Evolution of microstructure during the thermal processing of titania and vanadium-modified titania gels
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David M. Grant and Karen McKinlay School of Mechanical, Materials, Manufacturing Engineering and Management, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
Craig Bailey and Philip G. Harrison School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
Sol-gel materials of TiO2 and vanadium-modified TiO2 of nominal composition 4, 8, and 16 wt.% vanadium were prepared by evaporation of aqueous colloidal sols obtained by the hydrolysis of aqueous solutions of titanium(IV) chloride with the appropriate amount of vanadyl oxalate using aqueous ammonia followed by peptization of the resulting hydrated solids using nitric acid. The nature of the sol-gel materials and their behavior on calcinations at temperatures up to 1273 K were investigated using x-ray fluorescence, powder x-ray diffraction, transmission electron microscopy, and electron diffraction and FT-Raman spectroscopy. At 333 K, all the gels comprised small (about 5 ± 1 nm) particles of anatase together with traces of brookite. The particle size changed little on thermal treatment at 573 K, but increased significantly at higher temperatures and was accompanied by transformation to rutile. Incorporation of vanadium in the gels reduced the temperature at which rutile began to appear from 923 K in pure TiO2 to 773 K in the V/TiO2 gels. Only rutile was present at high temperatures, except for the 16 V/TiO2 gel, when small amounts of phase-separated vanadia were also observed. A 2–3% substitutional incorporation of V4+ ions in the tetragonal rutile lattice occurred at high temperatures, but the majority of the vanadium was present in an amorphous, highly dispersed fashion.
I. INTRODUCTION
Titanium and titanium alloys are used widely for biomedical applications such as prosthetic implants. Titanium implants were first introduced in the early 1970s,1 but more recently the use of titanium alloys, such as of Ti-6Al-4V, as biomaterials has become popular because of their superior mechanical properties and biocompatibility as well as enhanced corrosion resistance, when compared to unalloyed titanium and more conventional stainless steels and cobalt-chrome based alloys.2 The formation of a strong binding interaction between the implant and the bone tissue is important since it should lead to quick growth of the bone tissue thus reducing the convalescence time. However, poor mechanical properties of surface coatings can limit their use to nonload-bearing implants. Clinical studies of some coatings such as calcium phosphate show good a)
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J. Mater. Res., Vol. 18, No. 3, Mar 2003 Downloaded: 02 Apr 2015
bioactivity and enhancement of the bone implant interface.3 However, there are often difficulties in obtaining sufficient quality in the coating/substrate interface.4 The quality of the interface coating/substrate is important for the mechanical adhesion of the coating, the type of binding
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