Temperature Spectra Research Articles

Effects of cooling rate on <i>β</i> relaxation process and stress relaxation of La-based amorphous alloys

The dynamic relaxation process and stress relaxation process are two important processes which can reflect the microstructures of materials, for they are closely related to the diffusions, the glass transition phenomena and the microstructural heterogeneities. It is of great significance to explore the relationship among them. In the current research, the <i>β</i>-relaxation characteristics and stress relaxation behaviors of bulk and ribbon samples obtained by different cooling rates are systematically investigated by taking the typical La-based amorphous alloys as model systems. The experimental results demonstrate that the cooling rate is an important parameter for controlling the energy state of the glass system, which further affects its physical and mechanical properties. Based on the dynamical mechanical spectra, the larger the cooling rate, the greater the low-temperature internal friction is and the smaller the beta relaxation activation energy according to Arrhenius calculations, and the greater the broadening of the beta relaxation behavior in the temperature spectra, suggesting that the higher cooling rate leads to greater atomic mobility and a high degree of heterogeneity in the microstructure. Thermodynamic analysis is conducted to study the slow process of thermal activation and the fast process driven by stress. At low temperature, the activation volume of the strip sample is larger than that of the bulk sample, and the activation volume values of the two samples are almost the same, as the cooling rate only affect the <i>β</i> relaxation stage, but exert little effect on the <i>α</i> relaxation, which is consistent with the conclusion that the stress relaxation behavior and <i>β</i> relaxation behavior are related to the structural non-uniformity of the amorphous alloy. The stress relaxation tests show that the characteristic time of deformation decreases at higher cooling rate, the normalized stress decay is larger, it is easier to deform under an applied force field, and the deformation unit is more likely to activate to accommodate structural deformation. The correlation between stress relaxation and <i>β</i> relaxation of amorphous alloy is further confirmed, and the proportion of liquid-like region is proportional to the relaxation mode spectrum, which also shows that <i>β</i> relaxation and stress relaxation are consistent. Finally, by calculating relaxation enthalpy <inline-formula><tex-math id="M1">\begin{document}$ \Delta {H}_{{\mathrm{r}}{\mathrm{e}}{\mathrm{l}}} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20231417_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20231417_M1.png"/></alternatives></inline-formula>, the variation of microstructure heterogeneity with cooling rate is experimentally verified. The research sheds new light on further clarifying the relationship among <i>β</i> relaxation, deformation and microstructural heterogeneity of the amorphous alloy.

Near-infrared absorption and radiative cooling of naphthalene dimers (C10H8)2.

The radiative cooling of naphthalene dimer cations, (C10H8)2+ was studied experimentally through action spectroscopy using two different electrostatic ion-beam storage rings, DESIREE in Stockholm and Mini-Ring in Lyon. The spectral characteristics of the charge resonance (CR) band were observed to vary significantly with a storage time of up to 30 seconds in DESIREE. In particular, the position of the CR band shifts to the blue, with specific times (inverse of rates) of 0.64 s and 8.0 s in the 0-5 s and 5-30 s storage time ranges, respectively. These long-time scales indicate that the internal energy distribution of the stored ions evolves by vibrational radiative cooling, which is consistent with the absence of fast radiative cooling via recurrent fluorescence for (C10H8)2+. Density functional based tight binding calculations with local excitations and configuration interactions (DFTB-EXCI) were used to simulate the absorption spectrum for ion temperatures between 10 and 500 K. The evolution of the bandwidth and position with temperature is in qualitative agreement with the experimental findings. Furthermore, these calculations yielded linear temperature dependencies for both the shift and the broadening. Combining the relationship between the CR band position and the ion temperature with the results of the statistical model, we demonstrate that the observed blue shift can be used to determine the radiative cooling rate of (C10H8)2+.

A computational analysis of operational parameters influencing coal gasification in a lab-scale drop tube gasifier

This study uses a numerical simulation for coal gasification operation in a drop tube gasifier to investigate the effects of wall temperature and oxygen-to-coal (O/C) ratios on gasification. Coal gasification is an efficient approach to electricity generation, offering a cleaner alternative to conventional coal combustion methods. A 2D Computational Fluid Dynamics (CFD) model of the gasifier was employed to perform grid sensitivity analysis and subsequently compute the influences of varying wall temperatures (1000 K, 1250 K, and 1500 K) and O/C ratios (0.6, 0.8, 1, and 1.2) on the temperature profile, syngas composition, and velocity within the gasifier. Temperature profiling within the furnace defined a spectrum of maximum and minimum temperatures, with apex values recorded at 2100 K and lowest values at 1300 K for Cases 12 and 1, respectively. High O/C ratios favored the production of CO2 due to enhanced combustion reactions, whereas lower O/C ratios were conducive to higher yields of CO and H2, essential syngas components. Velocity profiles of particles within the gasifier increased with higher temperatures and O/C ratios, and the maximum velocity was 9 m/sec. In conclusion, this study offers valuable insights into optimizing operational parameters such as wall temperatures and O/C ratios to enhance the performance and efficiency of coal gasification processes in lab-scale gasifiers.

Thermal evolution of a polymer-nanoparticle binary mixture.

We experimentally probe the microscopic variations in a model polymer-nanoparticle (NP) binary mixture (mixture of polybutadiene and clay nanoplatelets) across a thermal evolution path for which Tevolution > Tg(polymer). The evolution of the NP dispersion, NP crystallinity, polymer chain-NP interface, and nature of polymer chain-NP interaction are mapped for a spectrum of temperatures and NP concentrations constrained by experiments. Multiple pieces of evidence indicate that thermal evolution does not influence the nature of interparticle dispersion and is also independent of NP concentration in the binary mixture. However, the NP crystalline order significantly reduces across the thermal evolution path. Thermal evolution induces a transition of a sharp polymer chain-NP interface to a diffuse interfacial layer. In contrast, an already diffuse polymer-NP interface existing in the binary mixture due to particle crowding at high NP concentrations undergoes no significant change in its nature across the evolution path. At all particle concentrations, thermal evolution changes the dominant interaction from polymer chain-polymer chain to polymer chain-NP. These insights aid in explaining the molecular origins of unique and anomalous behaviors shown by polymer-nanoparticle binary mixtures while undergoing thermal evolution.

Multiple free-radical-trapping and hydrogen-bonding-enhanced polyurethane foams with long-lasting flame retardancy, aging resistance, and toughness.

Flexible polyurethane foam (FPUF) is a ubiquitous material utilized in furniture cushions, mattresses, and various technical applications. Despite the widespread use, FPUF faces challenges in maintaining long-lasting flame retardancy and aging resistance, particularly in harsh environments, while retaining mechanical robustness. Here, we present a novel approach to address these issues by enhancing FPUF through multiple free-radical-trapping and hydrogen-bonding mechanisms. A hindered amine phosphorus-containing polyol (DTAP) was designed and chemically introduced into FPUF. The distinctive synergy between hindered amine and phosphorus-containing structures enables the formation of multiple hydrogen bonds with urethane, while also effectively capturing free radicals across a broad temperature spectrum. As a result, incorporating only 5.1 wt% of DTAP led to the material successfully passing vertical burning tests and witnessing notable enhancements in tensile strength, elongation at break, and tear strength. Even after enduring accelerated thermal aging for 168 hours, the foam maintained exceptional flame retardancy and mechanical properties. This study offers novel insights into material enhancement, simultaneously achieving outstanding long-lasting flame retardancy, toughness, and anti-aging performance.

Enhanced capacitive energy storage of NaNbO3-based relaxor via modulating the phase structure strategy for high power energy storage

A schematic diagram of the design strategy to achieve high energy storage performance via the phase structure strategy: (a) and (b) dielectric temperature spectra, (c) PFM phase images, and (d) slim unipolar P–E hysteresis loop.

Enhancement of hybrid organohydrogels by interpenetrating crosslinking strategies for multi-source signal recognition over a wide temperature range.

With substantial temperature differentials between summer and winter in polar regions, there exists a pressing necessity for flexible sensors capable of functioning across a broad temperature spectrum to facilitate the construction of a more intelligent human-machine interface. Nevertheless, developing flexible sensors resilient to extremely low temperatures remains a significant challenge. In this study, we present an organohydrogel capable of functioning ranging from ambient to -78 °C, enabling real-time monitoring of multi-source signals, including motion, physiology, speech, and pressure. We synthesize organohydrogel employing a singular methodology: interpenetrating network structures as matrix frameworks, dynamic hydrophobic linkages as the physical cross-linking points, and incorporating a bionic binder. H-Bonding and chain entanglement synergistic supramolecular interactions build the organohydrogel matrix with microphase-separated domains, which, together with the combination of binary solvents and inorganic salts, allows it to exhibit excellent properties, including large stretchability (≈1700%), high ionic conductivity (1.57 S m-1), admirable sensing sensitivity performance (gauge factor: GF = 6.47, S = 0.32 kPa-1), an exceptionally low-pressure detection threshold (≈1 Pa), enables wireless transmission of distress signals through human-machine interaction even at -78 °C, which makes it possible to use it in polar exploration and to give robots a "sense of touch" for a variety of deep-diving tasks.

A temperature-adjustable in situ infrared diffuse reflectance spectroscopy system for catalysts.

We introduce an innovative in situ infrared diffuse reflection rapid detection system, endowed with a temperature regulation function. This system is adept at conducting rapid infrared spectra scanning as well as simulating the catalytic environment of diverse reaction systems. The infrared absorption spectra of four kinds of Pt-based catalysts under vacuum conditions across a wide temperature spectrum ranging from -180 to 300 °C are obtained and analysed through IR correlation spectroscopy. A key finding is the notable variance in peak intensity within Pt/CeO2/CNT catalysts, highlighting a robust adsorption capacity for oxygen-containing groups at lower temperatures and a marked desorption at higher temperatures. By enabling rapid and accurate assessments of catalyst behavior under varying temperatures, it not only accelerates the evaluation process but also provides valuable insights that can guide the synthesis of more efficient catalysts.

Hexagonal-Ge Nanostructures with Direct-Bandgap Emissions in a Si-Based Light-Emitting Metasurface.

Si-based emitters have been of great interest as an ideal light source for monolithic optical-electronic integrated circuits (MOEICs) on Si substrates. However, the general Si-based material is a diamond structure of cubic lattice with an indirect band gap, which cannot emit light efficiently. Here, hexagonal-Ge (H-Ge) nanostructures within a light-emitting metasurface consisting of a cubic-SiGe nanodisk array are reported. The H-Ge nanostructure is naturally formed within the cubic-Ge epitaxially grown on Si (001) substrates due to the strain-induced nanoscale crystal structure transformation assisted by far-from-equilibrium growth conditions. The direct-bandgap features of H-Ge nanostructures are observed and discussed, including a rather strong and linearly power-dependent photoluminescence (PL) peak around 1562 nm at room temperature and temperature-insensitive PL spectrum near room temperature. Given the direct-bandgap nature, the heterostructure of H-Ge/C-Ge, and the compatibility with the sophisticated Si technology, the H-Ge nanostructure has great potential for innovative light sources and other functional devices, particularly in Si-based MOEICs.

Using Downwelling Far- and Thermal-Infrared Hyperspectral Radiance for Cloud Phase Classification in the Antarctic

The cloud phase is one of the most important parameters of clouds. In this paper, we propose a method for cloud phase classification that synergistically utilizes the far- and thermal-infrared bands based on the Atmospheric Emitted Radiance Interferometer (AERI) at the Atmospheric Radiation Measurement West Antarctic Radiation Experiment (AWARE) observatory in 2016. The possible features in the far- and thermal-infrared bands are analyzed based on the differences in the simulated cloud brightness temperature (BT) spectra with different cloud phases. Using the support vector machine (SVM) algorithm, four features are determined to identify the cloud phase, which include the BT at 900 cm−1, the slope of the fitted function of BT in the 900–1000 cm−1 interval, the BT difference (BTD) between 512 cm−1 and 726 cm−1, and the BTD between 550 cm−1 and 726 cm−1. Here, the performance of the proposed method is evaluated with Shupe’s and Turner’s method. The monthly average accuracy of the proposed method, the method without the two far-infrared features, and Turner’s method are about 76%, 36%, and 49%, respectively, which infer the good performance of the proposed method and also indicate that the far-infrared band features can effectively enhance cloud phase classification. It is notable that, compared to Shupe’s method, the accuracy for the proposed method is only 61% during the Antarctic summer, which results from the definitions of cloud phase and radiative effect. In addition, the accuracy is only 44% for Turner’s method in seasons with a low frequency of mixed clouds due to the significant effect of water vapor.

Unraveling concentration-dependent solvation structures and molecular interactions in water-in-salt electrolytes for enhanced performance of electric double-layer capacitors

Water-in-salt electrolytes (WiSEs) are increasingly recognized as advanced aqueous electrolytes for energy storage due to their inherent safety, wide electrochemical stability window (ESW) beyond 1.23 V, and relatively high ionic conductivity to viscosity ratio. Despite these advantages, a comprehensive understanding of the physicochemical and structural properties of WiSEs across a broad temperature spectrum remains elusive, thus limiting potential performance enhancements. In this study, the microscopic ion-ion and ion-water interactions in WiSE with potassium acetate (KOAc) as a model electrolyte were systematically analyzed in both bulk phase and electric double-layer (EDL). Concentration-dependent solvation structures, thermal and structural behaviors, and ionic transport properties were investigated through Raman spectroscopy, differential scanning calorimetry (DSC), X-ray diffraction (XRD), and analytical electrochemistry measurements. The phase diagram of the aqueous KOAc solution was constructed using low-temperature XRD to identify the solidified phases, and DSC was used to determine the phase transition temperatures in a wide temperature range from -120 °C to 80 °C. We also explored the temperature-dependent electrochemical performance of various concentrations of KOAc electrolytes, finding the 5 m KOAc shows optimal performance for EDLCs at room temperature and in sub-zero temperatures. Additionally, we proposed a novel concept of an optimal cutoff voltage for maximizing power, comparing it with other commonly used metrics for setting cutoff voltage. This study validates our approach and highlights its significance in balancing key performance parameters.

Flexible regulation engineering of titanium nitride nanofibrous membranes for efficient electromagnetic microwave absorption in wide temperature spectrum

Flexible regulation engineering of titanium nitride nanofibrous membranes for efficient electromagnetic microwave absorption in wide temperature spectrum

Hierarchical Phonon Scattering from Nano to Macro Scale in Ag-Nano/TiO2-Micro Particle-Decorated p-type Bismuth Telluride Bulk Composites.

We study the thermoelectric properties of a p-type Bi0.4Sb1.6Te3.4 (BST) composite with Ag nanoparticle-decorated TiO2 microparticles (US-Ag/TiO2). The dispersion of US-Ag/TiO2 particles, synthesized by an ultrasonication (US) method, into the matrix effectively decreases lattice and bipolar thermal conductivity, attributed to the scattering centers formed at nano and micro scales. The electron backscattering diffraction (EBSD) measurements revealed smaller grain sizes within the BST composite when paired with the US-Ag/TiO2 particle dispersion. These reduced grain sizes, alongside nanoparticle-decorated microparticles dispersed throughout the matrix, scatter phonons effectively from long- to short-wavelength phonons and subsequently decrease lattice thermal conductivity. While the power factors of the composites are reduced, significant suppression of lattice and bipolar thermal conductivity has led to an increase in the maximum zT value (1.4 at 325 K) for a 0.9 wt % US-Ag/TiO2 particle dispersion within the BST matrix. This particle dispersion in the BST composite consistently demonstrates a high zT value across an extensive temperature spectrum, leading to an exceptionally high average zTavg value (1.38 up to 400 K), which is superior to the other values from reported BST composites. Thus, this research indicates that the dispersion of nanoparticle-decorated microparticles within a thermoelectric material matrix can significantly improve thermoelectric performance, which has promising implications for practical applications in thermoelectric cooling and sustainable and economical energy harvesting technologies.

Mechanical properties of cubic boron nitride and diamond at dynamical pressure and temperature

We report the mechanical properties of cubic boron nitride (c-BN) and diamond under the combined impact of dynamical pressure and temperature, calculated using ab initio molecular dynamics. Our study revealed a pronounced sensitivity of the mechanical properties of c-BN to applied pressure. Notably, c-BN undergoes a brittle-to-ductile transition at ∼220 GPa, consistent across various dynamical temperatures, while diamond exhibits no such transition. Furthermore, the Vickers hardness profile for c-BN closely mirrors that of diamond across a spectrum of temperature–pressure conditions, highlighting c-BN's significant mechanical robustness. These results underscore the superior resilience and adaptability of c-BN compared to diamond, suggesting its potential as an ideal candidate for applications in extreme environments.

Exploring the caveats associated with estimating the properties of amorphous glassy thermoset

Structural-thermal-mechanical properties are examined for various cross-linked amorphous SU-8 samples via Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), and nanoindentation, respectively. It is found that room temperature FTIR spectra provide less cross-linking (%) estimation than baking temperature spectra due to the mobility effect of polymer chains. DSC results show that glass transition temperature (Tg) is increasing with the extent of cross-linking (%). However, the correlation of Tg with FTIR measured cross-linking (%) will not be accurate because during DSC characterization sample will undergo cross-linking. From nanoindentation, counter-intuitive results are obtained by the conventional method for reduced elastic modulus (Er) and hardness (H), i.e., decrease with an increase in cross-linking (%). The possible errors, i.e., physical phenomena and methodology, have been analyzed thoroughly for these trends. After minimization/elimination of physical phenomena errors, it is found that current analysis methods are not accurate to estimate Er and H for glassy polymers.

How sintering temperature affects the electrochemical performance of ultra-high nickel (Ni > 0.9) cathode material

The burgeoning demand for electric vehicles with extended driving ranges has propelled ongoing development efforts for ultra-high nickel (Ni > 0.9) cathode materials. Despite significant ongoing research focused on Ni-rich cathode materials, a more comprehensive foundational understanding of ultra-high nickel cathode materials is essential. In our research, we employed LiNi0.94Co0.06O2 as a model ultra-high nickel cathode material to systematically delve into the interplay between sintering temperature, structural features, and electrochemical behavior. Within a sintering temperature spectrum of 660–720 °C, we discerned that specimens produced at diminished temperatures manifest a reduced initial discharge capacity yet excel in cycling endurance. In stark contrast, their counterparts produced at augmented temperatures behave inversely. Identifying a singular sintering temperature that achieves equilibrium between initial discharge capacity and cycling performance proves elusive. Through X-ray diffraction and high-resolution transmission electron microscopy, it became evident that samples synthesized at lower temperatures exhibit pronounced lithium-nickel mixing and develop a thicker NiO layer on the surface, leading to compromised initial discharge performance and capacity. Utilizing focused ion beam scanning electron microscopy, differential capacity analysis, and in-situ X-ray diffraction, we confirm that samples synthesized at lower temperatures possess smaller particle sizes, enabling them to withstand volumetric expansion stress during cycling, resulting in enhanced cycling performance. In the realm of ultra-high nickel cathode materials, elevating the sintering temperature is a conduit to superior initial discharge efficiency and capacity. Yet, the imperative of preserving diminutive particle dimensions, as a stratagem to bolster cycling performance, stands out as a pivotal research frontier.

Joint measurement of electron density, temperature, and emission spectrum of Nd:YAG laser-produced tin plasma

We present the results of joint measurements of electron density (ne), temperature (Te), and emission spectra of an Nd:YAG-driven tin plasma. Collective Thomson scattering provides space- and time-resolved ne and Te data during drive laser irradiation, and extreme ultraviolet (EUV) emission spectra, which is space-resolved in the target normal, are measured using a flat-field grazing incidence spectrometer (GIS). As the distance from the target increased, the emission intensity quickly decreases, and the peaks of the spectra gradually shift to longer wavelengths. This can be explained by the rapid decrease in ne, and thus, self-absorption, with an increase in distance. We obtain the EUV spectra by calculating the transfer of photons along the line-of-sight of the GIS, using theoretical emissivity and opacity, and applying the measured spatial distribution of ne and Te. The results quantitatively demonstrate that the self-absorption effect is significant; the emission from the core regions is mostly reabsorbed by the surrounding plasma. The calculated spectra are compared with the measured spectra. While good agreement is achieved in the spectral region of 13.3 and 15.3 nm, considerable differences are found in the 12.5–13 and 15.5–17.5 nm region. The results demonstrate the significance of this joint measurement for further validation of the atomic process model considering self-absorption effect, which is critical for the future high-density, solid laser-driven EUV source.

Exploration of temperature driven conduction process and ferroelectric properties of Mn doped GdCrO3

This work delivers the research findings of the temperature dependent DC resistivity, AC impedance and ferroelectric polarization of GdCr1−xMnxO3 (x = 0 and 0.3). Mixed valence states of Cr (Cr3+ and Cr4+) are explored using the x-ray photoelectron spectroscopy analysis. The exponential decay of DC resistivity on escalating the temperature advocates the semiconducting-like nature for the probed samples. The DC resistivity data of these samples fit well into small-polaron hopping and variable range hopping models. The impedance attributes of these samples were scrutinized over a broad spectrum of temperatures at selected frequencies. The values of the real and imaginary parts of impedance unveil substantial reduction on raising the temperature, thereby signifying the increase in conductivity of the samples. Pristine sample displays an electrical relaxation peak at 65 °C, which translates towards the lower temperature at higher frequencies. Further, the semicircular behavior of Nyquist plots at higher temperatures indicates the reduction of the charge transfer resistance. The equivalent circuits of Nyquist plots are generated using Z-view software. From these plots, it is perceived that grain boundary resistance upsurges while the grain resistance and capacitance drops upon doping. The ferroelectric measurements reveal that the coercive field (Ec) values decrease whereas the values of maximum polarization (Pm), remnant polarization (Pr) and energy storage increase in 30% doped GdCrO3. These observations establish that electrical and ferroelectric properties of GdCrO3 system can be tuned with appropriate Mn doping.

Water vapor absorption spectroscopy and validation tests of databases in the far-infrared (50–720 cm−1). Part 2: H217O and HD17O

The present work is the second part of our systematic study of the absorption spectrum of the water vapor isotopologues by high resolution (≈ 0.001 cm−1) Fourier transform spectroscopy in the far infrared (50–721 cm−1). The room temperature spectra were recorded at the AILES beam line of the SOLEIL synchrotron with an absorption pathlength of 151.75 m. Here, we consider three spectra of a water vapor sample highly enriched in 17O. Line parameters retrieved from the three spectra were combined in a global list of 4432 water lines (assigned to 4651 transitions). The spectral calibration based on a statistical matching with about 370 accurate reference line positions of H216O allows for line center determinations with an accuracy of 5×10−5 cm−1 for well isolated lines of intermediate intensity. Six water isotopologues (H218O, H216O, H217O, HD18O, HD16O, and HD17O) were found to contribute to the spectrum. 460 and 99 of the measured H217O and HD17O transitions are newly observed by absorption spectroscopy. 69 H217O and 20 HD17O energy values of the ground (000) and first excited (010) states are newly determined.The present set of measured H217O line positions is combined with 24 literature sources to provide a list of 821 empirical energies for the first five vibrational states – (000), (010), (020), (100), and (001) – using the RITZ principle. A set of 332 rotational energies of the (000) and (010) states of HD17O is determined by merging the 465 HD17O transitions measured in the present study to eight literature sources.

Effects of operational parameters on plasma characteristics and liquid treatment of a DBD-based unipolar microsecond-pulsed helium atmospheric pressure plasma jet

A dielectric-barrier-discharge-based square unipolar microsecond-pulsed helium atmospheric pressure plasma jet (APPJ) was characterized by combining a simplified equivalent circuit model with a transferred charge (Q) measured by introducing an additional capacitance in series with the reactor. From Q-V plots, Cd and Ccell for DBD reactors under pulsed excitation were determined. Q-V plots were drawn for varying operational parameters, and the dissipated energy per cycle was evaluated. Operational parameters, such as the gas flow rate and pulse frequency, were varied, and the resulting changes in the plasma plume length, gas temperature, excitation temperature, discharge current, dissipated power, and optical emission spectra were examined. As an example of the application of the plasma jet, liquid media, including de-ionized water, were exposed to the APPJ, and their properties (pH and electrical conductivity) and concentrations of reactive species generated in the media were measured as functions of the operational parameters. Furthermore, changes in the plasma-activated media after storage for different durations and under different conditions were examined. The correlation between plasma characteristics and properties of plasma-treated liquid is discussed.