On the Comparison of Small Nitrogen and Phosphorus Oxide Cages

Ab initio electronic structure calculations, including a natural bond orbital (NBO) analysis, are employed to compare the stabilities of larger nitrogen oxide cages and phosphorus oxide cages relative to the cage compound c‐N₂O₃ , which has been previously investigated as a potential energetic oxidizer. The larger N O cages, c‐N₂O₆ and c‐N₄O₆ exhibit less internal strain but have significantly lower barriers to decomposition of 1.9 kJ mol⁻¹ and 5.6 kJ mol⁻¹ respectively, compared to 37.6 kJ mol⁻¹ for c‐N₂O₃, at the MP2/aug‐cc‐pVDZ level of theory. In contrast, the phosphorus oxide cage c‐P₂O₃ exhibits similar internal strain but has a significantly larger barrier to decomposition of 40.2 kJ mol⁻¹ compared to the 24.4 kJ mol⁻¹ of c‐N₂O₃ at CCSD(T)/CBS(Q‐5). Furthermore, NBO analysis shows that the P O bond is more ionic in nature compared to the N O bond. The reduced degree of ionic character leads to the kinetic instability of the nitrogen oxide cages and therefore renders them impractical as energetic oxidizers.     

Thermal degradation kinetics of thermotropic poly(p‐oxybenzoate‐co‐p,p′‐biphenylene terephthalate) fiber

An advanced heat‐resistant fiber (trade name Ekonol) spun from a nematic liquid crystalline melt of thermotropic wholly aromatic poly(p‐oxybenzoate‐p,p′‐biphenylene terephthalate) has been subjected to a dynamic thermogravimetry in nitrogen and air. The thermostability of the Ekonol fiber has been studied in detail. The thermal degradation kinetics have been analyzed using six calculating methods including five single heating rate methods and one multiple heating rate method. The multiple heating‐rate method gives activation energy (E), order (n), frequency factor (Z) for the thermal degradation of 314 kJ mol⁻¹, 4.1, 7.02 × 10²⁰ min⁻¹ in nitrogen, and 290 kJ mol⁻¹, 3.0, 1.29 × 10¹⁹ min⁻¹ in air, respectively. According to the five single heating rate methods, the average E, n, and Z values for the degradation were 178 kJ mol⁻¹, 2.1, and 1.25 × 10¹⁰ min⁻¹ in nitrogen and 138 kJ mol⁻¹, 1.0, and 6.04 × 10⁷ min⁻¹ in air, respectively. The three kinetic parameters are higher in nitrogen than in air from any of the calculating techniques used. The thermostability of the Ekonol fiber is substantially higher in nitrogen than in air, and the decomposition rate in air is higher because oxidation process is occurring and accelerates thermal degradation. The isothermal weight‐loss results predicted based on the nonisothermal kinetic data are in good agreement with those observed experimentally in the literature. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1923–1931, 1999     

Thermal degradation behavior and kinetics of porous polymer based on high functionality components

Two kinds of porous polymer were prepared based on high functionality components. Thermogravimetric analysis (TGA) is used to compare the thermal degradation behavior and kinetics of these two materials. The thermogravimetric tests of rigid polyurethane foam (H-RPUF) and polyurea aerogel (H-PUA) were carried out in nitrogen atmosphere at different heating rates. The thermal degradation characteristics of the porous polymer were obtained. The apparent activation energy (E_a) of thermal degradation of the porous polymer was investigated by model-free methods. The results showed that the thermal degradation temperature and ash content of H-RPUF were higher than those of H-PUA, and the volatile content was lower. With the rise of heating rate, thermal hysteresis effect of the two porous polymer was relatively high, while the release amount of volatiles was unchanged. For the Kissinger method, E_a of H-PUA and H-RPUF was 212.8 kJ mol⁻¹ and 157.4 kJ mol⁻¹, respectively. According to Starink method, the average activation energy of H-PUA and H-RPUF was 220.2 kJ mol⁻¹ and 107.2 kJ mol⁻¹, respectively. Obtained by Flynn-Wall-Ozawa model, the average activation energy of H-PUA and H-RPUF was 219.0 kJ mol⁻¹ and 111.5 kJ mol⁻¹, respectively. The data obtained from the three models all show that E_a of thermal degradation of H-PUA is higher than that of H-RPUF, and it is less likely to decompose.     

Substituent Effects on Thermodynamic and Detonation Properties of Polynitrobenzenes

Density functional theory (DFT) calculations were performed for a series of polynitrobenzene derivatives. Some nitrobenzenes with amino groups attached were also investigated as a benchmark or as a precursor. Heats of formation (HOF) were evaluated. The isodesmic reactions used for the prediction of HOFs are of permutation type in terms of the substituents. The HOFs increase non‐additively with increasing number of nitro groups. The attachment of the amino groups to polynitrobenzenes dramatically decreases the HOF. The HOF of hexanitrobenzene (HNB) is 344.05 kJ mol⁻¹ at the B3LYP/6‐311+G** level. This value is much larger than that of the widely used 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB), which engenders HNB a large chemical energy of detonation. The strengths of the group interactions were analyzed according to the disproportionation energy. The nearest‐neighbor interactions in polynitrobenzenes are in the range of 27.20–55.90 kJ mol⁻¹. The energy barrier for the internal rotation of nitro group in nitrobenzene is 24.6 kJ mol⁻¹. However, the energy barrier for the internal rotation of 2‐position nitro group of 1,2,3‐trinitrobenzene is as large as 216.3 kJ mol⁻¹. The chemical energies of detonation for polynitrobenzenes with three or more nitro groups are over 6000 J g⁻¹. Pentanitroaniline and HNB have good performances in terms of detonation velocity and pressure.     

Preparation and Characterization of Insensitive HMX/Graphene Oxide Composites

To improve the safety of HMX, a two‐dimensional (2D) graphene oxide (GO) was introduced to HMX by the solvent nonsolvent method. The morphology, composition, thermal decomposition characteristic were characterized by scanning electron microscopy (SEM), X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), thermogravimetry (TG) and differential scanning calorimetry (DSC). Compared to the previous reports, GO sheets exhibited better desensitizing effect than [60]Fullerene and CNTs. When 2.0 wt‐% GO sheets were added, the impact sensitivity of raw HMX decreased from 100 to 10 %, and the friction sensitivity reduced from 100 to 32 %. The DSC results proved that GO sheets were compatible with HMX. In addition, by determining the thermal decomposition kinetic parameters of the samples, it was found that the activation energy (E_a) of HMX with 2.0 wt‐% GO increased by 23.5 kJ mol⁻¹, suggesting that GO sheets could improve the thermal stability of HMX.     

The Kinetics of the Main Decomposition Process of Aminoguanidium 5,5′‐azobis‐1H‐tetrazolate

In this study, the kinetics of the thermal decomposition of aminoguanidinium 5,5′‐azobis‐1H‐tetrazolate (AGAT), which is one of the promising fuel candidates of the new gas generating agents for airbags, was investigated. The kinetic model that fits the main decomposition of AGAT was examined, and the activation energy was obtained. The main decomposition of AGAT was a single elementary process according to the result of mass spectrometry. The recommended kinetic model for the main decomposition of AGAT is Avrami–Erofeev equation (n=4). The activation energies for the main decomposition obtained under helium by non‐isothermal analysis and isothermal analysis were 207 and 209 kJ mol⁻¹, respectively.     

Thermal Behavior and Thermolysis Kinetics of the Explosive Trans‐1,4,5,8‐Tetranitro‐1,4,5,8‐Tetraazadecalin (TNAD)

Trans‐1,4,5,8‐Tetranitro‐1,4,5,8‐Tetraazadecalin (TNAD), a cyclic nitroamine, has been studied with regard to the kinetics and mechanism of thermal decomposition, using thermogravimetry (TG), IR spectroscopy, and pressure differential scanning calorimetry (PDSC). The IR spectra of TNAD have also been recorded, and the kinetics of thermolysis has been followed by non‐isothermal TG. The activation energy of the solid‐state process was determined by using the Flynn‐Wall‐Ozawa method. Compared with the activation energy obtained from the Ozawa method, the reaction mechanism of the exothermic process of TNAD was classified by the Coats‐Redfern method as a nucleation and nuclear growth (Avrami equation 1) chemical reaction (α=0.30–0.60) and a 2D diffusion (Valensi equation) chemical reaction (α=0.60–0.90). E_a and ln A were established to be 330.14 kJ mol⁻¹ and 29.93 (α=0.30–0.60) or 250.30 kJ mol⁻¹ and 21.62 (α=0.60–0.90).     

Thermal Decomposition Research on 1,5‐Diazabicyclo[3.1.0] Hexane (DABH) as a Potential Low‐toxic Liquid Hypergolic Propellant

1,5‐Diazabicyclo[3.1.0] hexane (DABH) was found a potential hypergolic liquid propellant. The physical and energetic properties of DABH, 2‐(dimethylamino) ethyl azide (DMAZ), and monomethyl hydrazine (MMH) were compared. The ignition delay time of DABH with nitrogen tetroxide was 1 ms, which was shorter than DMAZ and similar with MMH. The toxicology experiment showed that half lethal dose (LD₅₀) of DABH was 621.0 mg kg⁻¹, which suggested that DABH was promising to be used as low‐toxic liquid propellant. Thermal decomposition experiments showed that the apparent activation energy (E ) was about 66.3 kJ mol⁻¹. The thermal decomposition calculated results from Madhusudanan‐Krishnan‐Ninan integration, Satava‐Sestak integration and Achar differential methods were compared and the pre‐exponential factor were obtained.     

Chemical Kinetics of the Thermal Decomposition of NTO

The kinetics of thermal decomposition of 3‐nitro‐2,4‐dihydro‐3H‐1,2,4‐triazol‐5‐one (NTO) in the temperature interval from 200 °C to 260 °C was investigated using a glass Bourdon gauge. The overall decomposition reaction includes two distinct stages: the fast first‐order decomposition and the subsequent autocatalytic reaction. The importance of the first stage increases with increasing decomposition temperature and decreasing loading density of the Bourdon gauge (m/V). A period of preliminary heating, at a lower temperature, strongly influences the autocatalytic stage when the decomposition is carried out at a higher temperature. In the temperature domain 200–220 °C, the Arrhenius constants of the decomposition reaction are found to be close to the values usually observed for nitrocompounds: E=173 kJ/mol and log₁₀ k≈12.5 (s⁻¹). It is shown that a simple model of NTO decomposition based on an autocatalytic reaction of the m‐th order can describe the course of the decomposition at high temperature but the m number appears to be excessively high, up to 4. A new model of the decomposition is developed, including an initial monomolecular reaction, decomposition of the crystalline substance, and an autocatalytic reaction of NTO dissolved in liquid decomposition products. This model gives the common order of autocatalysis, m=1.     

Thermal Degradation of p-Hydroxybenzoic Acid in Macadamia Nut Oil,Olive Oil,and Corn Oil

p-Hydroxybenzoic acid (PHBA) plays a significant role in sustaining the oxidative stability of macadamia nut oil (MNO). However, PHBA undergoes thermal decarboxylation and loses its bioactive antioxidant properties. In this study, we determine PHBA degradation kinetics in oils at various heating temperatures, which provides fundamental understanding of PHBA thermal degradation in oils and oil quality changes during high-temperature processing. PHBA degradation kinetics in MNO, olive oil, and corn oil were evaluated at temperatures typical for cooking and frying. PBHA headspace concentration was measured using selected ion flow tube mass spectrometry. PHBA decarboxylation followed a zero-order reaction, where degradation could be affected by factors such as the type of oil matrix having different FA compositions, antioxidants, and component interactions. PHBA degradation activation energies (E _a) showed that PHBA was more stable against thermal decarboxylation in MNO (85 kJ mol^–1) than in olive oil (40 kJ mol⁻¹) or corn oil (22 kJ mol⁻¹). The higher enthalpy () of decarboxylation in MNO (82 kJ mol⁻¹) indicates that PHBA is more inhibited from decomposition than olive oil (37 kJ mol⁻¹) or corn oil (19 kJ mol⁻¹). Moreover, the negative entropy values () of PHBA degradation from MNO (−192 J mol⁻¹ K⁻¹), olive oil (−277 J mol⁻¹ K⁻¹), and corn oil (−325 J mol⁻¹ K⁻¹) indicates that these oils impart some inhibitory properties against PHBA thermal decarboxylation.     

Kinetics of Decomposition of Energetic Ionic Liquids

The Arrhenius‐type reaction rate parameters for the initiation reactions governing the thermal decomposition of several energetic ionic liquids (EILs) were determined by numerical techniques. The compounds chosen for this purpose were the energetic 4‐amino‐1,2,4‐triazolium nitrate (4ATN) and 1‐hydroxyethyl‐hydrazinium nitrate (HEHN). The supplementary compounds studied for comparison were 4‐amino‐1,2,4‐triazolium chloride (4ATCl) and ammonium nitrate (AN). The reaction rate parameters were obtained by an evolutionary genetic algorithm (GA) that compared the difference between the experimental and simulated species evolution profiles from the decomposition process. The experimental data were generated by confined rapid thermolysis (CRT). The decomposition process was simulated by applying conservation equations to the condensed and gas phases individually. The optimization module recovered the experimental species profiles with reasonable accuracy for all the compounds studied. The processes governing the decomposition of these energetic compounds were found to be autocatalytic in nature, and the autocatalytic agents were the strong acids generated by the initial decomposition step. The activation energy and pre‐exponential factor for the unimolecular decomposition step for 4ATN, HEHN, and 4ATCl were 167–188 kJ mol⁻¹ and 10¹⁶ s⁻¹, respectively, similar to previously determined values for AN.     

Thermal Decomposition of Aminonitrobenzodifuroxan

In this study, the thermal decomposition properties of aminonitrobenzodifuroxan are studied using a differential scanning calorimeter (DSC), a thermogravimeter (TG), an X‐ray diffractometer, a mass spectrometer (MS), and a Fourier transform infrared spectrometer (FTIR). The results demonstrate that aminonitrobenzodifuroxan undergoes thermal decomposition in the solid state. Under elevated temperatures, the decomposition primarily involves two steps: separation of nitro group and ring‐scission of the furoxan circles at 198.1 °C, and decomposition of the relatively stable residues (benzofuroxan circle) at 199.1 °C. Moreover, it is found that among the products, nitrogen dioxide undergoes oxidation and catalysis on the host molecule during the whole decomposition. Based on Kissinger and Ozawa functions, we deduce that the activation energies of these two reactions are 167.68 and 204.55 kJ mol⁻¹, respectively. The released energy (ΔH) of CL‐18 is −1781.8 J g⁻¹.     

Glycidyl Azide Polymer Crosslinked Through Triazoles by Click Chemistry: Curing,Mechanical and Thermal Properties

Glycidyl azide polymer (GAP) was cured through “click chemistry” by reaction of the azide group with bispropargyl succinate (BPS) through a 1,3‐dipolar cycloaddition reaction to form 1,2,3‐triazole network. The properties of GAP‐based triazole networks are compared with the urethane cured GAP‐systems. The glass transition temperature (T_g), tensile strength, and modulus of the system increased with crosslink density, controlled by the azide to propargyl ratio. The triazole incorporation has a higher T_g in comparison to the GAP‐urethane system (T_g−20 °C) and the networks exhibit biphasic transitions at 61 and 88 °C. The triazole curing was studied using Differential Scanning Calorimetry (DSC) and the related kinetic parameters were helpful for predicting the cure profile at a given temperature. Density functional theory (DFT)‐based theoretical calculations implied marginal preference for 1,5‐addition over 1,4‐addition for the cycloaddition between azide and propargyl group. Thermogravimetic analysis (TG) showed better thermal stability for the GAP‐triazole and the mechanism of decomposition was elucidated using pyrolysis GC‐MS studies. The higher heat of exothermic decomposition of triazole adduct (418 kJ ⋅ mol⁻¹) against that of azide (317 kJ ⋅ mol⁻¹) and better mechanical properties of the GAP‐triazole renders it a better propellant binder than the GAP‐urethane system.     

Cage Compounds as Potential Energetic Oxidizers: A Theoretical Study of a Cage Isomer of N2O3

Ab initio electronic structure calculations are employed to investigate the cage isomer of N₂O₃ (c‐N₂O₃) as a viable energetic oxidizer. c‐N₂O₃ is vibrationally stable with a large heat of formation of 7.95 kJ g⁻¹ and can produce larger enthalpies of combustion than other commonly used oxidizers such as ammonium perchlorate, O₂(l) and N₂O₄. c‐N₂O₃ is shown to have a unimolecular decomposition barrier of 24.4 kJ mol⁻¹ at the CCSD(T)/CBS(Q‐5) level of theory, and a dimer‐induced decomposition barrier of 100.8 kJ mol⁻¹. Although c‐N₂O₃ is predicted to perform well as an oxidizer, the low barrier to unimolecular decomposition is likely to render it impractical as an energetic oxidizer.     

Hermetic Thermal Behavior of 3,4‐Diaminofurazan (DAF)

Hermetic thermal behavior of 3,4‐diaminofurazan (DAF) was studied by DSC method with special high‐pressure hermetic crucibles. The complete exothermic decomposition process of DAF can be provided. The extrapolated onset temperature, peak temperature, and enthalpy of decomposition at a heating rate of 10 K min⁻¹ are 238.7 °C, 253.0 °C, and −1986 J g⁻¹, respectively. Self‐accelerating decomposition temperature and critical temperature of thermal explosion of DAF are 232.3 and 253.1 °C, respectively. Specific heat capacity of DAF was determined with a micro DSC method and the molar heat capacity is 140.78 J mol⁻¹ K⁻¹ at 298.15 K. Adiabatic time‐to‐explosion of DAF is about 90 s. The thermal stability of DAF is good.     

Thermal Decomposition,Kinetics and Compatibility Studies of Poly(3‐difluoroaminomethyl‐3‐methyloxetane) (PDFAMO)

The thermal decomposition of poly(3‐difluoroaminomethyl‐3‐methyloxetane) (PDFAMO) with an average molecular weight of about 6000 was investigated using thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). The kinetics of thermolysis were studied by a model‐free method. The thermal decomposition of PDFAMO occurred in a two‐stage process. The first stage was mainly due to elimination of HF and had an activation energy of 110–120 kJ mol⁻¹. The second stage was due to degradation of the polymer chain. The Fourier transform infrared (FTIR) spectra of the degradation residues showed that the difluoroamino groups decomposed in a two‐step HF loss at different temperatures. The remaining monofluoroimino groups produced by the incomplete elimination of HF were responsible for the two‐stage thermolysis process. The compatibility of PDFAMO with some energetic components and inert materials used in polymer‐bonded explosives (PBXs) and solid propellants was studied by DSC. It was concluded that the binary systems of PDFAMO with cyclotrimethylenetrinitramine (RDX), 2,4,6‐trinitrotoluene (TNT), 2,4‐dinitroanisole (DNAN), pentaerythritol tetranitrate (PETN), ammonium perchlorate (AP), aluminum powder (Al), aluminum oxide (Al₂O₃) and 1,3‐diethyl‐1,3‐diphenyl urea (C₁) were compatible, whereas the systems of PDFAMO with lead carbonate (PbCO₃) and 2‐nitrodiphenylamine (NDPA) were slightly sensitized. The systems with cyclotetramethylenetetranitroamine (HMX), hexanitrohexaazaisowurtzitane (CL‐20), 3‐nitro‐1,2,4‐triazol‐5‐one (NTO), ammonium nitrate (AN), magnesium powder (Mg), boron powder (B), carbon black (C. B.), diphenylamine (DPA), and p‐nitro‐N‐methylamine (PNMA) were incompatible. The results of compatibility studies fully supported the suggested thermal decomposition mechanism of PDFAMO.     

Structural and Preliminary Explosive Property Characterizations of New 3,4,5‐Triamino‐1,2,4‐triazolium (Guanazinium) Salts

Two new highly stable energetic salts were synthesized in reasonable yield by using the high nitrogen‐content heterocycle 3,4,5‐triamino‐1,2,4‐triazole and resulting in its picrate and azotetrazolate salts. 3,4,5‐Triamino‐1,2,4‐triazolium picrate (1) and bis(3,4,5‐triamino‐1,2,4‐triazolium) 5,5′‐azotetrazolate (2) were characterized analytically and spectroscopically. X‐ray diffraction studies revealed that protonation takes place on the nitrogen N1 (crystallographically labelled as N2). The sensitivity of the compounds to shock and friction was also determined by standard BAM tests revealing a low sensitivity for both. B3LYP/6–31G(d, p) density functional (DFT) calculations were carried out to determine the enthalpy of combustion (Δ_cH (1) =−3737.8 kJ mol⁻¹, Δ_cH (2) =−4577.8 kJ mol⁻¹) and the standard enthalpy of formation (Δ_fH° (1) =−498.3 kJ mol⁻¹, (Δ_fH° (2) =+524.2 kJ mol⁻¹). The detonation pressures (P (1) =189×10⁸ Pa, P (2) =199×10⁸ Pa) and detonation velocities (D (1) =7015 m s⁻¹, D (2) =7683 m s⁻¹) were calculated using the program EXPLO5.     

Tetrakis(nitratoxycarbon)methane (Née CLL‐1) as a Potential Explosive Ingredient: a Theoretical Study

Ab initio electronic structure calculations at the MP2/cc‐pVTZ level predict the vibrational stability of the theoretical molecule tetrakis(nitratoxycarbon)methane, designated CLL‐1. The gas phase enthalpy of formation, predicted to be +1029.3 kJ mol⁻¹ using the G3(MP2) method, and the estimated density of 1.87 g cm⁻³ are used to predict the explosive performance properties using the equilibrium thermochemical code CHEETAH. The predicted detonation velocity (8.61 km s⁻¹) and pressure (33.1 GPa) are similar to those of RDX, but with a significantly higher detonation temperature (6740 K). Finally, the stability of this theoretical molecule is investigated by calculating the lowest energy unimolecular decomposition pathways of the HCO₃N model compound as well as barriers to rearrangement upon interaction of two HCO₃N molecules.     

Preparation and Catalytic Activity of Co/CNTs Nanocomposites via Microwave Irradiation

Co nanoparticles supported on carbon nanotubes (CNTs) were prepared by microwave‐assisted heating of the hydrazine reduction in ethylene glycol (EG). The Co/CNT nanocomposites prepared by the microwave‐irradiation method (MIM‐Co/CNTs) were characterized by XRD, SEM, EDS, and BET. It was found that MIM‐Co/CNTs had compact coating, high cobalt loading, and large BET surface area. The obtained products for the thermal decomposition of ammonium perchlorate (AP) were investigated by DTA. The catalytic activity of MIM‐Co/CNTs was better than that of pure Co nanoparticles and Co/CNT nanocomposites by water‐bath method (WBM‐Co/CNTs). The addition of 5 wt.‐% MIM‐Co/CNTs decreased the high decomposition temperature of AP by 174.05 °C and increased the total DTA heat release by 0.799 kJ g⁻¹.     

Theoretical Study on Thermodynamic and Detonation Properties of Polynitrocubanes

We investigated the heat of formation (Δ_fH) of polynitrocubanes using density functional theory B3LYP and HF methods with 6‐31G*, 6‐311+G**, and cc‐pVDZ basis sets. The results indicate that Δ_fH firstly decreases (nitro number m=0–2) and then increases (m=4–8) with each additional nitro group being introduced to the cubane skeleton. Δ_fH of octanitrocubane is predicted to be 808.08 kJ mol⁻¹ at the B3LYP/6‐311+G** level. The Gibbs free energy of formation (Δ_fG) increases by about 40–60 kJ mol⁻¹ with each nitro group being added to the cubane when the substituent number is fewer than 4, then Δ_fG increases by about 100–110 kJ mol⁻¹ with each additional group being attached to the cubic skeleton. Both the detonation velocity and the pressure for polynitrocubanes increase as the number of substituents increases. Detonation velocity and pressure of octanitrocubane are substantially larger than the famous widely used explosive cyclotetramethylenetetranitramine (HMX).