S. Haupt et Hh. Strehblow, A COMBINED SURFACE ANALYTICAL AND ELECTROCHEMICAL STUDY OF THE FORMATION OF PASSIVE LAYERS ON FE CR ALLOYS IN 0.5 M H2SO4/, Corrosion science, 37(1), 1995, pp. 43-54
The passivity of Fe-Cr alloys has been examined in 0.5 M H2SO4 and the
results have been compared to those in 1 M NaOH. XPS and ISS examinat
ions were performed in close relation to electrochemical studies. The
specimens were transferred from the electrolyte to the ultra-high vacu
um chamber for surface analysis within a closed system to avoid contam
ination and oxidation of the metal surface during exposure to the labo
ratory atmosphere. The specimen pretreatment has a pronounced influenc
e on the composition of the metal surface and the composition of the p
assive layer formed on it. Cr is accumulated to a large extent within
the passive layer whereas the composition of the metal surface remains
unchanged. The formation of an Fe rich overlayer is much less pronoun
ced in comparison to the situation of strongly alkaline solutions. The
appearance and growth of the passive layer and the chemical changes o
ccur in close relation to the characteristic features of the electroch
emical polarization curve. The passive layer grows linearly with the e
lectrode potential and the log of time as expected for a high field me
chanism. The formation of Fe(II) and its oxidation to Fe(III) follows
similar characteristics as observed for pure Fe and its alloys in alka
line solution.