Viscoelastic Fluid Simulation with OpenFOAM

Since non-Newtonian fluids were discovered, their numerous interesting behaviours and potential uses have been investigated. Particularly, the frequency-dependent properties of wormlike micellar solutions have risen a good deal of interest among the scientific community. In this report, we have attempted to simulate those properties using the Giesekus model for viscoelastic fluids and, more precisely, we have tried to obtain a velocity profile with resonant behaviour inside a cylinder cavity. The computational environment chosen to perform the simulations is OpenFOAM, an open-source CFD program with great flexibility and capabilities. The results confirm a resonant response to oscillating boundary conditions, although perfect stationary-like velocity profiles were not obtained.2019/202

Polarized hydroxyapatite: wew insights and future perspectives through systematic electrical characterization at the interface

Design of hydroxyapatite (HAp) with customized electrical properties is of special interest for developing technological and biomedical applications with new improved functionalities. Polarized HAp, which is obtained by applying an external electric voltage at high temperature, has been successfully shown to be an alternative to doped-HAp that is limited by the biocompatibility of the dopants used. However, many aspects about such new material remain scarcely studied, as for example the relationship between the polarization conditions and the resultant electrical enhancement, hinder a solid progress in its application. In this work, polarized HAp has been extensively characterized using electrochemical impedance spectroscopy by means of proposing a unified electrical equivalent circuit model with physical sense. This allows to explain the properties of such material by separating the bulk and the interface contributions. Moreover, the limits of the polarization mechanism have been explored, enabling a precise control on the electrical resistivity of polarized HAp above or below the intrinsic resistivity of nonpolarized HAp. Overall, necessary insights on the polarization treatment have been reported, opening an appealing avenue for generating new biomedical and technological applications based on dopant-free polarized HAp.Peer ReviewedPostprint (published version

Regulating the superficial vacancies and OH- orientations on polarized hydroxyapatite electrocatalysts

Smart designs of hydroxyapatite (HAp) materials with customized electrical properties are drawing increasing attention for their wide range of potential applications. Such enhanced electrical properties directly arise from the number and orientation of OH- groups in the HAp lattice. Although different polarization treatments have been proposed to enhance the final conductivity by generating vacancies at high temperatures and imposing specific OH- orientations through electric voltages, no direct measurement showing the evolution that OH- groups undergo has been described yet. In this article, the first direct empirical observation that allows the characterization of both the generation of vacancies and the polarization of OH- groups is reported. The mechanisms behind the electrical enhancement are elucidated allowing to distinguish between charge accumulation at the crystal grains, which is due to the formed vacancies, and charge accumulation in the boundaries of particles. In addition, a linear dependence between the number of vacancies and the superficial charge is observed. Therefore, it is demonstrated that the charge accumulation at the micrometric grain boundaries has a great impact on the catalytic properties of the thermally stimulated polarized HAp. These results will be used for further optimization of the catalyst properties.Peer ReviewedPostprint (author's final draft

Sediment undulations on the Llobregat prodelta: Signs of early slope instability or sedimentary bedforms?

A field of sediment undulations has been mapped by means of high resolution multibeam bathymetry and seismic reflection profiles in the Llobregat River prodelta, off the city of Barcelona, Catalonia, Spain. Similar features had previously been recognized in other prodelta environments and interpreted either as downslope sediment deformation or sedimentary structures induced by bottom currents or hyperpycnal flows. Since the study area is undergoing significant offshore development, proper interpretation of such sediment undulations is needed for a correct risk assessment. The occurrence of the sediment undulations is restricted to the prodelta front on slope gradients between 3 and 0.2º. The undulations have developed at the edge and atop an area of gas bearing sediments within the Late-Holocene high-stand mud wedge. An evaluation is made of the characteristics of the sediment undulations in order to determine the most likely process for the origin of these structures. Amongst these characteristics are the continuity of the reflections and lack of diffractions in between different undulations, their size distribution (large to small) both from shallow to deep and with depth in section, the asymmetry (decreasing from proximal to distal), the crest to trough vertical distance on the landward side of the undulations (up to 0.5 m), and the lack of features that could indicate a progressive movement such as growth structures and drag folds. These characteristics indicate that the sediment undulations on the Llobregat River prodelta do not result from sediment deformation, but rather from the interaction of bottom currents generated by hyperpycnal flows from the Llobregat River with regional sea water circulation. Their identification as sediment waves implies that such features do not pose a major hazard for urther offshore development

Optimization of the physical and chemical properties of polarized hydroxyapatite catalysts

Although materials such as hydroxyapatite (Ca5(PO4)3(OH), HAp), have been studied for a while, still possess great interest due to the electrical properties and biocompatibility that offer in endless applications. The use of HAp as a catalyst is the research field in which this degree final thesis is focused. Aiming to enhance the catalytic activity of HAp, two projects have been carried out. In the first one, the main goal is to study the origin of its electrical properties and effect on the material. In order to observe that, two processes have been applied to samples, a thermal treatment which generated OH? vacancies in the HAp lattice and a thermal stimulated polarization (TSP) process allowing the reorientation of the remaining OH? groups acting as dipoles. The electrical properties which arise from the treatments have been successfully characterized using Raman spectroscopy, Zeta potential and Atomic Force Microscopy (AFM) techniques. The mechanisms behind the electrical enhancement have been elucidated allowing the distinction between charge accumulation at the crystal grains, which is due to the formed vacancies, from charge accumulation in the boundaries of particles, thus understanding the catalytic activation of HAp. In the second project, the main objective is to create porous HAp so that increasing the catalytic surface, the yield of the reaction increases too. The incorporation of HAp to a Pluronic® hydrogel matrix is performed giving result to a mixed viscous paste. By selecting the concentration of HAp, the viscosity of the aforementioned paste allows to create macrostructures, give them the desired shape and to maintain it by calcinating them later. The resulting porous HAp has its lattice structure un-altered which was determined through X-ray Diffraction and Raman spectroscopy. SEM microscopy corroborates the existence of pores and its dimensions. The flow rate absorption is performed to characterize the material. Finally, carbon fixation reactions using porous and non-porous HAp catalysts are performed and analyzed to observe if the porous HAp has better catalytic performance. The porous HAp yield is higher compared to the non-porous one, thus achieving the goal to optimize the material for a boosted catalytic activity.Aunque materiales como la hidroxiapatita (Ca5(PO4)3(OH), HAp), se han estudiado durante un tiempo, aún poseen un gran interés debido a las propiedades eléctricas y biocompatibilidad que ofrecen en un sinfín de aplicaciones. El uso de HAp como catalizador es el campo de investigación en el que se centra esta tesis final de grado. Con el objetivo de potenciar la actividad catalítica de HAp, se han llevado a cabo dos proyectos. En el primero, el objetivo principal es estudiar el origen de sus propiedades eléctricas y su efecto sobre el material. Para observar esto, se han aplicado dos procesos a las muestras, un tratamiento térmico que generó vacantes de OH? en la red de HAp y un proceso de polarización estimulada térmicamente (TSP) que permite la reorientación de los restantes grupos OH? actuando como dipolos. Las propiedades eléctricas que surgen de los tratamientos se han caracterizado con éxito mediante técnicas de espectroscopia Raman, potencial Zeta y microscopía de fuerza atómica (AFM). Los mecanismos detrás de la mejora eléctrica se han aclarado permitiendo la distinción entre la acumulación de carga en los granos de cristal, que se debe a las vacantes formadas, de la acumulación de carga en los límites de las partículas, entendiendo así la activación catalítica de HAp. En el segundo proyecto, el objetivo principal es crear HAp poroso para que al aumentar la superficie catalítica, también aumente el rendimiento de la reacción. Se realiza la incorporación de HAp a una matriz de hidrogel Pluronic® dando como resultado una pasta viscosa mixta. Al seleccionar la concentración de HAp, la viscosidad de la pasta mencionada permite crear macroestructuras, darles la forma deseada y mantenerla calcinando posteriormente. La HAp porosa resultante tiene su estructura reticular inalterada, que se determinó mediante difracción de rayos X y espectroscopía Raman. La microscopía SEM corrobora la existencia de poros y sus dimensiones. La absorción de agua se realiza para caracterizar el material. Finalmente, se realizan y analizan reacciones de fijación de carbono utilizando catalizadores HAp porosos y no porosos para observar si la HAp porosa tiene un mejor rendimiento catalítico. El rendimiento de la HAp porosa es mayor en comparación con el de la no porosa, logrando así el objetivo de optimizar el material para una actividad catalítica reforzada.Tot i que s'han estudiat materials com la hidroxiapatita (Ca5(PO4)3(OH), HAp) durant un temps, encara tenen un gran interès a causa de les propietats elèctriques i la biocompatibilitat que ofereixen en infinites aplicacions. L'ús de l'HAp com a catalitzador és el camp d'investigació en què es centra aquest treball de final de grau. Amb l'objectiu de millorar l'activitat catalítica de HAp, s'han dut a terme dos projectes. En el primer, l'objectiu principal és estudiar l'origen de les seves propietats elèctriques i l'efecte sobre el material. Per tal d'observar això, s'han aplicat dos processos a les mostres, un tractament tèrmic que va generar vacants d'OH a l'estructura de l'HAp i un procés de polarització estimulada tèrmicament (TSP) que permet la reorientació dels grups OH restants que actuen com a dipols. Les propietats elèctriques derivades dels tractaments s'han caracteritzat amb èxit mitjançant tècniques d'espectroscòpia Raman, potencial Zeta i microscòpia de força atòmica (AFM). Els mecanismes darrere de la millora elèctrica s'han dilucidat permetent la distinció entre l'acumulació de càrrega als grans de cristall, que es deu a les vacants formades, des de l'acumulació de càrrega als límits de les partícules, entenent així l'activació catalítica de l'HAp. En el segon projecte, l'objectiu principal és crear HAp porosa de manera que augmentant la superfície catalítica, també augmenti el rendiment de la reacció. La incorporació de HAp a una matriu d'hidrogel Pluronic® es realitza, donant com a resultat una pasta viscosa mixta. En seleccionar la concentració de HAp, la viscositat de la pasta esmentada permet crear macroestructures, donar-los la forma desitjada i mantenir-la calcinant-les posteriorment. El HAp porosa resultant no veu alterada la seva estructura, que es va determinar mitjançant la difracció de raigs X i l'espectroscòpia Raman. La microscòpia SEM corrobora l'existència de porus i les seves dimensions. L'absorció d'aigua es realitza per caracteritzar el material. Finalment, es realitzen i s'analitzen reaccions de fixació de carboni mitjançant catalitzadors d'HAp porosos i no porosos per observar si l'HAp porosa té un millor rendiment catalític. El rendiment de HAp porosa és superior en comparació amb el no porosa, aconseguint així l'objectiu d'optimitzar el material per a una activitat catalítica augmentada

Viscoelastic Fluid Simulation with OpenFOAM

Since non-Newtonian fluids were discovered, their numerous interesting behaviours and potential uses have been investigated. Particularly, the frequency-dependent properties of wormlike micellar solutions have risen a good deal of interest among the scientific community. In this report, we have attempted to simulate those properties using the Giesekus model for viscoelastic fluids and, more precisely, we have tried to obtain a velocity profile with resonant behaviour inside a cylinder cavity. The computational environment chosen to perform the simulations is OpenFOAM, an open-source CFD program with great flexibility and capabilities. The results confirm a resonant response to oscillating boundary conditions, although perfect stationary-like velocity profiles were not obtained.2019/202

Hydroxyapatite-based catalysts for CO2 fixation with controlled selectivity towards C2 products. Phenomenal support or active catalyst?

Permanently polarized hydroxyapatite (p-HAp) has been reported as a feasible green alternative to conventional catalysts for the selective conversion of CO2 into highly valuable chemical products. However, structural control and enhanced electrical properties achieved on p-HAp clearly contrast with other reported catalytic systems, where hydroxyapatite mainly acts as a support receiving much less attention. In this work we take advantage of the knowledge obtained on p-HAp to develop an HAp-based catalytic system composed of TiO2 nanoparticles deposited on p-HAp. It is important to stress that p-HAp is not only considered as a mechanical support but has been put in the spotlight for catalyst preparation and as an active catalytic part. Therefore, the use of p-HAp in this system has unveiled exceptional synergies with TiO2 attributed to the enhanced electrical properties of p-HAp, capable of attracting the photo-electrons generated in TiO2 nanoparticles avoiding electron–hole recombination. CO2 fixation reactions carried out under mild conditions (120 °C, 6 bar and under UV exposure) result in complete selectivity control of the C2 products, shifting from ethanol (201 µmol gcatalyst-1) for p-HAp alone to acetic acid (381 µmol gcatalyst-1) when TiO2 nanoparticles are loaded in the system. Considering the challenging CO2 activation energy and the high control of the selectivity achieved, we do believe that this novel approach can be considered as a starting point to explore other systems and reactions where control of the crystal structure and the enhanced electrical properties of HAp can play a crucial role in the final products, reaction conditions, yields and selectivities.Peer ReviewedPostprint (author's final draft

Decarbonization of polluted air by solar-driven CO2 conversion into ethanol using animal solid waste as catalyst

CO2 conversion to added value products using green processes in terms of source of energy, energy consumption, and/or management of raw materials obtained from waste materials are very attractive approaches for a modern sustainable society. In this work, such approaches are integrated, converting CO2 into ethanol by using polluted air as feeding gas. More specifically, recycled permanently polarized hydroxyapatite catalysts are prepared by applying a thermally stimulated polarization process to pork, beef, and chicken scrapped bones. The recycled bone catalysts are used to perform a series of reactions fed with polluted air and only powered with solar energy using a solar furnace. Reactions are conducted for 5 days and 1 month. Results demonstrate significant decarbonization, converting CO2 into valuable chemical products with high selectivity toward ethanol (up to 99.6%).Peer ReviewedPostprint (author's final draft

Permanently polarized materials: an approach for designing materials with customized electrical properties

The development of experimental procedures to transform conventional materials into new materials with unique properties has become a necessity in many fields, as for example catalysis, electronics, electrochemistry and biomedicine, among others. In recent years, the thermal stimulated polarization (TSP) treatment, which consists of applying a constant voltage at a high temperature, has been applied to hydroxyapatite, Ca5(PO4)3OH (HAp), leading to permanently polarized HAp (p-HAp). The enhanced electrical properties of p-HAp, which are the consequence of the controlled generation of vacancies, the specific orientation of the remaining OH– groups and the surface charge accumulation have been used for the catalytic fixation of CO2, CH4 and/or N2 under very mild conditions (<120 °C) and with accurate selectivity toward different reaction products (up to 95%). In this Perspective, we stablish the fundamentals of permanently polarized materials, providing the generalized concepts of the permanent polarized state and some representative examples of applying the TSP approach to a wide variety of materials. More specifically, we provide empirical evidence of the polarized state after applying the TSP treatment to quartz nanopowder, binary metal oxides (TiO2 and ZrO2) and different synthetic polymers, confirming the obtaining of enhanced electrical properties and the associated structural changes. Finally, the implications, challenges and perspectives of the polarized state are discussed considering different fields, such as catalysis, biomedicine, optics and electronics, sensors and energy storage devices.Peer ReviewedPostprint (author's final draft

Regulating the Superficial Vacancies and OH −

Smart designs of hydroxyapatite (HAp) materials with customized electrical properties are drawing increasing attention for their wide range of potential applications. Such enhanced electrical properties directly arise from the number and orientation of OH- groups in the HAp lattice. Although different polarization treatments have been proposed to enhance the final conductivity by generating vacancies at high temperatures and imposing specific OH- orientations through electric voltages, no direct measurement showing the evolution that OH- groups undergo has been described yet. In this article, the first direct empirical observation that allows the characterization of both the generation of vacancies and the polarization of OH- groups is reported. The mechanisms behind the electrical enhancement are elucidated allowing to distinguish between charge accumulation at the crystal grains, which is due to the formed vacancies, and charge accumulation in the boundaries of particles. In addition, a linear dependence between the number of vacancies and the superficial charge is observed. Therefore, it is demonstrated that the charge accumulation at the micrometric grain boundaries has a great impact on the catalytic properties of the thermally stimulated polarized HAp. These results will be used for further optimization of the catalyst properties.Peer ReviewedPostprint (author's final draft