High Temperature Region Research Articles

Controlling of Localization by Elemental-substitution Effect in Layered BiCh2-based Compounds LaO1−xFxBiS2−ySey

We report transport properties for layered BiCh2-based (Ch = S, Se) superconductors LaO1−xFxBiS2−ySey (x = 0.2, 0.5, y = 0–1.05) and the observation of possible weak antilocalization (WAL). Electrical resistivity and Hall coefficients for the Se-poor samples increase with decreasing temperature. The increase becomes less pronounced with increasing Se concentration, indicating a loss of insulating behavior. Interestingly, the moderately Se-substituted samples exhibit metallic behavior in the high-temperature region and a weak increase in the resistivity in the low-temperature regions, which implies the existence of carrier localization. The heavily Se-substituted compounds show metallic behavior in the entire-temperature region. Magnetoresistance measurements indicate that WAL is realized in the heavily Se-substituted systems. The WAL behavior is weakened by the changes in F and Se concentrations. A crossover state of the WAL and weak localization (WL) emerges around the moderately F-doped and Se-free LaO0.8F0.2BiS2. The change of the resistivity and Hall coefficient by the F and Se substitution clearly correlates to the difference of the magnetoconductance. We propose that the BiCh2-based system is a good platform for studying the relationship between localization and superconductivity because those states are tunable by element substitutions with bulk single crystals.

Li vaporization behavior and mechanical properties of Li8ZrO6 under high temperature reducing atmosphere

Li8ZrO6 sintered compacts are one of the promising candidates for innovative tritium breeding materials from the viewpoint of lithium density, but there are concerns such as a decrease in lithium atomic density and mechanical strength due to Li2O vaporization. In this study, we fabricated a two-phase mixed sintered body of Li8ZrO6 with a high lithium atomic density, as the main component, and relatively a large amount of Li2O, and thermally annealed it in an environment simulating actual use conditions to vaporize lithium. It is shown that this material is stable at 320°C, which is the main temperature in the blanket space, Li2O vaporizes and part of Li8ZrO6 changes to Li6Zr2O7 at least above 700°C, and vaporization of Li2O occurs more rapidly to finally become to a single phase of Li2ZrO3 at 800−900°C. In addition, it is shown that this material has a higher lithium density than Li2TiO3, one of the Japanese candidate materials, in a wide temperature range below 770 °C during the expected period of practical use of three years. Finally, it is concluded that loading Li8ZrO6-based material and Li2TiO3 in the high and low temperature regions, respectively, achieves the highest lithium density.

Simulation and experimental study of refuse-derived fuel gasification in an updraft gasifier

Refuse-derived fuel (RDF) made from the mixture of wood and loose rice husk increases the porosity of the fuel in the furnace to facilitate the gasification process. Simulation results show that CO is concentrated in the incomplete combustion zone and CO2 forms mainly in the fully burned area; CH4 forms in the reduction region, while H2 forms in the region of high temperature of the furnace. When the mixture composition was f=0.3, the CO concentration in the syngas reached about 21%, the H2 concentration reached about 2% and the CH4 concentration was too low to be ignored. When the mixture composition increased to f = 0.5, the CO concentration reached about 26%, the H2 concentration remained almost unchanged and the CH4 content increased to 6%. The calorific value of the syngas reached a maximum when f = 0.5 and the temperature of the reduction zone is in the range of 900K to 1200K. Air humidity affects CO concentration but not much on CH4 and H2 concentration as well as the syngas calorific value. The difference between simulation and experimental results is not more than 10% for CH4 concentration and not more than 14% for CO2 concentration. The power of the spark ignition engine is reduced by 30% when running on syngas compared to when running on gasoline.

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.

Numerical studies of flow patterns and fuel distribution of tandem-arranged multi jets in a hypersonic crossflow

In this study, the numerical analysis of the three-dimensional flow fields of a series of tandem-arranged equal-strength hydrogen jets injected into a Mach 8 hypersonic crossflow is presented. The study comparatively analyzes the flow field similarities and differences between different configurations, namely, single, double, and quadruple jets. The results indicate that downstream jets do not have a significant effect on the first Mach cell and only slightly lift the bow shock at downstream compared with the single jet case. Additionally, high-temperature regions in all cases are in close proximity to the hydrogen stoichiometric equivalence ratio interface, making the fuel more prone to pre-ignition. Moreover, flow patterns in inter-gap regions and vortex structures are compared casewise. In addition, hydrogen injected from each orifice is traced, and the mass fraction distribution contributed by each jet on the symmetry plane and the inter-gap region is analyzed to derive the mixing characteristics.

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.

Electronic structure and defects induced luminescence study of phase stabilized t-ZrO2 nanocrystals.

Luminescent tetragonal-ZrO2 nanocrystals were synthesized using an optimized combustion method without post-synthesis annealing and characterized using X-ray diffraction, electron microscopy, Raman, X-ray photoelectron spectroscopy, UV-Visible, photoluminescence spectroscopy, thermoluminescence and vibrating sample magnetometry. The as synthesized t-ZrO2 nanocrystals have a band gap of 4.65 eV and exhibit defect assisted blue emission (CIE coordinates 0.2294,0.1984) when excited with 270 nm. The defect states were qualitatively and quantitatively analyzed using thermoluminescence (TL) after irradiating nanocrystals with gamma and UV radiation at various doses. The TL glow curves show intense emission in the high temperature region from 523-673 K for both UV and gamma irradiated samples; however, another less intense TL peak was also observed in the low temperature region from 333-453 K with gamma irradiation at higher doses, indicating the formation of shallow trapping states. The activation energies, frequency factor and order of kinetics were estimated through the computerized glow curve deconvolution method for the shallow and deep traps for γ and UV- irradiated samples. The present study shows that phase stabilized t-ZrO2 nanocrystals are potential candidates for luminescence-based applications.

Thermogravimetric Analysis on Co-Gasification Characteristics of Sludge and Straw under CO2 Atmosphere

To maximize the potential energy utilization of agricultural and forestry wastes and sludge, experimental studies were conducted on the co-gasification characteristics of two types of sludge (municipal sludge, MS; paper-mill sludge, PS) and a typical biomass straw (ST) under CO2 atmosphere. In this paper, the main two stages of the gasification process, the pyrolysis in the low-temperature region and the CO2-gasification in the high-temperature region, were separately studied and analyzed. The experimental results showed that biomass could effectively promote the pyrolysis of the sludge in the low-temperature region and improve the gasification in the high-temperature region. Due to the complex interactions between components, the characteristic parameters presented obvious nonlinear rules during the co-pyrolysis and co-gasification processes. For the MS-ST mixtures, when increasing the ST content, (i) in the pyrolysis process, the initial reaction temperature gradually decreased, but the final reaction temperature, the peak reaction rate and the corresponding temperature, and the pyrolysis index gradually increased; (ii) in the gasification process, the initial reaction temperature, the reaction final temperature, and the temperature corresponding to the peak gradually increased. Combined with the reaction kinetics analysis of the co-pyrolysis and the co-gasification processes, 25% may be a reasonable mixing ratio for ST for the MS-ST mixtures, which had a relatively lower reaction temperature, relatively high pyrolysis index and low activation energy (26.58 kJ·mol−1 and 178.29 kJ·mol−1 for the co-pyrolysis and co-gasification processes, respectively). For the PS-ST mixtures, when increasing the ST content, (i) in the pyrolysis process, the initial reaction temperature, the peak reaction rate, the temperature corresponding to the peak and the pyrolysis index gradually decreased, but the final reaction temperature gradually increased; (ii) in the gasification process, the initial and final reaction temperatures and the temperature corresponding to the peak gradually decreased, but the peak reaction rate gradually increased. Combined with the reaction kinetics analysis of the pyrolysis and the gasification processes, 25% may be a reasonable mixing ratio for ST for the PS-ST mixtures, which had a relatively lower reaction temperature, relatively high pyrolysis index and low activation energy (64.29 kJ·mol−1 and 301.16 kJ·mol−1 for the co-pyrolysis and co-gasification processes, respectively). These findings can provide useful information for the co-gasification of sludge and straw under CO2 atmosphere.

High Temperature Deformation and Microstructural Evolution of Homogenized AA 2026 Alloy

AA 2026 is an improved version of AA 2024, an alloy with added Zr to reduce Fe and Si content and inhibit recrystallization during hot working. Al 2026 alloy has high strength and high damage resistance, so it is widely used in aircraft parts. In this study, in order to investigate the hot workability of AA 2026 and to optimize the hot forming parameters, hot compression tests were conducted in the temperature range of 300 to 450 o C, at a strain rate of 0.01 to 10 and in the 50% strain section. The true stress–true strain curve showed a dynamic softening phenomenon while the stress increased rapidly at a small strain and then remained steady. In order to evaluate its high temperature processability, the constitutive equations for flow stress, temperature, and strain were quantified based on the Arrhenius equation, and a process strain map was prepared. The peak stress accuracy of the constitutive equation was about 98.2%, which was consistent with the experimental data of AA 2026 under strain rate and temperature conditions. In addition, scanning electron microscopy (SEM) and backscattered electron diffraction pattern analyzer (EBSD) analyses were conducted to confirm the mechanism of the dynamic softening phenomenon. The CDRX phenomenon was confirmed under the high strain condition in the low temperature region and the DDRX phenomenon in the low strain condition in the high temperature region.

Mechanism of constriction in a high frequency pulsed welding arc

The phenomenon of arc constriction at high frequency pulsing was investigated experimentally using the monochromatic imaging method (MIM) on arcs generated with a thermionic electrode. Square pulses with 50% duty cycle between 75 A and 125 A (average of 100 A) were explored at frequencies of 1 kHz, 3 kHz, and 5 kHz. Constant current arcs of 75 A, 100 A, and 125 A were also investigated as a reference. The observations indicate that the high-temperature region of the arc (above 14,000 K) increase in volume during the pulse, to sizes larger than those corresponding to the pulse current applied in steady state (125 A), similarly during the background current, the size of the hot regions is smaller than under the same value of constant current (75 A). The size increase during the pulse is much more prominent than the decrease during the background. This net increase in the average size of the most electrically conductive region takes current away from the less conductive periphery of the arc. The pulse frequencies from 1 kHz to 5 kHz have significant effect on thermal delay from Joule region to convection region. The mechanisms identified explain the arc constriction observed experimentally. This new understanding allows for open arcs that can rival more complex plasma torches in heat concentration and in the ability to control the heat source from a welding arc using purely electronic means, without resorting to gas mixing or mechanical adjustments.

Thermal conductivity measurement system for molecules-based compounds available in a wide temperature region

The construction of a thermal conductivity measurement system designed for tiny molecules-based compounds is reported. We introduce complementary usage of chip-type RuO2 thermometers and E-type thermocouples in the sample part by using thin (ϕ 13μm) constantan and chromel wires. Two pairs of the constantan and chromel wires are used as lead wires for the four-terminal measurement of the resistance of RuO2 thermometers in the low-temperature region below about 20 K. Also, in the higher temperature region above 10 K up to room temperature with the overlapping range of 10-20 K, they are used as thermocouples for detecting temperature differences from that of the heat sink. We also compare a kind of resolution parameter of several sensors as a function of temperature to discuss the rational reason to select suitable sensors depending on the temperature region. Using the constructed apparatus, we report temperature dependences of the thermal conductivity of deuterated κ-(d8:BEDT-TTF)2Cu[N(CN)2]Br in a wide temperature range between 2 and 250 K. The result provides convincing evidence for the validity of the newly developed system for the thermal measurements of molecular crystals.

Structural and optical properties of a new structural modification of Na3+3xYb2−x(PO4)3:1% Eu phosphate, where x = 0,1-0,5 and prospective thermometric applications of the compound

The powders of Na3+3xYb2-x(PO4)3: 1% Eu3+ (where x = 0.1, 0.2, 0.3, 0.4 and 0.5) have been synthesized using thermal method in solid state. Their structural and spectroscopic properties were investigated by powder X-ray diffraction, microcalorimetric method (DSC), Raman, infrared, absorption and luminescence studies. It was find that the studied materials belong to the NASICON-type compounds and crystallize in rhombohedral or monoclinic type of structure. Photoluminescence of investigated samples presents typical emission of Eu3+ ions with the dominance of electric dipole transitions and near-infrared bands attributed to Yb3+ ions. Efficient red and infrared emissions under the excitation of 395 nm can be attractive for LED lighting. The highest Yb3+ emission intensity has been registered for the sample with the Na3.9Yb1.7(PO4)3: 1% Eu3+ composition (x=0.3). Ytterbium excited level can be populated by the energy transfer from the Eu3+ ions and can be enhanced by sample heating. Due to the non-radiative processes, the Eu3+ luminescence decay times monitored at 619 nm were bi-exponental. Because of the strong influence of temperature on emission intensities, obtained compounds can be useful for non-contact temperature readout, especially in the high-temperature region (above 600 K). The maximum value of relative sensitivity Sr is equal 2.91%K-1 at 855 K for the sample Na3+3xYb2-x(PO4)3: 1% Eu3+ (x=0.3).

Temperature-Dependent Anisotropy and Two-Band Superconductivity Revealed by Lower Critical Field in Organic Superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br

Resistivity and magnetization have been measured at different temperatures and magnetic fields in organic superconductors κ-(BEDT-TTF)2Cu[N(CN)2]Br. The lower critical field and upper critical field are determined, which allow to depict a complete phase diagram. Through the comparison between the upper critical fields with magnetic field perpendicular and parallel to the conducting ac-planes, and the scaling of the in-plane resistivity with field along different directions, we find that the anisotropy Γ is strongly dependent on temperature. It is realized that Γ is quite large (above 20) near T c, which satisfies the 2D model, but approaches a small value in the low-temperature region. The 2D-Tinkham model can also be used to fit the data at high temperatures. This is explained as a crossover from the orbital depairing mechanism in high-temperature and low-field region to the paramagnetic depairing mechanism in the high-field and low-temperature region. The temperature dependence of lower critical field, H c1(T), shows a concave shape in wide temperature region. It is found that neither a single d-wave nor a single s-wave gap can fit the H c1(T), however a two-gap model containing an s-wave and a d-wave can fit the data rather well, suggesting two-band superconductivity and an unconventional pairing mechanism in this organic superconductor.

Numerical simulation of the influence of fuel allocation method on regional NOx production in a single sector combustor

Aiming toward a single sector model of a central staged gas turbine combustor, this study developed a suitable numerical simulation calculation method coupled with a chemical reaction mechanism. A three-dimensional numerical simulation of the combustor was conducted on the basis of the validated numerical simulation method. The spatial production characteristics of NOx in each path of the combustor were analyzed by the plane integral method. The influence of payload and fuel allocation method on the NOx production of the combustor was also discussed. Results indicate the following. (1) Under 100% payload, the production of thermal NOx in the burnout zone contributed about 80% of NOx production due to the high temperature region, and the production of NOx in burnout zone (BOZ) contributed the highest, about 50% to the NOx fraction at the outlet of the combustor. The corner recirculation zone that contributed the least, which was about 10%. (2) As the payload increased from 30% to 100%, the NOx concentration at the outlet of the combustor increased exponentially by 75.58% and 156.85%. Thermal NOx was the most important NOx production path in each working condition and area, which contributed about 65–80% to the total production of NOx under different payloads. (3) The optimal fuel allocation method that suppressed NOx production and considered combustion performance was established. Under this method, the outlet NOx concentration was 13.03 ppm.

Effect of mechanical stirring on the tubular heating process of crude oil

Research on thermal behaviors under the synergy of mechanical stirring and tubular heating can reveal the effect mechanism of mechanical stirring, and determine the optimal stirring parameters. In this paper, the physical and mathematical models of heat transfer in crude oil storage tank under the synergy of tubular heating and mechanical stirring are established, the sliding grid technique is used to model the stirring impeller, which are further numerical calculated by the FVM. Our outcomes demonstrate that through the enhancement of convection, mechanical stirring significantly changes the thermal behaviors and enhances the heat exchange. Precisely, for a 1,000 m3 crude oil storage tank, the stirring of 350 rpm can increase the average velocity by 329%, the heating rate by 89%, and rise the average crude oil temperature from 42.311 °C to 42.586 °C during 2 h of heating. However, the higher crude oil temperature will cause a 1,613 W increase in heat loss power. The heating efficiency has also increased by 10%. Furthermore, mechanical stirring can promote a more uniform temperature distribution. Thus, the volume ratio in the low-temperature region decreases by 10% and that in the high-temperature region increases by 26%. The temperature variance decreases from 4.517 °C2 to 0.275 °C2. However, the velocity and temperature fields are almost the same under different stirring rates. With increasing stirring rate from 100 rpm to 700 rpm, the average heating rate can only increase by 0.026 °C/h, and temperature variance decreases from 0.596 °C2 to 0.086 °C2. With increasing stirring rate, the efficiency of the heating tube does not change significantly. The optimal stirring rate is determined as 350 rpm based on the fitting curve of temperature variance stabilization time and the comprehensive effect.

Alignment and rotational disruption of dust grains in the Galactic Centre revealed by polarized dust emission

ABSTRACT We study the alignment and rotational disruption of dust grains at the centre of our Galaxy using polarized thermal dust emission observed by SOFIA/HAWC+ and JCMT/SCUPOL at 53, 216, and 850 µm. We analysed the relationship between the observed polarization degree with total emission intensity, dust temperature, gas column density, and polarization angle dispersion. Polarization degree from this region follows the predictions of the RAdiative Torque (RAT) alignment theory, except at high temperatures and long wavelengths where we found evidence for the rotational disruption of grains as predicted by the RAdiative Torque Disruption mechanism. The grain alignment and disruption sizes were found to be around 0.1 and 1 µm, respectively. The maximum polarization degree observed was around p ∼ 13 per cent at 216 µm and comes from a region of high dust temperature, low column density, and ordered magnetic field. Magnetically enhanced RAT alignment (MRAT) was found to be important for grain alignment due to the presence of a strong magnetic field and can induce perfect alignment even when grains contain small iron clusters. We estimated the mass fraction of aligned grains using a parametric model for the fraction of the grains at high-J attractors and found it to correlate weakly with the observed polarization degree. We observe a change in the polarization ratio, from p216µm/p850µm < 1 to p216µm/p850µm > 1 at Td ≳ 35 K, which suggests a change in the grain model from a composite to a separate population of carbon and silicate grains as implied by previous numerical modelling.

Synthesis and analysis of structural, dielectric, and thermistor behaviour of zinc ferrite

This paper discusses the synthesis, dielectric properties, and applications of ZnFe2O4 for the thermistor. A high-temperature solid-state reaction method is used to create the polycrystalline ZnFe2O4 sample. The X-ray diffraction study identified the single spinel Cubic phase formation at room temperature without any impurities. The broadening of the XRD peaks determined structural parameters including crystallite size, microstrain, dislocation density, and percentage crystallinity which confirms the lower number of lattice defects in the ferrite. The dielectric properties of the sample are investigated as a function of temperature over selected frequencies. The high dielectric constant and low dielectric loss of the material suggest that it can be used in advanced energy storage systems. The minimal activation energies in the high-temperature region determined from the slope of the linear fit of the temperature-dependent curve indicate the enhancement of electrical conductivity. Looking into the strong dependence of resistivity on temperature, the thermistor parameters are evaluated using the resistance at different temperatures, which suggests its possible application for a thermistor as well as a temperature sensor. The calculation of different thermistor parameters such as thermistor constant, sensitivity factor, and activation energy confirms a negative temperature coefficient of resistance behavior of the ferrites at different temperatures and frequencies.

Temperature-driven complex dielectric and polaron-hopping mediated electrical conduction in aurivillius Gd2MoO6

In this work, aurivillius gadolinium molybdate (Gd2MoO6) was synthesized by the conventional solid-state route which was accompanied by cutting-edge characterization i.e., structural, and electrical, to give insight into the material characteristics required for possible high-temperature applications. The single-phase crystalline nature with monoclinic symmetry (C2/c, Space group-15) of Gd2MoO6 was confirmed by the X-ray diffraction (XRD) pattern. The average particle size was obtained to be ∼0.495 µm. The electrical conductivity and dielectric properties of a Gd2MoO6 plate capacitor were investigated in the frequency range between 10 Hz and 1 MHz and temperature from 473 to 773 K. A high dielectric constant (ε') of ∼3272 and low dielectric loss (δ) of ∼200 was observed at the low frequency and high-temperature regions, respectively. The Maxwell–Wagner interfacial polarization was found to be responsible for the decrease of the dielectric constant with increasing frequency. The behavior with the temperature of the frequency exponent (n) from the fitted conductivity spectra by Jonscher power law corresponds to the non-overlapping small polaron tunneling model between 473–673 K and correlated barrier hopping model at/over 673 K. The non-exponential Kohlrausch Williams-Watts function was introduced to fit the imaginary modulus (M′′) spectra and the activation energy was obtained to be 0.81 eV for grain and 0.94 eV for grain boundary conduction. The Nyquist plots(Z′vs.Z′′) differentiate the grain and grain boundary contribution and were fitted with the combinations of resistance (R), capacitance (C), and constant phase element (Q) in an equivalent circuit model(RC)(RCQ). Typical negative temperature coefficient of resistance behaviors of Gd2MoO6 suggest its possible application as thermistors in modern electronics circuits.

Mechanism of the glucono-δ-lactone induced soymilk gelation: Enthalpy and entropy transformation in the cross-linking of protein molecules

This study aimed to explore new techniques to regulate the quality of soy products. The glucono-δ-lactone (GDL) induced soymilk gelation process and the gel network structure characteristic were compared as a matter of temperature, and the role of reaction kinetics was discussed. Results showed that there were similarities in the development of Gʹ curves under different temperatures, whereas the gel network structures and the energy requirements of cross-linking reactions were different. In the high-temperature region (70 °C–95 °C), the exposure and binding of reactive groups were promoted. The activation enthalpy (ΔH*) required by protein aggregates decreased and the effect of entropy reduction (−TΔS*) was enhanced, which led to shorten the preaggregation time (tg) and increase the gelation rate (k), resulting in the formation of rough, porous gel network with high stiffness. By contrast, in the low-temperature region (40 °C–70 °C), high enthalpy contributions and low entropy changes were required, then a fine, soft, and tender gel network formed. Besides, a funnel-shaped model of the enthalpy–entropy energy transformation mechanism of soymilk gelation was proposed. The results of this study revealed that adjusting the enthalpy–entropy energy requirements of the protein cross-linking reaction could be utilized to the regulation of the network structure and quality of soymilk gels, which could enrich the reaction kinetics theory and provide innovative ideas for food quality control technology from the perspective of energy requirement and energy input.

Intermediate-temperature creep behaviors of an equiatomic VNbMoTaW refractory high-entropy alloy

As one of refractory high-entropy alloys (RHEAs), VNbMoTaW is considered to be a promising candidate for elevated-temperature application. However, its creep behavior is rarely reported. In the present work, the compressive creep behaviors of an equiatomic VNbMoTaW RHEA with a grain size of 138 ± 36 μm were well studied over an intermediate temperature range (973–1173 K) and under high applied stress (130–520 MPa). The stress exponent of the alloy is found to remain stable (∼1) at relatively low temperatures (973–1073 K), whereas a stress-dependent transition behavior occurs at high temperatures (1123–1173 K), i.e., the stress exponent of the alloy changes from ∼1 in the low stress region (130–390 MPa) to ∼ 4 in the high stress region (390–520 MPa). Meanwhile, the creep activation energy increases from 139 to 156 kJ mol−1 at low temperatures to 307–373 kJ mol−1 at high temperatures. The low stress exponent and low activation energy at low temperatures suggest that the creep is controlled by dislocation pipe diffusion. The low stress exponent and relatively high activation energy in the high-temperature low-stress region suggest that the creep is controlled by lattice diffusion. In the high-temperature high-stress region, the prevalent dislocations detected by the post-mortem microstructural observation, the high stress exponent, and high activation energy suggest that the creep deformation is controlled by a lattice diffusion mediated dislocation climb process. These findings provide a fundamental understanding of the creep behavior and deformation mechanism of VNbMoTaW, which can be applied to design advanced creep-resistant RHEAs.