Internal Standard-Assisted Ab Initio MD Simulation for Comparative Thermal Stability and Decomposition mechanisms of Energetic Materials

This work presents the synthesis of mono- and dicationic ionic liquids (ILs) that combine the cations 1-butyl-3-methylimidazolium ([C4MIM]+), 1-decyl-3-methylimidazolium ([C10MIM]+), 1,4-bis(3-methylimidazolium-1-yl)butane ([C4(MIM)2]2+), and 1,10-bis(3-methylimidazolium-1-yl)decane ([C10(MIM)2]2+) with the anion dodecanoate ([C11COO]-), along with a study into their thermal stability and mechanism for thermal decomposition. Thermal stability was investigated using the Kissinger-Akahira-Sunose (KAS) isoconversional method to determine the isoconversional activation energies (E α ) and compensation effect to calculate the pre-exponential factor (ln A α ). The results showed that there was no significant difference in the thermal stabilities between the ILs, with all compounds being thermally stable up to 450 K. The thermal decomposition mechanism was analyzed using nuclear magnetic resonance (NMR), electrospray ionization mass spectrometry (ESI-MS), and thermogravimetric analysis coupled with Fourier-transform infrared spectroscopy (TGA-FTIR). The main decomposition pathways were nucleophilic substitution at the lateral or spacer chain and the methyl group.

Experimental and theoretical studies on the thermal stability and decomposition mechanism of HFO-1336mzz(Z) with POE lubricant

In the present study, a series of aliphatic polyesters based on succinic acid and several diols with 2, 4, 6, 8, and 10 methylene groups, namely poly(ethylene succinate) (PESu), poly(butylene succinate) (PBSu), poly(hexylene succinate) (PHSu), poly(octylene succinate) (POSu), and poly(decylene succinate) (PDeSu), were prepared via a two-stage melt polycondensation method. All polyesters were semicrystalline materials with Tm ranging from 64.2 to 117.8 °C, while their Tg values were progressively decreasing by increasing the methylene group number in the used diols. Thermogravimetric analysis (TGA) revealed that the synthesized poly(alkylene succinate)s present high thermal stability with maximum decomposition rates at temperatures 420–430 °C. The thermal decomposition mechanism was also evaluated with the aid of Pyrolysis–Gas chromatography/Mass spectrometry (Py–GC/MS), proving that all the studied polyesters decompose via a similar pathway, with degradation taking place mainly via β–hydrogen bond scission and less extensive with homolytic scission.

TG/DTG-DSC and high temperature in-situ XRD analysis of natural thaumasite

Thermal decomposition mechanism and kinetics of gemcitabine

Thermal stability and thermal decomposition mechanism of octamethyltrisiloxane (MDM): Combined experiment, ReaxFF-MD and DFT study

Thermal stability and decomposition mechanism of dicationic imidazolium-based ionic liquids with carboxylate anions

A study on the preparation of Cr2O3 from (NH4)2Cr2O7 based on thermal decomposition including the thermal decomposition temperature effect, mechanism and kinetics

Thermal decomposition kinetics and mechanisms of long alkyl chain ionic liquids with carboxylate anions

Recently, LiNi0.5Mn1.5O4, denoted as LNMO, has attracted a lot of research attention as a promising high-energy density cathode material based on its higher operating voltage at ~4.7V vs. Li+/Li compared to the parent material, LiMn2O4.[1] On the other hand, the poor cycle and calendar life of LNMO, especially at elevated temperatures, still remain one of the major challenges in its widespread usage. Extensive research has addressed some key factors determining its capacity and rate performance, such as cation ordering, route of synthesis, stoichiometry, heat treatment, particle morphology, particle size, transition metal substitution, and the Li-insertion/de-insertion mechanism of this material.[2-7] Unlike the widely studied electrochemical performance and reaction mechanism, the thermal stability of LNMO, which could greatly impact the safety of LIBs, has received little attention. This lack of interest probably could be attributed to the assumption that the excellent thermal stability of the delithiated LNMO can be naturally inherited from its parent material LiMn2O4, for which only a subtle structural rearrangement takes place without the oxygen release up to 500 °C in the fully delithiated state.[8] Therefore, LixMn2O4 has been regarded as a thermally safer cathode material than layered materials, such as LixCoO2, LixNi0.8Co0.15Al0.05O2 and LixNi1/3Co1/3Mn1/3O2. All of these structurally layered materials undergo a series of phase transitions with accompanied oxygen release below 300°C in their charged states. However, for LNMO, what was overlooked at is that when a quarter of the Mn is replaced by Ni, the thermodynamics of the material inevitably changes yielding a very different thermal stability than its parent LiMn2O4. Unfortunately, little research has been published on the thermal stability of LNMO materials and their doped derivatives; the research focus has been on their reactivity with the electrolyte using calorimetric measurements thus far.[9-11] There are very few studies correlating thermal stability neither with structural differences (ordered or disordered) nor with oxygen-releasing structure changes during heating for LNMO. To further understand the thermal stability of both ordered (o-) and disordered (d-) LNMO in the delithiated state, we applied a combination of in situ synchrotron time-resolved x-ray diffraction (TR-XRD) coupled with mass spectroscopy (MS) and in situ x-ray absorption spectroscopy (XAS) during heating. This combination allowed us to simultaneously monitor the phase transformations (by TR-XRD) and the accompanying gas evolution (e.g., oxygen by MS) as well as the local- and electronic-structural changes with an elemental selective capability (by XAS) during thermal decomposition. Through this systematic investigation, the mechanism of thermal decomposition and the oxygen release behavior of (electrochemically) delithiated d- and o-LNMO during heating have been explored in terms of changes in crystal structures, chemical compositions and valance of the transition metals. We also investigated the impact of doping (e.g., Zn and Fe) on the thermal- and electrochemical cycling- stability of LNMO materials using the above in situ x-ray tools. Some of preliminary results regarding doped LNMO materials will also be presented in the meeting. Acknowledgement This work was supported by the U.S. Department of Energy, the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies under Contract No. DE-AC02-98CH10886. Use of the National Synchrotron Light Source was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-98CH10886.

We report the comparative study of photoacoustic (PA) fingerprint spectra, thermal decomposition, and stability mechanism of some phenyl and bis series energetic compounds named 1-(2-methoxy,-3,5-dinitrophenyl)-1H-1,2,3-triazole ( S5), 1-(3-methoxy, 2, 6 dinitrophenyl) 1H-1, 2, 3 triazole ( S10), 1-(4-nitrophenyl)-1H-1,2,3-triazole ( S8), and 2,6-bis ((4-(nitromethyl)-1H-1,2,3-triazol-1-yl)methyl) pyridine ( S9). Fourth harmonic wavelength, i.e., 266 nm of pulse duration 7 ns and 10 Hz repetition rate obtained from Q-switched Nd: YAG laser, was used to record the thermal PA spectra of these compounds under controlled pyrolysis condition in the range of 30-350 ℃. The PA fingerprint spectra are produced due to entire molecule vapor along with principal functional byproduct NO2 molecule. NO2 molecule is a major gas released during thermal decomposition due to weakest nature of C-NO2 bond. Further, NO2 molecules are involved in photodissociation process due to π*← n transition and converted into NO molecules inside the PA cell due to excitation by 266 nm wavelength. The combined results of PA and gas chromatography-mass spectrometry (GC-MS) spectra along with thermo gravimetric-differential thermal analysis (TG-DTA) data confirm the thermal decomposition mechanism process that can be completed in multiple steps. In addition, GC-MS spectra also confirm the release of NO and NO2 molecules. The effect of incident laser energy and data acquisition time has been carried out for understanding the behavior of acoustic modes. Finally, the thermal quality factor "Q" is measured to test the stability of compounds.

In the present study, poly(butylene succinate) (PBSu) and its bionanocomposites containing 1, 2.5, and 5 wt.% biochar (MSP700) were prepared via in situ melt polycondensation in order to investigate the thermal stability and decomposition mechanism of the materials. X-ray photoelectron spectroscopy (XPS) measurements were carried out to analyze the surface area of a biochar sample and PBSu/biochar nanocomposites. From XPS, it was found that only physical interactions were taking place between PBSu matrix and biochar nanoadditive. Thermal stability, decomposition kinetics, and the decomposition mechanism of the pristine PBSu and PBSu/biochar nanocomposites were thoroughly studied by thermogravimetric analysis (TGA) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). TGA thermograms depicted that all materials had high thermal stability, since their decomposition started at around 300 °C. However, results indicated a slight reduction in the thermal stability of the PBSu biochar nanocomposites because of the potential catalytic impact of biochar. Py-GC/MS analysis was employed to examine, in more detail, the thermal degradation mechanism of PBSu nanocomposites filled with biochar. From the decomposition products identified by Py-GC/MS after pyrolysis at 450 °C, it was found that the decomposition pathway of the PBSu/biochar nanocomposites took place mainly via β-hydrogen bond scission, which is similar to that which took place for neat PBSu. However, at higher biochar content (5 wt.%), some localized differences in the intensity of the peaks of some specific thermal degradation products could be recognized, indicating that α-hydrogen bond scission was also taking place. A study of the thermal stability and decomposition pathway of PBSu/biochar bionanocomposites is crucial to examine if the new materials fulfill the requirements for further investigation for mulch films in agriculture or in electronics as possible applications.

Thermogravimetry, XPA, and ESCA were used to study the thermal stability and decomposition mechanism of [Cu(H2O)3μ-N(CH2PO3)3H4], [Zn(H2O)3μ-N(CH2PO3)3H4], Na8[CuN(CH2PO3)3]2·19H2O, and Na4[ZnN(CH2PO3)3]·13H2O in the atmosphere of air and argon. It was shown that the decomposition point, decomposition mechanism, and composition of the products being formed depend on the composition and structure of coordination compounds, and for Na8[CuN(CH2PO3)3]2·19H2O m Na4[ZnN(CH2PO3)3]·13H2O, also on the composition of the atmosphere. The stability of the complexes is affected by the configuration of the coordination polyhedron and by the electron density distribution in the coordination environment of a metal. The complex Na4[ZnN(CH2PO3)3] has the highest thermal stability in both air and argon (onset of decomposition at about 400°C).

SiO2 and Pd/SiO2 nanocomposites were prepared using sol–gel method and characterized by X-ray diffraction, Fourier transform infrared spectra, scanning electron microscopy and different heating rate thermogravimetric–differential thermogravimetric analysis. The apparent activation energies (Ea) were calculated using the Kissinger’s and Ozawa’s methods. The most probable kinetic mechanism functions were obtained by master plot method. The entropy (ΔS≠), enthalpy (ΔH≠) and activation free energy (ΔG≠) were calculated using three methods. The results demonstrated that the thermal decomposition processes of both materials are the three-step reactions. After thermal condition in air atmosphere, the introduced hydrophobic Si–CH3 group in Pd/SiO2 gel materials was completely decomposed into inorganic composition, and the Pd element was transformed into PdO and metallic Pd. The Ea values obtained by Kissinger’s method are close to those by Ozawa’s method. The Pd-doping can increase the thermal decomposition activation energies and improve the thermal stability of SiO2 material. The decomposition mechanisms for the three stages are the assumed random nucleation and its subsequent growth, irrespective of the Pd-doping. Compared with SiO2 material, the thermal decomposition of Pd/SiO2 requires more energy due to the increasing ΔH≠. The ΔH≠ values calculated by method II are nearly equal to the Ea values from the Kissinger’s and Ozawa’s methods, which indicated that the thermodynamic parameters obtained by method II are the most accurate.

The Na-ion battery technology appears as a reliable, sustainable, and environmentally friendly alternative to the Li-ion one, especially for stationary energy storage. As for the Li-ion technology, the safety aspect is of high importance to ensure large-scale development. In this work, we studied the thermal stability and decomposition mechanisms of carbon-coated Na3V2(PO4)2F3 and two fluorine-rich phases belonging to the solid-solution Na3V3+2–yV4+y(PO4)2F3–yOy (y = 0.07 and y = 0.12), that family of compounds being often considered among the most promising positive electrode materials for Na-ion batteries. This study shows the good thermal stability of these polyanionic materials and reveals that a low O2– for F– substitution has a very limited effect on the thermal stability of fully reintercalated materials recovered in the discharged state of the battery, whereas it has a beneficial impact for highly deintercalated ones, obtained by in-depth charges. Furthermore, whatever the state of charge and the oxygen content in NaxV2(PO4)2F3–yOy (1 ≤ x ≤ 3 and y = 0, 0.07 and 0.12), the thermal degradation leads, quite unexpectedly, to the formation of crystalline Na3V3+2(PO4)2F3 in addition to an amorphous phase. The fluorination of the partial oxygen for fluorine substituted material was clearly demonstrated by X-ray diffraction (XRD) and solid state nuclear magnetic resonance spectroscopy (NMR) on materials recovered after differential scanning calorimetry (DSC) analyses. The formation of a fully sodiated crystalline phase from the thermal degradation of the material obtained in charged states of the battery, with or without the presence of electrolyte, was never reported before.