Gel Oxidation of Titanium at Low Concentration of Sodium Hydroxide (NaOH)

Abstract

Gel oxidation is an effective thermochemical method for the preparation of bioactive titanium surfaces. This study aims to investigate the effect of low concentration of NaOH on gel oxidation of titanium when subjected to various temperatures. Titanium foils were soaked in NaOH aqueous solutions with the concentration of 0.5 M or 1.0 M, followed by oxidation in the range of 400°C to 800°C. The crystallinity of the film was determined using glancing angle X-ray diffraction (GAXRD). The microstructures were examined using field emission scanning electron microscope (FESEM). Focused ion beam milling (FIB) was used for cross-sectional imaging. At low NaOH concentration, the amount of sodium titanate hydrogel, if present, was too low to detect after gelation. Subsequent oxidation at 400°C was insufficient to form sufficient anatase and/or rutile to be detectable by GAXRD. Oxidation at 600°C and 800°C resulted in the detection of rutile. The concentration of the NaOH solution was important that it affected the dissolution or retention of the anatase passive oxidation layer whereby low concentrations of the NaOH solution (0.5 M and 1.0 M) resulted in a low degree of dissolution.