The goal in this paper is to review progress in two emerging topics in energetic materials science. These emerging two areas are fluorine and oxygen rich energetic crystals and polymers and environmentally friendly energetic material classes.

A general strategy for the design of high nitrogen systems with an adequate degree of stability has been elaborated. The design of nitro compounds in which terminal nitro groups are bonded to the chain of several heteroatoms is a specific case within the strategy. In the process of working out the strategy a number of new high nitrogen systems ( dinitrazenic acid or dinitroamide HN3O4 and it salts, nitrodiazene oxides RN3O3 and tetrazine dioxides ) were discovered.

A number of new types of nitro compounds (bicyclo nitro-bis-hydroxylamine, nitrohydrazine, nitrohydroxylamine, sulfo-N-nitroimide and bis-N-nitroimide were synthesized.

This study opens new prospects in the field of the synthesis of high energy materials.

Electrochemical oxidation of anions of polynitroalkanes (PNA) proceeds via one-electron transfer and results in the formation of unstable radicals. The radicals undergo fragmentation, abstraction of a hydrogen atom from the solvent, and reaction with aromatic compounds to form aryl-PNA. The yield of aryl-PNA depends on the structure of the radicals and on the electron donating properties of the aromatic substrates. Due to their electrophilic properties, PNA-radicals also react with compounds containing heteroatoms with unshared electron pairs resulting in formation of dinitromethylides. Under anodic electrolysis conditions dinitromethylides which have a carbanionic structure can effectively transfer the dinitromethyl group to other organic substrates. Electrochemical oxidation of anions of nitroazoles also proceeds via one-electron transfer to generate nitroazolyl radicals. Their principal reaction is abstraction of hydrogen from the solvent. However, electrolysis of nitroazoles in the presence of aromatic compounds results in formation of N-aryl derivatives in good yield. It has been shown that electrooxidation of mono oximes leads to formation of unstable nitroso dimers, while electrooxidation of vicinal dioximes results in formation of furoxans in high yield.

The need continues for new powerful but insensitive explosive ingredients, which match the performance of RDX with the insensitivity of TATB. One approach has been to take the inherent stability of an aromatic heterocycle, combine this with the explosive insensitivity and thermal stability associated with alternating amino and nitro groups, and to supplement the performance of the molecule with an energy contribution from the N-oxide functionality. The synthesis, characterization and properties (both sensitivity and performance) of aminonitropyridine-l-oxides and aminonitropyrimidine-1,3-dioxides will be described.

An improved nitration procedure has been developed for the synthesis of y-Tacot (3). The synthesis of y-DBBD (8) has been completed in three steps from 3 in 37% yield. y-DBBD (8) was found to be thermally stable up to 274 °C (decomposed) and insensitive to impact (hammer blow). Nitration of z-BDDB (6) and y-DBBD (8) gave carbonyl derivatives resulting from in situ hydroysis/oxidation of the corresponding tetranitro derivatives z-TBBD (7) and y-TBBD (9), respectively.

5-Amino-3-nitro-lH-1,2,4-triazole (ANTA) is a molecule with high stability. Aside from being an insensitive high explosive (IHE), it is also used as a synthon for other potential new IHEs. The crystal structure of ANTA was resolved by X-ray crystallography. However, when ANTA was recrystallized from 2-butanone, crystals with molecular packing characterized by extended planar sheets were obtained (ß-ANTA). The crystal density of ß-ANTA is 1.73 g/cm3, which is less dense than α-ANTA (p = 1.82g/cm3).

The high-nitrogen molecule, 5,5'-dinitro-3,3'-azo-1,2,4-triazole (DNAT) was calculated to have a high density and a positive heat of formation (AHf). In an attempt to prepare DNAT, we have studied the oxidation of ANTA with different oxidizers. It was found that DNAT is the reaction product when the potassium salt of ANTA was oxidized with potassium permanganate. However, when ANTA was oxidized with ammonium persulfate in aqueous medium, one of the reaction products obtained was the azoxy moleclue of DNAT (DNAzT). We are unable to determine the crystal densities of either DNAT and DNAzT because the crystals obtained were solvated with the crystallization solvents.

High resolution (sinθ/λ < 1.34 Å−1), low temperature (85 K) X-ray diffraction data has been used to map the deformation density and the derived electrostatic potential for three dinitramide salts. The traditional presentation of contour maps has been replaced with 3D views of the molecule. A comparison of the dinitramide ions from each salt is presented.

A recently-developed density functional procedure for computing gas phase heats of formation is briefly described and results for several categories of energetic compounds are summarized and discussed. Liquid and solid phase values can be obtained by combining the gas phase data with heats of vaporization and sublimation estimated by means of other relationships. Some observed functional group effects upon heats of formation are noted.

We are performing constant-NPT Monte Carlo calculations of the physical properties of crystalline TATB. Our approach is to employ an atomistic model in which the individual molecules are treated as semi-rigid entities. Each molecule is allowed to undergo rigid translations and rotations, and in some cases limited intramolecular flexibility is conferred on the molecules via exocyclic torsions. Additionally, the size and shape of the simulation box is allowed to vary. Our immediate interest is in computing the density, lattice energy, lattice constants, and other structural parameters as a function of temperature. Preliminary results indicate that simulations involving only two molecules suffice for calculations of the energy and density, but that more molecules are required to compute the lattice constants. Intramolecular flexibility is important, particularly at higher temperatures.

Studies of the growth of crystals of energetic materials under conditions of high acceleration in an ultracentrifuge are reported. When a saturated solution is accelerated in an ultracentrifuge, the solute molecules move individually through the solvent molecules to form a crystal at the outer edge of the tube if the solute is more dense than the solvent. Since there is no evaporation or temperature variation, convection currents caused by simultaneous movement of solvent and solute are minimized and crystal defects are potentially minimized. Crystal growth is controlled by the g-level of the acceleration. In addition, solution inclusions and bubbles migrate out of the saturated solution as a result of the pressure gradient induced by the g-force. We present results of TNT, RDX, and TNAZ grown at high g from various solutions.

The solubilities of the common propellant ingredients acetyl triethyl citrate (ATEC) and cellulose acetate butyrate (CAB) and their effects on RDX (cyclotrimethylenetrinitramine) unit cell dimensions were investigated. If there is appreciable solid solubility, solutions will form and will have enthalpies of fusion, melting temperatures, and other characteristics different from those of pure RDX. It is desirable to establish the properties of such mixtures when designing new propellant formulations. Samples were aged at an elevated temperature to speed the formation of solid solutions. A least-squares analysis of X-ray diffraction data was used to obtain the lattice parameters from which unit cell volume and solubility was deduced. Both ATEC and CAB caused an expansion of the unit cell, indicating the formation of a solid solution. The limit of solubility in the ATEC/RDX mixture appeared to be approximately 13 wt% ATEC, while the CAB/RDX limit is above 16 wt% CAB. In both mixes, the cell volume expanded linearly with increasing proportion of binder.

Optical properties of RDX (cyclotrimethylene-trinitramine) and HMX (cyclotetramethylenetetranitramine) were obtained from 2.5 to 18 gtm using scattering-corrected KBr pellet-FTIR transmission spectrometry. Absorption index (k) was measured directly and refractive index (n) was deduced using dispersion theory. At 10.6 μm the absorption coefficients were RDX, 2800 cm−1 and HMX, 5670 cm−1.

Energetic materials for missiles, gun munitions or pyrotechnic devices often are mixtures in a biphasic form, with a filler and a binder. To satisfy the user needs, an analysis of functional requirements together with constraints (safety, vulnerability, ageing, environment, disposal, price...) is useful to choose a convenient binder. From this point of view numerous synthetic energetic polymers proposed or developed as binders are reviewed with regard to their syntheses, processing, properties and possible uses. These polymers contain explosophore groups: C-NO2 aliphatic or aromatic, ONO2, NNO2, NF2 and N3.

Some research projects are suggested. Among them in the list of published polymers, following a NIMIC (NATO) suggestion, note the reason of a development interruption. Some dinitropolystyrene – polyvinyl nitrate mixtures or copolymers could exhibit interesting properties. For unknown reasons, some mixtures of crystalline filler- with polymeric binder, generally in a biphasic form, may also be monophasic for a same composition. What properties are modified between the both forms (e.g. combustion mechanisms, erosion, ideal character of the detonation) ? It is also interesting to pursue into a newly open route to thermo-plastic elastomers.

Many reactions of interest occur in the solid state, or with low mobility of the reactants or products, with the result that the physical mechanisms operative during the reaction determine the shape of the reaction rate-time profile; i.e. topochemistry is important. However, often improper account is taken of the physical mechanisms, resulting in erroneous values for the activation energy and kinetic constants.

An improved method of analysis is suggested, allowing the mechanisms of reaction to be determined explicitly. This thus allows the activation energy and kinetic constants to be determined with good theoretical justification. The method has been verified by studying the thermal decomposition of barium azide, where the activation energy was determined to better than 1%. The operative mechanisms so determined are in agreement with visual observations and the literature.

The solid-phase thermal decomposition of the insensitive energetic aromatic heterocycle 2,4- dinitroimidazole (2,4-DNI: mp 265–274°C) is studied utilizing simultaneous thermogravimetric modulated beam mass spectrometry (STMBMS) between 200° and 247°C. The pyrolysis products have been identified using perdeuterated and N-labeled isotopomers. The products consist of low molecular-weight gases and a thermally stable solid residue. The major gaseous products are NO, CO2, CO, N2, HNCO and H2O. Minor gaseous products are HCN, C2N2, NO2, C3H4N2, C3H3N3O and NH3. The elemental formula of the residue is C2HN2O and FTIR analysis suggests that it is polyurea- and polycarbamate-like in nature. The rates of formation of the gaseous products and their respective quantities have been determined for a typical isothermal decomposition experiment at 235°C. The temporal behaviors of the gas formation rates indicate that the overall decomposition is characterized by a sequence of four events; 1) an early decomposition period induced by impurities and H2O, 2) an induction period where CO2 and NO are the primary products formed at relatively constant rates, 3) an autoacceleratory period that peaks when the sample is depleted and 4) a final period in which the residue decomposes. Arrhenius parameters for the induction period are Ea = 46.9 ± 0.7 kcal/mol and Log(A) = 16.3 ± 0.3. Decomposition pathways that are consistent with the data are presented.

The thermal decomposition of HMX between 175°C and 200°C has been studied using the simultaneous thermogravimetric modulated beam mass spectrometer (STMBMS) apparatus with a focus on the initial stages of the decomposition. The identity of thermal decomposition products is the same as that measured in previous higher temperature experiments. The initial stages of the decomposition are characterized by an induction period followed by two acceleratory periods. The Arrhenius parameters for the induction and two acceleratory periods are (Log(A)= 18.2 ± 0.8, Ea = 48.2 ± 1.8 kcal/mole), (Log (A) = 17.15 ± 1.5 and Ea = 48.9 ± 3.2 kcal/mole), (Log (A) = 19.1 ± 3.0 and Ea = 52.1 ± 6.3 kcal/mole), respectively. The data can be used to calculate the time and temperature required to decompose a desired fraction of a test sample that is being prepared to test the effect of thermal degradation on its sensitivity or burn rates. It can also be used to estimate the extent of decomposition that may be expected under normal storage conditions for munitions containing HMX. The data, along with previous mechanistic studies conducted at higher temperatures, suggest that the process that controls the early stages of decomposition of HMX in the solid phase is scission of the N-NO2 bond, reaction of the NO2 within a “lattice cage” to form the mononitroso analogue of HMX and decomposition of the mononitroso HMX within the HMX lattice to form gaseous products that are retained in bubbles or diffuse into the surrounding lattice.

NTO (5-Nitro-2,4-dihydro-3H-1,2,4-triazol-3-one)is shown to form aphotochemical free radical in alkaline aqueous solution containing nitromethane (CH3NO2). The NTO free radical can also be produced by chemical reduction of NTO with hydroquinone in alkaline solution. Details of radical formation and assignment of the NTO radical to a nitro anion radical, having the NTO ring intact, are presented.

To examine the thermal decomposition of 5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one (NTO) in detail, isotopic labeling studies were undertaken. NTO samples labeled with 15N in three different locations [ N(l) and N(2), N(4), and N (6)] were prepared.1 Upon thermolysis, the majority of the NTO condensed-phase product was a brown, insoluble residue, but small quantities of 2,4,-dihydro-3H- 1,2,4-triazol-3-one (TO) and triazole were detected.2 Gases comprised the remainder of the NTO decomposition products. The analysis of these gases is reported herein along with mechanistic implications of these observations.

We report on laboratory studies of the thermal decomposition of TNT under a variety of conditions. Our goal is a better understanding of the soil contamination detection technique used in site characterization using cone penetrometers, in which hot filament pyrolysis results in small gaseous molecules, such as NO, which can be detected by a variety of methods to indicate the presence of explosives in the soil. Our laboratory studies use a long-path sampling cell and tunable infrared diode laser absorption, which provide sensitive, specific, time-resolved detection of several of the key decomposition products. In this paper, we present both the initial results of laboratory experiments on mixtures of soil and TNT, designed to simulate the operation of a cone penetrometer probe, and also results of a series of heated tube experiments which serve to relate the first type of experiment to previously reported TNT decomposition studies.

Data on the steady-state combustion in a constant-pressure bomb at 0.1–40 MPa are presented for energetic materials from the following classes: metal salts of organic explosive acids, salts of organic bases with inorganic oxidizing acids, explosive coordination compounds, and endothermic polynitrogen compounds.

For combustion of salts of organic bases with oxidizing acids it has been found that an increase in the oxidant redox potential, whose value serves as an estimate of the oxidizer reactivity, causes the burning rate value to increase. The same tendency has been disclosed for explosive coordination compounds which can formally be considered as metal-containing analogs of the salts of organic bases with oxidizing acids.

The introduction of a metal atom in an organic explosive acid has been shown to result generally in an enhancement of the burning rate, with the effectiveness of the metal as the combustion catalyst being dependent not only on the nature of the metal but on its position in the molecule as well.

Neither the nature of the metal, nor the nature and structure of the ligand really affects the combustion of coordination compounds of metal azides, whose combustion occurs at the expense of the heat produced in the decomposition process. All the coordination azides seem to have the same rate-limiting stage, namely, the decomposition of the intermediate HN3 and differ from one another by their burning temperatures. The similar behavior is also characteristic of metalless analogs of the coordination azides: salts of HN3 with amines.