Thermal decomposition of HAN-based liquid propellants

Measurements were made by FTIR spectroscopy to identify the thermal decomposition products of HAN, solid TEAN, and XM46 at atmospheric pressure in a nitrogen environment. The major detected decomposition species of HAN-water solutions were H2O, N2O, NO, NO2, and HNO3. The decomposition process was characterized by the following events: 1) an induction period followed by H2O evaporation, 2) the rapid evolution of N2O, NO, and HNO3, which supported a fast Occurrence of proton transfer, and 3) the formation of NO., most likely from HNO3, in the later stage of the decomposition. Solid HAN had the same decomposition products that were identified in aqueous HAN. However, the induction times of solid HAN were longer than those of HAN-water solutions at low initial set temperatures, perhaps because of a strong ion association. Solid TEAN produced IR-active decomposition species including H2O, NO, CO2, CO, N2O, and NO2. In XM46, a sequential decomposition of HAN and TEAN was revealed. Evaporation of H2O was followed by HAN dominated decomposition, producing N2O, NO, and HNO3. In the later stage, TEAN reactions became dominant to form CO2 and additional NO. Because of the interaction between HAN and TEAN in XM46, the evolution rate of the species that were related to HAN decomposition decreased compared with that of 9 M HAN, although the HAN concentration in XM46 is nearly 9 M. Because the induction times of XM46 were similar to those of 9 M HAN, it was conjectured that the initial detection of species in XM46 was governed mainly by the HAN decomposition, which occurred in the early stage of the XM46 decomposition. (C) 2001 by The Combustion Institute.