Thermal analysis of the prepared lignin/graphene oxide/polyurethane composite

Lignin/graphene oxide/polyurethane composite was prepared for removing polyaromatics from wastewater. X-ray and TEM are used for the characterization of the prepared composite. Thermal analysis was carried out for two reasons. One reason to ascertain the composite formation and the second to study the thermal stability of the synthesized composite. The kinetic parameters for each one of the decomposition steps were calculated through four methods of the non-isothermal decomposition kinetics calculations, and the kinetic mechanisms were determined by analyzing the thermal data by using thirty-five solid-state reaction models. The results showed that the mechanisms of decomposition steps depend on the type of starting materials. It was observed as the thermal decomposition that lignin passes through an unjustified mechanism. Graphene oxide shows a two-dimension diffusion mechanism. However, the synthesized Lignin/Graphene oxide/Polyurethane composite exhibits a chemical reaction mechanism (one and a half order and second order. The thermodynamic parameters ΔS^#, ΔH^# and ΔG^#, were also computed and discussed.     

Numerical study of countermeasure against thermal stimuli for HMX-based polymer-bonded explosives

ABSTRACT

An accurate thermal decomposition model of Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)-based polymer-bonded explosives is indispensable to the design of countermeasure against environmental thermal stimuli for certain explosive devices. However, the complicated chemical reactions occurring in decomposition of HMX-based polymer-bonded explosives pose great challenge to scientists. In this study, the thermal ignition kinetic model proposed by Tarver is implemented to study thermal decomposition of HMX-based polymer-bonded explosives using commercial software Abaqus, which does not only consider the thermal decomposition of HMX but also the polymer binders. The simulation results are compared to ODTX and Scaled Thermal Explosion Experiment (STEX) and reasonably good agreements are achieved. Then the thermal decomposition model is applied to analyze an explosive device exposed to environmental thermal stimuli. Furthermore, countermeasure against environmental thermal stimuli is suggested and analyzed quantitatively for the explosive device. The time to explosion and environmental temperature before ignition is calculated and analyzed for the explosive device under various heating rates.     

Chemical Kinetic Modeling of HMX and TATB Laser Ignition Tests

Recent high-power laser deposition experiments on octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) produced ignition times from milliseconds to seconds. Global chemical kinetic thermal decomposition models for HMX and TATB developed to predict thermal explosion experiments lasting seconds to days are applied to these laser ignition experimental data. Excellent agreement was obtained for TATB, while the calculated ignition times were longer than experiment for HMX at lower laser fluxes. Inclusion of HMX melting and faster reaction for liquid HMX in the HMX decomposition model improved the agreement with experiment at lower laser energies.     

Preparation and Characterization of the Solid Spherical HMX/F2602 by the Suspension Spray-Drying Method

Solid spherical octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine/fluororubber2602 (HMX/F₂₆₀₂) was prepared by the suspension spray-drying method as follows: firstly, thinning octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) was obtained by a solvent–anti-solvent method. Secondly, thinning HMX suspended in ethyl acetate solvent in a solution of a binder—F₂₆₀₂—was made into a suspension. Finally, the samples were prepared by spray drying. The samples were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectrometry (XPS), X-ray diffraction (XRD), and Fourier transform infrared (FTIR), and its thermal stability as well as mechanical and spark sensitivities were measured. The results of SEM showed that the grain of HMX/F₂₆₀₂ was solid spherical and the particle distribution was homogeneous. The results of XPS indicated that F₂₆₀₂ can be successfully coated on the surface of HMX crystals. Compared to raw HMX, th characteristic drop height was increased from 19.60 to 40.37 cm, an increase of 79.10%. The friction sensitivities of HMX reduced from 100 to 28% and the spark sensitivity of HMX/F₂₆₀₂ increased. The critical explosion temperatures of raw HMX and HMX/F₂₆₀₂ were 275.43 and 274.30°C, respectively. The amount of gas evolution of raw HMX and HMX/F₂₆₀₂ was 0.15 and 0.12 ml·(5 g)^?1, respectively. The results of DSC and vacuum stability tests (VSTs) indicate that the thermal stability of HMX/F₂₆₀₂ was equal to that of raw HMX and HMX and F₂₆₀₂ had good compatibility.     

Thermal characterization of mixtures of nitrotriazolone with HMX and RDX

Abstract

Thermal characterization of mixtures of nitrotria-zolone (NTO) with octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) has been carried out by means of differential scanning calorimetry and thermogravimetric analysis. It has been found that HMX decomposition temperature remains constant through the whole composition range. However NTO decomposition temperature decreases as the NTO/HMX ratio decreases. The RDX decomposition temperature keeps constant in all compositions studied. The RDX melting temperature decreases few degrees. The NTO decomposition appears at lower temperatures as the RDX content increases.     

1,3,3-trinitroazetidine (TNAZ). Study of thermal behaviour. Part II

Abstract

Thermal behavior of TNAZ (1,3,3 - trinitroazetidine) was studied by using differential scanning calorimetry (DSC), differential thermal analysis (DTA), and thermogravimetryc analysis (TGA).

It was found out that TNAZ is thermally more stable than RDX, but less stable than HMX and TNT. The reaction of intensive thermal decomposition starts at 183–230 °C, depending on heating rate, while the first exothermic reaction was observed at 178 °C at the heating rate of 1 °C/min.

By applying multiple heating rate DSC measurements and Ozawa's method the activation energy of 161.3 kJ/mol and pre-exponential factor of 8.27·10¹³ 1/s were calculated from DSC peak maximum temperature-heating rate relationship. By the same method the activation energy of 157.5 kJ/mol and pre-exponential factor of 4.55·10¹³ 1/s were calculated from DTA peak maximum temperature.

By applying Flynn-Wall isoconversional method it was calculated from DSC measurements that the activation energy equals between 140 and 155.6 kJ/mol at degrees of conversion ranging between 0.3 and 0.7, while pre-exponential factor ranges between 7.8·10¹² and 1.92·10¹³ 1/s.     

Characterization and Thermal Decomposition of Nanometer 2,2′, 4,4′, 6,6′-Hexanitro-Stilbene and 1,3,5-Triamino-2,4,6-Trinitrobenzene Fabricated by a Mechanical Milling Method

Nanometer 2,2?, 4,4?, 6,6?-hexanitro-stilbene (HNS) and 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) were fabricated on a high-energy ball mill. The particle sizes of nano-HNS and nano-TATB were 98.4 and 57.8 nm, respectively. An SEM analysis was employed to image the micron morphology of nano-explosives. The particle size distribution was calculated by measuring the size of 300 particles in SEM images. XRD, IR, and XPS analyses were used to confirm whether the crystal phase, molecule structure, and surface elements were changed by the milling process. Thermal decomposition of nano-HNS and nano-TATB was investigated by differential scanning calorimetry (DSC) and thermal-infrared spectrometry online (DSC-IR) analyses. Using DSC traces collected from different heating rates, the kinetic and thermodynamic parameters of thermolysis of raw and nano-explosives were calculated (activation energy (E_K), pre-exponential factor (lnA_K), rate constant (k), activation heat (ΔH^≠), activation free energy (ΔG^≠), activation entropy (ΔS^≠), critical temperature of thermal explosion (T_b), and critical heating rate of thermal explosion (dT/dt)_Tb). The results indicated that nano-explosives were of different kinetic and thermodynamic properties from starting explosives. In addition, the gas products for thermal decomposition of nano-HNS and nano-TATB were detected. Although HNS and TATB are both nitro explosives, the decomposition products of the two were different. A mechanism to explain the difference is proposed.     

Sensitivity of 2,6-Diamino-3,5-Dinitropyrazine-1-Oxide

ABSTRACT

The thermal and shock sensitivities of plastic bonded explosive formations based on 2,6-diamino-3,5-dinitropyrazine-1-oxide (commonly called LLM-105 for Lawrence Livermore Molecule #105) are reported. The One-Dimensional Time to Explosion (ODTX) apparatus was used to generate times to thermal explosion at various initial temperatures. A four-reaction chemical decomposition model was developed to calculate the time to thermal explosion versus inverse temperature curve. Three embedded manganin pressure gauge experiments were fired at different initial pressures to measure the pressure buildup and the distance required for transition to detonation. An Ignition and Growth reactive model was calibrated to this shock initiation data. LLM-105 exhibited thermal and shock sensitivities intermediate between those of triaminotrinitrobenzene (TATB) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazine (HMX).     

Compatibility and thermokinetics studies of octahydro- 1,3,5,7-tetranitro-1,3,5,7-tetrazocine with polyether-based polyurethane containing different curatives

A compatibility of energetic compound with polymeric matrices is of prime importance in the pre-formulation stage for developing of new energetic composite formulations. In the present work, the compatibility of octahydro-l,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) with polyether (PET) polyol (trade name SP-755)-based polyurethanes (PUs) containing different curatives such as 4,4?methylene diphenyl diisocyanate (MDI), isophorone diisocyanate (IPDI), 2,2,4-trimethylhexamethylene diisocyanate (TMDI), and toluene diisocyanate (TDI) has been studied by using a differential scanning calorimetry method. The PET-based PUs were prepared by polymerization between PET polyol and different curatives, then these PUs were further mixed with HMX to study the compatibility and kinetic parameters. Results show that the compatibility and thermal stability are significantly influenced by the different curatives, and suggested thermals stability by thermal data follow the order for a mixture of HMX/SP-755/MDI > HMX/SP-755/TDI > HMX/SP-755/IPDI > HMX/SP-755/TMDI. The thermal degradation kinetics has also been investigated through non-isothermal conditions using the Kissinger and the isoconversional ASTM E689 kinetic methods. The finding shows that there was a significant variation in the apparent activation energy for a mixture of HMX/SP-755/MDI, HMX/SP-755/IPDI, HMX/SP-755/TMDI, and HMX/SP-755/TDI, which were 365.8, 257.7, 134.9, and 241.1 kJ mol^?1, respectively. The apparent activation energies obtained from the Kissinger method at maximum peak temperature are in reasonable agreement and consistent with isoconversional ASTM E689 kinetic method.     

Synthesis and Thermal Decomposition Mechanism of the Energetic Compound 3,5-Dinitro-4-nitroxypyrazole

A novel energetic material, 3,5-dinitro-4-nitroxypyrazole (DNNP), was synthesized via nitration and nucleophilic substitution reaction using 4-chloropyrazole as raw material. The structure of DNNP was characterized by Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR), and elemental analysis. Its detonation properties were calculated and compared with those of other commonly used energetic compounds. The thermal decomposition mechanism of DNNP was studied by means of thermogravimetry and differential scanning calorimetry coupled with a mass spectrometry (DSC-MS). The results show that the detonation properties of DNNP were better than those of TNT and comparable to those of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). In addition, the thermal decomposition mechanism of DNNP was supposed. Initially, the O–NO₂ bond was broken, thereby producing a nitropyrazole oxygen radical. Subsequently, the nitropyrazole oxygen radical was decomposed by free radical cleavage of nitro or isomerized to nitritepyrazole and subsequently decomposed by free radical cleavage of the nitroso group. Finally, pyrazole ring fission occurred and produced N₂, NO, N₂O, and CO₂.     

Ignition and Growth Modeling of Shock Initiation of Different Particle Size Formulations of PBXC03 Explosive

The change in shock sensitivity of explosives having various explosive grain sizes is discussed. Along with other parameters, explosive grain size is one of the key parameters controlling the macroscopic behavior of shocked pressed explosives. Ignition and growth reactive flow modeling is performed for the shock initiation experiments carried out by using the in situ manganin piezoresistive pressure gauge technique to investigate the influences of the octahydro-1,3,5,7–tetranitro-1,3,5,7-tetrazocine (HMX) particle size on the shock initiation and the subsequent detonation growth process for the three explosive formulations of pressed PBXC03 (87% HMX, 7% 1,3,5-trichloro-2,4,6-trinitrobenzene (TATB), 6% Viton by weight). All of the formulation studied had the same density but different explosive grain sizes. A set of ignition and growth parameters was obtained for all three formulations. Only the coefficient G₁ of the first growth term in the reaction rate equation was varied with the grain size; all other parameters were kept the same for all formulations. It was found that G₁ decreases almost linearly with HMX particle size for PBXC03. However, the equation of state (EOS) for solid explosive had to be adjusted to fit the experimental data. Both experimental and numerical simulation results show that the shock sensitivity of PBXC03 decreases with increasing HMX particle size for the sustained pressure pulses (around 4 GPa) as obtained in the experiment. This result is in accordance with the results reported elsewhere in literature. For future work, a better approach may be to find standard solid Grüneisen EOS and product Jones-Wilkins-Lee (JWL) EOS for each formulation for the best fit to the experimental data.     

Control of the Particle Size of Submicron HMX Explosive by Spraying in Non-Solvent

Preparation and characterization of cyclotetramethylene tetranitramine (HMX; octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) submicron particles by spraying in non-solvent technology at different process parameters was investigated in this article. The results indicated that the process parameters, such as addition of surfactant, slurry, and anti-solvent temperatures; compressed air flow rate; slurry flow rate; stirring the anti-solvent; and nozzle diameter played important roles in controlling the performance of HMX submicron particles, such as particle size, size distribution, etc. The produced HMX particles by spraying in a non-solvent method were identified and characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The results showed that this method is simple for micronization of energetic materials and would be an effective method for large-scale preparation of submicron particles of HMX explosive. Finally, the optimum condition for the preparation of fine powder of HMX by spraying in a non-solvent method was proposed.     

Thermal behavior and compatibility study of dihydroxylammonium 3,4-dinitraminofurazan

A large number of nitramino-featured energetic salts have been reported and some of them show promising properties. Among them, the dihydroxylammonium 3,4-dinitraminofurazan (HADNAF) is easy to synthesize and shows high calculated detonation performances and acceptable thermal stability. The non-isothermal kinetics parameters of HADNAF including the apparent activation energy (E) and pre-exponential factor (A) of the exothermic decomposition reaction, and activation entropy (ΔS^≠), activation enthalpy (ΔH^≠), activation Gibbs free energy (ΔG^≠) at T_P0 of the reaction and the critical temperature of thermal explosion (T_b) were obtained by Kissinger’s and Ozawa’s method, respectively. Additionally, the compatibility of HADNAF with other materials (e.g. TNT, RDX, HMX, B, Mg) was tested by DSC method.     

Preparation and Properties of Surface-Coated HMX with Viton and Graphene Oxide

To improve the safety performance of HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) particles, the new carbon material graphene oxide (GO) and Viton were used to coat HMX via a solvent–slurry process. For comparison, the HMX/Viton/graphite (HMX/Viton/G) and HMX/Viton composites were also prepared by the same process. Atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and differential scanning calorimetry (DSC) were employed to characterize the morphology, composition, and thermal decomposition of samples. The impact sensitivity and shock wave sensitivity of HMX-based composites were also measured and analyzed. The results of SEM, XRD, and XPS indicate that the cladding layer of HMX-based composites is successfully constructed. HMX/Viton/GO composites exhibit better thermal stability compared to HMX and HMX/Viton. The results show that both impact and shock wave sensitivities of HMX/Viton/GO composites are much lower than that of HMX/Viton. In addition, GO sheets exhibit a better desensitizing effect than G sheets. These combined properties suggest that nano-GO has good compatibility with explosives and can be utilized as a desensitizer in HMX particles.     

Thermal behavior of hmx and metal powders of different grade

Abstract

The thermal decomposition characteristic of HMX influenced by the addition of aluminum, nickel, copper with different particle size (general and nano-meter) are studied by PDSC and TG. The results showed that nano copper had the greatest influence on the condensed-phase decomposition characteristic of HMX among the metal powders. Such catalysis effect will be weakened by the decrease of the content of metal powder or the increase of system pressure. Based on the kinetics result inferred from the isothermal DSC experiment, the mechanics of such influence are attributed to the efficacy of catalysis effect, secondary effect and reaction site effect.     

Kinetic parameters and geometry of the transition state of decarboxylation reactions of carboxyl and formyl radicals

Experimental data on the degradation of carboxyl radicals RCO ₂ ^. → R^. + CO₂ (where R is an alkyl or aryl) and formyl radicals ROC^.O → R^. + CO₂ (where R is an alkyl or aryl) in the liquid phase were analyzed in terms of the method of crossing parabolas. The kinetic parameters that characterize this decomposition were calculated. Using the density functional theory, the transition state was calculated for the reaction of methyl radical addition to CO₂ at the C and O atoms. A semiempirical algorithm was developed for the calculation of the geometric parameters of the transition state for decomposition reactions of carboxyl and formyl radicals and the reverse addition reactions of R^. with CO₂. The kinetic (activation energies and rate constants) and geometric (interatomic distances in the transition state) reaction parameters were calculated for 37 degradation reactions of various formyl and carboxyl radicals. The activation energies and geometric parameters of the transition state were calculated for the alternative addition reactions of R^. to CO₂:R^. + CO₂ → RCO ₂ ^. (where R is an alkyl or aryl) and R^. + CO₂ → ROC^.O (where R is an alkyl or aryl). A linear correlation between the interatomic distance r ^#(C...C) (or r ^#(C...O)) in the transition state and the reaction enthalpy ΔH _e was found for the degradation reactions of carboxyl and formyl radicals (at br _e = const). The enthalpies, activation energies, and interatomic distances in the transition state for the degradation of carboxyl and formyl radicals and their formation were compared.     

HMX Polymorphs: Gamma to Beta Phase Transformation

The process of conversion of a gamma (γ) polymorph of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) to a beta (β) polymorph is a challenging one. In order to obtain beta HMX from gamma HMX, a novel and economical method, using hot water, has been developed. The characterization of beta HMX using thermo-gravimetric and differential thermal analysis, high-performance liquid chromatography (HPLC), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, and impact sensitivity has been carried out toward its use for various military applications including advanced propellant formulation.     

Degradation of alkyl radicals via C-C bond dissociation: Kinetic parameters and transition state geometry

Experimental data on the gas-phase degradation of alkyl radicals of the type R¹CHR²C^?H₂ → CHR² = CH₂ + R^?1 were rationalized in terms of the method of crossing parabolas. The parameters characterizing the degradation were calculated. The semiempirical algorithm for the calculation of the geometric parameters of the transition state of methyl radical addition to olefins is extended over the reactions of degradation of alkyl radicals. The kinetic (activation energy) and geometric (interatomic distances in the transition state) parameters of the reaction were calculated for the degradation of alkyl radicals of various structures. For the degradation reactions involving the detachment of the methyl radical, a linear correlation between the transition-state interatomic distance r ^#(C…C) and the enthalpy of the reaction ΔH _e was revealed: r ^#(C…C) × 10¹⁰/m = 2.37 ? 1.19 × 10^?2 ΔH _e/kJ mol^?1. A similar relationship is observed for the ethylene elimination reactions: r ^#(C…C) × 10¹⁰/m = 2.40 ? 1.46 × 10^?2ΔH _e/kJ mol^?1. The enthalpies, activation energies, and transition-state interatomic distances for the degradation of alkyl radicals involving H^? and C^?H₃ detachment are compared.     

Numerical modeling of the effect of temperature and particle size on shock initiation properties of HMX and TATB

Abstract

The three-dimensional Eulerian reactive hydrodynamic code 3DE has been used to investigate the effects of particle size (and the remaining void or hole size) and of initial temperature on the shock initiation of heterogeneous explosive charges of HMX and TATB.

Shocks interacting with HMX and TATB containing various hole sizes have been modeled. The void fraction was held at 0.5% while the spherical hole sizes were varied from 5.0- to 0.00005 mm radius. The shock pressure was also varied.

As the hole size in TATB was varied from 5.0 to 0.5 mm, the explosive became more sensitive to shock. Decreasing the hole size to 0.0005 mm resulted in failure of the shock wave to build toward a propagating detonation. This is similar to the results previously reported for TNT.

HMX became more sensitive to shock as the hole size was varied from 0.5 to 0.005 mm. The hole size had to be decreased to 0.0005 mm before the explosive became less shock sensitive. Smaller hole sizes (0.00005 mm) resulted in failure of the shock wave to build to detonation.

At the same density, the most shock-sensitive explosive is the one with particle sizes between coarse and fine material. The shock sensitivity of HMX continues to increase with decreasing hole sizes for hole sizes where TNT or TATB fail.

The shock sensitivity of TATB, TNT, and HMX increases with initial temperature. TATB at 250°C is as shock-sensitive as HMX at 25°C. This is in agreement with experimental observations. The shock sensitivity of HMX is less dependent on temperature than TATB or TNT.     

EFFECTS OF HEATING RATE AND PARTICLE SIZE ON THE PRODUCTS YIELDS FROM RAPID PYROLYSIS OF BEECH-WOOD

ABSTRACT

Effects of pyrolysis temperature (300–1000 ^°C), heating rates (100, 500, 1000, and 10,000 ^°C/s), and particle sizes (53–63,104–120,177–270, and 270–500 urn) on the yields and formation rates of tar, light oils, total gases, and char from pyrolysis of beech-wood under 1 atm helium pressure were studied. Wood particles were pyrolyzed in strips of stainless steel wire mesh in a captive sample apparatus; and yields of products were measured in weight percent of original wood as a function of temperature for different heating rates and particle sizes. The overall weight loss achieved from pyrolysis of this wood was about 90%. The total yields of tar and light oils from pyrolysis of this wood accounted for up to 80% of the original wood above 400 ^°C. Due to the post-pyrolysis reactions of tar and light oils, the tar and light oils yields go through a maximum with pyrolysis temperature for all particle sizes and most heating rates studied here. As particle size increases from 53–63 μm to 270–500 μm the maximum tar yield decreases from 53% to about 38%. The maximum tar yield also decreases with increasing the heating rate from 70% at 100 ^°C/s to 48% at 10,000 ^°C/s heating rate. Theses results indicate that as the intra-panicle post-pyrolysis cracking reactions of tar increases at higher heating rates and with larger particles the tar yield decreases. Tar was also analyzed with GPC for the effects of above pyrolysis parameters on the tar molecular weight. The tar average molecular weight. remains relatively constant (M_w = 300 amu, M_n = 155 amu, and M_z = 483 amu) under helium atmosphere with pyrolysis temperature at 1000 ^°C/s heating rate and with 53/63 u m particle size. The average molecular weight of tar does not significantly varies with heaung rate, but it decreases as the particle size increases.