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"Carboxylatation" coating on zinc: A chemical conversion in organized molecular systems containing carboxylic acid.

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SURF Chemical conversion coatings on zinc surface based on hydrophobic carboxylic acid were developed and studied in this work. The long carbon chain carboxylic acid as heptanoic acid was solubilized or dispersed in different organized molecular systems (OMS) with the help of surfactant (Brij© 58, C16E20, HLB = 15.8). In a first step, the phase diagram Brij©58/HC7/water was established at 20 °C to determine the different one-phase or several phase domains, such as microemulsion, liquid crystal and emulsion. Several techniques were employed to characterize the phases and the localisation of the carboxylic acid in the OMS phase. Then the coatings, named "carboxylatation", were performed on galvanized steels in the OMS bath containing an oxidizing agent. After the degreasing and etching steps, the zinc substrate is oxidized into Zn2+ cations which precipitate in zinc carboxylate crystals. Coating morphology and composition were characterized by SEM and XRD. Then, stationary electrochemical techniques and climatic chamber tests was used to characterize the protective properties of the different coatings. The results show that the stability of the OMS is necessary to assure a good "solubilization" or dispersion of heptanoic acid in water. Nevertheless, carboxylic acid should be easily liberated from the OMS to react on the surface. In our case, the best choice is the use of a milky "pure" emulsion that is thermodynamically unstable, but sufficiently stable in time to assure a good dispersion and an easy transport and liberation of carboxylic acid on the zinc surface.

"in situ" XPS studies of laser induced surface cleaning and nitridation of Titanium

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SURF A titanium foil has been subjected to laser irradiation "in situ" in a pre-chamber of an X-ray photoemission spectrometer under different atmospheres (vacuum, Ar, O2, air, N2 and H2). As a result of these treatments, a high amount of the carbon contamination layer was removed and other changes in composition were induced. Nitridation was achieved by laser irradiation under nitrogen. The most effective treatment protocol included an initial cleaning procedure induced by irradiation in vacuum, followed by a second irradiation process performed under nitrogen. Partial nitridation is also observed when irradiating under synthetic air. Lateral and depth analysis of the nitrogen concentration around the laser spot has been also carried out. It is found that the outermost layers present a similar concentration of nitrogen. In addition, the measured nitrogen profile indicates that the amount of nitrogen within the laser spot region is relatively lower than within the immediately surrounding area. Almost no nitrogen remains in the spot area after sputtering for 30 min. A model is proposed to account for the observed titanium surface nitridation processes.

"Organic" pickling and passivation of stainless steels and new process for polishing brass

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Overview of processes offered by Messrs Poligrat where hazardous hydrofluoric acid has been replaced by unspecified organic acids. Also new process for chemical polishing and brightening of brass (BrassChem), a development of a similar process for copper (CuproChem). www.poligrat.co.uk