Reduced Agglomeration of Aluminum in Wide-Distribution Composite Propellants

Aluminum behavior (accumulation, agglomeration and ignition) is studied in a unique, wide-distribution, ammonium perchlorate/hydroxyl-terminated polybutadiene propellant formulation that results in low Al agglomeration, even at low pressures (1-30 atm). A fuel-rich, physically oxygenated binder matrix highly loaded with very fine ammonium perchlorate at a high fine ammonium perchlorate/binder ratio is found to have premixed flame conditions that produce minimal agglomeration (without ignition) of Al. Coarse ammonium perchlorate is added to the system in the form of either particles or pressed-ammonium perchlorate laminates (simulated coarse ammonium perchlorate). Both laminate and particulate systems show that with coarse ammonium perchlorate present, Al can agglomerate on coarse ammonium perchlorate via lateral surface migration from fuel matrix to the coarse ammonium perchlorate region. The particulate coarse ammonium perchlorate system also shows that Al can accumulate/agglomerate via settling on coarse ammonium perchlorate from above (in the direction of burning). Both systems show that with coarse ammonium perchlorate present, Al is ignited by the outer coarse ammonium perchlorate/fuel matrix canopy flames, which the laminates clearly show to be either split-diffusion or merged-partially-premixed, depending on pressure and diffusion length scale (fuel layer thickness). Thus a propellant formulation is proposed for reducing overall Al agglomeration through intrinsically reduced agglomeration in the fuel matrix and a reduced number of coarse ammonium perchlorate-particle agglomerates via higher fine ammonium perchlorate/coarse ammonium perchlorate ratio. [PUBLISHER ABSTRACT]