Experiments using stainless steel artificial pit (leadin-pencil) electrodes in ferric chloride and lithium chloride solutions were performed in order to determine the effects of key environmental factors such as chloride concentration and pH of the bulk solution on the central parameters utilized to characterize the pitting phenomenon-the repassivation potential E rp and the pit stability product under a salt film (i· x) saltfilm . For all the stainless steel alloys studied, a relative independence of the E rp to the pit depth was observed once sufficient anodic charge had been passed. The pit stability product under a salt film was seen to be largely insensitive to the pH of the bulk solution. E rp , on the other hand, was fairly independent of bulk pH only at the lower chloride concentrations of both lithium chloride and ferric chloride solutions. The two parameters were affected differently by variation in the chloride concentration of the bulk solutions. Increasing the chloride concentration resulted in a decrease in the value of (i·x) saltfilm for all alloys in both solutions. In ferric chloride, the value of E rp increased with increasing chloride concentration for Custom 465 and the austenitic steels, whereas it decreased across the same range for 17-4 pH. These trends were explained qualitatively using solution conductivity and alloying composition arguments. Finally, the results obtained from this study allowed for a rationalization of the phenomenology, enabling a method of measurement of the diffusion coefficient and the concentration at saturation of the Bstainless steel cation^within the pit, both of which agreed well with values obtained from the existing literature.

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This paper presents the experimental evaluation of a recently developed model for predicting the maximum pit size possible on a stainless steel surface under a certain set of atmospheric conditions. Prediction of the maximum pit size possible on 304L and 316L was accomplished by coupling the maximum cathode current available from a thin film of ferric chloride covering the steel's surface to the minimum current needed by a growing hemispherical pit. The experimental validation involved exposure tests of 304L and 316L steel samples covered by thin film of ferric chloride solution at a relative humidity of 97% with a loading density of 400 μg cm −2 . Evaluation of the maximum pit size model was done by comparing the pit size from the model with the pit size obtained from exposure tests at the same atmospheric conditions. The model was found to bound all of the experimental data for both alloys if it was assumed that the critical pit solution was between 60% and 80% of the saturation concentration.

Localized oxide spots were grown at the grain boundaries of a technically relevant 30 at.% Nb-Ti b-type titanium alloy to study the local electrochemical response. The grain boundaries selected were combinations of grains having different orientations and grain boundary angle. Crystallographic information of the grains and boundary angles were revealed by electron back scattering diffraction (EBSD) technique. Cyclic voltammetry is the electrochemical technique used to grow the oxides starting from 0 V and increasing the potential in steps of 1 V till 8 V at a scan rate of 100 mV s À1 in an acetate buffer of pH 6.0. Electrochemical impedance spectroscopy was used to investigate the electrical properties of the oxide/electrolyte interface in the frequency range between 100 kHz and 100 mHz. Important oxide parameters such as formation factor and dielectric number were determined from these measurements. Significant differences were observed for different grain boundaries. The semiconducting properties of the oxides at the grain boundaries were assessed by using Mott-Schottky analysis on a potentiostatically grown oxide. All the oxides showed n-type semiconducting properties where the donor concentration varies with the grain boundaries mentioned above. A flat band potential À0.25 AE 0.02 V versus standard hydrogen electrode is more or less the same for all the boundaries studied.