Tuning properties of electrically controlled solid propellants with co-oxidizer formulations

Extinguishment and reignition are important in the development of electrically controlled solid propellants (ECSPs) with on-demand control. An experimental study was carried out to explore the ignition, quenching, reignition, and combustion characteristics of an ECSP based on a co-oxidizer of sodium nitrate and ammonium perchlorate. In total five propellants were studied with varying ratios of sodium nitrate and ammonium perchlorate using polyethylene oxide as the binder. All formulations were solution cast, however, thermogravimetric analysis revealed no detectable residual solvent present in the final compositions, which may be an important factor for improving long term storage and alleviating variations in performance. Ignition delay was characterized over a range of voltages (80 – 200 V), with a blended oxidizer (25/75 sodium nitrate/ammonium perchlorate) formulation demonstrating the fastest ignition. High frequency reignition resulted in faster ignition delays, while very low frequency reignition resulted in longer ignition delays in comparison to the initial ignition delay. The low frequency reignition behavior was likely associated with the formation of inhibiting compounds. Propellant formulations with majority concentrations of sodium nitrate demonstrated pressure deflagration limits greater than a measurable limit of 13.8 MPa. Burning rates were measured as a function of pressure and applied voltage, and a modified Saint-Robert’s burning law was created coupling the combined effects of pressure and voltage over the experimental range. Burning rates increased with increasing ammonium perchlorate concentration.