Effect of buffer capacity on electrochemical corrosion behavior of alloy 800 in sulfate solutions

Electrochemical impedance spectroscopy in sulfate solution was compared in the presence and absence of potassium phosphate monobasic/sodium hydroxide (KH2PO4/ NaOH) buffering reagent. Cathodic polarization cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the behavior of hydrogen peroxide (H2O2) reduction in buffered and unbuffered solutions. Open-circuit potential measurements polarization resistance electrochemical impedance spectroscopy and potentiodynamic polarization were utilized to evaluate the corrosion behavior of Alloy 800 as affected by the buffer reagent. Results showed that reduction of H2O2 takes place at higher potentials and with lower charge-transfer resistance in buffered solutions. The Alloy 800 passive layer thickened in the presence of the buffering reagent and showed lower corrosion rate. The overall anodic potentiodynamic behavior was similar in both the buffered and unbuffered solutions. Because of its buffering properties the effect of the thiosulfate ion on corrosion behavior was also studied. It was shown that the addition of thiosulfate caused rapid dissolution of the passive film starting at -200 mV vs. silver/silver chloride (Ag/AgCl).