Ca/P in situ introduction for enhancing coating biocompatibility via plasma electrolytic oxidation in low-temperature molten salt

Abstract

Plasma electrolytic oxidation (PEO) is one of the most promising methods for synthesizing ceramic coatings on metallic substrates. Recently, PEO in molten salt electrolytes was found to be advantageous due to overcoming system heating and the formation of contaminants. However, the PEO in molten salt was conducted at a high temperature (T_m∼220 °C), limiting the introduction of different components such as Ca and P. This study realizes the employment of a low-temperature electrolyte based on a ternary eutectic system of Ca(NO₃)₂–NaNO₃–KNO₃ (T_m∼130 °C) jointly with the in situ introduction of Ca/P in the form of ammonium dihydrogen phosphate (ADP). The surface morphology, phase and chemical composition, wettability, and anti-corrosion performance were examined. The results indicate improved surface performance with the addition of 1 wt% ADP to the electrolyte. This surface preferably comprises the anatase phase of TiO₂ and exhibits enhanced biocompatibility and corrosion resistance in a biological environment.