Experimental phase function and degree of linear polarization curve of olivine and spinel and the origin of the Barbarian polarization behaviour

We explore experimentally possible explanations of the polarization curves of the sunlight reflected by the Barbarian asteroids. Their peculiar polarization curves are characterized by a large-inversion angle, around 30 degrees, which could be related to the presence of FeO-bearing spinel embedded in Calcium-Aluminum inclusions. In order to test this hypothesis, we have measured the phase function and degree of linear polarization of six samples of Mg-rich olivine and spinel. For each material, we have analysed the light scattering properties of a millimeter-sized grain and of two powdered samples with size distributions in the micrometer size range. The three spinel samples show a well-defined negative polarization branch with an inversion phase angle located around 24 degrees-30 degrees. In contrast, in the case of the olivine samples, the inversion angle is highly dependent on particle size and tends to decrease for larger sizes. We identify the macroscopic geometries as a possible explanation for the evident differences in the polarization curves between olivine and spinel millimeter samples. Although the polarization behaviour in near backscattering of the Barbara asteroid is similar to that of our spinel mm-sized sample in random orientation, this similarity could result in part from crystal retro-reflection rather than composition. This is part of an ongoing experimental project devoted to test separately several components of CV3-like meteorites, representative of the Barbarians composition, to disentangle their contributions to the polarization behaviour of these objects.Peer reviewe

Reaction pathways in the solid state synthesis of multiferroic BiFeO 3

The obtaining of multiferroicBiFeO3 as a pure single-phase product is particularly complex since the formation of secondary phases seems to be unavoidable. The process by which these secondary impurities are formed is studied by analyzing the diffusion and solidstate reactivity of the Bi2O3–Fe2O3 system. Experimental evidence is reported which indicates that the progressive diffusion of Bi3+ ions into the Fe2O3 particles governs the solidstatesynthesis of the perovskite BiFeO3 phase. However a competition is established between the diffusion process which tends to complete the formation of BiFeO3, and the crystallization of stable Bi2Fe4O9 mullite crystals, which tend to block that formation reaction

Microwave-induced fast crystallization of amorphous hierarchical anatase microspheres

The fabrication of hierarchical anatase microspheres with potential photocatalytic properties eventually comprises a consolidation step in which a high degree of crystalline order is typically achieved through conventional electric heating treatments. This however entails a substantial reduction in the specific surface area and porosity of the powders, with the consequent deterioration in their photocatalytic response. Here, we have tested the employ of microwave heating as an alternative energy-saving sintering method to promote fast crystallization. The results obtained suggest that under the microwave radiation, the TiO(2) hierarchical structures can effectively crystallize in a drastically reduced heating time, allowing the specific surface area and the porosity to be kept in the high values required for an improved photocatalytic performance

Kailo: a systemic approach to addressing the social determinants of young people’s mental health and wellbeing at the local level

This is the final version. Available on open access from Taylor and Francis via the DOI in this recordData availability: No data is associated with this article.The mental health and wellbeing of children and young people is deteriorating. It is increasingly recognised that mental health is a systemic issue, with a wide range of contributing and interacting factors. However, the vast majority of attention and resources are focused on the identification and treatment of mental health disorders, with relatively scant attention on the social determinants of mental health and wellbeing and investment in preventative approaches. Furthermore, there is little attention on how the social determinants manifest or may be influenced at the local level, impeding the design of contextually nuanced preventative approaches. This paper describes a major research and design initiative called Kailo that aims to support the design and implementation of local and contextually nuanced preventative strategies to improve children's and young people’s mental health and wellbeing. The Kailo Framework involves structured engagement with a wide range of local partners and stakeholders - including young people, community partners, practitioners and local system leaders - to better understand local systemic influences and support programmes of youth-centred and evidence-informed co-design, prototyping and testing. It is hypothesised that integrating different sources of knowledge, experience, insight and evidence will result in better embedded, more sustainable and more impactful strategies that address the social determinants of young people’s mental health and wellbeing at the local level.UK Prevention Research Partnershi

Sintering kinetic of Bi₄Ti₃O₁₂ based ceramics

The shrinkage behaviour in based-Bi4Ti3O12 ceramics has been studied by constant heating rate experiments (CHR). Undoped and WO3 doped BIT ceramics were prepared by two different ways: mixed oxide method and hidroxide-based coprecipitation method. Analyses of the initial and intermediate sintering stages were evaluated using different Coble’s based models. Sintering behaviour is modified by both, the dopant and the processing method. Powders obtained by the mixed oxide method sintered through a solid state mechanism, while coprecipitated powders sintered with the presence of a small amount of a transitory liquid phase.Se ha estudiado el comportamiento durante la sinterización de cerámicas basadas en Bi4Ti3O12 (BIT). Muestras sin dopar y dopadas con WO3 fueron preparadas por dos rutas diferentes: vía convencional por mezcla de óxidos y vía química por el método de coprecipitación de hidróxidos. Las variaciones en la contracción de las muestras se siguieron mediante ensayos de dilatometría. Para determinar los parámetros cinéticos se utilizaron diferentes modelos teóricos basados en los de Coble para los estados inicial e intermedio de la sinterización. Tanto el método de procesamiento como la cantidad de dopante modifican el comportamiento durante la sinterización de estas cerámicas. La sinterización de las muestras obtenidas por vía convencional se produce en estado sólido mientras que en aquellas obtenidas por vía química la sinterización se produce en presencia de una pequeña cantidad de fase líquida

Síntesis y evolución microestructural de cerámicas de BiFeO₃ modificadas con ZnO

BiFeO3 ceramic materials have received a great interest in the last years due to their potential application as multiferroic devices. However, the preparation of BiFeO3-based bulk ceramics shows serious difficulties related to the presence of secondary phases and the densification process. These problems result in a high electrical conductivity which up to now limits the technological applications of BiFeO3. However, it has been observed experimentally that the conductivity in these ceramics can be reduced by acting on their microstructure. In this framework, the present contribution is focused on the analysis of the microstructural changes promoted by superficial doping of the BiFeO3 ceramic particles with ZnO. The structural and microstructural characterization of the obtained materials reveals that the addition of ZnO results in a “solutedrag” effect. Due to this effect the dopant remains segregated at the grain boundaries so inhibiting the grain growth during sintering.Los materiales cerámicos de BiFeO3 han cobrado un gran interés en los últimos años por su posible aplicación como materiales multiferroicos. Sin embargo, la obtención de materiales densos de BiFeO3 presenta serias dificultades asociadas a la aparición de fases secundarias no multiferroicas y a la dificultad de densificación, problemas que se traducen en una elevada conductividad eléctrica e impiden, de momento, sus aplicaciones prácticas. No obstante, se ha observado experimentalmente que es posible reducir los problemas de elevada conductividad eléctrica en materiales cerámicos a través de modificaciones a nivel microestructural. Dentro de este contexto, en este trabajo se estudian las modificaciones microestructurales producidas al dopar superficialmente partículas cerámicas de BiFeO3 con ZnO. La caracterización estructural y microestructural de los materiales obtenidos revela que la adición de ZnO por el método de modificación superficial resulta en un efecto de “solutedrag” inhibiendo el crecimiento de los granos de BiFeO3 durante la sinterización

Influencia de las diferentes etapas de procesamiento sobre la microestructura de dispositivos multicapa basados en PZT

A comparative study of the influence of both rheological and processing parameters on the microstructure and reliability of multilayer ceramic chips based on PZT has been conducted. The multilayer chips were obtained by tape casting. Viscosity measurements of different slurries with various solids content have been correlated with both the thickness and the green density of the casted layers. The critical points of the thermal treatments, organics burn-out and sintering, have been identified. The green microstructure of the layers and the final microstructure of the sintered chips have been studied by SEM.<br><br>Se ha realizado un estudio comparativo de la influencia de los parámetros reológicos y de procesamiento sobre la microestructura y consistencia de chips multicapa de PZT obtenidos mediante un proceso de colado en cinta. Para ello se han realizado medidas de viscosidad de distintas barbotinas con diferente contenido en sólidos y su relación con el espesor y densidad en verde de las cintas obtenidas, se han identificado los puntos críticos del ciclo de quemado-sinterización y, mediante MEB se ha estudiado la microestructura en verde de las láminas coladas y la microestructura final de los chips multicapa fabricados