S. N. Asthana

Studies on CL-20: The most powerful high energy material

CL-20 is an attractive HEM having density (>2 g cm-3) and velocity of detonation (9400 m s-1) superior to HMX (1.9 g cm-3 and 9100 m s-1). During this study, CL-20 was synthesized to establish viability of efficient synthesis method. The compound synthesized at HEMRL was characterized by FTIR, 1H NMR and elemental analysis. Thermal studies (dynamic DSC and isothermal TG) were undertaken to determine kinetic parameters and understand the decomposition patterns. An attempt is made to explain the mechanism of decomposition of CL-20 on the basis of the data obtained by the authors and findings of other researchers. The activation energy values obtained during this work by adopting various approaches are close to the values reported for N-NO2 bond cleavage suggesting that it is global rate determining process rather than the collapse of cage structure. Mass spectra also provides evidences in this regard. Monitoring of decomposition products at high temperature supports these findings and brings out that NO2 initiates secondary decomposition processes because of entrapment in cage structure.

Glycidyl azide polymer (GAP) - an energetic component of advanced solid rocket propellants - a review

Abstract This paper reviews physico chemical, thermal, mechanical and ballistic characteristics of glycidyl azide polymer (GAP) and GAP based solid propellants. GAP offers propellant system with superior ballistics and high performance. Its potential as an energetic additive is attributed to the highly exothermic scission of -N3 bond structure accompanied by the release of energy of the order of 685 kJ/mole. Inclusion of GAP in propellant compositions leads to an improvement in their mechanical properties.

Synthesis, characterization and thermal studies of (Ni/Co) metal salts of hydrazine: potential initiatory compounds

Nickel hydrazinium nitrate (NiHN) and cobalt hydrazinium nitrate (CoHN) were prepared by reacting their respective metal nitrates with hydrazine hydrate at 25 and 65 degrees C. The compounds were characterized by metal content and infrared (IR) spectroscopy. Differential thermal analysis (DTA) results suggest that the nickel complex is relatively more stable than the cobalt complex. The activation energy determined by DTA and ignition delay measurements corresponds to an energy of activation (E(a)) of 80+/-4 kJ/mol for NiHN and that of 150+/-8 kJ/mol for CoHN. Thermo gravimetry (TG) also revealed more rapid decomposition of NiHN than that of CoHN in the temperature region of 215-235 degrees C. High temperature Fourier transform-infrared (FT-IR) studies indicated rupture of the Ni-Co-N bond as the primary step in the thermolysis. As regards sensitivity to mechanical stimuli, NiHN was found to be less impact sensitive while CoHN exhibited less friction sensitivity. The study revealed that NiHN could be used alone as well as in combination with oxidizer/fuel as initiators depending upon the specific requirements. The effect of silver azide and glass on the sensitization of NiHN was also studied. CoHN appears to be an effective ballistic modifier in enhancing burning rates of composite propellants.

Hydrazinium nitroformate (HNF) and HNF based propellants: A review

Abstract This paper reviews the studies carried out so far on HNF, which is emerging as potential oxidizer for futuristic propellant systems. Methods of synthesis of HNF including efforts to obtain HNF of desired particle size/shape have been discussed in detail. As purity of HNF has bearing on its thermal, physical and chemical characteristics, process parameters are being optimized to obtain high quality HNF with reproducible characteristics. Potential of HNF based propellants as propulsive force to missiles and space vehicles is also discussed in this paper. Problem areas in processing HNF based propellants have also been identified.

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.

Studies on thermoplastic elastomers based RDX-propellant compositions

Abstract This paper presents the results obtained during studies on 80% RDX propellant systems based on thermoplastic elastomers (TPEs) namely ethylene-vinyl acetate (EVA), triblock copolymers of styrene-butadiene/styrene-isoprene (Kraton), poly-urethane-ester-MDI (Estane) and copolymer of polybutylene terephthalate - polyether glycol (Hytrel) as binders, Dioctyl phthalate (DOP), triacetin (TA) and glycidyl azide polymer (GAP) were incorporated as plasticizers in the formulations. An attempt has been made to correlate structural features of TPEs with mechanical properties as well as glass transition temperature (Tg). Results obtained suggest that TPE-based RDX-propellants have the advantage of high insensitivity to impact and friction stimuli vis-à-vis nitrte ester based conventional propellants. EVA based propellents gave the best results in this regard. Ignition temperature for all the compositions was >200°C. EVA, Hytrel and Estane based formulations were found to be more energetic than Kraton based formulations. Incorporation of GAP resulted in the improvement in ballistics (Impetus and burn rates) as compared to DOP plasticised formulations. TA based compositions gave an intermediate value. Thermal decomposition pattern was determined by applying Differential Thermal Analysis (DTA) and Differential Scanning Calorimetry (DSC). An attempt has been made to explain the trends observed on the basis of the evidences generated during this study and theories proposed by other researchers.

Studies on thermal stability, autoignition and stabilizer depletion for shelf life of CMDB propellants

Abstract This paper reports the results of thermal stability of composite modified double base propellants (CMDB) by using tests applicable for double base propellants (DBP) and shelf life estimation of CMDB propellants by application of the autoignition test and monitoring stabilizer depletion by high performance liquid chromatography (HPLC). The Abel heat test results suggest the stability of CMDB propellants with or without additional stabilizer, whereas the Methyl Violet test indicated that CMDB propellants without resorcinol do not have stability comparable with DBP. Results of the Vacuum stability and B and J tests showed stability of CMDB propellants with resorcinol within acceptable limits. Aging did not change the DTA pattern to any appreciable extent. Autoignition test results gave a shelf life of 27.1 and 157.8 years for CMDB propellants at 40 and 30°C respectively. 2-NDPA depletion studies indicated a half life of 6–7 years and 26–30 years respectively for CMDB propellants at 40 and 30°C whereas carbamite depletion yielded a half life of 8–9 and 40–42 years. The activation energy ( E ) for aging of CMDB propellants was found to be 33 ± 1 kcal/mol.

Characterization and Thermal Analysis of Hydrazinium Nitroformate (HNF)

This paper reports studies undertaken on hydrazinium nitroformate (HNF) synthesized in HEMRL by a viable method. The purity of the synthesized HNF was determined by high-performance liquid chromatography, and the compound was characterized by elemental analysis, ultraviolet, infrared, nuclear magnetic resonance ( 1 H NMR and 13 C NMR), and electron impact mass spectroscopy. Detailed studies on the crystallographic nature and surface chemistry of HNF were undertaken by applying scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photo-electron spectroscopy (XPS). SEM shows layered needle-shaped crystals of HNF. The d values obtained in XRD spectra establish monoclinic structure, as reported by other investigators. TEM provides confirmatory data. The XPS study offers additional information regarding the surface chemistry of HNF. The evidence is in favor of intermolecular hydrogen bonding to a large extent. Thermal studies were also conducted as part of this work. Differential thermal analysis, thermogravimetry, and differential scanning calorimetry results reveal two-stage decomposition of HNF. DSC results correspond to the activation energy of ~150 kJ/mol for both the stages of decomposition.

Studies on effect of incorporation of BDNPF/A on burning rates of RDX/AP/AI filled CMDB propellants

Abstract This paper reports the effect of replacement of non -energetic plasticizer diethyl phthalate (DEP) by nitroplasticizer [1:1 mixture of bis (2,2 dinitro propyl) formal (BDNPF) and bis (2,2 dinitro propyl) acetal (BDNPA)] on burning rates and Isp of nitramine (RDX) / ammonium perchlorate (AP) based composite modified double base (CMDB) propellants. Addition of BDNPF/A led to overall 9–46% increase in burning rates, as well as gain in Isp to the order of 5–10 s in both the systems. Inclusion of copper chromite (C.C.) led to further improvement in burning rates. A typical aluminized (17.5%)- ecofriendly RDX (12.5%)-CMDB formulation gave burning rates of the order of 8–22 mm/s in the pressure range of 2.9–10.8 MPa with Isp (theoretical) of 264 s. Aluminized AP-CMDB propellant with low pressure combustion limit of 1.9 MPa and burning rates of 15–31 mm/s was also realized during this work. Superior oxygen balance and heat of formation of BDNPF/A compared to DEP appear to play contributory role in this regard. Heat feed back from intensified combustion near the deflagrating propellant surface may be facilitating the decomposition of condensed phase. This is clearly brought out from estimated activation energy values for BDNPF/A plasticized RDX propellants.

Studies on Combustion of Metallized RDX-Based Composite Modified Double-Base Propellants

This paper reports the results obtained during research work carried out on metallized cyclo trimethylene trinitramine (RDX)-composite modie ed double-base (CMDB)propellantswith theaim of realizing superiorburning rates as well as performance. Nickel (Ni) and titanium (Ti)-based formulations exhibited burning-rate characteristics superior to those for aluminized (Al) compositions, whereas zirconium (Zr)-based formulations gave the best results. An attempt has been made to explain the burning-rate pattern observed on the basis of combustion characteristics of metals. Among selected ballistic modie ers, basic lead salicylate (BLS)+Cu2O+carbon black (C-black) combination and copper chromite (Cu-chromite ) gave catalytic effect superior to that of ferric oxide (Fe2O3) and ferric acetyl acetonate (FeAA). Incorporation of 5% ammonium perchlorate (AP) of 5π size augmented the catalytic effect of ballistic modie ers remarkably. Thus, RDX (12.5%)-Zr (17.5%) CMDB formulation with 5% AP (5π) and two-parts Cu-chromite gave burning rates of the order of 4 ‐21 mm/s in the pressure range of 1‐10.8 MPa and pressure index value of 0.66 with Isp (theoretical ) of the order of 241 s. To take advantage of pyrophoric nature of Zr and superior heat of combustion of Al, a combination of both the metals was evaluated. Composition containing 13% Al and 4.5% Zr along with 12.5% RDX in a double-base matrix with 5% AP and two parts of Cu-chromite as additives gave stable combustion in the pressure range of 1 ‐10.8 MPa (burning rates 4‐18 mm/s) and Isp (theoretical ) of 259 s. Kinetic parameters obtained for RDX-CMDB formulations during differential thermal analysis studies (Ea 48 kcal/mole and A 7 :2 £ 10 19 ) established that the RDX decomposition is the rate-controlling step. Addition of Al did not have a remarkable effect on the kinetic parameters of thermal decomposition. However, Ni/Ti/Zrbrought down Ea and A valuesdrastically, suggesting thatheat feedbackcaused by efe cient combustion near the dee agrating propellant surface ine uences subglobal kinetics and facilitates the decomposition of condensed phase. Thermogravimetric and differential scanning calorimetry (DSC) results bring outthatFe2O3 andBLS +Cu2O +C-black do not play a catalytic rolein condensed-phase decomposition, whereas Cu-chromite and FeAA appear to catalyze both gas- as well as condensed-phase reactions.