Effect of metal additives on neutralization and characteristics of AP/HTPB solid propellants

Conventional ammonium perchlorate (AP) based solid propellant system has been used in rocket boosters and most tactile missiles. But the toxic chloride emissions from the combustion of AP during the rocket launch increase the air pollution by 1%. For the conversion of conventional AP based propellant into Green propellant there approaches can be used. These are scavenging propellants, Neutralizing propellants and Non-chlorine propellants. In present study an attempt is made to investigate the characteristics of neutralizing propellant with the help of different metal additives such as Al, Mg, and combined Al-Mg. The investigations were theoretically and experimentally carried out and the results compared with base composite solid formulation (AP/HTPB). Theoretical investigation on that addition of metal additives clearly indicated helps in the reduction of toxic HC1 without the compensation of performance. The burn rate study was carried out using Crawford strand burner setup in inert atmosphere under different pressure conditions ranges from 0.689 MPa to 4.136 MPa. A considerable enhancement in the burn rate of AP based solid propellant by 14.02% using pure metals as additives and by 54% using binary metal mixtures as additives was observed. Studies on HCl reduction of AP based propellant samples using gas bubbling setup shows that addition of Mg-15% to the base propellant enhances the HCl reduction by 47% but the propellant was porous in nature and addition of Al-Mg(15%) to the base propellant enhances the reduction by 37%. Thus, the binary metal mixtures in AP/HTPB based solid propellant resulted in better reduction of toxic HCl without reduction in performance than the sample without metal additives. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.