Heating Rate Dependence Research Articles

Organic compounds as temperature calibrants for fast scanning calorimetry

Organic compounds can be used as temperature calibrants in fast scanning calorimetry. Their advantages include ease of surface cleaning of the calorimetric chip and good thermal contact with the chip surface. Among several compounds tested, benzoic acid was identified as a convenient and reliable calibrant for temperatures below approximately 130 °C. However, organic calibrants often exhibit unusual heating rate dependencies of the onset temperatures of melting. This phenomenon can be semi-quantitatively explained by considering different heat flows within the sensor. Notably, the thermal resistance between the heater and thermopile, often overlooked, introduces an additional time constant that can sometimes result in a negative apparent thermal lag. In addition, the onset temperatures are influenced by factors such as sample position, thickness, surface wetting, and spreading. These factors limit the accuracy of transition temperature determinations to approximately ±1 K below 130 °C and ±5 K up to 220 °C.

Achieving tailorable nano-crystallization in a fully amorphous Zr50Cu42Al8 alloy

In this work, Zr50Cu42Al8 alloy was rapidly quenched into as-cast rod with nano-glass microstructure and fully amorphous as-spun ribbon, respectively. The different microstructure between the as-cast rod and as-spun ribbon results in the different glass transition, crystallization temperatures and their kinetics. The continuous heating transition (CHT) curves of the as-cast rod and as-spun ribbon derived from their heating rate dependence of onset crystallization temperature imply that the partial nano-crystallization stabilizes the amorphous remainders in the Zr50Cu42Al8 rod when annealed below ∼ 757 K, and give rise to the possibility to obtain nano-crystallization by annealing the fully amorphous ribbons within the temperature interval between the two CHT curves. It is as expected that the ribbons annealed at 730 K for 678 second and at 720 K for 3644 second respectively show similar microstructure and thermal properties to the as-cast rod. The results provide a valid way to achieve tailorable nano-crystallization in the fully amorphous alloys.

Calorimetric studies of yttrium doped non-conventional phase-change materials for improved performance

Though phase-change materials (PCMs) are regarded as constituent part of next-generation phase-change memory and other unfolding optoelectronic applications, the kinetics study of glass transition and crystallization, significant property in switching remains obscure in high-temperature region. Hence, this paper reports the investigation of glass transition and crystallization kinetics of Te(1-x) (GeSe0.5)Yx (TGSY) chalcogenide glass using differential scanning calorimetry (DSC) at heating rates 5, 10, 15, 20 °C/min. The effect of increasing Y quantity has been described by connecting structural relaxation kinematics during glass transition phenomena and devitrification while crystallization in chalcogenide glasses with their varied physicochemical characteristics. The inclusion of Y causes a discernible rise in the crystallization rate. The system is compatible with a strong glass-forming liquid, according to the Te(1-x) (GeSe0.5) Yx material fragility index. According to the average values of the kinetic exponent factors, there is heterogeneous nucleation for the investigated composition, which is subsequently followed by a two- or three-dimensional crystal growth phenomenon. Different glass stability criteria have been discussed based on the relationship between the characteristic temperatures. The CZW and CLX criteria were found to be inappropriate for discussing glass stability (GS) for the studied compositions based on the heating rate and composition dependencies of all criteria. The CYL criteria of Yuan et al. is the finest and it demonstrates the optimal ability for evaluating the GS, according to the data that was extracted from several GS criteria and their relative change parameters. By adding Y, thermal stability parameter and enthalpy emitted during the transition of glass and crystalline phases have been found to have an inverse relationship. All studied properties can conclude the application of studied material in phase-change material devices.

Glass transition temperatures and crystallization kinetics of a synthetic, anhydrous, amorphous calcium-magnesium carbonate.

We report the first calorimetric observations of glass transition temperatures and crystallization rates of anhydrous, amorphous calcium-magnesium carbonate using fast scanning differential scanning calorimetry. Hydrous amorphous Ca0.95Mg0.05CO3 · 0.5H2O (ACMC) solid was precipitated from a MgCl2-NaHCO3 buffered solution, separated from the supernatant, and freeze-dried. An aliquot of the freeze-dried samples was additionally dried at 250°C for up to 6 h in a furnace and in a high-purity N2 atmosphere to produce anhydrous ACMC. The glass transition temperature of the anhydrous Ca0.95Mg0.05CO3 was determined by applying different heating rates (1000-6000 K s-1) and correcting for thermal lag to be 376°C and the relaxational heat capacity was determined to be Cp = 0.16 J/(g K). Additionally, the heating rate dependence of the temperature that is associated with the corrected crystallization peaks is used to determine the activation energy of crystallization to be 275 kJ mol-1. A high-resolution transmission electron microscopy study on the hydrous and anhydrous samples provided further constraints on their compositional and structural states. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 1)'.

Role of heating rate on the triple-shape memory effect of amorphous polymers: A cooperative thermodynamic model

The triple-shape memory effect (triple-SME) in amorphous polymers arises from the staged structural rearrangement of their macromolecular chains upon heating. However, the working mechanism behind the heating-rate dependence of the triple-SME in shape memory polymers (SMPs) is not well understood due to the complex compositions. Herein, we adopt the extended free volume theory to investigate the effect of local vibration and structural rearrangement of macromolecular chains on the shape memory behavior of SMPs. By introducing the phase transition theory, the dependences of the glass transition, thermomechanical behavior, and triple-shape recovery behavior of SMPs on thermal history are then discussed. The accumulation of the remote free volume upon heating is identified as the driving force for the SME in SMPs. The effectiveness of the proposed model is further evaluated by applying it to predict the shape memory behavior of epoxy SMPs with dual- and triple-SMEs at various heating rates. This study is expected to provide a practical methodology for understanding the working mechanism of triple-SME in amorphous polymers.

Joining of dissimilar bulk metallic glasses with non-common supercooled liquid regions

We first successfully joined dissimilar bulk metallic glasses with non-common supercooled liquid regions via pulse current and obtained an amorphous structure joint, which exhibits an excellent tensile shear strength of ∼ 1.7 GPa. The joining process is derived from the Lasocka equation that the glass transition temperature and crystallization temperature of bulk metallic glasses increase with the heating rate, and the supercooled liquid region shifts toward the high-temperature region simultaneously. The difference in heating rate dependence of glass transition temperature and crystallization temperature of dissimilar bulk metallic glasses can be amplified at high heating rates and overlap the originally non-overlapped supercooled liquid phase region simultaneously. Especially, a new parameter K was introduced to screen the composition combinations of dissimilar bulk metallic glasses for this method. This method is a promising candidate for scaling up metallic glass sizes, realizing the successful joining of dissimilar BMGs, and providing a new idea for manufacturing amorphous alloy components with complex performance requirements.

The Experimental Investigation of Kinetics of Glass Transition of ZBLAN Glass by using Differential Scanning Calorimetry

A ZBLAN glass is a heavy metal fluoride (HMF) glass that possesses high thermal stability and excellent property as atransmitting material. The current study examines the thermal properties of ZBLAN glass utilizing Differential scanningcalorimetry (DSC) at various heating rates. The temperature of glass transition, Tg, is observed to vary with heating rate,indicating its kinetic nature. Through the use of Kissinger's and Augis- Bennett's methodologies and the heating ratedependency of Tg, the activation energy (E) has been determined. These methodologies have also been used to obtain thefragility index (m), which can be used to evaluate the glass forming ability (GFA) of the system. The fragility index found isgreater than 16, indicating that the ZBLAN glass is "fragile."

The growth and nanothermite reaction of 2Al/3NiO multilayer thin films

Nanothermite NiO–Al is a promising material system for low gas emission heat sources; yet, its reactive properties are highly dependent on material processing conditions. In the current study, sputter deposition is used to fabricate highly controlled nanolaminates comprised of alternating NiO and Al layers. Films having an overall stoichiometry of 2Al to 3NiO were produced with different bilayer thicknesses to investigate how ignition and self-sustained, high temperature reactions vary with changes to nanometer-scale periodicity and preheat conditions. Ignition studies were carried out with both hot plate and laser irradiation and compared to slow heating studies in hot-stage x-ray diffraction. Ignition behavior has bilayer thickness and heating rate dependencies. The 2Al/3NiO with λ ≤ 300 nm ignited via solid/solid diffusion mixing (activation energy, Ea = 49 ± 3 kJ/mole). Multilayers having λ ≥ 500 nm required a more favorable mixing kinetics of solid/liquid dissolution into molten Al (Ea = 30 ± 4 kJ/mole). This solid/liquid dissolution Ea is a factor of 5 lower than that of the previously reported powder compacts due to the elimination of a passivating Al oxide layer present on the powder. The reactant mixing mechanism between 300 and 500 nm bilayer thicknesses was dependent on the ignition source's heating rate. The self-propagating reaction velocities of 2Al/3NiO multilayers varied from 0.4 to 2.5 m/s. Pre-heating nanolaminates to temperatures below the onset reaction temperatures associated with forming intermediate nickel aluminides at multilayer interfaces led to increased propagation velocities, whereas pre-heating samples above the onset temperatures inhibited subsequent attempts at laser ignition.

Crystallization Study of Pb Additive Se-Te-Ge Nanostructured Alloys using Non-isothermal Differential Scanning Calorimetry

Nanotechnology started a new era in research and continuous escalations due to its potential applications. In modern optoelectronics, Pb additive nano-chalcogenides are becoming promising materials. For a memory and switching material, the thermal stability and glass-forming ability are vital, and the glass should be thermally stable from a technological point of view. This research article investigates the thermal behaviour of bulk (Se80Te20)94-xGe6Pbx (x = 0, 2, 4 and 6) samples synthesized using the melt quench procedure non-isothermal differential scanning calorimetry at four heating rates from 5 to 20°Cmin-1. Further, the overall crystallization study, which includes thermal stability, ease of glass formation, fragility, glass relaxation and glass-crystallization transformation kinetics of investigated alloys using different empirical formalisms, is reported and discussed. Compositional and heating rate dependence of recorded characteristic temperatures and other deduced parameters of reheated alloys are also discussed. The correlation between deduced parameters is also established to define the utility of these materials in practical applications.

Effects of manganese and terbium on the dosimetric properties of CaSO4

In this study, a new CaSO4 crystal doped with manganese and terbium is described and its potential for dosimetric applications is evaluated. Crystals were synthesized using the slow evaporation route, and were prepared in pellet form with the addition of Teflon. CaSO4 was doped with manganese and terbium at a concentration of 0.1 mol% in each case. The crystalline structure and optical properties of the crystals were evaluated by X-ray diffraction, Fourier transform infrared spectroscopy and photoluminescence. The suitability of these crystals for thermoluminescent (TL) and optically stimulated luminescent (OSL) dosimetry was also investigated. The material showed adequate OSL and TL characteristics, such as a TL glow curve with two peaks at approximately 205 °C and 325 °C, an adequate OSL decay curve, good reproducibility, and linearity of the luminescent signals, when irradiated with doses of between 200 mGy and 150 Gy. Two trapping centers located at 0.77 and 1.02 eV were revealed. The heating rate dependence was also evaluated. The lowest detectable dose was investigated by the TL and OSL techniques, and the results were presented in mGy for both methods. It was also observed that co-doping with Mn and Tb contributed to a reduction in fading compared to CaSO4:Mn and CaSO4:Tb.

Parametric dependency of a constitutive model describing solid state sintering of cemented carbides

This study focuses on an inverse modelling approach, using FEM to simulate the sintering of WC-Co powder using a continuum model. From a previously developed constitutive model of cemented carbide, the dependency of the material parameters is investigated in a sensitivity study. A value of sensitivity is assigned to all the material parameters and calculated at different steps in the sintering process, which represent its importance for capturing the shrinkage during sintering. The approach is that only the more sensitive parameters should be fitted when changing experimental setup or material composition, leaving the less important parameters constant, resulting in fewer tests and iterations. This approach is tested in an optimization of WC-Co powder sintering cycle, where the shrinkage curve is experimentally determined. It is concluded that some of the material parameters play a minor role in the modelling and could be set as constants in an optimization. The constitutive material model alone is unable to capture all features that appeared in the shrinkage curve during the experiment. Improvements of the model are discussed. An additional investigation, performed without heating rate dependency, shows that the remaining material parameters could compensate for the omitted heating rate for a known sintering cycle without losing accuracy.

Anomalous heating rate dependence and analyses of thermoluminescence glow curves in Gd doped ZnB2O4 phosphors

Here, we report the thermoluminescence (TL) characteristics and trapping parameters under beta ray excitations of pelletized Gd-incorporated ZnB2O4 synthesized through the gel combustion method. The chemical composition of the obtained Gd incorporated ZnB2O4 was confirmed using X-ray diffraction (XRD). The best doping concentration of Gd was 0.25 mass%, which resulted in the highest luminous efficiency. The glow curves of the pellet-formed samples exposed to β-irradiation at various doses showed glow peaks at about 79 °C, 133 °C and 276 °C with a heating rate of 2 °Cs−1. An anomalous heating rate effect was observed for the peak centered at 276 °C, but the TL intensity of the peak at 79 °C and 133 °C decreased with an increasing heating rate. The TL glow peaks were studied using Tm-Tstop, initial rise (IR), and variable heating rate (VHR) and Computerized glow curve deconvolution (CGCD) methods. In the range of 0.1–50 Gy, the total integral values of TL output increased linearly with increased dose. A complex glow curves are composed of six distinguishable peaks as revealed by the results obtained from IR and CGCD methods. The current results indicate that the ZnB2O4:Gd3+ phosphor is a suitable option in radiation dosimetry for environmental monitoring.

Shining a Hot Light on Emerging Photoabsorber Materials: The Power of Rapid Radiative Heating in Developing Oxide Thin-Film Photoelectrodes

The unique possibilities of rapid thermal processing (RTP) for overcoming two significant challenges in the development of oxide thin-film photoelectrodes are demonstrated. The first is the need to exceed normal temperature limits for glass-based F:SnO2 substrates (FTO, ∼550 °C) to achieve the desired density, crystallinity, and low defect concentrations in metal oxides. Flash-heating of Ta2O5, TiO2, and WO3 photoelectrodes to 850 °C is possible without damaging the FTO. RTP heating-rate dependencies suggest that the emission spectrum of the RTP lamp, which blue-shifts with increasing heating power, can significantly influence the crystallization behavior of wide-bandgap photoelectrodes (≥1.8 eV). The second challenge is avoiding the formation of structural defects, trap states, grain boundaries, and phase impurities, which can be particularly difficult in multinary metal oxides. RTP treatment of α-SnWO4, a promising photoanode material, resulted in an increase in grain size and favorable crystallographic reorientation, culminating in a new performance record.

Thermoluminescence properties and trapping parameters of TlGaS2 single crystals

TlGaS2 layered single crystals have been an attractive research interest due to their convertible characteristics into 2D structure. In the present paper, structural, optical and thermoluminescence properties of TlGaS2 single crystals were investigated. XRD pattern of the crystal presented five well-defined peaks associated with monoclinic unit cell. Band gap and Urbach energies were found to be 2.57 and 0.25 eV, respectively, from the analyses of transmittance spectrum. Thermoluminescence measurements were carried out above room temperature up to 660 K at various heating rates. One TL peak with peak maximum temperature of 573 K was obtained in the TL spectrum at 1.0 K/s. Curve fitting, initial rise and variable heating rate methods were used for analyses. All of those resulted in presence of a deep trapping level with activation energy around 0.92 eV. Heating rate dependence of the TL peak was also studied and it was indicated that peak maximum temperature shifted to higher temperatures besides decreasing TL intensity as the higher heating rates were employed.

Physical characterization and crystallization kinetics of amorphous BiSe chalcogenide glasses

The influence of Bi concentration on the thermal parameters viz temperatures of glass transition (Tgl) and crystallization (Tpc) of binary BixSe100-x glasses were studied experimentally. The activation energy of glass transition (EGl) has been estimated as the averaged value deduced based on Kissenger's relationship and its approximation. On the other hand, Afify and Aly methods help one to estimate the crystallization activation energy (Epc), the frequency factor (k0) and the order of reaction (n) with no approximation. The observed increase in EGl and Epc values resulted from increasing both Tgl and Tpc with increasing of the Bi content. The Lasocka relationship can describe the heating rate dependence of Tgl and Tpc. A good correlation between Tgl and Tpc was investigated. The attained results were discussed according to the distribution of the chemical bonds, the main coordination number (Nr), average heats of atomization (Hs), the mean bond energy (Es), the cohesive energy (CE), and the overall average bond energy (<E>) for BixSe100-x glasses.

Solid-Solid Phase Transformations and Their Kinetics in Ti-Al-Nb Alloys

The application of light-weight intermetallic materials to address the growing interest and necessity for reduction of CO2 emissions and environmental concerns has led to intensive research into TiAl-based alloy systems. However, the knowledge about phase relations and transformations is still very incomplete. Therefore, the results presented here from systematic thermal analyses of phase transformations in 12 ternary Ti-Al-Nb alloys and one binary Ti-Al measured with 4–5 different heating rates (0.8 to 10 °C/min) give insights in the kinetics of the second-order type reaction of ordered (βTi)o to disordered (βTi) as well as the three first-order type transformations from Ti3Al to (αTi), ωo (Ti4NbAl3) to (βTi)o, and O (Ti2NbAl) to (βTi)o. The sometimes-strong heating rate dependence of the transformation temperatures is found to vary systematically in dependence on the complexity of the transformations. The dependence on heating rate is nonlinear in all cases and can be well described by a model for solid-solid phase transformations reported in the literature, which allows the determination of the equilibrium transformation temperatures.

Torrefaction, temperature, and heating rate dependencies of pyrolysis of coffee grounds: Its performances, bio-oils, and emissions

The torrefaction pretreatment is of great significance to the efficient conversion of biomass residues into bioenergy. In this study, the effects of the three torrefaction temperatures (200, 250, and 300 °C) on the pyrolysis performance and products of coffee grounds (CG) were quantified. The torrefaction treatment increased the initial devolatilization and maximum peak temperatures of the CG pyrolysis. Activation energy of CG250 was lower than that of CG and more conducive to the pyrolysis. Torrefaction altered the distributions of the pyrolytic products and promoted the generation of C=C. Torrefaction changed the composition ratio of the pyrolytic bio-oils although cyanoacetic acid and 2-butene still dominated the bio-oils. The joint optimization pointed to pyrolysis temperature > 600 °C and torrefaction temperature ≤ 270 °C as the optimal conditions. Our experimental results also verified that torrefaction of CG may be more suitable at 200 and 250 °C than 300 °C.

Trapping centers in Bi12TiO20 single crystals by thermally stimulated current

Sillenite group compounds have been widely utilized in photocatalytic applications. One of the member of this group, Bi12TiO20 single crystal, was grown by Czochralski method. The structural properties were investigated by x-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. XRD pattern presented well-defined intensive peaks associated with cubic crystalline structure. SEM images indicated the crystal surface as almost uniform and smooth. Thermally stimulated current (TSC) experiments were performed in the 10–280 K temperature range to reveal shallow trapping centers in the Bi12TiO20 single crystal. Two peaks around 112 and 179 K were observed in the TSC glow curve. The analyses of these curves considering the curve fitting and peak shape techniques resulted in presence of two hole centers at 0.09 and 0.14 eV. Heating rate dependencies of peak maximum temperature and current were also investigated throughout the paper.

Phase Separation Behavior of Aqueous Poly(N-isopropylacrylamide) Solutions Studied by Scattering Experiments.

We have investigated the colloidal phase-separating dilute solution of aqueous poly(N-isopropylacrylamide) (PNIPAM) with a molecular weight of 1.24 × 105 by small-angle X-ray scattering (SAXS) as well as static and dynamic light scattering (SLS and DLS). Those scattering experiments provide us with the average size and size distribution of concentrated-phase droplets and the concentration cconc of the coexisting concentrated phase. While the average droplet size is almost constant above 35 °C in the temperature-scan experiments, it is a decreasing function of temperature above 35 °C in the temperature-jump experiments. This heating rate dependence of the average droplet size arises from the fact that concentrated-phase droplets in the aqueous PNIPAM solution grow only in a limited temperature range (31.5-35 °C). The scattering results on the temperature dependence of cconc are combined with previously reported results of turbidity and DSC, giving the phase diagram of the Type II phase behavior with the off-zero critical point at high molecular weight.

Activation energy during the crystallization transition for Se-based chalcogenide glasses

This work aims to research the crystallization transition kinetics aspects for Se60Ge15As25 and Se60Ge15Sn25 compositions, utilized differential thermal analysis technique under the non-isothermal condition at various heating rates. Crystallization temperature (Tc) has been discovered heating rate and composition dependence. Heating rate dependence of Tc reveals the activation energy of crystallization (Ec) values according to various methods. Kissinger, modified Kissinger, Takhor, Baswell, Augis-Benntt, Mahadeven and Gao-Wang methods are applied to determine (Ec). The outcome shows an unsuitable Takhor method for determination of the crystallization parameters of the studied composition. The highest value of Ec is observed for Se60Ge15As25 composition. This result is confirmed by frequency factor Ko, crystallization rate factor K data and attributed to the effective bands energies with As and Sn addition to host composition. The transformation mechanisms have been examined by the values of Avrami exponent n and dimensionality of growth m. According to Avrami index n, the crystallization mechanism was interpreted as two-dimensional growth for Se60Ge15 with Sn addition and three-dimensional growth with As addition.