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.