High Heat Of Formation Research Articles

Computational characterization of 2, 4, 6, 8, 10, 12, 13-heptaazatetracyclo [5.5.1.03,11.05,9]tridecanes as potential energetic compounds

The characters of high density and high heat of formation of cage molecules have attracted a lot of investigations as potential energetic materials. Several such compounds have been synthesized, e.g., octanitrocubane, hexanitrohexaazaisowurzitane (CL-20), and 4-trinitroethyl-2, 6, 8, 10, 12-pentanitrohexaazaisowurtzitane(TNE-CL-20). In the present study, a new cage compound, namely 2, 4, 6, 8, 10, 12, 13-heptaazatetracyclo [5.5.1.03,11.05,9] tridecane (HATT), was proposed. Density functional theory has been employed to study the geometric and electronic structures for a series of nitro derivatives of HATT at the B3LYP/6-31G(d,p) level. Thermodynamic properties derived on the basis of statistical thermodynamic principles are linearly correlated with the numbers of nitro group as well as the temperature. Detonation performance was evaluated based on the calculated densities and heats of formation. It is found that some title compounds have high densities of ca. 1.9 g cm−3, detonation velocities over 9.0 km s−1, and detonation pressures of about 40.0 GPa and may be novel potential candidates of high energy density compounds (HEDCs). Thermal stability and pyrolysis mechanism of the nitro HATTs were investigated by calculating the bond dissociation energies (BDE). In conjunction with the detonation performance and thermal stability, HATTs with no less than five nitro groups are recommended as the preferred candidates of HEDCs. These results provide basic information for the further studies of cage compounds.

Computational study of energetic nitrogen-rich derivatives of 1,4-bis(1-azo-2,4-dinitrobenzene)-iminotetrazole

The heats of formation (HOFs), electronic structure, energetic properties, and thermal stabilities for a series of 1,4-bis(1-azo-2,4-dinitrobenzene)-iminotetrazole derivatives with different substituents and substitution positions and numbers of nitrogen atoms in the nitrobenzene rings were studied using the DFT-B3LYP method. All the substituted compounds have higher HOFs than their parent compounds. As the number of nitrogen atoms in the nitrobenzene ring increases, the HOFs of the derivatives with the same substituent rise gradually. Replacing carbon atoms in the nitrobenzene with nitrogen atoms to form N-N bonds is very helpful in improving their HOFs. Most of the substituted compounds have higher HOMO-LUMO gaps than the corresponding unsubstituted compounds. Substitution of the -NO₂, -NF₂, or -ONO₂ group and an increase in the number of nitrogen atoms in the nitrobenzene rings are useful for enhancing their detonation performance. The substituents' substitution is not favorable for improving thermal stability. Considering detonation performance and thermal stability, five compounds may be considered potential candidates for high energy density compounds (HEDCs).

Why Are SnN4 (n = 1–4) Species “Missing”? Answers in a Broader Theoretical Context of Binary S–N Compounds

Computational investigations of the thermochemical stability and kinetic persistence of binary S(x)N(y) compounds, SN(2), S(2)N(2), S(3)N(2), S(4)N(2), SN(4), S(2)N(4), S(3)N(4), and S(4)N(4), explain why some S(x)N(y) stoichiometries exist but not others. There is no direct link between the Hückel 4n + 2 π-electron count rule and the computed heats of formation (per atom) of the lowest-energy neutral S(n)N(4) (n = 1-4) isomers, but kinetic persistence often is paramount. Thus, the five lowest-energy S(2)N(4) minima at the B3LYP/6-311+G(3df) density functional theory level (A1-A5) all not only have high computed heats of formation [Δ(f)H°(0 K) > 131 kcal/mol or >22 kcal/mol/atom] but also have low dissociation barriers (less than 21.5 kcal/mol for the most favorable pathways). For comparison, the persistent (but potentially explosive!) cyclic S(2)N(2)-c has about the same high heat of formation (per atom) as the least unfavorable S(2)N(4) isomer, but its barrier to ring opening (51 kcal/mol) is much higher. Although aromatic, both SN(4) (6π electron) and S(3)N(4) (10π electron) have low dissociation barriers and, like S(2)N(4), are also absent from the S-N binary family.

Tris(triazolo)benzene and Its Derivatives: High‐Density Energetic Materials

High-performance explosives: Tris(triazolo)benzene was synthesized and converted to its trinitro and trichloro derivatives (see scheme; R=NO(2), Cl). The heats of formation of this "high-nitrogen" compounds were calculated and combined with experimentally determined densities to determine detonation pressures and velocities. They exhibit high density, good thermal stability, high heats of formation, and moderate to good detonation properties.

Studies on energetic properties for nitrotetrazole substituted triazole and oxadiazole derivatives with density functional theory

The solid state heats of formation (HOF) for 14 designed compounds are calculated using the Politzer approach. The gas phase HOF are predicted with the density functional theory (DFT) B3PW91/6-31 G(d, p) method by means of designed isodemic reactions. All the designed compounds possess solid state HOF above 830 kJ/mol. Furthermore, the results consistently show that C-substituted tetrazoles possess higher HOFs than the corresponding N-substituted isomers. The crystal densities of the designed compounds were predicted with the cvff force field. All of the designed compounds had densities greater than 1.73 g/cm3. The detonation velocities and pressures were evaluated using the Kamlet–Jacobs equations, utilizing the predicted densities and solid state HOF. It was found that designed compounds have a detonation velocity above 8.3 km/s and detonation pressure over 30 GPa. The nitrogen content, oxygen balance and predicted performance implies that the designed molecules are expected to be candidates for high-energy materials (HEMs).

Computational Study on Substituteds-Triazine Derivatives as Energetic Materials

s-Triazine is the essential candidate of many energetic compounds due to its high nitrogen content, enthalpy of formation and thermal stability. The present study explores s-triazine derivatives in which different -NO2, -NH2and -N3substituted azoles are attached to the triazine ring via C-N linkage. The density functional theory is used to predict geometries, heats of formation and other energetic properties. Among the designed compounds, -N3derivatives show very high heats of formation. The densities for designed compounds were predicted by using the crystal packing calculations. Introduction of -NO2group improves density as compared to -NH2and -N3, their order of increasing density can be given as NO2>N3>NH2. Analysis of the bond dissociation energies for C-NO2, C-NH2and C-N3bonds indicates that substitutions of the -N3and -NH2group are favorable for enhancing the thermal stability ofs-triazine derivatives. The nitro and azido derivatives of triazine are found to be promising candidates for the synthetic studies.

Thermal decomposition kinetics of 1-methyl-3,4,5-trinitropyrazole

Thermal decomposition of 1-methyl-3,4,5-trinitropyrazole (MTNP) has been investigated using TG-DTA technique under nitrogen atmosphere. The compound showed good thermal stability with exothermic decomposition peak at 248 °C on DTA. Kinetic parameters were calculated from the DTA peak temperatures at different heating rates. The activation energy required for the thermal decomposition of MTNP according to Flynn–Wall–Ozawa and Friedman methods have been found to be 67.48 and 56.80 kcal mol −1 respectively. Due to the promising properties such as lower melting point, higher heat of formation, higher activation energy, higher density and better performance, MTNP may find use as melt cast and insensitive explosive applications in near future.

Theoretical studies on polynitrobicyclo[1.1.1]pentanes in search of novel high energy density materials

AbstractBicyclo[1.1.1]pentane is a highly strained hydrocarbon system due to close proximity of nonbonded bridge head carbons. Based on fully optimized molecular geometries at the density functional theory using the B3LYP/6-31G* level, densities, detonation velocities, and pressures for a series of polynitrobicyclo[1.1.1]pentanes, as well as their thermal stabilities were investigated in search for high energy density materials (HEDMs). The designed compounds with more than two nitro groups are characterized by high heat of formation and magnitude correlative with the number and space distance of nitro groups. Density was calculated using the crystal packing calculations and an increase in the number of nitro groups increases the density. The increase in density shows a linear increase in the detonation characteristics. Bond dissociation energy was analyzed to determine thermal stability. Calculations of the bond length and bond dissociation energies of the C-NO2 bond indicate that this may be the possible trigger bond in the pyrolysis mechanism. 1,2,3-Trinitrobicyclo[1.1.1]pentane (S3), 1,2,3,4-tetranitrobicyclo[1.1.1]pentane (S4), and 1,2,3,4,5-pentanitrobicyclo[1.1.1]pentane (S5) have better energetic characteristics with better stability and insensitivity, and as such may be explored in defense applications as promising candidates of the HEDMs series.

Synthesis and Energetic Properties of Bis‐(Triaminoguanidinium) 3,3′‐Dinitro‐5,5′‐Azo‐1,2,4‐Triazolate (TAGDNAT): A New High‐Nitrogen Material

AbstractThis paper describes the synthesis and characterization of bis‐(triaminoguanidinium)‐3,3′‐dinitro‐5,5′‐azo‐1,2,4‐triazolate (TAGDNAT), a novel high‐nitrogen molecule that derives its energy release from both a high heat of formation and intramolecular oxidation reactions. TAGDNAT shows promise as a propellant or explosive ingredient not only due to its high nitrogen content (66.35 wt.‐%) but also due to its high hydrogen content (4.34 wt.‐%). This new molecule has been characterized with respect to its morphology, sensitivity properties, explosive, and combustion performance. The heat of formation of TAGDNAT was also experimentally determined. The results of these studies show that TAGDNAT has one of the fastest low‐pressure burning rates (at 6.9 MPa) measured till date, 6.79 cm s−1 at 6.9 MPa (39% faster than triaminoguanidinium azotetrazolate (TAGzT), a comparable high‐nitrogen/high‐hydrogen material). Furthermore, its pressure sensitivity is 0.507, a 33% reduction compared to TAGzT.

Mechanical properties of intermetallic phases in multi-component Al–Si alloys using nanoindentation

The presence of additional elements in a multi-component Al–Si alloy system allows many complex intermetallic phases to form. The mechanical properties of different intermetallic phases have been investigated using nanoindentation. In particular, the hardness and modulus of a number of phases have been established for a range of alloy compositions. The results show that both hardness and reduced modulus increase as the Ni ratio of the Al–Cu–Ni phases increases. The elastic modulus can be correlated with the formation temperature of the intermetallic phases. The intermetallic phases with a high heat of formation have a strong binding between atoms and therefore, their elastic modulus is also higher.

Tetra-ol Glycidyl Azide Polymer Combustion Modeling

Tetra-ol glycidyl azide polymer (GAP) is one of the best candidates for the solid fuel of gas hybrid rocket system because of self-combustibility and high heat of formation. Combustion model of GAP was developed by Beckstead et al. and they applied it to tri-ol GAP successfully. We have applied this model to tetra-ol GAP as an initial attempt, and numerical simulation showed that maximum temperatures in the gas phase exceeded those of experimental results significantly, and calculated burning rates were much higher than strand burner data, thus, modification of the model taking account of combustion incompleteness was found to be necessary. Modifications of combustion model were made taking the residue analysis results into account as Blow Off Mechanism. Simulated final temperature in the gas phase and burning rate are lowered effectively and coincide well with experimental data adjusting kinetic parameters.

Extensive theoretical studies of a new energetic material: Tetrazino‐tetrazine‐tetraoxide (TTTO)

[1,2,3,4]Tetrazino-[5,6-e]-[1,2,3,4]tetrazine-[1,3,5,7]tetraoxide (TTTO, C2N8O4) was suggested to be a possible candidate of high energy density materials (HEDM). The most stable conformation of TTTO is a planar structure with C2h symmetry. Using various high-level ab initio methods including Gaussian-n, Complete Basis Set, Full Coupled Cluster, and W1U models of chemistry together with density functional theory based models, the enthalpies of formation of TTTO at 0 K and standard state were calculated precisely. Moreover, the rovibrational and nuclear magnetic resonance properties were predicted as well. The solid state TTTO was studied using the crystal packing models with the Dreiding force-filed and the plane-wave periodic local-density approximation density functional theory. Three stable polymorphous cells of TTTO have been found with either P212121 or P21/C symmetry. The high heat of formation (>200 kcal/mol), the high density (>2.0 g/cm3), the planar nonpolar electronic structure, and the perfect oxygen balance lead TTTO be a very promising HEDM with exceptional performance. This work provides the first theoretical support for further experimental synthesis and testing.

Combustion model of tetra-ol glycidyl azide polymer

Tetra-ol glycidyl azide polymer (GAP) is one of the best candidates for the solid fuel of gas hybrid rocket system because of self-combustibility, better mechanical property and high heat of formation, and comprehensive understanding of combustion phenomena is indispensable for such an application. Combustion model of GAP, which is one-dimensional three-phase mode combustion model, was developed by Beckstead et al. and they applied it to tri-ol GAP successfully. We have applied this model to tetra-ol GAP as an initial attempt, and numerical simulation showed that maximum temperatures in the gas phase exceeded those of experimental results significantly, and calculated burning rates were much higher than strand burner data, thus, modification of the model taking account of combustion incompleteness was found to be necessary. Combustion residues of GAP were investigated, and those were found to be composed of soot (black color), and high viscosity residue (HVR), and yellow powder which was only observed at high pressures. These residues were analyzed by means of SEM and FTIR, and mass balance was also measured. Modifications of combustion model were made taking the residue analysis results into account as Blow Off Mechanism. Simulated final temperature in the gas phase and burning rate are lowered effectively and coincide well with experimental data adjusting kinetic parameters.

Nitroamino Triazoles: Nitrogen‐Rich Precursors of Stable Energetic Salts

Abstract1‐Nitroamino‐1,2,3‐triazole (5) was synthesized and its zwitterionic structure was established using single‐crystal X‐ray diffraction. The calculated detonation properties for 4‐nitroamino‐1,2,4‐triazole (2) (P = 33.4 GPa, vD = 8793 m/s) and 1‐nitroamino‐1,2,3‐triazole (5) (P = 33.0 GPa, vD = 8743 m/s) are comparable with RDX. A new family of energetic salts 7–21 based on either the 1‐nitroamino‐1,2,3‐triazolate or the 4‐nitroamino‐1,2,4‐triazolate anion were prepared and characterized by vibrational spectroscopy (IR), multinuclear NMR spectra, elemental analyses, density, TGA and DSC. The heats of formation (ΔfH°298) and detonation properties for these stable salts were calculated using Gaussian 03 and Cheetah 4.0, respectively. Comparison of the properties of the 1,2,3‐ and 1,2,4‐triazolate salts indicates that while the 1,2,4‐derivatives are more stable thermally, the 1,2,3‐analogs invariably have higher heats of formation. In contrast to its salts, 1‐nitroamino‐1,2,3‐triazole (5) is extremely shock‐sensitive with an impact sensitivty of <1 J. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

DECOMPOSITION AND PERFORMANCEOFNEW HIGH NITROGEN PROPELLANTS AND EXPLOSIVES

As of late, molecules with high nitrogen content have received increased attention, due in large part to their novel energetic materials properties. At the Los Alamos National Laboratory, we continue to pursue the development and characterization of new high-nitrogen materials for applications in a wide variety of fields. In this work three molecules, triaminoguanidinium azotetrazolate (TAGzT), 3,6-bis-nitroguanyl-1,2,4,5-tetrazine and its corresponding bis-triaminoguanidinium salt, are studied all of which are high-nitrogen compounds with little or no oxygen, however, retain energetic material properties as a result of their high heats of formation. Because of this, the decomposition of this class of compounds have limited or no secondary oxidation reactions of carbon and hydrogen. Other materials discussed for comparison include 3,3'-azobis(6-amino-1,2,4,5-tetrazine)-mixed N-oxides (DAATO{sub 3.5}) and 3,6-bis(1H-1,2,3,4-tetrazol-5-ylamino)-s-tetrazine (BTATz) and the nitramine octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). The fact that many of these molecules approach 80% nitrogen content makes them potentially useful as gas generants or energetic materials with low flame temperatures, while simultaneously increasing the impulse of gun or rocket propellants. The burning rate, flash pyrolysis (T-jump/FTIR spectroscopy), explosive sensitivity and performance properties were determined. Some examples of interesting behaviors include that TAGzT exhibits one of the fastest low pressure burning rates yet measured for an organic compound,more » and 3,6-bis-nitroguanyl-1,2,4,5-tetrazine has one of the lowest pressure exponents yet measured for a pure organic compound.« less

Decomposition and Ignition of the High‐Nitrogen Compound Triaminoguanidinium Azotetrazolate (TAGzT)

AbstractThe high‐nitrogen compound triaminoguanidinium azotetrazolate (TAGzT) belongs to a class of C, H and N compounds that are free of both oxygen and metal, but retain energetic material properties as a result of their high heat of formation. Its decomposition thus lacks secondary oxidation reactions of carbon and hydrogen. The fact that TAGzT is over 80% nitrogen makes it potentially useful as a gas generant and energetic material with a low flame temperature to increase the impulse in gun or rocket propellants. The burning rate, laser ignition and flash pyrolysis (T‐jump/FTIR spectroscopy) characteristics were determined. It was found that TAGzT exhibits one of the fastest low‐pressure burning rates yet measured for an organic compound. Both the decomposition and ignition behavior of TAGzT are dominated by condensed phase reactions. T‐Jump/FTIR spectroscopy indicates that condensed phase reactions release about 65% of the energy, which helps to explain the high burning rate at low pressure.

Polymorph of 2,9-Dichloroquinacridone and Their Electronic Properties

2,9-Dichloroquinacridone is an industrially important bluishred pigment which falls in the category of hydrogen-bonded pigments. In addition to red single crystals, we have recently isolated black single crystals from the vapor phase. Structure analysis of both crystals revealed that the red phase is typically characterized by NH…O intermolecular hydrogen bonds and corresponds to the commercial product; whereas, in the black phase, there exist no intermolecular hydrogen bonds, quite contrary to our expectation. Furthermore, the molecule in the black phase is heavily deformed and has a higher heat of formation than that in the red phase. Because of this, the black phase can easily be transformed into the red phase by heating at about 530 K for several minutes. Additionally, molecular distortion upon crystallization is found to largely displace the absorption band toward longer wavelengths, giving rise to a black color in the solid state.

Thermal expansion of AuIn2

The thermal expansion of AuIn{sub 2} gold is of great interest in soldering technology. Indium containing solders have been used to make gold wire interconnects at low soldering temperature and over time, AuIn{sub 2} is formed between the gold wire and the solder due to the high heat of formation and the high inter-metallic diffusion of indium. Hence, the thermal expansion of AuIn{sub 2} alloy in comparison with that of the gold wire and the indium-containing solder is critical in determining the integrity of the connection. We present the results of x-ray diffraction measurement of the coefficient of linear expansion of AuIn{sub 2} as well as the bulk expansion and density changes over the temperature range of 30 to 500 C.

Triaminoguanidine Dinitramide, TAGDN: Synthesis and Characterization

AbstractTwo dinitramide salts with very high heat of formation have been identified, i.e. triaminoguanidine dinitramide (TAGDN) and guanylazide dinitramide (GADN). Thermochemical calculations showed that TAGDN‐propellants have a higher impetus than the corresponding GADN‐propellants at a given flame temperature. Due to the fact that a low flame temperature has to be prefered in a gun, TAGDN seems better suited as a component in gun propellants compared to GADN. TAGDN was thus synthesized, analyzed and characterized to determine some of its properties.

Enhanced tunnel magnetoresistance by hf-layer insertion in the AlO/sub x/ tunnel barriers

Summary form only given. Magnetic tunnel junctions consist of two ferromagnetic electrodes separated by an insulating barrier. The tunnel magnetoresistance(TMR) and junction resistance critically depend on the insulating layer quality. The defects in tunnel barrier or at the interfaces between barrier and metal electrodes could degrade MR ratio by introducing spin flip scattering. In this study, we have introduced the artificial modification of the oxide barrier by forming Hf oxide in the middle of the Al/sub 2/O/sub 3/ barrier. As Hf oxide has higher heat of formation (-268kcal/mole of Hf) than Al oxide (-202kcal/mole), the inserted Hf layer could act as oxide stabilizer and decrease the degree of disorder and defects in the barrier. Magnetic tunnel junctions of Hf(5nm)/NiFe(8nm)/IrMn(20nm)/CoFe(4nm)/Al oxide or Al-HfAl oxide/CoFe(3nm)/NiFe(15nm) were deposited by magnetron sputtering system. Tunnel barriers were formed by exposing the Al(1.4nm) layer or Al-Hf-Al(0.6/0.2/0.6nm) layer to ozone and oxygen mixture gas for tens of minutes.