IN CON-ON
with the note by Sato ,l I regret that my paper2 contains the erroneous conclusion that the temperature coefficient of the constant k, = (aq/aQ), (derived from the expressions of Sato and Coher? on the basis of the "place-exchange" mechanism of oxide-Mm growth) is zero.
I cannot agree however with the first sentence in the note,l which suggests that my conclusions on the mechanism of anodic am growth on iron in neutral solutions are altogether erroneous. My first paper on this subject? provided quantitative experimental data from galvanostatic and potentiostatic measurements in favour of the classical "field-assisted ion transport" mechanism developed by Verwep and Cabrera and Mott.6 Semi-quantitative data for the inverse logarithmic law were presented also by Kruger and Calvert' and their work is cited in my paper.4 Later, reviewing his older data with Cohen ,s Sate* concluded that his potentiostatic data can be represented not only by the direct logarithmic law but also by the inverse logarithmic law.
It is evident that the temperature dependence of kf cannot serve as a mechanistic criterion inasmuch as both laws predict a negative temperature coefficient, 7 = ( 8kij i3 7+) -=c 0.t The field dependence of T, (%/a log i), is however positive according to the classical model (equation ( 8) in my papera) and zero according to the "rotation" model (equation (3) in Sato's notel). My data2 make it possible to estimate that (%/a log i) = O-12 V.cm21C.deg. or cu 12 y0 per decade. This value exceeds by several times the experimental error and is further evidence in favour of the classical model of the film growth.
An error has crept into the last sentence of the Note, which should read " . . . the place-exchange mechanism is consistent not only with . . . " instead of " . . . inconsistent not only . . . "$ * Manuscript received 2 August 1971. t The negative sign of ( ak,j aT), in the note1 was omitted. The experimental resulta is (ak,/ XT') = -1.36 V.cm*/C.deg. $ We greatly regret this error in linguistic editing. This interesting polemic must now close: Ed.