THE EFFECT OF MOLYBDATE IONS ON THE TEMPERATURE-DEPENDENT PITTING POTENTIAL OF AUSTENITIC STAINLESS-STEELS IN NEUTRAL CHLORIDE SOLUTIONS


URGEN M., CAKIR A.

CORROSION SCIENCE, cilt.32, ss.841-852, 1991 (SCI İndekslerine Giren Dergi) identifier

  • Cilt numarası: 32 Konu: 8
  • Basım Tarihi: 1991
  • Dergi Adı: CORROSION SCIENCE
  • Sayfa Sayıları: ss.841-852

Özet

Temperature dependent pitting potential behavior of austenitic stainless steels was investigated in neutral chloride solutions between 10 and 70-degrees-C. Two chloride ion concentrations 0.1 and 0.5 M were chosen. Molybdate ion additions were between 0.01 and 0.1 M. While the pitting potential of AISI 304 stainless steels decreased continuously with temperature, AISI 316 stainless steel had a temperature independent region after 50-degrees-C. When molybdate ions were added into the solution, the pitting potential of AISI 304 stainless steel also became temperature independent after 50-degrees-C. The pitting potential change by the addition of molybdate ions, defined as inhibition efficiency, increased with increased molybdate/chloride ratio and temperature. The pitting inhibition efficiency obtained by the addition of sulphate ions decreased with the increasing temperature. The addition of molybdate ions after initiation of pitting in AISI 304 stainless steels, repassivated the pits and shifted the pitting potential. The pronounced beneficial effect of molybdate ions on the propagation of pitting is attributed to the conditions favoring the reduction and precipitation of the reduction products of molybdate ions.