Cross-sectional analysis of the surface ceramic layer developed on Ti metal by NaOH-heat treatment and soaking in SBF

Abstract

The surface structure developed on Ti metal after an NaOH and heat treatment and subsequent soaking in a simulated body fluid (SBF) was investigated using cross-sectional analysis involving SEM observations and EDX analysis, as well as an outer surface analysis involving SEM observations, thin-film X-ray diffraction, and Raman spectroscopy. A 1 μm-thick layer, which consisted of lathlike sodium hydrogen titanate (Na_xH_2-xTi₃O₇) elongated perpendicular to the surface, formed on the surface of the Ti metal after the initial NaOH treatment. This layer gradually changed into Ti metal at the boundary. The surface layer was densified by the subsequent heat treatment, accompanied by a transformation of the sodium hydrogen titanate into sodium titanate (Na₂Ti₆O₁₃), rutile, and anatase. The scratch resistance of the surface layer significantly increased after the heat treatment. When this Ti metal with a modified surface was soaked in SBF, apatite began to precipitate in the interior of the surface layer, filled the interspaces of the lathlike phases to integrate with the latter giving a dense composite structure, and grew over the surface layer.