DFT investigation on detonation properties and sensitivities of bridged triazolo[4,5-d]pyridazine based energetic materials

A series of bridged triazolo[4,5-d]pyridazine based energetic materials were optimized at B3LYP/6-311G(d, p) level of density functional theory (DFT), and their detonation properties and sensitivities were calculated. The results show that the  NN bridge/ N₃ group were beneficial to improve values of heats of formation while  NN bridge/ C(NO₂)₃ group can improve detonation properties remarkably. In view of the sensitivities, compound F2 possesses the minimum values of impact sensitivity which reveals that  NHNH bridge/ C(NO₂)₃ group will decrease the stability of the designed compounds. Take both of detonation properties and sensitivities into consideration, compounds C8, E7, E8, F8 were screened as candidates of potential energetic materials since these compounds possess similar detonation properties and sensitivities values to those of RDX. All the calculated results were except to shine lights on the design and synthesis of novel high energy density materials.     

Theoretical studies on the heats of formation, detonation properties, and pyrolysis mechanisms of energetic cyclic nitramines

Density functional theory calculations were performed to find comprehensive relationships between the structures and performance of a series of highly energetic cyclic nitramines. The isodesmic reaction method was employed to estimate the heat of formation. The detonation properties were evaluated by using the Kamlet-Jacobs equations based on the theoretical densities and HOFs. Results indicate the N-NO(2) group and aza N atom are effective substituents for enhancing the detonation performance. All cyclic nitramines except C11 and C21 exhibit better detonation performance than HMX. The decomposition mechanism and thermal stability of these cyclic nitramines were analyzed via the bond dissociation energies. For most of these nitramines, the homolysis of N-NO(2) is the initial step in the thermolysis, and the species with the bridged N-N bond are more sensitive than others. Considering the detonation performance and thermal stability, twelve derivatives may be the promising candidates of high energy density materials (HEDMs). The results of this study may provide basic information for the further study of this kind of compounds and molecular design of novel HEDMs.     

Theoretical study on the detonation properties of energetic TNAD molecular derivatives

Following the successful synthesis of the TNAD (1,4,5,8-tetranitro-1,4,5,8-tetraazadecalin), the amine reactant is theoretically replaced to yield the hypothesized TNAD molecular derivatives. Density functional theory (DFT) calculation method was applied to model TNAD and its derivatives. In this investigation, the target molecular volumes were initially obtained using the group additivity approach, and then transferred into molecular densities. The densities and the least square estimated enthalpies of formation (ΔH_f) of TNAD, and the corresponding derivatives, were obtained and the Kamlet–Jacobs empirical equations were used to determine the related detonation velocity and detonation pressure. The simulation results reveal that three of the TNAD molecular derivatives perform similarly to the traditionally used TNT (2,4,6-trinitrotoluene). Four other derivatives outperform TNT, with performance that approach that of RDX (1,3,5-trinitro-1,3,5-triazacyclohexane).     

Computational investigation of amine-oxygen exciplex formation

It has been suggested that fluorescence from amine-containing dendrimer compounds could be the result of a charge transfer between amine groups and molecular oxygen [Chu, C.-C.; Imae, T. Macromol. Rapid Commun. 2009, 30, 89.]. In this paper we employ equation-of-motion coupled cluster computational methods to study the electronic structure of an ammonia-oxygen model complex to examine this possibility. The results reveal several bound electronic states with charge transfer character with emission energies generally consistent with previous observations. However, further work involving confinement, solvent, and amine structure effects will be necessary for more rigorous examination of the charge transfer fluorescence hypothesis.     

Theoretical investigation on the structures,densities, and detonation properties of polynitrotetraazaoctahydroanthracenes

The polynitrotetraazaoctahydroanthracenes were optimized to obtain their molecular geometries and electronic structures at density functional theory–B3LYP/6‐31+G(d) level. Detonation velocities (D) and detonation pressures (P) were estimated for this nitramine compounds using Kamlet‐Jacobs equations, based on the theoretical densities (ρ) and heats of formation. It is found that there are good linear relationships between volume, density, detonation velocity, detonation pressure and the number of nitro group. Thermal stability of the compounds was investigated by calculating the bond dissociation energies and energy gap (ΔE_LUMO–HOMO). The simulation results reveal that molecule H performs similarly to famous explosive RDX. These results provide basic information for molecular design of novel high energetic density compounds. © 2011 Wiley Periodicals, Inc.     

Theoretical studies on the structures, densities, detonation properties and pyrolysis mechanism of energetic compounds containing pyridine ring

Density function theory has been employed to study a series of compounds containing pyridine ring at the B3LYP/6-31G* level. Detonation performance was evaluated by using the Kamlet–Jacobs equations based on the calculated densities and heats of formation. Some compounds have high densities (ca. 1.9 g cm⁻³) and good performance (detonation velocities over 9 km s⁻¹, detonation pressures about 39 GPa) and may be the potential candidates of high energy density materials. The thermal stability and the pyrolysis mechanism of the title compounds were investigated by the bond dissociation energies and the impact sensitivity predicted. Solvent effect has been investigated and it makes the title compounds more stable in solutions.     

Molecular design of prismane-based potential energetic materials with high detonation performance and low impact sensitivity

To develop new energetic materials, the eleven nitroester substitution derivatives of prismane were investigated at the B3LYP/6-311G** level of density functional theory (DFT). The gas phase heats of formation were calculated by isodesmic reactions and the solid-state heats of formation were obtained by the Politzer approach using the heats of sublimation for the designed compounds. The detonation velocities and pressures of all molecules were calculated by Kamlet–Jacobs equations based on molecular density and heat of detonation. The results show that the nitroester group in prismane is helpful for enhancing molecular detonation properties and power index. Among all molecules, 1,2,3,4-tetrnitroesterprismane has excellent detonation properties (detonation pressure = 40.05 GPa, detonation velocity = 9.28 km/s) and large power index value. The molecular stabilities were evaluated by calculating bond dissociation energies and characteristic heights (H₅₀). The results indicate that the bond dissociation energies of all molecules are above 80 kJ/mol, and all molecules have a larger H₅₀ value than hexanitrohexaazaisowurtzitane (CL-20, 12 cm). The obtained structure–property relationships may provide basic information for the molecular design of novel high-energy materials.     

Comprehensive assessment of physicochemical properties of new energetic materials

The review presents original methodological approaches and summarizes the results of research into the assessment of relationships between the structure of energetic organic compounds and their main physicochemical properties. A large number of experimental values of these parameters were statistically analyzed, and a database of the properties of explosives and rocket propellant ingredients was created. Based on the analysis and integration of these data, approaches were developed to evaluate the fundamental properties of energetic compounds of different chemical classes, such as the enthalpy of formation, the molecular crystal density, and the sensitivity to mechanical impacts. The explosive and ballistic characteristics were calculated. The comprehensive assessment was made of the possible applications of new substances and those poorly characterized by experimental methods.     

纳米结构储氢材料的计算研究与设计

对B原子掺杂的石墨烯、碳纳米管和富勒烯、MB2纳米管和ca表面覆盖的纳米管体系的氢气吸附和存储性能进行了第一原理计算,结果表明在表面曲率比较大的碳材料体系中掺B可以增强其对H2的吸附作用;过渡金属原子与H2由于Kubas作用而表现出很大的H2吸附能;碱土金属Ca离子化后的带电电荷的材料体系,由于与H2发生极化作用,也会增强氢气的吸附性能．综合我们的结果和储氢材料研究的最新进展,讨论了影响储氢材料性能的相关因素,就如何增强材料与H2之间的相互作用,使H2吸附能在0．2～0．4eV之间,能够在温和的条件下吸／放氢,并且具有较大的重量和体积储氢量等问题作了简要论述,这些原理对纳米结构储氢材料的设计有一定的指导意义．     

Accurate thermochemical properties for energetic materials applications. II. Heats of formation of imidazolium-, 1,2,4-triazolium-, and tetrazolium-based energetic salts from isodesmic and lattice energy calculations

A computational approach to the prediction of the heats of formation (DeltaH(f)degrees' s of solid-state energetic salts from electronic structure and volume-based thermodynamics (VBT) calculations is described. The method uses as its starting point reliable DeltaH(f)degrees' s for energetic precursor molecules and ions. The DeltaH(f)degrees' s of more complex energetics species such as substituted imidazole, 1,2,4-triazole, and tetrazole molecules and ions containing amino, azido, and nitro (including methyl) substituents are calculated using an isodesmic approach at the MP2/complete basis set level. On the basis of comparisons to experimental data for neutral analogues, this isodesmic approach is accurate to <3 kcal/mol for the predicted cation and anion DeltaH(f)degrees' s. The DeltaH(f)degrees' s of the energetic salts in the solid state are derived from lattice energy (U(L)) calculations using a VBT approach. Improved values for the alpha and beta parameters of 19.9 (kcal nm)/mol and 37.6 kcal/mol for the U(L) equation were obtained on the basis of comparisons to experimental U(L)' s for a series of 23 salts containing ammonium, alkylammonium, and hydrazinium cations. The total volumes are adjusted to account for differences between predicted and experimental total volumes due to different shapes of the ions (flat vs spherical). The predicted DeltaH(f)degrees' s of the energetic salts are estimated to have error bars of 6-7 kcal/mol, on the basis of comparisons to established experimental DeltaH(f)degrees' s of a subset of the salts studied. Energetic salts with the highest positive DeltaH(f)degrees' s are predicted for azido-containing cations, coupled with heterocyclic anions containing nitro substituents. The substitution of functional groups on carbon versus nitrogen atoms of the heterocyclic cations has interesting stabilization and destabilization effects, respectively.     

Computational study on energetic properties of nitro derivatives of furan substituted azoles

Density functional theory has been used to investigate geometries, heats of formation (HOFs), C-NO₂ bond dissociation energies (BDEs), and relative energetic properties of nitro derivatives of azole substituted furan. HOFs for a series of molecules were calculated by using density functional theory (DFT) and Møller–Plesset (MP2) methods. The density is predicted using crystal packing calculations; all the designed compounds show density above 1.71 g/cm³. The calculated detonation velocities and detonation pressures indicate that the nitro group is very helpful for enhancing the detonation performance for the designed compounds. Thermal stabilities have been evaluated from the bond dissociation energies. Charge on the nitro group was used to assess the impact sensitivity in this study. According to the results of the calculations, tri- and tetra-nitro substituted derivatives reveal high performance with better thermal stability.     

Accurate thermochemical properties for energetic materials applications. I. Heats of formation of nitrogen-containing heterocycles and energetic precursor molecules from electronic structure theory

The heats of formation of 1H-imidazole, 1H-1,2,4-trizazole, 1H-tetrazole, CH3NO2, CH3N3, CH3NH2, CH2CHNO2, HClO4, and phenol, as well as cations and anions derived from some of the molecules have been calculated using ab initio molecular orbital theory. These molecules are important as models for compounds used for energetic materials synthesis. The predicted heats of formation of the heterocycle-based compounds are in excellent agreement with available experimental values and those derived from proton affinities and deprotonation enthalpies to <1 kcal/mol. The predicted value for the tetrazolium cation differs substantially from the experimental value, likely due to uncertainty in the measurement. The heats of formation of the nitro and amino molecules, as well as phenol/phenolate, also are in good agreement with the experimental values (<1.5 kcal/mol). The heat of formation of CH3N3 is predicted to be 72.8 kcal/mol at 298 K with an estimated error bar of +/-1 kcal/mol on the basis of the agreement between the calculated and experimental values for DeltaH(f)(HN3). The heat of formation at 298 K of HClO4 is -0.4 kcal/mol, in very good agreement with the experimental value, as well as a W2 literature study. An extrapolation of the CCSD(T)/aug-cc-pV(Q,5) energies was required to obtain this agreement. This result suggests that very large basis sets (> or =aug-cc-pV5Z) may be needed to fully recover the valence correlation energy contribution in compounds containing elements with high formal oxidation states at the central atom. In addition tight d functions are needed for the geometry predictions. Douglas-Kroll-Hess (DKH) scalar relativistic corrections for HClO4 and ClO4- at the MP2 level with correlation-consistent DKH basis sets were predicted to be large, likely due to the high formal oxidation state at the Cl.     

Critical detonation diameters of highly dispersed energetic substances

The relationship between the critical detonation diameters of energetic substances and their specific surface area was revealed from the results of studying the detonation ability of a series of energetic substances [pentaerythritol tetranitrate (TEN), cyclotrimethylenetrinitramine (RDX), cyclotetramethylenetetranitramine (HMX), 2,4,6-trinitrophenylmethylnitramine (tetryl), benzotrifuroxan (BTF), hexanitrohexaazaisowurtzitane (CL-20), dinitrodifurazanylfuroxan (DNTF), dinitrodifurazanylfurazan (NTF), 1,1-diamino-2,2-dinitroethene (FOX-7)]. A mathematical expression for this relationship was suggested. The critical detonation diameters of highly dispersed (micrometer particles) energetic substances were determined by experiments and calculations. These diameters are in the range 0.06–0.8 mm, which makes these substances suitable for use in aerospace engineering, priming systems, detonation manifolds, and explosion logic devices.     

Substituent effects on heats of formation, group interactions, and detonation properties of polyazidocubanes

We have calculated the heats of formation (HOFs) for a series of polyazidocubanes by using the density functional theory (DFT), Hartree-Fock, and MP2 methods with 6-31G* basis set as well as semiempirical methods. The cubane skeleton was chosen for a reference compound, that is, the cubane skeleton was not broken in the process of designing isodesmic reactions. There exists group additivity for the HOF with respect to the azido group. The semiempirical AM1 method also produced reliable results for the HOFs of the title compounds, but the semiempirical MINDO3 did not. The relationship between HOFs and molecular structures was discussed. It was found that the HOF increases 330-360 kJ/mol for each additional number of the azido group being added to the cubane skeleton. The distance between azido groups slightly influences the values of HOFs. The interacting energies of neighbor azido groups in polyazidocubanes are in the range of 2.3 approximately 6.6 kJ/mol, which are so small and less related to the substituent numbers. The average interaction energy between nearest neighbor --N3 groups in the most stable conformer of octaazidocubane is 2.29 kJ/mol at the B3LYP/6-31G* level. The relative stability related to the number of azido groups of the title compounds was assessed based on the calculated HOFs, the energy gaps between the frontier orbitals, and the bond orders of the C--N3 and C--C bonds. The predicted detonation velocity of hepta- and octa-derivatives is over 9 km/s, and the detonation pressure of them is ca. 40 GPa or over.     

Amination of energetic anions: high-performing energetic materials

The new energetic materials 2-amino-5-nitrotetrazole (ANT, 1), 1-amino-3,4-dinitro-1,2,4-triazole (ADNT, 2), and both 1,1'-diamino-5,5'-bistetrazole and 1,2'-diamino-5,5'-bistetrazole (11DABT, 3 and 12DABT, 4) have been prepared by the amination of the parent anion with O-tosylhydroxylamine. The 5-H-tetrazolate anion has also been aminated using hydroxylamine O-sulfonic acid to both 1-aminotetrazole and 2-aminotetrazole (1AT, 5 and 2AT, 6). The prepared materials have been characterized chemically (XRD (1-4, 6·AtNO(2), 8), multinuclear NMR, IR, Raman) and as explosives (mechanical and electrostatic sensitivity) and their explosive performances calculated using the EXPLO5 computer code. The prepared N-amino energetic materials, which can also be used as new ligands for high energy-capacity transition metal complexes, exhibit high explosive performances (in the range of hexogen and octogen) and a range of sensitivities from low to extremely high.     

Stoichiography for investigation of the functional materials composition,structure, and properties

Principles of the stoichiography and differential dissolution method (DD) providing deep insight into the composition of mixtures containing unknown chemical compounds are considered. Compounds can be identified using their primary feature — the stoichiometry of elemental composition; reference samples of the compounds are not needed. The DD method makes it possible to analyze mixtures of crystalline and/or amorphous phases with constant and/or variable composition in the form of dispersed powders, ceramics, crystals, thin films and nanosize objects. Various aspects of the stoichiography and DD method application to investigation of composition, structure and properties of the functional materials are discussed.     

Measurement of specific heat and energetic characterization of materials up to high temperatures

A new DSC system has been developed which not only allows quantitative results in the temperature of –160C to 700C, but also allows the quantitative determination of a variety of material properties up to 1500C. For example, the specific heat of materials can be measured to at least 1400C, while enthalpies, etc. can be measured to 1500C.

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Zusammenfassung Ein neuartiges DSC Messystem (Netzsch DSC 404) wurde entwickelt, das sich durch hohe Reproduzierbarkeit der Basislinie, grosse Empfindlichkeit und breiten Temperaturanwendungsbereich (–160C bis 700C resp. bis 1500C) auszeichnet. Die Messanordnung ermöglicht die Verwendung von unterschiedlichen GasatmosphÄren als auch Messungen im Vakuum. Es werden Beispiele der Bestimmung von SchmelzvorgÄngen, der Glasumwandlungstemperatur, der KristallinitÄt und der spezifischen WÄrme, sowohl für Polymere als auch für anorganische Materialien dargestellt und diskutiert.

     

Improved prediction of heats of formation of energetic materials using quantum mechanical calculations

We present simple atom and group-equivalent methods that will convert quantum mechanical energies of molecules to gas phase heats of formation of CHNO systems. In addition, we predict heats of sublimation and vaporization derived from information obtained from the quantum-mechanically calculated electrostatic potential of each isolated molecule. The heats of sublimation and vaporization are combined with the aforementioned gas phase heats of formation to produce completely predicted condensed phase heats of formation. These semiempirical computational methods, calibrated using experimental information, were applied to a series of CHNO molecules for which no experimental information was used in the development of the methods. These methods improve upon an earlier effort of Rice et al. [Rice, B. M.; Pai, S. V.; Hare, J. Combust. Flame 1999, 118, 445] through the use of a larger basis set and the application of group equivalents. The root-mean-square deviation (rms) from experiment for the predicted group-equivalent gas phase heats of formation is 3.2 kcal/mol with a maximum deviation of 6.5 kcal/mol. The rms and maximum deviation of the predicted liquid heats of formation are 3.2 and 7.4 kcal/mol, respectively. Finally, the rms and maximum deviation of predicted solid heats of formation are 5.6 and 12.2 kcal/mol, respectively, an improvement in the rms of approximately 40% compared to the earlier Rice et al. predictions using atom equivalents and a smaller basis set (B3LYP/6-31G*).