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A small-angle x-ray scattering study of microstructure evolution during sintering of sol-gel-derived porous nanophase titania

Published online by Cambridge University Press:  31 January 2011

Vincent A. Hackley*
Affiliation:
Water Chemistry Program, University of Wisconsin, Madison, Wisconsin 53706
Marc A. Anderson
Affiliation:
Water Chemistry Program, University of Wisconsin, Madison, Wisconsin 53706
Steve Spooner
Affiliation:
Solid State Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831
*
a)Current address: National Institute of Standards and Technology, Ceramics Division, Gaithersburg, Maryland 20899.
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Abstract

The evolution of microstructure as a function of firing temperature in sol-gel derived porous titania xerogels was investigated by small-angle x-ray scattering (SAXS). SAXS curves for xerogels fired below 550 °C exhibit a well-defined structure peak. This peak indicates the presence of a high degree of order in the electron density correlations associated with the interparticle structure factor. Results from electron microscopy and SAXS give a primary particle mean diameter of 50 Å, while scaling analysis of the scattered intensity at large momentum transfer values yields the Porod exponent 4, indicating a sharp transition zone between the solid and void phases. The pore volume fraction of the unfired xerogel is consistent with random close-packing of spheres. The internal surface area decreases almost linearly with increasing firing temperature. Rapid grain growth and pore coarsening begin near 90% of theoretical density, and lead to a breakdown in pore interconnectedness and the development of isolated pores. Observed enhanced sintering properties may be attributed primarily to the large surface-to-mass ratio of the sol-gel particles. The SAXS curves were adequately fit using a bicontinuous phase model developed for late-stage spinodal decomposition structures. Alternatively, the microstructure can be described by a hierarchical close-packing of spheres model. SAXS results are compared with data from gas adsorption and electron microscopy.

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Articles
Copyright
Copyright © Materials Research Society 1992

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