Density-Dependent Liquid Nitromethane Decomposition: Molecular Dynamics Simulations Based on ReaxFF

The decomposition mechanism of hot liquid nitromethane at various compressions was studied using reactive force field (ReaxFF) molecular dynamics simulations. A competition between two different initial thermal decomposition schemes is observed, depending on compression. At low densities, unimolecular C–N bond cleavage is the dominant route, producing CH_3 and NO_2 fragments. As density and pressure rise approaching the Chapman–Jouget detonation conditions (~30% compression, >2500 K) the dominant mechanism switches to the formation of the CH_(3)NO fragment via H-transfer and/or N–O bond rupture. The change in the decomposition mechanism of hot liquid NM leads to a different kinetic and energetic behavior, as well as products distribution. The calculated density dependence of the enthalpy change correlates with the change in initial decomposition reaction mechanism. It can be used as a convenient and useful global parameter for the detection of reaction dynamics. Atomic averaged local diffusion coefficients are shown to be sensitive to the reactions dynamics, and can be used to distinguish between time periods where chemical reactions occur and diffusion-dominated, nonreactive time periods

Determination of the thermal stability of perfluoroalkylethers

The thermal decomposition temperatures of several commercial and custom synthesized perfluoroalkylether fluids were determined with a computerized tensimeter. In general, the decomposition temperatures of the commercial fluids were all similar and significantly higher than those for custom synthesized fluids. Correlation of the decomposition temperatures with the molecular structures of the primary components of the commercial fluids revealed that the stability of the fluids is not affected by intrinsic factors such as carbon chain length, branching, or cumulated difluoroformal groups. Instead, correlation with extrinsic factors revealed that the stability may be limited by the presence of small quantities of thermally unstable material and/or chlorine-containing material arising from the use of chlorine-containing solvents during synthesis. Finally, correlation of decomposition temperatures with molecular weights for Demnum and Krytox fluids supports a chain cleavage reaction mechanism for Demnum fluids and an unzipping reaction mechanism for Krytox fluids

Thermal Decomposition Kinetics of Cumene Hydroperoxide

The thermal decomposition and runaway reaction of cumene hydroperoxide (CHP) in cumene were studied by thermal analysis and by using the VSP-II adiabatic calorimeter. Decomposition kinetics were determined in various CHP concentrations in cumene. The reaction order of 20wt%, 35wt%, 50wt%, 65wt%, and 80wt% was determined to be 0.5, and the Arrhenius parameters were measured as Ea (kJmol−1) = 122.0 ± 3.0 and ln A (min−1 M1/2) = 30.0 ± 1.2. This new determination of the reaction order as equal to one half implies the same mechanism of decomposition regardless of CHP concentration. Chromatography and IR spectroscopy was combined with calorimetry data to determine the thermal decomposition kinetics. The preliminary rate determining step was considered to be the decomposition of CHP by dimer association. A reaction mechanism for CHP thermal decomposition is proposed

Thermal Decomposition Mechanism of Silver Nitrobenzoates

The infra-red spectra of silver salts of 3-mono-, 3,5-di-and 2,4,6-tri-nitro-benzoic acids have been recorded at elevated temperatures in a fabricated high temperature cell. The thermogravimetry i.e. TG analysis has also been carried out. The results of this study suggest that decomposition of these salts is a two stage process i.e. decarboxylation followed by explosion

Mechanism of Thermal Decomposition of Lignin

Differential thermal analysis studies of milled wood lignin and lignin carbohydrate complex at different heating rates showed three exothermic peaks. The heating rate is the factor that affects their sharpness and position. The peaks are sharp at low heating rates. Infrared spectra and scanning electron micrographs of the pyrolyzed lignin residues show that aliphatic scission of the lignin molecule at the onset of pyrolysis and progressive carbonization of the surface are the principal features of degradation; there is no intermediate compound formed during the pyrolysis

Thermal Decomposition of Diphenyl Tetroxane in Chlorobenzene Solution

The thermal decomposition of Cyclic Diperoxide of Benzaldehyde 3,6-diphenyl-1,2,4,5-tetroxane, (DFT) in chlorobenzene solution in the studied temperature range (130°C - 166°C) satisfactorily satisfies a first order law up to 60% conversions of diperoxide. DFT would decompose through a mechanism in stages and initiated by the homolytic breakdown of one of the peroxidic bonds of the molecule, with the formation of the corresponding intermediate biradical. The concentration studied was very low, so that the effects of secondary reactions of decomposition induced by free radicals originated in the reaction medium can be considered minimal or negligible. The activation parameters for the unimolecular thermal decomposition reaction of the DFT are ΔH# = 30.52 ± 0.3 kcal·mol-1 and ΔS# = -6.38 ± 0.6 cal·mol-1 K-1. The support for a step-by-step mechanism instead of a process concerted is made by comparison with the theoretically calculated activation energy for the thermal decomposition of 1,2,4,5-tetroxane.Fil: Bordón, Alexander Germán. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas y Naturales y Agrimensura; ArgentinaFil: Pila, Andrea Natalia. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas y Naturales y Agrimensura; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Modelado e Innovación Tecnológica. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Instituto de Modelado e Innovación Tecnológica; ArgentinaFil: Profeta, Mariela Inés. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas y Naturales y Agrimensura; ArgentinaFil: Jorge, María J.. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas y Naturales y Agrimensura; ArgentinaFil: Jorge, Lilian Cristina. Universidad Nacional del Nordeste. Facultad de Ciencias Veterinarias; ArgentinaFil: Romero, Jorge Marcelo. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas y Naturales y Agrimensura; ArgentinaFil: Jorge, Nelly Lidia. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas y Naturales y Agrimensura; Argentin

Mechanism of thermal decomposition of poly(ether ether ketone) (PEEK) from a review of decomposition studies

A review of the literature on the flammability and decomposition of poly(oxy-1,4-phenyleneoxy-1,4-phenylenecarbonyl-1,4-phenylene) (PEEK) is presented. This paper provides an overview of the flammability of PEEK and its decomposition mechanisms. Based on this literature, mechanisms have been suggested which attempt to explain the products formed at each stage of PEEK decomposition and indicate the intermediates which should be formed at each of these stages

The pyrolytic decomposition of metal alkoxides (di-acetoxy-di-t-butoxy-silane, DADBS) during chemical vapour deposition of thin oxide films

In this study the effects of the nature of metal alkoxides on their vapour pressures and thermal decomposition chemistry are reported. The vapour pressure and the volatility of a metal alkoxide strongly depends on the steric effect of its alkoxy group.\ud \ud The thermal decomposition chemistry of one metal alkoxide (di-acetoxy-di-t-butoxy-silane, DADBS) has been studied by mass spectrometry at temperatures between 423 and 923 K. The pyrolytic products were acetic acid anhydride and 2-methyl propene. The acetic acid anhydride is formed at temperatures above 473 K and 2-methyl propene is formed above 673 K by a ß -hydride elimination mechanism. In these steps, a 6-ring intermediate is supposed to be formed. The silicon acid finally remaining is proposed to react by poly-condensation to SiO2 coatings or powder

The Effect of Biochar Addition on Thermal Stability and Decomposition Mechanism of Poly(butylene succinate) Bionanocomposites

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