M. Asanuma et R. Aogaki, NONEQUILIBRIUM FLUCTUATION THEORY ON PITTING DISSOLUTION .1. DERIVATION OF DISSOLUTION CURRENT EQUATIONS, The Journal of chemical physics, 106(23), 1997, pp. 9930-9937
Following the foregoing papers, in this paper, mathematical procedures
to describe the time development of tile unstable nonequilibrium fluc
tuations in pitting dissolution are presented: First, general equation
s depicting the time development of the amplitudes of the fluctuations
are deduced, which are the same as those describing nucleation phenom
ena. Then, with the same definition as nucleation, the average values
of the fluctuations are decided, and measurable pitting current is cal
culated. Actually, some analytical equations are derived for some char
acteristic parts of the current-time transient. As a result, after app
lying a constant potential step to the electrode, a slow relaxation cu
rrent, which follows a double-layer charging current, is decided as th
e diffusion current of the fluctuations. This current gives the values
of passive film coverage and average critical concentration fluctuati
on on the completely active surface. Moreover, from the minimum curren
t attained by the diffusion current, the ratio of the average critical
concentration fluctuation to the autocorrelation distance is determin
ed. Finally, resultant pitting growth current arising from the unstabl
e growth of the fluctuations is deduced as a function of supporting-el
ectrolyte concentration and overpotential, which is attributed to the
fact that the instability occurs from the electrostatic interaction of
the solution particles in the double layer. (C) 1997 American Institu
te of Physics.