Combustion/Decomposition Behavior of HAN Under the Effects of Nanoporous Activated Carbon

Abstract

This work presents experimental results on thermal decomposition and combustion of hydroxylammonium nitrate (HAN)-based propellant (HAN—95 wt% water solution) in the presence of nanoporous activated carbon with a high specific surface area (SSA) up to 3000 m2/g. The activated carbon AC was obtained by primary carbonization of rice husk (RH) and subsequent activation of carbonized rice husk (CRH) with potassium hydroxide at the temperature of 700 °C in a rotating spherical furnace. Combustion of HAN in the presence of activated carbon (AC) was investigated in a constant-pressure bomb within the initial pressure range of 1–6 MPa. The linear burning rate (rb) increased for the system of HAN admixed with AC compared to those of the HAN alone. The rb of HAN with AC was equal to 400 mm s−1 at an initial pressure of 6 MPa. It was shown that nonporous AC is a good candidate as an additive for increasing the productivity (high burning rate, high gas exhaust, low initial pressure value for combustion propagation, and low commercial cost of the additive) of HAN-based propellants. Thermal decomposition of HAN-based propellant admixed with AC was assessed by DTA–TG method. Addition of AC reduces the temperature of the onset of HAN decomposition from 185 to 86 ± 0.5 °C. The obtained results allow to assume that addition of just 1% AC affects both the temperature of the onset of complete decomposition and maximum temperature of HAN decomposition. The increase in AC concentration up to 10% leads to a significant decrease in the temperature of HAN complete decomposition. The volatile products emitted during thermal decomposition of HAN doped with AC were characterized by electron ionization mass spectrometry analysis. The primary products of HAN decomposition at different heating rates (m/z = 33 (NH2OH), m/z = 63 (HNO3), etc.) were determined. Significant reduction of NOx emissions during thermal decomposition of HAN was observed. It is shown that addition of AC reduces the amount of NOx gases up to 30%.