Role of surface reactions in the transpassive dissolution of ferrous alloys in concentrated H3PO4

Iva Betova, Martin Bojinov (Corresponding Author), Tzvety Tzvetkoff

Research output: Contribution to journalArticleScientificpeer-review

10 Citations (Scopus)


The transpassive dissolution of a range of ferrous alloys (Fe–12% Cr, Fe–12% Cr–5% Mo, Fe–25% Cr, Fe–25% Cr–10% Mo) in concentrated H3PO4 was studied within the frames of an investigation of electropolishing mechanisms. Measurements by the contact electric resistance (CER) technique have demonstrated that in the transpassive region, the resistance of the anodic film first decreases with increasing potential due to enhanced conductivity of that film and then increases at higher potentials, indicating transpassive film growth. The release of soluble Cr(VI) as detected by rotating ring–disc measurements is the higher, the higher the Cr content in the alloy, and further increases upon addition of 10% Mo to the Fe–Cr alloys. Impedance spectra in the transpassive region have been found to include contributions both from the anodic film and a multistep transpassive dissolution reaction at the film/solution interface. The results were interpreted using a generalised model of transpassive dissolution. The kinetic parameters of the process were determined and the influence of alloy composition on their values is discussed in relation to the processes of anodic surface treatment.
Original languageEnglish
Pages (from-to)273-287
JournalApplied Surface Science
Issue number1-4
Publication statusPublished - 2003
MoE publication typeA1 Journal article-refereed


  • iron-chromium alloys
  • transpassive dissolution
  • surface reactions
  • impedance spectroscopy
  • kinetic model


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