Efecto del oxígeno no estequiométrico en las propiedades estructurales, morfológicas y magnéticas de la cobaltita YBaCo2O5+δ, obtenida por el método del precursor polimérico

Resumen: Las cobaltitas YBaCo2O5+δ son materiales con estructura tipo perovskitas, que muestra propiedades fisicoquímicas fascinantes. El oxígeno no estequiométrico brinda a estos materiales una elevada capacidad de almacenamiento y de movilidad de iones oxígeno, convirtiéndolos en promisorios para aplicaciones, como electrodos para celdas de combustibles de estado sólido, membranas para separación de oxígeno, sensores de oxígeno o catalizadores. Su comportamiento ferromagnético blando a temperaturas cercanas a ambiente, los convierte en materiales prometedores como sensores magnéticos, materiales magnetocalóricos y dispositivos magnéticos. Dichas propiedades fisicoquímicas, son dependientes del contenido de oxígeno presente en el material. Razón por la cual, en este trabajo se presenta el estudio de la dependencia de las propiedades estructurales, magnéticas y morfológicas de la cobaltita YBaCo2O5+δ, en función de la estequiometría de oxígeno. Por lo cual, muestras policristalinas fueron obtenidas por las rutas de síntesis de reacción en estado sólido y las rutas químicas del precursor polimérico clásico, modificado y no selectivo. Los mejores resultados de síntesis fueron obtenidos por el uso de la ruta de síntesis del precursor polimérico no selectivo, con temperaturas y periodos de calcinación de 1000 °C y 30 horas en atmósfera de aire. El oxígeno no estequiométrico fue variado por tratamientos térmicos en atmósfera de oxígeno puro, por 5 horas y a temperaturas de 350, 500 y 700 °C. Mostrando que este es mayor para muestras tratadas a 350 °C en atmósfera de oxígeno. Las propiedades estructurales, estudiadas por difracción de rayos X y refinamiento Rietveld, muestran la fase tetragonal con grupo espacial P 4/mmm y parámetros de red 3ap x 3ap x 2ap para 0,17 δ 0,29, y la fase ortorrómbica, con grupo espacial P mma y parámetros de red 2ap x 2ap x2ap para δ 0,3. El estudio de los modos vibracionales por espectroscopia infrarroja permite sugerir que la fase tetragonal se encuentra conformada por dos tipos de entornos de coordinación octaédricos –CoO6, mientras que la fase ortorrómbica presenta tres entornos de coordinación octaédricos –CoO6 diferentes. El comportamiento magnético de las cobaltitas fue estudiado mediante curvas de magnetización en función de temperatura y campo, obtenidas por magnetometría de muestra vibrante. Esta caracterización mostró que la cobaltita YBaCo2O5+δ sigue la ley de Curie-Weiss y presenta las transiciones de fases Para-Ferro-Antiferromagnético, típicas de estos materiales. También demostró, que el aumento del oxígeno no estequiométrico desplaza las temperaturas de las transiciones de fases magnéticas, hasta temperaturas cercanas a ambiente; estas fueron 293 K y 270 K para la fase ortorrómbica y 277 K y 192 K para la fase tetragonal. La cobaltita YBaCo2O5,29(2), que presentó una estequiometría de oxígeno intermedia, mostró un comportamiento magnético complejo, sugiriendo la coexistencia de la fase tetragonal y ortorrómbica. Se observó que las muestras policristalinas de la cobaltita YBaCo2O5+δ, se encontraban constituidas por partículas de forma irregular con tamaños inferiores a 1,0 μm y con un alto grado de aglomeración. No se observó un efecto significativo de la estequiometría de oxígeno sobre las propiedades morfológicas del material.Abstract: The YBaCo2O5+δ cobaltites are materials with perosvkite-like structure, which exhibit a variety of fascinating physicochemical properties. The non- stoichiometric oxygen makes these materials have high storage capacity and oxygen mobility, making them promising materials for technological applications such as electrodes for fuel cells, solid-state oxygen separation membranes, oxygen sensors or catalysts. Behavior as soft ferromagnetic materials at temperatures near room temperature, make them promising magnetocaloric materials and magnetic devices. These physicochemical properties are dependent non-stoichiometric oxygen material. In this work, the dependence of non-stoichiometric oxygen of structural, magnetic and morphological properties of cobaltiteYBaCo2O5+δ was studied. Polycrystalline samples were obtained by solid state reaction and chemical synthesis of classic, modified and non-selective polymeric precursor. The best results were found for the synthesis of non-selective polymeric precursor with calcination at 1000 ° C for 30 hours in air atmosphere. Non- stoichiometric oxygen was varied by heat treatments in pure oxygen atmosphere for 5 hours at temperatures of 350, 500 and 700 ° C. Showing that the non-stoichiometric oxygen is higher when the samples are heated to 350 ° C in oxygen atmosphere. The structural properties studied by X-ray diffraction and Rietveld refinement, showing the tetragonal phase with space group P4/mmm and cell parameters 3ap x 3ap x 2ap for 0.17 δ 0.29, and orthorhombic phase with space group Pmma and cell parameters 2ap x 2ap x 2ap for δ 0.30. Vibrational modes studied by infrared spectroscopy shows that the tetragonal phase is formed by two types of octahedral coordination environments -CoO6, whereas the orthorhombic phase has three different octahedral coordination environments –CoO6. The magnetic behavior of the cobaltite was studied by magnetization curves in function of temperature and magnetic field. These curves were obtained by vibrating sample magnetometer. The cobaltite YBaCo2O5+δ follow the Curie-Weiss law and show phase transitions Para-Ferro-Antiferromagnetic, which are typical of these materials. Also, the increase in the non-stoichiometric oxygen shifted temperatures of magnetic phase transitions up to temperatures close to room temperature; these are 293 K and 270 K, for the orthorhombic phase and 277 K and 192 K for the tetragonal phase. The cobaltite YBaCo2O5.29(2) worth not-stoichiometric oxygen intermediate, showed complex magnetic behaviors, suggesting the coexistence of the tetragonal phase and the phase orthorhombic. Polycrystalline samples cobaltite were constituted by irregularly shaped particles with sizes below 1.0 μm and with high degree of agglomeration or sintering. The non-stoichiometric oxygen did not significantly affect the morphology of the cobaltite Keywords: Layered cobaltite, double perovskites, magnetic oxides, magnetic transitions, non-stoichiometric oxygen, chemical synthesis, magnetic moment.Maestrí

Analysis of the influence of thickness on fire reaction performance in polyisocyanurate core sandwich panels

Sandwich panels (also known as insulated panels) have been traditionally used for industrial buildings and warehouses, but nowadays are being increasingly a favorable choice in building construction, mainly in wall cladding and roofing systems. This paper presents the results of an experimental and statistical comparative analysis of Fire Reaction development in sandwich panels consisting of steel sheeting and Polyisocyanurate (PIR) foam core. All these PIR core sandwich panels with joints kept the same dimensions (1000 mm × 1500 mm) + (500 mm × 1500 mm), but different thicknesses (30, 50, 100 and 150 mm). Five Single Burning Item (SBI) tests were carried out on individual PIR sandwich panels with vertical joints and their results were compared between themselves. It was possible to observe through an analysis of variance that there is an influence of the sample thickness in the individual results of the SBI test parameters; however, this variability has no significant influence on the Fire Reaction performance of the samples. Overall, the importance of these alternative sandwich panels is the increase in performance in the constructive processes and the offered comfort through its thermal insulation characteristics

Eggshells as agro‐industrial waste substitute for CaCO3 in glass foams: A study on obtaining lower thermal conductivity

In this work, discarded glass bottles (GB) and eggshells (ES) were used to produce foam glass designed for thermal insulation. The literature on the thermal conductivity of foam glasses produced with eggshells is sparse. This material was used as pore‐forming agent at 3% and 5% weight fractions to obtain a foam glass with low thermal conductivity. Homogenized powders were uniaxially pressed, and the compacts were fired at three temperatures (800, 850, and 900°C). Raw materials were characterized by chemical analysis and particle size distribution. The foam glasses were characterized by their porosity, phases, compressive strength, and thermal conductivity. The best insulating properties were obtained for the composition containing 5 wt% ES fired at 800°C. This sample displayed a porosity of 91.4% while its thermal conductivity was of 0.037 W/m.K, with a compressive strength of 1.12 ± 0.38 MPa. Crystalline phases were observed in samples fired at 850 and 900°C as a result of the devitrification process. The final properties of the materials are comparable to those of commercial foam glasses obtained from non‐renewable, more expensive raw materials, a great indicator that the studied compositions could be used as an environmentally friendly substitute

Understanding the mobility of potential nutrients in rock mining by-products: An opportunity for more sustainable agriculture and mining

The increase in demand for highly soluble fertilizers brings a global sustainability concern. Alternative sources for traditional fertilization are therefore needed. Rock powder use has been proposed as an alternative approach to soil remineralization. However, research on the agricultural potential of minerals and rocks as alternative sources of nutrients is limited to changes in soil chemical attributes or effects on crop yield. In this work, we report an experimental study addressing the dissolution of two silicate rock-derived powders (andesite and dacite) that were produced during mining activities in Southern Brazil. The rock powders were exposed to Milli-Q water at pH (7.4–8.8) range, in solutions of 0.1 mol L−1 citric acid at pH range 2.1–3.3, and Milli-Q water acidified with 0.5 mol l−1 acetic acid (pH 5–5.8), in a continuous mechanical rotatory shaker at room temperature. Dissolution kinetics were determined as a function of reaction times at 24 to 5760 h, and solution pH. Based on this kinetics, dissolution rates were determined for the individual powders and compared to expected values for aluminosilicates. Based on this comparison, it was shown that the application of andesite and dacite rock-derived powder to replace high soluble fertilizers is feasible due to high dissolution rates of their minerals. The average andesite dissolution rates in Milli-Q water, in citric acid solution, and in Milli-Q water acidified with acetic acid were 2.1 × 10−5, 1.92 × 10−1 and 6.3 × 10−4 mmol cm−2 s−1, respectively for Ca, being 183%, 22.6%, and 69.2% higher than for the dacite rock. This make andesite rock a potential substitute for carbonate-based liming. In contrast, the average dacite dissolution rates in Milli-Q water, in citric acid solution, and in Milli-Q water acidified with acetic acid were 1.05 × 10–5, 7.22 × 10−5, and 3.72 × 10−5 mmol cm−2 s−1, respectively for K, being 72.0%, 61.4%, and 73.6% higher than the andesite rock. This highlights its potential use as a K source for agriculture to replace highly soluble K-fertilizers

Particulate matter geochemistry of a highly industrialized region in the Caribbean: basis for future toxicological studies

Air pollution has become an important issue, especially in Caribbean urban areas, and, particulate matter (PM) emitted by different natural and anthropogenic sources causes environmental and health issues. In this work, we studied the concentrations of PM10 and PM2.5 sources in an industrial and port urban area in the Caribbean region of Colombia. PM samples were collected within 48-h periods between April and October 2018 by using a Partisol 2000i-D sampler. Elemental geochemical characterization was performed by X-ray fluorescence (XRF) analysis. Further, ionic species and black carbon (BC) were quantified by ion chromatography and reflectance spectroscopy, respectively. Using the Positive Matrix Factorization (PMF) receptor model, the contributions of PM sources were quantified. The average concentration of PM10 was 46.6 ± 16.2 μg/m3, with high concentrations of Cl and Ca. For PM2.5, the average concentration was 12.0 ± 3.2 μg/m3, and the most abundant components were BC, S, and Cl. The receptor model identified five sources for PM10 and PM2.5. For both fractions, the contributions of marine sea spray, re-suspended soil, and vehicular traffic were observed. In addition, PM2.5 included two mixed sources were found to be fuel oil combustion with fertilizer industry emissions, and secondary aerosol sources with building construction emissions. Further, PM10 was found to also include building construction emissions with re-suspended soil, and metallurgical industry emissions. These obtained geochemical atmospheric results are important for the implementation of strategies for the continuous improvement of the air quality of the Caribbean region

Multianalytical approach of stay-in-place polyvinyl chloride formwork concrete exposed to high temperatures

This work presents results of the first study of the variation by exposure to high temperatures from two stay-in-place polyvinyl chloride (SIP-PVC) formwork concrete exposed to the ISO 834 fire curve. A systematic sampling based on the proximity of the fire and the spalling of the concrete was carried out and microstructural, thermal, crystallographic and spectroscopic changes were studied according to the degree of affectation by fire using SEM, TGA-DTA, XRD and FTIR. The response to high temperature exposure of the microstructure of SIP-PVC formwork concrete after fire was established using the experimental results. Results show a relationship between the microstructure of concrete paste and exposure temperature, as well as, the relationship between exposure temperature and dehydration of calcium hydrates, CSH gel and Portlandite and decarbonation of Calcite. These reactions can be considered as tracers of the degree of exposure to high temperatures from stay-in-place PVC formwork concrete

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Release kinetics of multi-nutrients from volcanic rock mining by-products: Evidences for their use as a soil remineralizer

Great quantities of stone by-products are stored alongside different exploiting mines in south Brazil, which are becoming an unsustainable environmental issue. Powder materials of andesite and dacite rocks were obtained from two mining companies of Southern Brazil. The particle size classification of the materials was determined by sieving. The X-ray diffraction (XRD) technique was used to identify the mineral phases of the by-products and X-ray fluorescence (XRF) was applied to determine their chemical compositions. The concentrations of calcium (Ca), potassium (K), magnesium (Mg), phosphorus (P) and silicon (Si) released by the by-products were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). Dissolution rates of andesite and dacite rocks were measured in Milli-Q water, and in solutions of 0.1 mol L−1 citric acid, and Milli-Q water acidified with 0.5 mol L−1 acetic acid, as a function of reaction times at 24–96 h (short-term), and at 96–5760 h (long-term). The solutions were agitated continuously on a mechanical rotatory shaker at room temperature. The parabolic diffusion, simplified Elovich, and power function models were applied at both time slots of solid-solution reaction. The results indicated that the relationships of quantity of released multi-nutrients were well described by power equation: ln qt = ln a + b ln t. Dissolution rates were obtained based on the release of Ca, K, Mg, P and Si at a steady state under far from equilibrium conditions. Dissolution rates of both by-products were not affected, within the experimental uncertainty, by Milli-Q water. Although the by-products dissolution rates were unaffected by Milli-Q water, its rates are increased along the time. The dissolution of the by-products minerals was significantly affected by the pH of the solutions. The multi-elements release by both by-products in 0.1 mol L−1 citric acid solution was significantly larger than another solutions, indicating that exchangeable cations were readily available in citric acid solution. The results obtained from power function model in two reaction time intervals can contribute to estimate the multi-nutrients-supplying power of by-products to soil. The present study provides both to solving an environmental issue associated with Brazilian rock exploitation and to create an alternative for soil fertilization and a more sustainable agriculture