No abstract

No abstract

As a first step towards studying pitting corrosion of Zn in aerated neutral 1.0 M sodium thiosulphate solution (pH 6.6), we have reported the results of cyclic polarization measurements on the passivity and passivity breakdown of Zn in this solution. The recorded voltammograms involved two oxidation processes labeled as AI and AII, and two reduction processes labeled as CII and CI on the forward (anodic) and reverse (cathodic) scans, respectively. The cathodic peak CII was attributed to the reduction of the pitting corrosion products (process AII). On the other hand, the cathodic process CI was related to the reduction of Zn2+ species formed during the course of the forward scan (process AI and the subsequent formation of the passive region), and the reduction of the adsorbed S2O3 2− anions to S2− and SO3 2−. The reduction products of S2O3 2−, namely S2− and SO3 2− anions, were detected in solution as a function of starting potential and time of holding the electrode at a cathodic potential of −2.0 V (Ag/AgCl). These anions were found to cooperate with the aggressive S2O3 2− anion itself in passivity breakdown and initiation of pitting corrosion. The effect of solution temperature (15–70 ºC) on the cyclic polarization behaviour of Zn was also studied, and metastable and stable pitting events observed at high temperatures were discussed. The morphology of pitting was also studied by ex situ scanning electron microscopy (SEM) as a function of applied anodic potential, bulk concentration of S2O3 2− and solution temperature. Cross-sectional view of pits revealed the formation of irregular deep and shallow pits. The aspect ratios (the ratio of pit width to pit depth) of the growing pits were estimated as a function of potential, electrolyte concentration and solution temperature. The aspect ratio of the growing pits was found to be potential and concentration independent, while it increased with temperature.

The inhibiting behavior of polysorbate 80 on 6061 aluminum alloy corrosion was evaluated in 1.0 M Na

Pure cerium sulfate was prepared from economic natural resources using Egyptian monazite rare earth cake. About 90% of the former was extracted by tri-butyl phosphate in kerosene at the optimum conditions: 15% solvent concentration, equilibrium pH of 1.7, equilibrium time 7 min and O/A ratio of 1/1. The aim of the present work was studying the corrosion inhibition properties of cerium sulfate towards aluminum alloy AA6061 in two solutions; 1.0 M disodium hydrogen orthophosphate and 3.5 % sodium chloride (simulation of sea water). The corrosion inhibition was evaluated using electrochemical techniques under different experimental conditions. The results showed that, in the presence of cerium sulfate, the AA6061 surface is well protected due to formation of passive film composed of Ce2O3/Ce(OH)3 which precipitated on the electrode surface.