抄録
Polarization curves of Fe, Ni, Cr, Ni-18 mass% Cr alloy and Type 304 stainless steel were measured in aqueous fluoride solutions of various pH values from 1.9 to 11.7 at 303K. The concentration of fluoride ion was fixed at 0.2kmol·m-3 for all the solutions. Fe shows the very large current density of 101 to 102 A·m-2 beyond -500mVAg/AgCl at pH≤8.2 and beyond -100mV Ag/AgCl at pH 11.7. Ni shows the large current density beyond -200mV Ag/AgCl at pH≤3.2. However, two peaks appear in the curves at pH 5.8 and 8.2, and a passive region has the very small current density of 10-1 to 10-2 A·m-2 at pH 11.7. Cr does not show any active region but a passive region with the very small current density at any pH values. Ni-18 mass% Cr alloy shows that the current density increases with increasing potential at pH≤8.2, and that a passive region with very small current density appears at pH 11.7. Type 304 stainless steel behaves similarly as Cr such that they have very small current densities in the passive region at any pH values. No localized corrosion such as pit was found for all the materials.
