Procedures for suppressing premature exothermic decomposition in ammonium perchlorate

In order to enhance extinguishment reliability of controllable solid-propellant motors, an investigation has been made by differential thermal analysis to search for additives or techniques that could eliminate or inhibit the normal first exotherm of propellant grade ammonium perchlorate (AP). The first exotherm was eliminated by controlled heating of the AP for several minutes at 370-390°C. This technique was effective in the presence of fluorocarbon binder or copper catalysts. It was also found that the temperature at which this first AP exotherm occurred could be raised 85°C by adding 1.5% ammonium hexafluorophosphate. The additive was also effective when fluorocarbon binder was in contact with the AP. Although the first AP exotherm was strongly catalyzed by as little as 0.04% of copper nitrate, the catalysis was suppressed by the NKUPFe additive. Independent tests in a combustion-bomb and in a motor have demonstrated the increased extinguishment reliability suggested by the thermal analysis curves of AP containing 1% NH4PF6. The effect on AP decompositian and combustion exotherms has also been tested for a series of additives consisting of ammonium salts, flame retardants, Lewis acids, and transition-metal compounds.