Multifunctional additives for composite solid propellant

Peter Douglas Gilbert, Purdue University

Abstract

The fact that the characteristics of solid composite propellant can be modified through the incorporation of small amounts of additives has been established for some time. Unfortunately, due to the properties of many of these materials, a negative consequence is typically exhibited on a different parameter of the propellant, resulting in the requirement of multiple additives to attain the specifications of the propellant. A relatively new class of ingredients, termed “multifunctional additives”, is gaining attention as potential replacements to traditionally used property modifying materials. This report includes a review of currently available multifunctional additives, specifically those used as ballistic modifiers, as well as an investigation of two new materials in this function. Traditional burning rate modifiers for composite solid propellants typically detract from the overall energetics of a propellant formulation and decrease the specific impulse of the motor to which they are added. Transition metal complexes of the energetic ligand bistetrazolamine (BTA) are evaluated in this report as burning rate modifiers that maintain specific impulse of the non-catalyzed propellant. Iron-BTA, specifically, is investigated as a burning rate modifier and is compared to iron oxide. Additionally, four BTA complexes are assessed as ballistic modifiers with chemical equilibrium calculations to determine their effect on the specific impulse of the propellant. It is found that Fe-BTA would be successful as a multifunctional additive, both increasing the burning rate of AP/HTPB propellant and decreasing the loss in specific impulse relative to iron oxide. The second multifunctional additive evaluated in this report is ammonia borane (AB), a material that has been recently gaining attention due to its high content of hydrogen. AB is examined as both a fuel and performance enhancer, increasing the specific impulse of the propellant it is added to. The design of a propellant is described from the chemical equilibrium calculations to the implementation of a viable propellant and safety testing of the new formulation. In the end, it is determined that AB is not an ideal additive for AP based propellants, nor is it compatible with many popular prepolymer curatives in use today.

Degree

M.S.M.E.

Advisors

Son, Purdue University.

Subject Area

Aerospace engineering|Mechanical engineering

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