Heating Rate Dependence Research Articles

In situ monitoring of microstructure evolution during thermal processing of uranium-zirconium alloys using laser-generated ultrasound

Laser-generated ultrasound was used to monitor microstructure evolution during thermal processing of as-cast, polycrystalline binary uranium-zirconium metallic fuel alloys with compositions of U-20wt.%Zr (U-20Zr), U-50wt.%Zr (U-50Zr) and U-80wt.%Zr (U-80Zr). Ultrasonic waveforms were recorded during heating and cooling the samples from room temperature to >973 K and back. A phase transition temperature for all three compositions was estimated from the temperature at which an abrupt and rapid reduction in ultrasonic velocities was observed. Microstructural features on the length scale of tens of micrometers were inferred from the observation of scattering of ultrasonic waves by elastic heterogeneities above ~823 K in U-20Zr, while a hysteresis in the ultrasonic velocities of U-80Zr upon cooling was attributed to a partial retention of the high temperature phase following thermal annealing. The U-50Zr alloy exhibited a reversible viscoelastic response above 933 K, as evidenced by the observation of high frequency attenuation of the shear component of the waveforms at high temperature. Ultrasonic measurements were supplemented by in situ transmission electron microscopy (TEM). The TEM images revealed that the δ-U-Zr matrix in the three compositions underwent a spinodal decomposition above ~823 K into nanoscale regions. The ultrasonic measurements revealed larger, micron-scale structure evolution in the U-20Zr alloy at the same temperature. This large-scale structure is associated with heterogeneous regions having different Zr content. Our findings show the potential heating rate dependence of microstructural evolution in U-Zr alloys and highlight differences in the thermomechanical response and associated length scales during thermal annealing between single- and dual-phase compositions. These results demonstrate the utility of laser ultrasonics to rapidly and efficiently scan phase boundaries and monitor micrometer-scale structure evolution in metallic fuel alloys.

Precursory reaction of thermal cyclization for polyacrylonitrile

Simultaneous differential scanning calorimetry (DSC) and luminescence (LUM) measurements of polyacrylonitrile revealed that a precursory reaction progresses below the well-known endothermic cyclization reaction (i.e., peak temperature ca. 280 °C). The intensity of LUM increased above 90 °C, which is around the glass transition temperature. After the peak at 180–190 °C, the LUM intensity decreased with temperature up to 250 °C, i.e., below the onset temperature of cyclization reaction. Thermal signals cannot be seen on the DSC curve in the temperature range of the LUM peak. The activation energy (Ea) estimated from the heating rate dependence of the LUM peak temperatures was 122 kJ mol−1. However, the Ea obtained from the well-known exothermic peak temperatures of DSC measurements was 190 kJ mol−1. Electron spin resonance and nuclear magnetic resonance also support the chemical structure of the luminescence species. FT-IR and X-ray diffraction were also performed to confirm the change in chemical and physical structural. Finally, ab initio calculations suggest that thermally stable heterocyclic radical species with two to four fused six-membered rings are the main products of the precursory reaction.

Functional Thermal Stable Samples: Non-isothermal Calorimetric Analysis of MoO3–V2O5–TeO2 Oxide Glasses

In this research, xMoO3–(60 − x)V2O5–40TeO2 oxide glasses with (0 ≤ x ≤ 60) have been prepared by common melt-quenching method. Differential scanning calorimetry (DSC) at different heating rates (φ) was used to study non-isothermal thermal analysis, and also to gain more insight in to the Hruby index thermal stability, crystal growth index (n), glass forming tendency and so calorimetric characteristics of the present glasses. Also, the effects of the heating rate and MoO3 content on the glass transition temperature (Tg) and crystallization temperature (TCr) were studied. Further structural investigations were done by FESEM, EDX and Map. The glass transition temperature, glass transition region, the temperature corresponding to the onset of crystallization (Tx) and also the crystallization temperature were obtained at different heating rates; heating rate dependence of these parameters was employed estimate the key kinetic parameters of glass transition and crystallization activation energy by using Moyinhan, Ozawa, Kissinger and Avrami methods. Calorimetric curves were used to plot the specific heat capacity curves versus temperature at the constant pressure. In addition, the compositional dependence of the heat capacity and fragility parameter were investigated. Generally, results of this work show that the glass with x = 20 mol% has the highest thermal stability and glass forming tendency and samples having 10 and 20% of MoO3 are the optimal samples (with the least fragility) for thermomechanical applications and also in optical fibers.

Temperature correction at high heating rates for conventional and fast differential scanning calorimetry

The thermal lag of DSC is a heating rate independent constant and influences the measured onset temperature of melting peaks and must be taken into account during the temperature calibration. In the literature, however, non-linear behavior of the measured onset temperature is reported for the case of high scanning rates and the use of small samples. Based on a conventional heat transfer model of a DSC a general relation of the heating rate and sample mass dependence of the onset temperature is derived. The reason of this unusual behavior is that the time for the melting event is less than the equilibration time of the DSC. The approach presented can be used to correct the onset temperatures in the case of non-linear behavior, which may occur in conventional DSC and Fast DSC (using chip sensors).

Thermoluminescence glow curve analysis and evaluation of trapping parameters of dysprosium doped lanthanum calcium borate La2CaB10O19

The present work elucidates thermoluminescence study of Dy activated lanthanum calcium borate (La2CaB10O19) phosphors and determination of trapping parameters. Two glow curves located at 132 and 295 °C were observed and showed a linear TL response. The kinetic parameters of the glow peaks were evaluated using variable heating rate, repeated initial rise method and Computerized Glow Curve Deconvolution. Analysis of the main dosimetric peaks reveals that the values of the activation energy and pre-exponential factor are found to be 0.78–1.145 eV and 8.59 × 109–8.44 × 1011 s−1, respectively. The sample doped with 1% Dy3+ exhibits a good stability for the reusability. Besides, the found results indicate that the temperature maximum shifts to the higher temperature side as the heating rate increases. Contrary to previously expressed theoretical expectations, anomalous heating rate dependence was observed in Dy3+ doped La2CaB10O19 sample and a semi-localized transition model explaining the anomalous heating rate effect was employed.

Investigation of traps distribution in GaS single crystals by thermally stimulated current measurements

Thermally stimulated current (TSC) investigations of p-GaS (gallium sulfide) single crystals grown by Bridgman method were achieved by virtue of consecutive experiments carried out at various heating rates in between 0.4 and 1.0 K/s in the temperature range of 10–280 K. One single TSC peak around 148 K and overlapped, incomplete peaks in the end limit temperature of the experiments were observed in the spectrum recorded at constant heating rate of 1.0 K/s. Individual peak was analyzed utilizing curve fitting method. Existence of one trapping level centered at 0.11 eV was revealed by the analyses. Heating rate dependency of obtained TSC curve was also studied and it was shown that TSC intensity decreased besides increase of peak maximum temperature with heating rate. Characteristics feature of trapping mechanism was investigated in detail by employing different stopping temperature between 50 and 110 K. Analyses on Tm–Tstop dependency resulted in a presence of quasi-continuously distributed traps with activation energies ranging from 0.11 to 0.55 eV. The revealed trap was thought to be arising from intrinsic defect possibly created by VGa or antisite SGa.

Structural, Spectroscopic, and Kinetic Insight into the Heating Rate Dependence of Studtite and Metastudtite Dehydration

Uranyl peroxide minerals studtite (UO2O2·4H2O) and metastudtite (UO2O2·2H2O) are important materials in the nuclear fuel cycle. When heated, they dehydrate and transform to amorphous uranium oxides...

Heating rate dependence of coercivity and microstructure of Fe–B–P–Cu nanocrystalline soft magnetic materials

The nanocrystalline structure and soft magnetic properties of melt-spun Fe–B–P–Cu ribbons are largely influenced by heating rates for crystallization of amorphous precursors. In this study, we investigated the structure and soft magnetic properties of Fe84.8B4.9P9.5Cu0.8 (P-rich) and Fe84.8B10.9P3.5Cu0.8 (B-rich) melt-spun ribbons crystallized at two different heating rates, 0.67 K/s and 6.7 K/s, using transmission electron microscopy (TEM) and atom probe tomography (APT). The P-rich ribbon shows smaller coercivity regardless of the heating rates, while the B-rich ribbon shows large heating rate dependence of the coercivity. APT analyses have revealed that the size of Cu clusters in the P-rich nanocrystalline ribbon is larger than that in the B-rich nanocrystalline ribbon while their number densities are nearly the same. Also, the high heating rate led to a larger size and higher Cu concentration of the Cu clusters in both samples, indicating that the Cu clusters are effective as nuclei for α-Fe only when they are larger than a critical size. The solute partitioning behaviors between α-Fe and residual amorphous phase determined by APT analyses are consistent with the tie-lines between α-Fe and liquid phase in a calculated Fe–P–B ternary phase diagram. P was found to segregate at amorphous/α-Fe interface, suggesting the grain growth is controlled by the volume diffusion of P in the amorphous phase during their crystallization process.

Role of Ag microalloying on glass forming ability and crystallization kinetics of ZrCoAgAlNi amorphous alloy

Bulk metallic glasses (BMGs) with new chemical compositions (ZrCoAgAlNi) were fabricated and the effects of Ag minor addition on the glass forming ability (GFA) and crystallization kinetics were studied. The x-ray diffraction (XRD) test was applied to identify the amorphousness of BMGs or possible crystalline phases. Using differential scanning calorimeter (DSC), the thermal stability and crystallization kinetics under a non-isothermal condition at the different heating rates were studied. Considering the heating rate dependency of glass transition and crystallization kinetics, the activation energy was evaluated and measured for the mentioned processes. It was revealed that the rise in Ag content led to the decrease in activation energy for glass transition, while the activation energy for crystallization increased. The thermal stability and GFA were also studied and it was found that the Ag addition strongly affected the inherent features of BMGs. With the increase in Ag content, the atomic mobility and structural rearrangement changed in the material and consequently, the GFA and thermal stability were significantly improved.

Peculiarities of Microstructure Evolution and Property Changes of Titanium Alloys In Situ during Electric Forging

Abstract The experimental studies of the parameters of hot electric forging were carried out on industrial heat resistance (α + β), (near-α), and (α″ + β) titanium alloys. It was established that simultaneous fast Joule heating with a high-density electric current and an initial temperature of hot intense plastic deformation are important parameters for the electric forging of heat resistance titanium alloys. The heating rate dependence on electric current density and thermophysical properties of metal, as well as deformation temperature dependence on axial compression stress and mechanical strength of heated metal under compression as the main parameters of electric forging, were chosen. To calculate the processing parameters, we investigated the evolution of the thermophysical properties and mechanical strength of selected titanium alloys at a heating rate of 50°C·s−1 at a temperature up to 1,200°C. Microstructural evolution and the phase transformation temperature were determined using optical and scanning electron microscopes. The results show that the grinding efficiency of the coarse-grained microstructure depends on the increase of the heating rate, and the formation of uniaxial ultrafine alpha-phase grains depends on an increase of the compressive stress or decrease in the deformation temperature. It can be argued that the compressor blades made of titanium alloys for aircraft turbojet engines had increased ductility, stability, and high-cyclic fatigue strength, as well as increased operating life at ambient temperatures. The results can be used to model and calculate the rational parameters of electric forging to improve the operational properties of the final products.

Effect of bismuth incorporation on thermal properties of quaternary chalcogenide glass Se80Te15-xCd5Bix (x=0,5,10) alloys

Differential scanning calorimetry has been employed to investigate the thermal properties of Se80Te15-xCd5Bix (x = 0, 5, 10) glass system. The Variation of characteristic temperatures such as glass transition temperature (Tg), onset crystallization temperature (Tc), peak crystallization temperature (Tp) and melting temperature (Tm) are studied as a function of composition and heating rate. A stepwise increase in values of characteristic temperatures has been observed with the increase in heating rate. Further, obtained values of characteristic temperatures display decreasing trend with increase in bismuth concentration. The compositional and heating rate dependence of Thermal parameters such as glass forming ability (ΔT), thermal stability (Hg), enthalpy (ΔH) and entropy (ΔS) has been investigated. It has been observed that ΔT and Hg have lowest and highest values for Se80Te5Cd5Bi10 and Se80Te15Cd5 compositions respectively. Avrami index (n) and activation energy for crystallization (Ec) have been calculated for all the samples. Values of n obtained for Se80Te15Cd5, Se80Te15Cd5 Bi5 and Se80Te5Cd5Bi10 compositions are found to be 1.44, 2.16 and 2.16 respectively. Based on the obtained values of n, the nucleation process in alloys is discussed. It is noteworthy to mention that least value of Ec is observed for the alloy Se80Te5Cd5Bi10 containing the highest amount of bismuth. Furthermore, calculated thermal parameters are used to anticipate the electrical switching behavior of the alloys.

Critical analysis of the different glass stability criteria in chalcogenide glasses

In this endeavor, various glass stability criteria have been discussed by using two ternary alloys of SeTePb glassy system. These criteria can be obtained based on the interrelationship between the characteristic temperatures. Differential Thermal Analysis measurements under the non-isothermal conditions can be used for this purpose. Two groups of these criteria according to the onset and peak crystallization temperaturas have been studied as a function of composition. The heating rate and composition dependences of all criteria concluded that the C ZW and C LX criteria are not suitable to discuss the glass stability (GS) for the studied compositions. The extracted data from various GS criteria and their relative change parameters reveal that the criterion C YL of Yuan et al is best and it exhibits the best ability for apprising the GS.

Effects of Vacuum and Juice Concentration on Electrical Conductivity by the Ohmic Method: a Case Study of Sour Cherry

Electrical conductivity is a key parameter in ohmic heating. In this study, under vacuum conditions, sour cherry juice was concentrated up to 33% and 46.7% of the initial mass in order to have three levels of concentration. The samples were ohmically heated using three voltage gradients (10, 20, and 30 V/cm) under three pressure levels (atmospheric pressure and vacuum of − 30 and − 60 kPa). The dependence of electrical conductivity and heating rate on temperature, voltage gradient, and concentration was measured in the temperature range of (26.8 ± 0.3 °C, starting point) to (65.5 ± 0.6 °C) for all experiments. Compared with the pressure, the effect of juice concentration was more significant on the heating rate. A 60% reduction in the pressure resulted in an 11.3% drop in the heating rate, whereas a 46.7% change in the concentration led to a 30.7% decrease in the heating rate. The electrical conductivity decreased with increasing the concentration level and reducing the pressure (vacuum state). At a specific concentration, the multivariate linear regression models using temperature, pressure, and voltage gradient were found to be more accurate (R2 > 0.975).

Determining the fragility of bulk metallic glass forming liquids via modulated DSC

Temperature modulated DSC is used to study the fragility of three different bulk metallic glass forming liquids. Through applying various modulation frequencies, the dynamic glass transition shifts in temperature, allowing to determine the temperature dependence of the average relaxation time for each system. The resulting fragilities are compared with fragility investigations in literature obtained using thermo-mechanical analysis and the heating rate dependence of the calorimetric glass transition. Different methods to compare the data are evaluated and discussed.

Thermoluminescence characteristics of Bi12SiO20 single crystals

Trapping center properties of bismuth silicon oxide (Bi12SiO20) single crystals were investigated by thermoluminescence (TL) measurements performed in the 50–400 °C temperature range. Experimental TL curve recorded at heating rate of 1 °C/s presented two overlapped peaks around 279 and 362 °C. The heating rate dependency of TL curve was also studied for heating rates between 1 and 6 °C/s. The measured TL curves were analyzed using curve fitting, initial rise and different heating rate methods. The results of analyses indicated that TL glow curve is composed by two peaks associated with two discrete trapping centers at 0.81 and 1.10 eV. The revealed trapping centers were associated with intrinsic defects in the Bi12SiO20 compound under the light of previously reported papers. An energy band diagram was also plotted to indicate possible transitions within the forbidden band gap.

Reinflation of Warm and Hot Jupiters

Abstract Understanding the anomalous radii of many transiting hot gas-giant planets is a fundamental problem of planetary science. Recent detections of reinflated warm Jupiters orbiting post-main-sequence stars and the reinflation of hot Jupiters while their host stars evolve on the main sequence may help constrain models for the anomalous radii of hot Jupiters. In this work, we present evolution models studying the reinflation of gas giants to determine how varying the depth and intensity of deposited heating affects both main-sequence reinflation of hot Jupiters and post-main-sequence reinflation of warm Jupiters. We find that deeper heating is required to reinflate hot Jupiters than is needed to suppress their cooling, and that the timescale of reinflation decreases with increasing heating rate and depth. We find a strong degeneracy between heating rate and depth, with either strong shallow heating or weak deep heating providing an explanation for main-sequence reinflation of hot Jupiters. This degeneracy between heating rate and depth can be broken in the case of post-main-sequence reinflation of warm Jupiters, as the inflation must be rapid to occur within post-main-sequence evolution timescales. We also show that the dependence of heating rate on the incident stellar flux inferred from the sample of hot Jupiters can explain reinflation of both warm and hot Jupiters. TESS will obtain a large sample of warm Jupiters orbiting post-main-sequence stars, which will help to constrain the mechanism(s) causing the anomalous radii of gas-giant planets.

Annealing heating rate dependence of microstructure and multiferroic properties in Bi4Ti2.9Fe0.1O12/CoFe2O4 layered magnetoelectric composite films prepared by chemical solution deposition method

Lead-free magnetoelectric composite films of CoFe2O4 (CFO) and Bi4Ti2.9Fe0.1O12 (BTF) were prepared on the LaNiO3-coated Si substrate by chemical solution deposition. Though the CFO layer randomly grows on the LaNiO3 layer, the oriented growth of the BTF layer can be regulated by rapid annealing treatment. The results indicated that the annealing heating rate significantly affects the c-axis orientation of the BTF layer, thereby resulting in obvious changes in microstructure, leakage behavior, dielectricity and ferroelectricity of the BTF/CFO films. The BTF/CFO film prepared at the heating rate of 40 °C/s presents the most compact structure, minimum leakage current, maximum dielectric constant and the highest residual polarization of 28.8 μC/cm2. Moreover, the excellent magnetoelectric coupling performance along with the highest magnetoelectric coupling voltage coefficient αE of 20.1 V/cm∙Oe can be achieved in these conditions.

Determination of the Structural Relaxation Enthalpy Using a Mathematical Approach

Structural relaxation is a well-known phenomenon in amorphous materials such as amorphous solid dispersions. It is generally understood as a measure for molecular mobility and has been shown to impact certain material properties such as the dissolution rate. Several quantification methods to evaluate structural relaxation using differential scanning calorimetry have been proposed in the past, but all approaches exhibit disadvantages. In this work, a mathematical model was developed and fitted to calorimetric data enabling the analysis of the structural relaxation enthalpy by separating the structural relaxation peak from the underlying glass transition. The proposed method was validated using a parameter sensitivity analysis. Differently stressed amorphous samples were analyzed applying the new model and the results were compared to commonly applied quantification methods in literature. The proposed method showed high robustness and accuracy and overcame the observed disadvantages of the established methods. The heating rate dependence of the calculated structural relaxation enthalpy was in accordance with theoretical considerations of previous studies, supporting the validity of the results. Thus, the proposed model is suitable to accurately quantify the degree of structural relaxation and should be a valuable tool for further investigations regarding the impact of structural relaxation on material properties.

Late-time Kilonova Light Curves and Implications to GW170817

We discuss the late time (tens of days) emission from the radioactive ejecta of mergers involving neutron stars, when the ionization energy loss time of beta-decay electrons and positrons exceeds the expansion time. We show that if the e$^\pm$ are confined to the plasma (by magnetic fields), then the time dependence of the plasma heating rate, $\dot{\varepsilon}_d$, and hence of the bolometric luminosity $L=\dot{\varepsilon}_d$, are given by $d\log L/d\log t\simeq-2.8$, nearly independent of the composition and of the instantaneous radioactive energy release rate, $\dot{\varepsilon}$. This universality of the late time behavior is due to the weak dependence of the ionization loss rate on composition and on e$^\pm$ energy. The late time IR and optical measurements of GW 170817 are consistent with this expected behavior provided that the ionization loss time exceeds the expansion time at $t>t_\varepsilon\approx 7$~d, as predicted based on the early (few day) electromagnetic emission.

Effect of high heating rates on the melting behavior of embedded In nanoparticles

In nanoparticles embedded in an Al-rich polycrystalline matrix have been investigated concerning the kinetics of their melting behavior. The advantage of the present system lies in the fact, that two distinct populations of particles are intrinsically formed: facetted nanoparticles that are embedded within the matrix grains and that obey the facetted Wulff shape or slight deviations thereof and particles situated at the grain boundaries of the matrix that form curved interfaces with the matrix grains. This second fraction thus serves as an internal reference, since the particles at the grain boundaries melt at the bulk melting temperature. Utilizing an averaging procedure for the fast scanning calorimetry measurements and combining conventional differential scanning- and fast scanning calorimetry with microstructure investigations, we found strong evidence for the observation of a heating-rate dependence of the melting transformation of the matrix-embedded nanoparticles. This observation gives rise to discuss the kinetics of melting in cases where the most potent nucleant for melting, the surface, is deactivated.