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Laser-driven shock compression enables an experimental study of phase transitions at unprecedented pressures and temperatures. One example is the shock Hugoniot of magnesium oxide (MgO), which crosses the B1–B2-liquid triple point at 400–600 GPa, 10 000–13 000 K (0.86–1.12 eV). MgO is a major component within the mantles of terrestrial planets and has long been a focus of high-pressure research. Here, we combine time-resolved velocimetry and pyrometry measurements with a decaying shock platform to obtain pressure–temperature data on MgO from 300 to 1500 GPa and 9000 to 50 000 K. Pressure–temperature–density Hugoniot data are reported at 1500 GPa. These data represent the near-instantaneous response of an MgO [100] single crystal to shock compression. We report on a prominent temperature anomaly between 400 and 460 GPa, in general agreement with previous shock studies, and draw comparison with equation-of-state models. We provide a detailed analysis of the decaying shock compression platform, including a treatment of a pressure-dependent optical depth near the shock front. We show that if the optical depth of the shocked material is larger than 1 μm, treating the shock front as an optically thick gray body will lead to a noticeable overestimation of the shock temperature. [ABSTRACT FROM AUTHOR]

Room temperature ferromagnetism observed in polycrystalline MnGeP2 bulk samples was investigated by different experimental techniques. The magnetization measurements show a high temperature ferromagnetic phase with a critical temperature TC = 294.0 K and a low temperature magnetic phase transition at TN = 40.5 K. As these parameters (TC,TN) correspond to those of MnP, a ferromagnetic half-metal, whose composition of the samples was further characterized by x-ray diffraction and Rutherford backscattering measurements. They confirmed the presence of orthorhombic MnP precipitates. Electron paramagnetic resonance (EPR) and ferromagnetic resonance (FMR) measurements in the temperature range of T = 4 K to T = 380 K confirm the attribution of the magnetic phase to MnP and show no additional EPR or FMR signal associated with MnGeP2. We conclude that the magnetic properties of the polycrystalline MnGeP2 bulk samples grown by the horizontal gradient freeze technique are dominated by MnP inclusions and that phase pure chalcopyrite MnGeP2 is not ferromagnetic in contrary to previous reports. [ABSTRACT FROM AUTHOR]

Room temperature ferromagnetism observed in polycrystalline MnGeP2 bulk samples was investigated by different experimental techniques. The magnetization measurements show a high temperature ferromagnetic phase with a critical temperature TC = 294.0 K and a low temperature magnetic phase transition at TN = 40.5 K. As these parameters (TC,TN) correspond to those of MnP, a ferromagnetic half-metal, whose composition of the samples was further characterized by x-ray diffraction and Rutherford backscattering measurements. They confirmed the presence of orthorhombic MnP precipitates. Electron paramagnetic resonance (EPR) and ferromagnetic resonance (FMR) measurements in the temperature range of T = 4 K to T = 380 K confirm the attribution of the magnetic phase to MnP and show no additional EPR or FMR signal associated with MnGeP2. We conclude that the magnetic properties of the polycrystalline MnGeP2 bulk samples grown by the horizontal gradient freeze technique are dominated by MnP inclusions and that phase pure chalcopyrite MnGeP2 is not ferromagnetic in contrary to previous reports. [ABSTRACT FROM AUTHOR]

Rutile-type wide and ultrawide band-gap oxide semiconductors are emerging materials for high-power electronics and deep ultraviolet optoelectronics applications. A rutile-type GeO2-SnO2 alloy (r-GexSn1–xO2) recently found is one of such materials. Herein, we report low-temperature electron transport properties of r-GexSn1−xO2 thin films with x = 0.28 and 0.41. Based on resistivity and magnetoresistance measurements, along with the theory of quantum interference, it is suggested that Efros–Shklovskii variable-range hopping, i.e., hopping over the states within the Coulomb gap, is dominant at lower temperatures (T ≤ 10 and 15 K) in both r-Ge0.41Sn0.59O2 and r-Ge0.28Sn0.72O2. The negative and positive magnetoresistances observed at low temperatures are attributable to the quantum interference and field-induced spin alignment, respectively. The magnetoresistance measurements at higher temperatures suggest that both Mott variable–range hopping and thermally activated band conduction occur at T < 100 K and that almost pure thermally activated band conduction takes place at T ≥ 150 K. [ABSTRACT FROM AUTHOR]

Rutile-type wide and ultrawide band-gap oxide semiconductors are emerging materials for high-power electronics and deep ultraviolet optoelectronics applications. A rutile-type GeO2-SnO2 alloy (r-GexSn1–xO2) recently found is one of such materials. Herein, we report low-temperature electron transport properties of r-GexSn1−xO2 thin films with x = 0.28 and 0.41. Based on resistivity and magnetoresistance measurements, along with the theory of quantum interference, it is suggested that Efros–Shklovskii variable-range hopping, i.e., hopping over the states within the Coulomb gap, is dominant at lower temperatures (T ≤ 10 and 15 K) in both r-Ge0.41Sn0.59O2 and r-Ge0.28Sn0.72O2. The negative and positive magnetoresistances observed at low temperatures are attributable to the quantum interference and field-induced spin alignment, respectively. The magnetoresistance measurements at higher temperatures suggest that both Mott variable–range hopping and thermally activated band conduction occur at T < 100 K and that almost pure thermally activated band conduction takes place at T ≥ 150 K. [ABSTRACT FROM AUTHOR]

The deviation from stoichiometry and the understanding of its consequences are key factors for the application of kesterites as solar cell absorbers. Therefore, this study investigates the local atomic structure of off-stoichiometric Cu2ZnSnS4 (CZTS), Cu2ZnSnSe4 (CZTSe) and Cu2ZnGeSe4 (CZGSe) by means of Extended X-ray Absorption Fine Structure Spectroscopy. Temperature dependent measurements yield the bond stretching force constants of all cation-anion bonds in stoichiometric CZTS and CZTSe and nearly stoichiometric CZGSe. Low temperature measurements allow high precision analysis of the influence of off-stoichiometry on the element specific average bond lengths and their variances. The overall comparison between the materials is in excellent agreement with measures like ionic/atomic radii and bond ionicities. Furthermore, the small uncertainties allow the identification of systematic trends in the Cu–Se and Zn–Se bond lengths of CZTSe and CZGSe. These trends are discussed in context of the types and concentrations of certain point defects, which gives insight into the possible local configurations and their influence on the average structural parameters. The findings complement the understanding of the effect of off-stoichiometry on the local structure of kesterites, which affects their electronic properties and thus their application for solar cells. [ABSTRACT FROM AUTHOR]

In April and May 2023, Southeast Asia (SEA) encountered an exceptional heatwave. The Continental SEA was hardest hit, where all the countries broke their highest temperature records with measurements exceeding 42 °C, and Thailand set the region's new record of 49 °C. This study provides a comprehensive analysis of this event by investigating its spatiotemporal evolution, physical mechanisms, forecast performance, return period, and extensive impacts. The enhanced high-pressure influenced by tropical waves, moisture deficiency and strong land-atmosphere coupling are considered as the key drivers to this extreme heatwave event. The ECMWF exhibited limited forecast skills for the reduced soil moisture and failed to capture the land-atmosphere coupling, leading to a severe underestimation of the heatwave's intensity. Although the return period of this heatwave event is 129 years based on the rarity of temperature records, the combination of near-surface drying and soil moisture deficiency that triggered strong positive land-atmosphere feedback and rapid warming was extremely uncommon, with an occurrence probability of just 0.08%. These analyses underscore the exceptional nature of this unparalleled heatwave event and its underlying physical mechanisms, revealing its broad impacts, including significant health repercussions, a marked increase in wildfires, and diminished agricultural yields. [ABSTRACT FROM AUTHOR]

Background: In the mechanical testing of high-temperature structural materials, ultra-high temperature deformation measurement is very necessary and very challenging. Objective: To overcome the challenge of using single-camera stereo-digital image correlation (stereo-DIC) for ultra-high-temperature measurement. Methods: An ultraviolet single-camera stereo-DIC system combining active UV illuminations, an ultraviolet camera, a single UV narrow bandpass filter, a reflective prism and two reflectors was established. In addition, two types of high temperature speckle patterns were prepared A tensile test of C/C composites at 2600 °C was conducted to verify the effectiveness and accuracy of the developed technology. Results: The ultraviolet single-camera stereo-DIC system has excellent resistance to thermal radiation. As well, the two types of speckle patterns are available at 2600 °C. And the values of elastic modulus calculated by the developed technology and high-temperature extensometer are very close to each other, and the relative errors are less than 7%. Conclusions: The well matched strain results with high-temperature extensometer data demonstrates that the ultraviolet single-camera stereo-DIC is an effective ultra-high temperature deformation measurement technology and has great potential in characterizing the deformation response of materials at ultra-high temperatures. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a method of measuring the flexural elastic modulus of ceramics at an intermediate (~millimeter) scale at high temperatures. We used a picosecond laser to precisely cut microbeams from the location of interest in a bulk ceramic. They had a cross-section of approximately 100 μm × 300 μm and a length of ~1 cm. They were then tested in a thermal mechanical analyzer at room temperature, 500 °C, 800 °C, and 1100 °C using the four-point flexural testing method. We compared the elastic moduli of high-purity Al2O3 and AlN measured by our method with the reported values in the literature and found that the difference was less than 5% for both materials. This paper provides a new and accurate method of characterizing the high-temperature elastic modulus of miniature samples extracted from representative/selected areas of bulk materials. [ABSTRACT FROM AUTHOR]

Measurement of the thermophysical properties of liquid metals is a highly challenging task due to numerous problems encountered above the fusion point. Properties such as density and surface tension have been widely investigated, while few studies address thermal diffusivity. In this paper we describe an original methodology for estimating the thermal diffusivity of metals in the liquid state. The proposed experimental setup is based on the traditional flash method. Its design ensures that samples of liquid metal are self-contained, preventing contamination and allowing measurements at high temperature. Results for both solid and liquid iron and 304 stainless steel are presented and compared to data suggested by the literature for validation. Then, for the first time, thermal diffusivity measurement of liquid zirconium is performed giving results up to 2450 K. Giving the high sensitivity of the results to the thickness variation we propose a numerical approach to deal with this issue. [ABSTRACT FROM AUTHOR]

An experimental setup has been developed for the simultaneous measurement of the Hall coefficient (RH) and electrical conductivity (σ) of thermoelectric (TE) specimens in the temperature range of 300–700 K. The van der Pauw geometry is utilized for the RH and σ measurements. The sample holder geometry has been designed for diverse TE specimen dimensions and easy sample mounting. A special feature of the holder geometry is that the same sample can be used for other relevant thermoelectric measurements such as the Seebeck coefficient and thermal diffusivity. This minimizes measurement errors associated with compositional or doping inhomogeneities. In the absence of high temperature standard reference materials for Hall coefficient measurements, silicon samples with different doping concentrations have been used to verify the accuracy of the instrument. Additionally, the electrical conductivity data have been validated by measurements on the same samples in a calibrated setup. Repeat measurements indicate a maximum standard deviation of ±3% and ±0.5% for the RH and σ data in the studied temperature range. Furthermore, comparisons with the calibrated setup indicate deviations within ±3% for the σ data. The suitability of the measurement setup for TE specimens has been demonstrated using measurements on n-type (Mg2Sn) and p-type (Mg3Sb2) specimens with carrier concentrations in the range of 1019–1020 cm−3. [ABSTRACT FROM AUTHOR]

A series of Na(La1 − xEux)(WO4)2 (NLW) phosphors were directly generated without calcination and organic additive via reaction of the (La1 − xEux)(OH)SO4 template with Na2WO4 by hydrothermal reaction. The XRD results show that pure Na(La1 − xEux)(WO4)2 can be obtained by the reaction at 150 °C for 24 h or at 200 °C for 2 h under the molar ratio of WO42−/ Ln3+ = 5. The NaLa(WO4)2 has a tetragonal structure in I41/a space group, and has lattice parameters of a = b = 5.332 Å, c = 11.731 Å. The FT-IR results show that the SO42− and hydroxyl vibrations of the template were hardly observed in the product and confirmed that phase conversion is complete. The UV-vis analysis yield bandgap values of 4.07 and 3.94 eV for NaLa(WO4)2 and Na(La0.95Eu0.05)(WO4)2 respectively. Photoluminescence excitation (PLE) studies found two distinct strong excitation peaks at ~ 395 nm and ~ 465 nm, with the former slightly stronger and both significantly stronger than other excitation peaks/bands. Under 395 nm excitation, the phosphors exhibited the strongest red emission at 614 nm (5D0→7F2 transition of Eu3+). The optimal Eu3+ concentration was found to be as high as 25% due to the layered structure of NLW phosphor and well isolated Eu3+ activator by [WO4] polyhedron. An evaluation and comparison with other phosphors were conducted to assess the performance of optical temperature sensing. It was discovered that the NLW phosphor cannot be employed as a probe for optical thermometry via fluorescence intensity ratio (FIR) mode due to similar intensity loss rates with increasing temperatures for different emission peaks. The NLW was demonstrated to be well capable of temperature sensing via fluorescence lifetime (FL) mode. Fluorescence decay analysis found that higher measurement temperature shortened the lifetime of the 614 nm main emission, and the lifetime decreased in liner mode. The maximum absolute sensitivity (SA) and relative sensitivity (SR) are 43.0 × 10− 4 K− 1 (298–498 K) and 144 × 10− 4 K− 1(498 K), respectively. [ABSTRACT FROM AUTHOR]

New heat flow measurements collected at the Lesser Antilles Arc using a Hybrid Lister‐Outrigger probe and a new logging‐while‐tripping MeBo70 drilling approach provide the first high‐resolution (meter‐to‐cm‐scale) temperature‐depth measurements across the Lesser Antilles volcanic arc and offer new insight into heat and fluid transfer at a convergent oceanic margins. At multiple sites where logging‐while‐tripping MeBo temperature measurements were made, temperature increases linearly with depth in shallowly buried hemipelagic sediment but is isothermal or significantly hotter in deeper, courser‐grained sediments associated with mass flows. We interpret these isothermal zones as regions where advective heat flow—perhaps caused by convection or pressure‐driven advection—dominates. The implication is that apparently conductive heat flow regimes observed in the shallowest upper 5–10 m of hemipelagic sediment across the Lesser Antilles Arc measured using standard lister‐type probes may often unknowingly be influenced by deeper, advective flow along buried mass transport deposits at this site. Since mass transport deposits are ubiquitous on convergent margins, higher permeability mass transport deposits may play a fundamental and previously unrecognized role in fluid and heat transport. Plain Language Summary: How do sediments below the seafloor lose heat and what tools best measure this process? While some studies suggest that heat is exchanged primarily through conduction, other studies suggest advection—or direct movement of heat via fluid flow. One reason this question remains unresolved is that the high resolution temperature measurements required to assess whether conductive versus advective heat flow dominates at a particular site often do not exist. To address this issue, we provide the first meter‐to‐cm‐scale temperature‐depth measurements at the Lesser Antilles‐North American plate boundary. From these measurements, we show that advective heat flow appears to occur primarily in higher permeability landslide deposits. Since such deposits are typical for volcanic islands, advective heat flow may be more common in these settings than previously believed. Key Points: New heat flow measurements at the Lesser Antilles arc show evidence for advection within mass transport depositsAdvective heat flow in mass transport deposits at convergent margins may represent an important, under‐reported, source of heat flowThe MeBo acoustic logging thermistor provides a unique tool for identifying isothermal zones at high (m‐scale) vertical resolution [ABSTRACT FROM AUTHOR]

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Experiments accessing extreme conditions at x-ray free electron lasers (XFELs) involve rapidly evolving conditions of temperature. Here, we report time-resolved, direct measurements of temperature using spectral streaked optical pyrometry of x-ray and optical laser-heated states at the High Energy Density instrument of the European XFEL. This collection of typical experiments, coupled with numerical models, outlines the reliability, precision, and meaning of time dependent temperature measurements using optical emission at XFEL sources. Dynamic temperatures above 1500 K are measured continuously from spectrally- and temporally-resolved thermal emission at 450–850 nm, with time resolution down to 10–100 ns for 1–200 μ s streak camera windows, using single shot and integrated modes. Targets include zero-pressure foils free-standing in air and in vacuo, and high-pressure samples compressed in diamond anvil cell multi-layer targets. Radiation sources used are 20-fs hard x-ray laser pulses at 17.8 keV, in single pulses or 2.26 MHz pulse trains of up to 30 pulses, and 250-ns infrared laser single pulses. A range of further possibilities for optical measurements of visible light in x-ray laser experiments using streak optical spectroscopy are also explored, including for the study of x-ray induced optical fluorescence, which often appears as background in thermal radiation measurements. We establish several scenarios where combined emissions from multiple sources are observed and discuss their interpretation. Challenges posed by using x-ray lasers as non-invasive probes of the sample state are addressed. [ABSTRACT FROM AUTHOR]

Luminescence thermometry is the most versatile remote temperature sensing technique and can be employed from living cells to large surfaces and from cryogenic temperatures to the melting points of metals. Ongoing research aims to optimize the sensitivity of the ratio between the emission intensity from two coupled excited states. However, this approach is inherently limited to temperature-dependent processes involving only the excited states. Here, we develop a novel measurement technique, called luminescence intensity ratio squared (LIR2) for the Yb3+/Er3+ pair, that combines the temperature sensitivity of ground- and excited-state populations. We use Y3Al5O12:Er3+,Yb3+ nanoparticles as a promising model system with both visible and infrared emissions. To apply our method, we record two luminescence spectra at different excitation wavelengths and determine the LIR2 using one emission in each of the two spectra. The LIR2 testing with Y3Al5O12 nanoparticles showed a sensitivity increase of 70% in the visible region and an impressive 230% increase in the NIR region compared to the conventional LIR method. This enhances the measurement precision by a factor of 1.5–2.5. The LIR2 based on the visible upconversion emission is particularly useful for measurements of high temperatures, while the LIR2 based on the downshifted ∼1.5 μm emission may revolutionize temperature measurements of biological samples in the range of physiological temperatures. [ABSTRACT FROM AUTHOR]

Accuracy of a median nerve block is normally assessed by testing skin sensitivity on the medial and dorsal aspects of fetlock and pastern. The present study evaluated subjective and objective analysis of skin surface temperature obtained with two different infrared (IR) thermography cameras (a high-end [FLIR P640] and a smartphone IR thermography device [FLIR One®]) before and after anaesthesia of the median nerve. Thermographic images were obtained at 0, 30, 60 and 90 minutes after performing a median nerve block with 2% mepivacaine hydrochloride. The subjective analysis of thermographic images using the FLIR P640 camera found assessors had >50% agreement for the presence of a nerve block (p<0.01) based on assessment of skin temperature within the expected dermatome of the median nerve. The objective analysis found skin temperature increases in the treated leg using the FLIR One® in the dorsal fetlock, dorsal pastern and medial pastern at 60 minutes, and the lateral pastern at 90 minutes (p<0.05). The treated leg, imaged using the FLIR P640 camera, had increases in skin temperature at the medial aspect of the fetlock at 60 minutes and lateral pastern at 90 minutes (p<0.05). Images obtained with the P640 camera had higher resolution and finer thermal detail. The images obtained with the FLIR One® camera had a wider temperature range with overall higher temperature measurements than the images obtained using the P640 camera (p<0.001). Skin temperatures in horses should be interpreted with caution when using the FLIR One® camera. Furthermore, the FLIR One® device detected an increase in skin surface temperature in both treated and non-treated legs and should not be used for assessment of a median nerve block. Infrared thermography appears to be useful for determining the presence of a high regional nerve block such as the median nerve block by observing increased temperatures of the skin surface after perineural anaesthesia. Further studies with a larger sample size as well as investigating the use of thermography for assessment of other regional nerve blocks are warranted. [ABSTRACT FROM AUTHOR]

High-speed imaging and digital signal processing are used to measure temperatures and pressures produced by explosions of solid chemical energetic materials. These measurements are used to enhance understanding of hazards faced by personnel working or training near explosions. The techniques described provide a complement to point measurements. Peak incident pressures studied are between 21 and 138 kPa, a region important for injury studies of personnel exposed to airborne shock. [ABSTRACT FROM AUTHOR]

Radio frequency ablation has emerged as a widely accepted treatment for atherosclerotic plaques. However, monitoring the temperature field distribution in the blood vessel wall during this procedure presents challenges. This limitation increases the risk of endothelial cell damage and inflammatory responses, potentially leading to lumen restenosis. The aim of this study is to accurately reconstruct the transient temperature distribution by solving a stochastic heat transfer model with uncertain parameters using an inverse heat transfer algorithm and temperature measurement data. The nonlinear least squares optimization method, Levenberg-Marquardt (LM), was employed to solve the inverse heat transfer problem for parameter estimation. Then, to improve the convergence of the algorithm and reduce the computational resources, a method of parameter sensitivity analysis was proposed to select parameters mainly affecting the temperature field. Furthermore, the robustness and accuracy of the algorithm were verified by introducing random noise to the temperature measurements. Despite the high level of temperature measurement noise (ξ = 5%) and larger initial guess deviation, the parameter estimation results remained closely aligned with the actual values, with an overall ERMS consistently below 0.05. The absolute errors between the reconstruction temperature at the measurement points TC1, TC2, and TC3, and the actual temperature, remained within 0.33 °C, 2.4 °C, and 1.17 °C, respectively. The Levenberg-Marquardt algorithm employed in this study proficiently tackled the ill-posed issue of inversion process and obtained a strong consistency between the reconstructed temperature the actual temperature. [ABSTRACT FROM AUTHOR]

New systems and methods to access the temperature of the melt pool in welding processes have been developed to study phenomena, monitor behaviours, and even be used in closed-loop control strategies. Concerning arc welding processes, the arc radiation might impose a challenge to measure the temperature. However, heat input is the key point for welding quality. This work aims to evaluate the feasibility and detect potentialities of accessing the thermal field from the rear weld pool in the GTAW process by using in-house developed equipment. The original system was conceptualized based on a previous bichromatic method. Experiments were carried out with and without the wire feed addition, and welding parameters were varied to explore its impacts on the temperature measurement. A strategy to select the regions of interest (ROIs) within the weld pool was created, and the mean temperature was calculated and correlated to the weld bead features. This strategy was able to overcome the challenges imposed by the electrode/nozzle reflection and the arc radiation during the welding. The rear weld pool thermal field was shown to be an important source of data to provide hints of the weld bead features. The mean temperature can indicate geometrical changes in the weld bead. Furthermore, the technique has the potential to be used as a promising real-time process monitoring tool. [ABSTRACT FROM AUTHOR]

To realize precise directional spectral emissivity determination of solid materials under the atmosphere, an apparatus what covers the temperature region from 50 °C to 1000 °C and a spectral range of 3 μm–14 μm was developed. The measurement angle can be adjusted from 0° to 60° utilizing a stepper rotary stage. The reliability of the apparatus's reliability was confirmed by measuring the spectral emissivity of a SiC sample at high temperatures. Furthermore, the normal spectral emissivity of SiC was investigated from 50 °C to 1000 °C, and the directional spectral emissivity at 600 °C and 800 °C was shown. The influence of temperature and measurement angle on the spectral emissivity of SiC was analyzed in detail. Additionally, the cause of the silicon dioxide film on the surface of SiC after high temperature heating and its influence on spectral emissivity were explored. Finally, a detailed analysis of the uncertainty components of the emissivity measurement under varying temperatures and wavelengths was performed, and the results showed that the uncertainty of the apparatus was better than 0.05 in its measurement range. [ABSTRACT FROM AUTHOR]

A novel test setup called the asymmetric shock tube for experiments on nonideal rarefaction waves (ASTER) has been commissioned at Delft University of Technology. The ASTER, which works according to the principle of Ludwieg tubes, is designed to generate and measure the speed of small and finite amplitude waves propagating in the dense vapors of fluids formed by complex organic molecules, therefore in the nonideal compressible fluid dynamics regime. The ultimate goal of the associated research is to prove the existence of nonclassical gasdynamics. The setup consists of a high-pressure charge tube and a vacuum tank separated by a glass disk equipped with a breaking mechanism for rarefaction waves experiments. When the glass disk is broken, an expansion wave propagates into the tube in the direction opposite to the fluid flow. The propagation speed of this wave is measured using a time-of-flight method with the help of four fast-response pressure sensors placed equidistantly in the middle of the tube. The charge tube can withstand pressures and temperatures of up to 15 bar and 400 ∘ C . Preliminary rarefaction experiments were successfully conducted using dodecamethylcyclohexasiloxane, D 6 , as the working fluid and at pressures and temperatures of up to 9.4 bar and 372 ∘ C , respectively. The results of an experiment featuring the initial state for which a theoretical model predicts the nonclassical acceleration of rarefaction waves show that the propagation is qualitatively different from that put into evidence by experiments for which the propagation is classic. Upcoming setup improvements and experimental campaigns are planned with the objective of experimentally verifying the existence of nonclassical gasdynamics. [ABSTRACT FROM AUTHOR]

The article presents the estimation of temperature and emissivities of niobium and 100c6 steel around their melting points using techniques based on the minimization of the least squares norm or on Bayesian inference. Two models were considered for the spectral emissivity, including a linear variation with respect to the wavelength and independent spectral values. The measured data used for the solution of the parameter estimation problem were radiative fluxes collected from a five-wavelength pyrometer. The experimental apparatus used in this work was designed for the characterization of metal samples with sizes of few millimeters at high temperatures, combining aerodynamic levitation and laser heating. The use of the linear spectral emissivity model provided quite consistent results with the ordinary least squares estimator and with stochastic simulations using the Metropolis-Hastings algorithm. Similarly, the model of independent spectral emissivities resulted in accurate emissivities, but it required an informative prior for temperature, such as the known melting point of the metal sample. Therefore, whatever the inverse method used, a priori supplementary information in terms of emissivities or temperatures are needed due to the temperature-emissivity correlation and the unknow emissivity behavior. [ABSTRACT FROM AUTHOR]

The behavior of technical nanoparticles at high temperatures was measured systematically to detect morphology changes under conditions relevant to the thermal treatment of end-of-life products containing engineered nanomaterials. The focus of this paper is on laboratory experiments, where we used a Bunsen-type burner to add titania and ceria particles to a laminar premixed flame. To evaluate the influence of temperature on particle size distributions, we used SMPS, ELPI and TEM analyses. To measure the temperature profile of the flame, we used coherent anti-Stokes Raman spectroscopy (CARS). The comprehensible data records show high temperatures by measurement and equilibrium calculation for different stoichiometries and argon admixtures. With this, we show that all technical metal oxide nanoparticle agglomerates investigated reform in flames at high temperatures. The originally large agglomerates of titania and ceria build very small nanoparticles (<10 nm/"peak 2") at starting temperatures of <2200 K and <1475 K, respectively (ceria: Tmelt = 2773 K, Tboil = 3873 K/titania: Tmelt = 2116 K, Tboil = 3245 K). Since the maximum flame temperatures are below the evaporation temperature of titania and ceria, enhanced vaporization of titania and ceria in the chemically reacting flame is assumed. [ABSTRACT FROM AUTHOR]

In laser powder bed fusion (LPBF) additive manufacturing, melt pool characterization is one of the potential approaches toward rapid process qualification and efficient non-destructive evaluation of printed parts. Especially melt pool width measurement is crucial for understanding the print process regimes, estimating the solidified melt pool depth, and identifying any process anomalies, among other attributes of interest. While existing works focus on monitoring melt pools of single scan tracks or single layer prints, melt pool characterization for a multi-track multi-layer (MTML) LPBF print has not been extensively studied. In this work, we employ our lab-designed coaxial single-camera two-wavelength imaging pyrometry (STWIP) system to monitor in-situ melt pool properties during a MTML LPBF process. The STWIP-measured melt pool widths are validated using a serial sectioning machine (Robo-Met, UES). The in-situ STWIP and ex-situ Robo-Met measurement data are in close agreement with each other, having a mean absolute error and root mean squared error of 9.83 μm and 16.53 μm, respectively. Furthermore, we demonstrate the successful mapping of melt pool location and melt pool size on the printed MTML part. In sum, this work demonstrates the capability and the applicability of STWIP for accurate large-scale melt pool monitoring during LPBF processing of practical parts, thereby facilitating the development of LPBF process models and control strategies. [ABSTRACT FROM AUTHOR]

An inter-laboratory comparison involving three participants (PTB, CAE, TU Graz) was conducted on spectral emissivity measurements using experimental setups covering a temperature range from 1250 K to 4000 K and a spectral range between 0.6 µm and 20 µm. The main objective here was to carry out a European-level assessment of the coherency of spectral emissivity measurements at high temperatures. Three refractory materials (molybdenum, tungsten and isotropic graphite) were selected for this comparison. Samples were machined from the same batch of materials and then sandblasted and thermally annealed (PTB, CAE) to achieve uniform and stable surface properties and reduce potential scattering of results between participants. The spectral emissivity of the three materials was then measured by each of the three participants up to the maximum temperature attainable by the devices used. In the overlapping wavelength range from 600 nm to 1100 nm, all measurement methods were in good agreement with regards to their respective uncertainties. [ABSTRACT FROM AUTHOR]

Background: DIC is a widely used optical method that uses cameras to track the motion of an applied random surface pattern to measure the full-field deformation. Due to its non-contacting nature, DIC is very preferable to be used in the areas of high temperature experimental mechanics. One of the biggest challenges of DIC at extreme temperatures is the blackbody radiation emitted from the glowing surface of the specimen. This glow from the blackbody radiation of the specimen is relatively higher at longer wavelengths and lower at shorter wavelengths. Objective: Previously, studies have shown the usefulness of using shorter wavelength of lights such as blue filtered light (450 nm) and UV-A filtered light (365 nm) for high temperature measurements. By contrast, this study uses UV-C filtered technique which utilizes even shorter wavelength of filtered light (UV-C, 254 nm) to demonstrate its effectiveness at elevated temperatures. Methods: Four different DIC techniques using an unfiltered blue light (200–1000 nm), a blue filtered light (450 nm), a UV-A filtered light (365 nm), and a UV-C (254 nm) filtered light have been performed at extreme temperatures in this study. Results: It was found that the techniques using unfiltered blue, blue filtered, and UV-A filtered lights could only go up to a temperature of 900 °C, 1200 °C, and 1600 °C respectively before showing significant saturations in the images. Conclusions: The new UV-C DIC showed no sign of saturation even up to a temperature of 1600 °C while providing comparable axial displacement and coefficient of thermal expansion (CTE) data and therefore demonstrating the usefulness of this method in higher temperatures. We also include helpful recommendations for how to produce speckle patterns having sufficient contrast at UV-C wavelengths. [ABSTRACT FROM AUTHOR]

X‐ray Laue microdiffraction aims to characterize microstructural and mechanical fields in polycrystalline specimens at the sub‐micrometre scale with a strain resolution of ∼10−4. Here, a new and unique Laue microdiffraction setup and alignment procedure is presented, allowing measurements at temperatures as high as 1500 K, with the objective to extend the technique for the study of crystalline phase transitions and associated strain‐field evolution that occur at high temperatures. A method is provided to measure the real temperature encountered by the specimen, which can be critical for precise phase‐transition studies, as well as a strategy to calibrate the setup geometry to account for the sample and furnace dilation using a standard α‐alumina single crystal. A first application to phase transitions in a polycrystalline specimen of pure zirconia is provided as an illustrative example. [ABSTRACT FROM AUTHOR]

In this paper, we propose and demonstrate a network analysis optical frequency domain reflectometer (NA-OFDR) for distributed temperature measurements at high spatial (down to ≈3 cm) and temperature resolution. The system makes use of a frequency-stepped, continuous-wave (cw) laser whose output light is modulated using a vector network analyzer. The latter is also used to demodulate the amplitude of the beat signal formed by coherently mixing the Rayleigh backscattered light with a local oscillator. The system is capable of attaining high measurand resolution (≈50 mK at 3-cm spatial resolution) thanks to the high sensitivity of coherent Rayleigh scattering to temperature. Furthermore, unlike the conventional optical-frequency domain reflectometry (OFDR), the proposed system does not rely on the use of a tunable laser and therefore is less prone to limitations related to the laser coherence or sweep nonlinearity. Two configurations are analyzed, both numerically and experimentally, based on either a double-sideband or single-sideband modulated probe light. The results confirm the validity of the proposed approach. [ABSTRACT FROM AUTHOR]

Batteries play a crucial role as energy storage devices across various industries. However, achieving high performance often comes at the cost of safety. Continuous monitoring is essential to ensure the safety and reliability of batteries. This paper investigates the advancements in battery monitoring technology, focusing on fiber Bragg gratings (FBGs). By examining the factors contributing to battery degradation and the principles of FBGs, this study discusses key aspects of FBG sensing, including mounting locations, monitoring targets, and their correlation with optical signals. While current FBG battery sensing can achieve high measurement accuracies for temperature (0.1 °C), strain (0.1 μ ε ), pressure (0.14 bar), and refractive index (6 × 10−5 RIU), with corresponding sensitivities of 40 pm/°C, 2.2 pm/ μ ε , −0.3 pm/bar, and −18 nm/RIU, respectively, accurately assessing battery health in real time remains a challenge. Traditional methods struggle to provide real-time and precise evaluations by analyzing the microstructure of battery materials or physical phenomena during chemical reactions. Therefore, by summarizing the current state of FBG battery sensing research, it is evident that monitoring battery material properties (e.g., refractive index and gas properties) through FBGs offers a promising solution for real-time and accurate battery health assessment. This paper also delves into the obstacles of battery monitoring, such as standardizing the FBG encapsulation process, decoupling multiple parameters, and controlling costs. Ultimately, the paper highlights the potential of FBG monitoring technology in driving advancements in battery development. [ABSTRACT FROM AUTHOR]

When laser-induced breakdown spectroscopy (LIBS) was used in online equivalence ratio measurements, the spatial–temporal temperature gradient would lead to significantly varied baselines, which require real-time corrections. In this study, the correlation relationship between spectral intensity and broadband radiation was utilized as the physical constraint in automatic baseline correction. The pixel-to-pixel correlation coefficient on the wavelength ( R 2 ) was introduced as the "Correlation Spectrum", and the summation of all correlation coefficients ( s u m R 2 ) was used as an objective function. By maximizing s u m R 2 using Particle Swarm Optimization algorithm, the key parameters in the adaptive iteratively reweighted Penalized Least Squares (airPLS) method were automatically optimized. The baselines fitted by airPLS could adapt to the plasma excitation variations in a temperature range from 1458 to 1705 K, which improved accuracy in equivalence ratio measurements. The potential advantages of Correlation Spectrum in weak peak identification and broadening effect evaluation were also demonstrated. The benchmarked results suggested that the proposed approach can be conveniently employed in online LIBS measurements and improve its quantification performance. [ABSTRACT FROM AUTHOR]

Background: This review discusses high-speed thermal measurements and their significance in understanding solid materials' behavior, focusing on rapid loading conditions. Objective: While high-speed thermal measurements are challenging in some cases, these measurements provide unique insights into material response at high rates, by shedding light on failure modes, thermomechanical coupling, and thermal dissipation phenomena that are otherwise overlooked. Methods: The review presents various direct measurement techniques (contact and non-contact) relevant to high-speed loading, with emphasis on the frequently used ones in mechanics of materials applications: thermocouples, infrared detectors, and high-speed infrared cameras. Results: Pros and cons of each technique, alongside with typical applications are discussed. Understanding the interplay between thermal effects and mechanical responses opens new avenues for enhancing material performance and energy efficiency. Conclusions: This review is expected to serve as a valuable resource for researchers and practitioners seeking to leverage high-speed thermal measurements to drive innovation and advance materials science in various applications. [ABSTRACT FROM AUTHOR]

Precise density and thermal expansion measurements of refractory materials are extremely challenging due to the chemical reactions and thermal gradients at ultrahigh temperatures. The UV image technique has been successfully applied to the density measurements at high temperatures above 3000 K. However, intense radiation from the sample can blur the edge of the sample image, leading to uncertain measurements. In this study, we investigate the influence of the contrast between the UV background light and sample radiation (B–S) on density measurements. We find that lower B–S contrast can significantly affect the calibration factor that converts image pixels to real size, resulting in underestimated density with scattering and overestimated thermal expansion coefficients at ultrahigh temperatures. This result underscores the necessity of adequate B–S contrast to ensure the precision of density measurements using UV imaging methods for refractory materials beyond 3000 K. By considering the critical minimum value of the B–S contrast, we successfully measure the densities and thermal expansion coefficients of four refractory metal liquids (tungsten, rhenium, osmium, and tantalum) with the improved UV technique, which are crucial for high-temperature industries. This work will be valuable for other imaging methods measuring the thermophysical properties at ultrahigh temperatures. [ABSTRACT FROM AUTHOR]

A passive wireless high-temperature sensor for far-field applications was developed for stable temperature sensing up to 1000 °C. The goal is to leverage the properties of electroceramic materials, including adequate electrical conductivity, high-temperature resilience, and chemical stability in harsh environments. Initial sensors were fabricated using Ag for operation to 600 °C to achieve a baseline understanding of temperature sensing principles using patch antenna designs. Fabrication then followed with higher temperature sensors made from (In, Sn) O2 (ITO) for evaluation up to 1000 °C. A patch antenna was modeled in ANSYS HFSS to operate in a high-frequency region (2.5–3.5 GHz) within a 50 × 50 mm2 confined geometric area using characteristic material properties. The sensor was fabricated on Al2O3 using screen printing methods and then sintered at 700 °C for Ag and 1200 °C for ITO in an ambient atmosphere. Sensors were evaluated at 600 °C for Ag and 1000 °C for ITO and analyzed at set interrogating distances up to 0.75 m using ultra-wideband slot antennas to collect scattering parameters. The sensitivity (average change in resonant frequency with respect to temperature) from 50 to 1000 °C was between 22 and 62 kHz/°C which decreased as interrogating distances reached 0.75 m. [ABSTRACT FROM AUTHOR]

We present measurements of diamond formation in doubly shocked Stycast 1266 epoxy (comprising C, H, Cl, N, and O) using in situ x-ray diffraction. Epoxy samples were reshocked against a LiF window to pressures between 80 and 148 GPa in experiments at the Omega Laser Facility. The pressure and temperature conditions were diagnosed in situ using velocimetry and optical pyrometry, respectively. X-ray diffraction patterns of the compressed epoxy are consistent with cubic diamond (Fd 3 ¯ m), indicating that diamond can precipitate not only from twice-shocked CH polystyrene [Kraus et al. Nat. Astron. 1, 606 (2017)] at these conditions but also from twice-shocked CH polymers with the addition of oxygen, nitrogen, and chlorine. These results, in combination with previous works on CH, CH 2 , CH 4 , and methane hydrate, support that diamond often, but not always, forms from CH-based compounds at extreme pressures and temperatures, indicating that the chemical composition, thermodynamic compression path, and kinetics play an important role. [ABSTRACT FROM AUTHOR]

Multi-wavelength pyrometry is an efficient tool for measuring high temperatures in dynamic experiments. A fast 5-channel pyrometer was built and successfully employed in ion-beam heating experiments at the GSI Centre for Heavy Ion Research (Darmstadt, Germany). Temperatures of metallic samples heated by an intense focused heavy ion beam up to their melting points and beyond were measured with nanosecond time resolution and a spatial resolution of about 200 μm. The modular instrument has demonstrated its high versatility also for temperature measurements of exothermic reactions with millisecond temporal resolution. [ABSTRACT FROM AUTHOR]

The spectra and kinetics of selective and continuum thermodynamically equilibrium emission of electromagnetic radiation from Er2O3 microcrystals and a ruby single crystal in the visible and near-IR spectral regions under laser–thermal excitation by electric-discharge CO2 lasers at a wavelength λ = 10.6 µm in the cw and pulsed modes have been experimentally investigated. The effect of the delay of continuum emission fronts and intensity peaks relative to laser pulses is explained by the difference in the temperatures of the heated layer and electromagnetic radiation. The delay time of the electromagnetic emission maximum is the characteristic time for establishing thermal equilibrium. [ABSTRACT FROM AUTHOR]

Global emissions of nearly 30% stem from fossil fuel combustion for long-distance transportation vehicles. Therefore, investigations on newer alternatives for clean and green fuels is desired in pursuance of net-zero carbon emissions by 2050. Given this contemplation, the current study aims at studying the effect of ammonia addition, a carbon-free fuel, on laminar burning velocity of CH 4 /H 2 fuel blends at high-pressure and high-temperature conditions utilizing the high-pressure diverging-channel method. The NH 3 varies from 0% to 30% in the CH 4 /H 2 fuel blend by volume. With regard to adiabatic flame temperature, this NH 3 /CH 4 /H 2 mixture is comparable to pure CH 4 -air mixtures, but with a reduction in carbon emissions of about 26.6%. The research involves conducting measurements at high temperatures between 300 K and 750 K, pressures between 1 atm and 5 atm, and equivalence ratios between ϕ = 0.7 and 1.4. When the pressure is 5 atm, the obtained burning velocities of NH 3 /CH 4 /H 2 blends are analogous to that of CH 4 -air mixtures. The temperature exponent, α, does not change when the NH 3 fraction or pressure changes, but at high temperatures there is a slight shift in the pressure exponent, β. The experimental results suggest that the Okafor and Li kinetic models align well with the measurements made in the current work up to 5 atm, while the Reduced GRI Mech 3.0 mechanism overestimates the burning velocity values. Additionally, an increase in NH 3 fraction and pressure results in a decrease in burning velocity and NO formation due to the presence of NH i (i = 0–2) radicals. Overall, this study convincingly demonstrates the viability of NH 3 /CH 4 /H 2 -air mixtures as a practical alternative to reduce carbon emissions. • LBV measurement of NH 3 /CH 4 /H 2 -air flames at elevated temperature and pressures. • Co-dependency of α and β proposed in LBV correlation for varying NH 3 concentrations. • NH 3 addition reduces burning velocity and NO formation due to presence of NH i radicals. • Reaction pathway elucidates 34.2% reduction in NH 2 → HNO at high pressure condition [ABSTRACT FROM AUTHOR]

This work is devoted to the study of the processes that take place in the welding gap during explosive welding (EW). In the welding gap, when plates collide, a shock-compressed gas (SCG) region is formed, which moves at supersonic speed and has a high temperature that can affect the quality of the weld joint. Therefore, this work focuses on a detailed study of the parameters of the SCG. A complex method of determining the SCG parameters included: determination of the detonation velocity using electrical contact probes, ceramic probes, and an oscilloscope; calculation of the SCG parameters; high-speed photography of the SCG region; measurement of the SCG temperature using optical pyrometry. As a result, it was found that the head front of the SCG region moved ahead of the collision point at a velocity of 3000 ± 100 m/s, while the collision point moved with a velocity of 2500 m/s. The calculation of the SCG temperature showed that the gas was heated up to 2832 K by the shock compression, while the measured temperature was in the range of 4100–4400 K. This is presumably due to the fact that small metal particles that broke off from the welded surfaces transferred their heat to the SCG region. Thus, the results of this study can be used to optimize the EW parameters and improve the weld joint quality. [ABSTRACT FROM AUTHOR]

A high-speed two-color pyrometer has been developed that allows measuring the intensity of thermal radiation in temperature range of 100–3500°C with 2 μs time resolution. The analysis of main factors affecting the measurement of surface temperature in the conditions of its interaction with plasma is carried out. It is shown that at plasma temperature of more than 10 eV and moderate particles density, the wall plasma can be considered transparent to thermal radiation. Experimental studies on non-contact measurement of temperature of surface interacting with plasma on Globus-M2 tokamak and plasma gun test bench have been carried out. Sawtooth temperature fluctuations were detected on the wall of tokamak chamber near the exit of outer separatrix branch. The period of these flashes was 3–4 ms, and duration was 2 ms. The maximum wall temperature measured by a high-speed pyrometer exceeded temperature measured by infrared camera. Front surface temperature measurements of W-Li sample were carried out at plasma gun test bench under conditions of deuterium plasma jet cyclic action under loads simulating regimes of plasma current disruption in tokamak. The sample temperature reached more than 3000°C during ~ 1 ms. The thermal conductivity of the sample degraded with an increase in number of plasma exposure cycles, which was expressed in progressive decrease in target cooling rate after the pulse. Using a high-speed pyrometer, it is proposed to control the formation of heat-insulating foils on surface interacting with plasma. [ABSTRACT FROM AUTHOR]

In this work, the determination of the apparent activation energy of a global chemical reaction mechanism of the methane–air flames is revisited. The one-step formulation allows to derive the theoretical background for the method to measure the activation energy within the burner stabilised flame setup. The validity of this approach is demonstrated by using the numerical simulations with the detailed reaction model and direct thin filament pyrometry measurements of the temperature distribution in flame. The combination of numerical and experimental approaches allows us to find the activation energy for various mixture compositions. The prediction of numerical simulations and measured values of the activation energy is found to be in good agreement with each other and the data known from the literature. It is demonstrated that two critical phenomena need to be taken into account to obtain a reliable estimate of the activation energy: the flame blow-off and the onset of the diffusive-thermal instabilities. The effect of these critical events on the accuracy of the measurements is discussed as well as prospects of further investigation. [ABSTRACT FROM AUTHOR]

To ensure accurate estimation of mold heat flux, this study investigated the impacts of the thermocouples placement inserted in the mold wall, the temperature sampling rate (fs), and the noise level of temperature data on the precision of two-dimensional Inverse Heat Conduction Problem (2DIHCP). The results showed the accuracy of heat flux estimations decreases as the distance between the thermocouple and the mold surface increases, and it is recommended that the distance should not exceed 3 mm. The accuracy of the heat flux initially increases as fs increases from 5 to 10 Hz, reaches a relatively stable state as fs increases from 10 to 60 Hz, and eventually decreases as fs increases from 60 to 100 Hz. Additionally, higher temperature measurement errors typically lead to decreased accuracy in inverse analysis. 2DIHCP was employed to compute the heat flux for a mold simulator experiment, and the results demonstrated its effectiveness in reconstructing the mold heat flux at the meniscus level during the time lapse of a mold oscillation cycle. [ABSTRACT FROM AUTHOR]

Knowledge of the emissivity and thermal conductivity of thin metal films used in conjunction with multilayer mirrors for the spectral selection of radiation in the extreme-ultraviolet- and "soft"-X-ray wavelength ranges is necessary in order to correctly calculate the heating of film elements at high heat loads. Heating is associated with absorption in the film of a significant fraction of the incident intensity, and the concept of a high heat load is somewhat arbitrary, since even at an absorbed intensity level on the order of 1 W/cm2 a freestanding film can be heated in vacuum by several hundred degrees. In the first approximation, to estimate the thermal-conductivity coefficient, one could use tabular values for bulk samples of the corresponding metals or use the well-known Wiedemann-Franz law which links the thermal conductivity and the electrical resistivity of the sample; the latter is easier to measure. However, an analysis of the published data indicates significant errors that are possible when using any of these approaches. Therefore, in this work, we measure the thermal conductivity directly by processing the temperature distribution obtained by infrared (IR) pyrometry over a film sample mounted on a heated frame or heated by a flowing electric current. The thermophysical characteristics (thermal conductivity and emissivity) are determined for samples of film absorption filters based on Mo, Al, and Be of submicron thickness (from 100 nm), as well as for films of copper: a metal whose bulk samples have high thermal and electrical conductivity. As expected, significant differences are found between the thermal and electrical properties of the film materials and the properties of the same metals in monolithic samples. [ABSTRACT FROM AUTHOR]

A calibration-free multi-color pyrometry data analysis approach for determining the temporal change in the reciprocal temperature by only comparing the photomultiplier tube (PMT) responses to the system light emission is introduced. For Arrhenius reactions, analyzing the reciprocal temperature is particularly relevant for evaluating reactivity. The high accuracy of the proposed method is provided by eliminating the calibration step, which is made possible by considering the ratio of PMT signals as a function of time. The developed methodology is applicable to systems with continuous light emission spectra of the thermal nature that originate from condensed particulates. A demonstration of the data analysis approach was performed using aluminum powder burning in air. Four PMTs detected light emission during combustion that enabled analysis of six detector combinations to obtain a time-dependent signal ratio. Based on the temperature-dependent nature of light emission, the PMT response ratio provided the value of the reciprocal temperature change. All six detector combinations generated precisely coinciding results within time periods where the light emission trace behavior was relatively smooth that validated the data processing approach. It was also found that a non-smooth behavior of light emission led to significant deviations between outputs of different PMT combinations. This inconsistency between outputs was an indication of multi-temperature light emission whereas consistency between outputs corresponds to the single-temperature emission behavior. Using the calibration-free data processing approach, we isolated time periods where multi-temperature radiation is essential. Then, we further decoupled contributions from non-monotonic light emission signals and resolved two distinct temperatures responsible for observed radiation peculiarities.