Effect of fluorinated graphite on combustion of boron and boron-based fuel-rich propellants

Abstract

The effects of fluorinated graphite (CF^) with different fluorine contents (x = 0.08, 0.25, and 1.17) on the combustion of boron powder (B) and boron-based fuel-rich propellants were experimentally investigated. The propellants contain ammonium perchlorate (AP) (28%), magnalium alloy (8%), hydroxy-terminated polybutadiene (HTPB) (27%), and boron agglomerates (37%, in 300-, 600-, 850-, and 1180-/urn sizes), with immediate contact between CFA and amorphous boron (1:14 and 1:7 in mass ratio) by means of a small amount of polymethyl methacrylate binder. The reactions between boron and CF,,. were investigated by adiabatic calorimetry under oxygen, and thermogravimetry under argon, using different E/C¥X mixtures. The baselines of boron and different CFX were studied separately. Because of liberation of highly reactive products such as unsaturated fluorocarbon and fluorine from CFV decomposition, more heat is evolved due to boron reaction compared to the boron baseline without CFV. Possible exothermic reactions involved in the system containing C, B, O, and F quadruple elements were proposed. Propellants containing CF^ were found to increase the burning rate and/or pressure exponent compared to baseline propellants without CFX. An interpretation based on the intensive reactions among the decomposition products from CF,, AP, HTPB, etc., was proposed. Boron agglomerate size can affect the burning rate because of the mixed effects of boron as a heat sink, condensed phase reactions, and flame structures at different pressures.