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.     

Theoretical Prediction of Heats of Sublimation of Energetic Materials Using Pseudo‐Atomic Orbital Density Functional Theory Calculations

We present a predictive model for the heats of sublimation of the condensed phases of energetic materials that combine the empirical relations of Politzer with first‐principles density‐functional calculations of the electronic properties of the molecular surfaces. The distinct features of our methodology are the use of numerical pseudo‐atomic orbitals for the quantum mechanical calculation of the electronic charge density, as well as an improved technique for the molecular surface area determination. As applications, we used our model to predict heats of sublimation of energetic molecules CL‐20, HMX, RDX, TNT, FOX‐7, TATB, and LLM‐105, with the Politzer parameters fit based on a set of eight nitro‐aromatic molecules. In comparison with conventional quantum chemistry calculations, our approach is tremendously less computationally demanding, yet it still demonstrates competitive accuracy and predictive power.     

Molecular Orbital Based Design Guideline for Hypergolic Ionic Liquids

Currently, monomethyl hydrazine is the most widely used hypergolic rocket fuel. Due to its high toxic vapor, there is a thrust towards developing low‐toxic hypergolic fuels. Ultra‐low vapor pressure ionic liquids are one such potential category of fuels. However, designing ionic liquid with ignition delay comparable to monomethyl hydrazine is a challenge, because fundamental understanding of the hypergolic nature of ionic liquids is far from clear. This work used the computed energy gap values between the highest occupied molecular orbitals (HOMO) of the anions for a series of ionic liquids and the lowest occupied molecular orbital (LUMO) of HNO₃, and variation in the computed relative heats of formation, ΔH_f, of these anions to develop correlations to predict hypergol activity between an ionic liquid fuel and nitric acid as the oxidizer. The observed trends in HOMO LUMO energy gap and ΔH_f values can be used successfully to verify not only hypergolicity of known systems but also the lack of this phenomenon in OH⁻ and BF₄⁻ based ionic liquids. It was shown that through suitable substitution of electron withdrawing or electron donating groups in the anion, the energy gap and the ΔH_f values could be tailored into an optimal range that would have a high probability for the new system to exhibit hypergolic reactivity. To validate our method, we suggest herein new ionic liquid structures for synthesis and experimental screening.     

Thermochemistry of Species Potentially Formed During NTO/MMH Hypergolic Ignition

This paper deals with the gas‐phase thermodynamic properties of endothermic compounds potentially formed during monomethylhydrazine (MMH)/nitrogen tetroxide (NTO) hypergolic reactivity. The standard enthalpies of formation at 298.15 K are determined by means of quantum chemistry calculations along with protocols developed for these compounds. The resultant data, currently previously unavailable for almost all of these compounds, are potentially critical to the modeling of combustion chemistry of this bipropellant combination.     

Are DTTO and iso‐DTTO Worthwhile Targets for Synthesis?

Theoretical calculations were carried out for the isomeric di‐1,2,3,4‐tetrazine tetraoxides (DTTO and iso‐DTTO). The most important explosion performance parameters, the detonation pressure and detonation velocity, are dominated by the densities and not by the heats of formation of these compounds. Since DTTO and iso‐DTTO are unknown, reliable predictions of their crystal densities are crucial for an evaluation of the potential of these materials as explosives. In this study, the crystal densities were predicted using both Ammon’s Atom/Functional Group and Atom Code Volume Additivity Parameters and Quantum Mechanical molecular Volume methods, resulting in similar densities and explosion parameters. Although the likely uncertainties in our predicted density values are difficult to assess due to a lack of experimental data for closely related known compounds, our results demonstrate that Shechter’s originally proposed densities and performance parameters were grossly overestimated. Furthermore, it is shown that, based on our predicted density value ranges, DTTO and iso‐DTTO could match or substantially outperform the best state of the art explosives, such as CL‐20. Therefore, the synthesis of DTTO and iso‐DTTO should be further pursued.     

Extension of EOS non-iterative methods to density calculations: Correlation of saturated molar volumes and heats of vaporization

Soave's direct calculation procedures for the vapor pressure of pure compounds with cubic equations of state (EOSs), have been extended to the calculation of phase densities at saturation for Peng-Robinson (PR) type EOSs. These universal relations have been used to propose EOS-based correlation methods for the pure compound saturated liquid and vapor molar volumes, at temperatures higher than the normal boiling point. The methods yield satisfactory results independently of the molecular nature of the chemical under consideration. The results for phase densities are used to correct the heats of vaporization predicted by the ZVPR-EOS. Complete relative error information is provided for calculated heats of vaporization and correlated vapor and liquid phase molar volumes for more than one hundred compounds of industrial interest.     

基于第一原理力场预测热力学参数的探讨

讨论用第一原理全原子力场计算热力学参数的可行性.新开发的TEAM力场,在用气、液相基本性质验证后,不加任何参数调整,直接用于计算具有代表性的几个分子液体在不同热力学状态下的密度、蒸发焓、混合焓、亨利常数、饱和蒸气压等热力学参数.初步结果表明：液体密度和蒸发焓的预测结果良好,在较大范围内可获得与实验数据相吻合的结果;而混合焓的准确预测需要纯液体内聚能的高精度模拟数据;亨利常数的计算对液体的密度极为敏感.后两种性质的计算均可用全原子力场但需要高质量的力场参数.为了采用全原子力场计算气液相平衡数据,提出了一种半经验的、基于积分Clausius-Clapeyron方程的循环自洽方法计算液体的饱和蒸气压.     

Heats of Combustion and Formation of New Energetic Thermoplastic Elastomers Based on GAP,PolyNIMMO and PolyGLYN

Heats of combustion and formation of various energetic thermoplastic elastomers (ETPE), corresponding to linear copolyurethanes based on an energetic prepolymer and a diisocyanate, were measured by a calorimetric method. These ETPEs were synthesized from three different molecular weights of glycidyl azide polymer, from poly(3‐nitratomethyl‐3‐methyloxetane) and from poly glycidyl nitrate. The prepolymers were also analyzed for comparison with the corresponding ETPEs. A significant difference of the heats of formation was observed between the prepolymers and their ETPEs, while the heats of combustion were similar.     

Hypergolic Reactions of TNT

One way being considered to destroy trinitrotoluene (TNT) land or surf mines is to exploit its reactivity using darts containing chemicals, which, upon contact with TNT, cause instantaneous decomposition, but not detonation. To determine the best candidates to fill the darts, liquids, specifically amines, which react in a hypergolic fashion with TNT were examined for both the rate of reaction and amount of energy released. Micro‐calorimetry was used to measure heat release while spectroscopy and conventional peak intensity monitoring by chromatography were used to examine the rate of reaction. Calorimetry measurements showed little variation between different amines reacting with TNT (about 110–130 kJ mol⁻¹ TNT). TNT reaction with hydride actually produced more heat than with amines. Further, dinitrotoluene (DNT), which generates substantial heat, did not undergo a hypergolic reaction with amines suggesting that heat release is not the controlling factor for the hypergolic reactions. Rate constants, determined for the loss of TNT in dilute acetonitrile solution, clearly showed distinctions among the amines. The more primary amine functionalities in the amine compound, the faster it destroyed TNT. Hydrides or amine mixtures spiked with hydride decomposed substantially faster than the amines alone. However, a direct correlation between reaction rate and time‐to‐ignition was not observed.     

Molecular geometry effects and the Gibbs–Helmholtz Constrained equation of state

Differences in molecular size and shape have long been known to cause difficulties the modeling and simulation of fluid mixture behavior and generally manifest themselves as poor predictions of densities and phase equilibrium, often resulting in the need to regress model parameters to experimental data. A predictive approach to molecular geometry within the Gibbs–Helmholtz Constrained (GHC) framework is proposed. The novel aspects of this work include (1) the use of NTP Monte Carlo simulations coupled with center of mass concepts to determine effective molecular diameters for non-spherical molecules, and (2) the use of effective molecular diameters in the GHC equation to predict phase behavior of mixtures with components that have distinct differences in molecular size and shape. Numerical results for a CO₂–alkane, alkane–water and CO₂–alkane–water mixtures show that the proposed approach of combining molecular geometry with the GHC equation provides accurate predictions of liquid densities and two- and three-phase equilibrium.     

Prediction of vapor–liquid equilibrium for polymer solutions based on the COSMO‐SAC model

To extend the application of the COSMO‐SAC model to phase‐equilibrium calculations of polymer solutions, a new strategy for estimating the charge‐density profile, the cavity volume and the cavity surface area of polymer molecules is proposed by finding reasonable parameters for the corresponding repeating structure units. The molecular parameters for polymers are obtained by summing up the corresponding COSMO calculated values of the repeating units calculated by the algorithms of DMol3 (a density functional theory) or MOPAC (a semi‐empirical method). Combining with the COSMO‐SAC model, the activities and equilibrium pressures for several typical polymer solutions are satisfactorily predicted indicating that the proposed method can be used for the prediction of vapor–liquid equilibrium of polymer solutions. It was also found that both DMol3 and MOPAC can be used though the results obtained from them are slightly different. The results in this paper show that the method proposed has the potential to predict other phase‐equilibrium properties of polymer systems. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Diffusion of low‐molecular‐weight permeants through semi‐crystalline polymers: combining molecular dynamics with semi‐empirical models

A molecular dynamics‐based computational approach was used to study the diffusion of oxygen through a model semi‐crystalline polymer, namely linear low‐density polyethylene. The simulated molecules were validated by comparing the predicted properties with experimental values of available free volumes, on atomic scale, using positron annihilation lifetime spectroscopy and measured values of density. The semi‐crystalline polymer was considered as a composite network of a continuous amorphous phase and a dispersed crystalline phase. Based on this observation, the overall diffusion was simulated, including the diffusion through the crystalline phase, which has not been previously reported. A tight correlation was then achieved between experimental and simulated data by utilising several semi‐empirical and analytical models developed for composite materials. The proposed methodology in this work can be effectively used as a basis for designing polymer networks with controlled diffusion characteristics in a bottom‐up approach. © 2018 Society of Chemical Industry     

Hypergolic Behavior of Pyridinium Salts Containing Cyanoborohydride and Dicyanamide Anions with Oxidizer RFNA

A series of low‐cost, pyridinium cation‐based hypergolic ionic liquids (HIL) containing amine, butyl, or allyl substituents with cyanoborohydride [BH₃CN]⁻ and dicyanamide [DCA]⁻ anions were developed and characterized. The investigated physicochemical properties include melting and decomposition temperature, viscosity, density, heat of formation (ΔH_f) and specific impulse (I_sp). The ignition delay (ID) of all HILs was tested with the oxidizer RFNA. The HIL, 1‐allyl 4‐amino pyridinium dicyanamide, exhibited highest density (1.139 g cm⁻³) amongst the known pyridinium HILs. The heats of formation predicted on the basis of Gaussian 09 suit programs were within the range of − 30 to 356 kJ mol⁻¹. The structure of HIL, 1‐butyl 4‐aminopyridinium cyanoborohydride, was examined by single‐crystal X‐ray diffraction, which revealed hydrogen bonding between anion and cation as N1−H1N ⋅⋅⋅ N3=2.07 Å, N1−H2N ⋅⋅⋅ H1B1=2.18 Å, and N1−H2N ⋅⋅⋅ H2B1=2.21 Å, respectively. HIL (1‐allyl 4‐aminopyridiniun cyanoborohydride) exhibited highest I_sp of 228 s amongst the designed series.     

叠氮增塑剂与GAP黏合剂的相容性模拟计算

叠氮含能化合物在提高推进剂能量、改善燃烧性能、降低特征信号等方面优势明显,研究叠氮增塑剂与GAP的相容性可以促进叠氮含能化合物在推进剂中的应用。对6种叠氮含能化合物的生成热、玻璃化转变温度等进行了计算分析,探讨了它们作为含能增塑剂的使用性能。通过分子动力学模拟,发现6种叠氮化合物对内聚能密度和溶解度参数的贡献以范德华作用力为主,其贡献值约为静电力贡献值的1.0³.0倍。计算得到的目标叠氮化合物的溶解度参数与分子结构中的极性基团存在一定的正相关性,即极性基团含量越高,溶解度参数值越大。模拟模型中N100在GAP中的混溶均匀性都没有IPDI和MDI好,但GAP/N100、GAP/IPDI、GAP/MDI的溶解度参数均与纯GAP的相近。叠氮增塑剂DEGBAA与GAP、GAP/N100、GAP/IPDI、GAP/MDI之间的互溶性较理想,PEAA和TMNTA次之。DEGBAA的Tg和黏度都较低,更适合作GAP基推进剂的含能增塑剂。     

PNA Molecular Beacons Assembled by Post‐Synthetic Click Chemistry Functionalization

To avoid the tedious synthesis of functionalized peptide nucleic acid (PNA) monomers for probe development, we proposed a simple approach to modify PNA oligomers by post‐synthetic on‐resin click chemistry. PNA molecular beacons (MBs) were prepared by incorporation of azide‐containing monomers into the oligomer by automatic solid‐phase peptide synthesis and subsequent derivatization with pyrene moieties by copper‐catalyzed azide–alkyne cycloaddition. Two pyrene‐based quencher‐free PNA molecular beacons, a stemless MB and one possessing a stem–loop structure, targeting a portion of the cystic fibrosis gene, were successfully synthesized by using this method. Fluorescence studies showed that the stem–loop MB exhibited better discrimination of changes in excimer/monomer ratios as compared to the stemless MB construct.     

Correlation of Structure and Sensitivity in Inorganic Azides III. A Mechanistic Interpretation of Impact Sensitivity Dependency on Non‐bonded Nitrogen to Nitrogen Distance

Previously established correlations between impact sensitivity and minimum, non‐bonded, nitrogen to nitrogen distances in inorganic azides, imply that there must be a mechanism in operation, which can predict the non reaction of alkali metal azides and the violent decomposition of copper, silver, and lead azides. This paper examines the molecular orbitals used for bonding in the azides. The orbital energy level diagram indicates that the highest occupied molecular orbital, HOMO, are two, π type, non‐bonded orbitals, each occupied by an electron pair. The electron density lobes for these π type orbitals protrude into the space beyond both ends of the azide ion. These orbitals can overlap with ‘p’ and ‘d’ type orbitals on the metal cation, facilitating the transfer of the electron back to the metal cation; an integral part of the decomposition reaction. If an exciton is generated on the azide ion, the electron can migrate, via the extended three center MO, to the metal cation, leaving the positive hole on the terminal nitrogen atom. A similar hole on an adjacent azide, would allow the non‐bonding orbitals on each azide to interact. As the distance between neighboring azide ions decreases, it is postulated that these, non‐bonding, π type orbitals start to overlap and become bonding orbitals between adjacent azide ions. This process forms an unstable N₆ moiety, which leads to the formation of three nitrogen molecules from two original azide ions. Thus, a feasible mechanism for the reaction can explain the observation that azides with non‐bonded nitrogen to nitrogen distances of >300 nm do not show impact sensitivity but, as this distance decreases below 300 nm, the sensitivity increases. The non impact sensitive azides could respond to thermal stimulus, which increases the thermal motion, thus reducing the critical nitrogen to nitrogen non‐bonded distance and reducing the energy for exciton production. Further work is required on the energy changes for such a reaction.     

Reactor Modeling of Gas‐Phase Polymerization of Ethylene

A model is developed for evaluating the performance of industrial‐scale gas‐phase polyethylene production reactors. This model is able to predict the properties of the produced polymer for both linear low‐density and high‐density polyethylene grades. A pseudo‐homogeneous state was assumed in the fluidized bed reactor based on negligible heat and mass transfer resistances between the bubble and emulsion phases. The nonideal flow pattern in the fluidized bed reactor was described by the tanks‐in‐series model based on the information obtained in the literature. The kinetic model used in this work allows to predict the properties of the produced polymer. The presented model was compared with the actual data in terms of melt index and density and it was shown that there is a good agreement between the actual and calculated properties of the polymer. New correlations were developed to predict the melt index and density of polyethylene based on the operating conditions of the reactor and composition of the reactants in feed.     

Computational Studies on the Molecular Stability and Detonation Performance of Nitraminebenzene Derivatives as Novel High-Energy Materials

In this article the detonation performance and stability of the benzene derivatives were studied theoretically to facilitate further developments of energetic materials. The gas-phase heats of formation were calculated based on the isodesmic reaction. The solid-phase heats of formation and heats of sublimation were estimated in the framework of the Politzer approach. Molecular stability was calculated by bond dissociation energies and characteristic height. Detonation velocity and pressure were obtained according to Kamlet-Jacobs equations. The results show that all compounds have positive heats of formation, and compounds D1, D2, D3, E, and F have high detonation performance. In addition, the breaking of N?N bond may be initial step in initiation process. Furthermore, theoretical result suggestions that the most of derivatives have good thermal stability. These calculations could provide basic information that may prove useful for the molecular design of novel high-energy density materials.     

Generalized Flory–Huggins model for heat‐of‐mixing and phase‐behavior calculations of polymer–polymer mixtures

An extended and generalized Flory–Huggins model for calculating the heats of mixing and predicting the phase stability and spinodal diagrams of binary polymer–polymer mixtures is presented. In this model, the interaction parameter is considered to be a function of both temperature and composition. It is qualitatively shown that the proposed model can calculate the heats‐of‐mixing curves containing exothermic, endothermic, and S‐shaped or sigmoidal types and predict the spinodals, including the upper and lower critical solution temperatures, and closed‐loop miscibility regions. Using experimental results of analog calorimetry for four polymer mixtures of polystyrene/poly(vinyl chloride) (PS/PVC), polycarbonate (PC)/poly(ethylene adipate) (PEA), polystyrene/poly(vinyl acetate) (PS/PVAc), and ethylene vinyl acetate copolymer (EVA Co)/chlorinated polyethylene (CPE), the capabilities of the proposed functionality for the interaction parameter was studied. It is shown that this function can be used satisfactorily for the heat‐of‐mixing calculations and phase‐behavior predictions. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1328–1340, 2000     

Note: measuring the effective heats of combustion of transformer‐insulating fluids using a controlled‐atmosphere cone calorimeter

The effective heats of combustion of two commonly used transformer‐insulating fluids, a high molecular weight hydrocarbon fluid and a 50 cS silicone fluid, have been measured using a controlled‐atmosphere cone calorimeter. The study shows that the cone calorimeter is a good tool to measure the effective heats of combustion of transformer‐insulating fluids. Copyright © 2002 John Wiley & Sons, Ltd.