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Z7.12.1

Synthesis of TiO2 Nanoparticles Using Chemical Vapor Condensation Jie Wu1, Guo-Ren Bai1, Jeffrey A. Eastman1, Guangwen Zhou1, Vijay K. Vasudevan2 Materials Science Division, Argonne National Laboratory Argonne, IL 60439, U.S.A. 2 Department of Chemical and Engineering, University of Cincinnati Cincinnati, OH 45221, U.S.A.

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ABSTRACT Nano-sized TiO2 particles are of interest for many applications, including use as photocatalysts and in heat transfer fluids (nanofluids). In the present study, TiO2 nanoparticles with controllable phase and particle size have been obtained through homogeneous gas-phase nucleation using chemical vapor condensation (CVC). The phase and particle size of TiO2 nanoparticles under various processing conditions have been characterized using x-ray diffraction and transmission electron microscopy. Chamber temperature and pressure were found to be two key parameters affecting particle phase and size. Pure anatase phase was observed for synthesis temperatures as low as 600 °C with chamber pressure varying from 20-50 Torr. When the furnace temperature was increased to 1000 °C at a pressure of 50 Torr, a mixture of anatase and rutile phases was observed, with the predominant phase being anatase. The average particle size under all the experimental conditions was observed to be less than 20 nm. INTRODUCTION TiO2 is widely used in many diverse applications, including photocatalysis, paint, and electronics, and heat transfer fluids. A nanocrystalline microstructure is desirable in many of these applications. For example, nano-sized TiO2 particles exhibit unique photophysical and photocatalytic properties compared with bulk TiO2 [1, 2]; the sintering temperature of nanocrystalline TiO2 is much lower than that of micron-sized TiO2; nanofluids containing TiO2 nanoparticles are expected to have much higher thermal conductivity than that of the base fluids, leading to enhanced heat transport efficiency in heat transfer fluids[3, 4]. Many nanoparticle synthesis routes have been explored so far [5, 6], among which gas-phase synthesis techniques possess advantages including high purity, good size controllability and low cost. In the present study, chemical vapor synthesis (so-called chemical vapor condensation or CVC) of TiO2 nanoparticles based on homogeneous gas-phase nucleation has been carried out. In this method, small clusters (monomers) form by decomposition of a metal-organic precursor. These monomers then aggregate to form larger clusters, i.e., nanoparticles. Condensation of the particles occurs when the vapor is supersaturated. Similar procedures have been used in the past by others to produce powders or porous coatings [7, 8]. In the present study, the process was modified to allow dispersion of the nanoparticles into fluids. Observations of the thermal conductivity behavior of these nanofluids will be reported elsewhere [9]. Operation parameters affecting the particle phase and size have been investigated in this study. As will be demonstrated, the CVC process is found to be ideal for p