Corrosion of 304SS in acidic and neutral media as a function of molybdate ions concentration

The electrochemical behavior of 304SS stainless steels has been investigated in acidic and neutral media at 22 ^oC as a function of molybdate ions concentration.  Corrosion techniques that have been used include potentiostatic polarization, polarization resistance, and cyclic polarization measurements.  Measurements indicate that molybdate ions are very effective in improving resistance to general corrosion of 304SS when tested in 1M H₂SO₄ and become less effective in the presence of chlorides.  More importantly, low concentrations of molybdates have detrimental effect on the corrosion resistance of 304SS tested in 1M H₂SO₄+0.5M NaCl; relatively high concentrations of molybdate ions are needed in order to exhibit inhibition effect.  Furthermore, the presence of molybdate ions in sufficient concentrations enhances the resistance to pitting corrosion.  It is suggested that molybdate ions increase the resistance to general and pitting corrosion by lowering the current densities in active and passive regions, enhancing passivation in the process.