New directions in the science and technology of advanced sheet explosive formulations and the key energetic materials used in the processing of sheet explosives: Emerging trends.

This review presents the work carried out by the international community in the area of sheet explosive formulations and its applications in various systems. The sheet explosive is also named as PBXs and is a composite material in which solid explosive particles like RDX, HMX or PETN are dispersed in a polymeric matrix, forms a flexible material that can be rolled/cut into sheet form which can be applied to any complex contour. The designed sheet explosive must possess characteristic properties such as flexible, cuttable, water proof, easily initiable, and safe handling. The sheet explosives are being used for protecting tanks (ERA), light combat vehicle and futuristic infantry carrier vehicle from different attacking war heads etc. Besides, sheet explosives find wide applications in demolition of bridges, ships, cutting and metal cladding. This review also covers the aspects such as risks and hazard analysis during the processing of sheet explosive formulations, effect of ageing on sheet explosives, detection and analysis of sheet explosive ingredients and the R&D efforts of Indian researchers in the development of sheet explosive formulations. To the best of our knowledge, there has been no review article published in the literature in the area of sheet explosives.

Synthesis, characterization and evaluation of 1,2-bis(2,4,6-trinitrophenyl) hydrazine: a key precursor for the synthesis of high performance energetic materials.

1,2-Bis(2,4,6-trinitrophenyl) hydrazine (3) is one of the precursors in the synthesis of an important energetic material viz., hexanitrazobenzene. The simple and convenient lab scale synthesis of title compound (3) was carried out by the condensation of picryl chloride (2) with hydrazine hydrate at 30-50 degrees C in methanol based on the lines of scanty literature reports. Picryl chloride was synthesized by the reaction of picric acid (1) with phosphorous oxychloride based on the lines of reported method. The synthesized compound (3) was characterized by IR and 1H NMR spectral data. Some of the energetic properties of the synthesized compound have also been studied. The theoretically computed energetic properties of the title compound (3) indicated the superior performance in comparison to tetranitrodibenzo tetraazapentalene (TACOT) and hexanitrostilbene (HNS) in terms of velocity of detonation.

Environmentally compatible next generation green energetic materials (GEMs).

This paper briefly reviews the literature work reported on the environmentally compatible green energetic materials (GEMs) for defence and space applications. Currently, great emphasis is laid in the field of high-energy materials (HEMs) to increase the environmental stewardship along with the deliverance of improved performance. This emphasis is especially strong in the areas of energetic materials, weapon development, processing, and disposal operations. Therefore, efforts are on to develop energetic materials systems under the broad concept of green energetic materials (GEMs) in different schools all over the globe. The GEMs program initiated globally by different schools addresses these challenges and establishes the framework for advances in energetic materials processing and production that promote compliance with environmental regulations. This review also briefs the principles of green chemistry pertaining to HEMs, followed by the work carried out globally on environmentally compatible green energetic materials and allied ingredients.

Computer code to predict the heat of explosion of high energy materials.

The computational approach to the thermochemical changes involved in the process of explosion of a high energy materials (HEMs) vis-à-vis its molecular structure aids a HEMs chemist/engineers to predict the important thermodynamic parameters such as heat of explosion of the HEMs. Such a computer-aided design will be useful in predicting the performance of a given HEM as well as in conceiving futuristic high energy molecules that have significant potential in the field of explosives and propellants. The software code viz., LOTUSES developed by authors predicts various characteristics of HEMs such as explosion products including balanced explosion reactions, density of HEMs, velocity of detonation, CJ pressure, etc. The new computational approach described in this paper allows the prediction of heat of explosion (DeltaH(e)) without any experimental data for different HEMs, which are comparable with experimental results reported in literature. The new algorithm which does not require any complex input parameter is incorporated in LOTUSES (version 1.5) and the results are presented in this paper. The linear regression analysis of all data point yields the correlation coefficient R(2)=0.9721 with a linear equation y=0.9262x+101.45. The correlation coefficient value 0.9721 reveals that the computed values are in good agreement with experimental values and useful for rapid hazard assessment of energetic materials.

Advances in science and technology of modern energetic materials: an overview.

Energetic materials such as explosives, propellants and pyrotechnics are widely used for both civilian and military explosives applications. The present review focuses briefly on the synthesis aspects and some of the physico-chemical properties of energetic materials of the class: (a) aminopyridine-N-oxides, (b) energetic azides, (c) high nitrogen content energetic materials, (d) imidazoles, (e) insensitive energetic materials, (f) oxidizers, (g) nitramines, (h) nitrate esters and (i) thermally stable explosives. A brief comment is also made on the emerging nitration concepts. This paper also reviews work done on primary explosives of current and futuristic interest based on energetic co-ordination compounds. Lead-free co-ordination compounds are the candidates of tomorrow's choice in view of their additional advantage of being eco-friendly. Another desirable attribute of lead free class of energetic compounds is the presence of almost equivalent quantity of fuel and oxidizer moieties. These compounds may find wide spectrum of futuristic applications in the area of energetic materials. The over all aim of the high energy materials research community is to develop the more powerful energetic materials/explosive formulations/propellant formulations in comparison to currently known benchmark materials/compositions. Therefore, an attempt is also made to highlight the important contributions made by the various researchers in the frontier areas energetic ballistic modifiers, energetic binders and energetic plasticizers.

Synthesis, characterization and thermolysis studies on 3,7-dinitro-1,3,5,7-tetraazabicyclo[3,3,1]nonane (DPT): A key precursor in the synthesis of most powerful benchmark energetic materials (RDX/HMX) of today.

This paper reports studies undertaken on 3,7-dinitro-1,3,5,7-tetraazabicyclo[3,3,1]nonane (DPT). The synthesis of DPT was carried out by the nitration of hexamine based on the lines of reported method with minor modification. DPT was characterized by elemental analysis, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and (1)H nuclear magnetic resonance (NMR) techniques. Thermal stability of DPT was studied using thermogravimetry (TG) and differential scanning calorimetry (DSC). The thermal analysis studies revealed that DPT undergoes decomposition at 211 degrees C. Decomposition of DPT using TG-FTIR indicated the evolution of carbon dioxide, water and oxides of nitrogen as main gaseous products. The electrochemical behavior of DPT was studied using cyclic voltammetric (CV) studies. The experimentally determined sensitivity parameters indicated the insensitive nature of DPT towards external stimuli. The performance parameters of DPT, RDX and HMX have been computed using Linear Output Thermodynamic User Friendly Software for Energetic Systems (LOTUSES) code. The predicted properties of DPT are interesting and important from the point of process technology and/or safety. The work reported in this paper enriches the existing scanty research and development data on one of the key precursor used for synthesis of important high energy materials (HEMs).

Microwave assisted facile synthesis of {1/1,3-bis/1,3,5-tris-[(2-nitroxyethylnitramino)-2,4,6-trinitrobenzene]} using bismuth nitrate pentahydrate as an eco-friendly nitrating agent.

1-(2-Nitroxyethylnitramino)-2,4,6-trinitrobenzene (3a), 1,3-bis(2-nitroxyethyl nitramino)-2,4,6-trinitrobenzene (3b) and 1,3,5-tris(2-nitroxyethylnitramino)-2,4,6-trinitrobenzene (3c) were prepared by the nitration of 1-(2-hydroxyethylamino)-2,4,6-trinitrobenzene (2a) 1,3-bis(2-hydroxyethylamino)-2,4,6-trinitrobenzene (2b) and 1,3,5-tris(2-hydroxyethylamino)-2,4,6-trinitrobenzene (2c) using bismuth nitrate pentahydrate (eco-friendly nitrating agent) in tetrahydrofuran adsorbed on silica gel under microwave irradiation, respectively. Key intermediate compounds viz., 2a, 2b and 2c were synthesized by condensing picryl chloride, styphnyl chloride and 1,3,5-trichloro-2,4,6-trinitrobenzene with ethanol amine, respectively, based on the lines of the reported method. The synthesized compounds were characterized based on their physical constant, infrared (IR) spectroscopy and (1)H nuclear magnetic resonance (NMR) spectroscopy. The spectroscopic data obtained indicated the formation of nitrate esters (3a-3c). The nitration methodology adopted in the present study is of relevance in the context of green chemistry. The target compounds (3a-3c) synthesized using eco-friendly approach are of interest from the point of high energy materials (HEMs).

Electro-analysis of energetic materials.

Cyclic voltammetric studies of triaminoguanidine nitrate (TAGN), 3,3'-hydrazino bis(bis[6,6'-(3,5-dimethylpyrazol-lyl])-1,2,4,5-tetrazine (HBPT), 4,6-dinitrobenzofuroxan (DNBF) and 3,3'-diamino-4,4'-azoxyfurazan (DAAF) were carried out at different pH conditions in 50% aqueous acetonitrile using glassy carbon electrode. Optimum pH was selected for individual compounds. Influence of scan rate and concentration on the voltammetric response were studied in optimum pH. The number of electron transferred was determined by controlled potential coulometry. All compounds undergo diffusion controlled electrochemical reaction. Based on cyclic voltammetric results, differential pulse and square wave voltammetric methods have been developed for the analytical determination. Instrumental parameters such as initial scan potential, amplitude, pulse increment, pulse period, pulse width and frequency were studied. Optimum experimental conditions for each compound were obtained. After fixing optimum conditions, the effect of concentration was studied and calibration plot was arrived. These plots can be used to determine the traces of the above said four energetic materials.

Synthesis, characterization and thermolysis studies on new derivatives of 2,4,5-trinitroimidazoles: potential insensitive high energy materials.

This paper reports the synthesis of three new derivatives of 2,4,5-trinitroimidazole namely, 1-methyl-2,4,5-trinitroimidazole (III), 1-carboethoxy-2,4,5-trinitroimidazole (V) and 1-picryl-2,4,5-trinitroimidazole (VII). The title compounds (III) and (V) were synthesized by the nitration of 1-methyl-/1-carboethoxy-(2,4,5-triiodoimidazole) (II and IV) with fuming nitric acid at 0 degrees C and (VII) was synthesized by condensation of 2,4,5-triiodoimidazole (I) with picryl chloride to obtain 1-picryl-2,4,5-triiodoimidazole (VI) followed by its nitration with fuming nitric acid at 0 degrees C. The synthesized compounds have been characterized by elemental analysis, spectral and thermal techniques. The thermolysis studies using TG-DTA revealed exothermic decomposition of the nitroimidazoles (III, V and VII) with T(max) in the temperature range of 196-225 degrees C. The energy of activation obtained for these compounds was in the range 150-170 kJ/mol. The sensitivity data obtained for the newly synthesized compounds (III, V and VII) indicated their safe nature towards external stimuli (h(50%)>100 cm; friction>36 kg) and could be potential candidates for low vulnerable applications in the futuristic systems. The theoretically predicted performance parameters suggest that 1-methyl-2,4,5-trinitroimidazole (III), exhibits higher velocity of detonation (VOD: 8.8 km/s) compared to compounds V and VII (VOD: 7.6 and 8.41 km/s, respectively).

Method for preparation of fine TATB (2-5 microm) and its evaluation in plastic bonded explosive (PBX) formulations.

There is a need of fine 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) (2-5 microm) for various high explosive formulations to achieve desired mechanical strength, ease in processing and finally, provide better performance of end product. The reprecipitation method for TATB has been developed using concentrated sulfuric acid as a solvent. The reprecipitation parameters of TATB were optimized to achieve required fine TATB of particle size approximately 2-5 microm. The characteristic properties of fine TATB thus obtained have been confirmed by FTIR, DSC and TG-FTIR. The spectroscopic and thermal data obtained for fine TATB were compared with standard coarse TATB and found chemically unchanged during particle size reduction. In the present study, the preparation of fine TATB was also attempted using ultrasonication method. The fine (2-5 microm) TATB has been introduced to study in the bimodal high explosive formulations. High explosive formulations based on coarse (55 microm) and fine TATB ( approximately 2-5 microm) with 10% polyurethane were studied. It was observed that properties like bulk density (1.70 g/cm(3)), mechanical strength/compressed strength (115.9 mg/cm(2)), %elongation (6.36) were improved for fine TATB in comparison with coarse TATB ( approximately 55 microm) alone in high explosive formulations.

Synthesis, characterization and thermolysis studies on triazole and tetrazole based high nitrogen content high energy materials.

This paper reports the synthesis, characterisation and thermolysis studies of hydrazinium azotetrazolate (HAZ) and 1,1'-dinitro-3,3'-azo-1,2,4-triazole (N-DNAT). TGA and DSC results suggested that HAZ decomposes in the range of 150-180 degrees C and N-DNAT in the range of 160-170 degrees C, respectively. The pattern of decomposition of HAZ dihydrate and N-DNAT has been predicted with the help of pyrolysis GC/MS technique and a probable decomposition mechanism has been proposed. The theoretically predicted performance data suggests the potential nature of HAZ and N-DNAT for their use in propellant/explosive as well as in gas generator formulations.

Primary explosives: electrostatic discharge initiation, additive effect and its relation to thermal and explosive characteristics.

All explosives, under all conditions must be considered vulnerable to generation, accumulation and discharge of static charge. The low energy static hazards of the order as low as 2-3 mJ need to be guarded against in case of highly sensitive compounds namely primary explosives. The hazard is normally associated with manufacturing and filling operations due to discharge of static charge accumulated on a person supplying energy up to 20 mJ. To reduce the risk associated with static initiation hazard in the processing and handling of the explosives, the electrostatic sensitivity tests can provide an important input regarding electrostatic hazards. This paper presents electrostatic sensitivity data in terms of zero ignition probability data (E(SE0)) of some of the initiatory explosives such as nickel/cobalt hydrazinium nitrate, silver azide, lead azide and mercury salt of 5-nitro tetrazole. Similar data has also been presented for samples coated with polyvinyl pyrrolidone to study its effect on electrostatic sensitivity. The electrostatic spark sensitivity of some conventional and novel made to explain the increased spark sensitivity behavior on the basis of the possible primary explosives has been studied. The electrostatic spark sensitivity of primary explosives decreased in the order of AgN3 = NHN > PbN6 > MNT > CoHN > BNCP. A possible correlation of spark energy with approximation and assumption has been drawn with thermal, detonation and mechanical properties. The polyvinyl pyrrolidone coated samples followed the same order but interestingly with increased spark sensitivity. An attempt has been reasoning of dielectric nature of the materials or exothermic effects of decomposition products of PVP. The present work also reports the electrostatic spark sensitivity of cap compositions.

Synthesis, characterization and thermolysis of 1,1-diamino-2,2-dinitroethylene (FOX-7) and its salts.

The present paper discusses the efforts made in HEMRL to establish the synthesis of FOX-7 at 100 g/batch level. In the present study, 1,1-diamino-2,2-dinitroethylene has been synthesised by treatment of acetamidinium chloride with diethylmalonate to obtain 2-methyl-pyrimidine-4,6-dione which on nitration followed by hydrolysis gave FOX-7. The synthesised FOX-7 has been characterized by spectroscopic and thermal techniques. The data obtained confirms the structure of FOX-7. The sensitivity of FOX-7 towards mechanical stimuli indicated its insensitive nature. The theoretically computed explosive and ballistic parameters are close to that of RDX. The synthesised FOX-7 has been used as a precursor for the synthesis of potassium and guanidinium salts and the thermal analysis of these salts indicate their exothermic nature.

Diaminofurazan (DAF): Thermolysis and evaluation as ballistic modifier in double base propellant.

Diaminofurazan (DAF) is used as a precursor in the synthesis of many high performance insensitive high explosives. This paper reports the thermal studies on DAF and its evaluation as a ballistic modifier in double base propellant formulations. Differential scanning calorimetry (DSC) and differential thermal analysis (DTA) revealed that DAF shows two-stage decomposition, whereas the kinetics of initial stage of thermal decomposition of DAF evaluated from TG data gave activation energy (E(a)) of 67 kJ mol(-1). The evolution of gases containing species such as CN, NH, OH and oxides of nitrogen during thermal decomposition of DAF was also revealed by hyphenated TG-FTIR data. Evaluation of DAF as a ballistic modifier in RDX incorporated double base propellant formulations indicated that it brings down the pressure index to 0.20 compared to 0.70 for a control composition in the pressure range 6.9-8.8 MPa when used in combination with basic lead salicylate (BLS). It was observed that DAF does not have adverse effect on vulnerability and chemical stability of the propellant formulation.

Computer code for the optimization of performance parameters of mixed explosive formulations.

LOTUSES is a novel computer code, which has been developed for the prediction of various thermodynamic properties such as heat of formation, heat of explosion, volume of explosion gaseous products and other related performance parameters. In this paper, we report LOTUSES (Version 1.4) code which has been utilized for the optimization of various high explosives in different combinations to obtain maximum possible velocity of detonation. LOTUSES (Version 1.4) code will vary the composition of mixed explosives automatically in the range of 1-100% and computes the oxygen balance as well as the velocity of detonation for various compositions in preset steps. Further, the code suggests the compositions for which least oxygen balance and the higher velocity of detonation could be achieved. Presently, the code can be applied for two component explosive compositions. The code has been validated with well-known explosives like, TNT, HNS, HNF, TATB, RDX, HMX, AN, DNA, CL-20 and TNAZ in different combinations. The new algorithm incorporated in LOTUSES (Version 1.4) enhances the efficiency and makes it a more powerful tool for the scientists/researches working in the field of high energy materials/hazardous materials.

Quantum chemical, ballistic and explosivity calculations on 2,4,6,8-tetranitro-1,3,5,7-tetraaza cyclooctatetraene: a new high energy molecule.

Ab initio molecular orbital calculations have been carried out on 2,4,6,8-tetranitro-1,3,5,7-tetraazacyclooctatetraene, the tetramer of the series (NO(2)CN)(n) where n=1-4, using the Hartree-Fock theory with the 6-31 G(d) basis set. These calculations yield three conformers for the tetramer with D(4h), C(4h) and C(2) symmetries. The nonplanar conformer with the C(2) symmetry turns out to be 99.0 and 164.4kJmol(-1), respectively, lower in energy than the C(4h) and D(4h) conformers. The electron density topography - the density at the bond critical point - has been used as a measure of the CNO(2) strengths. Based on these bond strengths, heats of formation [obtained from the parametric model 3 (PM3) method] and specific decomposition energies, it may be concluded that (NO(2)CN)(4) is a promising candidate in the class of high energy molecules. Theoretically computed explosive (velocity of detonation, detonation pressure, etc.) and ballistic (characteristic velocity, specific impulse, etc.) parameters support these conclusions.

Effect of organic additives on the mitigation of volatility of 1-nitro-3,3'-dinitroazetidine (TNAZ): next generation powerful melt cast able high energy material.

1-Nitro-3,3'-dinitroazetidine (TNAZ) was synthesized based on the lines of reported method. Thermolysis studies on synthesized and characterized TNAZ using differential scanning calorimetry (DSC) and hyphenated TG-FT-IR techniques were undertaken to generate data on decomposition pattern. FT-IR of decomposition products of TNAZ revealed the evolution of oxides of nitrogen and HCN containing species suggesting the cleavage of C/N-NO(2) bond accompanied with the collapse of ring structure. The effect of incorporation of 15% additives namely, 3-amino-1,2,4-triazole (AT), 3,5-diamino-1,2,4-triazole (DAT), carbohydrazide (CHZ), 5,7-dinitrobenzofuroxan (DNBF), bis (2,2-dinitropropyl) succinate (BNPS), triaminoguanidinium nitrate (TAGN), 2,4,6-trinitrobenzoic acid (TNBA) and nitroguanidine (NQ) on the volatility of TNAZ was investigated by undertaking thermogravimetric analysis. The TG pattern brings out the potential of BNPS and TAGN as additives to mitigate the volatility of TNAZ. The influence of additives on thermal decomposition of pattern of TNAZ was also investigated by DSC. The DSC results indicated that the additives did not have appreciable effect on the melting point of TNAZ. Scanning electron microscopic (SEM) studies were carried out to investigate the effect of additives on morphology of TNAZ. This paper also discusses the possible mechanism involved in between the TNAZ and TAGN and BNPS. It appears that the formation of charge transfer complex formation between the TNAZ and TAGN/BNPS. The effect of addition of high explosives such as CL-20, HMX and RDX on thermo-physical characteristics of TNAZ is also reported in this paper.

Prediction of heat of formation and related parameters of high energy materials.

Heat of formation is one of the most important parameters in the performance prediction of explosive and propellant formulations and their individual ingredients. This paper reports the development of user-friendly computer code for the prediction of heat of formation based on two approaches. In first methodology, the logic of Benson's Group additivity method and in the second method, the logic of Pedley method was used for predicting the heats of formation of high energy materials (HEMs). The predicted heats of formation by Benson method for various classes of high energy materials gave deviation in the range of 2-10%, whereas nearly 10-15% deviation was observed using Pedley methodology in comparison to experimental values. The linear regression coefficient values (R(2)) of 0.9947 and 0.9637 are obtained for heat of formation values predicted by this code using methodologies I and II, respectively. The newly developed code LOTUSES (version 1.3) has been validated by calculating the heats of formation of standard explosives such as TNT, pentaerythritol tetranitrate (PETN), RDX, HMX, etc., To the best of our knowledge, no such code is reported in literature which can predict heats of formation values integrated with performance parameters of HEMs belonging to all categories of organic compounds viz. aliphatic, aromatic and heterocyclic materials. The code can also be used to obtain parameters such as velocity of detonation, C-J pressure, volume of explosion products, power index, temperature of explosion and oxygen balance of HEMs. The code has been developed in Visual Basic having enhanced Windows environment. This software namely LOTUSES 1.3 is an updated version of the earlier ones namely LOTUSES 1.1 and 1.2 which do not cater for the calculation of heat of formation and temperature of explosion of HEMs. LOTUSES 1.3 is, therefore, a totally integrated software for computing most of the vital parameters of HEMs requiring mainly the molecular structural information of an explosive under consideration.

Studies on diaminoglyoxime (DAG): thermolysis and evaluation as ballistic modifier in double base propellant.

This paper reports thermolysis of diaminoglyoxime (DAG) and its evaluation as a ballistic modifier in double base propellant formulations. Differential scanning calorimetry (DSC) and simultaneous thermal analysis (DTA-thermogravimetric (TG)) revealed that DAG decomposes in two stages. Kinetics of initial stage of thermal decomposition of DAG evaluated from TG data gave activation energy (E(a)) of 153 kJmol(-1). The high-temperature Fourier transform Infrared (FTIR) spectra of DAG suggested preferential cleavage of NO and CNH2 during decomposition. Mass spectral data also suggest possibility of similar process. The hyphenated TG-FTIR data also revealed the evolution of gases containing species, such as CN, NH, OH and oxides of nitrogen during thermal decomposition. Evaluation of DAG as a ballistic modifier in RDX incorporated double base propellant formulations indicated that it brings down the pressure index to 0.17 compared to 0.79 for a control composition in the pressure range 6.9-8.8 MPa when used in combination with basic lead salycilate (BLS). The study suggests that combination of DAG and BLS need to be optimized to achieve more remarkable effects than BLS alone. It was observed that DAG does not have adverse effect on vulnerability and chemical stability of the propellant formulation.

Establishment of process technology for the manufacture of dinitrogen pentoxide and its utility for the synthesis of most powerful explosive of today--CL-20.

This paper reviews the recent work done on the synthesis as well as characterization of dinitrogen pentoxide (DNPO). The physico-chemical characteristics of DNPO are also discussed. The review brings out the key aspects of N2O5 technology with relevance to realize modern and novel HEMs. The paper also includes the aspects related with establishing the synthesis facility of dinitrogen pentoxide at HEMRL by gas phase interaction of N2O4 with O3. The process parameters for the synthesis of N2O5 at 50 g/batch have been optimized. The synthesized dinitrogen pentoxide has been characterized by UV [204, 213, 258 nm (pi-->pi*) 378 and 384 nm (n-->pi*)] and IR (1428, 1266, 1249, 1206, 1044, 822, 750, 546 and 454 cm(-1)) spectroscopy. The DSC clearly showed the sublimation of N2O5 at 32 degrees C. The nitration studies on 2,6,8,12-tetraacetylhexaaza tetracyclo[5,5,0,0(3,11)0(5,9)]dodecane (TAIW) proved its viability in 2,4,6,8,10,12-hexanitro-2,4,6,8(10,12))-hexaazatetracyclo [5,5,0,0(3,11)0(5,9)]dodecane (CL-20) synthesis. The synthesized CL-20 and its precursors have also been subjected to hyphenated TG-FTIR studies to understand decomposition pattern.