Studies of the low temperature oxidation of alloys by X-ray photoelectron spectroscopy: CuZn

Effect of Cr Content on Corrosion Resistance of Low-Cr Alloy Steels Studied by Surface and Electrochemical Techniques

The electrochemical behavior of low alloyed Fe-Cr steels with 3 and 5% wt. of Cr in neutral Na2SO4 electrolyte combined with a detailed chemical and morphological characterization of these alloys performed by Auger electron spectroscopy, X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry and scanning electron microscopy are presented here. The corrosion of low alloyed Fe-Cr steels proceeds in the prepassive range, with the formation of corrosion surface films having a duplex structure with outer iron oxide/hydroxide layer and inner Cr oxide-rich layer. The thickness, composition, and the morphology of the surface films vary as a function of chromium content in the alloy as well as conditions of electrochemical tests (temperature). Even a low chromium content shows a beneficial effect on the corrosion performances of the Fe-Cr steels. The chromium as a more active component than iron of ferrite increases the anodic activity of this phase, which results in a rapid saturation of the surface with the anodic reaction products forming a fine crystalline-like and compact layer of corrosion products. In this way, the chromium acts as a modifier of formation/crystallization of the iron-rich surface film (mainly magnetite) in the prepassive range.

Adsorption of hexavalent chromium by polyacrylonitrile (PAN)-based activated carbon fibers from aqueous solution

Polyacrylonitrile (PAN)-based activated carbon fibers (PAC400 and PAC600) were prepared by heating Zn(NO₃)₂ pretreated-PAN at 400 °C and 600 °C for the removal of Cr(vi) from aqueous solution.

Initial oxidation of brass induced by humidified air

Complementary surface and near-surface analytical techniques have been used to explore a brass (Cu-20Zn) surface before, during, and after exposure in air at 90% relative humidity. Volta potential variations along the unexposed surface are attributed to variations in surface composition and resulted in an accelerated localized growth of ZnO and a retarded more uniform growth of an amorphous Cu₂O-like oxide. After 3 days the duplex oxide has a total mass of 1.3 μg/cm², with improved corrosion protective properties compared to the oxides grown on pure Cu or Zn. A schematic model for the duplex oxide growth on brass is presented.