ISSN 0004-881X

TiO₂ Thick Films by Electrophoretic Deposition

by H.Z. Abdullah^1,2* and C.C. Sorrell

1 School of Materials Science and Engineering, University of New South Wales, NSW 2052, Australia
2 Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia (UTHM), 86400 Parit Raja, Batu Pahat , Johor, Malaysia

Abstract

Electrophoretic deposition (EPD) is similar to electrochemical plating although, instead of deposition from solution, particles are deposited from suspension. It is possible to produce thin and thick films of very consistent thickness, even on irregularly shaped substrates, with very short deposition times. Also, the equipment necessary to deposit the films consists solely of a relatively inexpensive power supply. However, the films are only physically bonded to the substrate and permanent chemical adhesion must be effected by firing, which can have deleterious results on the mechanical properties of metallic substrates. In the present work, EPD has been used to deposit TiO2 films on high-purity Ti foil substrates (50 ìm thickness), followed by sintering.

Commercial TiO2 powder (Millenium Chemicals) of spherical morphology and particle diameter ~250 nm were dispersed in the non-aqueous medium acetyl acetone (5 g solid in 50 mL liquid) and deposited under the following conditions: Voltage = 5, 10, 20, and 30 V; time = 5, 10, 30, 60, 90, and 120 sec. All samples were fired at 800°C for 2 h in flowing argon (heating rate = 600°C/h). The compositions, microstructures, and thicknesses of the films were determined using: Optical microscopy, glancing-angle X-ray diffraction, Raman microspectroscopy, and field emission scanning electron microscopy (FESEM).

At the lowest voltage (5 V), the green films were not continuous; higher voltages yielded continuous green films. Sintering of the latter showed that the bulk density and grain size of the outer surface examined decreased as the deposition time and film thickness increased. This is likely a proximity effect of the Ti/TiO2 interface, where interdiffusion enhanced defect formation in TiO2 (viz. TiO2-x) and concomitant densification and grain growth. That is, the thickness of the thicker films exceeded the defect diffusion distance for these heating conditions. The grain morphology was consistent with these observations, where the well sintered thinner films showed low-energy facetted grains and the poorly sintered thicker film surfaces retained the original rounded TiO2 grain shape.

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