Evolution of microstructure during the thermal processing of aluminum-modified titania and aluminum/vanadium co-modified
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David M. Grant and Karen McKinlay School of Mechanical, Materials, and Manufacturing Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom
Philip G. Harrison School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom (Received 20 November 2003; accepted 17 March 2004)
Sol-gel materials of aluminum-modified TiO2 of nominal composition 5.7 wt% and 10.8 wt% aluminum and aluminum/vanadium co-modified TiO2 of nominal composition 5.7Al–3.5V wt% have been prepared by evaporation of aqueous colloidal sols obtained by the hydrolysis of aqueous solutions of titanium chloride with the appropriate amount of vanadyl oxalate and/or aqueous aluminum nitrate using aqueous ammonia followed by peptization of the resulting hydrated solids using nitric acid. The nature of the sol-gel materials and the behavior upon calcination at temperatures up to 1373 K have been investigated using x-ray fluorescence, x-ray powder diffraction, transmission electron microscopy, and electron diffraction. At 333 K, all the gels comprise small (approximately 5 ± 1 nm) particles of anatase together with traces of brookite and highly crystalline ammonium nitrate. The particle size changes little on thermal treatment at 573 K, but increases significantly at higher temperatures and is accompanied by transformation to rutile. Aluminum-modified gels stabilize the anatase phase from 923 K in unmodified TiO2 to 1023 K in the 6Al/TiO2 gel and 1173 K in the 11Al/TiO2 gel. The alumina in the co-modified gel has a dominating effect on stabilizing the anatase phase until 973 K. Only rutile is present at high temperatures, except for small amounts of phase-separated ␣-Al2O3 (Corundum). No substitutional incorporation of Al3+ ions in the tetragonal rutile lattice occurs at high temperatures. I. INTRODUCTION
Many biomedical applications such as prosthetic implants are made from titanium and titanium alloys. Implants of titanium were first introduced in the early 1970s,1,2 but more recently the use of titanium alloys, such as of Ti–6Al–4V, have become popular as they have 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.3 It is imperative that upon implantation a strong binding interaction between the implant and the bone tissue occurs that will lead to quick growth of the bone tissue thus reducing the convalescence time. Poor mechanical
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0250 1808
http://journals.cambridge.org
J. Mater. Res., Vol. 19, No. 6, Jun 2004 Downloaded: 16 Mar 2015
properties at the interface of a surface coating and an implant does limit their use to non-load-bearing implant surfaces. Clinical studies using calcium phosphate show good bioactivity and enhancement of the bone–implant interface.4 However, there are often difficulties in obtaining a sufficient b
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