Compositionally graded YSZ–NiO composites by surface laser melting

El pdf del artículo es la versión post-print.Laser surface melting has been applied to near eutectic NiO–YSZ sintered ceramics. The objective is to generate a functional gradient composite material with graded microstructure and composition. At low solidification rates the resultant material has a graded composition, with a severe NiO segregation towards the surface. A thick NiO layer whose thickness depends on the travelling speed is formed. Below this layer the microstructure is eutectic like with composition varying with depth. In contact with the ceramic, excess YSZ coming from the hypereutectic composition forms an almost continuous YSZ layer. The thickness of both segregated layers, NiO and YSZ can be controlled by traverse speed. Thickness decreases as travelling speed increases until a limiting travelling rate of 110 mm/h, at which no more segregation is found. Possible causes to explain the relevant NiO segregation towards the surface are discussed.Financial support from the Ministerio de Educación y Ciencia of Spain and the CE program FEDER under grant MAT2006-13005-C03-01 is gratefully acknowledged.Peer Reviewe

Probing high oxygen activity in YSZ electrolyte

The redox behavior of terbium and praseodymium doped yttria-stabilized zirconia (YSZ) is studied. The aim is to identify spectroscopic probes and a suitable experimental procedure to monitor the oxygen activity in YSZ electrolytes in solid oxide cells with spatial resolution and at operation conditions (e.g. at high temperatures). Sintered ceramics and crystals with 0.3 to 10 at% content of Pr or Tb ions in YSZ were prepared. Upon equilibration in atmospheres from 10-20to 100 bar PO2around 800 °C, the majority of these rare earth ions are in the 3 + oxidation state. At oxygen pressures above 0.001 bar, the small proportion of Tb4+and Pr4+formed give rise to intense optical absorption around 300 500 nm and to decreased reflectance. From the reflectance measurements it is shown that the Tb4+concentration increases as PO21/4, as correspond to the trapping of the holes generated upon the oxygen incorporation as Tb4+. This competitive absorption causes a decrease of the Tb3+luminescence. A quantitative relationship of the Tb3+luminescence intensity with PO2at 800 °C has been found, which is compatible with the trapping model. The spatial resolution of the experimental procedure could be very roughly estimated of the order of 100 µm

Procedimiento de preparación y materiales conformados basados en compuestos eutécticos binarios o ternarios de circonia

Referencia OEPM: P9600891.-- Fecha de solicitud: 19/04/1996.-- Titular: Consejo Superior de Investigaciones Científicas (CSIC).Procedimiento de preparación y materiales conformados basados en compuestos eutécticos binarios o ternarios de circonia. La presente invención está relacionada con la preparación de materiales con estructuras eutécticas micrométricas basados en mezclas de óxidos, conformados con dimensiones mili y submilimétricas mediante fusión zonal por láser con diferentes sistemas ópticos de focalización y control de los haces de los láseres. Su utilización es en el sector de la producción y conservación de energía, como elementos calefactores, refractarios, cátodos para plasmas de aire, electrodos, en componentes para celdas de combustión, microsensores de gas oxígeno, etc.Peer reviewe

Laser-assisted surface melting of Al2O3-YSZ eutectic ceramics

[ES] Se presenta un procedimiento para la densificación y/o texturado superficial de cerámicas de Al2O3-YSZ (circona estabilizada con itria) con composición eutéctica mediante fusión zonal asistida por láser. Haciendo un barrido con la radiación proveniente de un láser de potencia sobre piezas cerámicas conseguimos modificar la microestructura y densificar completatmente la capa superficial, con un espesor que va de 30 a 1000 μm. Por ejemplo, con línea estrecha de láser de diodo, fluencia de 1.23 kW/cm2 y velocidades de barrido de 0.14 mm/s, solidificamos capas de 560 μm. El resultado es una superficie de baja rugosidad y no porosa. La microestructura de la muestra es fina debido a su composición eutéctica. La interfase sólido-líquido en el proceso de crecimiento determina la orientación de la microestructura. Se estudia la forma de esta interfase tanto en cortes transversales como longitudinales, lo que permite analizar el efecto que sobre la microestructura tiene la superposición de barridos, que es una alternativa para tratar superficies extensas. Macroscópicamente la frontera entre barridos contiguos es suave. Sin embargo, su microestructura presenta discontinuidad en el espaciado entre las fases debido a la evolución microestructural en la región no fundida sometida a altas temperaturas y a la nucleación preferencial de Al2O3 al comenzar el crecimiento cristalino. Se analizan distintas posibilidades para disminuir el choque térmico inherente al proceso y que conduce a la formación de grietas paralelas a la dirección de procesado y de delaminación. Se observa una mejora importante cuando se precalienta la pieza a tratar, de modo que es posible procesar superficies de cerámicas eutécticas 99% densas.[EN] A procedure for surface densification and/or texturing of Al2O3-YSZ (yttria stabilised zirconia) ceramics with eutectic composition by means of laser surface melting is presented. By scanning a high-power laser beam on a ceramic surface, we achieve a textured and fully dense surface layer from 30 to 1000 microns thick. For example, using a thin diode laser line with fluence 1.23 kW/cm2 and 0.14 mm/s scan rate, the solidified layer has 560 μm depth. We get a low roughness and dense surface. The microstructure is fine (micron size) due to the eutectic composition. The orientation of the microstructure is determined by the shape of the solid-liquid interface in the solidification process. We study the shape of this interface in transverse and longitudinal cross-sections in single as well as overlapping scans, which are required to process large surfaces. From the macroscopic point of view, the transition between adjacent scans is smooth. However, the microstructure presents discontinuity in the interphase spacing due to microstructural evolution in the heat affected region as well as the nucleation of an Al2O3 layer at the beginning of the crystal growth. The thermal shock inherent to the procedure generates cracks longitudinal and transverse to the scanning direction, as well as delaminating cracks. We analyse different possibilities to reduce this thermal shock. The best results are obtained by preheating the substrate, allowing us to process surfaces of Al2O3-YSZ eutectic ceramics 99% dense.Financiación del Ministerio de Ciencia y Tecnología a través de los proyectos MAT2000-1495 y MAT2000-1533-C03-02.Peer reviewe

Transferring Axial Molecular Chirality Through a Sequence of On-Surface Reactions

Fine management of chiral processes on solid surfaces has progressed over the years, yet still faces the need for the controlled and selective production of advanced chiral materials. Here, we report on the use of enantiomerically enriched molecular building blocks to demonstrate the transmission of their intrinsic chirality along a sequence of on-surface reactions. Triggered by thermal annealing, the on-surface reac-tions induced in this experiment involve firstly the coupling of the chiral reactants into chiral polymers and subsequently their transformation into planar prochiral graphene nanoribbons. Our study reveals that the axial chirality of the reactant is not only transferred to the polymers, but also to the planar chirality of the graphene nanoribbon end products. Such chirality transfer consequently allows, starting from ad-equate enantioenriched reactants, for the controlled production of chiral and prochiral organic nanoarchi-tectures with pre-defined handedness

Unraveling the electronic structure of narrow atomically precise chiral graphene nanoribbons

This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposesRecent advances in graphene-nanoribbon-based research have demonstrated the controlled synthesis of chiral graphene nanoribbons (chGNRs) with atomic precision using strategies of on-surface chemistry. However, their electronic characterization, including typical figures of merit like band gap or frontier band's effective mass, has not yet been reported. We provide a detailed characterization of (3,1)-chGNRs on Au(111). The structure and epitaxy, as well as the electronic band structure of the ribbons, are analyzed by means of scanning tunneling microscopy and spectroscopy, angle-resolved photoemission, and density functional theoryThe project leading to this publication has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 635919), from the Spanish Ministry of Economy, Industry and Competitiveness (MINECO, grant nos. MAT2016-78293-C6, FIS2015-62538-ERC), from the Basque Government (grant nos. IT-621-13, PI-2015-1-42, PI-2016-1-0027), from the European Commission in FP7 FET-ICT “Planar Atomic and Molecular Scale Devices” (PAMS) project (contract no. 610446), from the Xunta de Galicia (Centro singular de investigación de Galicia accreditation 2016−2019, ED431G/09), and from the European Regional Development Fund (ERDF

Comparison of cytokines levels among COVID-19 patients living at sea level and high altitude

Background: At the end of 2019, a novel coronavirus denominated SARS-CoV-2 rapidly spread through the world causing the pandemic coronavirus disease known as COVID-19. The difference in the inflammatory response against SARS-CoV-2 infection among people living at different altitudes is a variable not yet studied. Methods: A descriptive cross-sectional study was performed in two Peruvian cities at different altitudes for comparison: Lima and Huaraz. Five important proinflammatory cytokines were measured including: IL-6, IL-2, IL-10, IFN-γ and TNF-α using ELISA assays. Results: A total of 35 COVID-19 patients and 10 healthy subjects were recruited from each study site. The mean levels of IL-6 (p < 0.03) and TNF-α (p < 0.01) were significantly different among the study groups. In the case of IL-6, patients from Lima had a mean level of 16.2 pg/ml (healthy) and 48.3 pg/ml (COVID-19), meanwhile, patients from Huaraz had levels of 67.3 pg/ml (healthy) and 97.9 pg/ml (COVID-19). Regarding TNF-α, patients from Lima had a mean level of 25.9 pg/ml (healthy) and 61.6 pg/ml (COVID-19), meanwhile, patients from Huaraz had levels of 89.0 pg/ml (healthy) and 120.6 pg/ml (COVID-19). The levels of IL-2, IL-10 and IFN-γ were not significantly different in the study groups. Conclusion: Patients with COVID-19 residing at high-altitude tend to have higher levels of inflammatory cytokines compared to patients living at sea level, particularly IL-6 and TNF-α. A better understanding of the inflammatory response in different populations can contribute to the implementation of therapeutic and preventive approaches. Further studies evaluating more patients, a greater variety of cytokines and their clinical impact are required.National Research Foundation of KoreaRevisión por pare

Tick and host derived compounds detected in the cement complex substance

Ticks are obligate hematophagous arthropods and vectors of pathogens affecting human and animal health worldwide. Cement is a complex protein polymerization substance secreted by ticks with antimicrobial properties and a possible role in host attachment, sealing the feeding lesion, facilitating feeding and pathogen transmission, and protection from host immune and inflammatory responses. The biochemical properties of tick cement during feeding have not been fully characterized. In this study, we characterized the proteome of Rhipicephalus microplus salivary glands (sialome) and cement (cementome) together with their physicochemical properties at different adult female parasitic stages. The results showed the combination of tick and host derived proteins and other biomolecules such as a-Gal in cement composition, which varied during the feeding process. We propose that these compounds may synergize in cement formation, solidification and maintenance to facilitate attachment, feeding, interference with host immune response and detachment. These results advanced our knowledge of the complex tick cement composition and suggested that tick and host derived compounds modulate cement properties throughout tick feeding