THERMOMECHANICAL COMBUSTION ENHANCER AND THE EFFECT OF COMBUSTION CATALYSIS ON THE BURN RATE AND INFRARED RADIATION OF MAGNESIUM-FLUOROCARBON-VITON PYROLANTS

A novel mechanism for combustion acceleration of pyrotechnics and solid propellants is introduced. The effect is based on mechanical action at the combusting surface leading to an increased effective surface area. The mass conversion rate increases, although the microscopic level burn rate (BR) is unaffected. Approximately a 70% and 80% acceleration of the burn rate from 3.6 to 6.1 mm/s and from 2.6 to 4.7 mm/s were observed, respectively, when 1% of expandable graphite (ExG) was mixed into an Magnesium-Teflon®-Viton® (MTV) and Magnesium-Graphite fluoride-Viton (MGV) containing 15% binder and consolidated to 95% of theoretical maximum density (TMD). A fourfold increase of the effective burn rate from 28 to 109 mm/s was achieved at a 85% consolidation at normal pressure with compositions containing 5% binder, a chemical catalyst, carbon fibers, a higher porosity, and a larger percentage of expandable graphite. Presumably, intumescent materials can accelerate any solid phases energetic material combustion, provided the surface temperature exceeds the expansion onset temperature of the intumescent material. The effect of thermomechanical and chemical combustion acceleration on the infrared (IR) band radiation energy of MTV is investigated. Expandable graphite enhances the IR performance of MTV even beyond that of graphite fluoride (GF) based compositions while chemical catalysis reduces the IR energy in most cases. Only soot combustion catalysts slightly increase the radiated energy compared to baseline MTV. The accelerating effect of expandable graphite can be addressed to mechanical action, thermal conduction, enhanced radiative feedback while its decelerating effect is caused by increased absorption and shielding of radiation.