Kinetics of zirconium oxidation by atomic and molecular oxygen at low pressures

The kinetics of zirconium oxidation have been studied in atomic and molecular oxygen at incident fluxes of 10(16)-10(17) particles cm(-2) s(-1) (which corresponds to pressures of 10(-2)-10(-1) Pa) i.e. under conditions simulating those of low Earth orbits. The experiments were carried out in the temperature range 873-1123 K. Kinetic data have been obtained for the initial stage of the process when oxygen reacts with metal in the absence of the oxide phase on the surface. Linear oxidation is observed at this stage. A linear dependence of oxidation rate on the oxygen incident flux (and, consequently, pressure) has been found. Strong enhancement of oxidation in atomic oxygen has been found (by one to two orders of magnitude) over the entire investigated temperature range. A substantial effect of diluent gases (argon, nitrogen, helium) on the rate of zirconium interaction with oxygen has been observed.