Characterization of the plasma electrolytic oxidation of titanium in sodium metasilicate

Plasma electrolytic oxidation (PEO) of titanium in sodium metasilicate at 200 mA/cm2 is investigated using real-time imaging and optical emission spectroscopy. It has been detected that during the PEO process the size of microdischarges becomes larger, while the number of microdischarges is reduced. The species and their ionization states present in PEO microdischarges are identified. The species originate both from titanium anode and from the electrolyte. The spectral line shape analysis of hydrogen Balmer line Hβ (486.13 nm) indicates the presence of two types of microdischarges during PEO. The discharges are characterized by relatively low electron number densities of Ne = 3.8 × 1015 cm−3 and Ne = 4.5 × 1016 cm−3. For electron temperature (Te) measurement we used Ti I lines at 398.18 nm and 501.42 nm and obtained Te in the range of 3700 ± 500 K. Surface coatings formed by PEO process were characterized by AFM, SEM-EDX and XRD. The main elemental components of PEO coatings are Ti, Si and O. The PEO coatings are partly crystallized and mainly composed of anatase, rutile, and amorphous SiO2.