Thermal decomposition mechanisms of bis(2-fluoro-2,2-dinitroethyl) formal (FEFO) and bis(2-fluoro-2,2-dinitroethyl) difluoroformal (DFF) from simultaneous thermogravimetric modulated beam mass spectrometry (STMBMS) measurements

The simultaneous thermogravimetric modulated beam mass spectrometry (STMBMS) technique has been applied to measure the vapor pressures and evaluate the thermal decomposition chemistry of two energetic liquids, bis(2-fluoro-2,2-dinitroethyl)formal (FEFO) and bis(2-fluoro-2,2-dinitroethyl)difluoroformal (DFF). The resulting heat of vaporization (ΔH_vap) and vapor pressure at 25°C are 20.3 ± 0.2 kcal/mol and 0.4 ± 0.1 millitorr for FEFO, and 17.3 ± 0.2 kcal/mol and 5.1 ± 1.1 millitorr for DFF. The thermal decomposition of FEFO indicates there are six major pyrolysis pathways. The results suggest that FEFO initially decomposes at 150°C by rearrangement of the nitro group ( NO₂) to the nitrite group ( O NO), followed by loss of NO. Some NO₂ is also formed at 170°C. Between 200°C–300°C, further pyrolysis occurs. In one pathway, the FEFO backbone remains intact and a high molecular-weight product is formed. The other three pathways involve scission of the FEFO backbone; one yielding CO₂ (possibly N₂O), one yielding CH₂O and CO, and one yielding C₃H₂NOF. Differences in the thermal decomposition behaviors in the liquid and gas phases are observed. In the thermal decomposition of DFF, the formal fluorine atoms stabilize the backbone structure. Numerous minor thermal decomposition products are also reported.     

Conducting nanocomposites of polyacrylamide with acetylene black and polyaniline

A conducting nanocomposite of polyacrylamide (PAA) with acetylene black was prepared via Na₂AsO₃‐K₂CrO₄ redox initiated polymerization of acrylamide in water containing a suspension of acetylene black. FTIR analyses confirmed the presence of PAA in the nanocomposites. The composite possessed lower thermal stability than AB and exhibited three stages of decomposition upto 430°C. DSC thermogram revealed three endotherms due to minor thermal degradation (at ∼100°C), melting and decomposition (at ∼230°C) and major decomposition (at ∼430°C). TEM analyses indicated the formation of globular composite particles with sizes in 30–70 nm range. In contrast to the very low conductivity of the base polymer the composite showed a dramatic increase in conductivity (0.19–6.0 S/cm) depending upon AB loading. Log (conductivity) –1/T plot showed a change in slope at ∼127°C indicating the manifestation of an intrinsic conductivity region and an impurity conductivity region. The activation energy for conduction as estimated from the slope of region I was 0.008 eV/mol. The C–V plot was linear showing a metallic behavior. For comparison in conductivity PAA‐polyaniline composite was also prepared which however displayed much lower conductivity values. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Thermal Decomposition of Tetraethylammonium Perchlorate

Thermal decomposition of tetraethylammonium perchlorate has been studied by thermogravimetry, differential thermal analysis and mass spectrometry. The title compound undergoes crystallographic transformation at 98°C and explodes at 298°C. The heat of phase transformation is calculated to be 2.5 kcal/mol. The mass spectral data suggest that the salt undergoes thermal decomposition into neutral particles which are then vapourized and ionized as well as oxidized.     

Studies on the thermal properties of poly(phenylene sulfide amide)

Thermal properties of poly(phenylene sulfide amide) (PPSA) prepared using sodium sulfide, sulfur, and thiourea as sulfur sources which reacted with dichlorobenzamide (DCBA) and alkali in polar organic solvent at the atmospheric pressure, were studied. The glass transition temperature (T_g), melting point temperature (T_m), and melting enthalpy (ΔH_m) of the related polymers were obtained by use of differential scanning calorimetry analysis. The results are: T_g = 103.4–104.5°C, T_m = 291.5–304.7°C, and ΔH_m = 104.4–115.4 J/g. Thermal properties such as thermal decomposition temperature and decomposition kinetics were investigated by thermogravimetric analysis under nitrogen. The initial and maximum rate temperatures of degradation were found to be 401.5–411.7°C and 437–477°C, respectively. The parameters of thermal decomposition kinetics of PPSAs were worked out to be: activation energy of degradation was 135 to 148 kJ/mol and the 60-s half-life temperature was 360 to 371°C. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1227–1230, 1997     

Catalytic thermal decomposition of carbonyl sulfide and its reaction with sulfur dioxide

The thermal decomposition of carbonyl sulfide (SCO) was studied in an integral reactor with various catalysts. An apparent activation energy of 28.7 kcal/mole was measured for SCO decomposition without a catalyst. In presence of a contact catalyst such as alumina or silica, the apparent activation energy was lowered to 5.6 kcal/mole. At temperatures below 635 °C, the main decomposition products of SCO were CO₂ and CS₂. At higher temperatures, the main products were CO and S. With pure chi-alumina, the decomposition of SCO at 550 °C was 35%, but when a stoichiometric quantity of SO₂ was added to SCO, about 90% of the SCO and SO₂ were converted at a much lower temperature (about 400 °C). The degree of interaction of SCO and SO₂ was greater with pure chi-alumina than when transition metals were present.     

Kinetic mechanism on Thermal Degradation of a Nitrate Ester Propellant

The thermal degradation of a double-base propellant has been studied to elucidate the rate-determining steps and the kinetic mechanism in a wide range of temperatures (60°C–200°C) by using modified Taliani test, thermogravimetry (TG), and temperature-varied Abel (TVA) test. The results indicate that the degradation process consists of two major reactions, homolysis and autocatalysis, depending on temperature and total pressure due to evolved gases. The activation energy for the homolysis was obtained to be 35–37 kcal/mol from Taliani and TVA tests, which fall in the range of the bond dissociation energy of the weakest bonds RO–NO₂. The activation energy for the autocatalysis was determined to be 46–49 kcal/mol from Taliani and TG methods. Those values observed for the two key reactions are totally opposite to reported values in the earlier literature. The temperature dependence of the reaction rates obtained in this study implies that the homolysis is the rate-determining step in the lower temperature range, the autocatalysis in the higher temperature range.     

The thermo–oxidative degradation of acrylonitrile–butadiene–styrene copolymers during processing as studied by chemiluminescence

The glow curve obtained upon processing acrylonitrile–butadiene–styrene copolymers (ABS), through various machines, reaches a peak at 180°C. The proper assignment of that peak has required the study of the chemiluminescence (CL) shown by related polymers such as: polybutadiene (PB), styrene–acrylonitrile copolymer (SAN), and polyacrylonitrile (PAN). Three hydroperoxide types associated with the structural units, that is, 1, 2, and cis- and trans-1,4, exhibiting CL peaks at 180, 240, and 340°C, respectively, have been identified in the PB sample. The activation energy (E_a), recorded for the hydroperoxides thermal decomposition, was 15.0 ± 1.0, 17.85 ± 0.9, 20.7 ± 0.8 kcal/mol. PAN shows a CL peak at 180°C. Its occurance is related to the color developed during the thermal treatment. That PAN peak has been attributed to the hydroperoxides generated on the acrylonitrile units neighboring the azomethinic structures. The corresponding E_a is 23.3 ± 1.0 kcal/mol. The same peak (having an identical position and E_a) has been identified with processed ABS and SAN copolymers. As is evident by CL studies, the processing induced oxidation mainly occurs within the SAN phase of the ABS copolymers, though it was also noted within 1,2 units of the PB phase.     

Thermal decomposition kinetics of photooxidized nylon 66

The thermoanalytical method offers a convenient means for testing a starting material before the end application. Differences in the kinetic parameters between neat and irradiated nylon 66 samples were estimated in the temperature range of 25°C–800°C by thermogravimetric analysis (TGA) and in the range of 25°C–300°C by differential scanning calorimetry (DSC). Under nitrogen flux the average activation energy for decomposition was in the range of 12.2–26.9 kcal/mol for the neat sample and 15.7–33.1 kcal/mol for the irradiated sample (250 h). Activation energy is affected by the process of bond breaking at the C? N bonds, which is the rate‐determining step of the decomposition in nylon 66. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2146–2150, 2003     

Thermal and kinetic study of manganese dithionate from absorbing or leaching solution via TG/XRD/IC analysis

ABSTRACT

Mangano-manganic oxide can be prepared through thermal decomposition of manganese sulfate from the absorption or leaching solution, so desulfurization by pyrolusite or leaching pyrolusite with sulfur dioxide should be fully exploited for the recovery of manganese salt. However, upon preparing MnSO₄ using above techniques, manganese dithionate is an inevitable by-product, which lowers the purity of the industrial raw material MnSO₄ and exerts negative influences on pyrolysis technology. Information regarding thermal decomposition of solid-state manganese dithionate is scarce. To recycle manganese dithionate efficiently, pyrolysis mechanism and kinetics were systematically investigated by thermal decomposition method. The characteristics of thermal decomposition products were determined by thermogravimetric analysis techniques (TG), X-ray diffraction (XRD), and Ion chromatography (IC). The experimental results revealed that both desulfurization and following dehydration of MnS₂O₆·H₂O were a one-step process, and the desulfurization occurred at about 150°C lower than the dehydration at 230°C. As increasing pyrolysis temperature to 900°C, the manganese sulfate was firstly formed, and to 1100°C, Mangano-manganic oxide was obtained by losing sulfur oxides. Consequently, the kinetic parameters for each decomposition steps of manganese dithionate were determined by the Coasts and Redfern (CR) integral method. The as-obtained experimental and kinetic results may provide theoretical guides for recycling manganese dithionate.     

Study of the thermal degradation of poly(N-vinyl-2-pyrrolidone) by thermogravimetry–FTIR

The thermal degradation of poly(N-vinyl-2-pyrrolidone) (PVP) was studied by dynamic thermogravimetric analysis (TGA) in the range 200–600°C under nitrogen and oxygen atmospheres at various heating rates. The apparent activation energy of the degradative process was determined by the application of kinetic treatments, giving an average value of 242 kj/mol in N₂, whereas in the presence of oxygen, two trends may be considered: At relatively low temperatures (200–400°C) and degrees of conversion, α, lower than 0.5, we obtained an average value of 199 kj/mol, whereas in the temperature interval 400–600°C with degrees of conversion higher than 0.5, the value of E_a was 306 kj/mol. Isothermal experiments carried out in N₂ in the interval 350–400°C gave an average value of E_a = 231 kj/mol, in good agreement with that obtained from dynamic treatments. The FTIR spectra of the volatile compounds evolved in degradation experiments carried out in N₂ as well as in the presence of oxygen suggest that PVP is thermally degraded, predominantly, by the release of the pyrrolidone side group and the subsequent decomposition of polyenic sequences. © 1993 John Wiley & Sons, Inc.     

Differential Scanning Calorimetric Study of HTPB based Composite Propellants in Presence of Nano Ferric Oxide

A comparative study of the thermal decomposition of ammonium perchlorate (AP)/hydroxy terminated polybutadiene (HTPB) based composite propellants has been carried out in presence and absence of nano iron oxide at different heating rates in a dynamic nitrogen atmosphere using differential scanning calorimetry. The pronounced effect was a lowering of the high temperature decomposition by 49 °C. A higher heat release up to 40% was observed in presence of nano ferric oxide (3.5 nm). The kinetic parameters were evaluated using the Kissinger method. The increase of the rate constant in the catalyzed propellant confirmed the enhancement of the catalytic activity of ammonium perchlorate. The scanning electron micrographs of nano Fe₂O₃ incorporated in HTPB revealed a well‐separated characteristic necklace‐like structure of α‐Fe₂O₃ particles at high magnification.     

Pyrolysis and thermo‐oxidative degradation of polycyclopentadiene

Thermal degradation of polycyclopentadiene polymer (PCPD) was investigated by pyrolysis gas chromatography (PGC) in the temperature range of 500–950°C. The nature and composition of the pyrolyzates at various temperatures are presented, and the mechanism of degradation is explained. The activation energy of decomposition (E_a) was obtained from an Arrhenius‐type plot using the concentration of the product ethylene (C₂) at different pyrolysis temperatures and the value was found to be 138 kJ mol⁻¹. Thermo‐oxidative degradation of PCPD in the presence of ammonium perchlorate (AP), the most commonly used oxidizer for polymeric fuel binders, was studied at a pyrolysis temperature of 700°C. The compositions of the products with varying amounts of AP are given, and the exothermicity of oxidative decomposition reactions is evaluated. The energetics of the degradation processes are compared with those of polybutadiene type polymers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 635–641, 2000     

Effect of copper chromite and copper chromitecopper oxide mixture catalysts on the thermal decomposition of ammonium perchlorate and composite solid propellant

Thermal decomposition of powdered ammonium perchlorate (AP), polystyrene (PS) and $\text{AP}\text{PS}$ propellant, catalysed by freshly-prepared CuCr₂O₄ and mixtures of CuCr₂O₄ and CuO, has been studied with a low concentration (1% by mass) of the catalysts. It appears that decomposition is increased due to heterogeneous catalysis. The kinetics of thermal decomposition of AP in the presence of CuCr₂O₄ in the orthorhombic region of AP have also been studied.     

Thermal gravimetric studies of manganese dioxide

The newly developed thermal gravimetric analytical procedure of manganese dioxide (MnO₂) was presented. Instead of the conventional representation of the weight loss based on the initial sample weight, the weight gain based on the sample weight at 1000°C was proposed. The usefulness of the newly defined axis, ie the weight gain vs temperature, on the investigation of manganese dioxide was demonstrated and discussed by showing the consistent, comparable thermal gravimetric data of electrolytic MnO₂, chemically prepared and thermally transformed beta-MnO₂s and the heat-treated electrolytic MnO₂s.     

Amine-functionalized metal–organic frameworks/epoxy nanocomposites: Structure-properties relationships

Amine-functionalized MIL-101(Cr)-NH₂ metal–organic frameworks (MOF-N)/epoxy nanocomposites with Excellent cure label and high thermal stability were developed. Structure–property relationship was discussed by comparison of the cure state, thermal and viscoelastic behavior of epoxy nanocomposites containing pristine MOF or MOF-N applying differential scanning calorimetry (DSC), thermogravimetric analysis, and dynamic mechanical analysis. Epoxy containing 0.3 wt% MOF-N exhibited high glass transition temperature (T_g) of 96°C compared with 85°C observed for epoxy/MOF system. Thus, MOF-N played the role of catalyst in epoxy/amine curing reaction. Correspondingly, a lower activation energy was obtained based on cure kinetics modeling based on DSC measurements. Besides, incorporation of low amount (0.5 wt%) MOF-N induced an early-state resistance against decomposition, featured by 11°C rise in decomposition temperature at 5% weight loss. This was ascribed to the formation of porous metallic oxides during thermal decomposition of MOF-N in the epoxy system acting as a heat barrier, which increased the activation energy of decomposition. Amine-functionalization considerably prevented from further oxidation of the inner part of the matrix.     

Decomposition of a Multi-Peroxidic Compound: Triacetone Triperoxide (TATP)

The thermal decomposition of triacetone triperoxide (TATP) was investigated over the temperature range 151 to 230 °C and found to be first order out to a high degree of conversion. Arrhenius parameters were calculated: activation energy, 151 kJ/mol and pre-exponential factor, 3.75×10¹³ s⁻¹. Under all conditions the principle decomposition products were acetone (about 2 mole per mole TATP in the gas-phase and 2.5–2.6 mole per mole in condensed-phase) and carbon dioxide. Minor products included some ascribed to reactions of methyl radical: ethane, methanol, 2-butanone, ethyl acetate; these increased at high temperature. Methyl acetate and acetic acid were also formed in the decomposition of neat TATP; the former was more evident in the gas-phase decompositions (151 °C and 230 °C) and the latter in the condensed-phase decompositions (151 °C). The decomposition of TATP in condensed-phase or in hydrogen-donating solvents enhanced acetone production, suppressed CO₂ production, and slightly increased the rate constant (a factor of 2–3). All observations were interpreted in terms of decomposition pathways initiated by O O homolysis.     

Pyrolysis kinetics of highly crosslinked polymethylsiloxane by TGA

The pyrolysis kinetics of highly crosslinked polymethylsiloxane (PMS) was investigated by thermogravimetric analysis (TGA) under both isothermal and elevated temperature conditions with several environmental gases, such as oxygen, nitrogen, air, and helium. A non-chain-scission mechanism composed of initiation, propagation, and termination was proposed to interpret the thermal degradation of highly crosslinked PMS. The mechanism was verified by the experimental results under isothermal conditions. The activation energy of initiation, E_i, was about 20–30 kcal/mol and the activation energy of propagation, E_p, was about 4–6 kcal/mol. These activation energies were found to be different for different gases. The activation energy of initiation for PMS in an aggressive atmosphere, such as oxygen, was lower than that in an inert atmosphere, such as nitrogen. But the activation energy of propagation for PMS was higher in an active environment than in an inert one. There were no direct conclusions about the thermal degradation of highly crosslinked PMS at elevated temperature. Based on thermogravimetric experiments, it is suggested that a pyrolysis process be conducted with a rate of temperature increase less than 10°C/min for preparing the silicon base inorganic membrane.     

The boron trifluoride monoethyl amine complex cured epoxy resins

The curing exotherm pattern is affected by the equivalent ratio of curing agent, boron trifluoride monoethylamine complex (BF₃ · MEA), to epoxy resin. The diglycidyl ether of 9,9-bis(4-hydroxyphenyl) fluorene (DGEBF) cures more slowly than the diglycidyl ether of bisphenol A (Epon 828). The glass transition temperatures (T_g's) of BF₃ · MEA cured Epon 828 are increased with inceasing concentration of curing agent (0.0450–0.1350 eq.) cured DGEBF. The activation energies for the thermal decomposition for BF₃ · MEA (0.0450–0.1350 eq.) cured DGEBF. The activation energies for the thermal decomposition for BF₃ · MEA (0.0450 eq./epoxy eq.) cured Epon 828 and DGEBF are almost equivalent 43 and 44 kcal/mol, respectively. DGEBF when added to DGEBA improves the T_g and char yield with the BF₃ · MEA curing system. The T_g of both resin systems can be increased by longer post cure, whereas the char yield does not appear to change significantly. No ester group formation is found for the BF₃ · MEA-cured DGEBF, although this has been previously reported for the DGEBA system. The BF₃ · MEA cure at 120°C is better than at 140°C because of vaporization and degradation of the curing agent at the higher temperature. The rapid gelation of the epoxy resin may be another reason for the lower degree of cure at high temperature.     

Colloidal Manganese Oxide Precursor to Octahedral Layered,OL-3 Materials

We report the one-pot synthesis of a hexagonal form of a layered manganese oxide material (OL-3) using mild conditions and low temperature. The oxidation of an aqueous solution of manganese acetate using tetramethylammonium hydroxide and hydrogen peroxide at 4 °C leads to the formation of a colloidal manganese dioxide solution. Colloidal MnO₂ was then flocculated using K ions, forming disordered layered manganese oxide nano-flakes having an R \(\bar 3\) m rhombohedral structure with lattice parameters a = 2.85 Å and c = 21.8 Å. The potassium manganese oxide nano-flakes were characterized using X-ray diffraction, electron microscopy, chemical analysis, thermal analysis, N₂ sorption, and UV/Visible spectroscopy. The results indicate that the colloidal manganese oxide nano-flakes flocculated into ultra-thin, disorderly-stacked hexagonal lamellar sheets composed of a material with the chemical composition of K_1.04MnO_2.34·0.6H₂O.     

Preparation of dense La0.7Ca0.3MnO3 ceramics from freeze-dried precursors

Sinterability of La_0.7Ca_0.3MnO₃ precursors, obtained by the freeze-drying method, is studied in order to develop a technique for preparation of dense (>95%) ceramics for CMR measurements and sputtering applications. Single phase powders, obtained by thermal decomposition at 650°C, were subjected to deagglomeration by ultrasonic or mechanical treatment. Sintering of deagglomerated powders for several hours at T=1200–1300°C allowed to achieve densities up to 97–98%. The best sinterability is demonstrated by mechanically processed powder, but further sintering of ceramics, obtained from this precursor, results in significant dedensification (up to 85% at 1300°C). Analysis of precursors and dedensified samples shows at high temperature decomposition of carbonates in closed pores to be the most probable reason for the observed process.