XII Iberian Meeting of Electrochemistry XVI Meeting of the ...

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XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society O D 02 Water Uptake Estimation in O rganic Coatings using Electrochemical Impedance Spectroscopy R. G. Duarte, 1,2 A. S. Castela, M. G. Ferreira 1 Instituto Superior Técnico, Chemical and Biological Eng. Dept/ICEMS, Av. Rovisco Pais, 1049-001 Lisbon, Portugal. b Escola Superior de Tecnologia do Barreiro/ IPS, 2830-144 Barreiro, Portugal. raquel.duarte@estbarreiro.ips.pt The water uptake in organic coating films can be estimated by EIS and, for this purpose, several models can be found in the literature [1,2,3]. The EIS method for the determination of the water uptake parameter presents several practical advantages compared with the more traditional ones, namely gravimetry, such as: it is a non destructive test, it can be used in every substrate and it can be applied in situ. These factors led to a wider use of such technique for the study of this parameter. In this presentation water uptake in PVC Plastisol films was estimate by EIS using models referred in the literature. The gravimetry technique was also used as a reference method. The influence of the salt concentration and ions type in the outer solution were also taken into consideration. In this study it was concluded that water uptake values estimated by EIS are influenced by the outer solution parameters, presenting higher values for films immersed in solutions containing cations with lower hydrated diameter and also for the more concentrated solutions. It was also verified that anions presented in the outer solution do not influence the water uptake values estimated by this technique. Likewise the film resistance is also influenced by the outer solution characteristics. however, the resistance evolution was opposite to the one determined for the water uptake. The gravimetric technique showed quite opposite results, in which the water uptake did not change with the cation characteristics and presented higher values for the solutions with lower concentration. Comparison between the water uptake values obtained by the EIS models and the ones obtained by gravimetry was also performed . References [1] D. M Brasher, A. H. Kingsbury, J. Appl. Chem., 1954 , 4, 62. [2] A. S. Castela, A. M. Simões, Corr. Sci., 2003, 45, 1647 [3] R. G. Duarte, A. S. Castela, M. G. S. Ferreira, Prog. Org. Coat, 2009, 65, 197 September, 811, 2010. ISEL - Lisbon 48
XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society O D 03 Novel electrochemical techniques for classical corrosion problems: the Scanning Vibrating Electrode applied to galvanized steel cut edges Alda Simões ICEMS & DEQB / Instituto Superior Técnico/ TULisbon Av. Rovisco Pais, 1049-001 Lisboa, Portugal alda.simoes@ist.utl.pt Space-resolved electrochemical techniques have recently been gaining grounds for development in corrosion studies. They are based upon micro-electrodes and of a nonintrusive approach, allowing scanning and mapping of a chosen property along an active surface. The scanning vibrating electrode technique (SVET) is particularly useful for peculiar systems like cut edges of coil-coated steel, which combine close contact between anode and cathode with very thin electrodes, resulting in high gradients of pH and ion concentration and generating severe limitations to the classical techniques. The SVET has good characteristics for this system and has been successfully applied to cut edges [1-4]. The study deals with the potentialities of space-resolved techniques for such a system and with the effect of corrosion inhibitors in solution on the current values and distribution. The conclusions are supported by other techniques, namely potentiodynamic polarization and electrochemical impedance spectroscopy. Mapping of the ionic currents reveals that the cathode shifts away from the anode as zinc corrosion products precipitate at the location of the peak cathodic current. The presence of different inhibitors leads to different results, depending on the efficiency and mechanism. Sodium phosphate inhibits corrosion at the cut edge by precipitation of zinc phosphate clusters with barrier properties, whereas benzotriazole can under some circumstances cause loss of cathodic protection. Acknowledgements: The collaborations of Juliana Custódio and of Dr. João Fernandes are greatly acknowledged. The research was partly sponsored by the European Research Fund for Coal and Steel (contract RFS-CR-04021). References: [1] F.Zou, H.S.Isaacs, D.Thierry, Corrosion Science, 2000, 42, 1149. [2] K. Ogle, S. Morel and J.Jacquet, J.Electrochem. Soc., 2006, 153(1), B1. [3] A.M. Simões, J. Torres, R. Picciochi, J.C.S. Fernandes, Electrochim. Acta 2009, 54, 3857. [4] J.V. Custódio, S.M.L. Agostinho, A.M.P. Simões, Electrochim. Acta 2010, doi:10.1016/ j.electacta.2010.03.072. September, 811, 2010. ISEL - Lisbon 49
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