Intermediate Temperature Region Research Articles

Thermo-rheological behaviour of styrene-butadiene-styrene, hard plastics with or without graphene oxide modified bitumens

With the increase in traffic volume and heavy vehicles, as the changes in climatic conditions, in recent years the design of the road surface has completely changed because it has to guarantee the suitable performance of the pavement. To this end, in recent decades, modifiers have been introduced into the bitumen and, currently, the most performing modifier is SBS (styrene-butadiene-styrene) polymer, but in recent years the investigation on the so-called green additives, obtained from recycled materials or of natural origin is growing. The study intends to investigate, from a rheological point of view, the possibility of using waste hard plastics also in combination with graphene oxide because considered a promising material for new binder generation. For this purpose, the influence that hard plastics, with or without graphene oxide addition, have on the bitumen performance compared to standard SBS-modified bitumens has been studied. The comparison has shown that the plastomeric additive can improve the rheological properties, in the intermediate and high in-service temperature region, while the graphene oxide addition acts on the transitions from viscoelastic to viscous material at high temperature; nevertheless, the aging reduces the effect. In addition, it was found that 4 %w/w of hard plastics improve the performance of bitumen and the rheological properties are not affected by the influence of aging.

Creep mechanisms and cavitation of AA5052 at intermediate stress and temperature region

Creep mechanism and cavitation of AA5052 were studied employing creep experiments at 200–350°C and stresses 15–70 MPa. The microstructural observations were then performed to assess grain growth and formation of cavities. The apparent activation energy was defined in a range of 154–166 kJ/mole. It was found that at higher normalised stress region ([Formula: see text]), the stress exponent was about 7 and at lower stresses it decreased to about 5. Microstructural instability, that is, grain growth, was detected during creep at a temperature of 300°C or higher. This phenomenon affected the strain rate and the governing mechanisms. Microstructure of the sample tested at 300°C revealed that the coalescence of cavities could occur at creep strains higher than 6.5%.

Experimental and modeling study on ignition kinetics of ethyl methyl carbonate

Ethyl methyl carbonate (EMC) is an essential electrolyte of lithium-ion batteries (LIBs), and the spontaneous ignition of electrolyte is considered to be an important inducement for the thermal runaway (TR) combustion of LIBs. To better understand its ignition chemistry and combustion kinetics, the ignition delay times (IDTs) of ethyl methyl carbonate were measured by using a Rapid Compression Machine (RCM) over a wide range of temperatures (810–980 K), pressures (20 and 40 bar), equivalence ratios (φ = 0.5, 1.0, and 2.0), and a fuel concentration of 2 %, yielding results that are in substantial variance with those calculated with detailed kinetics in the literature over the entire range of conditions investigated. An improved chemical kinetic model was developed to simulate the ignition and combustion characteristics of EMC under intermediate-temperature region by employing the updated kinetic parameters. Results show that the overall performance of the present kinetics model is substantially improved with respected to the prediction of ignition delay times, intermediate species profiles, as well as laminar flame speeds across different temperature, pressure, and equivalence ratio conditions. Furthermore, sensitivity and pathway analyses show that the ignition chemistry of EMC is mainly controlled by retro-ene reaction and H abstraction reactions.

The Activation Energy of Viscous Flow and Liquid–Liquid Structure Transition in Co-B Alloys

The temperature dependences of the kinematic viscosity during heating and cooling have been investigated in Co-B melts with a boron content of up to 30.8 at. A liquid–liquid structural transition was found, which is accompanied by an increase in the activation energy and cluster size, as well as a significant decrease in the density of the melt. The liquid–liquid structural transition was associated with the formation of clusters with a short-range order of Co23B6 in the intermediate temperature region. At low and high temperatures, clusters of the order of an atomic size are active participants in the viscous flow. It was shown that with an increase in the cluster size, the activation energy increases and the viscosity of melts decreases. The formation of large Co23B6 clusters during the cooling of melt with low boron content leads to undercooling and the appearance of the transition temperature region with high activation energy, although this region does not exist during the heating stage.

Effect of temperature on tensile behavior, fracture morphology, and deformation mechanisms of Nickel-based additive manufacturing 939 superalloy

In the current work, uniaxial tensile tests, including interrupted tests at room temperature, intermediate temperatures (650 ℃ and 700 ℃), and high temperatures (850 ℃ and 950 ℃), were conducted on the additive manufacturing 939 superalloy to investigate the mechanical properties, fracture behaviors, and deformation mechanisms. According to the experimental results, the tensile mechanical properties exhibit a significant temperature sensitivity, as the yield, tensile strength, and elongation decrease with the increase in temperature. The fracture surfaces show that the material exhibits obvious plastic fracture characteristics at room temperature. Moreover, many multi-slip system steps can be observed when the temperature rises. Furthermore, according to the result of the transmission electron microscopy, the deformation mechanism at room temperature is primarily controlled by the single slip system. As temperature rises to the intermediate temperature region, more slip systems are activated by thermal energy, which promotes the movement of dislocations. The deformation mechanism is mainly dominated by dislocation shearing γ'. When the temperature reaches the high temperature region, the deformation mechanism firstly demonstrates large-scale stacking faults, and then transforms into the dislocation by-passing and climbing mechanism. Finally, the relationship between temperature and the deformation mechanism is discussed and deduced.

Study on the ignition characteristics of CH4/H2/air mixtures in a micro flow reactor with a controlled temperature profile

The ignition characteristics of stoichiometric CH4/H2/air mixtures with different H2 dilution ratios were studied by using a micro flow reactor (MFR) with a controlled temperature profile. The weak flame positions of the mixtures were determined by the luminosity of CH∗, and the ignition temperatures (defined as the corresponding wall temperatures) were obtained. The ignition temperature of the mixture is smoothly decreased with a small amount of H2 addition, while the decrease of the ignition temperature is more rapid with increasing H2 dilution. One-dimensional computation with a detailed reaction mechanism was also conducted to study the ignition characteristics of the CH4/H2/air mixtures. The computational ignition temperature which is defined as the wall temperature at the peak of the heat release rate (HRR) peak is also obtained. Both the experimental and computational results show that the weak flame shifts to the lower temperature region with an increase of the H2 mole fraction. And the non-linear decrease of the ignition temperature of the CH4/H2/air weak flame versus increasing H2 dilution was also well reproduced by the numerical computation. The flame structures, primary exothermic and endothermic reactions of the CH4/H2/air weak flames were studied in detail. The importance of H and OH in the ignition process of the mixtures was analyzed, and the kinetic effects of H2 on the ignition of the mixture in the intermediate-temperature region (1000–1200 K) and high-temperature region (1200–1300 K) were elucidated. The analysis of the computational results reveals that the OH production routes in the intermediate-temperature region are substantially changed with different H2 dilutions, while the OH production routes at the peak of the heat release rate are not obviously influenced. In the end, the primary mechanism for the non-linear effects of H2 addition on the ignition temperatures of the CH4/H2 mixtures was clarified.

Elevated temperature tensile behaviour of 5183 aluminium alloy made by electrospark deposition additive manufacturing

This study focuses on the microstructure and tensile behaviour of the as-deposited 5183 Al–Mg alloy fabricated by electrospark deposition (ESD) additive manufacturing. Tensile tests were carried out at temperatures from 293K to 773K with strain rates from 1 × 10−4/s to 1 × 10−1/s, and the microstructure of the specimens was characterised by XRD, SEM, EBSD and TEM. The results showed that the initial microstructure consists of equiaxed grains of about 60 μm diameter with no oriented texture. As the deformation temperature increased from 293K to 773K, the alloy's UTS dropped from 292 MPa to 57 MPa, and elongation rose from 37% to 61%. The strain rate sensitivity was relatively low (less than 0.034) in the intermediate temperature region (293K–473K) and stepped up to 0.111 ± 0.003 when the experimental condition turned to elevated temperatures (573K–773K). The microstructure of specimens deformed at intermediate temperatures (293K–473K) revealed typical dislocation entanglement and dynamic recovery characteristics. Recrystallisation occurred at higher temperatures (573K–773K), and texture intensity fell to a minimum level. The deformation of the as-deposited 5183 aluminium alloy at elevated temperatures is a diffusion mechanism controlled by thermal activation, and the thermal activation energy is about 162 kJ/mol.

Structure, Oxygen Mobility, and Electrochemical Characteristics of La1.7Ca0.3Ni1 ‒ xCuxO4 + δ Materials

The Ruddlesden‒Popper phases pertain to numerous promising materials with the mixed ionic-electronic conductivity used in devices such as oxygen-conducting membranes, solid oxide fuel cells (SOFC), and electrolyzers, which operate in the intermediate temperature region. Their high total conductivity and oxygen mobility make these materials candidates for the mentioned applications. The structure, the oxygen mobility, and the electrochemical characteristics of the promising materials La1.7Ca0.3Ni1 – xCuxO4 + δ (x = 0–0.4) are studied. According to the high-precision XRD data, all synthesized materials are single-phased and have the tetragonal structure. The unit cell parameter c and the cell volume increase upon doping with copper. The content of overstoichiometric interstitial oxygen decreases with doping and the compositions with the high copper content become oxygen deficient. The samples are characterized by the nonuniform oxygen mobility. By and large, the trend for the decrease in the oxygen mobility with the increase in the Cu content is observed in the series of La1.7Ca0.3Ni1 – xCuxO4 + δ samples. By impedance spectroscopy studies, it is shown that the electrodes with the La1.7Ca0.3Ni1 – xCuxO4 + δ functional layers with the copper content x 0.2 have a higher electrochemical activity. The factors responsible for the efficiency of electrodes are analyzed. The results obtained in this study demonstrate that La1.7Ca0.3Ni0.6Cu0.4O4 + δ materials are the candidates for the air electrodes in electrochemical devices.

Mechanism of Polaronic Conduction in Olivine Phosphates: An Influence of Crystallite Size

We report the polaronic conduction mechanism in transition-metal phosphate with different crystallite sizes by performing broadband ac conductivity measurements. The conductivity spectra exhibited a frequency-independent dc conductivity at low frequencies, and the conductivity becomes frequency-dependent above the characteristic frequency. The temperature-dependent dc conductivity has been analyzed within the framework of Mott’s model of polaronic conduction, which exhibits non-Arrhenius behavior within the hopping conduction region. The apparent non-Arrhenius behavior is divided into three different regions depending on the type of lattice phonons associated with the bound charge carrier. Interestingly, at high temperatures, the dc conductivity is primarily determined by the polaron concentration, and it varies with temperature. To ascertain the temperature-dependent polaron concentration variation at high temperatures, the frequency-dependent conductivity spectra have been analyzed by scaling procedure individually on three distinct regions. The application of the Summerfield scaling law on the ac conductivity spectra at low- and intermediate-temperature regions follows the time–temperature superposition principle (TTSP). On the other hand, at high temperatures, the scaling of the ac conductivity spectra with the Summerfield scaling law was found to exhibit pronounced deviations. The scaling of the ac conductivity spectra at high temperatures was improved significantly using the random barrier model. We suggest that at high temperatures, the number density of polarons performing a long-range hopping process becomes a temperature-dependent quantity and increases with temperature.

Field evolution of magnetic phases and spin dynamics in the honeycomb lattice magnet Na2Co2TeO6 : Na23 NMR study

We report on the results of 23Na NMR in the honeycomb lattice magnet Na2Co2TeO6 which has been nominated as a Kitaev material. Measurements of magnetic shift and width of the NMR line as functions of temperature and magnetic field show that a spin-disordered phase does not appear up to a field of 9 T. In the antiferromagnetic phase just below the Neel temperature TN, we find a temperature region extending down to ~TN/2 where the nuclear spin-lattice relaxation rate 1/T1 remains enhanced and is further increased by a magnetic field. This region crosses over to a low temperature region characterized by the rapidly decreasing 1/T1 which is less field-sensitive. These observations suggest incoherent spin excitations with a large spectral weight at low energies in the intermediate temperature region transforming to more conventional spin-wave excitations at low temperatures. The drastic change of the low-energy spin dynamics is likely caused by strong damping of spin waves activated only in the intermediate temperature region, which may be realized for triple-q magnetic order possessing partially-disordered moments as scattering centers of spin waves. In the paramagnetic phase near TN, dramatic field suppression of 1/T1 is observed. From analysis of the temperature dependence of 1/T1 based on the renormalized-classical description of a two-dimensional quantum antiferromagnet, we find the field-dependent spin stiffness constant that scales with TN as a function of magnetic field. This implies field suppression of the energy scale characterizing both two-dimensional spin correlations and three-dimensional long-range order, which may be associated with an increasing effect of frustration in magnetic fields.

Enhanced Thermoelectric Performance of Yb-Filled Skutterudite with Bottom-Up Formed CoSi2 Nanoparticles.

It is known that Yb-filled skutterudite with excellent thermoelectric performance is promising for a power generation device in the intermediate temperature region. Here we created a new approach to obtain nanostructured materials by adding Si to Co-overstoichiometric Yb-filled skutterudite through high-energy ball milling, which embedded bottom-up formed CoSi2 nanoparticles into grain-refining Yb0.25Co4Sb12, synergistically resulting in the enhanced thermoelectric properties and room-temperature hardness. On one hand, the abundant grain boundaries and phase interfaces effectively blocked the propagation of medium-low frequency phonons, resulting in a lower lattice thermal conductivity. On the other hand, phase interfaces barrier nicely screened a portion of low-energy electrons, leading to an improved power factor. As a result, an enhanced peak ZT value of ∼1.43 at 823 K and a promising average ZT of ∼1.00 between 300 and 823 K were achieved in the Yb0.25Co4Sb12/0.05CoSi2 sample. Meanwhile, such nanostructures also enhanced the hardness through the collective contributions of second phase and fine grain strengthening, which made skutterudite more competitive in practical application.

Comparative studies on superconductivity in Cr3Ru compounds with bcc and A15 structures

Chromium (Cr) is a transition metal element with 3d orbital electrons. In most compounds containing Cr, due to the correlation effect, twofold features, namely localization and itinerancy are expected. The localization gives rise to a magnetic moment, while the latter exhibits as the effective coherent weight for conductivity. Here we report the physical properties of Cr3Ru compounds with body-centered cubic (bcc) and A15 structures by using multiple experimental tools. The resistivity measurements show sharp superconducting transitions at = 2.77 K and = 3.37 K for the bcc and A15 structures, respectively. A high residual resistivity exists in both phases. Magnetization measurements also show rather narrow superconducting transitions, with a clear hump feature in the intermediate temperature region (about 150 K), which may be ascribed to the remaining antiferromagnetic spin fluctuations. A pronounced second peak effect has been observed in magnetization hysteresis loops in the superconducting state only for samples with bcc structure. The specific heat coefficient reveals a clear jump at critical temperatures (). We find that s-wave gaps can be adopted to fit the low temperature specific heat data of both samples yielding ratios of about 3.6, indicating a moderate pairing strength. Interestingly, the Wilson ratios are 3.81 and 3.62 for the bcc and A15 phases, suggesting a moderate correlation effect of conducting electrons in the normal state. Besides, for samples with A15 structure, another specific heat anomaly occurs at about 0.85 K and is sensitive to magnetic fields. In addition, by applying high pressures, both systems will exhibit an enhancement of with a rate of about 0.019 K GPa−1 and 0.013 K GPa−1 for the bcc and A15 phases, respectively. Our combinatory results point to unusual behavior of both superconducting and normal states in these two Cr based alloys.

High thermoelectric properties of P-SiGe/Sr0.9La0.1Ti0.9−xZrxNb0.1O3 composite

SrTiO3 is a high temperature thermoelectric material with calcium titanite structure that is environmentally friendly and affordable, but the high thermal conductivity at high temperatures limits its development, so how to maintain high electrical properties while reducing thermal conductivity is the most important problem facing SrTiO3. SiGe and SrTiO3 are both thermoelectric materials in the intermediate and high temperature region and have a lot of commonalities, and it is likely to obtain high thermoelectric properties through the interfacial effect of both, however, there is not any study on the compound regulation of the two. Therefore, in this study, phosphorus (P)-doped SiGe was compounded with Zr, La and Nb co-doped SrTiO3. 3 mol.%SiGe(C)/97 mol.% Sr[Formula: see text]La[Formula: see text]Ti[Formula: see text]Zr[Formula: see text]Nb[Formula: see text]O3(Zr1Si3(C)) obtained by sintering under carbon reducing atmosphere shows a relatively large power factor of and low thermal conductivity of 2.88 Wm[Formula: see text]K[Formula: see text] at 1000 K, achieve a ZT value to 0.42 at 1000 K. This is at a high level in this study of SrTiO3 composite thermoelectric materials and provides a new idea for the subsequent study of composite modulation.

Fluctuation magnetoconductivity in superconducting Ca10(Pt4As8)(Fe2As2)5 single crystal

Fluctuation-induced conductivity up to μ0H = 14 T for superconducting Ca10(Pt4As8)(Fe2As2)5 single crystal was evaluated from the measured in-plane electrical resistivity, and it was analyzed by Aslamazov-Larkin (AL) theory for zero magnetic field and Ullah and Dorsey (UD) scaling method for magnetic field. A dimensional crossover of superconducting fluctuations from low-temperature three-dimension to high-temperature two-dimension was observed. When the dimensional crossover occurs, a temperature region in which two-dimensional and three-dimensional fluctuations occur simultaneously was found in the intermediate temperature region.

The Heat Capacity of PuO2 at High Temperature: Molecular Dynamics Calculations

Abstract A new generation of fast breeder reactors (FBRs) is under development with the objective of making nuclear energy more sustainable. Most promising reactor designs are loaded, at least during their early phase of deployment, with UO2–PuO2 mixed oxide fuel (MOX). Concentrations of plutonium dioxide that are foreseen for FBRs range up to 30 mol%. This highlights the need for a sound and deep knowledge of the thermophysical properties of PuO2. This statement is valid in the case of heat capacity, as evaluations on MOX fuel are usually carried out by using the Neumann–Kopp rule. Heat capacity is relevant for thermal conductivity and performance under transient conditions. However, measurements on the heat capacity of plutonium dioxide are scarce or even lacking at high temperature. Numerical methodologies such as molecular dynamics (MD) calculations have been employed to overcome the difficulties encountered in experimental measurements. Besides numerical also theoretical models have been applied as valuable tools for interpretation of enthalpy measurements. Nevertheless, due to the mentioned lack of experimental measurement issues such as the existence of the Bredig transition and the formation of defects at high temperatures are still debated in nuclear fuel research. Excess enthalpy seen in measurements of actinides oxides has been explained by means of either electronic disorder or anion disorder. In the case of plutonium dioxide, a common consensus has been reached on the hypothesis that anion disorder leads to a significant increase in heat capacity at high temperature. Konings and Beneš have developed a model that accounts for this phenomenon. Their correlation has been often included in models of heat capacity and employed for recommendations. However, in the high-temperature region, MD calculations showed an underestimation of model predictions that was not compensated by the presence of a peak of heat capacity that has been interpreted as the Bredig transition. Based on these observations, this paper presents MD evaluations on the heat capacity of PuO2 at high temperature that are mostly focused on the formation energy of oxygen Frenkel pairs (OFPs) and its correlation with the model proposed by Konings and Beneš. Besides an interatomic potential published in the open literature and developed in compliance with the experimental thermal expansion of PuO2, a second interatomic potential has been applied in calculations. This latter is featured by a lower formation energy of OFP. The contribution due to defects formation was calculated by means of a simplified theoretical model of heat capacity. Results of calculations in the very high-temperature domain showed an increase in the contribution due to OFP defects consistent with the model by Konings and Beneš. Predictions suggest the onset of a premelting transition around 85% of melting temperature without the presence of a peak of heat capacity. Major deviations from the recommended model have been noted in the intermediate temperature region where the effect of clustering of defects should play a significant role. Therefore, the value of formation energy of OFP proposed by Konings and Beneš could be interpreted as an effective value that accounts for the two processes (defects clustering and premelting transition) that could contribute, according to our results, to the heat capacity of plutonium dioxide at high temperature. This conclusion is consistent with the numerical evaluations of OFP formation energy that are in general higher than proposed by Konings and Beneš.

Numerical investigation of n-dodecane ECN spray and combustion characteristics using the one-way coupled Eulerian-Lagrangian approach

This work investigated the spray and combustion characteristics of the Engine Combustion Network (ECN) n-dodecane injections using a one-way coupled Eulerian-Lagrangian approach. The actual X-ray measured injector geometries from the Argonne National Laboratory were adopted for Eulerian simulations. The multi-phase flow was modeled using the Volume-of-Fluid (VoF) method with the high-resolution interface capturing scheme to track the fluid-gas interface. The generated parcel data from the Eulerian simulations were mapped and utilized in the Lagrangian simulations to ensure fidelity. The simulation results agree well with the experimental data in terms of the projected density, mass flow rates, spray penetrations, mixture distributions, and ignition delays. The diverging nozzle channel in the Spray C injector resulted in cavitation and air entrainment, which reduced the mass flow rate. Because of the low oxygen concentration, the low-temperature combustion (LTC) reactions made a significant contribution to the heat release process. In comparison, similar jet-flame structures were observed for the Spray A, C, and D cases, consisting of the upstream LTC region, midstream intermediate-temperature combustion region, downstream fuel-rich high-temperature combustion (HTC) region, and downstream premixed HTC region. The higher ambient temperature led to a more advanced combustion phasing but shorter lift-off length. As a result, the mixing time was reduced to result in a higher concentration of acetylene. In addition, upon increasing the injection pressure, no significant difference was observed in the jet flame structure. On the other hand, the higher injection velocity resulted in a higher flame tip and broader HTC region.

Spin chirality induced large topological Hall effect in magnetic Weyl semimetallic Eu2Ir2O7 (111) thin films

Antiferromagnetic (AFM) pyrochlore iridates are a fertile ground to hunt for a Weyl semimetallic state characterized by a linear crossing of two nondegenerate bands near the Fermi level ${E}_{F}$. Here, we demonstrate evidence of low-temperature anomalous and topological Hall effects in an antiferromagnetic ${\mathrm{Eu}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$(111) epitaxial thin film. The observed anomalous Hall effect is explained in terms of the momentum space Berry curvature associated with the Weyl nodes in the electronic band structure. The topological Hall effect reaches a large value ${\ensuremath{\rho}}_{xy}^{\text{THE}}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}10\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{\ensuremath{\Omega}}\phantom{\rule{0.16em}{0ex}}\text{cm}$ at 2 K. The topological nature of the Hall effect is attributed to the nonzero scalar spin chirality of the all-in-all-out/all-out-all-in (AIAO/AOAI) type noncoplanar AFM spin structure. The magnetoresistance (MR) shows a prominent negative variation ($\mathrm{MR}\ensuremath{\sim}10%$ at 2 K) below 10 K. The field dependence of MR below 5 K varies quadratically in the low-field regime, and above 40 kOe it shows a linear trend. The quadratic to linear crossover of the MR is explained by the field-induced ($H$) spin canting (spin chirality) of the static spins in the AIAO/AOAI spin structure. In the intermediate-temperature region MR of $15\ensuremath{-}25$ K exhibits a hysteretic response which is associated with field-induced domain switching of the AIAO/AOAI spin structure. This work highlights the interplay of magnetism and topology in a spin-orbit-coupled correlated electron system and unravels the possibility for realizing the Weyl phase in antiferromagnetic ${\mathrm{Eu}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$(111) thin films.

Investigation of Heat Transfer and Pressure Drop for R744 in a Horizontal Smooth Tube of R744/R404A Hybrid Cascade Refrigeration System—Part 1: Intermediate Temperature Region

In this study, the evaporation heat transfer characteristics of an intermediate temperature of R744 in a smooth horizontal tube, when operating as an indirect refrigeration system (IRS) among hybrid cascade refrigeration systems (HCRSs), are evaluated. Studies on the characteristics of intermediate-temperature evaporation heat transfer under the operating conditions of evaporators used in actual refrigeration systems, such as IRS, cascade refrigeration systems, and HCRS, used in supermarkets are lacking. Thus, this study provides basic data on the characteristics of evaporation heat transfer of R744 in the evaporators of refrigerators used in supermarkets. The tube employed to the evaporation experiment in this study was a horizontal smooth copper tube with a length of 8000 mm and an inner diameter of 11.46 mm. The experimental variables were measured over a wide range of mass flux of 200–500 kg/(m2·s), heat flux of 10–40 kW/m2, and saturation temperature of −40–0 °C. The main results are summarized as follows: (1) The application of Kandlikar’s correlation formula at an evaporation temperature of −20 °C in an IRS helps in a good prediction of the R744 evaporation heat transfer coefficient. (2) The pressure drop according to the heat and mass flux showed the same heat transfer coefficient trend, but the pressure drop at saturation temperature was different from the trend of heat transfer coefficient.

A-site Ca-doped layered double perovskite Pr1-xCaxBa0.94Co2O5+δ as high-performance and stable cathode for intermediate-temperature solid oxide fuel cells

Developing highly active and stable air electrode is crucial to large-scale commercialization of intermediate-temperature solid oxide fuel cells (IT-SOFCs). Herein we report A-site Ca-doped layered double perovskites, Pr1-xCaxBa0.94Co2O5+δ (PCxB0.94C, x = 0.1–0.3), as a family of promising cathode materials for catalyzing the oxygen reduction oxygen (ORR). Benefiting from enhanced electrical conductivity and promoted surface oxygen exchange/chemical diffusion rates, Pr1-xCaxBa0.94Co2O5+δ demonstrates an efficient ORR activity in intermediate-temperature region. The electrochemical performance of the samples is characterized by symmetrical half-cells and button fuel cells. Among all these compositions, Pr0.8Ca0.3Ba0.94Co2O5+δ (PC0.3B0.94C) exhibits the lowest polarization resistance (Rp) of 0.027 Ω cm2 at 700 °C. The peak power density (PPD) of 1114 mW cm-2 is achieved in the PC0.3B0.94C cathode-based button fuel cell at 700 °C, along with outstanding stability over a period of 130 h. The findings endow the potential utilization of the PC0.3B0.94C cathode for IT-SOFCs under the realistic conditions.

Characterization of the (Cu,C)Ba2Ca3Cu4O single crystals grown under high pressure

By using a high pressure and high temperature (3.7 GPa, 1120 ∘C) synthesis technique, we have grown (Cu,C)Ba2Ca3Cu4O single crystals. X-ray diffraction, scanning electron microscopy, resistivity, and magnetization measurements are carried out and all show that the samples have good quality. The single crystal has onset and zero-resistance transition temperatures of about 111 and 109.6 K, indicating a very narrow transition width, which is consistent with a rather sharp magnetization transition. Magnetization hysteresis loops (MHLs) are also measured, showing a pronounced second peak effect in the intermediate temperature region. The magnetic critical current density calculated from the MHLs at 77 K and 1.5 T is about 6.4 × 104 A cm−2. By using a criterion of 1 normal state resistivity, we have determined the irreversibility line which exhibits an irreversibility field of about 8 T at 77 K. Compared with other layered systems, it is easy to find that the irreversibility line is rather high and could be further improved with the optimized transition temperature of about 118 K as previously discovered in polycrystalline samples.