Thermal ignition behaviour of ammonium perchlorate in presence of fuel-rich compounds

Abstract

The thermal ignition behaviour of ammonium perchlorate has been investigated in the presence of fuel-rich compounds such as tetramethylammonium perchlorate, trimethylammonium nitrate, carbon and cellulose. The ignition characteristics, as studied by differential thermal analysis, have been found to be strongly influenced by self-decomposition and other physicochemical properties of the additives. For a simple system, an analytical model proposed on the basis of the coupling of two exothermic decomposition reaction kinetics and a heat-balance equation, appears to explain to some extent the observed trend in peak ignition temperature when the composition is varied. The salient features of the analysis, as regards its application to fuel-oxidizer interactions in general, have been pointed out.The importance of thermal ignition studies on condensed fuel-oxidizer systems arises mainly because of their extensive application in the field of propellants and explosives. Of the condensed systems, the mixtures involving ammonium perchlorate (AP) are of special interest due to their wide use in solid propellants. The thermal ignition behaviour of AP is known to be modified in the presence of catalysts, impurities and additives [1]. A systematic study of the differential thermal analysis (DTA) of AP in the presence of structurally similar, fuel-rich compounds, viz. methylammonium perchlorates (MAPs), was recently carried out in our laboratory [2]. It was observed that although AP shows two exotherms due to partial and complete decomposition at around 300 ~ and 400 ~ respectively [1] in DTA, it ignites in asingle step at around its partial decomposition temperature in the presence of small amounts of mono-, di-, tri-or tetramethylammonium perchlorate. Interestingly, the critical concentration of a MAP needed to cause ignition in a single step corresponds to a unique composition of the mixture, expressed in terms of its elemental stoichiometric coefficient, ~e [3]. However, some of the features in the DTA of the mixtures of AP and tetramethylammonium perchlorate (TMAP), such as the shift of the terminal exotherm to lower temperatures as a function of concentration, were not clearly explained.

Thermal ignition studies on metallized fuel-oxidizer systems

“…The decomposition characteristics of the binary mixtures of AN with various metals indicate the specific action of magnesium and zinc in lowering the decomposition temperature. A possible explanation for the low temperature decomposition is given in terms of the solid state reaction causing the fusion of AN which further reacts with the metal resulting in a highly exothermic reaction.The thermal characterization of various condensed fuel-oxidizer systems used in solid propellants and explosive compositions has been an important aspect of our earlier studies [1,2]. Highly metallized fuel rich compositions have found application in solid-fuel ram jet propulsion systems.…”