Morphological Characterization of Fumed Silica Aggregates

Abstract

Transmission electron microscopy has been used to evaluate the primary particle size distributions and aggregate structure of a fumed silica sample. The primary particle size distribution within an individual aggregate is narrow, with a geometric standard deviation of ∼ 1.2. The distributions of maximum diameters, projected areas, and average primary particle diameters were all skewed, and all were better described by a log-normal distribution than a normal distribution. The data confirmed the fractal description of the fumed silica aggregate structure, with a mass fractal dimension of 1.86. The fractal prefactor or lacunarity was evaluated from the aggregate volume and the maximum particle dimension, and found to have a value of 0.83 for this sample.

The assistance of Dr. Changhui Lei and Dr. J.G. Wen in acquiring the images is gratefully acknowledged. Portions of this work were carried out at the Center for Microanalysis of Materials, University of Illinois, which is partially supported by the U.S. Department of Energy under grant DEFG02-91-ER45439. Valuable discussions with Dr. John Parker, Dr. Edward Remsen, Dr. Michael Zimmerman, Mr. Anthony Shaw, and Mr. Thomas Weaver are gratefully acknowledged. The author appreciates permission of Cabot Microelectronics Corporation to publish this work.