Corrosion layers
grown on stainless steels (AISI 302, 316) polarized at the pitting potential
in alkaline solutions containing chloride, were identified by Raman spectroscopy.
Several binary alloys such as Fe-10Ni, Fe-6Mo, and Fe-18Cr, were studied
to separate the influence of the different alloys elements. A comparison
was also made with the layers formed on these alloys by voltametric cycling
(which allows the thickening of the passive layer), the anodic reverse
potential being in this case below the pitting potential. The parts played
by the two main elements, Cr and Mo are described. After the passivity
breakdown, i.e., once the chromia layer has broken down, the inner layer
is formed by tetravalent molybdate, the pitting initiation being related
to the passage of Mo from valency 6+ to valency 4+
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