Effect of UV irradiation and diffuse plasma on surface properties of micro-arc calcium phosphate coatings

The influence of UV irradiation or plasma of runaway electron preionized diffuse discharge (REP DD) post-modification on the surface properties of the calcium phosphate (CaP) coatings formed by the micro-arc oxidation (MAO) method was investigated. The formed MAO-coatings had porous structure and rough surface morphology with incorporation of spheroidal structural elements with inner pores. It was showed that the UV irradiation or REP DD post-treatment of the MAO-coatings led to the decrease of the coating contact angels with water from 20 to 0 or to 7 degrees, respectively. However, the free surface energy of the coatings did not change after post-treatments and equalled to 74±1 mJ·m⁻². The polar component of the free surface energy of the all types of the coatings exceeded almost 5–6 times the dispersion component that indicated the presence of strong polar bonds on the coating surface, e. g. OH- and PO₄-groups. (paper)