The corrosion behavior of the amorphous Fe-8Cr-metalloid alloys containing phosphorus as a metalloid element is largely affected by the amount of phosphorus. Immersion tests in concentrated 9 M H2SO4 solution open to air at 30°C show that the corrosion resistance of amorphous Fe-8Cr-20P alloy is very much higher than that of amorphous Fe-8Cr-13P-7C alloy. The corrosion loss of the amorphous Fe-8Cr-20P alloy is hardly detected by a microbalance even though the open circuit potential is initially in the active region of chromium. By contrast, the amorphous Fe-8Cr-13P-7C alloy shows active dissolution initially and the corrosion loss of this alloy increases gradually with immersion time. Only 30 mV difference in the initial open circuit potentials is responsible for the difference in the passivation behavior, with spontaneous passivation of the Fe-8Cr-20P alloy without initial active dissolution and delayed spontaneous passivation of the Fe-8Cr-13P-7C alloy with initial active dissolution. The presence of phosphorus ennobles the open circuit potentials of Fe-8Cr-13P-7C and Fe-8Cr-20P alloys sharply from the active region to the passive region of chromium by suppressing the anodic dissolution and accelerating the cathodic reactions of hydrogen evolution and oxygen reduction. XPS analysis indicates that the chromium content in the passive film increases with time of immersion following the ennoblement of the open circuit potential. The passivity of the Fe-8Cr-20P alloy which has a higher corrosion resistance than that of the Fe-8Cr-13P-7C alloy is maintained by the passive film in which chromium is less enriched in comparison with the passive film on the Fe-8Cr-13P-7C alloy. Phosphorus and chromium enhance synergistically the corrosion resistance. Phosphorus stimulates passivation and chromium forms the passive oxyhydroxide film.
|Publication status||Published - 1994 Sept|
ASJC Scopus subject areas
- Chemical Engineering(all)
- Materials Science(all)