Thermal behavior of new oxidizer ammonium dinitramide

Ammonium dinitramide (ADN) is a promising new oxidizer for solid propellants because of its high oxygen balance and high energy content, and halogen-free combustion products. One of the characteristics needed for solid propellants is stability. Heat, light, and moisture are factors affecting stability during storage, manufacture, and use. For practical use of ADN as a solid propellant, clarification of the mechanism of decomposition by these factors is needed to be able to predict lifetime. This study focused on thermal decomposition of ADN. Exothermal behavior of ADN decomposition was measured by isothermal tests using high-sensitive calorimetry (TAM) and non-isothermal tests using differential scanning calorimetry (DSC). Based on these results, analysis of the decomposition kinetics was conducted. The activation energy determined by TAM tests was lower than that from DSC tests. Thus, the decomposition path in TAM tests was different from that in DSC tests. The amount of ADN decomposition predicted from TAM tests was closer to that found under real storage conditions than the amount of decomposition predicted from DSC tests. Non-isothermal tests may not be able to precisely predict the lifetime of materials with a decomposition mechanism that changes with temperature, such as ADN. The lifetime predicted from DSC results was much longer than that from TAM tests especially at low temperature. It is necessary to use isothermal tests to predict the long-term stability at low temperature.     

Theoretical study of the thermal decomposition of the 5-methyl-2-furanylmethyl radical

The thermal decomposition of the 5-methyl-2-furanylmethyl radical (R(1)), the most important primary radical formed during the combustion and thermal decomposition of 2,5-dimethylfuran (a promising next-generation biofuel), was studied using CBS-QB3 calculations and master equation (ME)/RRKM modeling. Because very little information is available in the literature, the detailed potential energy surface (PES) was investigated thoroughly. Only the main pathways, having a kinetic influence on the decomposition of R(1), were retained in the final ME/RRKM model. Among all the channels studied, the ring-opening of the 5-methyl-2-furanylmethyl radical, followed by ring enlargement to form cyclohexadienone molecules is predicted to be the easiest decomposition channel of R(1). The C(6) cyclic species formed can undergo unimolecular reactions to yield phenol and to a lesser extent cyclopentadiene and CO. Our calculations predict that these species are important products formed during the pyrolysis of 2,5-dimethylfuran (DMF). Other channels involved in the decomposition of R(1) lead directly to the formation of linear and cyclic unsaturated C(5) species and constitute an additional source of cyclopentadiene and CO. High-pressure limit rate constants were computed as well as thermochemical properties for important species. ME/RRKM analysis was performed to probe the influence of pressure on the rate coefficients and pressure dependent rate coefficients were proposed for pressures and temperatures ranging, respectively, from 10(-2) bar to 10 bar and 1000 to 2000 K.     

Theoretic studies on the kinetics and mechanism of multi-channel gas-phase unimolecular reactions of 1-chloropropane and 2-chloropropane

The potential energy surfaces of the gas-phase unimolecular decomposition reactions of 1-chloropropane and 2-chloropropane are investigated by various quantum chemical methods including CCSD(T), CCSD, GBS-QB3, C3B3, MP4, MP2, and B3LYP. Modified strong collision/RRKM theory was used to calculate the unimolecular rate constants as a function of pressure and temperature. It is found that the major reaction pathway is the HCl elimination. It is predicted that bond dissociation reactions have negligible contribution to the overall rate constant. The computed rate constants are compared with the available experimental data.     

Preparation, thermal decomposition and lifetime of Eu(III)-phenanthroline complex doped xerogel

The main purpose of this work is proposing a new method of using non-isothermal formal kinetics analysis to predict the lifetime of luminescent complex materials. The Eu(III)-phenanthroline complex doped xerogel has been in situ synthesized by a catalyst-free sol-gel method. The photoluminescence spectra and TG curves of the xerogel verify the formation and decomposition of Eu(III)-phenanthroline complex in xerogel. The decomposition of the xerogel formally occurs in three steps. The Friedman and FWO isoconversional methods and multivariate non-linear regression method are used for formal kinetic analysis. The overall decomposition process below 800 °C is fitted by three-step consecutive reaction. The best fitted model for each step is F_n (n order reaction, the corresponding function f(α) is (1 − α)ⁿ). Correlation coefficient is 0.99956. The lifetime values of xerogel at different temperatures are predicted based on non-isothermal kinetic models by the 5% decomposition of europium organic complex.     

Characterization of a sucrose/starch matrix through positron annihilation lifetime spectroscopy: unravelling the decomposition and glass transition processes

The triplet state of positronium, o-Ps, is used as a probe to characterize a starch-20% w/w sucrose matrix as a function of temperature (T). A two-step decomposition (of sucrose, and then starch) starts at 440 K as shown by a decrease in the o-Ps intensity (I(3)) and lifetime (τ(3)), the latter also disclosing the occurrence of a glass transition. Upon sucrose decomposition, the matrix acquires properties (reduced size and density of nanoholes) that are different from those of pure starch. A model is successfully established, describing the variations of both I(3) and τ(3) with T and yields a glass transition temperature, T(g) = (446 ± 2) K, in spite of the concomitant sucrose decomposition. Unexpectedly, the starch volume fraction (as probed through thermal gravimetry) decreases with T at a higher rate than the free volume fraction (as probed through PALS).     

Ab initio MRD-CI study of the spectrum of the TeO molecule employing relativistic effective core potentials

Potential energy curves and properties of the low-lying electronic states of tellurium oxide have been computed using a configuration interaction treatment that includes the spin-orbit coupling interaction. Relativistic effective core potentials (RECPs) are used to describe the inner shells of both the Te and O atoms. Good agreement is obtained for the spectroscopic constants of the X1-X2(3)sigma-, a1delta, and b1sigma+ states for which experimental data are available. The ratio of the parallel and perpendicular b-X transition moments, as well as the radiative lifetime of the b state, was computed, and both results were also found to be in good agreement with measurement. The energetic order of the electronic states in TeO appears to be very similar to that observed for the isovalent O2 molecule, but the Rydberg valence-mixing effects that are so prominent in the latter's spectrum (e.g., for the Schumann-Runge bands) are totally absent in TeO.     

Storage lifetime management and thermal hazard assessment of thermally reactive material

This is a novel idea: replacing highly dangerous and complex testing of solid thermally reactive materials through smart technology. We investigated the prediction of the storage lifetime and the thermal impact of thermally reactive material by different thermal analysis models: differential scanning calorimetry (DSC) for non-isothermal tests versus DSC isothermal tests. Two kinds of kinetic models were compared for evaluating appropriate kinetic parameters of thermal decomposition, and then the thermal hazard parameters were estimated by cartridge package simulation, which could result in reliable thermal hazard properties of a thermal reactive material’s thermal decomposition. We also determined the unsafe characteristics of a thermally reactive material stored in a depot under lifetime, so as to prevent runaway reactions that induce incidents by heat attack during storage. We were interested in an effective and smart analysis technology to reduce energy consumption of the dangerous testing. There are also calls for a smart testing technology which is the achieved object here for reducing energy consumption and avoiding runaway reaction disaster of thermally reactive materials.     

Homogeneous decomposition mechanisms of diethylzinc by Raman spectroscopy and quantum chemical calculations

The gas-phase decomposition pathways of diethylzinc (DEZn), a common precursor for deposition of Zn-VI compounds, were investigated in detail. The homogeneous thermal decomposition of DEZn in N2 carrier was followed in an impinging-jet, up-flow reactor by Raman scattering. Density Functional Theory calculations were performed to describe the bond dissociation behavior using the model chemistry B3LYP/6-311G(d) to estimate optimal geometries and Raman active vibrational frequencies of DEZn, as well as anticipated intermediates and products. Comparison of the measured DEZn decomposition profile to that predicted by a 2-D hydrodynamic simulation revealed that simple bond dissociation between zinc and carbon atoms is the dominant homogeneous thermal decomposition pathway. The calculations suggest several reactions involving intermediates and Raman scattering experiments confirming the formation of the dimer (ZnC2H5)2. In a different set of experiments, photolysis of DEZn gave evidence for decomposition by beta-hydride elimination. The results suggest that beta-hydride elimination is a minor pathway for the gas-phase homogeneous pyrolysis of diethylzinc. A reasonable transition state during beta-hydride elimination was identified, and the calculated energies and thermodynamic properties support the likelihood of these reaction steps.     

Tuning the physisorption of molecular hydrogen: binding to aromatic,hetero-aromatic and metal-organic framework materials

We present a study on the binding properties of molecular hydrogen to several polar aromatic molecules and to a model for the metal-oxide corner of the metal organic framework materials recently investigated as promising supports for hydrogen storage. Density functional theory employing the Perdew Wang exchange-correlation functional and second order Møller-Plesset calculations are used to determine the equilibrium structures of complexes with molecular hydrogen and their stability. It is found that for most hetero-aromatics the edge sites for molecular hydrogen physisorption have stabilities comparable to the top sites. The DFT predicted binding energies compare favorably with those estimated at MP2 level, and get closer to the MP2 results for increased electrostatic contributions (induced by the polar aromatics) to the intermolecular interaction. Vibrational frequencies are also computed at the DFT level, and infrared activities of the H₂ stretching frequency are compared for the various complexes. Pyrrole, pyridine and n-oxide pyridine are predicted to form the more stable complexes among one-ring aromatics. The computed binding energies to metal-organic framework materials are in good agreement with experimental observations. It is suggested that replacement of the organic linker in MOF materials with some of the more efficient aromatics investigated here might contribute to enhance the H₂ storage properties of mixed inorganic–organic materials.     

N,N′-二苯胺基己二酰胺β-晶型成核剂的热分解动力学分析

基于热重分析、微商热重分析及示差热分析研究了N,N′-二苯胺基己二酰胺β-晶型成核剂在空气气氛中的热分解动力学;通过利用Friedman方程和Flynn-Wall-Ozawa(FWO)方程对其热分解过程进行动力学分析求得了其热分解表观活化能;同时利用Achar-Brindly-Sharp方程和Coats-Redfern方程研究了其热分解机理,用等温热重分析法测得了失重10%时的寿命方程.结果表明,N,N′-二苯胺基己二酰胺β-晶型成核剂的表观活化能为138.66kJ.mol-1,其热分解反应的机理函数符合Mample法则,反应级数n=3/2,动力学方程为G(α)=α3/2,寿命方程为:lnτ=-51.877+2.922 2×104/T.     

Competition Between Concerted and Stepwise Dynamics in the Triplet Di‐π‐Methane Rearrangement

The molecular dynamics of the triplet‐state Zimmerman di‐π‐methane rearrangement of dibenzobarrelene were computed with B3LYP and M06‐2X density functionals. All productive quasiclassical trajectories involve sequential formation and cleavage of C? C bonds and an intermediate with lifetimes ranging from 13 to 1160 fs. Both dynamically concerted and stepwise trajectories are found. The average lifetime of this intermediate is significantly shorter than predicted by either transition‐state theory or the Rice–Ramsperger–Kassel–Marcus model, thus indicating the non‐statistical nature of the reaction mechanism.     

Synthesis,structure, electronic and vibrational spectra of 9-(Diethylamino)-benzo(a)phenoxazin-7-ium-5-N-methacrylamide

The electronic and vibrational spectra of 9-(Diethylamino)-benzo(a)phenoxazin-7-ium-5-N-methacrylamide (Nile Blue-5-N-methacrylamide) are measured, and the results are compared with the theoretical values obtained by quantum chemical calculations. The geometry, electronic transitions, charge distribution, and the IR normal modes of this new dye and of its precursor Nile Blue have been computed by using Density Functional Theory (DFT) method with the functional B3LYP and the 6-31G(d) Gaussian basis set. The molecular properties of the two dyes, predicted and observed, are very similar in the electronic ground state. In the excited state, however, the longer lifetime and larger fluorescence quantum yield of the Nile Blue-5-methacrylamide is ascribed to an inhibition of the twisted intramolecular charge transfer (TICT) process, when the NH2 is substituted by the methacrylamide in the 5-position of the aromatic extended ring of the dye. The change in charge density of the N atom in 5-position, as well as the difference in dipole moment and ionization potential of the two dyes molecules, explain the attenuation of TICT process. The vibration spectra of both dyes are simulated properly by using the DFT method.     

Microscopic approaches to liquid nitromethane detonation properties

In this paper, thermodynamic and chemical properties of nitromethane are investigated using microscopic simulations. The Hugoniot curve of the inert explosive is computed using Monte Carlo simulations with a modified version of the adaptative Erpenbeck equation of state and a recently developed intermolecular potential. Molecular dynamic simulations of nitromethane decomposition have been performed using a reactive potential, allowing the calculation of kinetic rate constants and activation energies. Finally, the Crussard curve of detonation products as well as thermodynamic properties at the Chapman-Jouguet (CJ) point are computed using reactive ensemble Monte Carlo simulations. Results are in good agreement with both thermochemical calculations and experimental measurements.     

Adiabatic thermokinetics and process safety of pyrotechnic mixtures

Pyrotechnic mixtures are susceptible to explosive decompositions. The aim of this paper is to generate thermal decomposition data under adiabatic conditions for fireworks mixtures containing potassium nitrate, barium nitrate, sulfur, and aluminum which are manufactured on a commercial scale. Differential scanning calorimeter is used for screening tests and accelerating rate calorimeter is used for other studies. The self heat rate data obtained showed onset temperature in the range of 275?C295?°C for the fireworks atom bomb, Chinese cracker and palm leaf cracker. Of the three mixtures studied, atom bomb mixture had an early onset at 275?°C. The mixtures in general showed vigor exothermic decompositions. Palm leaf mixture exhibits multiple exotherm and reached a final temperature of 414?°C. The thermal decomposition contributes to substantial rise in system pressure. The heats of exothermic decomposition and Arrhenius kinetics were computed. The kinetic data are validated by comparing the predicted self heat rates with the experimental data.     

Monte Carlo determination of the oscillator strength and excited state lifetime for the Li 22S → 22P transition

A recently developed Monte Carlo method is used to compute the 2²S → 2²P transition dipole moment of Li. This approach employs a guided Metropolis random walk with quantum Monte Carlo “side” walks to sample the required probability distributions. The transition dipole moment is employed to obtain the oscillator strength and excited-state lifetime. Our most accurately converged calculations yield an oscillator strength of 0.742(7) and excited-state lifetime of 27.41(35) ns. These results are in excellent agreement with precise experimental measurements of 0.742(1) and 27.29(4) ns, respectively. In addition, single-state expectation values are computed for both states. Monte Carlo parameters, such as the time step size and the convergence time, are varied in order to study their effect on computed results.     

Investigation on the thermo-mechanical properties and thermal stability of polylactic acid tissue engineering scaffold material

Thermogravimetric analysis and dynamic mechanical analysis were combined with scanning electron microscopy to analyze the thermo-mechanical properties and thermal stability of polylactic acid (PLA) foams fabricated using a solvent-free solid-state gas foaming method. The dependence of decomposition time and the lifetime on the PLA cell size was evaluated based on the thermal decomposition kinetic analyses. The results show that PLA specimens with larger cell sizes can be made at lower saturation gas pressures, which will ensure that the fabricated PLA foams have a shorter decomposition time, better flexibility, and are more satisfactory for medical requirements of tissue engineering scaffold (TES) material. The current work may help to optimize the PLA foaming parameters and precisely design PLA foams with different decomposition times according to specific TES requirements of different organ structures.     

Electronic states and spectroscopic properties of SiTe and SiTe+

Ab initio based configuration interaction calculations have been carried out to study the low-lying electronic states and spectroscopic properties of the heaviest nonradioactive silicon chalcogenide molecule and its monopositive ion. Spectroscopic constants and potential energy curves of states of both SiTe and SiTe+ within 5 eV are reported. The calculated dissociation energies of SiTe and SiTe+ are 4.41 and 3.52 eV, respectively. Effects of the spin-orbit coupling on the electronic spectrum of both the species are studied in detail. The spin-orbit splitting between the two components of the ground state of SiTe+ is estimated to be 1880 cm(-1). Transitions such as 0+ (II)-X1Sigma(+)0+, 0+ (III)-X1Sigma(+)0+, E1Sigma(+)0+ -X1Sigma(+)0+, and A1Pi1-X1Sigma(+)0+ are predicted to be strong in SiTe. The radiative lifetime of the A1Pi state is less than a microsecond. The X(2)2Pi(1/2)-X(1)2Pi(3/2) transition in SiTe+ is allowed due to spin-orbit mixing. However, it is weak in intensity with a partial lifetime for the X2 state of about 108 ms. The electric dipole moments of both SiTe and SiTe+ in their low-lying states are calculated. The vertical ionization energies for the ionization of the ground-state SiTe to different ionic states are also reported.     

Computational analysis of some possible initial steps in the unimolecular thermal decompositions of 1,3-diazacyclobutane and its 1,3-dinitramine derivative

Summary We have investigated some possible initial steps in the unimolecular thermal decompositions of 1,3-diazacyclobutane and its 1,3-dinitramine derivative, the latter being selected as the simplest example of a symmetric cyclic nitramine. Vibrational analyses were used to identify normal modes that, in the extreme limits, would correspond to bond rupture and molecular decomposition. The energy requirements for ring fragmentation and N-N bond-breaking were computed at the MP4/6-31G level, using SCF 3-21G optimized structures. It was concluded that ring-fragmentation is a probable initiating step in the decomposition of the unsubstituted molecule, and that it is roughly competitive with N-N bond scission for the dinitramine. The nitronitrite rearrangement is predicted, on the basis of SCF calculations, to be less likely than either of the other two processes. It is proposed that N-N bond-breaking may be of primary importance for nitramine stability, but that energetic performance may be determined more by decomposition pathways having energy barriers.     

Hydrogen bond lifetime for water in classic and quantum molecular dynamics

The lifetime of hydrogen bonds in water at T = 298 K and p = 0.1 MPa is computed by means of classic molecular dynamics with eight different potentials of pair lifetime interaction and Car-Parinello molecular dynamics. The results obtained using various computational techniques for hydrogen bond life-times are compared. It is shown that they can differ from one another by several times. The dependence for the hydrogen bond lifetime computed in our numerical experiment upon the method of its determination is found.     

多羧酸根铕二元配合物的合成及光谱分析

分别以1,3,5-苯三甲酸(H₃BTC)、苯六甲酸(H₆MTA)和1,2,3,4,5,6-环己六甲酸(H₆CCA)为配体合成了Eu(III)的二元发光配合物Eu(BTC)·2H₂O, Eu₂(MTA)·4H₂O 和Eu₂(CCA)·4H₂O. 通过元素分析、红外光谱和等离子体原子发射光谱对其化学组成进行了结构表征, 表征结果与理论吻合良好. 利用荧光分度计, 研究了所制备配合物室温条件下的荧光性能(荧光激发光谱、发射光谱、荧光寿命和量子效率), 结果表明: 该三种配合物在紫外光照射下, 均发射Eu(III)离子的特征红光, 其中Eu₂(MTA)·4H₂O(量子效率＝10.25%, 荧光寿命＝0.36 ms)的荧光性能最好, 这说明配体H₆MTA 的能级与Eu³⁺离子能级匹配程度很好. 另外, 通过热分析对配合物的热稳定性进行了分析, 结果表明: 该三种配合物均具有良好的热稳定性, 主要分解温度远高于其他β-二酮配合物.