Different Performance of Factors Affecting the Estimation of the Corrosion Rate in Magnesium Alloys by Implementation of the Common Methods for Electrochemical Measurements

financial support for this work from the Ministry of Science and Innovation of Spain (MAT 2009-13530)Peer reviewe

Exploring the interfacial neutral pH region of Pt(111) electrodes

The interfacial properties of Pt(111) single crystal electrodes have been investigated in the pH range 3 < pH < 5 in order to obtain information about the acidity of electrosorbed water. Proper experimental conditions are defined to avoid local pH changes while maintaining the absence of specifically adsorbed anions and preserving the cleanliness of the solution. For this purpose, buffer solutions resulting from mixtures of NaF and HClO4 are used. Total charge curves are obtained at different pHs from the integration of the voltammetric currents in combination with CO charge displacement experiments. Analysis of the composition of the interphase as a function of the pH provides information for the understanding of the notion of interfacial pH.Support from MINECO (Spain) through project CTQ2013-44083-P is greatly acknowledged. RMH thankfully acknowledges support from Generalitat Valenciana under the Santiago Grisolia Program (GRISOLIA/2013/008). PS thankfully acknowledges to the Generalitat Valenciana the award of a valid grand

New insights into the Pt(hkl)-alkaline solution interphases from the laser induced temperature jump method

The interfacial properties of platinum single crystal electrodes in contact with alkaline aqueous solutions (pH = 13) have been investigated using the laser induced temperature jump method. This technique offers insights into the net orientation of water dipoles in contact with the electrode surface by recording the coulostatic potential changes after a sudden increase of the interfacial temperature in the submicrosecond time scale. This information is intimately related with the magnitude and sign of charge separation at the interphase and the resulting electric field. In all cases, water shows a net orientation with the hydrogen towards the metal at the lowest investigated potential value, reflected in negative potential transients. The magnitude of the water orientation decreases as the applied potential increases. Eventually, the sign of the potential transient changes, reflecting a reorientation of the water dipoles. The potential where such inversion takes place follows the order Pt(110) < Pt(100) < Pt(111) in accordance with the observed behavior in acid solution and the trend of the work function. For Pt(111) the change of sign of the laser induced potential transient takes place at the onset of hydroxyl adsorption. For the three surfaces, when the pH is decreased to ca. pH = 11, a slow response is detected at potentials values above the inversion point. This could be due to a fast adsorption process or to a slow reorientation of water. After the introduction of steps on the (111) terrace, the inversion shifts to the double layer region, allowing the unambiguous identification of the inversion with a change on the net orientation of the water molecules. For stepped surfaces, a second inversion of the laser induced potential transient is observed that could be related with an effect of the local charge on steps disrupting the ordering of the water network. Comparison with analogous results in acid solution gives information about the local distribution of charges on the stepped surfaces.This work has been financially supported by the MINECO (Spain) project no. CTQ2016-76221-P

Study of the interface Pt(111)/ [Emmim][NTf2] using laser-induced temperature jump experiments

The interface between a Pt(111) electrode and a room temperature ionic liquid, 1-ethyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide, was investigated with the laser-induced temperature jump method. In this technique, the temperature of the interface is suddenly increased by applying short laser pulses. The change of the electrode potential caused by the thermal perturbation is measured under coulostatic conditions during the subsequent temperature relaxation. This change is mainly related to the reorganization of the solvent components near the electrode surface. The sign of the potential transient depends on the potential of the experiment. At high potential values, positive transients indicate a higher density of anions than cations close the surface, contributing negatively to the potential of the electrode. Decreasing the applied potential to sufficiently low values, the transient becomes negative, meaning that the density of cations becomes then higher at the surface of the electrode. The potential dependence of the interfacial response shows a marked hysteresis depending on the direction in which the applied potential is changed.Support from MINECO (Spain) through project CTQ2013-44083-P is greatly acknowledged. Paula Sebastian acknowledges to the Generalitat valenciana for the award of vali + d gran

Investigating the M(hkl)| ionic liquid interface by using laser induced temperature jump technique

The interface between several Room Temperature Ionic Liquids (RTILs) in contact with both Au(hkl) basal planes and Pt(111) was studied by using cyclic voltammetry and Laser Induced Temperature Jump Technique (LITJT). Three RTILs, based on the imidazolium cation and the [Tf2N] anion were investigated: [Emmim][Tf2N], [Emim][Tf2N] and [Bmmim][Tf2N]. These three RTILs were selected with the aim to analyse how the balance between the different ion-ion interactions influences the interfacial properties of the M(hkl)|RTIL interface. It was found that the voltammetric response of the Au(hkl)|[Emmim][Tf2N] was highly sensitive to the geometry of the active surface sites, displaying sharp spikes superimposed to a capacitive voltammetric current. Conversely, these sharp spikes disappeared when [Bmmim][Tf2N] replaced [Emmim][Tf2N], although the capacitive voltammetric current profile was essentially maintained. This result is most likely related to the increase of the van der Waals interactions in the [Bmmim][Tf2N]. When [Emim][Tf2N] was analysed, the increase of the hydrogen bond interactions due to the hydrogenation of C2 (second carbon at the imidazolium ring) resulted also in the disappearance of the voltammetric spikes. The laser measurements showed that the highest values of the potential of maximum entropy (pme) in RTIL media correspond to the atomically closest packet surface structures, following the order: Au(111)>Au(100)>Au(110), in agreement with work function values. The measurement with Pt(111) revealed that the voltammetric profiles for this surface are featureless in all cases. However, the laser experiments revealed that solvent restructuration, as a function of both value and direction of the applied potential, is dependent on the type of cation. Finally, the interface Au(hkl)|Choline chloride:urea Deep Eutectic Solvent (DES) was also investigated by using cyclic voltammetry and LITJT. The voltammetric response of DES was also sensitive to the orientation of the Au single crystal, and the cyclic voltammograms displayed distinct sharp and characteristic features. Nevertheless, the laser response could not provide a value of the pme for the Au(hkl)|DES interface, likely due to the complex chemical structure of the DES which, in addition, strongly adsorbs on Au(hkl)

Characterization of the interfaces between Au(hkl) single crystal basal plane electrodes and [Emmim][Tf2N] ionic liquid

The interface between Au(hkl) basal planes and the ionic liquid 1-Ethyl-2,3-dimethyl imidazolium bis(trifluoromethyl)sulfonil imide was investigated by using both cyclic voltammetry and laser-induced temperature jump. Cyclic voltammetry showed characteristic features, revealing surface sensitive processes at the interfaces Au(hkl)/[Emmim][Tf2N]. From laser-induced heating the potential of maximum entropy (pme) is determined. Pme is close to the potential of zero charge (pzc) and, therefore, the technique provides relevant interfacial information. The following order for the pme values has been found: Au(111) > Au(100) > Au(110). This order correlates well with work function data and values of pzc in aqueous solutions.Financial support from MINECTO through project CTQ2013-44083-P is greatly acknowledged. P. Sebastian also acknowledges MECD for the award of a FPU grant

Elucidating the Structure of the Cu-Alkaline Electrochemical Interface with the Laser-Induced Temperature Jump Method

A detailed description of the Cu–electrolyte interface is vital to understand the electrocatalytic properties of Cu surfaces. Herein, we combine cyclic voltammetry and the laser-induced temperature jump technique to describe the structure of the Cu(111) and Cu(100) | electrolyte interfaces in 0.1 M NaOH in a glass-free electrochemical cell. The laser-induced potential transients recorded at different potentials provided information of the surface charge distribution, which allowed us to calculate the potential of maximum entropy (pme), which can be considered as a good estimation of the potential of zero charge (pzc) of Cu(111) and Cu(100). We found that pzcCu(111) > pzcCu(100), following the same order as their respective work function values. Interestingly, the estimated pzc appears to be located at the onset potential of the OH* voltammetric feature for Cu(111) and Cu(100), which suggests that this feature shifts with the pzc of each crystallographic orientation. This is the first study that provides the experimental evidence of charge distribution at the Cu–solution interface under alkaline conditions.M.E.-E. gratefully acknowledges the Villum Foundation for the award of a Villum Young Investigator Grant (project number 19142). J.M.F. thanks the MCINN (FEDER) (Spain) project PID2019-105653GB-100

La derivación de responsabilidad de las obligaciones de la Seguridad Social en el caso de sucesión de empresa

La sucesión de empresa o subrogación empresarial es una figura que se encuentra recogida en el artículo 44 del Real Decreto Legislativo 1/1995, de 24 de marzo, por el que se aprueba el texto refundido de la Ley del Estatuto de los Trabajadores (en adelante, E.T.). El objetivo de este trabajo es analizar, desde un punto de vista tanto teórico como práctico, la forma en la que esta figura se concreta en nuestro ordenamiento jurídico, nuestra jurisprudencia y en un caso real concreto y complejo como el que aquí se expone. Para ello estructuraré el trabajo en cuatro grandes capítulos. El primero constituirá una aproximación al concepto de la sucesión empresarial. Los siguientes consistirán en el análisis pormenorizado de un caso real sobre sucesión de empresa siendo, el segundo capítulo, sobre su tramitación en vía administrativa ante la Tesorería General de la Seguridad Social, el tercero, sobre la vía judicial tramitada ante el Juzgado Contencioso Administrativo y, por último, el cuarto capítulo versará sobre la fase de apelación ante el Tribunal Superior de Justicia. El trabajo termina con un capítulo de carácter concluyente en el que, analizada la regulación jurídica española, la jurisprudencia y la aplicación en un asunto particular, se plantean las conclusiones a las que se ha llegado tras el estudio

Comportamiento en agua de mar del sistema de pinturas aplicado a soldaduras realizadas en planchas de acero imprimadas

El pintado de las uniones soldadas es un tema de gran importancia práctica pues no hay que olvidar que rara es la estructura de ingeniería en la que no interviene la soldadura durante las distintas fases de su construcción. Esta técnica de unión está teniendo un uso cada vez más creciente y ha sustituido completamente al tornillado, remachado, etc. Un ejemplo lo tenemos en la industria de construcción de barcos, donde una parte de los trabajos de fabricación corresponde a operaciones de soldadura. Una vez finalizado el ensamblaje de la estructura de acero, la misma se recubre con un sistema de protección anticorrosiva. A pesar de ser el pintado de las soldaduras una situación corriente en la práctica y de la frecuencia con que el recubrimiento empieza a fallar justamente en ellas (mientras el resto de la superficie permanece en perfecto estado), se observa falta de información sobre el tema y sobre cuáles son las variables responsables de los problemas encontrados. Se han apuntado diferentes teorías para explicar el deterioro acelerado del recubrimiento de pintura sobre el cordón de soldadura. En un principio se pensó en la acción de factores metalúrgicos propios de la zona soldada (tensiones residuales, tamaño de grano). En determinados casos se ha comprobado que, efectivamente, la existencia de inclusiones y diferencias de composición o de estructura entre la zona de fusión y áreas colindantes pueden originar importante corrosión en las uniones soldadas. Sin embargo, de acuerdo con investigaciones realizadas por la British Ship Research Association de Gran Bretaña (BSRA) la soldadura en sí no parece afectar demasiado el comportamiento de los sistemas de pintura en agua de mar. Es mucho más probable que la falla de las pinturas sea debida a las numerosas irregularidades superficiales, tanto en el cordón de soldadura como en el metal vecino al mismo. Se debe tener en cuenta que la zona de soldadura presenta singularidades que complican extra ordinariamente la correcta aplicación del revestimiento orgánico y que son potencialmente peligrosas en relación con su comportamiento. Entre ellas cabe mencionar el desnivel superficial producido por la soldadura, la presencia de salpicaduras de metal fundido y las mismas asperezas del cordón, que motivan que la pintura líquida ti en da a fluir hacia los valles, dejando los puntos más altos con un espesor de película notablemente inferior. Al mismo tiempo, la curvatura en la vecindad de la zona de unión es un lugar propicio para la acumulación de humedad y suciedad provocando así fallas en el recubrimiento . El proceso de soldadura deja sobre la superficie metálica partículas de escoria y trazas de fundente. Según la naturaleza del electrodo utilizado estos subproductos pueden contener residuos alcalinos y sales solubles (p. ej. cloruros), a menudo altamente higroscópicos, capaces de atacar las pinturas saponificares o promover ampollamiento en la película de pintura por acción osmótica. Además del peligro que supone la posibilidad de desprendimiento del óxido de soldadura de la superficie, arrastrando consigo Ja película de pintura, dicho óxido puede estimular la aparición de focos de corrosión al ser catódico con relación al acero, contribuyendo también de esta manera a la inestabilidad del recubrimiento protector. Por otra parte, las películas de óxido, como de cualquier otro tipo de suciedad, impiden el contacto íntimo de la pintura con el acero, condición fundamental para que el recubrimiento pueda desarrollar su capacidad protectora.Material digitalizado en Prebi-Sedic

Copper underpotential deposition at gold surfaces in contact with a deep eutectic solvent: New insights

The electrodeposition of copper on a polycrystalline gold electrode and on Au(hkl) single crystals was investigated in a deep eutectic solvent (DES). The DES employed consisted of a mixture of choline chloride and urea (1:2). The Au(hkl)/DES interface was studied using cyclic voltammetry in the capacitive region. The blank voltammograms showed characteristic features, not previously reported, that demonstrate the surface sensitivity of this solvent. Copper electrodeposition was then studied and it was found that this takes place through the formation of an underpotential deposition (UPD) adlayer, demonstrating the surface sensitivity of this process. Voltammetric profiles showed similarities with those obtained in aqueous solutions containing chloride, suggesting that the copper UPD in this DES is strongly influenced by the presence of chloride.Financial support from MINECO through projects CTQ2016-76221-P (AEI/FEDER, UE) and TEC2014-51940-C2-2-R (AEI/FEDER, UE) are greatly acknowledged. P. Sebastian also acknowledges MECD for FPU grant