Contribution of solid-phase heat release to AP composite-propellant burning rate.

Experimental and analytical approaches were applied to deduce the solid-phase surface temperature of ammonium perchlorate (AP) and to evaluate the effect of AP solid-phase decomposition rate on burning rate. Several batches of AP, of various particle sizes, were modified by irradiation with 9.8 X 10 rad of Co and by thermal shock in liquid N2. Under slow heating rates, both types of modified AP decompose several times faster than conventional AP. However, propellants containing the modified AP burned at the same rate as propellants containing conventional AP. A mathematical model was developed to re-examine Beckstead and Hightower's observations of the crystallographic phase transition from orthorhombic to cubic structure in burning AP. By considering the effects of both conductive heat transfer and subsurface heat release, along with transients after AP extinguishment, a calculated solidphase surface temperature of approximately 442°C was obtained. No change in surface temperature was calculated when upper limit values of subsurface heat-generation rates were considered. Since subsurface heat generation did not affect calculated surface temperature and since AP modified to have higher decomposition rates did not affect propellant burning rate, it is concluded that AP subsurface reactions are not a factor in controlling propellant burning rate at pressures above 500 psi.