Thermodynamic modeling of La₂O₃-SrO-Mn₂O₃-Cr₂O₃ for solid oxide fuel cell applications

ISSN:0884-2914ISSN:2044-532

Thermodynamic Assessment of the La-Fe-O System

The La-Fe and the La-Fe-O systems are assessed using the Calphad approach, and the Gibbs energy functions of ternary oxides are presented. Oxygen and mutual La and Fe solubilities in body-centered cubic (bcc) and face-centered cubic (fcc) structured metallic phases are considered in the modeling. Oxygen nonstoichiometry of perovskite-structured La1±x Fe1±y O3−δ is modeled using the compound energy formalism (CEF), and the model is submitted to a defect chemistry analysis. The contribution to the Gibbs energy of LaFeO3 due to a magnetic order-disorder transition is included in the model description. Lanthanum-doped hexaferrite, LaFe12O19, is modeled as a stoichiometric phase. Δf,elements°H 298K (LaFe12O19)=−5745kJ/mol, °S 298K (LaFe12O19)=683J/mol·K, and Δf,oxides°G (LaFe12O19)=4634−37.071T (J/mol) from 1073 to 1723K are calculated. The liquid phase is modeled using the two-sublattice model for ionic liquids. The calculated La-Fe phase diagram, LaO1.5-FeO x phase diagrams at different oxygen partial pressures, and phase equilibria of the La-Fe-O system at 873, 1073, and 1273K as a function of oxygen partial pressures are presente

Two-step thermochemical solar-to-fuel efficiency computation of strontium and chromium doped lanthanum manganite perovskite oxides using CALPHAD

Reducing greenhouse gas emissions and profiting on novel synthetic fuels to store and buffer energy from renewable sources (such as solar or wind) is a prime strategy to encounter the global energy challenge. Here, two-step thermochemical fuel production is an energy technology utilizing intermittent solar power to convert water and carbon dioxide into syngas, a renewable fuel that can be stored easily and mitigate CO2 emissions. Success of the technology relies on the discovery of materials with a high thermochemical solar-to-fuel efficiency. Perovskites have attracted much attention recently due to impressive fuel productivity[1, 2]. Although a high fuel productivity shows the feasibility of a material, it does not imply that it is the optimum and most efficient material as it depends largely on the operation of the solar-to-fuel reactor [3, 4]. Literature on thermochemical solar-to-fuel efficiency of perovskites is limited and none of the existing studies measures the thermodynamic properties in the entire temperature range relevant for solar-to-fuel production, namely 1000-1800K. In this work, we use oxygen nonstoichiometry from CALPHAD data libraries on A-site doped La1-xSrxMnO3-δ and B-site doped perovskite La0.6Sr0.4Mn1-yCryO3-δ in a relevant temperature range of 1073-1873K to determine the solar thermochemical efficiency. The oxygen nonstoichiometry and thermodynamic properties extracted from CALPHAD libraries are compared to earlier studies of La1-xSrxMnO3-δ for thermochemical fuel production. We discuss diffferences between the earlier extrapolated models and the CALPHAD descriptions on the presented material examples. Specifically, we show thermochemical equilibrium models of fuel productivity supplemented by validations with experimental results on La1-xSrxMnO3-δ in literature. We make predictions on the most efficient material in the composition space La1-xSrxMn1-yCryO3-δ for different conditions. It is shown that the amount of experimental work can be reduced substantially by using the CALPHAD approach and further making predictions for multi-component systems that would be practically unattainable without this method. The solar-to-fuel field will benefit directly from additional thermodynamic data on perovskites in the relevant temperature range. Further, we provide guidelines in terms of key CALPHAD experiments that enables a mapping of the thermodynamic properties of a wide compositional space of perovskites to find materials with a high thermochemical efficiency. 1. McDaniel, A.H., et al., Sr-and Mn-doped LaAlO3−δ for solar thermochemical H2 and CO production. Energy & Environmental Science, 2013. 6(8): p. 2424-2428. 2. Bork, A.H., et al., Perovskite La0.6Sr 0.4Cr1− xCoxO3−δ solid solutions for solar-thermochemical fuel production: strategies to lower the operation temperature. Journal of Materials Chemistry A, 2015. 3(30): p. 15546-15557. 3. Scheffe, J.R., D. Weibel, and A. Steinfeld, Lanthanum–Strontium–Manganese Perovskites as Redox Materials for Solar Thermochemical Splitting of H2O and CO2. Energy & Fuels, 2013. 27(8): p. 4250-4257. 4. Yang, C.-K., et al., Thermodynamic and kinetic assessments of strontium-doped lanthanum manganite perovskites for two-step thermochemical water splitting. Journal of Materials Chemistry A, 2014. 2(33): p. 13612-13623

Thermodynamic modeling of La2O3-SrO-Mn2O3-Cr2O3 for solid oxide fuel cell applications

The thermodynamic La-Sr-Mn-Cr-O oxide database is obtained as an extension of thermodynamic descriptions of oxide subsystems using the calculation of phase diagrams approach. Concepts of the thermodynamic modeling of solid oxide phases are discussed. Gibbs energy functions of SrCrO4, Sr2.67Cr2O8, Sr2CrO4, and SrCr2O4 are presented, and thermodynamic model parameters of La-Sr-Mn-Chromite perovskite are given. Experimental solid solubilities and nonstoichiometries in La1−x Sr x CrO3−δ and LaMn1−x Cr x O3−δ are reproduced by the model. The presented oxide database can be used for applied computational thermodynamics of traditional lanthanum manganite cathode with Cr-impurities. It represents the fundament for extensions to higher orders, aiming on thermodynamic calculations in noble symmetric solid oxide fuel cell

Plastic Deformation Behavior in Steels during Metal Forming Processes: A Review

The plastic deformation occurs in steels during metal forming processing such as rolling, forging, high-pressure torsion, etc. which modify mechanical properties of materials through the grain refinement, and the shape change of objects. Several phenomena in the scope of plastic deformation, such as hardening, recovery, and recrystallization are of great importance in designing thermomechanical processing. During the last decades, a focus of research groups has been devoted particularly to the field of metals processing of steel parts through plastic deformation combined with specific heat treatment conditions. In this review chapter, the current status of research work on the role of plastic deformation during manufacturing is illuminated

Quench sensitivity of Al–Mg–Si alloys: A model for linear cooling and strengthening

In this work quench-induced precipitation during continuous cooling of five Al-Mg-Si alloys is studied over a wide range of cooling rates of 0.05 K/min - 2x10^4 K/min using Differential Scanning Calorimetry (DSC), X-ray diffraction, optical microscopy (OM), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and hardness testing. The DSC data shows that the cooling reactions are dominated by a high temperature reaction (typically 500 °C down to 380 °C) and a lower temperature reaction (380 °C down to 250 °C), and the microstructural analysis shows they are Mg2Si phase formation and B’ phase precipitation on dispersoids, respectively. A new, physically-based model is designed to model the precipitation during the quenching as well as the strength after cooling and after subsequent age hardening. After fitting of parameters, the highly efficient model allows to predict accurately the measured quench sensitivity, the volume fractions of quench induced precipitates, enthalpy changes in the quenched sample and hardness value

Impaired Rho GTPase activation abrogates cell polarization and migration in macrophages with defective lipolysis

Infiltration of monocytes and macrophages into the site of inflammation is critical in the progression of inflammatory diseases such as atherosclerosis. Cell migration is dependent on the continuous organization of the actin cytoskeleton, which is regulated by members of the small Rho GTPase family (RhoA, Cdc42, Rac) that are also important for the regulation of signal transduction pathways. We have recently reported on reduced plaque formation in an atherosclerotic mouse model transplanted with bone marrow from adipose triglyceride lipase-deficient (Atgl−/−) mice. Here we provide evidence that defective lipolysis in macrophages lacking ATGL, the major enzyme responsible for triacylglycerol hydrolysis, favors an anti-inflammatory M2-like macrophage phenotype. Our data implicate an as yet unrecognized principle that insufficient lipolysis influences macrophage polarization and actin polymerization, resulting in impaired macrophage migration. Sustained phosphorylation of focal adhesion kinase [due to inactivation of its phosphatase by elevated levels of reactive oxygen species (ROS)] results in defective Cdc42, Rac1 and RhoA activation and in increased and sustained activation of Rac2. Inhibition of ROS production restores the migratory capacity of Atgl−/− macrophages. Since monocyte and macrophage migration are a prerequisite for infiltrating the arterial wall, our results provide a molecular link between lipolysis and the development of atherosclerosis