TiO2 Coating by Gel Oxidation

Abstract

Gel oxidation is a thermochemical method for the production of an oxide film on a metallic substrate, where the metallic substrate is subjected to gelation by immersion in NaOH solution, followed by oxidation.These films are prepared for biomedical implant coating. Continuous and discontinuous gelled and TiO2 films of submicron thickness were produced on high-purity Ti foil substrates (50μm thickness) by soaking in NaOH solutions (0.5M, 1.0M, 5.0M, and 10.0M). Gelation involved soaking at 60°C for 24 hours. After drying in air for 24 hours, the samples were heated at 300ºC/hour and soaked for 1 hour in air at 400ºC, 600ºC, and 800°C. The compositions, microstructures, and thicknesses of the films were determined using: glancing-angle X-ray diffraction, Raman microspectroscopy, and field emission scanning electron microscopy (FESEM). Raman microspectroscopy revealed the formation of an amorphous sodium titanate gel layer following chemical treatment. As expected, the thickness of the gel layer increased with increasing NaOH concentration. However, the two highest concentrations (5.0M and 10.0M) resulted in a cracking of the gel layer upon drying in air. TiO2 did not crystallize during heating at 400ºC but rutile formed directly upon heating at 600ºC and 800ºC. It can be concluded that the concentration of NaOH and the temperature change the thickness and phases of the titania.

Keywords

• titania
• thick films
• gel oxidation
• glancing-angle x-ray diffraction
• raman microspectroscopy