Electrochemical Behavior of Sn‐Ag Alloys in Sodium Fluoride Solutions

Passivation and corrosion behavior on Ag, Sn and Sn‐Ag alloys were studied using various electrochemical techniques, i.e. open‐circuit, potentiodynamic polarization and impedance measurements. The specimens were polarized between –1000 and 500 mV vs. saturated calomel electrode (SCE) in naturally oxygenated NaF solution of different concentrations. The results of potentiodynamic polarization showed that each of i_corr and i_c increases with increasing either Sn% or F^‐ concentration. EIS measurements under open circuit conditions confirmed well this behavior. The effect of temperature was also studied in 0.5M NaF at temperature range of 291K to 333K. The corrosion current i_corr was observed to increase with temperature for the same electrode. The activation energy was calculated according to Arrhenius equation and its value was found to decrease considerably with increasing the Sn content in the alloy.     

Electrochemical behaviour of Mo‐containing austenitic stainless steels in buffer solution

The effect of pH on the electrochemical behavior of austenitic stainless steels in naturally aerated and nitrogen‐deaerated buffer solutions has been studied. Potentiodynamic and ac impedance techniques were used. The results indicate that corrosion current (I_corr) decreases with pH. By examining the impedance data for the seven tested steels under various conditions, it seems that the total resistance (R_T) value is a suitable indication parameter for explaining the role of molybdenum and the other supplementary alloying additions (Ni, N, Cu and Mn) on the passive film behaviors as a function of pH of the forming solutions. As a general trend, the R_T values for all steels tended to be lower in the basic buffer than in the acidic solutions.