Structural Design of 5 mol.% Yttria Partially Stabilized Zirconia (5Y-PSZ) by Addition of Manganese Oxide and Direct Firing

In this study, 5Y-PSZ-based ceramics with 15 mol.% of manganese oxide were obtained from PSZ + MnO2 powders mixtures by pressing and direct firing. The resulting materials show a stable cubic fluorite structure with only minor traces of segregated manganese oxides and relative density from 90% to 98%. The linear thermal expansion coeffcient is in the order of 10^-5 K^-1 at 500 K and increases gradually with temperature, due to the onset of a contribution of chemical expansion, reaching about 13x10^-6 K^-1 at 1100 K. These results are suitable for prospective applicability as buffer layers to minimize degradation and delamination of electrolyte/oxygen electrode interfaces in solid electrolyte cells. The electrical conductivity remains close to 1 S/m at 973 K and close to 7 S/m at 1273 K, suggesting mixed conductivity with a prospective contribution to electrode processes occurring at electrode/electrolyte interfaces. Guidelines for further improvement were also established by a detailed analysis of the impact of heating/cooling rate, firing temperature, and time on those properties, based on Taguchi planning.publishe

Characterization of ZrO2-Y2O3-MnO2 solid solutions as components for reversible solid oxide cells

Long-term degradation remains the main issue for the viability of reversible solid oxide fuel/electrolysis cell (SOFC/SOEC) technology as practical hydrogen production and energy storage systems. While some lifetime-limiting factors are common in both regimes, the major specific degradation mechanism in SOEC regime relates to the delamination phenomena. The experimental and modelling results suggest that high oxygen pressures can develop in electrolyte near the anode/electrolyte interface resulting in formation of voids at the grain boundaries, intergranular fractures, cracks in anode, and anode delamination; all factors contribute to irreversible degradation. The objective of this work was the characterization of ZrO2-Y2O3-MnO2 solid solution in order to design a functional material with oxygen storage ability that may be used as inclusion into electrolyte membrane or as interlayer between electrolyte and oxygen electrode with the purpose of delay or prevent degradation and irreversible changes. ((ZrO2)1-x(Y2O3)x)1-y(MnOn)y ceramics (x = 0.02-0.05, y = 0.05-0.15) were prepared by solid-state reaction route and sintered in air at 1400-1600°C. XRD results showed the formation of singlephase solid solutions with cubic fluorite-type structure for the compositions with x = 0.05, while the ceramics with lower yttria content comprised 2 or more phases based on different polymorphs of zirconia. The characterization of materials included microstructural studies (SEM/EDS), thermal analysis (thermogravimetry, dilatometry), measurements of electrical conductivity as function of temperature and oxygen partial pressure, and determination of ionic transference numbers by modified e.m.f. method. Increasing Mn content was found to results in increase of the total electrical conductivity and electronic contribution under oxidizing conditions, while ionic transport dominates under reduced oxygen partial pressures. Electrical measurements showed also a slow relaxation of electrical conductivity on redox cycling that possibly can be attributed to a variable solubility of Mn cations in fluorite lattice.publishe

Mixed Ionic-Electronic Conductivity, Redox Behavior and Thermochemical Expansion of Mn-Substituted 5YSZ as an Interlayer Material for Reversible Solid Oxide Cells

Manganese-substituted 5 mol.% yttria-stabilized zirconia (5YSZ) was explored as a prospective material for protective interlayers between electrolyte and oxygen electrodes in reversible solid oxide fuel/electrolysis cells. [(ZrO2)0.95(Y2O3)0.05]1−x[MnOy]x (x = 0.05, 0.10 and 0.15) ceramics with cubic fluorite structure were sintered in air at 1600 °C. The characterization included X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), thermogravimetry and dilatometry in controlled atmospheres, electrical conductivity measurements, and determination of oxygen-ion transference numbers by the electromotive force (EMF) technique. Mn-substituted 5YSZ solid solutions exhibit variable oxygen nonstoichiometry with manganese cations in a mixed 2+/3+ oxidation state under oxidizing conditions. Substitution by manganese gradually increases the extent of oxygen content variation on thermal/redox cycling, chemical contribution to thermal expansion and dimensional changes on reduction. It also deteriorates oxygen-ionic conductivity and improves p-type electronic conductivity under oxidizing conditions, leading to a gradual transformation from predominantly ionic to prevailing electronic transport with increasing x. Mn2+/3+→Mn2+ transformation under reducing atmospheres is accompanied by the suppression of electronic transport and an increase in ionic conductivity. All Mn-substituted 5YSZ ceramics are solid electrolytes under reducing conditions. Prolonged treatments in reducing atmospheres, however, promote microstructural changes at the surface of bulk ceramics and Mn exsolution. Mn-substituted 5YSZ with 0.05 ≤ x < 0.10 is considered the most suitable for the interlayer application, due to the best combination of relevant factors, including oxygen content variations, levels of ionic/electronic conductivity and thermochemical expansion

Desarrollos electrónicos y fotónicos en sistemas de comunicaciones ópticas

En este trabajo se hace una breve descripción de las principales líneas de investigación y desarrollo del grupo de Sistemas de Comunicaciones Ópticas. Dentro del grupo se desarrollan las siguientes líneas de trabajo:Fotónica en Microondas y RF (MW & RF Photonics) consiste en actividades de I+D en tecnologías y dispositivos fotónicos que procesen, controlen, reciban o generen señales de MW y RF. Entre los sistemas más conocidos que operan en MW se encuentran los radares, conformador de haces, comunicaciones satelitales, transpondedores satelitales, enlaces de radio, a los cuales mediante tecnología fotónica se intenta agregarle o mejorarle alguna de sus características.Facultad de Ingenierí

Efficient low-loaded ternary Pd-In2O3-Al2O3 catalysts for methanol production

Pd-In2O3 catalysts are among the most promising alternatives to Cu-ZnO-Al2O3 for synthesis of CH3OH from CO2. However, the intrinsic activity and stability of In2O3 per unit mass should be increased to reduce the content of this scarcely available element and to enhance the catalyst lifetime. Herein, we propose and demonstrate a strategy for obtaining highly dispersed Pd and In2O3 nanoparticles onto an Al2O3 matrix by a one-step coprecipitation followed by calcination and activation. The activity of this catalyst is comparable with that of a Pd-In2O3 catalyst (0.52 vs 0.55 gMeOH h−1 gcat-1 at 300 \ub0C, 30 bar, 40,800 mL h−1 gcat-1) but the In2O3 loading decreases from 98 to 12 wt% while improving the long-term stability by threefold at 30 bar. In the new Pd-In2O3-Al2O3 system, the intrinsic activity of In2O3 is highly increased both in terms of STY normalized to In specific surface area and In2O3 mass (4.32 vs 0.56 g gMeOH h−1 gIn2O3-1 of a Pd- In2O3 catalyst operating at 300 \ub0C, 30 bar, 40,800 mL h−1 gcat-1).The combination of ex situ and in situ catalyst characterizations during reduction provides insights into the interaction between Pd and In and with the support. The enhanced activity is likely related to the close proximity of Pd and In2O3, wherein the H2 splitting activity of Pd promotes, in combination with CO2 activation over highly dispersed In2O3 particles, facile formation of CH3OH

Tension-Compression Loading with Chemical Stimulation Results in Additive Increases to Functional Properties of Anatomic Meniscal Constructs

Objective: This study aimed to improve the functional properties of anatomically-shaped meniscus constructs through simultaneous tension and compression mechanical stimulation in conjunction with chemical stimulation. Methods: Scaffoldless meniscal constructs were subjected to simultaneous tension and compressive stimulation and chemical stimulation. The temporal aspect of mechanical loadingwas studied by employing two separate five day stimulation periods. Chemical stimulation consisted of the application of a catabolic GAG-depleting enzyme, chondroitinase ABC (C-ABC), and an anabolic growth factor, TGF-b1. Mechanical and chemical stimulation combinations were studied through a full-factorial experimental design and assessed for histological, biochemical, and biomechanical properties following 4 wks of culture. Results: Mechanical loading applied from days 10–14 resulted in significant increases in compressive, tensile, and biochemical properties of meniscal constructs. When mechanical and chemical stimuliwere combined significant additive increases in collagen per wet weight (4-fold), compressive instantaneous (3-fold) and relaxation (2-fold) moduli, and tensile moduli in the circumferential (4-fold) and radial (6-fold) directions were obtained. Conclusions: This study demonstrates that a stimulation regimen of simultaneous tension and compression mechanical stimulation, C-ABC, and TGF-b1 is able to create anatomic meniscus constructs replicating the compressive mechanica

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe

Correction to: Cluster identification, selection, and description in Cluster randomized crossover trials: the PREP-IT trials

An amendment to this paper has been published and can be accessed via the original article

Alterações redox e estimuladas eletricamente em materiais para células reversíveis pilha/eletrolisador

This project is focused on the study of dynamic changes in the composition, structure, microstructure and electrochemical properties of solid electrolyte cell materials, for prospective operation in reversible electrolyzer/fuel cell modes, at high temperatures, as well as the corresponding changes in performance. Thus, the main objective of this thesis was to develop novel materials and concepts for enhanced tolerance to electrochemical reversibility and self-healing approaches to revert ageing, seeking materials with oxygen storage capacity, ability to block the cation diffusion and related phenomena and also with the capacity to capture diffusing contaminants. An introduction of the fuel cell, seeking its employ as reversible system and associated degradation issues of the fuel cell elements were overviewed in Chapter 1, based on relevant literature. Main materials employed as fuel cell components and some possible mitigation strategies in order to prevent the severe effects of degradation also were reviewed in this chapter. In Chapter 3 one studied composition changes and corresponding impact on redox stability, defect chemistry, transport properties, thermochemical expansion and other relevant properties of yttria partially stabilized zirconia with co-additions of Mn, intended for application as buffer layers. The design of these compositions was guided by analysis of the impact of Mn and redox conditions on stability and transport properties. In Chapter 4 one studied [(ZrO2)0.95(Y2O3)0.05]0.85(MnO1.5)0.15] buffer layers, processed by direct firing of powder mixtures, for prospective applicability as buffer layer at the oxygen electrode/electrolyte interface of solid electrolyte cell, in order to minimize the risks of degradation and delamination. The generic firing schedule was selected by the Taguchi planning and the contribution of each individual factor in the properties of the materials were discussed. Similarly, samples with composition [(ZrO2)1-x(Y2O3)x]1-y(PrO1.5)y] (x≤0.05; 0.05≤y≤0.15) were prepared considering a model system for sealing strategies, oxygen storage and the ability to eliminate the delamination in SOEC mode (Chapter 5). Transport properties, thermochemical expansion and other relevant properties were studied for its employ as buffer layer in the oxygen/electrolyte interface using Taguchi planning to select the firing condition. Strontium titanate-based materials were prepared by partial substitution of La by Sr in the A site and Mo by Ti in the B site. One studied the impact of these substitutions on structure, microstructure, electrical transport properties, thermochemical and dilatometric behavior, and a defect chemistry model was proposed. The detailed studied carried out in chapters 3-6 provided useful information for the preparation of fuel cells and the preliminary electrochemical test reported in the chapter 7. This chapter includes detailed studied about: a) reactivity between fuel electrode based materials and buffer layer (YCTO), b) deposition of fuel electrodes onto traditional 8YSZ electrolyte with and without modification of cell performance by CGO and Ni-CGO infiltration and/or application of YCTO buffer layer with electrochemical preliminary screening, c) preliminary screening of the fuel cell performance with the buffer layers prepared in chapter 3-5, employing commercial LSM electrodes.Este projeto está focado no estudo de alterações dinâmicas na composição, estrutura, microestrutura e propriedades de materiais para células eletroquímica de eletrólito sólido de alta temperatura, sob polarização catódica/anódica alternada, visando operação reversível entre os modos de eletrolisador e pilha de combustível. Assim, o objetivo principal desta tese foi desenvolver novos materiais e conceitos para maior tolerância à reversibilidade eletroquímica e abordagens de auto-regeneração para reverter o envelhecimento, buscando materiais com capacidade de armazenamento de oxigênio, capacidade de bloquear a interdifusão de catiões e fenómenos relacionados e também com a capacidade de captura de contaminantes, limitando a sua difusão. No Capítulo 1 apresenta-se uma introdução às células de combustível, com ênfase em sistemas reversíveis e as questões de degradação dos componentes destas células eletroquímicas. Neste capítulo também foram revistos os principais materiais empregados como componentes de células de combustível e algumas possíveis estratégias de mitigação para prevenir os graves efeitos da degradação. No Capítulo 3 foram estudadas mudanças de composição de zircónia parcialmente estabilizada com ítria, com co-adições de Mn, e o seu impacto na estabilidade redox, química de defeitos, propriedades de transporte, expansão termoquímica e outras propriedades relevantes, visando utilização como camada tampão. Este estudo foi orientado pela análise do impacto de adições de Mn e condições redox na estabilidade desses materiais e nas propriedades de transporte. No Capítulo 4 foram preparados materiais de composição nominal [(ZrO2)0,95(Y2O3)0,05]0,85(MnO1,5)0,15], preparados por queima direta de misturas de pós, para potencial aplicação como camada tampão na interface elétrodo de oxigênio / eletrólito da célula de eletrólito sólido, a fim de minimizar riscos de degradação e delaminação. O ciclo de queima genérico foi estudado por planeamento de Taguchi, sendo analisados os efeitos de diversos fatores em propriedades relevantes. Da mesma forma, foram estudadas no Capítulo 5 amostras de diversas composições no sistema [(ZrO2)1-x(Y2O3)x]1-y(PrO1,5)y] (x≤0,05; 0,05≤y≤0,15), visando estratégias de camadas tampão com capacidade de auto-selagem, armazenamento de oxigênio e prevenção de delaminação em condições de operação como eletrolisador. Foi usado planeamento Taguchi para estudar a interação entre composição e condições de queima na estrutura, densificação e condutividade elétrica. No Capírulo 6 foram estudados materiais à base de titanatos de estrôncio com substituição parcial de La por Sr no sítio A e Mo por Ti no sítio B, visando aplicação como material de elétrodo de combustível. Foi estudado o impacto destas substituições na estrutura, microestrutura e propriedades de transporte elétrico, comportamento termoquímico e dilatométrico e foi proposto um modelo de química de defeitos. O estudo detalhado realizado nos capítulos 3-6 forneceu informações úteis para a preparação de células a combustível e o teste eletroquímico preliminar relatado no capítulo 7. Este capítulo inclui estudos detalhados sobre: a) reatividade entre materiais à base de elétrodo de combustível e camada tampão (YCTO), b) deposição de elétrodos de combustível no eletrólito 8YSZ tradicional com e sem modificação do desempenho da célula por infiltração de CGO e Ni-CGO e / ou aplicação de camada tampão YCTO com avaliação eletroquímica preliminar, c) avaliação preliminar do desempenho de camadas tampão desenvolvidas nos capítulos 3-5, usando um elétrodo LSM comercial.Programa Doutoral em Ciência e Engenharia de Materiai