ON THE ROLE OF TUNGSTEN OR MOLYBDENUM IN IMPROVED PASSIVATION TO AUSTENITIC STAINLESS STEEL IN PHOPSPHORIC ACID POLLUTED BY SULFIDES

 

Abdellah Guenbour,^a Mohammed Essahli,^a Ali Benbachir,^a Lucien Aries,^b
and Rachid Boulif ^c

 

^a Laboratoire de Corrosion - Electrochimie, Faculté des Sciences ,Avenue Ibn Battouta , B.P 1014,
Rabat, Morocco. E-mail: guenbour@fsr.ac.ma

^b Laboratoire de Traitement de Surface, Faculté des Sciences ,Université Paul Sabatier 31062,
Route de Narbonne, Toulouse - Cedex, France

^c Centre de Recherche des Phosphates Minéraux (CERPHOS), Avenue Moulay
Ismail –Casablanca(Maroc)

 

Abstract

The study passive state behavior of 18Cr-10Ni, 16Cr-14Ni-4W and 18Cr-10Ni-1.5Mo austenitic stainless steels has been performed in -phosphoric acid polluted by sulfides ions using electrochemical techniques, X ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS).

The addition of W or Mo. to austenitic SS induced a decrease of dissolution of rate and affects the nature of passive film. The passive film formed in an overlap of two layers with the external layer rich in W (VI), Mo (VI) and non-metallic elements (O and P). The improved resistance of SS alloys with W is related to formation the film rich in oxide of chromium and tungsten with a little concentration of sulfide. The role of Mo is attributed to formation the film of oxide chrome and molybdenum sulfide. It assumed that Mo prevents the formation of ferrous sulfide.