On feasibility of reducing metal fuel content and operating temperatures in chemical oxygen generators.

摘要

Chemical oxygen generators are widely used in aircraft, submarines, spacecraft, and other applications, problems such as combustion instabilities and a risk of fire may be present. For example, due to malfunction of an oxygen generator, fire occurred onboard the Mir Space Station in 1997. It is thus important to improve the process stability and fire safety of chemical oxygen generators. Chemical compositions for oxygen generators include an oxygen source such as sodium chlorate (NaClO3), a transition metal oxide as a catalyst, and a metal fuel to provide energy for self-sustaining combustion. Eliminating or decreasing the metal fuel would decrease the operating temperatures and improve the fire safety of the generators. To make a well-founded conclusion on the feasibility of this approach, information on the decomposition and adiabatic combustion temperatures of NaClO3-based compositions with different concentrations of catalyst and metal fuel is required. In the present thesis, thermogravimetric analysis of NaClO3 mixtures with different concentrations of Co3O4 catalyst and metal fuel (iron and tin) is conducted. For the same mixtures, thermodynamic calculations are carried out. A strong effect of nanoscale Co3O4 powder on the decomposition temperature of NaClO3 is reported. For each mixture, comparison of the measured decomposition temperatures and calculated adiabatic combustion temperatures provides the values of temperature margin available for heat loss in the oxygen generator. Addressing the feasibility of decreasing the decomposition temperature of NaClO3 by high-energy mechanical milling of its mixtures with Co3O4 is studied. In addition, an experimental setup for studies on decomposition/combustion of oxygen-generating compositions under conditions close to those in industrial devices has been designed and tested.