K. Fushimi et al., Evaluation of heterogeneity in thickness of passive films on pure iron by scanning electrochemical microscopy, ISIJ INT, 39(4), 1999, pp. 346-351
Scanning electrochemical microscopy (SECM) was applied to evaluate the hete
rogeneity of a passive film formed on a pure iron electrode in deaerated pH
8.4 berate solution. A probe current image of SECM was measured with a tip
-generation/substrate-collection (TG/SC) mode in deaerated pH 8.4 berate so
lution containing 0.03 mol dm(-3) Fe(CN)(6)(4-) as a mediator. The differen
ce in thickness of passive films formed on two iron plates at different pot
entials could be evaluated from the probe current image. The probe current
image of the passivated iron surface with distinctive crystal grains was co
mposed of the patch patterns, the shapes of which coincided completely with
the shapes of the substrate crystal grains. The probe current flowed above
the grain surface oriented to {100} plane was less than that above the gra
in surface oriented to {110} or {111} plane. The grain orientation dependen
ce of probe current was ascribed to the difference in thickness of passive
films formed on the crystal grains.