The pH and potential dependencies of the steady‐state iron dissolution and hydrogen evolution reactions were determined for zone‐refined iron in H2‐saturated acidic sulfate solutions. The mechanistic significance of the data is examined in detail. The results of this investigation serve to resolve the conflict concerning the mechanism of iron dissolution in noninhibiting media and to provide an experimental and mechanistic base for the interpretation of the electrochemical behavior of the active iron electrode in inhibiting media.

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The electrochemical behavior of titanium in deoxygenated acidic chloride solutions, with and without additions of Ti(III) and Ti(IV) ions, has been determined and compared with that observed in acidic sulfate media. A monolayer mechanism has been developed for the active‐state dissolution and passivation of titanium in acidic media. According to this mechanism, the metal is oxidized in a sequence of one‐electron charge‐transfer reactions which results in the formation of adsorbed reaction intermediates corresponding to each of the relevant valence states of titanium (+1, +2, +3, +4) and which leads to Ti(III) ions in solution in the active and active‐passive transition regions. The mechanism is in quantitative agreement with the experimental results for both chloride and sulfate media. In acidic chloride solutions, as well as in acidic sulfate solutions, the rates of oxidation at a passive titanium surface of Ti(III) ions in solution to Ti(IV) and of reduction at an active‐state surface of Ti(IV) ions in solution to Ti(III) are directly proportional to the concentrations of Ti(III) and Ti(IV), respectively. The reduction of Ti(IV) at an active surface is responsible for the fact that, at a critical concentration of Ti(IV), an active‐state surface passivates. In localized corrosion systems, active and passive surfaces are in simultaneous contact with the electrolyte within the occluded cell, and the aforementioned oxidation and reduction reactions serve to couple the active‐state and passive‐state electrochemical systems. Such electrolyte‐coupled active‐passive systems are capable of generating the critical concentration of Ti(IV) required to passivate the active‐state surface, a fact which explains random spontaneous cessation of localized corrosion (self‐healing). The critical concentration of Ti(IV) is much greater in chloride solutions than in sulfate media and takes much longer to attain. Consequently, the halide ion functions as a promoter of localized corrosion.

A study was made to determine whether a magnetic field, such as that associated with a thermonuclear reactor, might adversely affect the corrosion behavior of metallic surfaces in contact with a flowing electrolyte. In metal/ flowing‐electrolyte systems, electrochemical reactions dependent on the metal/ electrolyte interfacial potential difference are affected by an applied magnetic field as a consequence of the Lorentz forces acting on the charged components of the flowing electrolyte. A theoretical analysis of the magnetic field effect was developed, and its validity established by experiments involving the normalTi/H2SO4 false(H2‐normalsaturatedfalse) system. Quantitative agreement between theoretical and experimental results was obtained for the electrochemical behavior of Ti in 1N H2SO4 (mean flow velocity: 0–650 cm/sec) over the available range of magnetic flux density (0–2.1 Tesla). Although the experimental work employed discrete Ti electrodes set in the wall of nonconducting Pyrex glass pipe, the theory was extended to include metallic pipes, i.e., the “conducting‐wall” case, for which case the “wall‐shorting” effect was shown to be negligible. In addition to the adverse effect of a magnetic field on the “uniform” corrosion behavior of metals, the imposition of a magnetic field can also result in enhanced susceptibility to stress corrosion cracking, localized (pitting or crevice) corrosion, oxidation and reduction of solution species, and electrochemical decomposition of the electrolyte. The aforementioned processes, to name a few, are all potential dependent and, consequently, subject to the magnetic field effect.

Ru-implanted titanium near-surface alloys were generated by ion implantation, characterized (Ru concentration/ depth profiles) by Rutherford backscattering, and subsequently anodically oxidized to form electrocatalytically active RuxTil_xOJTi electrodes. The electrochemical behavior of the metallic-like electrodes was investigated in acidic chloride, perchlorate, and sulfate media. A correlation between the rate of the C12 evolution reaction and the Ru-implant profiles established that the reaction is first order in the concentration of Ru(IV) in the oxide at the oxide/solution interface, and enabled an in situ evaluation of the latter quantity. The Tafel slope for the C12 evolution reaction is 40 mV, i.e., o E/O log i = 2.303 (2RT/3F). The reaction order with respect to chloride ion concentration, 0 log i/0 log [C1-], approaches 1.0 and 2.0 at high and low chloride Concentrations, respectively. A modified Volmer-Heyrovsky mechanism, one in which the role of adsorbed chloride ions is taken into account, is shown to be consistent with the aforementioned diagnostic parameters.ion implantation, a nonequilibrium doping technique, enables the controlled introduction of virtually any element into the near-surface region of any substrate, typically to a depth up to a few hundred nanometers. The concentration/depth profile of the implanted species (determined, for example, by Rutherford backscattering) *Electrochemical Society Active Member. may be tailored over a wide range by varying the energy of the incident ions and the number of ions (coulombs of charge) implanted at each energy. As a surface modification technique, ion implantation has found widespread application for improving the electronic, optical, tribological, and corrosion characteristics of materials (1-4). The rates of many technologically important electrochemical charge transfer reactions occurring at elec-) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.255.6.125 Downloaded on 2015-06-03 to IP