The effect of air exposure on the corrosion behavior of amorphous Fe-8Cr-Mo-13P-7C alloys in 1 M HCl

Amorphous Fe-8Cr-13P-7C alloy is corroded severely in 1 M HCl open to air. The addition of more than 2 at% molybdenum is effective in promoting spontaneous passivation. According to XPS analysis, chromium accumulates continuously in the surface film on molybdenum-containing alloys throughout the immersion experiment for 20 h, whereas for the molybdenum-free alloy an initial slight increase in chromium concentration in the surface film is followed by an almost continuous decrease. Molybdenum and phosphorus are deficient in the air-formed film but become concentrated in the film with immersion time. The Mo 4+ species which is the constituent of the passive film on molybdenum metal is increased. Air exposure for 30 min prior to the polarization or immersion experiment in 1 M HCl raises the open circuit potential of specimens and retards the enrichment of chromium in the passive film on molybdenum-bearing alloys.