Synthesis of Titania coated Alumina Particles by a Hybrid Sol-gel Method
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Synthesis of Titania coated Alumina Particles by a Hybrid Sol-gel Method A.D. Schmidt1 , S.B. Majumder2 , P.S. Dobal2 , R.S. Katiyar2 , and D.C. Agrawal3 1 Goshen College, Department of Chemistry, Goshen, IN, USA 2 Department of Physics, University of Puerto Rico, San Juan, PR 00931-3343 3 Materials Science Program, Indian Institute of Technology, Kanpur, 208016, India ABSTRACT Modifying their surface with a coating of another ceramic material can dramatically alter the properties of ceramic particles. In the present work we have demonstrated that the Al2 O3 particles can be successfully coated by TiO 2 using a novel sol-gel technique. The nature of these coatings was predicted on the basis of scanning electron microscopy imaging in conjunction with the micro-Raman scattering measurements. The surface morphology of these particles shows that either individual or group of sub-micron alumina particles are coated with the nanocrystalline titania particles. The thickness of the titania coating could be varied by changing the precursor sol concentration. Amorphous titania was converted to anatase phase at 400o C and upon further heating it started transforming to rutile phase, and both these phases coexisted in the coated particles that were heat treated up to 800o C. The mechanical strength of the titania coating was measured qualitatively by ultrasonicating the coated powders for longer duration to observe that titania coatings are strongly adhered with the alumina particles.
INTRODUCTION Coating a ceramic particle with another material can be useful for a number of applications. One such use is to uniformly coat the ceramic particle with organic binder in order to disperse it uniformly into the ceramic matrix.[1]. The other use has been to distribute sintering aid in ceramic matrix, thus bohemite coating is reported to enhance the green state plasticity and sintered density of Si3 N4 ceramics [2]. Coating silica on alumina particles are found not only to improve the sintered density of alumina, but also form mullite, an important high strength ceramic compound [3]. In colloidal processing of ceramic composite the interaction forces can be altered by changing the surface properties of ceramic particles by coating with another ceramic material to achieve hetero-coagulation [4]. Sol-gel processing has been found to be effective in coating the ceramic particle with an amorphous gel coating of another ceramic. Metal alkoxide or salts are used as precursor material to prepare an amorphous gel layer around the ceramic particles [5-6]. The effectiveness of the gel coating on ceramic particles are demonstrated through TEM analysis, however, the nature of these coatings after calcinations have not been studied adequately [5]. In this work we have studied the nature of titania coating on alumina particles by calcining these coated particles in a wide range of temperature (as dried at 80o C to 800o C) in air. Titania coating is expected to enhance the sinterability of alumina and these powders could be used as low loss microwave
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