Initial Steps of Thermal Decomposition of Dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate Crystals from Quantum Mechanics

Dihydroxylammonium 5,5?-bistetrazole-1,1?-diolate (TKX-50) is a recently synthesized energetic material (EM) with most promising performance, including high energy content, high density, low sensitivity, and low toxicity. TKX-50 forms an ionic crystal in which the unit cell contains two bistetrazole dianions {c-((NO)N3C)-[c-(CN3(NO)], formal charge of ?2} and four hydroxylammonium (NH3OH)+ cations (formal charge of +1). We report here quantum mechanics (QM)-based reaction studies to determine the atomistic reaction mechanisms for the initial decompositions of this system. First we carried out molecular dynamics simulations on the periodic TKX-50 crystal using forces from density functional based tight binding calculations (DFTB-MD), which finds that the chemistry is initiated by proton transfer from the cation to the dianion. Continuous heating of this periodic system leads eventually to dissociation of the protonated or diprotonated bistetrazole to release N2 and N2O. To refine the mechanisms observed in the periodic DFTB-MD, we carried out finite cluster quantum mechanics studies (B3LYP) for the unimolecular decomposition of the bistetrazole. We find that for the bistetrazole dianion, the reaction barrier for release of N2 is 45.1 kcal/mol, while release of N2O is 72.2 kcal/mol. However, transferring one proton to the bistetrazole dianion decreases the reaction barriers to 37.2 kcal/mol for N2 release and 59.5 kcal/mol for N2O release. Thus, we predict that the initial decompositions in TKX-50 lead to N2 release, which in turn provides the energy to drive further decompositions. On the basis of this mechanism, we suggest changes to make the system less sensitive while retaining the large energy release. This may help improve the synthesis strategy of developing high nitrogen explosives with further improved performance

Thermal Analysis and Sensitivity Studies on Guanylurea Dinitramide (GUDN or FOX-12) Based Melt Cast Explosive Formulations

Guanylurea dinitramide (GUDN or FOX-12) is a stable salt of dinitramidic acid with good thermal stability, and is a good candidate for insensitive formulations. Thermal analysis reveals the compatibility of GUDN with benchmark explosives such as RDX and TNT in melt cast explosive formulations. The paper describes a thermal and sensitivity study of GUDN with RDX and TNT. In the present study GUDN was evaluated as a possible replacement for RDX/TNT based aluminized and non aluminized melt cast explosive formulations. The thermal properties of the composition were investigated as well as its sensitivity to impact and friction. Its thermal decomposition behavior was compared to a control composition based on RDX and TNT. The thermal and sensitivity results proved the worth of these compositions for melt cast explosive applications

Theoretical and Experimental Investigation of Flow Straighteners in U-type Pulse Tube Cryocoolers

Presented at the 16th International Cryocooler Conference, held May 17-20, 2008 in Atlanta, Georgia.The U-type Pulse Tube Cryocooler (PTC) involves a change in the direction of gas flow as it proceeds from the regenerator to the pulse tube. The sharp U-bend has an adverse effect on pulse tube cooling action due to formation of eddies and undesirable mixing in the cold end of the pulse tube. The present work deals with experimentation and CFD modeling related to U-type PTCs. Two cases of ‘U’ bends have been studied; gradual ‘U’ bends and sharp ‘U’ bends. Experimentation has been carried out using copper screens of 100-mesh size as flow straighteners. The optimum performance in terms of low temperature for the case of a gradual U bend was achieved with a stack of 18 flow-straightener screens. The no-load temperature for this case of a gradual ‘U’ bend, with and without flow straighteners, was 57.7 K and 88.8 K, respectively, for a charging pressure of 16 bar. When the gradual 180 degree bend at the cold end was replaced by a sharp U bend, the no load temperature increased from 88.8 K to 137 K without flow straighteners. In order to understand the role of flow straighteners in PTC, a CFD model was developed in FLUENT. The flow straighteners are modeled as a homogeneous porous medium. The results show that the flow straighteners significantly affect velocity patterns in the pulse tube. The theoretical study showed that there exists an optimum number of flow straighteners which improve the cooling power and efficiency of the pulse tube cryocooler. This was in agreement with the experimental results obtained earlier

Biological Evaluation of 1, 2-bis (2, 4, 6-Trinitrophenyl) Hydrazine

1, 2-Bis (2, 4, 6-trinitrophenyl) hydrazine (3) and its precursor (2) were screened for its antimicrobial properties, namely, antifungal activity against Aspergilus niger and Alternaria aletrnata and antibacterial activity against Bacillus substalis and Xanthomonas campstris at different concentrations (0.5 % and 1%). The antimicrobial result exhibits the promising biological activity

Review of Promising Insensitive Energetic Materials

During the last twenty years military explosives, and energetic materials in general, have changed significantly. Worldwide, research and development programs are active in developing promising insensitive HEMs with higher performance. This has been due to several factors, which include new operational requirements such as Insensitive Munitions (IM), but it is also due to the availability of new materials and to new assessment and modelling techniques. The present review focuses on the basic idea and necessity for IM, and the conditions, technical requirements and tests for IM. The review also explains the various promising insensitive high explosives, their synthesis and formulation used in different propellants

Environmentally benign synthesis of aromatic nitro compounds using silica supported inorganic nitrates

250-251Simple, rapid, clean and environmentally benign synthesis of aromatic nitro compounds by using inorganic nitrates as nitrating agents adsorbed on silica gel as a solid support has been reported

Studies of antimicrobial activity of picryl amino pyridine N-oxides

1675-1677Biologically active picryl amino pyridines and their N-oxide have been successfully synthesized and screened for their antimicrobial potency to set-up the structure activity relationships and found to possess better antibacterial activity than antifungal activity

Novel synthesis of biologically active nitro heterocyclic compounds

54-57Different nitro heterocyclic compounds possessing diverse biological activity have been successfully synthesized by simple, rapid and environmentally benign method using bismuth nitrate supported on silica gel and were screened for their antimicrobial properties to set up the structure activity relationship