Potential and morphological transitions during bipolar plasma electrolytic oxidation of tantalum in silicate electrolyte

摘要: Abstract Surges in the cell potential, due to an increased overpotential for hydrogen evolution, and transitions ceramic oxide coating morphology during plasma electrolytic oxidation (PEO) of tantalum under a pulsed bipolar current regime at 1000 Hz silicate electrolyte are investigated using real-time imaging gas analytical scanning electron microscopy, X-ray photoelectron spectroscopy supplementary potential-controlled electrochemical measurements. The coatings, which contained Ta2O5, TaO incorporated silicon species, revealed nodular that transformed with treatment time “pancake” type then “coral reef” type. first potential surge occurred only cathodic coinciding spark intensity, more vigorous emergence structures reduction porosity. later increases both anodic coincided intensification sparking, establishment silicon-rich structures, formation comparatively thick coating. kinetics growth differed significantly between three morphological stages. Electrochemical measurements showed discharges evolution subsequent pulse, is proposed be impeding near surface increasing resistance ionic transport.