Spectroscopic and real-time imaging investigation of tantalum plasma electrolytic oxidation (PEO)

We present the results of plasma electrolytic oxidation (PEO) of tantalum in 12-tungstosilicic acid at 70 mA/cm2. For the characterization real-time imaging and optical emission spectroscopy (OES) were used. It has been detected that relatively small microdischarges (cross-sectional area < 0.1 mm2) are dominant throughout the PEO, while the presence of medium-size microdischarges (cross-sectional area from 0.1 mm2 to 0.2 mm2) and large microdischarges (cross-sectional area > 0.2 mm2) become noticeable only at later times of PEO. The elements and their singly charged positive ions present in PEO microdischarges are identified using standard OES technique. The spectral line shape analysis of first two hydrogen Balmer lines shows presence of two microdischarges during PEO. These discharges characterize relatively low electron number densities Ne ≈ 0.9 × 1015 cm− 3 and at Ne ≈ 2.2 × 1016 cm− 3. A simple OES technique was introduced to test optical thickness of hydrogen Balmer lines emitted during PEO process.