Detonability of Solid Composite Propellants

Abstract

The thin film platinum resistance thermometer (heat flux gage) has been successfully applied to measurement of heat fluxes from initiators for solid propellants. Heat fluxes measured were as high as 1000 Btu/ft 2 -sec from hot, particleladen reaction products of pyrotechnic igniters. Results of heat flux studies and ignition of propellants by these igniters show good agreement with independent propellant ignition studies in shock tubes and radiation furnaces. Nomenclature H = heat or energy} = time \ T L rrii Dimensions = temperature = length .."» = slope of the ith. straight line segment, T6~l q(t) = heat flux at time t from start of igniter action, HL~26~l t = time from start of igniter action, B = temperature at the terminus of the ^'th straight line segment, T -temperature at zero time, T = thermal responsitivity (square root of the product of Ti To r density, heat capacity, and thermal conductivity) = time at terminus of the ith. straight line segment, 0 = time at the terminus of last straight line segment # (0 n = t), 6 = time variable of integration, 6A theoretical model of propagation of detonation in propellants is presented. This model is based on the hypothesis that detonation is propagated by the same rate controlling chemical reactions that occur during normal burning of the propellant. In particular, it is assumed that a grain burning of the oxidizer occurs and that the rate of linear-surface decomposition (pyrolysis) of the oxidizer can be used to describe the rate of detonation reaction. Kinetic data on the surface decomposition of ammonium perchlorate, which were obtained by the hot plate-linear pyrolysis technique, suggests that sublimation of ammonium perchlorate (with an apparent activation energy of ^22 kcal/mole) is the rate controlling step in the surface decomposition of this oxidizer. A discussion is presented on how these data can be used in conjunction with the detonation model to calculate the minimum (critical) diameters at which detonation can propagate in a cylindrical charge of solid propellant. The possible effect of various propellant parameters, i.e., oxidizer binder ratio, oxidizer particle size, confinement, etc., on the detonation process is discussed. The role of ignition, diffusion and heat conduction processes in the detonation and rapid deflagration of solid composite propellants is discussed. A preliminary theoretical approach to accelerating burning in porous propellant is also presented. This approach indicates that porous burning in rocket motors containing solid composite propellants can lead to very rapid chamber pressure build-up, so that an explosion could occur within several milliseconds after porous burning begins.

The burning mechanism of ammonium perchlorate- based composite solidpropellants

“…Because ;:his gasification process occurs in depth below che surface and because the activation energy for this process is 30 kcal/mole, the apparent activation energy during linear surface pyrolysis (as opposed to bulk degradation) is expected to be about 15 kcal/mole*. Thus, the approximate value of 20 kcal/mole obtained by several linear pyrolysis studies (38)(39)(40)(41), is in good agreement with bulk degradation data. (See also the review of these data by Refs.…”

“…Neither infrared(25) nor mass spectroscopic (26) investigations could reveal the presence of the NH4CI04 molecule in the gas phase. Thus, as is generally agreed (22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(38)(39)(40)(41)(42)(43)(44)(45), AP degradation involves as a first step dissociative sublimation of a loosely held NH 3 :HCI0 4 complex, physically adsorbed at the decomposing AP surface. Further chemical reaction between the resulting gaseous NH 3 and HCI0 4 is then possible depending on the prevailing physical conditions.…”

The Role of Binder in Composite Propellant Combustion

“…The rate-controlling process of the gas phase reaction between the NH_ and HNO evolved from the oxidizer was assumed to be N0 2 --> NH 2 + HN0 2 (9) with the NOp arising from the relatively rapid decomposition of the HNO .…”

“…Particular emphasis will be placed on discussing the influence of conventional oxygen lean binders on the burning rate-pressure dependence in terms of the recent "Two-Temperature" (5) postulate the the "Thermal Layer" (6) theory of combustion. Examples of such linear surface pyrolysis rates are shown in Figure 1 which is compiled from reported data (5,8,9). Numbers in parentheses indicate References at end of paper.…”

A. An Analytical and Experimental Study of the Erosive Burning of Composite Propellants. B. Modeling of Single Particle Aluminum Combustion

“…and E »were chosen as 16,900 cal/mole and 22,000 cal/mole, respectively, tuei ox f36^ the former value based on data of Cohen, Fleming, and Derr and the (35) latter based on data of Andersen and Chalken.…”