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 PC 04 Electrochemical control on the formation of mixed 11- mercaptoundecanoic acid and octanethiol self-assembled monolayers on Au(111) Zoilo González-Granados, Rafael Madueño, Manuel Blázquez, Teresa Pineda Dpto. Química Física y Termodinámica Aplicada, Universidad de Córdoba, Córdoba, SPAIN tpineda@uco.es Self assembled monolayers (SAMs) of terminal-functionalized alkanethiols are less organized structures than their alkanethiol partner monolayers. The bigger size of the terminal group and/or the repulsive interactions between equally charged groups are mostly responsible for this disorder. One strategy that can be followed in order to have a better organized monolayer is the dilution of the functional groups by using a mixed monolayer with a determined ratio of the alkanethiol. In this sense, the mixed monolayers can show either a homogeneous distribution of the molecules with different chemical nature or a phase separated behaviour. Any of these properties are useful depending on the applications. In this work, we present a study of the mixed monolayer formed from 11-mercaptoundecanoic acid (MUA) and octanethiol (OT) at different MUA/OT molar ratios. Taking advantage of the different electrochemical behaviour of these two molecules on an Au(111) single crystal electrode (Figure 1), we prepare these monolayers under electrochemical control from an alkaline aqueous solution [1]. Figure 1. Cyclic voltammetry of 1 mM MUA and 1 mM OT in 0.1 M NaOH aqueous solution on a Au(111) single crystal electrode. The differences between the oxidation (deposition) and reduction (desorption) potentials for these two monolayers can serve as a way of quantification of the composition of the mixed MUA- OT layer obtained not only by potentiodynamic but also by potentiostatic methods. Acknowledgments: Project CTQ2007/62723, Junta de Andalucía and Universidad de Córdoba. References [1] García Raya, D.; Madueño, R.; Blázquez, M.; Pineda, T.; J. Phys. Chem. C, 2010, 114, 3568. September, 811, 2010. ISEL - Lisbon 82
XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society PD 01 In-situ study of corrosion morphology of a duplex stainless steel in a concentrated LiBr solution and in an impure phosphoric acid solution by confocal laser scanning microscopy (C LSM) R. Leiva-García 1 , M.J. Muñoz-Portero 1 , J. García-Antón 1 1 Univ. Politécnica de Valencia, Ingeniería Electroquímica y Corrosión (IEC), Dep. Ingeniería Química y Nuclear, Camino de Vera s/n, 46022 Valencia, Spain. jgarciaa@iqn.upv.es Corrosion has been mainly studied using large-scale experiments. However, corrosion mechanisms occur on a smaller scale. Therefore, it can be useful to develop smaller scale methods and experimental methodologies. In this way, it will be possible to study reduced surfaces. The aim of this work is the study of the corrosion morphology of a duplex stainless steel (UNS 1.4462) in a concentrated aqueous LiBr solution (992 g/L) and in an impure phosphoric acid solution, containing chlorides and sulfates. The electrochemical techniques used were cyclic potentiodynamic curves and galvanodynamic curves. Tests were carried out in a minicell developed by this research group. This cell can be put in the stage of a confocal laser scanning microscope. In this way, the in-situ observation of the corrosion process at microscopic scale is possible. All the tests were made at 25 ºC. The LiBr solution is an aggressive solution that provokes localized corrosion in the duplex stainless steel. During the potentiodynamic curves, pits appear in the electrode surface when the pitting potential is reached. These pits grow until affect the entire electrode surface. When this growth is observed at higher magnifications (200x and 500x), the formation of new small pits is observed in the unaffected area (covered with the corrosion product) closed to the corrosion front. Then, this corrosion front reaches the pits and the observed surface ends completely damaged. In the case of the galvanodynamic curves, a pit appears in the electrode surface when the pitting potential point is reached and it goes growing in a sequential way with the increase of the current density. With regard to the impure phosphoric acid solution, the potentiodynamic and galvanodynamic tests indicate that corrosion of duplex stainless steel is generalized in this medium. The images obtained at different magnifications (100x - 500x) show how the grain boundary of the tested stainless steel goes being revealed with the increase of the current density. Despite of the presence of impurities, their concentration is not critical to produce a localized corrosion attack. Therefore, the developed minicell is useful to study the morphological differences among different kinds of corrosion attack at microscopic scale. Acknowledgments: We wish to express our gratitude to MICINN (CTQ2009-07518), to F EDER, to MAEC (PCI Mediterraneo C/8196/07, C/018046/08, D/023608/09) for their financial support and to Dr. Asunción Jaime for her translation assistance. September, 811, 2010. ISEL - Lisbon 83
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