Mechanism Of Thermal Decomposition Research Articles

Performance and reaction mechanism of pyrite(FeS2)-based catalysts for CO reduction of SO2 to sulfur

In this study, an iron sulfide catalyst (PAC) was prepared to catalyze the reaction of CO reducing SO2 to sulfur to satisfy the high activity and stability of the catalyst, simplify the preparation process, and remove the sulfurization process. The physicochemical properties, reduction activity of the iron sulfide catalyst, and reaction mechanism of PAC-catalyzed CO reduction of SO2 were then systematically investigated. The results indicated that the optimum reaction conditions were a FeS2 proportion of 6 wt%, a reaction temperature of 550 °C, an airspeed of 5000 h−1, and a CO/SO2 molar ratio of 2.6:1. Under these conditions, the SO2 conversion of PAC was stabilized at over 99.5% with a sulfur yield of up to 95.5% within 850 min without deactivating the active component or deteriorating the sulfate. This proves that PAC has very high catalytic activity and stability. The XRD and in situ XRD characterization showed that the reduced PAC contained primarily Fe7S8 in the sulfur phase, while no sulfate and sulfite were found. The reaction mechanism of the PAC-catalyzed CO reduction of SO2 can be divided into the FeS2 thermal decomposition mechanism and the COS intermediate product mechanism.

Premature thermal decomposition behavior of 3,4-dinitrofurazanfuroxan with certain types of nitrogen-rich compounds

3,4-Dinitrofurazanfuroxan (DNTF), as a high-energy-density material, features good thermal stability and wide applications. This study aimed to elucidate the thermal decomposition mechanism of DNTF combined with nitrogen-rich compounds containing N–H. The thermal stabilities of DNTF and its hybrid systems were investigated using differential thermal analysis/thermogravimetry (TG), vacuum stability test, and accelerating rate calorimetry under isothermal, non-isothermal, and adiabatic conditions, respectively. Results showed that the thermal stability and thermal safety of DNTF significantly decreased after combining with nitrogen-rich compounds containing N–H. Calculation results showed that the activation energy of the DNTF hybrid systems was significantly lower than that of DNTF. The TG-IR was used to monitor the generation of fugitive gases during the thermal decomposition of the DNTF/5-aminotetrazole (5-ATZ) hybrid. Moreover, the nitrogen-rich molecules containing N–H interacted extensively with DNTF, and this interaction accelerated the thermal degradation of DNTF.

Pirazol Temelli Yeni Bir Kopolimerin [poli(1,3-difenil-1H-pirazol-5-il metakrilat-ko-stiren)] Termal Bozunma Kinetiği

In the present study, a new copolymer containing pyrazole substituted 1,3-diphenyl-1H-pyrazol-5-yl methacrylate (DPMA) and styrene (St) units, [poly(DPMA-co-St)], was synthesized. Thermal degradation kinetics of the copolymer system was investigated in detail with the thermogravimetric analysis (TGA) technique. An increase in the thermal stability of the copolymer from 252.02 °C to 274.89 °C was observed depending on the change in heating rate (5 °C/min – 20 °C/min). The thermal degradation activation energies of the copolymer were 149.37 kJ/mol and 140.99 kJ/mol, respectively, with the Kissinger and Flynn-Wall-Ozawa methods in the conversion range of 9% - 21%. The thermal degradation mechanism of the copolymer was investigated in the light of different kinetic methods such as Coats-Redfern, Tang, Madhusudanan, Van-Krevelen and Horowitz-Metzger. The results showed that the thermal decomposition mechanism of the copolymer proceeds through a one-dimensional diffusion-type deceleration mechanism, namely the D1 mechanism, at the optimum heating rate of 20 °C/min, especially according to the Coats-Redfern method.

Kinetic Study and Thermal Decomposition Mechanisms of Superthermite–Based Nitrocellulose Nanocomposite

ABSTRACT As ferric oxide is a well-known catalyst, aluminum can act as a high energy dense material. Ferric oxide/aluminum can experience nanothermite reaction with novel synergistic characteristics. On the other hand, nitrocellulose (NC) is the most energetic polymeric matrix. This study reports on the facile development of thermite-based NC nanocomposite. Ferric oxide nanoparticles (NPs) of 5 nm size and aluminum NPs of 80 nm size were dispersed in acetone. Colloidal ferric oxide/aluminum NPs were integrated into NC matrix via anti-solvent technique. Nanothermite particles offered an increase in NC decomposition enthalpy by 38.59% using differential scanning calorimetry (DSC). The apparent activation energy of NC was reduced by 14% and 14.5%, using Friedman and OZAW models, respectively. Activation energy at different conversion extent was evaluated, and decomposition mechanisms have been suggested to be heterogeneous solid phase reaction. The developed NC nanocomposite is considered bespoke material for first-fire ignition systems; where molten solid particle and high decomposition enthalpy are highly appreciated.

Biochar Synthesis from Mineral- and Ash-Rich Waste Biomass, Part 1: Investigation of Thermal Decomposition Mechanism during Slow Pyrolysis.

Synthesizing biochar from mineral- and ash-rich waste biomass (MWB), a by-product of human activities in urban areas, can result in renewable and versatile multi-functional materials, which can also cater to the need of solid waste management. Hybridizing biochar with minerals, silicates, and metals is widely investigated to improve parent functionalities. MWB intrinsically possesses such foreign materials. The pyrolysis of such MWB is kinetically complex and requires detailed investigation. Using TGA-FTIR, this study investigates and compares the kinetics and decomposition mechanism during pyrolysis of three types of MWB: (i) mineral-rich banana peduncle (BP), (ii) ash-rich sewage sludge (SS), and (iii) mineral and ash-rich anaerobic digestate (AD). The results show that the pyrolysis of BP, SS, and AD is exothermic, catalyzed by its mineral content, with heat of pyrolysis 5480, 4066, and 1286 kJ/kg, respectively. The pyrolysis favors char formation kinetics mainly releasing CO2 and H2O. The secondary tar reactions initiate from ≈318 °C (BP), 481 °C (SS), and 376 °C (AD). Moreover, negative apparent activation energies are intrinsic to their kinetics after 313 °C (BP), 448 °C (SS), and 339 °C (AD). The results can support in tailoring and controlling sustainable biochar synthesis from slow pyrolysis of MWB.

Thermal decomposition study of perchlorate-based metal-free molecular perovskite DAP-4 mixed with ammonium perchlorate

The molecular perovskite energetic materials (H2dabco)[NH4(ClO4)3] (DAP-4, H2dabco2+ = 1,4-diazabicyclo[2.2.2]octane-1,4-diium), limits its separate application in explosives duo to the severe negative oxygen balance. Therefore, it is of great significance to study the thermal decomposition performance of DAP-4 in the presence of AP oxidant. In this work, the differential scanning calorimetry-thermogravimetry-mass spectrometry-fourier transform infrared spectroscopy (DSC-TG-MS-FTIR) coupling technique, thermal decomposition kinetics, and in-situ FTIR method were used to analyze the thermal decomposition characteristics, and the variation of condensed phase characteristic groups of DAP-4 and the DAP-4/AP mixtures. The results show that AP has negligible effect on thermal decomposition temperature of DAP-4 but can prolong the total decomposition time of DAP-4 by 5.55 min. In addition, thermal decomposition of AP and DAP-4 in the mixture is independent of each other, and the thermal decomposition mechanism of DAP-4/AP mixtures is more complicated than that of DAP-4 alone. Thermal decomposition of DAP-4/AP mixture firstly experiences decomposition of AP at low temperature, the inside crystal transformation of DAP-4, the H+ transfer, and then cage skeleton collapse-induced redox reaction to generate large amount of heat which can shift forward the high-temperature decomposition peak of AP.

Physicochemical properties and volatile formation mechanism of medium‐chain triacylglycerols during heating

Medium-chain triacylglycerols (MCTs), including caprylic acid (C8), a mixture of caprylic acid and capric acid (C8+C10), and high-MCT coconut oil (HMCO), were heated at 180°C. Their volatile profiles were analyzed to determine the MCT degradation mechanisms. As heating time increased to 10h, secondary oxidation products and acid value of all samples increased continuously. Ketones, alkanes, fatty acid anions, fatty acid esters, and lactones were found in all heated MCTs. 2-Hexanone and heptane were detected in C8 after 2 h of heating, and 2-heptanone, heptanal, methyl octanoate, γ-octalactone, and δ-octalactone were detected after 4 h. For the C8+C10, ketones, alkanes, and aldehydes were first observed. Hydrolysis and decarboxylation seem to occur first for ketone and alkane formation. Cracking and cyclization may occur later for fatty acid esters and lactones in heated MCTs. This result can help to understand thermal decomposition mechanisms of saturated fatty acids like MCTs. PRACTICAL APPLICATION: Medium-chain triacylglycerols (MCTs) have been used in cosmetic and fragrance industries due to their high oxidative stability, relatively high polarity, and smooth textures. In addition, MCTs have gained popularity among consumers for their health beneficial effects. MCTs could be used as major continuous phases for many food ingredients receiving high thermal energy for cooking. The results of this study can provide basic and useful information on the physicochemical properties and thermally decomposed volatile profiles from MCTs, which can help to produce stable processed products with lengthy shelf-lives in the food industry.

Ultra-high temperature reaction mechanism of LiNi0.8Co0.1Mn0.1O2 electrode

Lithium-ion batteries have attracted much attention due to their high energy density and excellent power performance, and are gradually becoming the power source of electric vehicles. However, the safety issues dominated by battery thermal runaway remain a crucial obstacle that hinders lithium-ion batteries to have higher energy density and lower cost. The cathode material plays a critical role in the energy density and thermal runaway of batteries. To address this issue, this study explores the thermal decomposition mechanism of LiNi0.8Co0.1Mn0.1O2 electrode at above 1000 °C. Experimental results indicate that the LiNi0.8Co0.1Mn0.1O2 cathode together with the aluminum current collector generates immense heat at 1000–1200 °C. This reaction is quite like the thermite reaction, according to the data from XRD, XPS, and SEM & EDS tests. However, the oxygen donor comes from the LiNi0.8Co0.1Mn0.1O2 cathode. Full cell experiments confirm the existence of the thermal decomposition reaction that occurs at the LiNi0.8Co0.1Mn0.1O2 electrode at ultra-high temperature. The existence of this reaction at ultra-high temperature explains the heat release mechanism for the thermal runaway of high-energy lithium-ion batteries, extending our vision on the battery failure mechanisms. This finding will benefit better electrode design of lithium-ion batteries with reduced thermal runaway hazard.

Preparation of nanoporous flake molybdenum powder by sol-gel reduction method

Due to the unique microstructure, nanoporous materials, have great potential application in the fields of catalysis, sensing and fabrication of advanced materials. This study mainly focuses on the thermal decomposition mechanism of ammonium paramolybdate and nanoporous flake molybdenum powder fabrication. The decomposition process was clarified and verified. The approximate molar formation enthalpy and some thermodynamic data of ammonium paramolybdate and its related decomposition products under experimental conditions were estimated by enthalpy change values of decomposition reaction in the various stages. Nanoporous flake molybdenum powder was fabricated by sol-gel reduction method at different pH values. The mechanism of transition from ammonium paramolybdate to molybdenum powder was elucidated. The results show that the morphology of products in each stage is hereditary. With the increase of pH value, the reaction was complete and the powder morphology gradually became flake and the shape distribution was uniform and distribution. When the pH is 5, through inert gas passivation treatment, the final molybdenum powder has a uniform particle size of about 65 nm and a specific surface area of about 7.5 m 2 /g. The nanoporous powder with such a special morphology and microstructure has potential prospects in the field of functional materials such as catalysis. • Heredity was found in the mechanism of AHM to Mo transformation. • CA can not only be used as complexing agent, but also control the pH value of the solution. • The morphology of MoO 3 and Mo particles gradually became flakes with the increase of pH value. • Inert gas passivation can reduce and concentrate the PSD and decrease agglomeration. • Nanoporous flaky Mo powder was prepared by sol-gel reduction method with high specific surface area.

Atomistic characterisation of graphite oxidation and thermal decomposition mechanism under isothermal and Non-Isothermal heating scheme

The oxidation of graphene-based material (i.e. graphite, graphene) is a reaction of immense importance owing to its extensive industrial application (i.e. nanocomposites, flame retardants, energy storage). Although immense experimental works were carried out for identifying the thermal degradation and oxidation process of graphene, they generally lack atomistic-level observation of the surface reactions, thermal formation pathways from solid to product volatiles and structural evolutions during oxidation. To analyse the favourable properties of graphene from its carbon-chain molecular structure viewpoint, it is essential to investigate graphene-based materials at an atomic level. This study bridges the missing knowledge by performing quantitative reactive forcefield coupled molecular dynamics simulation (MD-ReaxFF) to determine the oxidation kinetics of graphite under computational characterisation schemes with temperatures ranging from 4000 K to 6000 K. The kinetics parameters (i.e. activation energy) were extracted through proposed numerical characterisation methods and demonstrated good agreement with the thermogravimetric analysis experiments and other literature. Activation energy at 193.84 kJ/mol and 224.26 kJ/mol were extracted under the isothermal scheme by two distinct characterisation methods, achieving an average relative error of 11.3 % and 2.5 % compared to the experiment data, which is 218.60 kJ/mol. In comparison, the non-isothermal simulations yielded 214.53 kJ/mol, with a significant improvement on the average relative error of 1.86 %.

Critical Review of Thermal Decomposition of Per- and Polyfluoroalkyl Substances: Mechanisms and Implications for Thermal Treatment Processes.

Per- and polyfluoroalkyl substances (PFASs) are fluorinated organic chemicals that are concerning due to their environmental persistence and adverse human and ecological effects. Remediation of environmental PFAS contamination and their presence in consumer products have led to the production of solid and liquid waste streams containing high concentrations of PFASs, which require efficient and cost-effective treatment solutions. PFASs are challenging to defluorinate by conventional and advanced destructive treatment processes, and physical separation processes produce waste streams (e.g., membrane concentrate, spent activated carbon) requiring further post-treatment. Incineration and other thermal treatment processes are widely available, but their use in managing PFAS-containing wastes remains poorly understood. Under specific operating conditions, thermal treatment is expected to mineralize PFASs, but the degradation mechanisms and pathways are unknown. In this review, we critically evaluate the thermal decomposition mechanisms, pathways, and byproducts of PFASs that are crucial to the design and operation of thermal treatment processes. We highlight the analytical capabilities and challenges and identify research gaps which limit the current understanding of safely applying thermal treatment to destroy PFASs as a viable end-of-life treatment process.

Thermal Decomposition Mechanism of Molecular Perovskite Energetic Material (C6NH14)(NH4)(ClO4)3(DAP‐4)

AbstractThe recently developed ammonium perchlorate‐based molecular perovskite has been demonstrated to exhibit excellent comprehensive performance as an energetic material. This ABX3‐type molecular perovskite energetic material consists of a high symmetry ternary structure framework stabilized through ionic bonds. In this work, the thermal decomposition mechanism of (C6NH14)(NH4)(ClO4)3 (DAP‐4) was extrapolated by analyzing its thermal decomposition characteristics, gas products, kinetic parameters, and condensed phase change results along with temperature‐varying, with the help of DSC‐TG‐MS‐FTIR and in‐situ FTIR experiment. The results show that a rapid reaction occurs once the decomposition of DAP‐4 starts at 383.7 °C, with the maximum thermal weight loss rate reaches 97.4 %. By using Kissinger's and Ozawa's method, the calculated activation energy of thermal decomposition of DAP‐4 was estimated to be 124.3 kJ/mol and 128.6 kJ/mol, respectively, demonstrating good reliability of our results. The gas products during the thermal decomposition were found mainly include NH3, H2O, HNCO, HCN, CO, HCl, and CO2. The decomposition process of DAP‐4 contains three stages. The first stage involves crystal form changes and H+ transfer of DPA‐4, followed by the collapse of the cage skeleton in the second stage. The third stage mainly involves a rapid redox reaction at high temperatures to generate great heat.

A ReaxFF MD based effect investigation of diamino curing agents in the initial thermo-oxidative pyrolysis of epoxy resins

To explore the influence of curing agents on the oxygen participated thermal decomposition mechanisms of the epoxy resin, the epoxy-O2 models, cured by 3,3-DDS, 3,3-SDA, 3,3-SSDDS, and 4,4-DDS, respectively, were first established. The ReaxFF-based MD simulation is applied to track the initial reactions of the pyrolysis. The results show that the O2 is much easier to transfer in the crosslinked epoxy matrixes at the spark temperature. The epoxy rings at the end of epoxy chains are likely to be attacked by the oxygen under high temperature, releasing the tens of CH2O, as the dominant product type. More than 65 wt% large-size molecules remained in the systems, indicating a nice thermal resistance. Based on the DFT calculation, the 4,4-DDS-type epoxy chain shows the highest reactivity with oxygen, which the lowest HOMO energy. 4,4-DDS is going to protect the carbon backbones of epoxy by scarifying, at the initial pyrolysis.

Thermal stability and decomposition mechanism of synthetic covellite samples

Thermal stability and decomposition mechanism of synthetic covellite samples

Molecular dynamics simulation of initial thermal decomposition mechanism of DNTF.

In order to understand the thermal decomposition characteristics of 3,4-Bis(3-nitrofurazan-4-yl)furoxan (DNTF), the thermal decomposition reaction of DNTF at 300-4000K temperature programmed and constant temperatures of 2000K, 2500K, 3000K, 3500K, and 4000K was simulated by ab initio computational molecular dynamics method. The thermal decomposition mechanism of DNTF at different temperatures was analyzed from the aspects of product evolution, cluster, potential energy curve, and reaction path. The analysis of products shows that the initial small molecular products are NO, NO2, CO, CO2, and N2, and the final small molecular products are CO2 and N2. In the early stage, the ring-opening reaction of furoxan in DNTF structure is the main trigger reaction, and the C-C bond is broken at the initial stage of reaction. The carbon chain structure produced by decomposition forms various cluster structures in the form of C-N bond. In addition, it was found that temperature significantly affects the decomposition rate of DNTF, but does not change its initial decomposition path.

Probing the Reaction Mechanisms of 3,5-Difluoro-2,4,6-Trinitroanisole (DFTNAN) through a Comparative Study with Trinitroanisole (TNAN).

To probe the thermal decomposition mechanisms of a novel fluorinated low-melting-point explosive 3,5-difluoro-2,4,6-trinitroanisole (DFTNAN), a comparative study with trinitroanisole (TNAN) was performed under different heating conditions. The thermal decomposition processes and initial reactions were monitored by DSC-TG-FTIR-MS and T-jump-PyGC-MS coupling analyses, respectively. The results show that fluorine decreased the thermal stability of the molecular structure, and the trigger bond was transferred from the ortho-nitro group of the ether to the para-nitro group. The possible reaction pathway of DFTNAN after the initial bond breakage is the rupture of the dissociative nitro group with massive heat release, which induces the ring opening of benzene. Major side reactions include the generation of polycyclic compounds and fluorine atom migration. Fluorine affects the thermal stability and changes the reaction pathway, and fluorinated products appear in the form of fluorocarbons due to the high stability of the C-F bond.

Computational investigation of thermal decomposition mechanism of 5-nitro-5-R-1,3-dioxane compounds

This paper features the results of the computational study of thermal decomposition reaction of 5-nitro-5-R-1,3-dioxane compounds, with R = H, Br, and CH3. Computational calculations were performed with M06-2X, MPWB1K, PBE0 and ωB97X-D functionals, and 6–311 + G(d,p) basis set in gas phase and also in solution with DMSO, at different temperatures. The kinetic and thermodynamic data obtained indicate a favoring of the reaction when the molecule presents substituent groups in position 5 and when carried out in DMSO, the stability of the molecules in their energetic components was discussed, too. For R = H two different reaction mechanisms were proposed and studied. Wiberg bond indices were obtained for the reactions studied and the results were examined in terms of bond formation and bond breaking progress as well.

Meso-Simulation Study on Thermal Decomposition Mechanism of Solid Propellant

From the microscopic point of view, combining experiment with simulation, the thermal decomposition mechanism of solid propellant was discussed. At first, the thermo gravimetric curves of HTPB film and propellant were studied based on DSC-TG thermal analysis experiment technology. The thermal decomposition process of propellant was simulated by establishing the physical model of meso-structure cell. The results show that the simulation is consistent with the experimental trend. The above research is helpful to further understand the thermal decomposition mechanism of propellant.

Material-scale flammability characteristics of epoxy-based coating systems

Flammability of intumescent coatings at the materials-scale is “expected” to have an impact on their fire resistance offered to the steel member. However, to what extent and at what stage during the exposure to an imposed fire curve in a furnace are not thoroughly established. The role of different functionality of the flame-retardant additives in this process is also not clear despite a thorough understanding of their thermal decomposition mechanisms. In an effort to better understand some of these aspects, in this work, model systems based on different flame-retardant additives in epoxy are chosen to cover various strategies (like intumescent, radical quenching, and endothermic behavior) that are typically employed to reduce the flammability of a coating system. The flame-retardant additives chosen are ammonium polyphosphate, tetrabromobisphenol-A, 9,10-dihydro-9-oxa-10-phosphaphenanthrene oxide, and aluminum trihydroxide. The effects of flame-retardant additives on the curing, thermal decomposition, and flammability of epoxy resin are investigated. Reactive flame-retardant additives, in particular, are found to reduce the enthalpy associated with curing of epoxy by more than 45%. However, as the amount of hardener incorporated in these formulations is not controlled despite the presence of reactive flame-retardant additives, this had a negative effect on the thermal decomposition behavior of the epoxy/flame-retardant formulations, and consequently on the calculated decomposition activation energies. Heating rate seems to be a dominating parameter influencing the flammability of the formulations. Peak heat release rate values, irrespective of the formulation, increased by more than 1382%–1970% by changing the heating rate in a pyrolysis flow combustion calorimeter from 6°C/min to 100°C/min. As the flammable volatiles released per unit time are higher at high heating rates, ignition and subsequent flaming of the coating occurred in the furnace tests, where a cellulosic fire curve was simulated. This has significantly influenced the fire resistance times.

Synthesis, characterization, crystal structures and thermochemical properties of five lanthanide complexes with mononuclear and binuclear structures

Five new lanthanide complexes were synthesized by two different experimental methods: two mononuclear complexes and three binuclear complexes. Their chemical formula is: [Gd(2-Cl-4-FBA)3(terpy)H2O]1.5H2O(1); [Dy(2-Cl-4-FBA)3(terpy)H2O]·0.5H2O(2)) (2-Cl-4-FBA = 2-chloro- 4-fluorobenzoate,terpy = 2,2′:6′,2″-terpyridine); [Ln(3,4-DFBA)3(5,5′-DM-2,2′-bipy)(H2O)]2(Ln = Pr(3),Er(4);[Ln(3,4-DFBA)3(5,5′-DM-2,2′-bipy)]2(Ln = Ho(5)) (3,4-DFBA = 3, 4-difluorobenzoate,5,5′-DM-2,2′-bipy = 5,5′-dimethyl-2,2′-bipyridine). A series of characterization and properties of the complexes were studied, such as elemental analysis, single crystal X-ray diffraction, thermogravimetric analysis, fluorescence properties and so on. The coordination number of complexes 1–2 is 9, showing a muffin geometry. The results show that complex 1–5 crystallized in the triclinic system and space group Pī. Complexes 1 and 2 are isostructural except for the number of free water molecules. Complexes 3–5 are binuclear molecules with different structures. Although the structures of the five complexes are different, they all form one and two-dimensional supramolecular structures along a chain and a plane. The thermal decomposition mechanism of complexes 1–5 was studied by synchronous thermal analyzer infrared spectroscopy (TG/DSC-FTIR). The results show that the coordination water, neutral ligand and acidic ligand are lost in turn when the complex undergoes thermal decomposition. And the three-dimensional infrared images of gas escaping during the thermogravimetric process were analyzed. In addition, the solid state fluorescence spectra of complex 2 was measured and the results showed that the characteristic fluorescence of Dy(III) ion was emitted.