Mixtures of ammonium perchlorate particles and polybutadiene binder appear to exhibit preferential accumulation of one or the other component on the pyrolyzing surface over a range of rocket-operating pressures. At low pressures, the surface layer is enriched with the oxidizer, and at high pressures, it is enriched with the binder. The degree of accumulation of the oxidizer is found to be higher for smaller particle size. These experimental data can be explained by the difference in activation energies for pyrolysis of the oxidizer and the binder. The particle size effect is explained by consideration of nearly identical surface temperatures for the oxidizer and binder in mixtures with fine particles, but different temperatures for those with coarse particles. The results obtained are important to the explanation of the mechanism of plateau burning rate exhibited by certain composite propellants.

Satyanarayanan R. Chakravarthy

Department of Aerospace Engineering

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

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IIT Madras

Surface layer dynamics in the pyrolysis of ammonium perchlorate-hydrocarbon binder propellants

Combustion, Explosion and Shock Waves

Nano-aluminium particles of ∼50 nm size, produced at this laboratory, are added to composite solid propellants based on ammonium perchlorate and hydroxyl-terminated poly-butadiene binder that exhibit plateau burning rate trends and those including burning rate catalysts. The nano-aluminized propellant burning rates are compared with corresponding micro-aluminized and non-aluminized ones in the 1-12 MPa pressure range. The mid-pressure extinction of the matrixes containing the fine-sized ammonium perchlorate particles in the propellant along with the binder is investigated in all the cases to understand the mechanism of plateau-burning. Further, the variations in aluminium content, the aluminium size (within nano- and micro-ranges), bimodal combination of nano- and micro-aluminium are considered. Ferric oxide and titanium dioxide are the burning rate catalysts considered. Large scale accumulation of aluminium is observed not only in micro-aluminized matrixes, but also in nano-aluminized ones as clusters of 1-5 μm size. Since aluminium is added at the expense of the coarse ammonium perchlorate particles to preserve the total-solids loading in the present formulations, addition of micro-aluminium decreases the burning rate; whereas, nano-aluminized propellants exhibit ∼80-100% increase in the burning rate under most conditions. The near-complete combustion of nano-aluminium close to the burning surface of the propellant provides heat feedback that controls the burning rate. Mid-pressure extinctions of matrixes and plateau burning rates of propellants are washed out when nano-aluminium is progressively added beyond 50% in bimodal aluminium blends, but low pressure-exponents are observed in the nano-aluminized propellant burning rates at elevated pressures. Adjusting the plasticizer content in the binder alters the pressure range of plateau burning rates in non-aluminized propellants. Catalysts increase the burning rate by ∼50-100% in non-aluminized and micro-aluminized propellants, but in nano-aluminized propellants, the μm-sized catalyst does not affect the burning rate significantly; whereas, the nanometre size catalysts increases the burning rate merely by ∼5-15%. © 2009 The Combustion Institute.

Combustion and Flame

Effect of nano-aluminium in plateau-burning and catalyzed composite solid propellant combustion

33rd Joint Propulsion Conference and Exhibit

Pressure dependence of burning rate of ammonium perchlorate-hydrocarbon binder solid propellants

31st Joint Propulsion Conference and Exhibit

Binder melt flow effects in the combustion of AP-HC composite solid propellants

Nonsteady Burning and Combustion Stability of Solid Propellants

Measuring Thermodynamic Properties of Burning Propellants

22nd Joint Propulsion Conference

Steady state one-dimensional pyrolysis of oxidizer-binder laminates

Geothermal Energy and the Eastern US: Fifth technical information interchange meeting, Minutes

Journal	Combustion, Explosion and Shock Waves
Publisher	Kluwer Academic/Plenum Publishers
ISSN	00105082
Open Access	No