Encapsulated Nitrogen-Rich Energetic Additives in AP/HTPB Propellants

The present study reports, for the first time, the combustion characteristics of an AP/HTPB composite solid propellant containing nitropyrazole-based energetic materials. Three nitropyrazole-based insensitive energetic compounds, namely 4-Hydroxy-3,5-dinitropyrazole (OHDNP), 4-Amino-3,5-dinitropyrazole (LLM-116), and Ammonium 4-amino-3,5-dinitropyrazol-1-ide (ADNP), were used for propellant formulation. A total of three propellants (EAP-1, EAP-2, and EAP-3), containing 77% ammonium perchlorate (AP) as oxidizer and 16% fuel/binder mixture with 4% aluminum and 3% nitropyrazole derivatives as energetic additives, were studied. The propellants were characterized using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The propellants were found to be insensitive to impact and friction during mechanical stability tests. The decomposition kinetics and activation energies of propellants were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). EAP-3 was observed to decompose at 273.2 °C at a linear heating rate of 10 °C/min. The heat of combustion and surface temperature of the propellant were measured to determine combustion behavior. The burning rates of the propellants were determined over a pressure range of 2-7 MPa. EAP-2 exhibited a pressure exponent of 0.39 and a burn rate of 10.8 mm/s at 7 MPa. The Static motor test was conducted for EAP-2 with a steady state chamber pressure of 3.1 MPa, and a thrust of 50.47 N was measured.