Condensed-phase processes during combustion of solid gun propellants. I. Nitrate ester propellants

Burning grains of the nitrate ester gun propellants M9, M30, and JA2 were extinguished, and the burned surfaces examined microscopically and by infrared (IR) spectroscopy. Studies were carried out at pressures ranging from atmospheric (0.1 MPa to 2.0 MPa). Scanning electron microscopy examination of quenched samples burned at these low pressures indicates that the surface layers affected by combustion are only a few microns in thickness. Examination by photoacoustic Fourier-transform IR spectroscopy and by microreflectance Fourier-transform IR spectroscopy indicates that the main change in the IR spectra of these extinguished surfaces is the presence of a weak carbonyl absorption peak in the region near 1730 cm(-1); this is consistent with the idea that a principal initial step is condensed-phase conversion of nitrate ester groupings to aldehyde or ketone groupings through loss of NO2 by N-O cleavage followed by loss of a-hydrogen. In agreement with the scanning electron microscopy results, depth-profiling (carried out by surface-abrasion and by cross-section examination) indicates that in these nitrate ester propellants only the top few microns have undergone chemical change. (C) 2001 by The Combustion Institute.