Development of a dual-spectroscopic system to rapidly measure diisopropyl methyl phosphonate (DIMP) decomposition and temperature in a reactive powder environment

Abstract

The development of systems to measure and optimize emerging energetic material performance is critical for Chemical Warfare Agent (CWA) defeat. In order to assess composite metal powder efficacy on CWA simulant defeat, this study documents a combination of two spectroscopic systems designed to monitor the decomposition of a CWA simulant and temperature rises due to combusting metal powders simultaneously. The first system is a custom benchtop Polygonal Rotating Mirror Infrared Spectrometer (PRiMIRS) incorporating a fully customizable sample cell to observe the decomposition of Diisopropyl Methyl Phosphonate (DIMP) as it interacts with combusting composite metal particles. The second is a tunable diode laser absorption spectroscopy (TDLAS) used to monitor increases in background gas temperatures as the composite metal powders combust. The PRiMIRS system demonstrates a very high signal to noise ratio (SNR) at slow timescales (Hz), reasonable SNR when operating at faster timescales (100 Hz), and capabilities of resolving spectral features with a FWHM resolution of 15 cm−1. TDLAS was able to monitor temperature rises between room temperature and 230 ± 5 °C while operating at 100 Hz. For testing, liquid DIMP was inserted in a preheated stainless steel (SS) cell to generate DIMP vapor and (Al–8Mg):Zr metal powders were ignited in a SS mount with a resistively heated nichrome wire at one end of the cell. The ignited particles propagated across the cell containing DIMP vapor. The path averaged gas temperature in the preheated SS cell rises rapidly (100 ms) and decays slowly (<5 s) but remains below 230 °C during particle combustion, a temperature at which the thermal decomposition of DIMP is not observed over similarly short timescales (seconds). However, when combusting particles were introduced to the DIMP vapor (heterogeneous environment), spectral signatures indicative of decomposition product formation, such as isopropyl-methyl phosphonate (IMP) and isopropyl alcohol, were observed within seconds.