Thermal ignition studies on metallized fuel-oxidizer systems

Abstract

The thermal ignition behaviour of various mixtures of organic fuels, magnesium and ammonium nitrate (AN) has beeh examinect by differential thermal analysis technique. It has been observed that the thermal decomposition/ignition of organic fuel-AN mixtures is modified significantly in the presence of magnesium metal. 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. It is generally noticed, however, that the ignition of these systems becomes increasingly difficult with high Ioadings of metallic ingredients. The solid oxidizer, although used as a minor component, plays an important role in the ignition and sustenance of combustion. In a recent study [3] involving the hypergolicity of hybrid propellants, it has been observed that some solid organic fuels which by themselves are non-hypergolic, ignite readily with liquid oxidizers, such as nitric acid on mixing with metal powders, This synergistic ignition behaviour was explained in terms of the increased exothermicity of the system, primarily due to the exothermal reactions between the fuels and the 0xidizei" in the preignition stage These results led us to study whether a similar effect coUld be observed with solid oxidizers, instead of nitric acid, on subjecting the mixture to controlled heating. If so, the decomposition/ignition of the metaltized systems could take place at relatively low temperatures, thereby facilitating the ignition process.In the present investig~ition the ignition behaviour of various magnesium containing fuels mixed With ammonium nitrate (AN) has been examined by differential thermal analysis (DTA) technique. Most of the organic fuels chosen in the present study, such as carbon, benzidine (BZ), thiocarbohydradize