Ignition, combustion, and agglomeration of encapsulated aluminum particles in a composite solid propellant. I. Theoretical study of the ignition and combustion of aluminum with fluorine-containing coatings

Abstract

This paper gives a brief review of methods for modifying metallic fuels for composite solid propellants, including the application of coatings onto aluminum particles (encapsulation). Requirements for the coating material are formulated. By means of thermodynamic calculations, it is shown that some fluorine-containing coatings reduce the content of the condensed phase in the propellant combustion products without decreasing the specific impulse. A mathematical model for the ignition of a single encapsulated particle is proposed. Calculations show a decrease in the ignition time of an aluminum particle with a fluorine-containing coating.

Ignition, combustion, and agglomeration of encapsulated aluminum particles in a composite solid propellant. II. Experimental studies of agglomeration

“…Both factors facilitate the ignition of the particles, resulting in an increase in the burning rate of the particle-air suspensions. Mathematical modeling of the ignition of an aluminum particle with a fluorine-containing coating was performed in [1].…”

“…Although the idea of influencing the agglomeration process by applying special coatings on particles is not new, there have been a few studies in this direction (see the references in [1]). The goal of the present work was to perform an experimental study of the combustion of model solid propellants containing aluminum powders with fluorine-containing coatings.…”

“…In this respect, methods based on physical or chemical modifications of the metal are promising. A brief review of existing methods is given in [1]. When using a metal powder in a propellant, it is necessary that the modification do not have a significant effect on the powder particle size distribution and do not deteriorate the energy characteristics of the propellant.…”

“…In [1], we performed thermodynamic calculations of the equilibrium composition of the combustion products of a conditional aluminized propellant containing a small amount (not more than 5% of the mass of aluminum) fluorine-containing materials used to produce polymer coatings on aluminum particles. The calculations show that the presence of these materials not only does not reduce the energy characteristics of the propellant but in some cases results in a certain increase in the vacuum void impulse and in a reduction in the content of the condensed phase in the combustion products.…”

“…Then, the effect of the coatings on agglomeration can be related to their heat resistance: for coatings with higher heat resistance, the metal is less oxidized, the strength of the holding bond is lower, and the agglomerate size is smaller. As is assumed in [1], in the initial stage of aluminum particle ignition, the coating prevents oxidation, i.e., the growth of the oxide layer. The oxidation starts after the decomposition (disappearance) of the coating; at this time, on the particle there is only a thin initial oxide layer.…”