Fatigue improvement and residual stress relaxation of shot-peened alloy steel DIN 34CrNiMo6 under axial loading

Shot-peening treatment was applied to a quenched and tempered DIN 34CrNiMo6 steel to improve its high-cycle R: -1 axial fatigue strength. Compared with the machined condition, the increase in the fatigue limit was 21.8%. S-N curves for shot-peened and the as machined condition were presented and compared with those obtained in previous research for rotating bending fatigue, including curves for mirror-polished specimens. The applied shot-peening treatment in this work (I-sp: 8A and 200% coverage) for quenched and tempered (Q + T) DIN 34CrNiMo6 steel introduced a compressive residual stress field and an increase in surface roughness, as well as minor variations in microstructure, hardness and the FWHM (full width of the diffraction peak at half maximum intensity) parameter. The introduced compressive residual stress field tended to reduce when an external stress is applied. This was due to the onset of plastic strain. In this paper, two types of quasi-static tests were conducted by applying an axial stress with six different magnitudes and in the two directions (compressive or tensile). This was in order to assess their influence on the relaxation of surface residual stresses. Due to the introduced compressive residual stresses, if the applied stress was compressive, the onset of plastic deformations was achieved with a lower stress magnitude. In addition, surface residual stress relaxation under cyclic applied stress was evaluated at four different stress magnitudes. Due to the cyclic-softening behaviour of this Q + T steel, its cyclic mechanical properties must be considered to assess the onset of plastic strains. With the experimental data, a logarithmic model to predict the evolution of surface residual stresses with the number of cycles for different applied stress magnitudes was presented.The authors wish to acknowledge the financial support received from the Department of Research and Development of the Basque Government, the UPV/EHU University, through the Research Project Reference: Grupos GV IT947-16

Unraveling the role of the thermal and laser impacts on the blackening of cinnabar in the mural paintings of Pompeii

The blackening of red cinnabar (α-HgS) pigment has traditionally been explained by its conversion into black metacinnabar (β-HgS). Scarce is however the scientific evidence that supports this hypothesis in polychrome artworks. As such transition occurs at around 345 °C, the thermal impact of the eruption of Mount Vesuvius in 79 AD could have induced this structural change of the pigment present in the mural paintings of Pompeii. This work aims to assess whether the mentioned volcanic eruption could be responsible of the cinnabar blackening through the formation of metacinnabar. The thermodiffractometry study of cinnabar-decorated fresco mock-ups stated that the formed β-HgS is not stable, observing its reversion into α-HgS. Moreover, sublimation of the cinnabar pictorial layer was registered, also when the cinnabar paint layer was protected by a coating of pyroclastic materials. In real blackened cinnabar Pompeian samples, it was not possible to identify metacinnabar by X-ray diffraction (XRD), but evidence of sublimation of mercury due to the thermal impact was observed. Hence, this blackening seems to be related mainly to the presence of calomel (Hg2Cl2) and a gypsum (CaSO4·2H2O) crust as degradation products of red cinnabar and the calcite mortar, respectively, and not to the formation of metacinnabar. Finally, laser-based techniques could also induce modifications in the HgS crystalline structure, resulting in an amorphous black product. Therefore, the elemental and molecular study of the species promoted by laser impact was carried out to avoid false positives in the metacinnabar detection or when the decorated surface has been subjected to laser cleaning.The research leading to these results has received funding from “la Caixa” Foundation (Silvia Pérez-Diez, ID 100010434, Fellowship code LCF/BQ/ES18/11670017). This work has been supported by the project IT1446-22 for Consolidated Research Groups, funded by the Basque Country Government. The authors acknowledge as well the funding provided by University of the Basque Country through the Institutionally Sponsored Open Access

Structural and Magnetic Properties of FeNi Films and FeNi-Based Trilayers with Out-of-Plane Magnetization Component

FeNi films of different thickness and FeNi/(Fe, Co)/FeNi trilayers were prepared by magnetron sputtering deposition onto glass substrates. The permalloy films had a columnar microstructure. The detailed analysis of the magnetic properties based on the magnetic and magneto-optical measurements showed that at thicknesses exceeding a certain critical thickness, hysteresis loops acquire a specific shape and the coercive force of the films increase sharply. The possibility of the estimation of the perpendicular magnetic anisotropy constant using the Murayama equation for the thickness dependence of saturation field was demonstrated. The results of studies of the structural and magnetic properties of FeNi films laminated by Fe and Co spacers with different thickness are presented.This research was funded by the Russian Science Foundation (RSF), project no. 22-29-00980, https://rscf.ru/en/project/22-29-00980/ and in part by the Research Groups of the UPV-EHU

Influence of synthetic method on the properties of La0.5Ba0.5FeO3 SOFC cathode

Power Point presentado en The Energy and Materials Research Conference - EMR2015 celebrado en Madrid (España) entre el 25-27 de febrero de 2015Perovskite type (ABO3) oxides have been widely studied as SOFC cathode materials at high temperatures. Given that several of the challenges hindering SOFC technology are consequence of the high operation temperature (about 1000ºC) [1,2], an important goal is to reduce it to 600-800ºC. To minimize this effect new perovskite-type mixed ionic-electronic conducting oxides have been widely studied as promising IT-SOFC cathodes. Among them, iron perovskites (LSF) seem to be good candidates mainly for their appropriate thermal expansion match with YSZ electrolytes and their good catalytic activity for the oxygen reduction [3,4]. The properties of these compounds and thus their cell performance depends on several factors: the right choice of A and B elements, the amount of doping cations (A1-xAx) and some structural parameters such as the tolerance factor [5], the average size of the A-site cations () and the A cation size disorder (σ2(rA)). Studies on the influence of the hole-doping (x) in the A-site of LSF perovskites have shown good cathode performances in compounds with intermediate doping levels [6]. The change of and σ2(rA) indicate that better performances are observed for highest and lowest σ2(rA) [7]. External parameters, such as the synthetic method, are also important factors that influence the final properties [8]. In this sense it has been observed that porosity, grain size and morphology of the compounds strongly depend on the sample preparation techniques. In this research, a La0.5Ba0.5FeO3 perovskite has been synthesized by two different methods (ceramic and glycine-nitrate routes) in order to study the synthetic method influence on the properties of this compound as IT-SOFC cathode material. This composition has been chosen due to its intermediate hole doping level (0.5) and high average size of the A-site cations ( = 1.48 Å, when rA are standard 12-coordinate ionic radii), these parameters, according with previous studies should show interesting properties for its use as SOFC cathode. It has been observed that the two La0.5Ba0.5FeO3 compounds show different room temperature crystal structure depending on the synthesis route. The sample obtained by the ceramic method has higher oxygen vacancy content, but in the other hand the SEM micrographs show that glycine-nitrate process leads to a compound with porous structure and particles with nanometric grain sizes. At 700 or 800ºC the electrical conductivity of both samples is similar but the sample obtained by glycine-nitrate route shows better electrochemical performance. The ceramic sample has lower adherence than the glycine counterpart and this derivates in higher values of polarization resistance. It is believed that this is a consequence of the heterogenous morphology of this sample. Therefore, it seems that the glycine-nitrate synthetic method is a more appropriate technique for preparing perovskite cathodes

Designing multifunctional pigments for an improved energy efficiency in buildings

Materials science offers solutions that when are combined can offer important energy savings in the building sector. In this study, high reflectance coating and thermal storage capacity are combined with the aim of improving energy efficiency in buildings. For this issue a multifunctional pigment having a phase change material adsorbed on its surface and a high total solar reflectance has been manufactured. The total solar reflectance of the pigment will make the paint to reflect the sunlight radiation in the infrared part of the spectrum reducing the amount of absorbed radiation. This high reflection provides a surface level effect as is a passive stimulus-responsive solution that acts with sunlight radiation. On the other hand, the thermal storage capability provides a bulk level effect as is passive stimulus-responsive solution acting by temperature changes, making it possible to use constructive materials as a thermal energy storage media. The preparation process is described and the pigment is characterized conveniently. The thermal performance of corresponding pigmented coatings was evaluated by an experiment simulation in which different boxes were covered with the coating containing the multifunctional pigment and traditional pigmented coating on their tops. The indoor air temperature and the interior temperature of the substrate were measured obtaining differences of 4–5°C.European Union Seventh Framework Programme, FP7-NMP-2010-Small-5 (under grant agreement no 280393) Dpto. Educación, Política Lingüística y Cultura of the Basque Goverment, IT-630-13 Ministerio de Ciencia e Innovación, MAT2013-42092-R Engineering and Physical Sciences Research Council, EP/I00393

SOFC development at CNH2

Abstract del 4th International Symposium on the Catalysis for Clean Energy and Sustainable Chemistry. Bilbao, Spain July 9-11 (2018).Solid oxide fuel cells (SOFC´s) are devices that convert chemical energy from reactants into heat and electricity with high efficiency. Usually, these systems operate at high temperatures (600-1000ºC) and are able to run with different fuels. Here we present the current activities that are being carried out at the Solid Oxide laboratory of the Hydrogen National Centre in Spain, which is focused on the development and electrochemical characterization of SOFC materials and devices

SOFC development at CNH2

Abstract del 4th International Symposium on the Catalysis for Clean Energy and Sustainable Chemistry. Bilbao, Spain July 9-11 (2018).Solid oxide fuel cells (SOFC´s) are devices that convert chemical energy from reactants into heat and electricity with high efficiency. Usually, these systems operate at high temperatures (600-1000ºC) and are able to run with different fuels. Here we present the current activities that are being carried out at the Solid Oxide laboratory of the Hydrogen National Centre in Spain, which is focused on the development and electrochemical characterization of SOFC materials and devices

Optimization of the large scale synthesis of the LSF-20 cathode material for SOFCs

Póster presentado en: 21st World Hydrogen Energy Conference 2016. Zaragoza, Spain. 13-16th June, 2016Solid oxide fuel cells (SOFCs) have the potential to be one of the cleanest and most efficient energy technologies for direct conversion of chemical fuels to electricity. Economically competitive SOFC systems appear poised for commercialization, but widespread market penetration will require continuous innovation of materials and fabrication processes to enhance system lifetime and reduce cost. Additional requirements arise for the technologies for synthesis of SOFC materials. These requirements originate from the demands for large scale SOFC industrial production. In this sense, solution combustion synthesis (SCS) is a simple and reproducible method used to obtain several types of ceramic oxides for a variety of applications. A typical SCS procedure utilizes a self-sustained exothermic reaction among well-mixed reactants to achieve the rapid and economical synthesis of particulate products. Up to 2008, SCS method has been adopted to fabricate more than 1000 kinds of oxide powders over more than 65 countries [1]. The properties of the resulting powders (crystalline structure, amorphous structure, crystallite size, purity, specific surface area and particle agglomeration) depend heavily on the adopted processing parameters [2,3]. The objective of this work is to obtain, on a large scale, the perovskite-type oxide La0.8Sr0.2FeO3 that shows promising properties as cathode for SOFC applications. In this study, the optimization of the large scale synthesis has been realized by the glycine-nitrate combustion method (Figure 1). In this sense, first of all, the effect of some parameters such as temperature, glycine/nitrate ratio and times and cooling rates used in the temperature treatments, that play a key role in the final properties of the obtained materials, has been analyzed. The characterization has been realized by ICP (inductively coupled plasma atomic emission spectroscopy) XRD (X Ray diffraction), SEM (scanning electron microscopy) and dilatometry.This research has been funded by the Ministerio de Economía y Competitividad (MAT2013-42092-R) with co-financing FEDER-EU) and Dpto. Educación, Política Lingüística y Cultura of the Basque Goverment (IT-630-13). The authors thank SGIker (UPV/EHU) technical support

Effect of the A cation size disorder and synthesis conditions on the properties of an iron perovskite series

Póster presentado en The Energy and Materials Research Conference - EMR2015 celebrado en Madrid (España) entre el 25-27 de febrero de 2015Solid state chemistry thrives on a rich variety of solids that can be synthesized using a wide range of techniques. It is well known that the preparative route plays a critical role on the physical and chemical properties of the reaction products, controlling the structure, morphology, grain size and surface area of the obtained materials. This is particularly important in the area of ABO3 perovskite compounds given that they have for long been at the heart of important applications [1]. Particularly, perovskite systems such as La1-xSrxFeO3 (LSF) are now receiving researchers attention for their interesting applications [2-4] such as ceramic membranes (CMs) for oxygen separation, solid oxide fuel cells (SOFCs) electrodes for efficient power generation, catalysts for complete oxidation of CO in vehicle engines, etc. In order to develop these advanced materials, combustion methods (glycine-nitrate, urea based, and other modifications) have been proposed as one of the most promising methods for their synthesis [5,6]. This method consists of a highly exothermic self-combustion reaction between the fuel (usually glycine, urea or alanine) and the oxidant (metal nitrates), that produces enough heat to obtain the ceramic powders. The characteristics (including purity, structure and size) of the combustion synthesis oxide powders are typically determined by several synthetic parameters, such as the species of fuel and oxidizer reactants, the fuel/oxidizer ratio, and the subsequent sintering treatment after combustion process [7]. In the other hand, physical properties of these perovskite materials are very sensitive to changes in the doping level (x), the average size of the A cations (), and the effects of A cation size disorder (σ2(rA)) quantified as σ2(rA) = – 2 [8]. Our searching approach to find the optimum synthetic conditions for new materials within the LSF system has been based on the study of only one of the indicated parameters isolated from the rest. In this sense, this study is focused on the effect of the variation of the cation size disorder, calcination temperature and the fuel/oxidizer ratio of glycine/nitrate on the structural, morphological, electrical and catalytic properties of a series of Ln0.5M0.5FeO3-δ perovskites (Ln = La, Sm; M = Ba, Sr)

Scalable synthetic method for SOFC compounds

Although economically competitive SOFC systems seems to be ready for commercialization, a broad inventory of key starting materials and fabrication processes are needed to enhance systems and reduce costs. These necessities are raised by the demands for large scale SOFC industrial production. Taking into account these reasons, we have synthesized the mean components of a fuel cell, on a large scale, by the glycine nitrate combustion method. The synthesized different components of SOFC have been the interconnector protective coating (MnCo1.9Fe0.1O4), contact layer (LaNi0.6Fe0.4O3), cathode (La0.6Sr0.4FeO3), interlayer (Sm0.2Ce0.8O1.9), electrolyte (ZrO2)0.92(Y2O3)0.08 and anode (Ni0.3O-(ZrO2)0.92(Y2O3)0.08) material, obtaining reproducible pure samples and amounts up to 12 g for each batch, being able to increase easily this amount to lots of hundred of grams. The obtained materials have been characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES) and X-ray fluorescence (XRF), X-ray diffraction (XRD), dilatometry, scanning electron microscopy (SEM), particle size distribution and conductivity measurements.Ministerio de Economía, Industria y Competitividad (MAT2016-76739-R) (AEI/FEDER, UE) and (MAT2015-2015-86078-R) Dpto. Educación del Gobierno Vasco (IT-630-13) European Regional Development Fund (ERDF). Ministerio de Economía y Competitividad (BES-2014-068433