Artículos (Ingeniería y Ciencia de los Materiales y del Transporte)

URI permanente para esta colecciónhttps://hdl.handle.net/11441/11377

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A Novel, Simple and Highly Efficient Route to Obtain PrBaMn2O5+δ Double Perovskite: Mechanochemical Synthesis
(MDPI, 2021-02) García-García, Francisco J.; Sayagués de Vega, María Jesús; Gotor Martínez, Francisco José; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Junta de Andalucía
In this work, a mechanochemical route was proposed for the synthesis of the PrBaMn2O5+ (PMBO) double layered perovskite phase. The mechanochemical reaction between Pr6O11, BaO2, and MnO powders with cationic stoichiometric ratios of 1/1/2 for Pr/Ba/Mn was performed using highenergy milling conditions in air. After 150 min of milling, a new phase with perovskite structure and cubic symmetry consistent with the A-site disordered Pr0.5Ba0.5MnO3 phase was formed. When this new phase was subsequently annealed at a high temperature in an inert Ar atmosphere, the layered PrBaMn2O5+ phase was obtained without needing to use a reducing atmosphere. At 1100 C, the fully reduced layered PrBaMn2O5 phase was achieved. A weight gain was observed in the 200–300 C temperature range when this fully reduced phase was annealed in air, which was consistent with the transformation into the fully oxidized PrBaMn2O6 phase. The microstructural characterization by SEM, TEM, and HRTEM ascertained the formation of the intended PrBaMn2O5+ phase. Electrical characterization shows very high electrical conductivity of layered PBMO in a reducing atmosphere and suitable in an oxidizing atmosphere, becoming, therefore, excellent candidates as solid oxide fuel cell (SOFC electrodes).
Consolidation by MF-ERS of mechanically alloyed Al powder
(Elsevier, 2019-07) Sánchez Caballero, Eduardo; Ternero Fernández, Fátima; Astacio López, Raquel; Cuevas, F. G.; Montes Martos, Juan Manuel; Cintas Físico, Jesús; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; Ministerio de Economía y Competitividad (MINECO). España; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Universidad de Sevilla. TEP971: Ingeniería de Materiales Avanzados
The aim of this work is to study the viability of producing, by medium-frequency electrical resistance sintering (MF-ERS), compacts from mechanically alloyed aluminium powders. The MF-ERS process was carried out using different values of current intensity (6, 8, 10 and 11 kA) and dwelling (heating) times (400, 700 and 1000 ms). Results were compared with compacts processed by the conventional cold pressing and sintering route (850 MPa and 650 C-1h). Depending on the processing route different properties were obtained. The final porosity of the MF-ERS compacts (23.6e7%) can be as low, under the tougher tested sintering conditions, as that of the conventionally produced compacts (6%). The compacts obtained by MF-ERS are less ductile, with lower compression strength than that obtained by the conventional route. Furthermore, a similar electrical resistance and higher microhardness can be reached by the MF-ERS process, despite the duration of the consolidation process is only a fraction of that of the conventional process.
Deposición sol-gel de hidroxiapatita bioactiva sobre titanio poroso
(ECIMED, 2017) Peón Avés, Eduardo; Domínguez-Trujillo, Cristina; Pérez, H.; Galván, J.C.; Rodríguez-Ortiz, José Antonio; Pavón Palacio, Juan José; Torres Hernández, Yadir; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; Ministerio de Ciencia e Innovación; Junta de Andalucía; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER)
Introducción: el titanio y algunas de sus aleaciones son considerados la mejor opción para fabricar implantes permanentes, debido a sus excelentes propiedades mecánicas y resistencia a la corrosión en el ambiente fisiológico, además de su buena biocompatibilidad y osteointegración. Objetivo: solucionar algunas de las limitaciones más significativas de los implantes de titanio: fenómenos de fatiga y falla de la biointerfase. Métodos: muestras de titanio qp grado IV con porosidad de 250-355 μm, fueron obtenidas por la técnica de space-holder (50 % vol. NH4HCO 3, 800 MPa y 1250 ºC durante 2 h en alto vacío), produciéndose buen balance entre rigidez y resistencia mecánica del material. Detrás los sustratos de titanio poroso fueron recubiertos con hidroxiapatita obtenida vía sol-gel, por inmersión, secadas a 80 ºC y tratadas térmicamente a 450 ºC durante 5 h en vacío. La formación de fase, morfología de la superficie, microestructura interfacial, capacidad de infiltración y sección transversal de los recubrimientos, fue investigada por diferentes métodos de análisis químicofísico Resultados: los análisis de espectroscopia infrarroja de transformada de Fourier y difracción de rayos X mostraron la cristalinidad de la fase y la homogeneidad en la composición química del recubrimiento. La evaluación micromecánica y adherencia del recubrimiento (curvas de P-h y resistencia al rayado) demostraron una buena adherencia del recubrimiento al sustrato metálico. El recubrimiento fue poroso sin evidencia de formación de grietas. Estos poros aparecen interconectados formando una red continua, característica morfológica que es una ventaja para permitir la circulación de fluido fisiológico, cuando se utiliza el sistema para aplicaciones biomédicas. Conclusiones: la cristalinidad satisfactoria y adhesión entre el recubrimiento y el sustrato sugieren el sistema como promisorio para aplicaciones en el desarrollo de implantes ortopédicos.
Effect of pH Hydrolysis on the Recovery of Antimony from Spent Electrolytes from Copper Production
(MDPI, 2023-05) Díaz Gutiérrez, Eduardo; Maldonado Calvo, José A.; Gallardo Fuentes, José María; Paúl Escolano, Antonio; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Universidad de Sevilla. TEP973: Tecnología de Polvos y Corrosión; Universidad de Sevilla. TEP123: Metalurgia e Ingeniería de los Materiales
This study examined how pH hydrolysis affects the recovery process for antimony extracted from spent electrolytes. Various OH⁻ reagents were used to adjust the pH levels. The findings reveal that pH plays a crucial role in determining the optimal conditions for extracting antimony. The results show that NH₄OH and NaOH are more effective compared to water, with optimal conditions at pH 0.5 for water and pH 1 for NH₄OH and NaOH, resulting in average antimony extraction yields of 90.4%, 96.1%, and 96.7%, respectively. Furthermore, this approach helps to improve both crystallography and purity related to recovered antimony samples obtained through recycling processes. The solid precipitates obtained lack a crystalline structure, making it difficult to identify the compounds formed, but element concentrations suggest the presence of oxychloride or oxide compounds. Arsenic is incorporated into all solids, affecting the purity of the product, and water showing higher antimony content (68.38%) and lower arsenic values (8%) compared to NaOH and NH₄OH. Bismuth integration into solids is less than arsenic (less than 2%) and remains unaffected by pH levels except in tests with water, where a bismuth hydrolysis product is identified at pH 1, accounting for the observed reduction in antimony extraction yields.
Electrical discharge consolidation of Al and Ti powders
(Elsevier, 2022-07-29) Ternero Fernández, Fátima; Aranda Louvier, Rosa María; Urban, Petr; Astacio López, Raquel; Montes Martos, Juan Manuel; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER)
In this paper, electrical-discharge-consolidation (EDC technique) experiments were carried out with an equipment based on the technology developed for the stud welding technology. The main advantage of the EDC technique is its high speed, on the order of milliseconds or less, which makes it particularly interesting when a high final porosity is aimed, or when the inherent nanostructure of the powders needs to be preserved. Compacts of Ti and Al were consolidated with this technique, both directly from loose powders and from cold pressed green compacts. Two different configurations (200 V – 66 mF and 800 V − 1.1 mF) were tested. Relative density, microhardness, electrical resistivity and metallographic and SEM studies were carried out to understand the changes in powder particles caused by the electrical discharge. The use of a high capacitance in the capacitors bank, despite the use of a lower voltage, results in a better consolidation process.
Estimating of bootstrap confidence intervals for freight transport matrices
(Elsevier, 2014) Benitez, Francisco G.; Romero Pérez, Luis Miguel; Caceres, Noelia; Castillo Granados, José María del; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Universidad de Sevilla. TEP118: Ingeniería de los Transportes
Freight transport studies require, as a preliminary step, a survey to be conducted on a sample of the universe of agents, vehicles and/or companies of the transportation system. The statistical reliability of the data determines the goodness of the outcomes and conclusions that can be inferred from the analyses and models generated. The methodology contained herein, based on bootstrapping techniques, allows us to generate the confidence intervals of origin-destination pairs defined by each cell of the matrix derived from a freight transport survey. To address this study a data set from a statistically reliable freight transport study conducted in Spain at the level of multi-province inter-regions has been used.
Exploring strengths and weaknesses of mobility inference from mobile phone data vs. travel surveys
(Taylor & Francis, 2020-01) Cáceres, Noelia; Romero Pérez, Luis Miguel; García Benítez, Francisco; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Junta de Andalucía; Programa Torres Quevedo (PTQ); Universidad de Sevilla. TEP118: Ingeniería de los Transportes
Origin–destination (OD) matrices serve as a basis for travel demand modelling. Traditionally, they are derived from travel surveys that collect detailed trip information but with several shortcomings. Mobile phones are regarded as a useful source of information on people’s daily mobility. This work explores the use of mobile data in the context of mobility studies by comparing matrices derived from both types of sources over the same region. The results reveal many common features in the trip information. Moreover, although the use of mobile technology may raise questions for short trips, the huge representativeness of this technology captures the mobility in OD connections extensively regardless the area. This is crucial for non-populated areas (e.g. industrial parks or educational campuses), which constitute important mobility hotspots. Based on these findings, an applicable data fusion approach to obtain the optimum accuracy from these heterogeneous sources is presented and applied
Gallium-containing mesoporous nanoparticles influence in-vitro osteogenic and osteoclastic activity
(Elsevier, 2024-09) Kurtuldu, Fatih; Mutlu, Nurshen; Friedrich, Ralf P.; Beltrán, Ana M.; Liverani, Liliana; Detsch, R.; Alexiou, Christoph; Galusek, Dušan; Boccaccini, Aldo R.; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; European Union (UE). H2020; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Universidad de Sevilla. TEP123: Metalurgia e Ingeniería de los Materiales
Mesoporous silica nanoparticles were synthesized using a microemulsion-assisted sol-gel method, and calcium, gallium or a combination of both, were used as dopants. The influence of these metallic ions on the physicochemical properties of the nanoparticles was investigated by scanning and transmission electron microscopy, as well as N2 adsorption-desorption methods. The presence of calcium had a significant impact on the morphology and textural features of the nanoparticles. The addition of calcium increased the average diameter of the nanoparticles from 80 nm to 150 nm, while decreasing their specific surface area from 972 m2/g to 344 m2/g. The nanoparticles of all compositions were spheroidal, with a disordered mesoporous structure. An ion release study in cell culture medium demonstrated that gallium was released from the nanoparticles in a sustained manner. In direct contact with concentrations of up to 100 μg/mL of the nanoparticles, gallium-containing nanoparticles did not exhibit cytotoxicity towards pre-osteoblast MC3T3-E1 cells. Moreover, in vitro cell culture tests revealed that the addition of gallium to the nanoparticles enhanced osteogenic activity. Simultaneously, the nanoparticles disrupted the osteoclast differentiation of RAW 264.7 macrophage cells. These findings suggest that gallium-containing nanoparticles possess favorable physicochemical properties and biological characteristics, making them promising candidates for applications in bone tissue regeneration, particularly for unphysiological or pathological conditions such as osteoporosis.
Improvement of the balance between a reduced stress shielding and bone ingrowth by bioactive coatings onto porous titanium substrates
(Elsevier, 2018-03) Domínguez Trujillo, Cristina; Ternero Fernández, Fátima; Rodríguez Ortiz, José Antonio; Díaz Pavón, Juan José; Montealegre-Meléndez, Isabel; Arévalo Mora, Cristina María; García Moreno, Francisco; Torres Hernández, Yadir; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; Junta de Andalucía; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Ministerio de Economia, Industria y Competitividad (MINECO). España; Universidad de Sevilla. TEP123: Metalurgia e Ingeniería de los Materiales
Commercial pure titanium is known as good substitute for cortical bone tissue. Nevertheless, stress-shielding and the lack of osseointegration are still some limitations to solve. In this study, porous titanium substrates were manufactured by space-holder technique (50 vol% of NH4HCO3 with particle size between 250 and 355 μm). The obtained stiffness and yield strength of specimens were compatible with cortical bone tissue. The substrates were coated with three layers of Bioglass® 45S5 (BG) by dripping sedimentation, a new and economic technique. The porosity and surface characterization were performed by Archimedes' method, image analysis, X-ray micro computed tomography and confocal laser microscopy, while the mechanical behavior was analyzed by ultrasound technique, uniaxial compression and micro-mechanical testing. Homogeneity, infiltration efficiency and coating integrity were evaluated. The adhesion of the coating was better on porous titanium substrates than on full dense ones. Finally, the bioactivity of the BG coating was determined via immersion in Simulated Body Fluid. The formation and growth of hydroxyapatite on the substrate were studied by scanning electron microscopy and X-ray diffraction analysis. The results showed hydroxyapatite formation in both coated full dense and porous samples. These features indicate the improvement of osseointegration for this sort of load bearing Ti implants
In Vitro Bone Cell Behavior on Porous Titanium Samples: Influence of Porosity by Loose Sintering and Space Holder Techniques
(MDPI, 2020-05-25) Civantos, Ana; Giner García, Mercedes; Trueba Muñoz, Paloma; Lascano, Sheila; Montoya García, María José; Arévalo Mora, Cristina María; Vázquez Gámez, María de los Ángeles; Allain, Jean Paul; Torres Hernández, Yadir; Universidad de Sevilla. Departamento de Citología e Histología Normal y Patológica; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; Universidad de Sevilla. Departamento de Medicina; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Junta de Andalucía; Universidad Complutense de Madrid
A great variety of powder metallurgy techniques can produce biomimetic porous titanium structures with similar mechanical properties to host bone tissue. In this work, loose sintering and space holder techniques, two frequently used metallurgical techniques, are compared to evaluate the influences of porosity (content, size, morphology and wall roughness), mechanical properties (stiffness and yield strength) and in-vitro cellular responses (adhesion and proliferation of myoblasts and osteoblasts). These comparisons are made to achieve the best balance between biomechanical and bifunctional behavior of a partial porous implant for cortical bone replacement. Cell adhesion (filopodia presence) and spreading were promoted on both porous surfaces and fully dense substrates (non-porous control surfaces). Porous scaffold samples designed using 50 vol.% NaCl space holder technique had an improved bioactive response over those obtained with the loose sintering technique due to higher roughness and scaffold pore diameter. However, the presence of large and heterogeneous pores compromises the mechanical reliability of the implant. Considering both scenarios, the substrates obtained with 40 vol.% NH4HCO3 and pore size ranges between 100 and 200 μm provide a balanced optimization of size and strength to promote in-vitro osseointegration.
Influence of Temperature on Mechanical Properties of AMCs
(MDPI, 2020-06) Caballero, E.S.; Ternero Fernández, Fátima; Urban, Petr; Gómez Cuevas, Francisco de Paula; Cintas Físico, Jesús; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; Ministerio de Economía y Competitividad (MINECO). España; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER)
This research focused on studying the effect of temperature on the mechanical properties of aluminium matrix composites (AMCs) obtained by a powder metallurgy route. Aluminium powder was milled at room temperature for 5 h and using di erent atmospheres in order to achieve di erent amounts of reinforcement. The atmospheres employed were vacuum, confined ammonia, and vacuum combined with a short-time (5 and 10 min) of ammonia gas flow. After mechanical alloying, powders were consolidated by cold uniaxial pressing (850 MPa) and vacuum sintering (650 º C, 1 h). hardness and tensile tests, on consolidated samples, were carried out at room temperature. Subsequently, the effect of temperature on both properties were evaluated. On one hand, the UTS and hardness were measured, again at room temperature, but after having subjected the sintered samples to a prolonged annealing (400 ºC, 100 h). On the other hand, the tensile and hardness behaviour were also studied, while the samples are at high temperature, in particular 250 ºC for UTS, and in the range between 100 and 400 ºC for hardness. Results show that the use of ammonia gas allows achieving mechanical properties, at room and high temperature, higher than those of the commercial alloys EN AW 2024 T4, and EN AW 7075 T6.
Influences of the solid load on the microstructure and compressive behavior of Fe2O3 scaffolds manufactured by freeze-casting using stearic acid as dispersant agent
(Elsevier Ltd, 2022) Lloreda Jurado, Pedro Javier; Pérez-Puyana, Víctor Manuel; Romero García, Alberto; Sepúlveda Ferrer, Ranier Enrique; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; Universidad de Sevilla. Departamento de Ingeniería Química; Ministerio de Ciencia e Innovación (MICIN). España; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER)
Porous materials manufactured by freeze-casting are demonstrating potential application as oxygen carriers for the production and purification of hydrogen, or anode material for lithium-ion batteries. However, to obtain the required pore morphology and sufficient mechanical strength, the suspension processing parameters must be controlled. Fe2O3 nanoparticles/camphene suspensions were fabricated using stearic acid as the dispersant agent showing a low-viscosity (130 mPa⋅s) with a high solid volume fraction (0.3). Suspensions show a shear-thinning behavior according to the Sisko model and a maximum packing fraction of 0.569 estimated from a zero porosity sample. A modified Krieger and Dougherty model was introduced to incorporate the influence of the particleaspect ratio. The Fe2O3 scaffolds manufactured by freeze-casting shown a gradient pore size along the freezing direction, which was diminished with the solid volume fraction, the compression strength was improved with the pore size reduction and fitted according to the minimum solid area model.
Magnetic properties of iron powder sintered by medium-frequency electrical resistance sintering
(Elsevier, 2022) Astacio López, Raquel; Urban, Petr; Ternero Fernández, Fátima; Aranda Louvier, Rosa María; Montes Martos, Juan Manuel; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; Ministerio de Economía y Competitividad (MINECO). España; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Universidad de Sevilla. TEP971: Ingeniería de materiales avanzados
Medium-frequency electrical resistance sintering (MF-ERS) is a technique that uses the application of pressure and heat, heat coming from the Joule effect, simultaneously to metallic powders. In this study, this technique consolidates commercial iron powders, and the porosity distribution and hysteresis curves of the compacts were analysed. Compact consolidated by conventional powder metallurgy (PM) was compared with the results obtained.
Mechanical alloying and amorphization of Ti75Cu25 alloy
(Elsevier, 2022) Urban, Petr; Astacio López, Raquel; Aranda Louvier, Rosa María; Ternero Fernández, Fátima; Cintas Físico, Jesús; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; Ministerio de Economia, Industria y Competitividad (MINECO). España; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Universidad de Sevilla. TEP971: Ingeniería de Materiales Avanzados
Ti-Cu alloys are used in dental and medical applications, due to their good mechanical properties, corrosion resistance and antibacterial properties. These properties are sensitive to microstructure and can be improved by formation of intermetallic compounds or amorphization of crystalline Ti-Cu powder. This study focuses on the amorphization of Ti75Cu25 powders prepared by mechanical alloying (MA). Ball milling, up to 60 h, of Ti and Cu powders leads to an amorphous structure. Laser granulometry, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were carried out for different milling times. Future research on consolidation of amorphous powder via electrical resistance sintering will be performed to obtain bulk samples with amorphous phase and/or nanocrystalline phase with Ti3Cu and/or Ti2Cu intermetallic compounds.
Medium-Frequency Electrical Resistance Sintering of Soft Magnetic Powder Metallurgy Iron Parts
(MDPI, 2021-06) Astacio López, Raquel; Ternero Fernández, Fátima; Cintas Físico, Jesús; Gómez Cuevas, Francisco de Paula; Montes Martos, Juan Manuel; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; Ministerio de Economía y Competitividad (MINECO). España; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Universidad de Sevilla. TEP971: Ingeniería de Materiales Avanzados
The fabrication of soft magnetic Fe parts by the medium-frequency electrical resistance sintering (MF-ERS) technique is studied in this paper. This consolidation technique involves the simultaneous application to metallic powders of pressure and heat, the latter coming from the Joule effect of a low-voltage and high-intensity electric current. Commercially pure iron powder was used in the consolidation experiences. The porosity distribution, microhardness, electrical resistivity and hysteresis curves of the final compacts were determined and analysed. The results obtained were compared both with those of compacts consolidated by the conventional powder metallurgy (PM) route of cold pressing and vacuum furnace sintering, and with fully dense compacts obtained by double cycle of cold pressing and furnace sintering in hydrogen atmosphere.
Milling amorphous FeSiB ribbons with vibratory ball and disc mills
(Elsevier, 2024-05-15) Aranda Louvier, Rosa María; Astacio López, Raquel; Urban, Petr; Soto Aranda, Beatriz; Gómez Cuevas, Francisco de Paula; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; Ministerio de Economía y Competitividad (MINECO). España; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Universidad de Sevilla. TEP971: Ingeniería de Materiales Avanzados
Fe, Si and B powders, mixed with atomic composition Fe78Si9B13, are subjected after arc melting to a melt spinning process, which is optimized to obtain the greatest amount of amorphous ribbon. The amorphous ribbons are milled to powder form in a vibratory ball mill and a vibratory disc mill, taking care of maintaining the amorphous character. Ribbons and powders have been characterized by X-ray diffraction (XRD), laser diffrac- tion, SEM and TEM microscopy, and differential scanning calorimetry (DSC). The amorphous character and particle size of the powders are characterized as a function of the mill charge and the milling time. It is shown that the use of the ball mill is appropriate for obtaining small quantities of amorphous or nanocrystalline powder, while the disc mill can process larger quantities of powder in a shorter time. The particle sizes obtained for milling times between 10 and 150 min range between 26 and 412 μm, ready for use in powder metallurgy processes.
Modelling and Simulation of the Electrical Resistance Sintering Process of Iron Powders
(Korean Institute of Metals and Materials, 2020-07) Montes Martos, Juan Manuel; Cuevas, F. G.; Viña Reina, Francisco Javier de la; Ternero Fernández, Fátima; Astacio López, Raquel; Sánchez Caballero, Eduardo; Cintas Físico, Jesús; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Ministerio de Educación y Ciencia (MEC). España; Universidad de Sevilla. TEP971: Ingeniería de Materiales Avanzados
In this paper, the process known as Electrical Resistance Sintering under Pressure is modelled, simulated and validated. This consolidation technique consists of applying a high-intensity electrical current to a metallic powder mass under compression. The Joule efect acts heating and softening the powders at the time that pressure deforms and makes the powder mass to densify. The proposed model is numerically solved by the fnite elements method, taking into account the electrical–thermal–mechanical coupling present in the process. The theoretical predictions are validated with data recorded by sensors installed in the electrical resistance sintering equipment during experiments with iron powders. The reasonable agreement between the theoretical and experimental curves regarding the overall porosity and electrical resistance suggests that the model reproduces the main characteristics of the process. Also, metallographic studies on porosity distribution confrm the model theoretical predictions. Once confrmed the model and simulator efciency, the evolution of the temperature and the porosity felds in the powder mass and in the rest of elements of the system can be predicted. The infuences of the processing parameters (intensity, time and pressure) as well as the die material are also analyzed and discussed.
Nickel Wick by Continuous Freeze-Casting: Influences of the Particle Size on the Capillarity and Mechanical Properties
(MDPI AG, 2021) Lloreda Jurado, Pedro Javier; Chicote, Laura; Chicardi Augusto, Ernesto; Sepúlveda Ferrer, Ranier Enrique; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER)
The aim of this work was to study the effect of the particle size range, the freeze casting temperature and sintering temperature on the capillarity performance and mechanical properties of Ni wicks manufactured by freeze-casting. The use of Ni/camphene-polystyrene suspensions creates wicks with an open porosity above 80% and average pore sizes of 38 μm to 17 μm by tailoring the particle size ranges and freezing temperatures employed. The incorporation of PS and the use of a continuous freeze-casting process reduces the particle sedimentation and generates a highly interconnected pore structure with regular pore sizes across the sample. The capillarity performances exhibit a fast and complete water adsorption, especially in Ni wicks freeze-casted at 10 °C and sintered at 800 °C, but only when the smaller particle size range is used do Ni wicks achieve sufficient mechanical strength.
Physical proximity of chromatin to nuclear pores prevents harmful R loop accumulation contributing to maintain genome stability
(National Academy of Sciences, 2017) García Benítez, Francisco; Gaillard, Hélène; Aguilera López, Andrés; Genética; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; European Research Council (ERC); Ministerio de Economía y Competitividad (MINECO). España; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER); Ministerio de Educación, Cultura y Deporte (MECD). España
During transcription, the mRNA may hybridize with DNA, forming an R loop, which can be physiological or pathological, constituting in this case a source of genomic instability. To understand the mechanism by which eukaryotic cells prevent harmful R loops, we used human activation-induced cytidine deaminase (AID) to identify genes preventing R loops. A screening of 400 Saccharomyces cerevisiae selected strains deleted in nuclear genes revealed that cells lacking the Mlp1/2 nuclear basket proteins show AID-dependent genomic instability and replication defects that were suppressed by RNase H1 overexpression. Importantly, DNA–RNA hybrids accumulated at transcribed genes in mlp1/2 mutants, indicating that Mlp1/2 prevents R loops. Consistent with the Mlp1/2 role in gene gating to nuclear pores, artificial tethering to the nuclear periphery of a transcribed locus suppressed R loops in mlp1∆ cells. The same occurred in THO-deficient hpr1∆ cells. We conclude that proximity of transcribed chromatin to the nuclear pore helps restrain pathological R loops.
Pore morphology evolution and atom distribution of doped Fe2O3 foams developed by freeze-casting after redox cycling
(Elsevier Editora Ltda, 2021) Lloreda Jurado, Pedro Javier; Hernández-Saz, Jesús; Chicardi Augusto, Ernesto; Paúl Escolano, Antonio; Sepúlveda Ferrer, Ranier Enrique; Universidad de Sevilla. Departamento de Ingeniería y Ciencia de los Materiales y del Transporte; European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER)
Chemical looping water splitting systems operate at relatively high temperatures (450–800 °C) to produce, purify, or store hydrogen by the cyclic reduction and oxidation (redox) of a solid oxygen carrier. Therefore, to improve long-term operation, it is necessary to develop highly stable oxygen carriers with large specific surface areas. In this work, highly interconnected doped Fe2O3 foams are fabricated through the freeze-casting technique of a submicrometric camphene-based suspension to prevent Fe sintering and pore clogging during redox operation. The influence of the dopant elements (Al and Ce) over the pore morphology evolution, and redox performances are examined. The use of an Fe2O3 porous structure with initial pore size above 100 microns shows a significant reduction of the sample densification, and the addition of Al2O3 by the citrate method prevent the rapid formation of an Fe3O4 layer at the foams struts that diminish the reoxidation rate step in the redox processing.

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