Thermochimica Acta最新文献

Currently, the commonly used performance evaluation approach for accelerating rate calorimeters (ARCs) is based on di‑tert‑butyl peroxide (DTBP). However, DTBP is not a certified reference material that contains untraceable and inaccurate thermodynamic and kinetic parameters. To address this issue, an evaluation approach using Joule heat was proposed. The key point of this approach is the use of Joule heat to simulate the exothermic process of a chemical reaction. First, an evaluation apparatus with reaction rate feedback control was developed. Subsequently, exothermic reaction experiments using the DTBP/toluene solution were simulated. The experimental results indicated that the thermodynamic and kinetic parameters obtained using this approach align with the preset values and exhibit good repeatability. This approach is traceable and can be traced back to the International System of Units, which facilitates reliable performance evaluation of commercial ARCs.

A comprehensive investigation into the curing kinetics of composites based on bisphenol A aniline benzoxazine resin (BA-a) and microcrystalline cellulose (MCC) modified by phosphorylation (MCC-pH), was conducted in this study. For this purpose, differential scanning calorimetry (DSC) analysis, at different heating rates, was used to examine the curing process. The kinetic parameters as a function of conversion were determined using isoconversional approaches, i.e., iterative Kissinger-Akahira-Sunose (it-KAS), Trache-Abdelaziz-Siwani methodology (TAS), and Vyazovkin methodology. The incorporation of MCC-pH reduced considerably the curing temperatures, indicating their catalytic effect. A combination of isoconversional methods and multi-step kinetic fitting was done to elucidate the effect of adding MCC-pH on BA-a curing. The reported data exhibited the enhanced reactivity of the composite systems, which was associated with the acceleration of the regular polymerization reaction. The possible pathway of the polymerization in the presence of phosphorylated cellulose was also discussed.

Machine learning is an emerging approach to predict thermal decomposition temperature in the field of energetic materials, while an assessment of the descriptor applicability is still lacking. In this work, we have systematically established 5 general descriptor sets for 1091 compounds and combined them with 9 algorithms to construct a suite of predictive models with mean absolute error ranging 41–29 K, which is comparable to the cutting-edge endeavors. Our study emphasizes the significant influence of multi-level structural interactions on the thermal stability and decomposition of energetic materials, contributing insights conducive to the development of corresponding descriptors.

This study delves into the phase transformations of fifteen pure elements utilizing a synergistic approach combining arc-melting, a pyrometer, and its temperature vs. time output. Employing cooling curve recording tactics during arc-melting with an elite temporal resolution pyrometer unravels double recalescence in refractory metals (‘Mo,’ ‘Nb,’ ‘Ta,’ ‘W’). Metalloids, including ’B,’ ’Si,’ and ’Ge,’ exhibit unique characteristics, with ’Si’ showcasing a gravity-defying protrusion along the temperature gradient. The pyrometer’s output for fcc (‘Ni,’ ‘Co’) and bcc (‘Hf,’ ‘Mo,’ etc.) primary solidifying phases is synonymous. Recalescence striations in the cooling graph depict a balance between factors favoring and impeding nucleation. In cases of ambiguous pyrometer signals, the implementation of an alternative approach enhances the quality of the temperature vs. time graph. In the future, a fresh contact method design concept in this study would address other pyrometer limitations, such as repeatability concerns and constant emissivity value usage in an entire experiment.

In this study, gamma-alumina (γ-Al₂O₃) particles were used to create a regular and strong network of unsaturated polyester (UP) resins by controlling the targeted free radicals and proportional adsorption of alkyd chains. The composite exhibited 80 %, 42 %, 46.39 %, and 60.31 % increases in the storage modulus, toughness, tensile strength, and flexural strength, respectively, compared with the Neat UP resin. A simultaneous study of the mechanical and physical characteristics and curing kinetics showed that the significant improvement in the mechanical and physical characteristics of the UP/Al 1 composite was due to the increase in the network regularity resulting from the targeted control of free radicals by γ-Al₂O₃ particles and the proportional adsorption of alkyd chains. The significant decrease in the values of K and E_D (Vyazovkin–Sbirrazzuoli diffusion factor (D-factor)) for the UP/Al 1 composite (-22.8 and 27.7 kJ/mol, respectively) compared to that of the Neat UP resin (-9.4, and 40.3 kJ/mol, respectively) confirms a significant increase in network regularity resulting from γ-Al₂O₃ particles.

Mixtures of butyric acid and putrescine form a crystalline amine carboxylate complex in a 2:1 molar ratio irrespective of the initial molar component mixture ratio. This was confirmed through X-ray diffraction, FTIR spectroscopy and elemental analyses. Thermogravimetric analyses proved this complex to be significantly less volatile than the pure constituent components. In thermogravimetric temperature scans, a 90% mass loss of the complex was achieved at 143.4 °C while the same level was achieved at 68.1 °C for both the pure putrescine and butyric acid. A gas permeability parameter Φ_A = M_AD_AP_A/RT (g m^–1s^–1) was developed to quantitatively describe the volatility of the respective components through a stagnant gas layer. This parameter is a function of only material properties and temperature and adequately described the observed mass loss behaviour of pure components as well as the newly formed complex. In a preliminary field trial, mixtures of putrescine and butyric acid were less effective than pure putrescine for attracting flies. This can be attributed to the lower volatility of the putrescine/butyric acid complex and the subsequent suppression of the release rate of the active compounds.

Organic phase change materials (PCMs) suffer from low thermal conductivity and easy leakage, which limit their application in heat storage and thermal management. In this work, porous AlN skeletons were synthesized to solve these problems of paraffin PCM. Using Al powders as raw material, porous AlN skeletons were prepared through the ice-templated method and the direct nitridation reaction. The skeletons were impregnated with paraffin to prepare phase change composites (PCCs). The thermal conductivity of the PCC with 55.6 wt% AlN reaches 9.1 W m⁻¹ K⁻¹ in the axial direction, which is 4550 % of paraffin. This PCC retains a high enthalpy of 105 J g⁻¹ and has good thermal stability. Moreover, the porous AlN skeletons can effectively absorb paraffin so that all PCCs maintain a stable shape. This study provides a simple and efficient method to synthesize porous AlN and to solve the heat conduction and leakage issues of PCMs.

Thermogravimetric curves are measured and modeled to quantify the changes induced by dilute acid or hot water washing on the devolatilization of short- and long-aged potato crop residues. The pretreatments cause more similar behaviors. A six-step devolatilization mechanism for four pseudo-components, previously developed for raw materials, is still applicable. The activation energies remain unvaried whereas small changes in the pre-exponential factors describe the displacement of the devolatilization process at higher temperatures. Instead, the nature and amounts of pseudo-components are significantly modified, especially for dilute acid washing and the short-aged sample. The pseudo-components pectin-hemicellulose and cellulose-starch are enriched in hemicellulose and cellulose, respectively. The corresponding total amounts of volatile generated increase from 19 up to 23–26wt% and from 19–26 up to 37–45wt%, in the same order. The volatile product yields released from the pseudo-component lignin-protein are practically unaltered, but lignin is likely to become largely predominant.

Papers by our group [1] (Grady et al., 2013) and another group [2] (Paul et al. 2012) examined crystallization of random copolymers of ethylene and methacrylic acid after room temperature annealing. Similar conclusions were reached concerning the crystallization process; primary crystals were either unchanged or changed very little after annealing while secondary crystallization occurred over long time scales after annealing. The current work confirms these general conclusions for four different cations (Zn²⁺, Na⁺, Li⁺ and Mg²⁺), with the latter two not studied in either of the previous studies. Even after 6 years of annealing at room temperature, the crystallization rate is constant with logarithmic time, i.e. the material continues to crystallize. The acid copolymer does not crystallize with room temperature annealing, although secondary crystals of the acid copolymer thicken with annealing.

In this review article, the author briefly shares his personal experience of exploring the phenomenon of variable activation energy. Isoconversional methods frequently yield variable activation energy, E_α, which depends on conversion, α. It is emphasized that isoconversional kinetic analysis should not be limited to simply evaluating and reporting the E_α dependencies. Deeper insights into the thermal kinetics are gained by exploiting the intrinsic properties of the E_α dependencies. These properties can be defined as diagnostic, exploratory, predictive, modelistic, and intermediary. Thanks to them one can generate mechanistic hypotheses, test the validity of assumed temperature dependencies of the process rates, forecast the kinetics beyond experimental conditions, determine parameters of kinetic models, and evaluate the preexponential factors and reaction rate constants. The article provides a practical overview of these properties of the E_α dependencies and illustrates their usage by instructive examples.