Thermoanalytical studies on CTPB‐NH4ClO4 composite solid rocket propellants

Abstract

AbstractPremature reignition of controllable solid propellant motors, a factor affecting the extinguishment reliability, has been attributed to the first exotherm of NH4ClO4. Detailed studies were made(1) on suppressing the first exotherm of NH4ClO4 with the use of materials like NH4BF4, NH4PF6, (NH4)2TiF6 etc. The present paper deals with the thermal decomposition kinetics of carboxy‐terminated polybutadiene (CTPB)‐NH4ClO4 propellant with NH4BF4 as an additive to suppress the first exotherm of NH4ClO4.The techniques employed in this study include: differential scanning calorimetry (DSC) for the thermal decomposition studies, and strand‐burner for the measurement of propellant burning rates. DSC experiments were conducted on the propellants at pressures of ambient, 17 kg/cm2 and 40.82 kg/cm2; at a constant heating rate under an inert atmosphere of nitrogen. The burning rate of the propellant samples were determined in the pressure range of ambient to 70 kg/cm2 in an atmosphere of nitrogen.The burning rates were found to increase with pressure at each of the concentrations of the additive. The decrease in burning rate with the increase in concentration of the additive, at pressures of 35 kg/cm2 and below is attributed to the excess of ammonia formed during the decomposition of both NH4ClO4 and NH4BF4. At pressures above 35 kg/cm2, the increase in burning rate with the increase in concentration of the additive is attributed to the increased concentration of the metal ion (boron) in NH4BF4. These observations are in agreement with those of Mayer(1) et al., and Glaskova(2).