the -free solutions. The start of transformation of into is greatly shortened. facilitates the diffusion process of soluble species through the passive layer ( and basic ) but impedes the diffusion process through .

Effect of silicon alloying addition on the corrosion behaviour of aluminium in some aqueous media

The corrosion behaviour of three Al–Si alloys was studied after galvanostatic passivation in 0.1 M sodium tartrate, sulfate and borate solutions using EIS techniques. The degree of passivation depends on the anion type, the degree of polarization and the alloy composition. It was also found that increase in pH led to a decrease in polarization resistance Rp. The effect of formation voltage, Vf, on the growth and dissolution kinetics of the oxide grown on the alloys was studied. The polarization resistance value increases as Vf increases up to a certain value; above this the Rp value decreases. This critical Vf depends on the alloy composition and the test solution. The kinetics of oxide layer dissolution in the absence and presence of Cl− ions was also studied. Increase in immersion time leads to a more severe attack by Cl− ions as shown by the decrease in the value of Rp. At low Cl− ion concentration the value of Rp is higher than that in chloride ion free sulfate solutions, because the rate of passive film repair is much higher than that of barrier layer dissolution. However, at high Cl− ion concentration penetration of Cl− through defects in the barrier layer leads to formation of an oxyhalide layer.

Electrochemical behaviour of some PbSb alloys in sulphuric acid solutions I: Effect of chloride ions

Abstract The electrochemical behaviour of Pb−(0−8.0)%Sb alloys in 0.5 M H2SO4 solutions containing chloride ions was investigated using impedance and polarization measurements. The presence of chloride ions was found to retard, to varying extents, the selective leaching of the alloys containing 4.65%Sb, while it increased the insulating properties of the anodic layer on the alloys containing less antimony. This is attributed to the precipitation of PbCl2 as well as PbSO4 and Sb2O3 on the alloys. The presence of chloride ions also affects the cyclic galvanostatic polarization curves in many respects, especially the appearance of a step corresponding to the formation of Sb2O3.

Evaluation of Tolerance of Some Elemental Impurities on Performance of Pb-Ca-Sn Positive Pole Grids of Lead-Acid Batteries

ABSTRACT: The electrochemical performance of positive pole grids of lead-acid batteries made of Pb-0.08%Ca-1.1%Sn alloys without and with 0.1 wt% of each of Cu, As or Sb and with 0.1 wt% of Cu, As andSb combined was investigated by electrochemical methods in 4.0 M H 2 SO 4 . The corrodibility ofalloys under open-circuit conditions and constant current charging of the positive pole, the positivepole gassing and the self-discharge of the charged positive pole were studied. All impurities (Cu,As, Sb) were found to decrease the corrosion resistance, R corr after 1/2 hour corrosion, but after 24hours an improvement in R corr was recorded for Sb containing alloy and the alloy with the threeimpurities combined. While an individual impurity was found to enhance oxygen evolution reac-tion, the impurities combined significantly inhibition this reaction and the related water loss prob-lem was improved. Impedance results were found helpful in identification of the species involvedin the charging/discharging and the self-discharge of the positive pole. Impurities individually orcombined were found to increase the self-discharge during polarization (33-68%), where Sb con-taining alloy was the worst and impurities combined alloy was the least. The corrosion of the pos-itive pole grid in the constant current charging was found to increase in the presence of impuritiesby 5-10%. Under open-circuit, the self-discharge of the charged positive grids was found to increasesignificantly (92-212%) in the presence of impurities, with Sb-containing alloy was the worst. Theimportant result of the study is that the harmful effect of the studied impurities combined was notadditive but sometimes lesser than any individual impurity. Keywords: Positive pole; Pb-Ca-Sn alloys; Lead-acid batteries; recycled Lead