: The literature describing the mechanism of combustion in composite rocket propellants exhibiting hi-plateau burning has been reviewed. A wide distribution of AP particle size in a definite coarse/fine ratio is required to ensure adequate interstitial spacing resulting in abnormally depressed burning due to interference of the fine AP fraction combustion by the binder melt layer. Titanium dioxide added to the formulation acts to increase the binder melt layer viscosity restoring normal burning at low and high pressures, leaving abnormal burning and a plateau or mesa effect at intermediate pressures. The use of dimeryl-diisocyanate curative produces a unique plateau at lower pressures due to increased binder liquefaction. Formulation variables can be adjusted to tailor the pressure levels and burn rates of the plateaus formed.

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Composite Propellants with Bi-Plateau Burning Behaviour

Solid Propellant Combustion: Surface Disproportionation

: This document is the final report of the Caltech Multidisciplinary University Research Initiative (MURI), Investigations of Novel Energetic Materials to Stabilize Rocket Motors, ONR Contract No. N00014-95-1-1338. With a one-year no-cost extension, the program covered the period 1 October 1995 to 30 September 2001 and involved Principal Investigators at nine Universities. In addition, for three years, funds from another source supported research by seven Russian research groups. Participants in the Caltech MURI provided technical oversight of that work. A second MURI devoted to the same general subject was carried out at the University of Illinois at Urbana- Champaign (UIUC). The two programs were largely complementary. Some of the sections in this report have been co-authored by representatives of both MURIs. Similarly, the final report of the UIUC MURI will contain some duplication of material covered in this document. The Caltech MURI was a multidisciplinary program devoted to research on fundamental problems of the chemistry, combustion and gas dynamics of novel energetic propellants and their unsteady behavior in rocket motors. This program achieved significant progress towards the ultimate overall objective of research in this field, to identify and quantify the influences of propellant composition on the stability of motions in a solid propellant rocket motor. To attain that objective it is essential to support cross-disciplinary effort between propellant chemists and researchers; combustion researchers; and researchers concentrating on the dynamics of solid rocket combustors. This MURI program was the first sustained effort to accomplish the necessary collaborations among faculty and students in universities, with participation by representatives of government laboratories and industry; in the many respects described in this report the program has been highly successful.

Investigations of Novel Energetic Materials to Stabilize Rocket Motors

Specially formulated ammonium perchlorate HTPB propellants exhibit plateau behavior in their burning rates as pressure is increased. Several things affect the prominence of these plateaus, including binder curative, AP particle ratio, and presence of a ballistic modifier additive. The effect of pressure on the nature of extinguished propellant surfaces obtained is shown in scanning electron microscope micrographs. Using an SEM, it is possible to determine surface structures and compositions for comparison with propellant burning rate behavior. Four propellant formulations were tested over a range of pressure that bracketed the plateaus. The formulations varied in AP particle ratio, binder curative type, and the presence'of an additive.- The SEM analysis was able to correlate the burning rate behavior in terms of the appearance of the coarse AP particles relative to the surrounding matrix of fine AP and binder. Plateaus result from temporary degrees of suppressed burning of the fine AP component, due to binder melt layer interference.

D. Boxx

Papers

SEM Analysis of Extinguished Propellant Surfaces