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The effect of current density, pH, and temperature on the anodic behavior, cathodic behavior, and corrosion of magnesium in aqueous solutions has been studied. A tentative mechanism for the anodic oxidation of magnesium is postulated. Local corrosion and/or undermining of metallic magnesium at the anode are appreciable and may, in fact, account for the observed low anodic current efficiencies of magnesium. An intergranular type of corrosion occurs at cathodically polarized magnesium at elevated temperatures. A hydrogen embrittlement theory is proposed to explain intergranular cathodic corrosion. ) 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 2015-03-19 to IP ) 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 2015-03-19 to IP Vol. 105, No. 5 CORROSION OF POLARIZED MAGNESIUM 247 6C ) 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 2015-03-19 to IP

The formation of cathodic films was observed under the microscope during electrolysis of chromium plating solutions at various CrO~:SO4 ratios. The microscopic observations were correlated with galvanostatic and potentiostatic polarization data. It was found that an amorphous oxide film formed in chromic acid solutions. This film also formed, as a transient stage prior to chromium deposition, in solutions containing sulfate at CRO3:SO4 ratios ranging from 200:1 to 65: 1. Chromium deposition was associated with transformations at the cathode surface that involved the breakup of the amorphous oxide film and the appearance of a viscous film. The nature and formation of these two types of cathodic films are discussed with reference to findings of other investigators.Although the deposition of chromium from chromic acid solutions is an important industrial process little is known about its mechanism. Dubpernell (1) in a critical review of the available literature on the subject came to the conclusion that even the simplest questions about chromium plating cannot be answered with the present knowledge. A critical area of dis-* Electrochemical Society Active Member. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 131.155.81.2 Downloaded on 2015-01-05 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 131.155.81.2 Downloaded on 2015-01-05 to IP Vol. 117, No. 8 ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 131.155.81.2 Downloaded on 2015-01-05 to IPABSTRACT Tetraphenylethylene, triphenylethylene, stilbene, I,I diphenylethylene, and styrene were utilized as model compounds. Cyclic voltammetry in tetrahydrofuran, NBu4C]O4, showed that the radical anions of these compounds were protonated in this medium and are therefore stronger nucleophiles than poly-

Galvanostatie polarization data with simultaneous microscopic observations of a Pt cathode surface were obtained in conventional chromium plating baths. The results show that the deposition of chromium on bright activated platinum is preceded by heavy evolution of hydrogen and a prolonged shift of potential during which the formation of a chromic oxide film may be observed at the cathode surface at higher current densities. The final shift of potential just prior to the establishment of metal deposition was found to be associated with a distinct decline of gas evolution regardless of the presence or absence of the chromic oxide film which, when formed, was observed to disintegrate before steady-state conditions of Cr deposition were reached. These observations are compared with those made earlier with Fe electrodes and the results are discussed in the light of possible processes involved in bringing about the shift of the potential to the value of Cr deposition. * Electrochemical Society Active Member.

The formation of cracks in chromium coatings obtained from conventional baths at the bright plating range of current density and temperature can be reduced or eliminated by employing controlled plating interruptions. The interruptions, to be effective, must a) allow dissipation or cause deactivation of the cathode film and b) be frequent enough to prevent the incremental increases of the deposit thickness associated with the formation of sets of cracks. The technique puts no restriction on i) the type of plating interruptions as long as they meet the above specified conditions, the exact control of their frequency, iii) the concentration of the plating bath, iv) the current density and temperature, v) the thickness of the crack-free coating and vi) the type of the substrate, but requires knowledge of the critical thickness at which formation of cracks begins. Plating interruptions may cause loss of luster; appearance deteriorating as the frequency of interruptions increases. With interruptions suitably chosen, chromium becomes crack-free and remains bright on the microscale; thus is acceptable for buffing.