This study was conducted to investigate the time
dependence of the critical current density for anodic
protection . The systems studied were AISI 1 0 18 carbon
steel in 67 percent and 93 percent H2so4 , and Type 3 16
s/s in 67 percent H2so4.

Potentiodynamic polarization was used to obtain
data for both systems. Plots of the logarithm of the
critical current density (icrit) versus the logarithm of
the time to passivate were made. From these plots the
current - time relations for the systems were obtained .
The equations describing the data for carbon steel in 67
percent and 93 percent H2 so4 were substantially different;
this indicates that the passive film on carbon steel in
67 percent H2so4 is electrically different from the film
formed in the 93 percent acid. On the other hand, the
equations for the carbon and stainless steel in 67 percent
H2so4 were very similar; this implies that both films have
similar electrical properties in this acid.
For the stainless and carbon steels in 67 percent
H2so4 , the critical current density changed slightly com pared
to more pronounced changes in the time to passivate.
For the carbon steel in the 93 percent acid , more propor tional
changes were observed for the current density with
respect to time.

Galvanostatic passivation was also used in this study
in order to predict the effects of anode surface area on
the critical current density and its time dependence. The
results indicate that there is no relation whatsoever between
the anode surface area and the critical current density;
instead, it is the polarization technique used that
affects the results obtained. The equation describing the
galvanostatic (constant current) data resembled the equations
obtained with the potentiodynarnic technique. However,
lower current densities were observed with the former.