Abstract
Exposure of tantalum filaments between 2400 and 2800 K to non-equilibrium partiallydissociated oxygen (1.6 x 10-2 ≦ Po ≦ 2.7 x 10-1 Pa) is shown to increase both the steady-state dissolved oxygen concentrationand the rate of tantalum oxide desorption. Yet thesame quadratic correlation between tantalum oxide loss and dissolved oxygen concentration as observed for diatomic oxygen exposure is found to be preserved under conditions of oxygen atom impingement. This experimental observation is used to demonstrate that Rideal-type (direct atom impact) reaction steps are not responsible for metal oxide formation and desorption in the O(g)/Ta(s) system. Rather, a Langmuir-Hinshelwood (adatom interaction) reaction mechanism, combined with atomic oxygen chemisorption probabilities approximately twice those of incident molecular oxygen, suffice to explain the Ta-oxidation kinetic data reported herein.
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