Flash sintering of complex oxides

BiFeO3 is one of the most promising multiferroic (materials combining two or more ferroic properties in the same phase) materials. Preparation of high quality BiFeO3 ceramics is quite challenging. The temperature required for processing is relatively high and partial decomposition takes place damaging the properties of the material. Moreover, the Curie temperature of BiFeO3 is within the same temperature range required for conventional sintering. The volume change during Curie transition produces damage in the obtained pellets. In this work high density ceramics of BiFeO3 have been obtained from nanostructured powders, prepared by direct mechanochemistry, followed by FLASH sintering. For FLASH sintering experiments, the original set up developed in Prof. Raj’s lab has been used using linear heating rate. Effect of Flash sintering conditions, namely applied voltage and current intensity, has been investigated. It has been observed that for applied voltages of 50 Vcm-1 or larger sintering occurs almost instantly once certain temperature is reached, corresponding to a FLASH regime. For lower applied voltages densification takes place progressively in a kind of field assisted or FAST regime. For FLASH experiments, densification takes place at furnace temperatures at low as 480ºC within few seconds, while conventional heating requires temperatures above 850ºC. Interestingly, under FLASH conditions pure phase materials with high density were obtained, while for those materials obtained in the FAST regime mixtures were obtained. This behavior could be explained by the effect of applied voltage on the temperature of the Curie transition. Electrical properties of the samples obtained by FLASH were characterized using complex impedance spectroscopy at different temperatures. It was concluded that resulting materials were electrically insulating. It is worth mentioning that no reduction in the sample was observed, while for samples prepared by spark plasma sintering (SPS) it has been previously reported lower resistivity and activation energy values due to reduction in the samples during the SPS experiment

Reaction flash sintering for producing high quality functional ceramics within seconds

For ceramic materials, it has been recently shown in literature that applying a small electric field and a small DC current through a sample produces sudden sintering (within seconds) at relatively low temperatures. This method is known as Flash Sintering and it has been applied to number of materials. In this work it is shown that both chemical reaction and sintering can be combined into a single flash sintering experiments. This new approach is known as Reaction Flash Sintering. To demonstrate the feasibility of this method, a multiferroic material, BiFeO3, is prepared from a stoichiometric mixture of Bi2O3 and Fe2O3 oxides. Thus, in a single process, dense nanostructured BiFeO3 ceramics are obtained by applying an electric field of 50 V cm-1 and with a current limit of 35 mA mm-2 within seconds at a furnace temperature of about 625 °C. The resulting materials were pure-phase perovskites without any evidence of secondary phases, sillenite or mullite, that are commonly present in materials prepared by conventional procedures. Moreover, samples were electrically insulating, as measured by complex impedance spectroscopy. It is shown here that the synthesis of pure single-phase ceramics of complex oxides from stoichiometric mixtures of single oxides is possible by reaction flash sintering, even for materials difficult to prepare by conventional procedures. This discovery is a breakthrough in materials preparation

Inter-Individual variability in insulin response after grape pomace supplementation in subjects at high cardiometabolic risk: role of microbiota and miRNA

Scope Dietary polyphenols have shown promising effects in mechanistic and preclinical studies on the regulation of cardiometabolic alterations. Nevertheless, clinical trials have provided contradictory results, with high inter‐individual variability. This study explores the role of gut microbiota and microRNAs (miRNAs) as factors contributing to the inter‐individual variability in polyphenol response. Methods and Results 49 subjects with at least two factors of metabolic syndrome are divided between responders (n = 23) or non‐responders (n = 26), depending on the variation rate in fasting insulin after grape pomace supplementation (6 weeks). The populations of selected fecal bacteria are estimated from fecal deoxyribonucleic acid (DNA) by quantitative real‐time polymerase chain reaction (qPCR), while the microbial‐derived short‐chain fatty acids (SCFAs) are measured in fecal samples by gas chromatography. MicroRNAs are analyzed on a representative sample, followed by targeted miRNA analysis. Responder subjects show significantly lower (p < 0.05) Prevotella and Firmicutes levels, and increased (p < 0.05) miR‐222 levels. Conclusion After evaluating the selected substrates for Prevotella and target genes of miR‐222, these variations suggest that responders are those subjects exhibiting impaired glycaemic control. This study shows that fecal microbiota and miRNA expression may be related to inter‐individual variability in clinical trials with polyphenols

A national data-based energy modelling to identify optimal heat storage capacity to support heating electrification

Heating decarbonisation through electrification is a difficult challenge due to the considerable increase in peak power demand. This research proposes a novel modelling approach that utilises easily accessible national-level data to identify the required heat storage volume in buildings to decrease peak power demand and maximises carbon reductions associated with electrified heating technologies through smart demand-side response. The approach assesses the optimal shifting of heat pump operation to meet thermal heating demand according to different heat storage capacities in buildings, which are defined in relation to the time (in hours) in which the heating demand can be provided directly from the heat battery, without heat pump operation. Ten scenarios (S) are analysed: two baselines (S1–S2) and eight load shifting strategies (S3–S10) based on hourly and daily demand-side responses. Moreover, they are compared with a reference scenario (S0), with heating currently based on fossil fuels. The approach was demonstrated in two different regions, Spain and the United Kingdom. The optimal heat storage capacity was found on the order of 12 and 24 h of heating demand in both countries, reducing additional power capacity by 30–37% and 40–46%, respectively. However, the environmental benefits of heat storage alternatives were similar to the baseline scenario due to higher energy consumption and marginal power generation based on fossil fuels. It was also found that load shifting capability below 4 h presents limited benefits, reducing additional power capacity by 10% at the national scale. The results highlight the importance of integrated heat storage technologies with the electrification of heat in highly gas-dependent regions. They can mitigate the need for an additional fossil-based dispatchable generation to meet high peak demand. The modelling approach provides a high-level strategy with regional specificity that, due to common datasets, can be easily replicated globally. For reproducibility, the code base and datasets are found on GitHub

Vliv DSC tepelné setrvačnosti na vývoj krystalizační kinetiky

Influence of added thermal resistance on crystallization kinetics, as measured by differential scanning calorimetry (DSC), of the Se70Te30 glass was studied. The increase of thermal resistance was achieved by adding polytetrafluorethylene discs of different thicknesses (up to 0.5 mm) in-between the DSC platform and the pan with sample. Increase of the thermal resistance led to an apparent decrease (by more than 30%) in the crystallization enthalpy. Significant change of model-free kinetics occurred: apparent activation energy E of the crystallization process decreased (by more than 20%) due to the DSC data being progressively shifted to higher temperatures with increasing heating rate. The model-based kinetics was changed only slightly; the DSC peaks retained their asymmetry and the choice of the appropriate model was not influenced by the added thermal resistance. The temperature shift caused by added thermal lag was modeled for the low-to-moderate heating rates.Pomocí diferenční skenovací kalorimetrie byl sledován vliv přidaného tepelného odporu na měřená kinetická data pro krystalizaci sklovitého Se70Te30

Study of the thermal decomposition of historical metal threads

In this work, it is reported that thermal analysis techniques such as differential thermal analysis and thermogravimetric analysis are very useful for evaluating metals threads and fibres used in the manufacture of historical artifacts. Thermal analysis has been used to characterize the silk, cotton and linen employed as supports and the copper, silver and aluminium as the metallic components in the studied threads. Other organic compounds, mainly added for the conservation of the threads, have also been characterized.The financial support of the Spanish Commission Interministerial of “Economia y Competitividad” (Plan Estatal 2013–2016 Retos–Proyectos I+D+i) under Project BIA2014-55318-R is also acknowledged

Seville history insight through their construction mortars

Seville is intimately linked to its historic role and extensive cultural heritage. The city has been occupied by Romans, Arabs and Christians, who built important historical buildings. Roman (first–second centuries) and Arabic (eleventh century) buildings, medieval Shipyard (thirteenth century), San Isidoro and Santa Maria de las Cuevas monasteries (fifteenth century), Santa María de las Cuevas (fifteenth century modified in eighteenth century), El Salvador Church (eighteenth century), the Royal Ordnance building (eighteenth century) and Santa Angela de la Cruz convent (twentieth century) performed with lining mortars, and mortars used in building stones (City Hall and Marchena Gate), all of them located in Seville (Spain), have been studied. Ninety-four mortar samples (employed as structural, plaster, coating) originally used or applied in restoration processes have been collected to perform an archaeometry study. The ratio of CO2 mass loss to hydraulic water (H2O) mass loss, and the mineralogical characterization by X-ray diffraction has been used to compare the mortars used in the different historical periods. Mainly hydraulic mortars were widely used in all these studied monuments as most mortars showed CO2/H2O ratios within the 4–10 range. Moreover, the thermal analysis curves also showed a broad temperature range for the thermal decomposition of the carbonate fraction of the mortars.Peer reviewe