Portugaliae
Electrochimica Acta

Ionic conductivity measurements, X-ray diffraction analysis and thermal studies have been carried out on polymer electrolyte films prepared by the addition of zinc trifluoromethanesulphonate (triflate) to polyethylene oxide), PEO. In general this electrolyte system was found to behave in a manner similar to other divalent salt-based electrolytes with an increase in crystalline morphology as the concentration of the salt component in the electrolyte was decreased. The conductivity isotherms calculated for this system show an almost constant level of ionic conductivity over the entire range of composition studied.

Guaiacol is an undesired compound in some natural products, mainly because of its aroma. In this work, the voltammetric determination of guaiacol by oxidation at a carbon paste electrode following a cathodic accumulation was first tried, with no sucess, because there was no accumulation of the compound. On the contrary, it was found that there is accumulation of a product formed after oxidation of guaiacol, probably a dimeric product, that can be determined by reduction. Using an accumulation time of 5 minutes and a potential at which guaiacol is being oxidized, a determination limit of 2 ug/L was obtained by cathodic stripping voltammetry, a value about ten times lower than that obtained in the anodic determination. The method was applied to the determination of guaiacol in cork stoppers.

The inhibitive effect of thiourea, 2-amino [4-p-chlorophenyl] thiazole and different derivatives of their condensation products, N-2[4-p-chlorophenyl] 2-thiazolyl] thiocarbamide on the corrosion of mild steel in 20% formic acid solution has been studied using weight loss and electrochemical polarisation techniques. Different concentrations of inhibitors and temperatures have been tested. The inhibition efficiencies calculated by both the techniques are in fairly good agreement except at higher concentrations of some inhibitors. The results observed have been discussed in the light of the molecular structures of the compounds and their adsorption on the surface of the corroding metal. All the inhibitors have been found to be good inhibitors. The polarisation measurements indicate that these inhibitors influence both anodic and cathodic reactions and thereby they contribute to reduce the corrosion rate.

Voltammetric studies on copper, nickel and cupronickel alloys of various compositions in neutral chloride solutions revealed that the passivation is due to the formation of duplex film consisting of inner compact Cu2O layer with outer chloro hydroxy layer. Under transient cyclic polarisation conditions, the presence of nickel hindered the passive film formation decreasing its thickness and ohmic conductivity. The reduction of these passive films to copper was markedly favoured by chloride ions. The presence of nickel in the alloy hindered the reduction of these passive films.