Abstract
The spectrum, 8000-2700A, emitted during the combustion of pellets of the pyrotechnic illumination compositions Mg/M(NO3)2, where M = Ca, Sr, Ba, was studied, qualitatively as a function of ambient pressure and of height in the flame. High speed (4700pps) films of some flames were also made. In the spectrum from the base of flames at higher ambient pressures, spectral lines and bands of wavelength longer than 4000A were in emission, superimposed on a continuum; below 4000A, discrete spectral features occurred only in absorption against the flame, continuum. This phenomenon is readily explained by the wavelength dependence of the emissivity of the condensed oxide particles which emitted the continuum. The particle temperature may have been higher than the flame gas temperature. The combustion of Mg/PTFE pellets, containing 30 to 60 per cent weight fuel, was also investigated. The flames from, these pellets showed a clearly defined reaction-zone which was characterised, at low ambient pressures, by emission of the Swan C2 bands. At 20 torr the flame was separated from the pellet and the pellet's surface was covered with pinheads of light. The shape of the burning-time/ambient pressure curve (760-20 torr) for Mg/PTFE pellets depended on the formulation, the PTFE particle size and, at the lowest ambient pressures, on the ambient atmosphere. For most compositions, an intermediate region was found in which, the burning-time decreased with decreasing pressure. The extent of the overall Mg/PTFE combustion reaction decreased with pressure below 100 torr. These observations are consistent, with the postulate that surface fluoridation of metal particles occurred on the surface of burning Mg/PTFE pellets and that this reaction, which is assumed to have a slow initial step, controlled the burning-rate at pressures less than 100 torr.