Heating Rate Dependence Research Articles

Effects of chemical composition and mean coordination number on glass transitions in Ge–Sb–Se glasses

Glass transitions in the Ge–Sb–Se glasses were investigated by means of differential scanning calorimetry (DSC) under non-isothermal conditions. The glass transition temperature [Formula: see text], activation energy of glass transition [Formula: see text], and fragility index as functions of the mean coordination number (MCN) and atomic percent of Ge were examined. The maximum value of [Formula: see text] in each group of the glasses occurred at the chemically stoichiometric composition, suggesting a glass transition threshold. The [Formula: see text] and fragility index were calculated from the heating rate dependence of [Formula: see text]. Both [Formula: see text] and fragility index show the minima at MCN = 2.4 which can be attributed to the structural phase transition of a covalently glassy network at MCN = 2.4. The analysis of the experimental results suggests that both the chemical composition and MCN have significant effects on the glass transitions in Ge–Sb–Se glasses.

Crystallization/Melting Kinetics and Morphological Analysis of Polyphenylene Sulfide

AbstractCrystallization and melting kinetics of polyphenylene sulfide (PPS) are determined using fast scanning calorimetry. The temperature dependence of half‐time crystallization of isothermally melt‐crystallized PPS shows a downward convex curve with a minimum at 160 °C. The minimum crystallization half‐time is about 3 s. The analysis of heating rate dependence of the melting temperature reveals a zero‐entropy‐production melting temperature of the sample. The microstructure of the sample, which is prepared by fast scanning calorimetry, is investigated by small‐angle X‐ray scattering and polarizing optical microscopy. The crystallinity and lamellar thickness of the sample annealed for 400 s decrease with decreasing crystallization temperature. The size of spherulites becomes small as the isothermal temperature is decreased. Transcrystalline morphology is observed near the surface between the sample and nitrogen gas at a crystallization temperature of 120 °C. The thickness of the transcrystalline layer disappears as the isothermal temperature is increased.

Impact of the heating rate on the annealing behavior and resulting mechanical properties of UFG HSLA steel

The formability of materials with ultrafine grained (UFG) microstructures produced by severe plastic deformation processes is often limited due to low strain hardening capabilities and strain localizations. Most commonly, heat treatments are used to regain the formability. However, conventional furnace heat treatments can lead to grain growth and significant losses in strength. One approach to address this issue is to increase the heating and cooling rates of the heat treatments. The present work focuses on the heating rate dependencies of the microstructure evolution and resulting mechanical properties of a UFG high strength low alloy (HSLA) steel. Electron backscatter diffraction (EBSD) measurements are used to characterize the microstructure and texture. Bending tests and uniaxial tensile tests are conducted to provide insight into the mechanical properties that are related to the obtained microstructures, with an emphasis on the tendency for strain localizations. The investigations reveal a distinct effect of the heating rate on the annealing behavior, i.e., continuous vs. discontinuous growth. Thus, resulting microstructures and mechanical properties are not only a function of time and temperature but also depend on the heating rate. In this context, the application of laser annealing is shown to be a suitable approach to impede strain localizations in the form of shear bands without sacrificing much of the strength of the UFG material obtained by severe plastic deformation.

Kinetics of glass transition of GeySe94-yIn6 (y = 10, 15 and 20) chalcogenide glasses under non-isothermal condition

ABSTRACTKinetics of glass transition of GeySe94-yIn6 (y = 10, 15 & 20) glassy alloys has been studied under non-isothermal condition using Differential Scanning Calorimetery (DSC). The glassy alloys have been prepared by rapid quenching of melt technique. For structure characterization, XRD and EDAX techniques have been used. DSC thermograms have been recorded at heating rates 5, 10, 15 and 20 K/min. from room temperature to 823 K. Lasocka's empirical relation has been used to study the heating rate dependence of glass transition temperature. Activation energy of glass transition, evaluated from Kissinger Peak shift method, increases with increase of Ge content in GeySe94-yIn6 (y = 10, 15 & 20) glassy series.

Physical and thermal characterization and glass stability criteria of amorphous silver-vanadate-tellurate system at different heating rates: Inducing critical Ag2O/V2O5 ratio

Transition metal oxide containing glasses (TMOGs) have unique thermal properties. This work gives an insight into the thermal stability and the compositional dependence of thermal properties for the understudied glasses. Also, physical, some optical and thermal characterization of 40TeO2-(60−x)V2O5-xAg2O glasses have been investigated in the compositional range of 0≤x≤50mol%. DSC experiments were performed on powder samples with a weight of 5mg, within the temperature range of 30–400°C at heating rates φ=2.5, 5, 7.5 and 10K/min, to obtain the glass transition temperature (Tg) and crystallization temperature (Tcr). The heating rate dependence of Tg has been used to study the applicability Kissinger formula describing the glass transition, in order to determine the glass transition activation energy (Ea). Ea values show that it ranged from 563.22kJ/mol to 268.36kJ/mol, indicating that (in relation/justification to other thermal and structural data) less fragility and so higher thermal stability is devoted to in the case of x=20mol%. The previously reported optical absorption spectra and optical band gap (Eg) by the same author were used to evaluate the refractive index (n),which both Eg and n have a behavior change at critical content of x=20mol%, implying to a drastic structural change with increasing Ag2O. Also, the physical parameters such as density (ρ), molar volume (Vm), oxygen molar volume (VO∗), oxygen packing density (OPD), molar refraction (Rm) and metallization criterion (M) have been evaluated and discussed, showing a behavior change at x=20mol%. Different glass stability parameters and different criteria of fragility have been checked, which show that glass with x=20 has the good stability among the present glasses. In brief, glass with x=20 has relatively high thermal stability, high glass forming tendency, higher OPD and VO∗, and so lower non-bridging oxygen ions (NBOs), which show that it is suitable option and promising material for optical and optoelectronic devices such as base semiconductor in solar cells and optical fibers because of its resistance against thermal attacks and also its narrower band gap.

Non-isothermal crystallization kinetics of \(Cd_{10} Se_{90}\) chalcogenide glass

The structure and kinetics of the crystallization reaction of amorphous \(Cd_{10} Se_{90}\) were studied at different heating rates (5–30 K/min) under non-isothermal conditionsby X-ray powder diffraction, scanning electron microscopy (SEM) and differential thermal analysis (DTA) techniques. The Johnson–Mehl–Avrami(JMA) and isoconversional models were used to describe the DTA crystallization data.A strong heating rate dependence of the activation energy was observed when the data were analyzed using Matusita method. This variation of the activation energy was confirmed by the application of the isoconversional methods of Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO), Tang, Starink, and Friedman. These methods showed that the activation energy of crystallization is not constant but varies with the degree of conversion and hence with temperature. This variation indicates that the transformation from amorphous to crystalline phase is a complex process involving different mechanisms of nucleation and growth.

Glass transition kinetics aspects of amorphous Se60Ge15As25 and Se60Ge15Sn25 compositions

This work aims to research the glass transition kinetics aspects for Se60Ge15As25 and Se60Ge15Sn25 compositions, utilized differential thermal analysis technique under the non-isothermal condition at various heating rates. Glass transition temperature (T g) has been discovered heating rate and composition dependence. Composition reliance of T g can be comprehended with the correlation between T g and coordination number and mean bond energy also for the investigated compositions. Heating rate dependence of T g reveals the activation energy of glass transition (E g) values according to various methods for T g with various definitions. The estimated E g values have been discovered enlarging with temperature throughout the glass transition region. The relative error (e %) for Kissinger’s activation energy and its related parameters have been resolved and discussed. The correlation between glass transition and crystallization temperatures reveals that the crystallization process is more sensitive to heating rate than glass transition process. The critical heating rate value reflects that the Se60Ge15As25 composition is the most thermal stable composition. Fragility index values have been assessed by various relations and categorized the compositions under review as strong glasses.

Impact of sucrose crystal composition and chemistry on its thermal behavior

Though crystalline sucrose is an abundant and highly refined organic compound, its thermal behavior is complex and not fully understood. The objective of this research was to investigate the influence of the composition and chemistry of the sucrose crystal on its thermal behavior, especially as related to the origin of the small endothermic DSC peak observed for most cane sucrose sources, but not for beet sucrose sources, using a variety of analytical methods and techniques. Based on the evidence herein, we assert that the presence of the small endothermic DSC peak is associated with the onset of thermal decomposition of sucrose within mother liquor occlusions, initiated by hydrolysis and mediated by the composition and chemistry of the sucrose crystal. Any factor that affects the composition and chemistry of the sucrose crystal will in turn influence its resultant thermal behavior. This assertion further explains the complex sucrose thermal behavior issues that have heretofore not been completely elucidated, including the wide variation in the literature reported melting temperature values (location of Tmonset), the variation in the number and magnitude (ΔH) of the endothermic DSC peaks obtained, and the heating rate dependency of the melting temperature.

Crystallization kinetics of tellurium-rich Se–Te–Sn glassy alloys

Differential scanning calorimetry (DSC) has been used to study the non-isothermal crystallization kinetics of Se30Te70−xSnx (for x = 0, 1.5 2.5 and 4.5) glassy alloys. Characteristic kinetic parameters say glass transition temperature (T g), peak crystallization temperature (T p) and melting temperature (T m) are determined from the DSC curves, recorded at four different heating rates, i.e., 9, 12, 15, 18 K min−1. The characteristic temperatures T g, T c and T m are found to increase with an increase in Sn concentration as well as with the heating rate (α). The increase in T g, T p and T m may be ascribed to the increase in cross-linking of amorphous network due to the dispersion of Sn into the Se chains. The activation energy of glass transition (E g), crystallization activation energy (E c) and Avrami exponent (n) have been evaluated from the heating rate dependence of T g, T c and T p using Kissinger, Mahadevan, Augis-Bennett and Moynihan methods. Thermal stability and glass-forming ability of amorphous Se30Te70−xSnx alloy have also been examined. Our results show that Se30Te70−xSnx composition, with thermal stability parameter H R > 0.5, is thermally stable and has characteristics of good glass former. Further, the composition corresponding to x = 1.5 is found to be thermally more stable as compared to the other compositions.

Comment on “Re-exploring the double-melting behavior of semirigid-chain polymers with an in-situ combination of synchrotron nanofocus X-ray scattering and nanocalorimetry” by Ivanov et al. [European Polymer Journal 81 (2016) 598–606.

Ivanov et al., European Polymer Journal 81 (2016) 598–606, conclude that “the phenomenon of the double (or multiple) melting behavior [in poly(trimethylene terephthalate) (PTT)] is not necessarily coupled to the melting–recrystallization processes and can be observed even in the absence of any recrystallization”. To further clarify this long standing issue, the multiple-melting behavior of isothermally crystallized PTT was examined using differential scanning calorimetry (DSC) and fast scanning chip calorimetry (FSC) in a wide range of heating rates (0.1Ks−1–60,000Ks−1). The critical heating rate to suppress recrystallization, βcritical, was determined as 2000Ks−1 from the analysis of heating rate dependence of melting temperature. Melting peaks observed below βcritical are due to the melting of recrystallized crystals, which are formed during slow heating. On the other hand, above βcritical, a single endothermic peak originated from the melting of initially formed crystals is observed. The result of thermal analysis strongly suggests that a single population of crystals is formed during isothermal crystallization of PTT. The heating rate of 1000Ks−1, as used by Ivanov et al., was therefore not fast enough to suppress recrystallization.

Kinetics and thermal stability of the Ni62Nb38–x Ta x (x=5, 10, 15, 20 and 25) bulk metallic glasses

We studied thermal stability and its relationship to the glass-forming ability (GFA) of the Ni62Nb38–xTax (x=5, 10, 15, 20, 25) bulk metallic glasses (BMG) from a kinetic point of view. By fitting the heating-rate dependence of glass transition temperature (Tgonset) and crystallization temperatures (Txonset and Txpeak) of the Ni62Nb38–xTax BMG using the Vogel-Fulcher-Tammann (VFT) equation, we obtained the ideal glass transition and crystallization temperatures (Tg0 and Tx0) and the fragility parameter (m), and also constructed continuous heating transition (CHT) diagrams for crystallization of the BMG. The CHT diagrams of the BMG indicate enhanced thermal stability by Ta addition; the Tg0 as well as the Tx0 also illustrates this improved stability limit. The compositional dependence of m, which agrees well with that of the reduced glass-transition temperature, indicates a strong correlation between liquid fragility and glass-forming ability in the present alloy system. These results provide new evidence for understanding thermal stability, liquid fragility, and GFA in BMG.

Photo-transferred thermoluminescence of shallow traps in β-irradiated BeO ceramics

Photo-transferred thermoluminescence signals from beryllium oxide (BeO) ceramics were measured in the low temperature range of 10–300K. Samples irradiated at room temperature using a Sr90/Y90 beta source were cooled down to 10K and trapped charges were photo-transferred at this low temperature using the light from a high power blue LED emitting at ~470nm (2.6eV). Thermoluminescence glow curve recorded at 0.2K/s heating rate exhibited three peaks around 90, 160 and 185K. The analyses of the TL peaks of the glow curve were accomplished using curve fitting, differential and peak shape methods. Results obtained from these techniques are in good agreement about the presence of three trapping centers in BeO ceramics with activation energies of 0.24, 0.48 and 0.56eV. Moreover, the analyses indicated that first-order kinetics (slow retrapping) is the dominant mechanism in the luminescence process. Heating rate dependence of the glow curves was also investigated between 0.2 and 0.8K/s rates.

Glass transition kinetics and thermal stability of Se82 − xTe18Sbx (x = 0, 4, 8 and 12 at %) glassy alloys

Glass transition kinetics of Se82−xTe18Sbx (x = 0, 4, 8 and 12 at.%) glassy alloys has been studied using differential scanning calorimetry (DSC). DSC runs were taken at different heating rates (5, 10, 15 and 20 K/min) for each samples. Heating rate dependence of glass transition temperature (Tg) has been studied using Lasocka empirical relation. Activation energy of glass transition (Eg) has been determined using Kissinger and Moynihan’s relation. Effect of Sb concentration on glass transition temperature and activation energy has been studied. Thermal stability of Se82 − xTe18Sbx glassy alloys has also been investigated using Dietzal relation, Saad and Poulin relation, Hurby parameter (Hr) and Lie and Liu parameter (γ). Compositional dependence of parameters investigated for thermal stability has also been studied.

Crystallization kinetics of poly(butylene terephthalate) and its talc composites

ABSTRACTCrystallization kinetics of poly (butylene terephthalate) (non‐talc‐PBT) and its 0.1 wt % talc composites (talc‐PBT) was determined for a wide range of cooling rates and isothermal temperatures. The critical cooling rate to suppress crystallization is 2000 K s−1 for non‐talc‐PBT and 7000 K s−1 for talc‐PBT. The cooling rate dependence of the total enthalpy change and heating rate dependence of enthalpy of cold crystallization are quantitatively discussed on the basis of the Ozawa's method. For isothermal crystallization, the annealing‐temperature (Tiso) dependence of crystallization half‐time (t1/2) shows a bimodal curve with two minima. Talc shortens the t1/2 at Tiso above 340 K and acts as a heterogeneous nucleation agent. Tammann's approach revealed that the t1/2 is shortened by pre‐nucleation for non‐talc‐PBT but not for talc‐PBT. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44739.

Investigation and evaluation of the glass stability criteria for Se60Ge15X25 (X = Sn, As) compositions

Study of the glass stability for amorphous Se60Ge15X25 (X = Sn, As) compositions has been performed by determination and evaluation of the widely used and more recently glass stability (GS) criteria. Calorimetric differential thermal analysis (DTA) measurements have been used under non-isothermal conditions at different heating rates. GS criteria have been determined based on the interrelationship of the estimated characteristic temperatures from DTA curves. All GS criteria are found to be heating rate and composition dependence. Their values and behaviors indicated that the most stable composition against devitrification with As addition. The calculated criteria values based on the onset crystallization temperature Tx and the maximum (peak) crystallization temperature Tc exhibit a similar behavior as a function of heating rate and composition, whereas both of them have incompatible values. The relative change parameter of GS criteria as well as their heating rate and composition dependence reflects that the more suitable and sensitive GS criterion, for the studied compositions, is Saad and Poulain’s criterion Ks and the less one is Lu and Liu’s criterion KLL for two studied compositions.

Melting and recrystallization kinetics of poly(butylene terephthalate)

Melting of original crystals and their recrystallization during heating were successfully separated for isothermally crystallized poly(butylene terephthalate) (PBT). The corresponding kinetics was determined and quantitatively discussed for a wide range of heating rates (0.1–100,000 K s-1) using fast-scanning chip calorimetry (FSC) and differential scanning calorimetry (DSC). The double melting peaks observed on the FSC curves are assigned to the melting of original crystals (low-temperature peak) and recrystallized and/or reorganized crystals (high-temperature peak). Heating rate dependence of the degree of recrystallization has been evaluated and the kinetics was discussed on the basis of Ozawa's method. Compared with the melt-crystallization and cold-crystallization, recrystallization kinetics is the fastest process. This is because many crystal remnants, which do not transform into the isotropic melt, act as athermal nuclei, and accelerate recrystallization.

Thermal and structural characterization of the Bi2‐xSmxSr2Ca2Cu3O10+δ glass‐ceramic system

AbstractIn this work, investigations on the crystallization and oxidization kinetics of the Sm substituted BiSrCaCuO glass‐ceramic system were performed. It has been shown that the Sm ions changed the glassification properties of the BiSrCaCuO system. While fully glass samples were obtained for low Sm‐substitution levels (x=0.2 and x=0.4), the Sm containing particles on the surface have grown especially at high Sm‐substitution levels (x>0.6) and glassification problem increased. Nonisothermal crystallization kinetics including activation energy for crystallization, Ea, and Avrami parameter, n, of the samples prepared was investigated using differential thermal analysis (DTA) at four different uniform heating rates. The values of glass transition temperature and crystallization temperature exhibited compositional and heating rate dependence. Ea value of the samples showed an increase with increasing the Sm concentration. The Avrami parameter, n, was found approximately 4.5, suggesting the growth of small particles with an increasing nucleation rate. The calculated values of the oxidization rates and the activation energy for oxygen out‐diffusion process, E, indicated that the oxygen deficiencies by the Sm substitution in the unit cell of BiSrCaCuO were formed and more oxygen atoms were absorbed to fill the oxygen deficiencies in the system.

From ultrafast to slow: Heating rate dependence of the glass transition temperature in metallic systems

When a solid crosses the glass transition, viscous flow sets in and the glass transforms into a supercooled liquid. The glass transition temperature exhibits a heating rate dependence which was previously observed to follow a Vogel–Fulcher–Tammann (VFT) equation. Here we report on a change in the heating rate dependence of the glass transition, determined by the distinct increase in the specific heat capacity, of a metallic glass. We combine standard techniques such as differential scanning calorimetry with recently developed ohmic heating techniques in order to cover seven orders of magnitude in heating rate. Contrary to previous reports, our results show that the change of the glass transition temperature cannot be described by a single VFT equation. Instead we find two distinct regimes which independently follow a VFT expression.

Some Predicted Effects of Minerals on the Generation of Petroleum in Nature

The presence of some minerals can strongly influence the composition of laboratory pyrolysates. The question is whether similar effects may also occur in nature, thereby influencing the gas–oil ratio and other bulk compositional characteristics. A series of experiments have been conducted at varying heating rates to examine this issue. Three source rocks that vary significantly in mineralogy (a quartz-rich, a calcite-rich, and a clay-rich sample), namely, the Alum shale, Bowland shale, and Toolebuc oil shale, respectively, were tested by Rock-Eval pyrolysis, open-system pyrolysis gas chromatography (PyGC). and bulk kinetic parameters to check for the existence or otherwise of mineral matrix effects (MMEs). Kerogen and whole-rock samples were then pyrolyzed at three heating rates using closed-system [microscale sealed vessel (MSSV)] pyrolysis to examine the heating rate dependency upon hydrocarbon aromaticity, gas–oil ratio, and total yield. The solvent extract of one Bowland shale sample was used as a ref...

Quantitative understanding of two distinct melting kinetics of an isothermally crystallized poly(ether ether ketone)

Abstract The multiple melting peaks of isothermally crystallized poly(ether ether ketone) were investigated by fast-scanning chip calorimetry over a wide range of heating rates from 500 to 60,000 K s −1 . The analysis of heating rate dependence of melting temperatures revealed that there are two crystal populations with distinct melting kinetics for the samples prepared at different crystallization temperatures, 170 °C ≤ T iso ≤ 270 °C. For each T iso , the two melting temperatures of the metastable crystals without prior reorganization or superheating (i.e. zero-entropy-production melting temperatures) were constantly 20 K and 30 K, respectively, higher than T iso . We first discuss this behavior quantitatively based on the Lauritzen-Hoffman nucleation approach. Finally we conclude that these increases in temperature are linked to the number of stems which construct the secondary surface nuclei. The existence of two crystal populations can be caused by differences in the stability of the crystal or “local” differences in the free energy of the surrounding melt.