Weakly nonlinear nonaxisymmetric oscillations of capillary bridges at small viscosity

Weakly nonlinear nonaxisymmetric oscillations of a capillary bridge are considered in the limit of small viscosity. The supporting disks of the liquid bridge are subjected to small amplitude mechanical vibrations with a frequency that is close to a natural frequency. A set of equations is derived for accounting the slow dynamics of the capillary bridge. These equations describe the coupled evolution of two counter-rotating capillary waves and an associated streaming flow. Our derivation shows that the effect of the streaming flow on the capillary waves cannot be a priori ignored because it arises at the same order as the leading (cubic) nonlinearity. The system obtained is simplified, then analyzed both analytically and numerically to provide qualitative predictions of both the relevant large time dynamics and the role of the streaming flow. The case of parametric forcing at a frequency near twice a natural frequency is also considere

Mechanical integrity of ceramic-metal composite materials: Influence of microstructure and processing route

Mención Internacional en el título de doctorThe world population growth and its derived demands encourage the search and commissioning of eco-friendly, sustainable and long-lasting resources. In this regard, the field of Materials Science and Engineering is committed to the investigation and production of materials able to withstand harsh operating conditions without compromising the environment or their nominal properties. These severe working scenarios – such as high temperature, wear or corrosive applications – fit in different sectors, like power generation (fusion nuclear reactors), mining or aeronautics. A broad branch of this type of materials correspond to hardmetals or cemented carbides, metal-ceramic composites comprised by a predominant net of tungsten carbide (WC) particles embedded in a cobalt (Co) binder. This combination has been strongly rooted to the industry due to its outstanding properties, especially regarding hardness and toughness, two valuable properties in the niche of cutting tools. However, the relatively recent inclusion of W and Co in European and American critical raw materials and toxicity lists – REACH and NTP – have driven the study of alternative materials. In this sense, there exist two approaches: the partial or total substitution of Co, and seeking for a WC competitor as ceramic phase. With respect to the binder phase, iron (Fe) based alloys have proven to be excellent candidates as Co substitutes. Moreover, the addition of alloys such as chromium (Cr), nickel (Ni) or aluminium (Al) has demonstrated to improve oxidation and corrosion resistance of these materials, among other properties. Concerning the substitution of the ceramic phase, materials based in titanium carbonitride – Ti(C,N) –, also referred to as cermets, have arisen as very promising options, on the basis of providing advantages like high wear resistance or chemical stability. The combination of both strategies implies a challenge, but also the most sustainable option. In this regard, Ti(C,N)-Fe15Ni cermets have attained dense samples with a homogeneous microstructure, evidencing excellent metal-ceramic wettability. Moreover, the development of a core-rim structure in the carbide has been avoided, thus approaching the biphasic configuration of hardmetals. The present thesis has continued with this investigation line, proposing a flexible and systematic methodology with which to ease the task of designing and producing alternative hard materials. This method integrates the tools for thermodynamic simulation, validation and experimental processing. The inclusion of new alloying elements – Cr and Al – and different compositions have been evaluated, comparing the roles of WC and Ti(C,N). Furthermore, the effects exerted by the processing route have been carefully assessed, as the final properties of the material greatly depend on this decisive parameter. These attributes are also influenced by the final microstructure which, at the same time, is affected by the processing step or material composition, as well as other factors. This synergy among parameters and the characterisation of their effects on the material have enabled to attain an optimum combination of composition, microstructure and mechanical properties. Materials have been characterised in terms of their density, final composition – X-ray spectroscopy and X-ray diffraction at room/high temperature – microstructure, magnetic properties, corrosion resistance or mechanical properties, among other techniques. With respect to their mechanical evaluation, it is worth highlighting the performance of massive nanoindentation analyses, with which the intrinsic hardness of each constituent phase could be extracted.El incremento de la población mundial y las demandas derivadas en consecuencia impulsan los esfuerzos en investigación hacia la búsqueda y puesta en servicio de recursos ecológicos, sostenibles y duraderos. En este sentido, el campo de la Ciencia e Ingeniería de Materiales tiene por compromiso el estudio y la producción de materiales que puedan brindar una prestación en condiciones extremas sin comprometer el medio ambiente, garantizando el mantenimiento de sus propiedades en todo momento. Estos escenarios de servicio severos – por ejemplo, alta temperatura, desgaste o trabajo en ambientes corrosivos – tienen aplicación en diversos campos, tales como la generación de energía (reactores nucleares de fusión), la minería o la aeronáutica. Una amplia rama de estos materiales corresponde a los metales duros o carburos cementados, unos materiales compuestos metal-cerámicos formados por una red predominante de partículas de carburo de wolframio (WC) embebidas en una matriz de cobalto (Co). Esta combinación ha estado fuertemente arraigada a la industria gracias a sus excelentes propiedades, sobre todo en cuanto a dureza y tenacidad, altamente valorables en el nicho de las herramientas de corte. Sin embargo, la inclusión en los últimos años del W y el Co en la lista europea de materias primas críticas y en programas toxicológicos tanto europeos como norteamericanos – REACH y NTP – han dirigido los estudios hacia la búsqueda de materiales alternativos. En este aspecto, existen dos estrategias: la sustitución parcial o total de la matriz metálica, y el cambio del WC por otra fase cerámica. Respecto a la matriz, las aleaciones base hierro (Fe) han demostrado ser claras opciones como competidoras del Co. Además, la adición de aleantes como el cromo (Cr), el níquel (Ni) o el aluminio (Al) ha manifestado una evidente mejora en cuanto a la resistencia a oxidación y corrosión de estos materiales, entre otras propiedades. En cuanto a la sustitución de la fase cerámica, los materiales basados en carbonitruro de titanio – Ti(C,N) –, también denominados cermets, se han establecido como excelentes candidatos, gracias a ventajas como su alta resistencia al desgaste o estabilidad química. La combinación de ambas estrategias supone un reto, pero también la opción más sostenible. En este sentido, los cermets Ti(C,N)-Fe15Ni han demostrado alcanzar muestras densas con microestructuras homogéneas, evidenciando una excelente mojabilidad metal-cerámica. Además, se ha evitado la evolución de una estructura de tipo core-rim en el carburo, aproximándose así a la configuración bifásica de los carburos cementados. En esta tesis se ha continuado con dicha línea de investigación, proponiendo una metodología flexible y sistemática para el diseño y producción de materiales duros alternativos con la que facilitar esta tarea. Este método aúna las herramientas de simulación termodinámica, validación y procesamiento experimental. Se ha estudiado la adición de nuevos elementos – Cr y Al – y diferentes composiciones, comparando los roles del WC y el Ti(C,N). Además, se han enfocado los esfuerzos en la evaluación de los efectos provocados por la ruta de procesamiento, un importante parámetro del que dependen en gran medida las propiedades finales del material. Al mismo tiempo, éstas también están altamente influenciadas por la microestructura final, que a su vez se ve afectada por el procesado o la composición, además de otros factores. Esta sinergia entre parámetros y la caracterización de sus efectos en el material han permitido llegar a una óptima combinación de composición, microestructura y propiedades mecánicas. Los materiales se han caracterizado en base a su densidad, composición final – espectroscopía de rayos-X y difracción de rayos-X a temperatura ambiente/alta –, microestructura, propiedades magnéticas, resistencia a corrosión o propiedades mecánicas, entre otras técnicas. Respecto a la evaluación mecánica, cabe destacar los análisis de nanoindentación masiva con los que se han extraído los valores intrínsecos de dureza de cada una de las fases constituyentes.This Doctoral Thesis was a collaboration between Universidad Carlos III de Madrid – Grupo de Tecnología de Polvos (GTP) – and Universidad Politècnica de Catalunya – Centro de Integridad Estructural, Fiabilidad y Micromecánica los Materiales (CIEFMA). This investigation was financed by the Spanish Government (Agencia Estatal de Investigación) through the projects MAT2015-70780-C4-P and PID2019-106631GB-C41/C43, and grant BES-2016-077340 (FPI-2016), as well as the Regional Government of Madrid through the programmes MULTIMAT-CHALLENGE – ref. S2013/MIT-2862 – and ADITIMAT – ref. S2018/NMT-4411.Programa de Doctorado en Ciencia e Ingeniería de Materiales por la Universidad Carlos III de MadridPresidente: Daniele Mari.- Secretario: José Manuel Sánchez Moreno.- Vocal: Ana María de Oliveira e Rocha Sen

The cluster model: A simulation of the aerogel structure as a hierarchically-ordered arrangement of randomly packed spheres

A new structural model based on the premises widely used for describing the structure of aerogels has been introduced. These structures have been described as an assemblage of randomly-packed spheres in several hierarchically-ordered levels. A new algorithm has been developed for constructing our models from these premises using computer simulation. Subsequently, several applications have been simulated to characterize real systems, obtaining textural parameters such as the specific surface area, specific porous volume or the apparent density of the systems, based on the Monte Carlo technique and on geometrical considerations. The object of these is to test the ability of the models to explain the structure of some real aerogels. This Cluster Model has also been applied as an initial approach to the study of the mechanical properties of aerogels. Results support the general conclusion that these models are useful for explaining the structure of aerogels.Ministerio de Ciencia y Tecnología MAT2002-00859Junta de Andalucía TEP 011

Nanostructured sonogels

Acoustic cavitation effects in sol-gel liquid processing permits to obtain nanostructured materials, with size-dependent properties. The so-called "hot spots" produce very high temperatures and pressures which act as nanoreactors. Ultrasounds force the dissolution and the reaction stars. The products (alcohol, water and silanol) help to continue the dissolution, being catalyst content, temperature bath and alkyl group length dependent. Popular choices used in the preparation of silica-based gels are tetramethoxysilane (TMOS), Si(OCH3)4 and tetraethoxysilane (TEOS), Si(OC 2H5)4. The resultant "sonogels" are denser gels with finer and homogeneous porosity than those of classic ones. They have a high surface/volume ratio and are built by small particles (1 nm radius) and a high cross-linked network with low -OH surface coverage radicals. In this way a cluster model is presented based on randomly-packed spheres in several hierarchical levels that represent the real sonoaerogel. Organic modified silicates (ORMOSIL) were obtained by supercritical drying in ethanol of the corresponding alcogel producing a hybrid organic/inorganic aerogel. The new material takes the advantages of the organic polymers as flexibility, low density, toughness and formability whereas the inorganic part contributes with surface hardness, modulus strength, transparency and high refractive index. The sonocatalytic method has proven to be adequate to prepare silica matrices for fine and uniform dispersion of CdS and PbS quantum dots (QDs), which show exciton quantum confinement. We present results of characterization of these materials, such as nitrogen physisorption, small angle X-ray/neutrons scattering, electron microscopy, uniaxial compression and nanoindentation. Finally these materials find application as biomaterials for tissue engineering and for CO2 sequestration by means the carbonation reaction.Ministerio de Ciencia y Tecnología MAT2005-158

Aportaciones de la neurociencia cognitiva a la estimulación auditiva musical de 0 a 6 años

Este artículo forma parte de una investigación más amplia acerca de la actitud y la aptitud que los maestros generalistas de 2º ciclo de Educación Infantil de los colegios públicos de Valencia tienen para estimular auditivamente a sus alumnos a partir de la discriminación auditiva y la escucha comprensiva de las audiciones musicales, con el fin de desarrollar el oído interno y la capacidad atencional. A lo largo de este trabajo se explica cómo afecta al cerebro infantil una continua estimulación sensorial, concretamente la auditiva, desde el ámbito neurológico

Diatomite releases silica during spirit filtration

The purpose of this study was to ascertain whether diatomite is an inert filter aid during spirit filtration. Surely, any compound with a negative effect on the spirit composition or the consumer’s health could be dissolved. In this study different diatomites were treated with 36% vol. ethanol/water mixtures and the amounts and structures of the extracted compounds were determined. Furthermore, Brandy de Jerez was diatomite- and membrane-filtered at different temperatures and the silicon content was analysed. It was found that up to 0.36% by weight of diatomite dissolved in the aqueous ethanol and amorphous silica, in the form of hollow spherical microparticles, was the most abundant component. Silicon concentrations in Brandy de Jerez increased by up to 163.0% after contact with diatomite and these changes were more marked for calcined diatomite. In contrast, reductions of more than 30% in silicon concentrations were achieved after membrane filtration at low temperatures

Formation of siliceous sediments in brandy after diatomite filtration

Brandy is quite a stable spirit but sometimes light sediment appears. This sediment was separated and analysed by IR and SEM-EDX. It was revealed that the sediment is composed mostly of silica and residual organic matter. Silica was present as an amorphous phase and as microparticles. In an attempt to reproduce the formation of the sediment, a diatomite extract was prepared with an ethanol/water mixture (36% vol.) and a calcined diatomite similar to that used in brandy filtration. This extract was added to unfiltered brandy in different amounts. After 1 month, the Si concentration decreased in all samples and sediments with similar compositions and features to those found in the unstable brandy appeared. The amounts of sediment obtained were directly related to the decrease in Si concentration in solution. Consequently, it can be concluded that siliceous sediment in brandy originates from Si released during diatomite filtration

Absorption capacity, kinetics and mechanical behaviour in dry and wet states of hydrophobic DEDMS/TEOS-based silica aerogels

This work is a new approach to the study of the structural, mechanical and absorption properties of hybrid organic/inorganic silica-based aerogels. Diethoxydimethylsilane and tetraethoxysilane have been used as precursors. Changes in properties such as specific surface area, porous volume, pore radius, and surface texture and chemistry were researched as a function of the relative organic content. In addition, the absorption properties were tested for different organic liquids. The discrepancy in the absorption mechanisms and the kinetics of pure inorganic and hybrid samples were discussed. It was confirmed that swelling occurs in samples with high organic content, which, in turn, governs the absorption process. Finally, the mechanical behaviour was studied by uniaxial compression. A significant rise of the rupture strain up to 0.45 and a 10-fold decrease in the Young’s modulus to 7.8 MPa were measured in the dry samples by increasing the organic content. The mechanical response of the samples after saturation by the absorption of two reference oily liquids, namely, common motor oil and liquid polydimethylsiloxane, was also compared with the behaviour of dry samples. The presence of liquid within the sample reduced the value of the mechanical parameters in almost all cases. Moreover, the inclusion of organic chains also made the wet aerogels highly deformable. In summary, these first results suggest that tuning the organic ratio of the hybrid aerogels allows the control of not only the structural and mechanical properties but also the absorption properties.Junta de Andalucía P09-TEP-546

Reinforced silica-carbon nanotube monolithic aerogels synthesised by rapid controlled gelation

This work introduces a new synthesis procedure for obtaining homogeneous silica hybrid aerogels with carbon nanotube contents up to 2.50 wt.%. The inclusion of nanotubes in the highly porous silica matrix was performed by a two-step sol–gel process, resulting in samples with densities below 80 mg/cm3. The structural analyses (N2 physisorption and SEM) revealed the hierarchical structure of the porous matrix formed by nanoparticles arranged in clusters of 100 and 300 nm in size, specific surface areas around 600 m2/g and porous volumes above 4.0 cm3/g. In addition, a relevant increase on the mechanical performance was found, and an increment of 50% for the compressive strength and 90% for the maximum deformation were measured by uniaxial compression. This reinforcement was possible thanks to the outstanding dispersion of the CNT within the silica matrix and the formation of Si–O–C bridges between nanotubes and silica matrix, as suggested by FTIR. Therefore, the original synthesis procedure introduced in this work allows the fabrication of highly porous hybrid materials loaded with carbon nanotubes homogeneously distributed in the space, which remain available for a variety of technological applications

High-temperature wettability in hard materials: Comparison of systems with different binder/carbide phases and evaluation of C addition

Metal-ceramic wettability is a decisive parameter in the high-temperature sintering of hard materials. Wettability tests enable the study of this property with minimum material waste, especially useful in the search of alternative systems to WC-Co hardmetals. In this investigation, Fe-based binders – FeNiCr and FeCrAl – were tested on Ti(C,N) and WC substrates, aiming to assess: the high-temperature interactions, the dissolutive character of the liquid phase and the nature of the interphases generated, and the influence on sintering behaviour. As a result, FeNiCr led to excellent wetting scenarios for both ceramics, whereas FeCrAl alloys induced the formation of aluminium oxides. The effect of C addition on wettability was also evaluated, resulting in an improvement of this property by the inclusion of this element in the binder phase. Inspection of the microstructures resultant from powder metallurgy processing of the different configurations confirmed their excellent correlation with wettability results. As a consequence, the effectivity of this technique as a model of the sintering scenario could be asserted.The current investigation was supported by the Spanish Government (Agencia Estatal de Investigación) and European Union through the project AEI/10.13039/501100011033 (PID2019-106631GB-C41/C43) and grants BES-2016-077340 and Margarita Salas, as well as the Regional Government of Madrid through the program ADITIMAT, ref. S2018/NMT-4411. The authors would like to acknowledge and thank CERATIZIT Group (Mamer, Luxembourg), for their contribution to the processing of the hard materials, and Johannes Pötschke, from Fraunhofer Institute for Ceramic Technologies and Systems IKTS, for providing binderless WC substrates. Funding for APC: Universidad Carlos III de Madrid (Read & Publish Agreement CRUE-CSIC 2022)