SBIR-STTR Award

Propellant formulations require that very high concentrations of oxidizer be used to obtain increased performance. Unfortunately, the greater the content of solids in the formulation, the more difficult the propellant mixing and casting becomes. Conventionally, hydrocarbon solvents are added to reduce the mix viscosity and facilitate mixing. The solvents are removed with heat and vacuum prior to casting. The addition of heat accelerates the curing of the propellant, thereby reducing the pot-life of the mix. Using supercritical fluids in place of the organic solvents improves processing. No heat or vacuum is required to remove the critical gas at the termination of mixing, therefore, allowing the pot-life to be increased. Anticipated benefits/potential commercial applications - higher performance propellants are possible due to increased solids loadings. Repeatability and batch-to-batch mixing will be improved because mixing can be performed in the presence of a larger amount of diluent. Applications could be extended to cast explosives, ceramics and composite manufacturing.Key words: supercritical fluids, mixing, propellant, high solids, reduced viscosity

This Phase II effort is directed at applying critical carbon dioxide as a processing diluent for the manufacture of high total solid rocket propellants. The Phase I effort demonstrated that a ninety percent total solids inert composite propellant could be mixed at thirty-five degrees celsius in one hour mixing time. The simulated propellant was formulated with various mixtures of thirty and two hundred micron sodium chloride as the inert replacement for the energetic ammonium perchlorate oxidizer. This program will utilize critical fluid processing to prepare energetic, high total solids propellants and demonstrate the feasibility of the process with small motor ballistic performance tests. Three types of propellant formulations will be utilized in this program; a baseline, industry standard, composite propellant; and energetic minimum signature propellant; and a conventionally difficult to process tepanol, ammonium perchlorate propellant. The key objective of this program is to determine if the critical fluid processing technique can be used to process formulations with oxidizer particle size distributions of less than two microns. Previous hazards testing studies have shown that propellants with oxidizer particle sizes of two microns or less show a substantial decrease in overall hazards sensitivity class from class 1.1 to class 1.3 successful critical fluid processing of small particle oxidizer propellants is expected to lead to high energy class 1.3 formulations. Costs savings are also expected to be realized from the reduced processing times and extended pot-life obtained from the low temperature critical fluid process. Anticipated benefits/potential commercial applications - one benefit anticipated from this research is the ability to mix high and very high total solids propellants which have much reduced sensitivities. Higher energy propellants would allow larger pay loads or increased range for solid motors with little or no increase in motor dimensions.

Keywords:
Supercritical, Carbon Dioxide, Propellant, Insensitive, Diluent