抄録
The corrosion of iron has been protected with passive films (Fe_2O_3 and Fe_3O_4) in the various solutions. In this work, the formation of (Fe_3O_4) film in H_2SO_4 solution and its corrosion resistance were studied using the electrochemical technique. The anodic I-V curves were measured from -0.6 to 5V vs. Ag/AgCl. An iron rod (99.99%, 5mmφ) was used as working electrode. The counter electrode was Pt wire, the reference electrode was Ag/AgCl. Sample solution used 0.5〜2.0 mol/dm^3 H_2SO_4 solutions. The sonication was prepared with using ultrasonic cleaner (28, 45 and 100 kHz, 100W). The first passivation potential (Flade potential ) and second passivation potential were observed in the stationary state and sonication. The current did not flow over the second passivation potential. The current flowed at the first passivation potential because Fe_2O_3 film was destroyed by the sonication. The current did not flow over the second passivation potential. An iron was dissolved as current flowed (Fe^<2+>→Fe_2O_3). The Fe_2O_3 film was enough covered on the surface at the Flade potential, the formation of Fe_2O_3 film increased with increasing of potential. (Fe^<2+>+O_2→Fe_2O_3) . However, the current flowed again, and Fe_3O_4 film was formed (Fe2C>3 + O2 - Fe3O4). The passive film was destroyed with liquid flow and sonication. The passive film which was formed at second passivation potential was firm film comparing with that at the first passivation potential. The passivation film at the second passivation potential had good corrosion resistance.
