FUEL-OXIDIZER MIXTURES: THEIR STABILITIES AND BURN CHARACTERISTICS

Abstract

A survey of the stability and performance of eleven solid oxidizers and thirteen fuels was performed by differential scanning calorimetry, simultaneous differential thermolysis, and hot-wire ignition. Sugars, alcohols, hydrocarbons, benzoic acid, sulfur, charcoal, and aluminum were used as fuels; all fuels except charcoal and aluminum melted at or below 200 °C. It was found that the reaction between the oxidizer and the fuel was usually triggered by a thermal event, i.e., melt, phase change, or decomposition. Although the fuel usually underwent such a transition at a lower temperature than the oxidizer, the phase change of the fuel was not always the triggering event. When sugars or sulfur were the fuels, their phase change usually triggered their oxidation. However, three oxidizers, KNO3, KClO4, and NH4ClO4, tended to react only after they underwent a phase change or began to decompose, which meant that their oxidization reaction, regardless of the fuel, was usually above 400 °C. KClO4–fuel mixtures decomposed at the highest temperatures, often over 500 °C, with the ammonium salt decomposing almost 100 °C lower. Mixtures with ammonium nitrate (AN) also decomposed at much lower temperatures than those with the corresponding potassium salt. With the exception of the oxidizers triggered to react by the phase changes of the polyols and sulfur, the oxidizer–fuel mixtures generally decomposed between 230 and 300 °C, with AN formulations generally decomposing at the lowest temperature. In terms of heat release, potassium dichromate–fuel mixtures were the least energetic, generally releasing less than 200 J g−1. Most of the mixtures released 1000–1500 J g−1, with potassium chlorate, ammonium perchlorate, and AN releasing significantly more heat, around 2000 J g−1. When the fuel was aluminum, most of the oxidizers decomposed below 500 °C leaving the aluminum to oxidize at over 800 °C. Only two oxidizers reduced the temperature of the aluminum exotherm—chlorate and potassium nitrite. To go to temperatures above 500 °C, unsealed crucibles were necessary, and with these containers, the endothermic volatilization of reactants and products effectively competed against the exothermic decomposition so that heat release values were artificially low.