Effects of Innovative Insensitive Energetic Materials: 1,1-Diamino-2,2-Dinitroethylene (FOX-7) on the Performance of Solid Rocket Propellants

Abstract

The microstructure physico-chemical properties of 1,1-diamino-2,2-dinitroethylene (FOX-7) and the probable formation of FOX-7/CL-20 and FOX-7/HMX co-crystals were analyzed by scanning electron microscopy (SEM) and molecular dynamics (MD) simulation, respectively. Several industrial- and research-type of hydroxyl-terminated polybutadiene (HTPB), nitrate ester plasticized polyether (NEPE) solid propellants and composite modified double-base (CMDB) propellants containing different mass fraction of FOX-7 with the same nominal composition were prepared and experimentally analyzed. The effects of FOX-7 on the combustion properties (strand burning rate and pressure exponent) and hazardous properties as well as the associated thermal decomposition were investigated, and compared with those of the propellant without FOX-7. The results indicate that the energetic properties (theoretical specific impulse and density) of NEPE and CMDB solid propellants decrease with an increase in mass fraction of FOX-7 in the formulations with a partial replacement of HMX or RDX by FOX-7, while their mechanical sensitivities decrease significantly. The friction sensitivity and impact sensitivity of NEPE propellant decrease from 100% to 88% and from 27.5 cm to 38.0 cm, respectively. The burning rate and pressure exponent of NEPE solid propellant increase with a partial replacement of HMX by FOX-7 in the formulation; the burning rates of the CMDB propellants as well increase with increasing mass fraction of FOX-7 in the formulations, while the pressure exponent of CMDB propellant decreases from 0.88 to 0.75 in the pressure range of 2–22 MPa when 20% of RDX is replaced by FOX-7 in the formulation. The maximum tensile strength of NEPE solid propellant increases from 0.84 MPa to 1.06 MPa at +20 °C and from 0.68 MPa to 0.75 MPa at +50 °C, respectively, while the elongation of propellant decreases from 83.2% to 33.9% and from 86.1% to 32.5%, respectively. The maximum tensile strength and elongation of CMDB propellants containing FOX-7 are higher than those of propellant without FOX-7 at 20 °C. When RDX is substituted completely by FOX-7, σm is increased by 2.32% and em is increased by 12.73%.