R. R. Sanghavi

Studies on Triple Base Gun Propellant Based on Two Energetic Azido Esters

Triple base propellant is the workhorse propellant because it possesses several advantages like reduced flash, flame temperature, and erosion of the barrel as compared to double and single base propellant. Hence, efforts are going on worldwide to increase its performance by increasing its energy using energetic plasticizers and binders. In the present article, nonenergetic plasticizer dibutyl phthalate (DBP) is replaced by two energetic azido ester plasticizers, tris(azido acetoxy methyl) propane (TAAMP) and bis(azido acetoxy) bis(azido methyl) propane (BABAMP), in triple base composition and their different properties are studied. Experimental closed vessel (CV) results (loading density 0.2 g/cm3) clearly indicate that the triple base composition with 2% DBP has force constant 1018 J/g, which is increased to 1026 and 1030 J/g on replacement of DBP by 1 and 2% TAAMP, respectively. Mechanical properties of propellant compositions containing 1 and 2% TAAMP (compression strength 279 and 291 kgf/cm2, percentage compression 11.2 and 10.5, respectively) are also better than those of composition containing DBP (compression strength 275 kgf/cm2 and 10.3% compression). Similarly, 1 and 2% replacement of DBP by BABAMP shows further rise in energy (1032 J/g, 1038 J/g respectively) than that of compositions containing 1 and 2% TAAMP. These two compositions also exhibit better mechanical properties (compression strength 311.2 and 312.3 kgf/cm2, % compression 11.0 and 10.5, respectively) than compositions containing 1 and 2% TAAMP. The differential thermal analysis (DTA) results brought out the fact that the compositions containing energetic plasticizers revealed maximum decomposition temperature in the range of 172–174°C which is close to DBP plasticized triple base gun propellants (174°C). The energetic plasticized propellant compositions of both (TAAMP and BABAMP) showed sensitivity data in the range of (H50 19 to 22 cm, F of I 25 to 29 and friction insensitivity 19.2 kg) acceptable limit for gun propellant.

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.

Closed-Vessel and Thermal Studies on Triple-Base Gun Propellants Containing CL-20

This study was undertaken to see the effect of the replacement of picrite by 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) (5, 10, and 15%) in triple-base gun propellants. Experimental results of a closed-vessel test at a loading density of 0.2 g/cm 3 indicate improvement in energetics of the CL-20-incorporated compositions. The force-constant values obtained were 1046, 1071, and 1095 J/g for 5, 10, and 15% CL-20-based formulations, compared with 1028 J/g for conventional picrite composition as the control. Similar trends were observed for linear burning-rate coefficient β 1 values. The selected energetic plasticizers N-(n-butyl)-N-(2-nitroxyethyl) nitramine (Bu-NENA) and bis-2,2 dinitro propyl formal/acetal (BDNPF/A) were also evaluated for their effectiveness in CL-20-containing gun-propellant compositions. Thermal analysis was carried out using differential scanning calorimeter and thermogravimetric analyzer. Replacement of picrite by CL-20 resulted in an increase in AH values (by differential scanning calorimeter) compared with that of control composition. Weight-loss data (from thermogravimetric analyzer) showed a similar trend. The CL-20-based compositions were found relatively more sensitive to friction stimuli (12-17 kg) compared with control composition (19.2 kg).

Combustion and thermal behaviour of ballistically modified eva and estane based RDX-AP propellants

Abstract This paper reports the findings of the combustion and thermal studies on RDXAP based propellants with ethylene vinyl acetate (EVA) and polyurethane-ester-MDI (Estane) binder systems plasticised with triacetin (TA) and glycidyl azide pre-polymer (GAP). Effect of incorporation of selected ballistic modifiers namely iron oxide, copper chromite, basic lead salicylate+cuprous oxide+carbon black combination and sodium borohydride (adsorbed on aluminium oxide) was also studied during this work. Incorporation of GAP as plasticizer in place of TA led to improvement in F by 36–52 J/g. Closed vessel evaluation results were in close agreement with the theoretically predicted performance. Burn rate enhancement by ballistic modifiers was observed in both acoustic burn rate experiments as well as closed vessel test. A major finding was the realization of pressure index value of the order of 0˙65–0˙68 with copper chromite in the high pressure regions (14–200 MPa) which is not reported earlier. DTA and DSC studies indicate that RDX decomposition is the major process during propellant degradation and ballistic modifiers catalyse condensed-phase/near-surface reactions involving GAP.

Studies on different types of nitrocellulose in triple base gun propellant formulations

Currently triple base propellants are used for tank gun ammunition. Nitroguanidine (NQ) propellant is the most promising among them due to various advantages like low flame temperature, flashlessness, low barrel erosion, long shelf life, etc. Therefore, it will continue to be used in the field of gun propulsion systems for several years to come. However, there is scope for enhancing the performance of triple base propellant with respect to energy level and mechanical properties. Nitrocellulose (NC) is the energetic binder cum fuel used in the triple base composition propellant and constitutes a sizeable percentage of the compound. Hence, one of the promising triple base compositions was selected, and a systematic study was carried out by using different types of NC (having varying percentages of nitrogen content) to study the variation in mechanical properties, energy content, linear burning rate coefficient, and pressure exponent. The results are discussed in this paper.