Decomposition and flame structure of hydrazinium nitroformate

Abstract

The decomposition of hydrazinium nitroformate (HNF) was studied in a hot quartz cell and by dropping small amounts of HNF on a hot plate. The species formed during the decomposition were identified by ultraviolet-visible absorption experiments. These experiments reveal that HONO is formed. The HONO formation is followed by formation of NO2. NO is not a first gaseous product. It is only detected if a HNF particle ignites. N2O is observed in the absorption spectrum of HNF decomposition gases. An intermolecular hydrogen atom transform mechanism is proposed to describe the HNF decomposition. This mechanism has similarities with observations in aromatic nitrocompounds. Absorption experiments have been carried out to resolve neat HNF flame structure at sub-atmospheric and elevated pressures (0.03 - 1 MPa). These experiments were carried out in a window bomb with sapphire windows. The obtained absorption spectra were used to determine NO concentration and NO-temperature above the surface. The HNF flame was found to reach temperatures close to adiabatic near the burning surface. These high temperatures were reached with still considerable amounts of NO present (mole fraction >0.1). During the combustion of HNF at low pressures, yellow condensate was found in the window bomb. The absorption spectrum of a solution of this material was found to be similar to that of HNF. This indicates that transition to the gas phase occurs by evaporation or by ejection of small particulates (or a combination of both). A model for the combustion of HNF is presented. This model accounts for the three phases observed during the combustion of HNF (solid, liquid and gas phase). Yetter’s mechanism for nitramine combustion is used for kinetic calculations in the gas phase. The mechanism is extended by the proposed decomposition mechanism. The results of the model calculations are in agreement with experimental observations: NO-decomposition to N2 and O2 was calculated to be very slow. Species profiles obtained from Planar Laser-Induced Fluorescence (PLIF), absorption (CN and NH at 1 atm, and NO and OH at various pressures) and emission spectroscopies (NH2 * and CH* at 1 atm) are compared with the model calculations.