Search Results (439)

In this work, the catalytic effect of a mechanochemically synthesized Co–Fe metal–organic framework (Co–Fe-MOF) on the thermal decomposition behavior of composite ammonium perchlorate–aluminum (AP-Al) systems was studied. The structural and morphological properties of the synthesized catalyst were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The results confirmed the formation of a highly dispersed Co–Fe-MOF structure with a heterogeneous surface morphology and uniformly distributed active regions, as observed by SEM. The thermal decomposition behavior of the composites based on AP was studied using differential scanning calorimetry (DSC) at different heating rates. The addition of Co–Fe-MOF significantly affected the thermal decomposition process, moving the main exothermic decomposition step towards lower temperatures. At 5 wt.% of catalyst, the decomposition temperature decreased from 438–467 °C to 358–398 °C. The kinetic parameters were evaluated using the Kissinger and Ozawa–Flynn–Wall methods. The activation energy decreased from around 191–200 kJ·mol⁻¹ for pure AP and 184–194 kJ·mol⁻¹ for the AP-Al system to 95–109 kJ·mol⁻¹ after the introduction of 5 wt.% of Co-Fe-MOF. The observed catalytic activity is associated with accelerated electron transfer processes involving the redox couples Co³⁺/Co²⁺ and Fe³⁺/Fe²⁺, which favor the decomposition of AP and the oxidation of aluminum. The results demonstrate that the mechanochemically synthesized Co–Fe-MOF is an effective catalyst to improve the thermokinetic performance of AP-based energetic systems. Full article

This study investigates the effect of controlled acid demineralization of coal shale from Shubarkol Komir JSC using HCl solutions with concentrations of 9–37% by mass on its structural characteristics, the kinetics of thermal decomposition, and the ability to concentrate rare and dispersed trace elements in the solid residue from the hydrodemetallization of the heavy fraction of coal tar. Analysis of IR spectroscopy, TG/DTG and isoconversional kinetics showed that acid treatment leads to the removal of carbonate and partially iron-containing phases while maintaining the aluminosilicate framework, increasing the structural uniformity of the matrix and moving to a more ordered thermal decomposition mechanism. The activation energy in the range of α = 0.1–0.7 is 83–87 kJ/mol for all modified samples, increasing to 96.20 kJ/mol at α = 0.9 for CS100. It has been established that the ability of coal shale to concentrate rare and dispersed trace elements in the solid residue of hydrodemetallization changes non-monotonically: the total content of trace elements reaches a maximum of 1452.19 g/t with moderate acid treatment (CS50) and sharply decreases to 137.85 g/t with deep demineralization (CS100). It has been shown that the degree of acid treatment acts as a controlled parameter that allows for purposefully regulating the ability of coal shale to concentrate rare and dispersed trace elements in the process of hydrodemetallization of heavy hydrocarbon raw materials. Full article

High-energy insensitive energetic materials are currently a research focus. Octogen (HMX) is one of the best-performing nitramine explosives, but its poor crystal morphology causes high mechanical sensitivity, limiting its application. This study proposed a method combining spheroidization, nanosizing, and coating desensitization. Nano-SiO₂ and TiO₂ were used to modify methyl methacrylate (MMA), and HMX/PMMA composite energetic microspheres were successfully prepared with the assistance of an ultraviolet (UV) lamp for catalytic polymerization. Molecular dynamics simulations determined the optimal particle ratios, and the effects of modifier content on morphology, crystal form, thermal stability, mechanical properties, and static mechanical properties were experimentally investigated. The prepared HMX/PMMA/modifier microspheres exhibited uniform size, dense structure, excellent performance, and ideal coating. Thermal decomposition kinetics showed that the activation energy of HMX/PMMA/SiO₂ (0.75 wt% SiO₂) increased by 79.86 kJ/mol and 27.55 kJ/mol compared with raw HMX and HMX/PMMA, respectively. Its impact sensitivity was 3.6 times that of raw HMX, and its friction sensitivity was twice that of raw HMX. Static mechanical analysis revealed that the compressive strength of HMX/PMMA/SiO₂ (0.75 wt% SiO₂) and HMX/PMMA/TiO₂ (0.5 wt% TiO₂) microspheres increased by 7.3 MPa and 6.1 MPa, respectively, over HMX/PMMA, indicating significant improvement. Overall, HMX/PMMA/SiO₂ and HMX/PMMA/TiO₂ microspheres prepared by photoinitiated emulsion polymerization exhibited excellent thermal stability and mechanical properties. Full article

Background/Objectives: The thermal stability and degradation kinetics of β-lactam antibiotics are critical for understanding their behavior under processing and storage conditions. This study investigates the thermal decomposition of meropenem, ceftriaxone sodium, and cefazolin sodium in order to evaluate their kinetic parameters, assess the presence of the compensation effect, and determine isokinetic temperatures. Methods: Thermal analysis was performed using simultaneous TG/DTG/DSC measurements. Non-isothermal degradation experiments were conducted at four different heating rates. Kinetic parameters were evaluated using two isoconversional methods (Friedman and Flynn–Wall–Ozawa) and ASTM E698-based approach to obtain average activation energies. To determine the pre-exponential factor (A), the Coats–Redfern method was applied using multiple kinetic models. The resulting lnA—E_a pairs obtained from different models were used to construct lnA = f(E_a) correlations, enabling the evaluation of the compensation effect and calculation of isokinetic temperatures (T_iso). Results: All three β-lactam antibiotics exhibited consistent kinetic behavior across the applied models, with the F3 reaction model providing the best fit based on R² values. A clear linear relationship between lnA and E_a was observed, confirming the presence of an enthalpy–entropy compensation effect. However, significant differences in isokinetic temperatures were obtained indicating variability in kinetic compensation behavior among the studied compounds. Conclusions: The thermal degradation of the investigated β-lactam antibiotics follows a consistent kinetic framework, supported by isoconversional and model-fitting approaches. Nevertheless, the absence of a unique isokinetic temperature suggests differences in transition-state stabilization and enthalpy–entropy balance, likely driven by structural variations among the compounds. Full article

Coal gasification fine ash (CGFA) is a carbon–mineral composite solid waste whose valorization is severely hindered by poor interfacial compatibility with organic media due to its highly polar surface. Here, we report a surface alkylation strategy using haloalkanes with variable chain lengths to systematically tune the surface chemistry and thermo-oxidative behavior of CGFA. Comprehensive spectroscopic characterizations (XPS, FTIR, and ¹³C NMR) confirm successful grafting of alkyl chains, which increases aliphatic C-H content from 24.8% to 43.9% while reducing polar carboxyl groups from 7.9% to 1.6%, with the mineral framework remaining intact. Thermogravimetric analysis reveals that alkylation lowers the onset decomposition temperature from 358 °C to 295 °C and enhances the maximum mass-loss rate. Kinetic analysis shows that grafted alkyl chains act as low-energy initiation sites, reducing the initial activation energy to 95 kJ/mol, while the later-stage oxidation becomes diffusion-limited. Notably, long straight-chain alkylation achieves the best performance, whereas branched chains are less effective due to steric hindrance and pore blockage. This work establishes a clear chain-length-dependent structure–thermal response relationship, positioning alkylated CGFA as a designable precursor for functional carbon materials, intelligent char-forming agents, and tunable components for energy or responsive material systems. Full article

Given the depletion of conventional oil and gas resources, oil shale represents a promising alternative source of hydrocarbons that can be recovered through pyrolysis. This study examines the thermal decomposition of raw oil shale from the Tarfaya deposit and its decarbonized concentrate, studied by thermogravimetric analysis at different heating rates (5, 10, 20 and 40 °C/min). Pretreatment with acetic acid enabled the selective removal of calcite, confirmed by elemental, XRF, and XRD analyses, which revealed a relative enrichment in silica and dolomite in the oil shale concentrate. Pyrolysis of the raw shale occurs primarily between 300 and 500 °C, with a conversion rate of approximately 30%. In contrast, for the oil shale concentrate, the pyrolysis process begins at a relatively low temperature, within a wider temperature range (260–520 °C). Kinetic analysis based on Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS) methods shows that at a conversion rate of 60%, the activation energy achieves 14.09 kJ/mol and 10.78 kJ/mol, respectively. The results indicate that the selective removal of calcite by acetic acid treatment facilitates kerogen pyrolysis by reducing mineral–organic interactions. Indeed, calcite dilutes the reactive organic fraction and can act as a physical barrier limiting heat and mass transfer within the oil shale. Its removal improves, on the one hand, the accessibility of kerogen to thermal cracking and promotes its decomposition, and on the other hand, reduces the amount of residue after pyrolysis. In addition, the kinetic analysis based on Criado master curves reveals changes in the reaction mechanism after decarbonation treatment depending on the heating rate (β). A shift from a two-dimensional Avrami–Erofeev model (A2) to a three-dimensional model (A3) was observed at a low heating rate (β = 5 °C/min), suggesting a change in nucleation and growth dynamics during kerogen decomposition. At high heating rates (10, 20 and 40 °C/min), the thermal decomposition of kerogen combines several reaction mechanisms depending on the temperature range considered. Full article

The study presents a comprehensive report on the kinetic and thermodynamic parameters of carbide crystallization in CrMnFeCoNi, CrMnFeCoNiV_0.5, and CrMnFeCoNiMo_0.5 HEAs. This study considers only carbon resulting from the decomposition of the process control agent, which diffuses and becomes trapped within the HEA structure (0.79–0.91 wt.% C). The crystallization and growth of the carbides were monitored through thermal analysis and thermo-XRD at different temperatures. The activation energy was calculated using the Kissinger and Flynn/Wall/Ozawa methods, and the crystallization kinetics were evaluated using the Avrami–Erofeev model. The results of the XRD analyses and DTA curves of the CrMnFeCoNi, CrMnFeCoNiV_0.5, and CrMnFeCoNiMo_0.5 HEAs showed the following nanocarbide crystallization sequences: M₇C₃→MC→M₃C₂, M₂₃C₆, and MC→M₆C, respectively. The transitions observed in the DTA curves were associated with M₇C₃, M₂₃C₆, and MC phases with activation energies (E_a) of 238–251, 188–203, and 326–341 kJ/mol, respectively. Furthermore, kinetic analyses indicate that the crystallization of M_xC_y-type carbides occurs via nucleation. Full article

We present a rapid screening method to assess the aging of diesel blends containing fatty acid methyl esters (FAME) produced from two contrasting feedstocks: refined sunflower oil (SFME) and used cooking oil (UCO). Diesel–FAME blends at several biocomponent concentrations (0–50% v/v) were subjected to accelerated thermal aging at 90, 120 and 150 °C and monitored by peroxide value (PV), anisidine value (AV) and acid value measurements. Kinetic analysis of PV and AV trends, supported by Arrhenius plots, reveals feedstock-dependent oxidation pathways: UCO-FAME exhibits higher initial PV and AV and a faster progression to secondary oxidation products, whereas SFME accumulates hydroperoxides more at moderate temperatures and decomposes more slowly. The method distinguishes formation-dominated and decomposition-dominated regimes, quantifies apparent rate constants as functions of temperature and FAME content, and identifies an inflection in apparent activation behavior for UCO blends near 120 °C. The novelty of this work lies in the direct comparison of blend oxidation kinetics for refined versus waste-derived FAME and in proposing a practical, rapid protocol for identifying unstable feedstocks to support improved quality control of diesel–FAME blends. Full article

To elucidate the physicochemical mechanisms underlying the violent explosion triggered by nylon (PA) jet penetration into explosive reactive armor, the thermal decomposition behavior of RDX and the influence mechanism of PA on its thermal reaction were studied by reaction molecular dynamics simulation and quantum chemical calculation, which were compared with experimental research. The study reveals that the decomposition of RDX is primarily initiated through pathways such as N–NO₂ homolysis, HONO elimination, and concerted ring-opening. The addition of PA reduces the energy barrier for N–N bond homolysis and provides hydrogen atoms to initiate HONO elimination via a heterogeneous pathway with a lower energy barrier, thereby promoting the initial decomposition of RDX. The free radicals produced by the decomposition of PA and RDX participate in a synergistic reaction, efficiently yielding stable products and significantly altering the distribution of intermediate species. The introduction of PA lowers the activation energy barrier for RDX decomposition and supplies hydrocarbon fragments as fuel for the reaction, facilitating rapid decomposition and initiation. This work clarifies the dual mechanism by which PA promotes RDX detonation from the perspective of microscopic reaction kinetics, providing theoretical insights for understanding and modulating the response of explosives under complex impact conditions. Full article

Fly ash (FA) from Zhundong coal combustion features high alkali/calcium content and a low Si/Al ratio, limiting its potential for conventional utilization. To enable its high-value application, six size-fractionated samples (FA1–FA6) were characterized via laser particle sizing, SEM-EDS, XRF, XRD, FT-IR, and TGA, to elucidate particle-size-dependent physicochemical and thermal properties. The results show that the size distribution centered at 48–150 μm (~71%). With decreasing size, the morphology shifted from irregular aggregates to smooth vitreous spheres. The chemical composition exhibits significant elemental segregation; the SiO₂ content decreases with decreasing particle size, while active components such as CaO, MgO, and Fe₂O₃ are significantly enriched in fine particles. The thermal conversion behavior is regulated by particle size: The combustion reaction under an air atmosphere conforms to the second-order kinetic model, with the activation energy decreasing from 192.73 kJ·mol⁻¹ for coarse particles (>150 μm) to 63.53 kJ·mol⁻¹ for fine particles (<43 μm); under a nitrogen atmosphere, the weight loss originates from the removal of structural water and the decomposition of carbonates, and fine particles exhibit a higher pyrolysis activation energy (504.15 kJ·mol⁻¹) in the high-temperature stage (850–940 °C) due to being rich in high-crystallinity carbonates. The results of this study elucidate the structure–activity relationship of “particle size-composition-activity” for Zhundong coal fly ash and propose a graded utilization scheme where coarse fractions are suitable for low-grade building fillers, while fine fractions can be used as feedstocks for coal pyrolysis catalysts and functional adsorbents, providing a theoretical basis for its targeted resource utilization based on particle size fractionation. Full article

This study presents a definitive framework for Cocos nucifera (coconut) shell valorization, integrating high-resolution thermogravimetry with advanced machine learning. Physicochemical analysis confirms a high-energy feedstock (45.7% carbon, 71.5% volatiles), with SEM/XEDS and FTIR revealing heterogeneous, lignocellulosic, catalytic-rich structural matrix. TG/DTG analysis identified distinct degradation windows: hemicellulose (135–395 °C), cellulose (270–430 °C), and protracted lignin decomposition (275–675 °C). Kinetic modeling indicates that pyrolysis follows a third-order (F3) continuous degradation mechanism across the studied range, supported by high correlation coefficients ($R^2$ = 0.93–0.96). The mean kinetic and thermodynamic parameters—specifically an activation energy of 165 kJ·mol⁻¹ (calculated across the 10–60 wt% conversion range during hemicellulose and cellulose pyrolysis), a positive activation enthalpy (159 kJ·mol⁻¹), and a Gibbs free energy of activation (155 kJ·mol⁻¹)—suggest that the thermochemical conversion of coconut shell is an endothermic, non-spontaneous process with moderate energy requirements. Furthermore, the integration of kNN machine learning yielded near-perfect predictive metrics ($R^2\approx 1.000$) using optimized hyperparameters ($k=85$ for TG, $k=100$ for DTG, and $k=50$ for conversion). These findings suggest that coconut shells can be efficiently valorized as a high-energy feedstock, with data enabling reliable and optimized prediction of thermal degradation to minimize experimental waste. Full article

This study investigates the kinetics of lipid oxidation and the antioxidant activity of lycopene in tomato pomace using a combined computational–experimental approach. A reaction mechanism describing initiation, propagation, hydroperoxide formation, and radical scavenging was implemented in ANSYS Chemkin 2025 R2 and simulated under controlled conditions at 50, 70, and 90 °C for up to 12 h. The model was validated using experimental measurements of linoleic acid, lycopene, and hexanal obtained from thermally treated tomato pomace. The results showed a strong temperature dependence of oxidation processes, with minimal changes at 50 °C and a transition to a propagation-dominated regime at 90 °C. Linoleic acid degradation reached 18.17% after 12 h at 90 °C, accompanied by a significant increase in hexanal formation, while lycopene loss remained below 5%. The model accurately reproduced experimental trends, with high correlation coefficients (R² = 0.9761 for linoleic acid, 0.9899 for lycopene, and 0.9982 for hexanal). Hydroperoxides were identified as key intermediates, accumulating prior to decomposition into volatile products. The results demonstrate that the proposed kinetic model provides a reliable tool for predicting lipid oxidation behavior in tomato by-products and highlights the critical influence of temperature on oxidative stability. Mean percentage errors ranged from 10.03% (hexanal) to 23.52% (linoleic acid), consistent with the complexity of the matrix. Full article

Environmental fires pose a serious threat to energy security, ecosystems and public safety, whilst traditional halogenated flame retardants suffer from limitations such as high environmental residue risks and insufficient flame-retardant efficacy. In this study, sodium alginate (SA) was utilised as the matrix, with the incorporation of ammonium polyphosphate (APP) and phytic acid (PA), in conjunction with SiO₂-APTES surface modification, to prepare nitrogen–phosphorus synergistic bio-based flame-retardant gels. The present study systematically investigated the influence of the N/P molar ratio on the gelation kinetics, rheological behaviour, microstructure and flame-retardant performance of the gel. The study revealed a nitrogen–phosphorus coupled gas–solid two-phase synergistic flame-retardant mechanism. The results indicate that at an N/P ratio of 1/4, the gel forms a stable dual-network structure comprising ionic cross-links and Si–O–P covalent bonds. In the gas phase, the thermal decomposition of APP releases inert NH₃, which dilutes oxygen and quenches gas-phase radicals (·OH, ·H). In the condensed phase, the phosphate groups of PA-catalysed SA form Si–O–P covalent bonds with SiO₂ under the mediation of APTES, creating a dense, insulating char layer. In comparison with the control group (N/P = 0/0), the optimal gel sample (N/P = 1/4) demonstrated a 33% increase in shear stress, a 10% reduction in the peak heat release rate (HRR), a 75% decrease in total smoke production (TSP), and a 150% increase in char layer thickness after combustion, while maintaining adequate mechanical strength, thermal stability, and environmental friendliness. This work provides novel insights and strategies for the development of green, highly efficient flame-retardant materials for environmental fire prevention and control. Full article

Mechanically activated pyrite plays an important role in gold extraction and coal utilization, but its reactivity may change markedly during storage. This study investigates how air deactivation during storage affects the crystal structure and subsequent thermal decomposition behavior of mechanically activated pyrite. Pyrite was mechanically activated and then stored in air for 0, 7 and 180 days. X-ray diffraction (XRD) combined with Rietveld refinement was used to characterize variations in lattice parameters and unit-cell-related structural features, while non-isothermal thermogravimetric–differential scanning calorimetry (TG-DSC) under an argon atmosphere, together with the Flynn–Wall–Ozawa (FWO) method, was applied to evaluate the decomposition kinetics. Air deactivation induced a non-monotonic evolution of lattice parameters and unit-cell volume, which is attributed to combined effects of residual stress relaxation and air-induced surface-related modification during storage. All samples exhibited two mass-loss stages during heating, reflecting stepwise thermal decomposition, and their decomposition behavior varied systematically with deactivation time. The apparent activation energy depended on both conversion fraction and deactivation degree, and nucleation-and-growth-type mechanisms were found to dominate the decomposition process, with their relative contributions evolving with storage time. These results clarify how prior air-deactivation history influences the structural evolution and subsequent thermal decomposition behavior of mechanically activated pyrite and provide useful insight for its storage and utilization in related processes. Full article

As a key type of precursor material in the nuclear fuel cycle process, plutonium oxalate has long played a critical role in the purification and conversion of plutonium. Its crystallization behavior directly affects the subsequent production process and properties of plutonium oxide. This review systematically summarizes the research progress of plutonium oxalate crystals in thermodynamics, crystallization kinetics, and crystal morphology. It introduces the structural characteristics of plutonium oxalate crystals, their solubility in nitric acid-oxalic acid mixed systems, and the thermodynamic properties such as the redox stability of plutonium oxalate crystals of different valence states. It also summarizes the nucleation, growth, and coprecipitation kinetics of plutonium oxalate crystals. The diversity of plutonium oxalate crystal morphologies and their influence on subsequent thermal decomposition are discussed. Full article