Electrochemical impedance spectroscropy study on the behavior of reinforced concrete elements under loading

Concrete is a material of porous nature that, when humidified, becomes an ionic conductor whose apparent conductivity depends on the ionic load (typically based on OH−, Ca2+, Na+, and K+) and the amount of available free water. Under conditions of partial pore-saturation, the amount of free water can be modulated by an external load, which leads to observable changes in electrical properties such as conductivity and capacitance. Moreover, metallic reinforcements, either as bars or fibers, represent an additional parallel conduction path but of an electronic nature in this case. The free water develops a double-layer capacitance structure at the metallic interfaces, with associated charge-transfer resistance, representing an additional contribution to the capacitive behavior that can be modulated with an external load. The dependence that the electrical and/or ionic conducting properties of concrete and reinforced concrete elements have on the available free water makes them suitable for transductors in various sensing and self-sensing applications discussed in the text.Xunta de Galicia | Ref. ED431B2021/1

Influence of pH and temperature in the performance of Zn phosphate conversion coatings

Financiado para publicación en acceso aberto: Universidade de Vigo/CISUGThe influence of variations in temperature (from 50 ◦C to 70 ◦C) and pH (2.4 and 2.9) in the Zn phosphate conversion treatment of a high-strength steel was assessed in this study. The effect of the temperature changes depends on the pH of the bath. The results evidenced an enhanced corrosion resistance with the increased temperature for baths at pH 2.4, whereas no relevant differences were concluded for baths at pH 2.9. This latter pH condition provided a better surface coverage, even with lower coating masses, than the former value. The microstructural analysis showed the development of films composed of smaller crystals for the treatments at pH 2.9. Impedance spectroscopy was established as a powerful tool with great potential for characterising phosphate layers. The accuracy of this methodology greatly depends on the equivalent circuit used for the simulation. A model based on the transmission line allows the reliable estimation of the percentage of exposed area (coating efficiency), the identification of changes in the film conductivity, and the qualitative analysis of its structureXunta de Galicia | Ref. ED431B2021/1

A comprehensive structural and electrochemical study on the performance of Mn-phosphate layers

Several manganese phosphating routes, including the influence of immersion time (15 min. and 30 min.), addition of accelerators (Ni(NO3)2, 2 g/l), modification in the activation stage (increased concentration in the activator), and ultrasonic stirring, were used to obtain films with a variety of characteristics. This research uses the following common analytical methods for the phosphate characterisation: scanning electron microscopy (SEM) and electrochemical techniques (potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS). Thus, modifications in the coating mass, covering efficiency, surface appearance, and chemical composition/structure could be determined. This study showed that accelerators induced the formation of thicker layers (up to 125 % bigger), whereas ultrasonic stirring assisted with reducing the crystal sizes and developing denser films (up to 50 % reduction in the icorr values). The dry frictional tests showed that the wear behaviour depended on the phosphate thickness, crystal density, and film tortuosity. A fine-grained structure or a thick film contributed to an improved wear performance (near 80 % reduction in the coefficient of friction), but grains that are too fine along with an intricate structure worsened the behaviour under frictional forces.Universidade de Vigo/CISU

Corrosion resistance of a water-borne resin doped with graphene derivatives applied on galvanized steel

Financiado para publicación en acceso aberto: Universidade de Vigo/CISUGThe present work reports the effect of adding Graphene Oxide (GO) and reduced Graphene Oxide (rGO) in the corrosion protection provided by a water-borne resin applied on a galvanized steel substrate. Three concentrations, 0.05, 0.1 and 0.15 (all wt%) were tested. The results were markedly affected not only by the concentration of particles but also by their nature. Although the zeta potential values suggested good dispersibility of the particles in the resin, certain aggregation was observed, mainly in rGO 0.1 wt% and rGO 0.15 wt% formulations. The electrochemical impedance spectroscopy (EIS) technique characterised the free films' transport properties. The results suggested that the aggregation strongly influenced the film morphology. The rGO 0.1 wt% and rGO 0.15 wt% formulations exhibited percolating pores that facilitated the electrolyte uptake through the films. The EIS technique was also used to study the protective performance of the films when applied to the metallic substrate. The results confirmed the harmful effect of the particle's aggregation. The results were interesting for the rGO 0.05 wt% system, which displayed long-lasting protection properties. This performance was explained considering its good barrier properties and the zinc surface passivation by the generation of zincite, ZnO

Effect of substrate microstructure on corrosion resistance of cast and forged anodised 6082 Al alloy

This work addresses the effect of the surface morphology of a 6082-aluminium alloy on the characteristics of the anodic layer generated by an anodising process using two current densities. The samples tested were horizontal direct chill (HDC), vertical direct chill (VDC) cast billets, and the same material after forged + T6 ageing treatment. Samples were anodised in a mixed citric acid‑sulphuric acid electrolyte using 0.5 A⋅dm−2 and 1.5 A⋅dm−2. D.C. current densities. The protective character of the oxide layer was studied by electrochemical impedance spectroscopy (EIS) in 0.1 M NaCl solution. Microstructural characterisation revealed that the microsegregation and forging processes have a significant effect on the growth of the oxide layer as well as on the optimum anodising conditions. The EIS study showed that the corrosion protection provided by the oxide layer on Al6082 alloy was strongly affected by the manufacturing process, with thinner oxide layers obtained for cast billets. Heat treatment and forging homogenise the microstructure, which positively affects anodising and modifies the growth rate and thickness of the oxide layer. This effect makes obtaining a thicker oxide layer with good corrosion protective properties possible by using lower current densities for forged samples.Xunta de Galicia | Ref. ED431B 2021/14Universidade de Vigo/CISU

Application of receiver operating characteristic (ROC) methodology in biological studies on marine resources: sex determination of Paracentrotus lividus (Lamarck, 1816)

The receiver operating characteristic (ROC) curve is usually used in biomedicine as an indicator of the accuracy of diagnostic tests. However, this measure of discrimination has been little used in other areas, such as animal biology or ecology. We present a novel application of an ROC analysis in which gonad colour was used to determine the sex of Paracentrotus lividus (Lamarck, 1816), a sea urchin of considerable commercial interest. A better classifier than gonad colour was obtained by transforming these colours through flexible logistic generalized additive models.Peer Reviewe

Surface waters of the NW Iberian margin: upwelling on the shelf versus outwelling of upwelled waters from the Rías Baixas

A set of hydrographic surveys were carried out in the Ría of Vigo (NW Spain) at 2–4 d intervals during four 2–3 week periods in 1997, covering contrasting seasons. Residual exchange fluxes with the adjacent shelf were estimated with a 2-D, non-steady-state, salinity–temperature weighted box model. Exchange fluxes consist of a steady-state term (dependent on the variability of continental runoff) and a non-steady-state term (dependent on the time changes of density gradients in the embayment). More than 95% of the short-time-scale variability of the exchange fluxes in the middle and outer ría can be explained by the non-steady-state term that, in turns, is correlated (R2>75%) with the offshore Ekman transport. Conversely, 96% of the variability of exchange fluxes in the inner ría rely on the steady-state term. The outer and middle ría are under the direct influence of coastal upwelling, which enhances the positive residual circulation pattern by an order of magnitude: from 10 2 to 10 3 m3s−1. On the contrary, downwelling provokes a reversal of the circulation in the outer ría. The position of the downwelling front along the embayment depends on the relative importance of Ekman transport (Qx, m3s−1km−1) and continental runoff (R, m3s−1). When Qx/ R>7±2 the reversal of the circulation affects the middle ría. Our results are representative for the ‘Rías Baixas’, four large coastal indentations in NW Spain. During the upwelling season (spring and summer), 60% of shelf surface waters off the ‘Rías Baixas’ consist of fresh Eastern North Atlantic Central Water (ENACW) upwelled in situ. The remaining 40% consists of upwelled ENACW that previously enters the rías and it is subsequently outwelled after thermohaline modification. During the downwelling season (autumn and winter), 40% of the warm and salty oceanic subtropic surface water, which piled on the shelf by the predominant southerly winds, enters the rias

«Botellon» and alcohol and other drug use in youth

El objetivo de este trabajo es analizar la relación existente entre la participación en el botellón (reuniones de jóvenes en espacios públicos para beber, charlar, etc.), el abuso de alcohol y otras drogas y la realización de conductas vandálicas en jóvenes. Para ello se ha realizado una encuesta escolar en centros educativos de Secundaria, Bachillerato, ciclos de Formación Profesional y Universidad en la ciudad de Lugo. La muestra, de edades comprendidas entre los 12 y los 30 años, fue dividida en tres grupos en función de su consumo de alcohol y la participación en el botellón, y se analizó el nivel de abuso de drogas, los problemas asociados con esos abusos y el grado de implicación en actos vandálicos. Los resultados muestran que aquellos que participan habitualmente en el botellón presentan mayores problemas con el alcohol y otras drogas. Son también los que más actos vandálicos realizan. Esa relación se observa con mayor intensidad en los estudiantes más jóvenes. El incremento del riesgo en los adolescentes asociado a la práctica del botellón es explicado por la presión del grupo de amigos hacia el consumo y por la mayor accesibilidad al alcohol y otras drogas en estos contextosThe main aim of this paper is to analyze the relationships of involvement in the "botellon" (meetings of youth in public places to drink, chat, etc.) with alcohol/other drug abuse and vandalism in young people. A school survey was performed in centres of Compulsory Secondary School (E.S.O.), high school, professional training and University education in Lugo, NW Spain. The sample (aged 12 to 30) was split into three groups according to alcohol use and botellon involvement; drug abuse, drug-related problems and vandalism were assessed in each group. Results indicate that regular botellon attendants display more problems with alcohol and other drugs, as well as higher involvement in vandalism; this relationship is stronger among young students. The increase in adolescent risk associated with the practice of the botellon is explained by peer group pressure to use drugs and the greater accessibility of alcohol/other drugs in these contextsS

Modelling spatial patterns of distribution and abundance of mussel seed using Structured Additive Regression models

As mussel farming depends on sources of natural mussel seed, knowledge of factors is required to regulate both the spatial distribution and abundance of this resource. These spatial patterns were modelled using Bayesian STructured Additive Regression (STAR) models for categorical data, based on a mixed-model representation. We used Bayesian penalized splines for modelling the continuous covariate effects and a Markov random field prior for estimating the spatial effects

Air-sea CO2 fluxes in the Atlantic as measured during the FICARAM cruises

A total of fourteen hydrographic cruises spanning from 2000 to 2008 were conducted during the spring and autumn seasons between Spain and the Southern Ocean, under the framework of the Spanish research project FICARAM. The performed underway measurements are processed and analysed to describe the meridional air-sea CO2 fluxes (F CO2) along the Atlantic Ocean. The data was organised into different biogeochemical oceanographic provinces, according mainly to the thermohaline characteristics. The obtained spatial and temporal distributions of F CO2 follow the generally expected patterns and annual trends. The Subtropical regions in both hemispheres alternated the CO2 source and sink nature from autumn to spring, respectively. On the other hand, Tropical waters and the Patagonian Sea clearly behaved as sinks of atmospheric CO2 like the waters of the Drake Passage during autumn. The obtained results during the cruises also revealed significant long-term trends, such as the warming of equatorial waters (0.11±0.03 Cyr−1) and the decrease of surface salinity (−0.16±0.01 yr−1) in tropical waters caused by the influence of the Amazon River plume. This reduction in surface salinity appears to have a direct influence over the CO2 storage rates, fostering the uptake capacity of atmospheric CO2 (−0.09±0.03 molm−2 yr−1). An analysis of the biogeochemical forcing on the CO2 fugacity (fCO2) variability performed from an empirical algorithm highlighted the major role of the Amazon River input in the tropical North Atlantic fluxes. In addition, it has provided a quantitative measure of the importance of the thermodynamic control of F CO2 at temperate latitudes