Fast Burning Rocket Propellants Based on Silicone Binders - New Aspects of an Old System

摘要

Fast burning rocket propellants based on ammonium perchlo-rate (AP) and polydimethylsiloxane (PDMS) binders have been formulated and basically characterized in aluminized and non aluminized versions. The thermodynamic performance of PDMS bound propellants is limited b the evaporation point of silicon dioxide (crystaobalite at 2863 K), which is formed during the combustion. The maximum specific impulses calculated with an expansion ratio of 70:1 are I_(SP) = 2340 N s/kg (238s) for AP/PDMS and I_(SP) = 2430 N s/kg (247 s) for AP/Al/PDMS formulations. With a tri-modal AP-fraction of 200 #mu#m, 30 #mu#m and 2 #mu#m it was possible to achieve process able propellants with 83% and 84% solid loading. They give burning rtes close to 60 mm/s at 10 MPa and pressure exponents between 0.5 and 0.6 in the range of 7 - 25 MPa. The thermodynamic specific impulse of these systems was calculated to I_(SP) = 2319 N s/kg (236 s) for AP/PDMS and I_(SP) = 2403 N s/kg (245 s) for AP/Al/PDMS formulations at 70:1 expansion ratio. Measurements of the glass transition point by DMA and TMA detected a time dependent partial crystallization of the used PDMS close to T_G in the temperature range from -44 deg C to -60 deg C. Basic tests reveal high thermal and chemical stability with flash points over 300 deg C and zero detonation sensitivity at 50 mm diameter. The property profile, so far propellants with high burning rates and operating pressures together with a high thermal stability and a low vulnerability.