Abstract
ABSTRACTPassive and corrosion behaviors of Alloy 22 in chloride and fluoride containing solutions, changing the heat treatment of the alloy, the halide concentration and the pH of the solutions at 90°C, was investigated. The study was implemented using electrochemical techniques, which included open circuit potential monitoring over time, potentiodynamic polarization and electro-chemical impedance spectroscopy (EIS) measurements carried out at open circuit and at passiv-ity potentials. Corrosion rates obtained by EIS measurements after 24 h immersion in naturally aerated solutions were below 0.5 m/year. The corrosion rates were practically independent of solution pH, alloy heat treatment and halide ion nature and concentration. EIS low frequency resistance values increased with applied potential in the passive domain and with polarization time in pH 6 - 1M NaCl at 90ºC. This effect was attributed to an increase in the oxide film thick-ness and oxide film aging. High frequency capacitance measurements indicated that passive ox-ide on Alloy 22 presented a double n-type/p-type semiconductor behavior in the passive potential range.
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