Temperature Gradient Conditions Research Articles

Influence of Natural External Forcings on Interdecadal Variation of Global Land Monsoon over the Last Millennium in CESM-LME

Abstract Interdecadal variations of the global land monsoon have been previously attributed to internal fluctuations of the climate system, but the role of natural external forcings was underexplored. Here, we investigate this issue by using the Community Earth System Model ensemble simulations over the last millennium (LM) (AD 950–1850). Our analysis reveals that the surface temperature, with two dominant structures (global cooling/warming and longitudinal sea surface temperature gradient in the tropical Pacific, which affects the Walker circulation), predominantly shapes the leading forced mode of the global land monsoon. This mode, representing 19% of the total variance, manifests as consistent features across South Asia, the southern part of East Asia, North Australia, South America, and western South Africa, contrasting with other monsoon regions. Under global cooling conditions, the monsoon intensity is enhanced in the northern parts of the East Asian and eastern parts of the North and South African monsoons, but it decreases in the other monsoon regions. Under weak Walker circulation conditions, changes in atmospheric circulation in response to the sea surface temperature gradient in the tropical Pacific are associated with a substantial attenuation of almost all land monsoon regions. It was further shown that the global mean surface temperature and the tropical Pacific temperature gradient jointly account for 75% of the total variance in the leading mode of the global land monsoon, with 29% and 46% as their respective contributions. Furthermore, our results suggest that volcanic eruptions are the dominant external forcing for these variations. These findings provide valuable insights for future research on global monsoon dynamics. Significance Statement Our study using the Community Earth System Model reveals that surface temperature significantly impacts decadal global land monsoon (GLM) variations during the last millennium. Two key factors in relation to global-scale cooling/warming and changes in the tropical Pacific sea surface temperature gradient affect the GLM’s leading forced mode. The leading forced GLM features remain consistent across regions like South Asia, southern East Asia, North Australia, South America, and western South Africa. Under global cooling, monsoon intensities in most land monsoon regions are enhanced, while they are reduced in northern East Asian land monsoon regions. In contrast, weak tropical Pacific temperature gradient conditions cause a decrease in intensities in almost all land monsoon regions. Additionally, the global mean surface temperature and the tropical Pacific temperature gradient account for 75% of the total variance in the leading forced GLM variations, contributing 29% and 46%, respectively. Notably, volcanic eruptions emerge as the key external factor influencing these variations.

Theoretical study on the effect of temperature gradient on contact-free scanning for scanning ion conductance microscopy

Scanning ion-conductance microscopy (SICM) is a non-contact, high-resolution, and in-situ scanning probe microscope technique, it can be operated in probing the physical and chemical properties of biological samples such as living cells. Recently, using SICM to study the effects of microenvironment changes such as temperature changes on response of the biological samples has attracted significant attention. However, in this temperature gradient condition, one of the crucial but still unclear issues is the scanning feedback types and safe threshold. In this paper, a theoretical study of effect of the temperature gradient in electrolyte or sample surface on the SICM safe ion-current threshold is conducted using three-dimensional Poisson-Nernst-Planck, Navier-Stokes and energy equations. Two temperature gradient types, sample surface and two types of pipettes with different ratio of inner and outer radii are included, respectively. The results demonstrate that the local temperature of the electrolyte and then sample surface significantly affect the ion flow, shape of the approach curves and thus safe threshold in SICM pipette probe for contact-free scanning. There is a current-increased and decreased phases for approaching the surface with higher temperature and two current-decreased phases for surface with lower temperature. Based on this shape feature of approach curves, the change rate of current is analysis to illustrate the possibility for contact-free scanning of slope object. The results indicate that with the decrease of the normalized tip-surface distance, the coupling effect of large slope angle and local high temperature makes the increase in change rate of ion current not significant and then it challenging to realize contact-free scanning especially for higher surface temperature.

Biochemically Programmable Isothermal PCR.

Isothermal PCR can be performed by imposing a static temperature gradient that continuously circulates reagents through denaturing, annealing, and extension conditions inside a PCR tube. But despite early promise, these systems have yet to demonstrate performance and repeatability sufficient for adoption in validated laboratory tests because the rate-limiting extension step is inherently short and cannot be increased independently of the other stages in a temperature cycle. Here, a discovery that enables isothermal PCR to be achieved with statistically robust repeatability that meets or exceeds diagnostic assay requirements (false positive/negative rate <8% at 95% confidence) by manipulating the interplay between the DNA replication biochemistry (via the amplicon GC content) and the microscale circulatory flow inside a PCR tube is reported. Surprisingly, optimal performance depends on selecting primer sequences that replicate high GC content amplicons, contradicting established PCR primer design rules. This innovative thermocycling approach accelerates PCR to speeds rivaling ultra-fast instruments, enabling rapid, repeatable isothermal DNA analysis across a range of targets relevant to diagnostics and pathogen detection.

Determination of a normal orogenic palaeo-geothermal gradient with clay mineral and organic matter indices: a review

A collection of large data sets from different orogenic belts was compiled for a correlation between organic matter (OM) versus clay mineral (CM) indices calibrated with the vitrinite reflectance, (VR) vs Kübler-Indices (KI) method. Data selection was based on a normal geothermal gradient (25 to 35 °C/km) as determined in previous studies, e.g. by maturity modelling and clay mineral reaction progress calculations. In the Lower Austroalpine (Eastern Switzerland, European Alps) a 20 myr lasting metamorphic overprint caused an OM–CM thermal equilibrium among the indices used. The observed correlation enables to determine gradual changes in metamorphic factors such as pressure, temperature and time causing sensitive shifts of the gradient slope in the range of normal gradients. For New Caledonia, an identical correlation has been determined. Prior to re-equilibration of the VR/KI indices, sediments in New Caledonia of diagenetic to incipient metamorphic grade underwent a high-pressure subduction event. VR/KI indices are in or close to equilibrium, while slight differences in OM vs CM indices allow for a better understanding of polyphase conditions, especially with respect to pressure. Temperature estimations are identical despite of their poly-phase metamorphic history, which was mainly controlled by the last orogenic thermal event lasting > 5 to < 10 myr. In the eastern Helvetic Alps and Northern Calcareous Alps similar correlations were found with slightly different slopes. Comparison between different regions is possible when using KI standardization and same data discrimination. In both parts of the Alps a complex thermal history of short durations (< 5.0 myr for the Northern Calcareous Alps to 10 myr for the Helvetic Alps) caused similar VR/KI trends, but disequilibrium is suggested by weaker regression parameters. The following correlation is calculated for a moderate geotherm (55 to 74 mWm2, mean = 61 mWm2) and normal temperature gradient conditions (25 to 35 °Ckm−1): KI = 1.134e−0.305VR, (R2 = 0.880, n = 462) with VR given as %Rmax, KI as Δ°2θ (limited to values between 0.2 to 1.0 Δ°2θ). With increasing depth (z) a VR gradient of 1.4 ± 0.2%Rmaxkm−1 is determined and a KI gradient of 0.09 ± 0.002 Δ°2θ km−1 is observed. The study illustrates that a normal geotherm can be described by VR/KI correlation, even if different heating episodes may occur. For the detection of a poly-phase or plurifacial thermal history, several indices of clay minerals and organic matter with very different kinetics should be used, as e.g. demonstrated by strong differences in smectite content at equal VR/KI values versus structural depth. A specific interest is given to the correlation of vitrinite like solid bitumen reflectance as an alternative method to VR, the persistent preservation of liptinite macerals and the stability range of clay minerals and sub-greenschist facies critical minerals compared with VR/KI data. Until now, despite the Alps in this study, systematic liptinite maceral studies have not been published in other orogenic settings.

Influence of Solid-Phase and Melt-Quenching Na3Fe2(PO4)3 Polycrystal Production Technology on Their Structure and Ionic Conductivity

This article studies the influence of solid-phase (type 1 samples) and melt-quenching (type 2 samples) technological modes of obtaining Na3Fe2(PO4)3 polycrystals on their structures and ion-conducting properties. α-Na3Fe2(PO4)3 polycrystals of the 1st type are formed predominantly under an isothermal firing regime, and the synthesis of the 2nd type is carried out under sharp temperature gradient conditions, contributing to the formation of glassy precursors possessing a reactive and deformed structure, in which the crystallization of crystallites occurs faster than in precursors obtained under isothermal firing. The elemental composition of α-Na3Fe2(PO4)3 type 2 polycrystals is maintained within the normal range despite the sharp non-equilibrium thermodynamic conditions of synthesis. The microstructure of the type 1 Na3Fe2(PO4)3 polycrystals is dominated by chaotically arranged crystallites of medium (7–10 μm) and large (15–35 μm) sizes, while the polycrystals of type 2 are characterized by the preferential formation of small (3–4 μm) and medium (7–10 μm) crystallites, causing uniaxial deformations in their structure, which contribute to a partial increase in their symmetry. The advantage of type 2 polycrystals is that they have higher density and conductivity and are synthesized faster than type 1 samples by a factor of 4. The article also considers the issues of crystallization in a solid-phase precursor from the classical point of view, i.e., the process of the formation of small solid-phase nuclei in the metastable phase and their growth to large particles due to association with small crystallites using phase transitions. Possible variants and models of crystallite growth in Na3Fe2(PO4)3 polycrystals, as well as distinctive features of crystallization between two types of samples, are discussed.

Predicting rapid growth behavior in solidified eutectic ceramic composites using infrared thermal imaging and thermal field simulation during laser directed energy deposition

Cylindrical Al2O3/GdAlO3 binary in situ oxide eutectic ceramic composite, with a glossy surface and high relative density, has been fabricated using the laser directed energy deposition method (LDED) with optimized process parameters. In a novel and innovative approach, infrared thermal imaging and the finite element method (FEM) have been combined for the first time to capture the temperature field distribution across different regions of the molten pool during the LDED processing of the binary oxide eutectic ceramic composite, thereby synergistically obtaining the solidification characteristics. With an increase in the scanning rate, the temperature gradient within the molten pool decreases from 3.38 × 105 K/m to 1.62 × 105 K/m, while it shows minimal variation with fluctuations of the laser power. Under the conditions of high temperature gradients and rapid non-equilibrium solidification characteristic of LDED, the Al2O3/GdAlO3 (GAP) binary eutectic ceramic composites, which exhibit typical high melting entropy and faceted/non-faceted growth modes, exhibit complex and variable microstructure morphology. A combination of regular/irregular models, including JH (Jackson-Hunt), MK (Magnin-Kurz), GK (Guzik-Kopyciński) and TMK (Trivedi-Magnin-Kurz), is employed to investigate and predict the growth and transformation of microstructures. The JH and TMK models fairly predict the rod-like regular eutectic microstructure inside the colony and lamellar regular eutectic within adjacent layers, respectively. The “Chinese-script” irregular microstructure at the interface between the colony and the layers is consistent with the MK and GK models. The as-deposited eutectic ceramic composite presents ultra-fine microstructures, clear and strongly bonded phase interfaces with low strain energy, contributing to its microstructure stability after high temperature heat treatment at 1773 K for 200 h, and achieving a minimum microstructure coarsening rate of 0.0005 μm/h.

Synthesis of sulfide mineral crystals by incongruent methods using the example of Cu-Fe-S and Cu-Fe-Se systems

Research subject. Understanding the structure and thermodynamic properties of sulfide minerals is important for studying the paragenesis of sulfide formation on Earth and in space, as well as for analyzing technological issues in the processing of ores and polysulfide product concentrates. There is a lack of experimental and theoretical information on many representatives of the Cu-Fe-S and Cu-Fe-Se systems. Aim. To synthesize crystals in the Cu-Fe-S and Cu-Fe-Se systems at the lowest possible temperatures for the subsequent study of their physical properties, while solving the main problem of materials science related to interrelations between composition, structure, and properties. Materials and methods. Crystal synthesis was carried out by the solution-melt method in a stationary temperature gradient, in evacuated sealed quartz glass ampoules. Two types of ampoules were used in the experiment, standard and long. The ampoules were filled with a charge and a salt mixture of RbCl-LiCl of eutectic composition, evacuated and sealed, then placed in several quartz or ceramic glasses. The glasses were placed in tubular furnaces such that the ends of the ampoules with the charge were located closer to the center of the furnace, and the opposite ends were closer to the edge to create a temperature gradient. For standard ampoules, the hot end temperature was 520–469℃, and the cold end was 456–415℃. For long ones: 470℃ – hot end and 340℃ – cold. The synthesis duration ranged from three to four months. Results. Depending on the composition of the charge, crystals of chalcocine Cu2S, bornite Cu5FeS4, chalcopyrite CuFeS2, isocubanite CuFe2S3, and iron-containing dicopper sulfide with an iron content of up to 8 at % and various equilibrium associations with their participation and with the participation of pyrite FeS2 and pyrrhotites Fe1–xS were obtained. Copper dendrites were also found in some samples. In addition, crystals of a phase with the approximate composition of CuFeSe2 were obtained. It is shown that due to different combinations of oxidation states of all three elements dissolved in a salt electrolyte, it is possible to obtain phases with almost any stoichiometric ratio. Chalcopyrite and isocubanite are reliably detected using Raman spectroscopy. In this case, some samples are locally characterized by the “absence” of a spectrum, which probably indicates the metallic (semi-metallic) properties of the samples. Conclusion. Using the Cu-Fe-S and Cu-Fe-Se systems as an example, the possibility of obtaining sulfide crystals in a RbCl-LiCl salt melt up to a eutectic temperature of 313℃ is shown. Due to the low synthesis temperature, the synthesis should be carried out over several months, resulting in crystals a fraction of a millimeter in size.

Influence of Prandtl number on the chaos transition for pure natural and Rayleigh–Bénard convections inside a rectangular cavity

A peculiar flow instability known as multiple chaos transitions was recently reported for the free convection in an enclosure where the direction of the temperature gradient changes continuously; it has been explained to be attributed to the competition for dominance between pure natural and Rayleigh–Bérnard convections. In this study, the chaos transition of free convection is investigated when a horizontal or vertical temperature gradient forms in a rectangular cavity. Analyses are conducted under a laminar flow regime, with Prandtl numbers ranging from 0.01 to 50 and Rayleigh numbers up to 109. In the horizontal temperature gradient, the chaos-transition Rayleigh number increases monotonically with the Prandtl number. However, under vertical temperature gradient conditions, it reaches the maximum value at approximately Pr = 0.5. Contrary to the general knowledge that higher-Prandtl number fluids effectively stabilize natural convection, a free convection in a vertical temperature gradient initiates a new flow instability when the Prandtl number is over 1.0, where momentum and thermal diffusions balance each other. The oscillation pattern, 2D phase trajectory, power spectral density, and Poincaré point of equivalent thermal conductivity are used to assess the free-convection flow instability.

Experimental study on the influence of inlet pressure on the flow parameters at the reverse flow boundary of vortex tube and its relation with energy separation performance

The performance of the vortex tube (also known as the Ranque-Hilsch tube) is significantly influenced by the inlet pressure and the internal flow processes, which can be categorized into two distinct flows: the center and the outer flow. The reverse flow boundary, acting as the interface between the two flows, plays a crucial role in energy separation. However, the research on the location of the reverse flow boundary and the associated flow parameters and energy transfer at this boundary are still insufficient. Therefore, this research employs the measurement method of interpolation probe to analyze the distribution of the reverse flow boundary and the specific flow parameters at this boundary. These parameters include static pressure gradient, angular velocity, and static temperature gradient, which substantially impact energy separation. A qualitative analysis of the energy transfer process in the vortex tube by examining mass flow in the reverse area and tangential and axial velocities are further delved. This analysis covers momentum transfer, heat transfer, and turbulent heat transfer processes resulting from the compression and expansion processes. The findings provide a research direction for exploring the energy separation performance of vortex tubes.

Experimental re-melting of a continental crust: probing the deep storage zone of Campi Flegrei and Vesuvius magmas

Mantle magmas interact with surrounding rocks during their ascent and storage in the continental crust, leading to open system processes as wall rock partial melting. In this study, we have experimentally investigated the reactions between a leucosome depleted migmatite and a primitive K-basaltic of Campi Flegrei (Italy). Experiments were carried out at pressure of 0.8 GPa temperatures from 1250 °C to 1050 °C and constant temperature and thermal gradient conditions. The experimental products consist of biotite-free migmatite, glass and crystals of clinopyroxene, olivine, plagioclase and Cr-spinel with proportions that vary as a function of temperature. Open system isothermal experiments indicate that the chemistry of melts and phase relationships are controlled by the high Al2O3 content of leucosome depleted migmatite with the glass composition shifting from K-trachybasalt towards shoshonite as the temperature decreases from 1200 °C to 1125 °C. At temperatures \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\le$$\\end{document}1150°C, migmatite assimilation is not exclusively due to the assimilation fractional crystallization process because evidence of mingling and mixing is observed. T-gradient experiment shows melt composition ranging from shoshonite to phono-tephrite moving from the slightly crystalline zone (T = 1250 –1210 °C) at the bottom of the capsule towards the highly crystalline zone (T = 1160 –1140 °C). This SiO2-constant trend indicates that at temperature below the basalt solidus, the assimilation of leucosome depleted crust is represented almost exclusively by the biotite breakdown, leading to the increase in Al, Mg, Fe, Ti, and K activities in the system. The shoshonitic composition obtained in our experiments could represent the parental magma for both Campi Flegrei volcanic district and Vesuvius magmatic systems, indicating modification in a deep storage zone through mixing with the partial melts derived from restitic continental crust.

Nitrate denitrification rate response to temperature gradient change during river bank infiltration.

Nitrate attenuation during river bank infiltration is the key process for reducing nitrogen pollution. Temperature is considered to be an important factor affecting nitrate attenuation. However, the magnitude and mechanism of its impact have not been clear for a long time. In this study, the effects of temperature and temperature gradient on the nitrate denitrification rate were investigated via static batch and dynamic soil column simulation experiments. The results showed that temperature had a significant effect on the denitrification rate. Temperature effects were first observed in denitrifying bacteria. At low temperatures, the microorganism diversity was low, resulting in a lower denitrification rate constant. The static experimental results showed that the denitrification rate at 19°C was approximately 2.4 times that at 10°C. The dynamic soil column experiment established an exponential positive correlation between the nitrate denitrification decay kinetic constant and temperature. The affinity of denitrifying enzymes for nitrate in the reaction substrate was ordered as follows: decreasing temperature gradient (30°C → 10°C) > zero temperature gradient (10°C) > increasing temperature gradient condition (0°C → 10°C). This study provides a theoretical basis for the biogeochemical processes underlying river bank infiltration, which will help aid in the development and utilization of groundwater resources.

Numerical simulation of temperature gradient effects on gallium nitride crystal growth by sodium-flux method

During the growth of gallium nitride single crystals by sodium-flux method, temperature significantly impacts crystal quality. In this study, the mechanism of the effect of different temperature gradients on crystal growth is analyzed in depth using a combination of numerical simulation and experiment. The experimental results show that epitaxial growth of crystals occurs under positive temperature gradient conditions, while there is dissolution of seed crystals under negative temperature gradient conditions. The temperature, flow, and concentration data of the melted material during crystal growth were calculated using numerical simulation. The simulation findings reveal that the distribution of solution supersaturation varies according to temperature. High supersaturation at the bottom of the melt is favorable for crystal epitaxial growth on the surface of seed crystals under a positive temperature gradient. Meanwhile, low supersaturation at the top of the melt suppresses the hard polycrystalline layer here. Under negative temperature gradient conditions, low supersaturation at the bottom of the melt may lead to remelting of seed crystals, which is consistent with the experimental phenomenon. Furthermore, we propose an optimized heat source profile. This profile manages high supersaturation near seed crystals, aiding continuous growth. Finally, we have applied the curve in an applied way by proposing a multi-stage heating device, based on which the desired arbitrary temperature profile can be modulated. This research has broad applications in a variety of crystal growth experiments using fluid as the mother phase.

Computational Model of Effective Thermal Conductivity of Green Insulating Fibrous Media.

Modelling effective thermal properties is crucial for optimizing the thermal performance of materials such as new green insulating fibrous media. In this study, a numerical model is proposed to calculate the effective thermal conductivity of these materials. The fibers are considered to be non-overlapping and randomly oriented in space. The numerical model is based on the finite element method. Particular attention is paid to the accuracy of the results and the influence of the choice of the representative elementary volume (REV) for calculation (cubic or rectangular parallelepiped slice). The calculated effective thermal conductivity of fibrous media under different boundary conditions is also investigated. A set of usual mixed boundary conditions is considered, alongside the uniform temperature gradient conditions. The REV rectangular slice and uniform temperature gradient boundary conditions provide a more accurate estimate of the effective thermal conductivity and are therefore recommended for use in place of the usual cubic representative elementary volume and the usual mixed boundary conditions. This robust model represents a principal novelty of the work. The results are compared with experimental and analytical data previously obtained in the literature for juncus maritimus fibrous media, for different fiber volume fractions, with small relative deviations of 7%. Analytical laws are generally based on simplified assumptions such as infinitely long fibers, and may neglect heat transfer between different phases. Both short and long fiber cases are considered in numerical calculations.

Mass transfer in the snow strata under conditions of large temperature gradients

In the winter of 2022-2023, a study of the crystal structure of hoarfrost horizons on the slopes of Mount Elbrus was carried out in conditions of the low-snow winter period. By means of a digital portable microscope the data were obtained, according to which, the average size of crystals of hoarfrost is 1.5- 2.5 mm, and the most frequent form of crystals of hoarfrost is flat skeletal, columnar faceted and columnar semi-skeletal forms. The study confirmed the previously observed regularity that mass transfer in the snow column depends on the magnitude of the temperature gradient, the degree of water vapor saturation in the transit zones which, among other things, are influenced by the snow cover thickness and absolute height.

A step-by-step thermo-elastoplastic analysis of laser beam welding

In recent years, laser beam welding has emerged as a significant contact-free fusion method due to its advantages such as high laser advance speed and minimal thermal distortion. Automation further increases its attractiveness in various industries. However, specific conditions related to temperature gradient, chemical composition, welding speed and mechanical boundary conditions can lead to solidification cracks. These cracks originate from microcracks within the weld and occur during solidification. The mushy zone is particularly prone to solidification cracking due to the dendritic morphology and entrapped liquid phases. To address this problem, this study makes a step-by-step approach using finite element simulations on the macro- and microscale. It first locates the mushy zone macroscopically using a heat source model and then analyzes the evolving dendritic microstructure at the microscopic level in a simplified manner, considering thermal and elastoplastic effects. This enables a more thorough understanding of the critical states at micro- and macroscale which may lead to solidification cracking.

Thermomechanical modeling of dissimilar-material interfaces in composite structures

Due to the heterogeneities in material properties of strongly-bonded multi-material composite structures, there exist singularities of the stress fields at the material interface as well as the interface corners on the bounding surfaces. The finite-element method is probably the only plausible option to analyze the stress around such interfaces between dissimilar materials subjected to combined thermo-mechanical loading. In this article, we propose a novel mathematical model for the computational analysis of coupled thermo-elastic fields with perfectly bonded interfaces of dissimilar isotropic/orthotropic composite-material structures. A scalar function of the spatial variables, namely, the displacement function, is used to integrate the temperature field and the associated displacement-function field to obtain two nonhomogeneous partial-differential equations of equilibrium that govern two thermo-mechanical sub-problems defined in terms of the appropriate conditions of orthogonal temperature gradients. For a specific temperature field, obtained as a steady-state solution of the given thermal problem, the two thermo-mechanical sub-problems are solved independently to obtain the full-field solution of the thermo-elastic problem using the method of superposition. As an alternative to the conventional computational approach, we employed a single variable semi-analytical method of solution to determine the thermo-mechanical response of the multi-material composite structures. The continuity of the temperature and the heat flux in the thermal field problem and the continuity of the displacement and the traction vectors are utilized in the elastic field problem to determine the appropriate algebraic equations suitable for nodal application at the interfaces as well as interface corners on the boundaries of the respective problems. The quantitative comparison of the present displacement-function solutions to several mixed-boundary-value problems with those obtained by the conventional finite-element method verifies the high accuracy and effectiveness of the present method. This computational model has potential applications in identifying near-interface high-stress locations as well as possible critical regions of the physical boundary of composite structures subjected to mixed modes of thermal and mechanical loadings.

Compositional Grading of Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;/ZrO&lt;sub&gt;2&lt;/sub&gt;/SUS304 Hybrid Materials Using Centrifugal Slurry Methods and Spark Plasma Sintering

Ceramic/ metal functionally graded materials (FGMs) have been promising to sustain coating structures working under super high temperature as well as high temperature gradient conditions. Compositional gradients in the FGMs can be engineered according to functional performance requirements. This study aims to fabricate Al2O3/ZrO2/SUS304 hybrid FGMs with continuous compositional gradient manners using a combination of centrifugal slurry methods and spark plasma sintering (SPS). The compositional gradients in the FGMs were investigated on microstructures with elemental distributions and hardness on the cross sections of the FGMs. It was demonstrated that the compositions of ZrO2 and SUS304 continuously varied in the FGMs, while Al2O3 resided only on ZrO2-rich sides, which can effectively enhance the fracture toughness of the ZrO2-rich layer. Ball milling treatments can make the Al2O3 layer more formed in the ZrO2-rich layer. With increasing the amount of Al2O3, the Al2O3 layer resided closer to the top of the ZrO2 surfaces in the FGMs subject to ball milling treatments, which can prevent the crack propagation from the ZrO2 top surfaces.

Features of Structures and Ionic Conductivity of Na3Fe2(PO4)3 Polycrystals Obtained by Solid Phase and Melt Methods

This article investigates the structures and conductive properties of polycrystals of Na3Fe2(PO4)3 obtained by solid-state and melt synthesis methods using concentrated optical radiation. It has been established that in the melt synthesis method, the material is synthesized under significantly non-equilibrium thermodynamic conditions, leading to the creation of deformations in the sample, which contribute to the enhancement of ionic conductivity. Additionally, the synthesis duration is reduced by half. Through a comparative assessment of the structural parameters and conductive properties of these materials, it is demonstrated that polycrystals obtained by the melt method exhibit better texture and higher ionic conductivity. The occurrence of deformations during the synthesis of α-Na3Fe2(PO4)3 under high temperature-gradient conditions indicates the elasticity of the crystalline framework {[Fe2(PO4)]3−}3∞. It is concluded that the non-equilibrium thermodynamic conditions of α-Na3Fe2(PO4)3 synthesis promote the formation of deformations in the crystalline structure of polycrystals, leading to a partial increase in symmetry and ionic conductivity.

Nonlinear vibration characteristics of elastically supported FRP cylindrical shells under temperature gradient conditions: Theoretical and experimental studies

The nonlinear free vibrations of elastically supported fiber-reinforced polymer cylindrical shells (FRPCSs) under temperature gradient conditions are investigated using both theoretical and tested techniques. A dynamic model of the FRPCSs with consideration of such complex thermal conditions is firstly established based on the first-order shear deformation theory in conjunction with Hamilton’s principle, the Galerkin method, the artificial spring technique, etc. Numerical results at room temperature and in a uniform thermal environment with classical or arbitrary boundary conditions are utilized to give a rough validation of this model. Subsequently, a thermal-vibration system is set up to measure the nonlinear natural frequencies of two FRPCS specimens subjected to four different temperature gradient conditions in free-free boundary constraints, and iterative calculations are performed to identify the temperature-dependent material properties. Finally, the detailed comparisons of calculated and experimental results provide a solid validation of the proposed model. This study offers a practical model tool to forecast the nonlinear free vibrations of the FRPCSs in a complex thermal environment, which can be readily adjusted and extended to other forms of composite shells. Also, the predicted and measured results can help assess the structural thermal-vibration behaviors when the temperature gradient effect needs to be considered. Communicated by Makoto Ohsaki.

Development of in-situ Delayed Hydride Cracking tests using neutron imaging to study the H redistribution in Zr-2.5%Nb

Delayed Hydride Cracking (DHC) is a failure mechanism that occurs in Zr alloys under certain conditions of hydrogen concentration, temperature and stress gradient. In service, hydrogen produced by corrosion reaction can be incorporated in Zr alloys and if the solid solubility is exceeded, hydrogen precipitates as zirconium hydride. The presence of a stress concentrator, such as a crack, generates the hydrogen diffusion and precipitation to the high stress zone beginning the DHC process. In this work, in-situ DHC tests in air at 250°C were performed at ANTARES, the neutron imaging facility of the FRM-II reactor. Samples of Zr2.5%Nb produced from extruded tubes and pressure tubes were studied using a stress rig specially modified to perform DHC tests in the neutron beam. H redistribution during mechanical testing was followed in-situ by registering the changes in neutron transmission. The results were compared with the images obtained by light optical microscopy after the tests. The results highlight the capabilities of neutron imaging to analyze time-dependent H distribution during DHC crack growth.