Combustion Mechanism of Ammonium-Nitrate-Based Propellants

This paper discusses results obtained by studying a row of progressively complicated ammonium-nitrate-based systems: ammonium nitrate/catalyst, ammonium nitrate/catalyst/hydroxy terminated polybutadiene, ammonium nitrate/catalyst/hydroxy terminated polybutadiene/ammonium perchlorate, and ammonium nitrate/catalyst/hydroxy terminated polybutadiene/ammonium perchlorate/Al. The successive addition of ammonium perchlorate and Al to the binary mixture of a catalyzed ammonium nitrate/binder yields a regular increase in the burning rate, accompanied by a small change in the pressure exponent. On the basis of flame-structure investigation by fine tungsten-rhenium thermocouples, it has been determined that the surface temperature of catalyzed ammonium nitrate as well as ammonium-nitrate-based propellants is controlled by the dissociation reaction of the salt occurring at the surface. An analysis of the results obtained suggests a combustion mechanism of ammonium-nitrate-based propellants, which is based on the leading role of heat release in the condensed phase.