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Polycrystalline silicon wafers coated with Na2CO3 were oxidized in ambient air with P(H2O) = 24 mm in the temperature range 702 to 1052C. Initial oxidation followed cubic kinetics due to the linear change in composition of the oxide film with oxidation. At longer times the oxidation became parabolic as the concentration of and, therefore, diffusivity of hydroxyl in the oxide became nonlinear with the sodium concentration in the film. This occurs at lower concentration of sodium, where the presence of sodium is manifested in the formation of hydroxyl by an autocatalytic reaction. Untreated specimens oxidized as controls during these experiments showed similar behavior due to vapor phase transport of Na2O. (Author)