Electrochemical corrosion behaviours of Fe68Ni14-xMoxSi2B16 metallic glasses in 1N HCl and 1N H2SO4

Abstract

Electrochemical corrosion behaviours of five Fe₆₈Ni_14-xMo_xSi₂B₁₆ glasses with x=0, 1, 2, 3 and 4 have been investigated in both 1 N HCl and 1 N H₂SO₄ solutions using potentiodynamic polarization and a.c. impedance spectroscopic techniques. The polarization and impedance results show that all the alloys possess inferior corrosion resistance which has been attributed to the low Ni content on one hand and the absence of passivators such as Cr and P on the other. Interestingly the alloys have been found to show weak passivation in more aggressive HCl and not in relatively mild H₂SO₄ solution. This has been explained in terms of dual behaviours of Mo in HCl and H₂SO₄ based on impedance data and literature work. The present study attempts to correlate impedance data with polarization data through the parameter polarization resistance and indicates that both values are comparable only when an alloy undergoes active dissolution and not when it exhibits passivity.