Condensed-phase processes during combustion of solid gun propellants. II. Nitramine composite propellants

Burning samples of nitramine composite solid gun propellants were quenched, and the burned surfaces examined microscopically and by chemical analysis. Studies were carried out on XM39 and M43 propellants, on an HMX-polyester composition (HMX2) and on pure RDX, at pressures ranging from atmospheric ( 0.1 MPa to 2.0 MPa). Scanning electron microscopy examination of quenched s amples burned at these low pressures indicates that a liquefied layer 100 t o 300 mu thick forms during combustion of these nitramine compositions. Bub bles are present, especially at the lower pressures, Gas chromatography mas s spectrometry analysis suggests that in the case of XM39, ethyl centralite stabilizer is depleted in the surface layers relative to the plasticizer a cetyl triethyl citrate. High-performance liquid chromatography studies indi cate that for XM39 (and presumably for M43), HMX2, and RDX, the surface lay ers exhibit formation of the mechanistically significant nitrosoamines MRDX (also known as ONDNTA) and DRDX Examination of the burned surfaces of XM39 and of HMX2 by photoacoustic Fourier-transform infrared spectroscopy and b y microreflectance Fourier-transform infrared spectroscopy indicates the pr esence of increased amounts of binder and its decomposition products. Exami nation of the burned surface of RDX by photoacoustic Fourier-transform infr ared indicates the presence of RDX decomposition products. These observatio ns suggest the occurrence of a significant amount of condensed-phase decomp osition. Depth profiling, by surface-abrasion and by cross-section examinat ion, indicates that in the nitramine propellants the molten oxidizer laver is overlain by a layer (similar to 20 mu thick) of binder and its decomposi tion products. The roles of vaporization and of thermal decomposition in th e liquid layers of the nitramine propellants are also discussed; it appears that both play significant roles. (C) 2001 by The Combustion Institute.