Decomposition of hydroxylammonium nitrate in a low pressure flowing thermal capillary system

• Published in: Journal of molecular liquids 2018-07, Vol.262, p.396-404
• Main Authors: Kidd, Forrest G., Taylor, Nicholas R., Lemmer, Kristina M.
• Format: Article
• Language: English
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2018.04.065

Hydroxylammonium nitrate (HAN) is a potential monopropellant for plasma-based electric propulsion thrusters. However, little is known about the thermal decomposition of HAN at pressures typically encountered in aerospace applications. In this study, using residual gas analysis (RGA) we examine the production of nitrous oxide (N2O), nitrosamide (H2N2O), and nitroxyl (HNO) by thermally decomposing HAN exposed to pressures between 2 and 50 mTorr. Initial expectation was that NO and NO2 would be the primary species producing signal at 30 and 46 m/z respectively. Kinetic modeling studies of HAN solution, however, attributed these signals to HNO and H2N2O, respectively. Thermal decomposition was achieved by passively injecting an aqueous HAN solution into a flowing thermal capillary and detecting the gas products with mass spectrometry. N2O and H2N2O produced relatively small signal with a minor pressure dependence at low temperatures and no pressure dependence above ~460 K. HNO produced a much larger signal relative to N2O and H2N2O and exhibited a high level of pressure dependence as temperature increased above the onset of thermal decomposition, ~393 K. These results indicate that the formation of N2O, H2N2O, and HNO is occurring not only in the bulk solution but possibly on the surface of the aqueous HAN solution and in the vapor phase immediately above the solution surface. The kinetics and mechanism of possible decomposition pathways to form these species are discussed. [Display omitted] •Mechanism for decomposition of Hydroxylammonium Nitrate is investigated.•Pressure and temperature dependence examined using residual gas analysis.•Experiments at low pressure resulted in novel products (H2NNO, HNO).