Nitrogen Tetroxide Corrosion Products

Study of the phenomenon of flow decay, begun on earlier programs, was continued with a change to MSC PPD-2A propellant N2O4 0.6 percent NO. Flow decay occurs with this propellant, even when dry less than 0.1-percent water equivalent, as a result of deposits of the solid corrosion product, NOFeNO34. It was found that the presence of excess water in amounts up to the general use limit of 0.2 percent changed the characteristics of the deposits formed when nitrogen tetroxide is heated, then cooled prior to or during flow. Instead of the crystalline solid NOFeNO34 which is deposited from dry propellant, gelatinous or viscous liquid phases are formed in wet propellant. The appearance of these deposits is governed by an equilibrium solubility limit similar to that observed for the solid deposits in dry propellant. The gelatinous or viscous liquid deposits were not observed to adhere to and plug valves and orifices, as does NOFeNO34, but they did clog filters. Chemical additives previously shown to be effective in dissolving and eliminating NOFeNO34 were not effective against the deposits obtained from wet propellant. Traces of aluminum and titanium were detected in flow decay deposits obtained from flow systems with aluminum and titanium tanks.