Suchergebnisse

Guefoams (guest-containing foams) are a new-class of open-cell cellular materials that extend the properties of conventional foams by incorporating guest phases that convert them into multifunctional materials. This manuscript describes the development of pitch-derived composite guefoams that contain two types of inclusions: iron nanoparticles embedded in the cellular skeleton and activated carbon particles as guest phases. The activated carbon particles significantly increase the specific surface area and gas adsorption capacity. When these materials are exposed to low-intensity magnetic fields, the iron nanoparticles confer a high magneto-inductive capacity that enables ultrafast heating and rapid desorption of adsorbed species. The ability of these materials to act as preconcentrators for volatile organic compounds (VOCs) is demonstrated in this work using toluene as a proof of concept. The Guefoams developed here have greater preconcentration capabilities than current state-of-the-art systems while also being significantly more energy efficient due to the magnetic induction controlled desorption process. This unparalleled blend of properties makes these guefoams a valuable tool for energy-efficient VOCs management. ; This work was supported by the Spanish Agencia Estatal de Investigación (AEI), the Spanish Ministry of Science and Innovation, and the European Union (FEDER and NextGenerationEU funds) [grants MAT2016-77742-C2-2-P and PDC2021-121617-C21]. The author would also like to acknowledge the financial support received from the Conselleria d'Innovació, Universitats, Ciència, i Societat Digital of the Generalitat Valenciana through grant GVA-COVID19/2021/097.

Classrooms at any educational institution have become high-risk sites for contagion during past and present pandemic periods caused by the SARS-CoV-2 (COVID-19) viral siege, given the prolonged time educators and students spend in joint activity. Among the several strategies employed by educational institutions to minimize the outbreak of contagion are regulating classroom capacity and studying the optimal spatial arrangement of students. The architectural features of each classroom, which include corridors, ventilation components, total volume, and maximum capacity, among other factors, have a direct impact on the risk of human contagion. This work is a proposal to optimize the spatial arrangement of students to minimize the risk of contagion, considering not only the distance between them, but also the different architectural features in the classrooms. The analyses conducted in the different scenarios conclude with a comparison of risk in terms of the arrangement of students that various educators would have used at different education levels in their classrooms based solely on intuitive criteria. The results indicate that in some situations, the locations chosen by educators can double the risk of infection compared to optimal arrangements. ; This research was funded by the Spanish "Agencia Estatal de Investigación" (AEI) and European Union (FEDER funds) through grant PDC2021-121617-C21. This research was also funded by the Conselleria d'Innovació, Universitats, Ciència, i Societat Digital of the Generalitat Valenciana through grant GVA-COVID19/2021/097.

The design of multifunctional materials is a current demand for high-end technological applications that need to combine different functions unable to be accomplished by a single material. The aim of this work is to present, at first glance, a new family of recently patented multifunctional porous materials developed by locating granular phases with specific functionality (guests) within the cavities of open-pore cellular materials (hosts) and, at second glance, the use of a set of these materials for the preconcentration and management of volatile organic compounds (VOCs). These materials (herein known as Guefoams, acronym for Guest-containing foams), present host foams and guest phases that are not bonded and therefore allow fluids to pass through. The processing method is the gas pressure infiltration of a host precursor into preforms containing particulate guest phases covered by a NaCl martyr coating, which is later dissolved in water. The manuscript shows the manufacture and characterization of a specific set of Guefoams composed of aluminum foams that incorporate both steel particles and activated carbon particles as guest phases into the same material. These guest phases make the materials highly adsorbent and susceptible to rapid desorption by magnetic induction, two properties never achieved with traditional foams that transform these materials into perfect candidates for preconcentration and energy-efficient management of VOCs. The manuscript concludes with a discussion on advisible properties to consider when exploring the use of these materials in the mentioned applications. ; The author acknowledges financial support from the Spanish "Agencia Estatal de Investigación" (AEI) and European Union (FEDER funds) through grant MAT2016-77742-C2-2-P.

The development of porous materials with hierarchical porous structures is currently of great interest. These materials exhibit properties representative of different pore scales and thus open up the possibility of being used in new applications. In this paper, a method for the preparation of silver foams with hierarchical porous structures is discussed. Here, the replication method, which is typically used to produce coarse-pore foams, is merged with dealloying, which is commonly used to manufacture small-pore foams. For this purpose, packed NaCl particles (hard template) were infiltrated with 75%Al–25%Ag alloy (whose so-called soft template is the Al-rich phase). Both the hard and soft templates were removed by water dissolution and dealloying with HCl or NaOH solutions, respectively. Extensive characterization of the resulting materials revealed pores ranging from a few nanometers to hundreds of micrometers. The materials were characterized by their antibacterial performance against Gram-positive and Gram-negative bacteria and showed significantly higher activity than both silver foams prepared by sintering pure Ag particles and silver nanofoams produced by chemical dealloying. The combinations of pores of different sizes and the resulting high internal specific surface area have a decisive influence on the antibacterial capacity of these new materials. ; The authors acknowledge partial financial support from the Spanish Agencia Estatal de Investigación (AEI) and the European Union (FEDER funds) through grant MAT2016-77742-C2-2-P. F.C.D. also acknowledges financial support from the Generalitat Valenciana through the "Santiago Grisolía" grant (code GRISOLIA/2017/187).

Traditional metal foams, which are incapable to meet the heat dissipation demands of today's electronics industry, were recently reformulated by the incorporation of thermal inclusions of graphite flakes that enhance their heat dissipation efficiency. In this work we manufacture, by means of a one-pot liquid metal infiltration synthesis, new layer-structured multicomponent materials that consist of aluminium foam components alternated with aluminium/diamond composite components. The thermal conductivity of aluminium/diamond components can substantially vary with processing conditions, which allow the nano-dimensional control of reaction products at the aluminium-diamond interface. The experimental and analytical results, plus finite element modelling, revealed that the low thermal resistance interface between components derived from the one-pot synthesis route, allowed multicomponent materials to significantly improve the thermal dissipation of traditional foams since aluminium/diamond components acted as effective thermal guides capable of transferring heat to the aluminium foam components where dissipation was achieved by forced convection. ; The authors acknowledge partial financial support from the Spanish Agencia Estatal de Investigación (AEI) and European Union (FEDER funds) through grant MAT2016-77742-C2-2-P.

The work needed to mechanically drive molten metal into a porous solid preform when producing a composite material by infiltration can significantly exceed the energy change required for thermodynamically reversible infiltration. We measure, by quantitative metallographic analysis of partially infiltrated, particle- or fiber-based non-metallic preforms, the evolution with saturation of the three interfaces present during the process. Results show that irreversible energy losses in the infiltration of alumina preforms by molten copper, aluminium or aluminium-tin alloy cannot be ascribed to the creation of liquid meniscus surface area at intermediate metal saturation. This result agrees with similar observations in soil science and gives experimental confirmation of predictions from a recent simulation of capillarity-dominated metal infiltration [Acta Mater., vol. 210, 2021, 116831]. ; This work was chiefly sponsored by the Swiss National Science Foundation (FNS), Project No. 200021 149899. J.M. Molina-Jordá acknowledges funding from the Spanish "Agencia Estatal de Investigación" (AEI) and the European Union (FEDER funds) through grant MAT2016-77742-C2-2-P.

Remaining silicon in SiC-based materials produced via reactive infiltration limits their use in high-temperature applications due to the poor mechanical properties of silicon: low fracture toughness, extreme fragility and creep phenomena above 1000 °C. In this paper SiC–FeSi2 composites are fabricated by reactive infiltration of Si–Fe alloys into porous Cf/C preforms. The resulting materials are SiC/FeSi2 composites, in which remaining silicon is reduced by formation of FeSi2. For the richest Fe alloys (35 wt% Fe) a nominal residual silicon content below 1% has been observed. However this, the relatively poor mechanical properties (bending strength) measured for those resulting materials can be explained by the thermal mismatch of FeSi2 and SiC, which weakens the interface and does even generate new porosity, associated with a debonding phenomenon between the two phases. ; Authors would like acknowledge the financial support received from the Generalitat Valenciana (PROMETEO II/2014/004-FEDER, PhD grant Vali+d and Santiago Grisolia program, GRISOLIA/2013/023), and the European Union's Seventh Framework Programme (FP7/2007-2013) under the HELM project, Grant agreement no. 280464 are gratefully acknowledged.

Recent advances in cellular materials for active thermal management applications involve the integral design of their porous structure. In this work, open-cell aluminum foams with porosities in the range of 0.60–0.76 are developed, containing pores with spherical geometry and a bimodal pore size distribution. The fabrication strategy involves the use of the replication method by infiltration with liquid aluminum of porous preforms formed by packing NaCl spheres of two largely different sizes (7 mm and 1 mm average diameter), which are then removed by water dissolution. The paper describes cellular materials with different proportions of coarse and fine pores. Their detailed characterization by pore volume fraction, pressure drop, permeability, thermal conductivity and heat transfer coefficient is supported by analytical schemes. In addition, these materials were characterized under realistic operating conditions using computational fluid dynamics simulations. The material with 67 percent coarse pores and 33 percent fine pores, which has the highest porosity (and thus permeability), has the most appealing heat dissipation properties with the lowest pressure drops, making it an excellent candidate for emerging thermal management applications in electronic systems. ; The authors gratefully acknowledge partial financial support from the Spanish "Agencia Estatal de Investigación" (AEI) and European Union (FEDER funds) through grants MAT2016-77742-C2-2-P and PDC2021-121617-C21. The authors would also like to acknowledge the financial support received for the same purpose from the Conselleria d'Innovació, Universitats, Ciència, i Societat Digital of the Generalitat Valenciana through grant GVA-COVID19/2021/097. F.Ç. Durmus also acknowledges financial support from the Generalitat Valenciana through a "Santiago Grisolía" grant (GRISOLIA/2017/187). L.P. Maiorano also acknowledges the financial support from the University of Alicante through grant UAFPU2019-33 "Programa Propio para el fomento de la I+D+i del Vicerrectorado de Investigación y Transferencia de Conocimiento".

The process of liquid silicon infiltration is investigated for channels with radii from 0.25 to 0.75 [mm] drilled in compact carbon preforms. The advantage of this setup is that the study of the phenomenon results to be simplified. For comparison purposes, attempts are made in order to work out a framework for evaluating the accuracy of simulations. The approach relies on dimensionless numbers involving the properties of the surface reaction. It turns out that complex hydrodynamic behavior derived from second Newton law can be made consistent with Lattice-Boltzmann simulations. The experiments give clear evidence that the growth of silicon carbide proceeds in two different stages and basic mechanisms are highlighted. Lattice-Boltzmann simulations prove to be an effective tool for the description of the growing phase. Namely, essential experimental constraints can be implemented. As a result, the existing models are useful to gain more insight on the process of reactive infiltration into porous media in the first stage of penetration, i.e. up to pore closure because of surface growth. A way allowing to implement the resistance from chemical reaction in Darcy law is also proposed. ; The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement nº 280464, project "High-frequency ELectro-Magnetic technologies for advanced processing of ceramic matrix composites and graphite expansion" (HELM).

The ten articles [1–10] included in this Special Issue on "Liquid Metals" do not intend to comprehensively cover this extensive field, but, rather, to highlight recent discoveries that have greatly broadened the scope of technological applications of these materials. Improvements in understanding the physics of liquid metals are, to a large extent, due to the powerful theoretical tools in the hands of scientists, either semi-empirical [1,5,6] or ab initio (molecular dynamics, see [7]). ; This work was supported by the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement 280464, project "High-frequency Electro-Magnetic technologies for advanced processing of ceramic matrix composites and graphite expansion" (HELM) and "Ministerio de Economía y Competitividad" through project MAT2011-25029.

This paper aimed to improve the electrochemical activity of a pitch-derived open-pore graphite foam (GF) by an electrochemical coating of reduced graphene oxide (RGO) and platinum particles without significantly affecting its 3D-structure. RGO was synthesized using cyclic voltammetry (CV) from a 3 g L−1 GO and 0.1 M LiClO4 solution. For the electrodeposition of Pt particles, an alternating current method based on electrochemical impedance spectroscopy (EIS) was used. A sinusoidal voltage from a fixed potential Ei was varied following a selected amplitude (ΔEac = ± 0.35 V) in a frequency range of 8 Hz ≤ fi ≤ 10Hz, where i = 500. This method proved its efficiency when compared to the traditional CV by obtaining more highly electroactive coatings in less synthesis time. For samples' characterization, physical measures included permeability, pressure drop, and nitrogen adsorption isotherms. The electrochemical characterization was performed by CV. The surface morphology and chemical composition were examined using field emission electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDX), respectively. RGO improved the electron transfer rate constant of GF, and a more homogeneous coating distribution of reduced size Pt particles was obtained. ; This research was funded by the Spanish Agencia Estatal de Investigación (AEI) and the European Union (FEDER funds) contracts (MAT2016-77742-C2-1-P, MAT2016-77742-C2-2-P).

The synthesis of reduced graphene oxide onto magnesium discs by electrochemical and chemical methods is presented in this work. The surface morphology and atomic composition were investigated using field emission scanning electron microscopy and energy dispersive X-ray spectroscopy. The corrosion rate of different samples was analyzed in physiological saline 0.9 wt % NaCl solution by potentiodynamic polarization, electrochemical impedance spectroscopy and scanning electrochemical microscopy. As a result of the different treatments, a progressive decrease in the corrosion rate of the magnesium disc in the corroding environment was obtained, reaching up to 80% of reduction for the chemically modified sample. ; The authors wish to thank the Spanish Agencia Estatal de Investigación (AEI) and European Union (FEDER funds) for the financial support (contracts MAT2016-77742-C2-1-P and MAT2016-77742-C2-2-P).

The preparation and use of Guefoams as heterogeneous catalyst is reported. The Guefoam catalyst consists of an open-pore Al-Si foam that accommodates a freely mobile guest phase (Ni/CeO2/Al2O3 particles) in its cavities, with neither a physical nor a chemical matrix-guest bond. A eutectic Al-12Si alloy was used as a low-melting matrix precursor to prevent thermal sintering of the active phase during liquid metal infiltration. CO2 methanation was chosen as the reaction test. The activity and CH4 selectivity (close to 100%) achieved with the Guefoam catalyst were similar to those obtained with a packed bed of the same active phase particles, but with the advantages of a structured reactor such as robustness and ease of handling. The thermal conductivity of the Guefoam catalyst is significantly improved with regard to the packed bed of active phase particles, which reduces the temperature gradients in the catalytic reactor, as demonstrated by computational fluid dynamic modelling. Since the permeability of the Guefoam catalyst is 2.7 times that of the packed bed, the pressure drop caused by the passage of a fluid through the novel material is reduced, resulting in a significantly higher catalytic performance index than the packed bed. ; Financial support from the Spanish Agencia Estatal de Investigación (AEI), the Spanish Ministry of Science and Innovation and the European Union (FEDER and NextGenerationEU funds) [projects MAT2016-77742-C2-2-P, PDC2021-121617-C21 and CTQ2015-67597-C2-2-R] and the Conselleria d'Innovació, Universitats, Ciència, i Societat Digital of the Generalitat Valenciana [projects GVA-COVID19/2021/097 and PROMETEO/2018/076, PhD grant of C.Y. Chaparro GRISOLIAP/2017/177 and contract of E. Bailón APOSTD/2019/030]. L.P. Maiorano also acknowledges the financial support from the University of Alicante through grant "Programa Propio para el fomento de la I+D+I del Vicerrectorado de Investigación y Transferencia de Conocimiento" (UAFPU2019-33).