Advancements in plasma electrolytic oxidation with particle suspensions: A novel approach for the direct incorporation of calcium carbonate

• First-ever incorporation of calcium carbonate particles into PEO coatings. • Nano-sized calcium carbonate synthesized via carbonation route. • Dibasic phosphate electrolyte led to hydroxyapatite co-precipitation in a PEO bath. • Particles modified oxide layer structure and promoted its significant thickening. • Calcium carbonate was homogeneously distributed across the coating surface. Plasma electrolytic oxidation (PEO) enables efficient metal surface modification via spark-driven incorporation of bath additives. Due to some fundamental limitations of the PEO process and the specific nature of carbonates, the latter have been relatively overlooked as valuable bath components. Concurrently, carbonate-based PEO coatings show promise for applications in photocatalysis, adsorption, corrosion protection, and biomedicine. This study introduces an unconventional strategy to facilitate carbonate inclusion into the PEO layer, using a bath formulation with calcium carbonate (CC) and hydroxyapatite (HA) particles as a model system. The PEO bath was the product of physicochemical interactions between a Na 2 HPO 4 electrolyte and CC nanoparticles synthesized via a carbonation route. Meanwhile, these interactions were traced and attributed to competing dissolution-precipitation and chemisorption phenomena. PEO was conducted on titanium in near-DC mode, applying a limiting voltage of 450 V. The resulting coating displayed typical PEO features, was rich in Ca and P, moderately porous, and approximately 25 µm thick. Raman spectroscopy detected CC, HA, carbonate HA, anatase, and amorphous TiO 2 , evenly distributed across the surface. In addition, the mechanism of coating growth under these conditions was described and discussed. This work provides practical evidence of the feasibility of carbonate incorporation via PEO, presents a confirmed approach to integrating CC particles into PEO coatings, and lays groundwork for their specialized applications.