Sensitivity and Stability Improvements of NEPE Propellants by Inclusion of FOX-7

The performances of NEPE (Nitrate Ester Plasticized Polyether) propellants containing 1,1 diamino-2,2-dinitroethylene (FOX-7) were evaluated by means of theoretical calculation, combustion, mechanical and sensitivity experiments. It was found that, by the replacement of Cyclotetramethylene tetranitramine (HMX) with FOX-7 in NEPE propellants, the density (ρ) was maintained to be the same 1.80 g cm⁻³, whereas the combustion temperature (T_c) decreased from 3700 K to 3592 K. The meaN molecular weight of combustion gas (M_c) was slightly increased (from 27.28 to 27.48 g mol⁻¹) and the theoretical specific impulse (I_sp ^o) was decreased from 2615 to 2560 N s kg⁻¹. The content of FOX-7 was in the range of 0 % to 34 % in the formulation of NEPE propellant. It was also shown that the burning rate was increased along with the elevated pressure exponents from 0.44 to 0.48. Moreover, the tensile strength of the propellants at +20 °C and +50 °C was improved from 0.84 and 0.68 MPa to 1.06 MPa and 0.75 MPa, respectively, while the maximum elongation decreased from 64.1∼86.1 % to 32.5∼45.3 %. In terms of safety, the friction sensitivity of the propellant was improved (initiation probability decreases from 100 % to 88 % under pressure of 2.45 MPa) and the impact sensitivity (H₅₀) increased from 6.74 N m to 9.31 N m (2.5 kg hammer).