Temperature-controlled growth of micro- and nanocrystals on the surface of NiO+CuO/TiO2/Ti composites

Abstract

The functional properties of oxide coatings on metals depend on the composition and structure of their surface. In this work, the change with temperature of air annealing of the surface of NiO + CuO/TiO2/Ti composites formed by the combination of plasma electrolytic oxidation of titanium in the phosphate-borate-tungstate electrolyte containing nickel and copper acetates and impregnation in the solution of nickel and copper nitrates was studied. It has been shown that varying the annealing temperature allows one to form the ensembles of micro- and nano-sized crystals of different composition and structure on the surface. CuO crystals are formed on the surface at annealing temperature T = 500 ÷ 700 °C, NiWO4 crystals are present at T = 750 ÷ 850 °C, and Ni2.62Ti0.69O4 whiskers - at T ≥ 900 °C. The data obtained suggest that the remaining electrolyte and impregnating solution accumulated on the surface and in the pores, as well as the transport of titanium from the coating depth to the surface, play an important role in the formation of crystals. It was summarized that air annealing at given temperatures of complex oxide coatings can be effective for controlling their architecture and surface composition at the micro- and nanolevels and, therefore, their functional properties.