A. D. Yfantis

Novel corrosion-resistant films for Mg alloys

Abstract A novel method for the corrosion inhibition of Mg alloys, based on the formation of a thin polyacrylic–polypyrrole film, is presented. The film was created after simple immersion of the samples in a specially formulated emulsion of polyacrylic and polypyrrole polymers. The synthesis conditions were studied, as well as the resulting corrosion resistance of coated magnesium foils (AZ31) in terms of corrosion rate in neutral aqueous NaCl solutions. The relative ratio of polyacrylic polymer to polypyrrole was found to be important for the film properties. Furthermore, only in situ polymerisation of pyrrole in the polyacrylic emulsion can provide advanced corrosion properties in relatively thin films (2–5 μm). Blending of polypyrrole powder with the polyacrylic emulsion gives rise to thick films (20 μm) with reduced corrosion-inhibition properties. The corrosion rate was only weakly dependent on the film thickness of these novel coatings. We argue that the mechanism of corrosion inhibition is related to the formation of a thin passive layer of chemisorbed polypyrrole polymers or oligomers on the native magnesium oxide of the surface. The structure is further stabilised by polyacrylic polymer chains interacting as dopants of polypyrrole. The method is environmentally friendly: non-toxic chemicals are used, no rinsing is required, etc. The advanced corrosion-inhibition properties of the films, as well as the simple application process on the metal surface, provide significant potential for the industrial application of the method.

Highly conductive polypyrrole films on non-conductive substrates

Abstract We report on a method to deposit thin films of conductive polypyrrole powder on non-conductive substrates. This is a new method in contrast to the usual way of preparing polypyrrole films by anodic deposition on metal substrates. Polypyrrole tosylate is synthesized by chemical oxidation of pyrrole with ammoniumpersulfate in aqueous solution. We optimized the conductivity by variation of the reaction conditions. Then we produced smooth films of polypyrrole by testing several methods of film deposition. All of these samples were characterized by conductivity and by X-ray photoelectron spectroscopy (XPS) measurements, and compared to electrochemically produced polypyrrole films.

Polypyrrole doped with fluoro-metal complexes: thermal stability and structural properties

Chemically produced polypyrrole powders doped with the fluoro-complexes fluoro-aluminates, fluoro-zirconates, fluoro-titanates and fluorides are synthesized and characterized by both XPS and four-probe conductivity measurements. The results show that the polypyrrole powders produced were doped with fluorides and with fluoro-metal complexes (Zr, Ti, Al) of different coordination numbers. Also, a significant incorporation of sulfates originating from the oxidant was determined. The relative concentration of the sulfates and of the respective fluoro-metal complexes is strongly affected by the size of these dopants and much less from their concentration in the solution. The aging process of these polymers is investigated. We have found that there are two main mechanisms, the oxidation of the polymeric chain by water and oxygen as well as the reaction of fluoride ions with low coordination fluoro-complexes to form stable complexes of higher coordination number. In the case of polypyrrole powder doped with fluorides, the mobility of these counter-ions leads to the formation of gaseous species. Polypyrrole powders doped with fluoro-zirconates and fluoro-titanates exhibit both good stability in contrast to those doped with fluoro-aluminates and fluorides.