A simple and straightforward synthesis of 5,5-diamino-4,4-dinitramino-3,3-bi-1,2,4-triazole by the selective nitration of 4,4,5,5-tetraamino-3,3-bi-1,2,4-triazole is presented. The interaction of the amino and nitramino groups improves the energetic properties of this functionalized bitriazole. For a deeper investigation of these properties, various nitrogen-rich derivatives were synthesized. The new compounds were investigated and characterized by spectroscopy (H-1 and (CNMR)-C-13, IR, Raman), elemental analysis, mass spectrometry, differential thermal analysis (DTA), X-ray analysis, and impact and friction sensitivities (IS, FS). X-ray analyses were performed and deliver insight into structural characteristics with which the stability of the compounds can be explained. The standard enthalpies of formation were calculated for all compounds at the CBS-4M level of theory, revealing highly positive heats of formation. The energetic performance of the new molecules was predicted with the EXPLO5 V6.02 computer. A small-scale shock reactivity test (SSRT) and a toxicity test gave a first impression of the performance and toxicity of selective compounds.

Energetic Materials Based on 5,5'-Diamino-4,4'-dinitramino-3,3'-bi-1,2,4-triazole.

Ammonium nitrate (AN)-based composite propellants have several major problems, namely, a low burning rate, poor ignitability, low energy, and high hygroscopicity. The addition of a burning catalyst proved to be effective in improving the burning characteristics of AN-based propellants. In this study, the burning characteristics of AN-based propellants supplemented with MnO2 as a burning catalyst were investigated. The addition of MnO2 is known to improve the ignitability at low pressure. The most effective amount of MnO2 added (ξ) for increasing the burning rate is found to be 4 %. The increasing ratio with ξ is virtually independent of the burning pressure and the AN content. However, the pressure exponent unfortunately increased by addition of MnO2. The apparent activation energy of the thermal decomposition for AN and the propellant is decreased by addition of MnO2. From thermal decomposition kinetics it was found that MnO2 could accelerate the thermal decomposition reaction of AN in the condensed phase, and therefore, the burning characteristics of the AN-based propellant are improved.

Burning Characteristics of Ammonium Nitrate‐based Composite Propellants Supplemented with MnO2

Three isomeric dinitropyrazoles (DNPs) were synthesized starting from readily available 1H-pyrazole by slightly improved methods than described in the literature. 3,4-Dinitropyrazole (3), 1,3-dinitropyrazole (4), and 3,5-dinitropyrazole (5) were obtained and compared to each other with respect to thermal stability, crystallography, sensitivity and energetic performance. Two isomers (3 and 4) show high densities (1.79 and 1.76gcm(-3)) and interesting thermal behavior as melt-castable materials (3: T-melt.=71 degrees C, T-dec.=285 degrees C;5: T-melt. = 68 degrees C, T-dec.=171 degrees C). Furthermore, eight salts (sodium, potassium, ammonium, hydrazinium, hydroxylammonium, guanidinium, aminoguanidinium and 3,6,7-triamino-[1,2,4]triazolo[4,3-b][1,2,4]triazole (TATOT) of 3 and 5 were synthesized in order to tune performance and sensitivity values. These compounds were characterized using H-1, C-13, N-14, N-15 NMR and IR spectroscopy as well as mass spectrometry, elemental analysis and thermal analysis through differential scanning calorimetry. Crystal structures of 14 compounds were obtained (3-7, 10-12 and 15-20) by low-temperature single crystal X-ray diffraction. Impact, friction and electrostatic discharge (ESD) values were also determined by standard methods. The sensitivity values range between 8.5 and 40J for impact and 240N and 360N for friction and show mainly insensitive character. The energetic performances were determined using recalculated X-ray densities, heats of formation and the EXPLO5 code and support the energetic character of the title compounds. The calculated energetic performances (V-D: 6245-8610ms(-1);p(CJ): 14.1-30.8GPa) were compared to RDX ((O2NNCH2)(3)).

Isomers of Dinitropyrazoles: Synthesis, Comparison and Tuning of their Physicochemical Properties.

The influence of fullerene additives on the combustion behaviour of cyclotrimethylene trinitramine/ammonium perchlorate composite modified double-base (RDX/AP-CMDB) propellants are investigated by thermogravimetricdifferential thermogravimetric (TG-DTG) analysis, burning rate tests, and scanning electron microscopy observations. The difference between lead salicylate (F-Pb) and bismuth citrate acid (CP-Bi) as combustion modifiers has also been examined. TG-DTG investigations show that the addition of all additives advanced and accelerated the evaporation of nitroglycerin (NG). The addition of Extracted Fullerene Soot (EFS), C60 and carbon black (CB) additives obviously accelerated the liquid  phase decomposition of NG. Also, the solid phasedecomposition of nitrocellulose (NC) and the liquid phase  decomposition of RDX were accelerated by 0.5 per cent Fullerene Soot (FS)/2.5 per cent CP-Bi/0.5 per cent copper adipic acid (J-Cu) composite catalyst. The addition of all composite catalysts promoted the decomposition of ammonium perchlorate (AP) except 0.5 per cent EFS/2.5 per cent CP-Bi/0.5 per cent J-Cu composite catalysts. It is well known that there exists dark zone in the flame structure of RDX-CMDB propellant, but in our observation, the dark zone vanished with the addition of 10 per cent AP to the forenamed propellant. The burning rates were increased at low pressure but reduced at high pressure by all catalysts except 0.5 per cent EFS/2.5 per cent CP-Bi/0.5 per cent J-Cu and 0.5 per cent C60/2.5 per cent CP-Bi/0.5 per cent J-Cu which reduced the burning rates at every tested pressure. The pressure exponents of tested propellants were reduced by 0.5 per cent FS/2.5 per cent CP-Bi/0.5 per cent J-Cu with a factor of 17 per cent . The quenched surface observations significantly differed with the additions of diverse composite catalysts, which were consistent with the burning rate results.Defence Science Journal, 2009, 59(3), pp.284-293, DOI:http://dx.doi.org/10.14429/dsj.59.1522

http://publications.drdo.gov.in/ojs/index.php/dsj/article/download/1522/652

RDX/AP-CMDB Propellants Containing Fullerenes and Carbon Black Additives

The combustion wave structure and thermal decomposition process of HMX were examined in order to elucidate the burning rate characteristics of HMX. The combustion wave can be divided into three zones: nonreactive solid-phase, surface reaction, and gas-phase reaction zones. Measurements with micro-thermocouples revealed that the heat flux produced in the surface reaction zone is approximately equal to the heat flux transferred back from the gas phase to the burning surface. Accordingly, the reaction process in the suface reaction and the gas phase zones plays a dominant role in the burning rate of HMX. The gas phase reaction zone consists of a two-stage reaction process: the first stage is the exothermic rapid reaction process between NO2 and aldchydes, and the second stage is the exothermic slow reaction process between NO and N2O and remaining fuel species. The luminous flame zone which is determined to be the second stage reaction process approaches rapidly the burning surface as pressure increases. However, the luminous flame reaction appears to be little responsible for the burning rate of HMX.

Examinations of the quenched burning surface of HMX samples revealed that the burning surface melts and forms a noncrystallized intermediate material. The surface structure appears to be different from the structure of thermally degraded HMX samples which were obtained by a thermogravnmetric analysis.

Combustion mechanism of HMX

The thermal decomposition characteristics of RDX, binders, and RDX composite propellants were studied using thermal analytical techniques. Three kinds of binders were tested to elucidate the role of binder on the burning rate of the propellants. There were no apparent correlations between the thermal decomposition rates of binders and the burning rates of propellants, whereas there was a correlation between the decomposition temperature and the burning rate of the propellants.

It is found that the major factor which controls the burning rate is the initial thermal-decomposition stage of the binders. Thus, the burning rate of nitramine composite propellants appeared to be largely dependent on the physical and chemical properties of binder.

H. Maruizumi

Papers

Thermal Decomposition of RDX Composite Propellants