Study of the influence of phosphoric acid in steel anaerobic corrosion via the hydrogen evolution reaction.

Although it is well known that the phosphate species are quiet electrochemically inert when considering their calculated redox potential, few studies since the end of 80’s reported electrochemical phenomenon observed in the reduction domain which were linked to the presence of phosphate species. Some authors proposed that phosphate ions and weak acids in general catalysed the electrochemical reduction of water [1-3] following the kind of reactions written above: Electrochemical reactions H2PO4- + e- Had + HPO42- (1) Had + H2PO4- + e- H2 + HPO42- (2) Acido-basic equilibrium H2PO4- + OH-- H2O + HPO42- (3) Combining the reactions, the reduction of water was obtained 2 H2O + 2e- H2 + 2OH- (4) Marinovic and Despic [1] assumed that the hydrogen evolution was more likely to occur from species other than water, since the bond between the hydrogen atom and the rest of the molecule is weaker in weak acid compared with the hydrogen-oxygen bond in a water molecule. This was shown on silver electrodes [2] and also on platinum ones [1]. In a previous work [3], we showed that phosphate ions exhibited the same electrochemical behaviour on stainless steel. A theoretical model was proposed according to the experimental data the model showed that a significant quantity of molecular hydrogen was produced by the mechanism presented above. In the present paper, the influence of phosphoric acid on hydrogen evolution reaction has been studied by voltammetry on platinum and stainless steel rotating disc electrodes. A linear correlation between acid concentration and the absolute value of the current at certain reduction potential has been verified. The effect of the pH value of the solution in the obtained current has demonstrated to be strongly related to the dissociation state of the acid. In a second part, as the hydrogen evolution reaction is the principal cathodic reaction of metal corrosion in anaerobic aqueous environments, the role that weak acids can play in this process was studied. Corrosion experiments on carbon steel were carried out in phosphoric acid solution under anaerobic conditions. The influence of hydrogen in the solution was also studied. In the absence of oxygen, a substantial increase of corrosion rate was found when carbon steel samples were submerged in low phosphoric acid concentration solution compared to that obtained in distilled water

Hydrogen production by electrolysis of a phosphate solution on a stainless steel cathode

The catalytic properties of phosphate species, already shown on the reduction reaction in anaerobic corrosion of steels, are exploited here for hydrogen production. Phosphate species work as a homogeneous catalyst that enhances the cathodic current at mild pH values. A voltammetric study of the hydrogen evolution reaction is performed using phosphate solutions at different concentrations on 316L stainless steel and platinum rotating disk electrodes. Then, hydrogen is produced in an electrolytic cell using a phosphate solution as the catholyte. Results show that 316L stainless steel electrodes have a stable behaviour as cathodes in the electrolysis of phosphate solutions. Phosphate (1 M,pH 4.0/5.0) as the catholyte can equal the performance of a KOH 25%w solution with the advantage of working at mild pH values. The use of phosphate and other weak acids as catalysts of the hydrogen evolution reaction could be a promising technology in the development of electrolysis units that work at mild pH values with low-cost electrodes and construction materials

Combining phosphate species and stainless steel cathode to enhance hydrogen evolution in microbial electrolysis cell (MEC)

Microbial electrolysis cells (MEC) must work around neutral pH because of microbial catalysis at the anode. To develop a hydrogen evolution cathode that can work at neutral pH remains a major challenge in MEC technology. Voltammetry performed at pH 8.0 on rotating disk electrodes showed that the presence of phosphate species straightforwardly multiplied the current density of hydrogen evolution, through the so-called cathodic deprotonation reaction. The mechanism was stable on stainless steel cathodes whereas it rapidly vanished on platinum. The phosphate/stainless steel system implemented in a 25 L MEC with a marine microbial anode led to hydrogen evolution rates of up to 4.9 L/h/m2 under 0.8 V voltage, which were of the same order than the best performance values reported so far. Keywords: Hydrogen; Microbial electrolysis cell (MEC); Stainless steel; Phosphat

Molecular evolution of aphids and their primary ( Buchnera sp.) and secondary endosymbionts: implications for the role of symbiosis in insect evolution.

Aphids maintain an obligate, endosymbiotic association with Buchnera sp., a bacterium closely related to Escherichia coli. Bacteria are housed in specialized cells of organ-like structures called bacteriomes in the hemocoel of the aphid and are maternally transmitted. Phylogenetic studies have shown that the association had a single origin, dated about 200-250 million years ago, and that host and endosymbiont lineages have evolved in parallel since then. However, the pattern of deepest branching within the aphid family remains unsolved, which thereby hampers tin appraisal of, for example, the role played by horizontal gene transfer in the early evolution of Buchnera. The main role of Buchnera in this association is the biosynthesis and provisioning of essential amino acids to its aphid host. Physiological and metabolic studies have recently substantiated such nutritional role. In addition, genetic studies of Buchnera from several aphids have shown additional modifications, such as strong genome reduction, high A+T content compared to free-living bacteria, differential evolutionary rates, a relative increase in the number of non-synonymous substitutions, and gene amplification mediated by plasmids. Symbiosis is an active process in insect evolution cis revealed by the intermediate values of the previous characteristics showed by secondary symbionts compared to free-living bacteria and Buchnera

Valoracion economica de servicios ambientales mediante la aplicacion del experimento de eleccion (choice experiment): Caso experimental en relictos de Nothofagus alessandri (Ruil), VII Region del Maule.

70 p.En el presente estudio se llevó a cabo una valoración económica de los servicios ambientales proporcionados por el bosque de Ruil mediante la aplicación de la metodología de valoración Choice Experiment. El objetivo fue analizar la aplicabilidad de este método, en la valoración de los servicios ambientales proporcionados por el Recurso Forestal Ruil(Nothofagus alessandri) existentes en la Región del Maule. El trabajo de campo se realizó en las comunas de Chanco y Empedrado, debido a que en ellas se concentra una importante proporción del recurso forestal Ruil. Con este propósito se realizó una encuesta a 160 familias de las comunas de Chanco y Empedrado, donde se realizaron 98 y 62 encuestas respectivamente. Se evaluaron 3 atributos (servicios ambientales) que proporciona el bosque de Ruil, los cuales fueron: superficie de Ruil efectivamente protegida, belleza escénica y el establecimiento de programas de protección y conservación de especies que habitan en estos bosques. Los resultados indican que los atributos más importantes para la población son superficie de Ruil efectivamente protegida y el establecimiento de programas de protección y conservación de especies que habitan en los bosques de Ruil, ya que la muestra encuestada esta dispuesta a pagar $787 y$371 mensuales por familia por cada uno de estos atributos respectivamente. Por otro lado, las variables sociodemográficas edad, educación e ingreso presentan una relación significativa con la elección de escenarios por parte de los entrevistados, siguiendo una tendencia similar a la presentada por otros estudios de este tipo. La metodología aplicada permitió valorar adecuadamente la disposición a pagar de los individuos por los servicios ambientales proporcionados por el recurso forestal Ruil. Por tal motivo, estudios de este tipo permiten una mejor comprensión de alternativas potenciales a la hora de gestionar los recursos naturales. La comparación de las disposiciones a pagar de los entrevistados, por cada uno de los servicios ambientales del recurso natural estudiado, índica la importancia relativa que estos le dan a cada uno de los servicios. Los resultados proporcionados por el estudio, pueden contribuir a diseñar mejores estrategias de conservación y protección del recurso forestal Ruil, enfocados en el manejo de los servicios y bienes ambientales que éste proporciona

Multivariable control for a three-phase rectifier based on deadbeat algorithm

This paper presents a deadbeat control technique applied in a voltage source rectifier to regulate both the dc voltage (active power) and reactive power injected to the grid. As the deadbeat control is based on the system model, it leads to a faster response, without overshoot and no need to tune the controller parameters. Hence, it is used to fully control the voltage source rectifier, achieving a fast dynamic response for both the dc voltage and the power factor at the point of connection. However, there are some issues related to the high amount of power required to reach the references –especially in the dc voltage¬ in a few control steps. The proposed technique also protects the equipment by limiting the maximum power drained to/from the source. The mathematical development is made as a function of the converter power in order to limit it, but at the same time tracking the references with high dynamics, characteristic typical of deadbeat control

Des aspects positifs issus des recherches en biocorrosion : de la production d'hydrogène aux biopiles à combustible

La corrosion induite par des microorganismes ou biocorrosion est un problème qui génère de lourdes pertes économiques mondiales (plusieurs milliards d'euros par an). Malgré de nombreux progrès dans la compréhension des mécanismes, la complexité du phénomène a empêché de trouver des solutions définitives au problème et inspire encore beaucoup de travaux de recherche. La participation dans le phénomène de biocorrosion de mécanismes catalytiques induits par les acides faibles a été étudiée dans ce travail. Un autre objectif de la thèse a été d'exploiter les phénomènes catalytiques mis en évidence dans les recherches en biocorrosion pour réaliser d'autres applications : production d'énergie dans des biopiles à combustible ou production d'hydrogène par voie électrochimique dans des conditions douces. Les travaux ont montré que la présence des acides faibles et des acides aminés dans des biofilms pourrait jouer un rôle important dans la biocorrosion des aciers en accélérant le phénomène par la catalyse de la réduction de l'eau. La réversibilité de ce mécanisme, pressentie et prouvée, pourrait expliquer l’augmentation de la corrosion lorsque l'hydrogène produit est évacué (consommation, agitation, …). Par ailleurs, les phosphates permettent la production d'hydrogène par électrolyse dans des conditions douces de pH (pH 4,0 - 8,0) avec une performance égale ou meilleure que celle de l'électrolyse alcaline. Enfin, les matériaux industriels, tels que l'acier et le titane, pourraient être utilisés pour la fabrication d’électrodes enzymatiques en vue d’une utilisation dans des biocapteurs ou des microsystèmes. L’utilisation du système glucose oxydase/glucose dans une pile à combustible aqueuse dont la cathode est en acier inoxydable, permet d’améliorer les performances de la pile grâce à la production du peroxyde d'hydrogène qui est très facile à réduire. En outre, l’utilisation de matériaux avec des microstructures comme les aciers grenaillés mériterait d’être approfondie pour exploiter la remarquable réactivité qu’ils présentent par rapport aux électrodes lisses. ABSTRACT : Microbially influenced corrosion or biocorrosion is a problem that generates heavy global economic losses (several billion euros per year). In spite of the progress made on the understanding of the underlying mechanisms, the complexity of the phenomenon has prevented finding definitive solutions to the problem and continues to inspire many research works. The participation in biocorrosion of catalytic mechanisms induced by weak acids was studied in this work. Another objective of the thesis has been to take advantage from catalytic phenomena found in biocorrosion research to apply them in other areas: energy production with biofuel cells or electrochemical hydrogen production in mild conditions. This work has shown that the presence of weak acids and amino acids inside biofilms could play a major role in steel biocorrosion accelerating the phenomenon through the catalysis of the water reduction reaction. The reversibility of this mechanism, discerned and proved here, could explain the corrosion increase when hydrogen is removed (bacterial consumption, agitation ...). In addition, phosphates allow the production of hydrogen by electrolysis in mild pH conditions (pH 4.0 - 8.0) with an equal or better performance than those found in alkaline electrolysis. Finally, industrial materials like stainless steel and titanium could be used in the fabrication of enzymatic electrodes for biosensors or microsystems. The use of the glucose oxidase/glucose system in an aqueous fuel cell with a stainless steel cathode, allows the improvement of the cell performance thanks to the production of hydrogen peroxide that is easily reduced. Moreover, the use of materials with microstructured surfaces like sandblasted steels deserve to be studied in detail to exploit the remarkable reactivity they present compared to smooth electrodes

A recursive paradigm for aligning observed behavior of large structured process models

The alignment of observed and modeled behavior is a crucial problem in process mining, since it opens the door for conformance checking and enhancement of process models. The state of the art techniques for the computation of alignments rely on a full exploration of the combination of the model state space and the observed behavior (an event log), which hampers their applicability for large instances. This paper presents a fresh view to the alignment problem: the computation of alignments is casted as the resolution of Integer Linear Programming models, where the user can decide the granularity of the alignment steps. Moreover, a novel recursive strategy is used to split the problem into small pieces, exponentially reducing the complexity of the ILP models to be solved. The contributions of this paper represent a promising alternative to fight the inherent complexity of computing alignments for large instances.Peer ReviewedPostprint (author's final draft

Anti-atherogenic properties associated with the antioxidant activity from the hydrophilic extracts of Halimeda incrassata (Chlorophyta, Bryopsidales)

Seaweeds are a source of natural antioxidants having potential application in oxidative stress and associated diseases. In this work, anti-atherogenic properties associated with the antioxidant activity from the hydrophilic extracts of Halimeda incrassata were studied. The phenolic content assessed inthe aqueous extract and fraction phenolic acids (FPA) was 0.13 ± 0.05 and 0.47 ± 0.09 mg of gallic acid equivalents (GAE)/g dry seaweed, respectively. In DPPH?, radical scavenging assay fractions exhibited a dependent concentration. The seaweeds extract inhibited the desoxirribose oxidation in the presenceor absence of EDTA (IC50 = 1.91± 0.09 mg/mL) (IC50 = 2.95 ± 0.01 mg/mL). In vivo antioxidant properties of FPA-H.incrassata were investigated in rats with a CCl4-induced liver injury. Pre-treatment with H.incrassata led to approximately 50% reductions in liver TBARS levels. The treatment with H. incrassataFPA also increased the activity of the CAT enzyme, which in turn resulted in an enhanced antioxidantdefense. The expression of Catalase by PCR-RT technique demonstrated a higher gene expression when compared with that which was observed in the CCl 4-treated group. Antiatherogenic properties were studied in the inhibition of lipoprotein oxidation mediated by Cu2+ or HRP/H2O2, free radicalscavenging, and metal ion chelation, and it was dose dependent with a higher concentration needed for the aqueous extract than for the FPA fraction. Antioxidant activity was also improved in macrophages as evaluated in the cell supernatant (by TBARS formation); and by luminol enhanced chemiluminescence after cell activation with zymosan; and a degree of cell lipoperoxidation wasdecreased by the Halimeda incrassata extract. The results of this work add to the antioxidant potential of the seaweed for its application in oxidative stress associated conditions.Fil: Vidal-Novoa, Alexis. Universidad de la Habana. Facultad de Biología; CubaFil: Costa-Mugica, Ariadna. Universidad de la Habana. Facultad de Biología; CubaFil: Zulueta Díaz, Yenisleidy de Las Mercedes. Universidad de la Habana. Facultad de Biología; Cuba. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Química Biológica de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Centro de Investigaciones en Química Biológica de Córdoba; ArgentinaFil: Diaz-Gutierrez, Daylín. Universidad de la Habana. Facultad de Biología; CubaFil: de Oliveira e Silva, Ana, Mara. Universidade de Sao Paulo; BrasilFil: Vazquez, Ana María. Center For Molecular Inmunology; CubaFil: Claudina, Zaldívar-Munoz. Universidad de la Habana. Facultad de Biología; CubaFil: Dalva, Assuncao Portari de Mancini. Institute Butantan Sao Paulo; BrasilFil: Mancini-Filho, Jorge. Universidade de Sao Paulo; Brasi