Gel oxidation is an effective thermochemical method for the preparation of bioactive titanium surfaces. This study aims to investigate the effect of low NaOH concentration on gel oxidation of titanium subjected to various oxidation 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 filfn was determined using glancing angle X-ray diffraction (GAXRD). At low NaOH concentration, the amount of sodium titanate hydrogel, if present, was too low to detect. 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.
Recent studies revealed the incorporation of sodium removal treatment in between alkali and heat treatments to prepare a sodium-free bioactive surface on titanium. This method has been reported to be more effective than conventional alkali and heat treatments to promote titanium osteointegration. This study aims to investigate the surface properties of high purity titanium after subjected to alkali treatment and subsequent sodium removal treatment. High purity titanium foils were immersed in 5 M NaOH at 60 °C for 24 hours followed by immersion in diluted HCl acid and/or distilled water at 40 °C for a period of time. The surface morphology and composition were examined using Field Emission Scanning Electron Microscope/Energy-Dispersive X-Ray Spectroscopy (FESEM/EDS). The surface wettability was evaluated by water contact angle. The surface functional groups were analysed using Fourier Transform Infrared Spectroscopy (FTIR). It was revealed that alkali and subsequent sodium removal treatments have rendered these samples high wettability and surface energy with the introduction of hydroxyl groups. Furthermore, diluted HCl treatment, water treatment and combination of both treatments removed sodium from the surfaces of alkali-treated titanium effectively (<5wt% Na) without altering existing hydroxyl groups.
Alkali and heat treatments were first introduced by Kim et al. to prepare a bioactive surface on titanium. This method has been proven very effective and widely used in biomaterial researches to promote titanium osteointegration. This study aims to investigate further the effect of heat treatment on surface morphology of high purity titanium. High purity titanium foils were immersed in 5 M NaOH at 60°C for 24 hours followed by heat treatment at 400°C, 500°C, 600°C, 700°C and 800°C for 1 hour in air atmosphere. The surface morphology was examined using Field Emission Scanning Electron Microscope (FESEM). The surface topography and surface roughness were obtained using Atomic Force Microscopy (AFM). A structure transformation accompanied by significant grain growth were observed as temperature increased from 400°C to 800°C. As temperature increased, the grain coarsened and became larger in size which is in good agreement with the increasing surface roughness. A sudden decrease in surface roughness of titanium at 800°C might be due to the spallation of oxide layer.
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