Synthesis of Zirconium-Titanium oxide mixed layers on Ti substrates by plasma electrolytic oxidation and plasma-enhanced electrophoresis

Abstract

This work was carried out to elucidate the mechanism underlying the formation of zirconium and titanium oxide mixed layers on titanium substrates via plasma electrolytic oxidation (PEO) and plasma-enhanced electrophoresis. A series of constant high anodic currents were applied to KOH-based electrolytes containing ZrO2 nanoparticles with four different concentrations of K4P2O7. Scanning electron microscopy observations indicated that the coating layer formed in the electrolyte without K4P2O7 was underdeveloped owing to the absence of phosphate ions, which act as a complexing agent for uniform coating growth. Compositional analyses using X-ray diffraction and X-ray photoelectron spectroscopy revealed that the coating layer formed in the electrolyte with 0.015 M K4P2O7 consisted predominately of ZrO2, whereas increasing amounts of additional Zr compounds, such as ZrTiO4, and Zr-P compounds were found in the coating layers formed in the electrolytes with 0.03 and 0.045 M K4P2O7. The formation of such compounds could be mainly attributed to electrochemical reactions between ZrO2 and other components in the electrolytes owing to the high electrical energy of microarcs. Consequently, excessive phosphate ions in the electrolytes with 0.03 and 0.045 M K4P2O7 act as reactants for the formation of Zr-P compounds rather than complexing agents for the growth of the oxide layer. (C) 2017 Elsevier B.V. All rights reserved.