Grain boundary electrochemistry of β-type Nb-Ti alloy using a scanning droplet cell

Localized oxide spots were grown at the grain boundaries of a technically relevant 30 at.% Nb-Ti ß-type titanium alloy to study the local electrochemical response. The grain boundaries selected were combinations of grains having different orientations and grain boundary angle. Crystallographic information of the grains and boundary angles were revealed by electron back scattering diffraction (EBSD) technique. Cyclic voltammetry is the electrochemical technique used to grow the oxides starting from 0 V and increasing the potential in steps of 1 V till 8 V at a scan rate of 100 mV s−1 in an acetate buffer of pH 6.0. Electrochemical impedance spectroscopy was used to investigate the electrical properties of the oxide/electrolyte interface in the frequency range between 100 kHz and 100 mHz. Important oxide parameters such as formation factor and dielectric number were determined from these measurements. Significant differences were observed for different grain boundaries. The semiconducting properties of the oxides at the grain boundaries were assessed by using Mott–Schottky analysis on a potentiostatically grown oxide. All the oxides showed n-type semiconducting properties where the donor concentration varies with the grain boundaries mentioned above. A flat band potential −0.25 ± 0.02 V versus standard hydrogen electrode is more or less the same for all the boundaries studied.