Michio Yoneya

Temperature Dependence of Surface Crystal Structures of Iron Passivated at −400 mV in a Borate Buffer Solution

The temperature dependence of surface crystal structures of iron passivated at -400 mV SCE was investigated in a borate buffer solution. The size of particle-like structures on the passivated iron surface increases with passivation temperature. Iron surfaces passivated at higher temperature are smoother. Under passivation at 25 and 40°C, the terrace is as narrow as less than 2 nm and atomic arrays with 1D order were observed; under passivation at the other higher temperature, terraces appear wider and atomic arrays with long-range 2D order were observed on the 5 nm wide terraces at 60°C. At lower temperatures (25 and 40°C) defect sites were observed in the 20% region; at higher temperature, defect sites gradually disappeared and a defect-free crystal structure was observed at 60°C. After attainment of passivity, the growth of the passive films obeyed Arrhenius law.