H. W. Pickering

Characteristic features of alloy polarization curves

Abstract The different tendencies for dissolution of the individual components of alloys produce unique polarization behavior that is not seen in pure metals. This behavior, which is just as prevalent in base metal as in noble metal alloys, is often obscured in the polarization curves by other reactions, e.g. H 2 evolution. Four distinct polarization regions are identified and characterized in terms of the tendency for selective dissolution, surface enrichment of the more noble component and the stability of a planar surface. The greater the difference in the standard reduction potentials of the metals in the alloy, ΔE °, the more pronounced are the alloy features. The alloy composition is important in determining which alloy features occur. Stress corrosion susceptibility is greatest for one type of alloy dissolution.

Effect of KI on Improving Copper Corrosion Inhibition Efficiency of Benzotriazole in Sulfuric Acid Electrolytes

A synergistic effect exists when benzotriazole (BTAH) and iodide ions are used together to prevent the corrosion of copper in sulfuric acid. The nature of this effect has been studied systematically by using electrochemical techniques and X-ray photoelectron spectroscopy. The synergistic effect is due largely to the formation of a film of Cu(IBTA) complex and is probably polymeric in nature. This new complex film greatly depresses copper dissolution.

Analysis of Hydrogen Evolution and Entry into Metals for the Discharge‐Recombination Process

A mechanistic model has been developed which for the first time considers the effect of hydrogen entry into a metal on the kinetics of the hydrogen evolution reaction (h.e.r.). The model enables computation of (i) the hydrogen surface coverage and surface concentration; (ii) the hydrogen adsorption, absorption, discharge and recombination rate constants; and (iii) the h.e.r. coverage‐dependent transfer coefficient, α, and the exchange current density , from a knowledge of the steady‐state hydrogen permeation current, cathodic charging current, hydrogen overvoltage, and hydrogen diffusivity. The model predicts a linear relationship between the permeation flux and the square root of the hydrogen recombination flux, and provides an analytical method to determine the cathodic potential range for operation of a coupled discharge‐recombination mechanism of the h.e.r. With modifications the model can treat permeation data for which (i) the mechanics of the discharge step involve a (proposed) selvedge reaction, and (ii) surface hydrogen coverages are relatively high as in the presence of poisons (e.g., or ). Some of the existing literature data for hydrogen permeation in iron and nickel in acid and alkaline solutions are successfully analyzed.

The significance of the local electrode potential within pits, crevices and cracks

Abstract A reveiw of the experimental measurements of the electrode potential within pits, crevices and cracks shows a significant number of similar findings for several commercially important alloy systems. Recent results for crevicing in iron give further insight into the relationship of the important parameters within the cavity: IR drop, Flade or passivation potential and solution composition. The key relationship for stable crevice corrosion is that the electrode potential in the crevice is less oxidizing than the Flade potential of the crevice solution. The consequences of this finding are discussed for pitting corrosion, stress corrosion and corrosion fatigue. Some expected consequences regarding the initiation of localized corrosion are presented. In this mechanism, the modified solution compositions that are found inside occluded cells promote local cell action through their influence on the potential shift, e.g. acidification facilitates local cell action by shifting the Flade potential in the noble direction.

Important early developments and current understanding of the IR mechanism of localized corrosion

Some principles of current distribution within recesses that were developed last century by Carl Wagner are a basis for understanding crevice corrosion that occurs by the recently proposed (1985) so-called IR mechanism, where I is the ionic current flowing out of the crevice or pit, and R is the resistance of the crevice/pit electrolyte. Subsequent experimentation and modeling have shown its applicability for describing the two broad classifications of crevice corrosion: crevice corrosion that occurs immediately, and the delayed form that occurs after an induction period. The mechanisms IR > ΔΦ* criterion, where ΔΦ* is the difference between the applied potential, E SURF , and the electrodepotential of the active/passive transition, E A/P , has also been applied in grain boundary corrosion and crack initiation, subsurface corrosion inside pores of sintered metals and alloys, rebar corrosion in concrete, pitting corrosion, lace-like pitting, hydrogen absorption and crack initiation during anodic protection. scaling to other size crevices, and describing the critical crevice corrosion temperature.

Interpretation of impedance data for reinforcing steel in alkaline solution containing chlorides and acetates

Abstract Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry were used to study the corrosion of reinforcing steel in a simulated pore solution with and without additions of chloride ions (0.5 M KCl), and calcium magnesium acetate (CMA) (0.2 M). The latter is considered as a possible deicing agent. Under open-circuit conditions, the initial rest potential ( E r ) shifted in the noble direction and the charge transfer resistance ( R ct ) increased, but after a few days E r moved in the negative direction and simultaneously R ct decreased, whereas the double layer capacitance ( C dl ) and depression angle of the charge transfer semicircle increased. R −1 ct rose with increasing C dl . The impedance and voltammetric measurements indicated that the addition of CMA to the simulated pore solution diminished the corrosion rate and increased the protectiveness of surface films.

Effect of the applied potential on the potential and current distributions within crevices in pure nickel

Abstract The electrode potential profile within a crevice was measured in situ during crevice corrosion of nickel in 1N H 2 SO 4 under conditions of effective convective mixing of the crevice and bulk electrolytes. Oxidizing power was investigated by applying potentials in the passive region. A steep potential gradient and constant pH were always measured during crevice corrosion. The magnitude of the potential drop and the distance into the crevice of the passive-to-active transition, X pass, both increased linearly with increasing applied potential, in accordance with the IR >ΔΦ∗ criterion. The in situ measured potential E pass at X pass was, at all times, constant and in the range of the passive-to-active transition for the polarization curve of the bulk solution.

Ion sputtering of alloys

Based on an idealized model of ion sputtering of a binary alloy which consists of an easy‐to‐sputter and a difficult‐to‐sputter metal, a mass transfer calculation was carried out. Solutions for both the initial transient and subsequent steady‐state concentration profiles, and the excess (sputtered) amounts of the easy‐to‐sputter component were obtained. For typical sputtering rates it is found that the sputtering enhanced diffusivity must be ≫10−17 cm2 s−1 before an interdiffusion zone can form. The analysis is of special significance since it shows that even when the alloy components have greatly different sputtering tendencies: (a) nonpreferential sputtering is always obtained after an induction period, the latter of which depends on the effective alloy interdiffusivity and the overall rate of sputtering and (b) the attainment of nonpreferential sputtering requires that the new surface continuously readjusts its composition in the direction of enriching in the difficult‐to‐sputter component. Similar res...

Application of a quartz crystal microbalance to the study of copper corrosion in acid solution inhibited by triazole-iodide protective films

When one uses one side of a quartz crystal microbalance as the working electrode in electrochemical experiments, mass changes can be monitored continuously with a sensitivity of a few nanograms per square centimeter. In this study the working electrode consisted of electrolytically deposited copper, exposed to 0.1M sodium sulfate at pH 3, open to the atmosphere and in some cases containing H{sub 2}O{sub 2}. Upon addition of one of the inhibitors, benzotriazole (BTA), tolyltriazole (TTA), carboxy-benzotriazole (CBT), or these inhibitors plus potassium iodide, the rate of frequency change decreases markedly. After removal of the inhibitors from the corrosive medium by fast solution exchange there is a marked continuing protective effect of the inhibitor films in the cases of BTA + KI and TTA + KI with the latter being the most stable and protective of all of the films. The results were qualitatively the same in the more corrosive solution containing H{sub 2}O{sub 2}.

Potential Distribution, Shape Evolution, and Modeling of Pit Growth for Ni in Sulfuric Acid

Growth of artificial pits in the Ni/sulfuric acid system was investigated using a microprobe technique for the potential monitoring and pH measurements within the pits, as well as routine electrochemical, solution analysis, and metallographic techniques. The measured data and the observed changes in shape of the pit with time demonstrate that the IR voltage drop mechanism of localized corrosion operates for this system. Experimental results are in good agreement with the results of mathematical modeling. It is also found that the increase in Ni{sup ++} ions and in pH within the pit have a destabilizing effect on the pit growth process and that this effect can be explained within the framework of the IR voltage drop mechanism.