Agglomerate Formation During Drying

Published

February 1, 2003

Author(s)

A Vertanessian, Andrew J. Allen, M J. Mayo

Abstract

The evolution of agglomerate structure during drying of particles from suspension has been studied for a nanocrystalline Y2O3 (8 mol %)-stabilized ZrO2 powder. Agglomerates in drying and dried suspensions were examined at the smallest size scales (100 nm to 1 mm) using ultra-small angle x-ray scattering (USAXS) and the largest size scales (100 nm to 10mm) using scanning electron microscopy (SEM). The results were correlated with the degree of particle dissolution in each suspension (measured by flame absorption spectroscopy of the suspension filtrate) and the zeta potential of the particles in suspension prior to drying. Results show that large agglomerates readily form across a pH range from 2 to 9. The fact that Y+3 ion dissolution varies by over 4 orders of magnitude in this range leads to the conclusion that there is little correlation between the degree of Y dissolution and agglomeration in this system (Zr ion dissolution was below the detection limit at all pH values studied). Though the size and quantity of agglomerates did not vary appreciably across the pH range, there was a noticeable change in agglomerate morphology as the isoelectric point was approached, at approximately pH 8. Here USAXS shows the particles in suspension to have a layered interior structure, with small primary particles aggregated in sheets to form each blocky particle. This is in contrast to the more rounded agglomerates formed away from the isoelectric point, which appear to be composed of the same primary particles arranged in chain-like structures. Both USAXS and SEM of powders from the dried suspensions confirm that the structures seen after drying are the same as those present in suspension. The two structural morphologies are explained in terms of diffusion-limited versus reaction-limited aggregation, respectively.

Citation

Journal of Materials Research

Volume

18 No. 2

Pub Type

Journals

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Keywords

aggomeration, drying, microstructure characterization, powders, small-angle x-ray scattering, suspensions

Citation

Vertanessian, A. , Allen, A. and Mayo, M. (2003), Agglomerate Formation During Drying, Journal of Materials Research, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=850624 (Accessed December 26, 2024)