Investigating the evolution of the optical emission spectra of HMX with reaction regime

The visible wavelength spectrum of HMX was studied during the different reactions rates associated with burning, deflagration and detonation. For burning, the material was ignited by a butane flame in air at atmospheric pressure leading to millisecond burn times. A modified BAM impact test was used for deflagration, resulting in a 20 µs impact- initiated partially confined reaction. Detonation was achieved in a column of HMX pressed to a density of 84 ± 2 % TMD; PDV measurements allowed the CJ-pressure to be calculated at 24.0 ± 0.5 GPa, and the reaction front velocity was measured at 7.8 ± 0.3 kms⁻¹. When burning spectral emission was found to originate mainly from alkali metal impurities, with the 589 nm sodium peak dominating the spectrum. With the higher reaction temperatures and pressures of deflagration, the redshift and broadening of the Na spectral peak were measured, along with the continuous competing greybody emission. From greybody portions of the spectra, temperatures of 4000 K in deflagration and 7000 K in detonation were calculated. The temperature increase is likely caused by the higher pressure shock of the detonation front compressing air filled interstitial pores in the material, leading to multiple localization mechanisms that drive a greater temperature than that achievable by chemical reaction alone.