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The early stage of corrosion of copper by moist air containing 0.5% sulfur dioxide (75% relative humidity at 25~ has been studied. Scanning electron microscopy, Auger electron spectroscopy, and transmission electron microscopy have been used to examine the surface topography, surface chemistry, and microstructure of copper foils before and after exposure to the corrosive atmosphere. The analyses show that in the initial stage of corrosion a mixture of copper oxide and copper sulfide forms on the surface. Reduction of sulfur dioxide to sulfide on the metal surface indicates that sulfur dioxide is a cathodic depolarizer in the early stages of corrosion.

This investigation examined the effects of serum proteins addition on the anodic and cathodic polarization behavior of implant alloy316L stainless steel in saline. Cyclic anodic potentiodynamic polarization was used to determine the four critical parameters associated with passive film breakdown and repassivation: corrosion potential, pitting potential, repassivation potential, and reverse scan hysteresis. Cathodic potentiodynamic polarization was used to study the effects of serum proteins on the Tafel slope and limiting current density of the reduction reaction. Three different conditions of solution purging were investigated. Resu/ts were compared with in vivo (hamster) tests. The corrosion potential was significantly affected by aeration conditions in saline as well as in 10% serum. The pitting potential was shifted marginally in the positive direction by serum proteins. While proteins did not affect the cathodic reduction mechanism, their adsorption decreased the reduction kinetics.KEY WORDS: implant, in vitro, in vivo, orthopaedic, protein, serum, stainless steel.

The open-circuit potential (E"p) of alloy 600 in lithiated water at 25 to 200°C is more negative than the RHE potential, which indicates that the alloy exhibits a mixed electrode potential under these conditions. In the 200 to 350°C range, E op is close to the RHE potential.The inner layer of the oxide film formed at 200°C and above is composed of MeO, white its outer layer is probably composed of Me00H or Me(OH) 2 .With increasing temperature, the film thickness increases moderately between 25 and 200°C, but increases drastically above 200°C.The AC impedance measurements show significant changes in the electrochemical properties of films starting from 150°C.At 250°C, semiconductivity of the film changes from p-type at lower temperatures to n-type at higher temperatures.The occurrence of changes in the properties of oxide films was established by ex situ and in situ experiments (AES, semiconductivity, and AC impedance, respectively). ABSTRACTA thermodynamic perspective of the initial stages of copper tarnishing in moist air-S02 is presented. Previous experimental work has shown that in such a system the initial tarnish film consists mostly of a mixture of copper(I) oxide and copper(1) sulfide. Equilibrium criteria are used to calculate the Tonic composition of the adsorbed water layer on the surface of the untarnished and the tarnished metal at various gas precursor concentrations. Using the adlayer chemistry, the electrode potentials of the redox reactions in the system are determined. Thermodynamically stable corrosion products are then calculated. The ability of S02 dissolved in water to act as a cathodic depolarizer in this system, thereby forming sulfide in the tarnish film, is demonstrated.