THE EFFECT OF GRAIN SIZE REDUCTION AND PHOSPHOROUS ALLOYING ON THE CORROSION PROPERTIES OF NANOCRYSTALLINE COBALT AND COBALT-PHOSPHOROUS ALLOYS IN A 0.1 M NaOH SOLUTION

摘要

The corrosion properties of nanocrystalline Co and Co-1.1 and 2.1 wt% P (7 to 20 nm grain size) were studied in a 0.1 M NaOH solution. All tested samples exhibited active-passive-transpassive behavior. While anodic polarization curves and EIS responses for poly- and nanocrystalline Co had very similar behavior, Co-P showed higher passivation current densities and reduced polarization resistances. XPS analysis revealed that the passive film (>10 nm thick) formed in the primary passivation range was consisted of mainly Co(OH)_2. The passive film (<10 nm thick) formed during secondary passivation consisted of complex compounds such as Co(OH)_2, Co_3O_4, Co_2O_3, and Co(OH)_3.