Effect of Microstructure and Temperature on Electrochemical Behavior of Niobium in Phosphate-Buffered Saline Solutions

In this study, the corrosion behavior of Nb with different microstructures, cold-rolled and annealed, was studied in phosphate buffered saline (PBS) solutions in the temperature range of 37 to 67 degrees C. The chemical composition and electronic properties of the passive film were investigated using X-ray photoelectron spectroscopy (XPS) and Mott-Schottky analysis. The results show that the annealed sample exhibits better corrosion resistance. Mott-Schottky analysis revealed that the passive films formed on niobium surfaces show n-type semiconductor behavior. The measured donor density is dependent on the frequency of the Mott-Schottky analysis, which can be eliminated by fitting the impedance data at different frequencies. The microstructure of the metal substrate affects the donor density of the passive film but not the flatband potential. No pitting or trans-passive behavior was observed for any samples up to 0.9 V and 67 degrees C. No significant difference of the chemical composition was observed among the passive films formed at 0.35 V on different treated samples. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.003302jes] All rights reserved.