title: Aggregate Morphology Evolution by Sintering: Number & Diameter of Primary Particles.
abstract: The structure of fractal-like agglomerates (physically-bonded) and aggregates (chemically- or sinter-bonded) is important in aerosol synthesis of nanoparticles, and in monitoring combustion emissions and atmospheric particles. It influences also particle mobility, scattering, and eventually performance of nanocomposites, suspensions and devices made with such particles. Here, aggregate sintering by viscous flow of amorphous materials (silica, polymers) and grain boundary diffusion of crystalline ceramics (titania, alumina) or metals (Ni, Fe, Ag etc.) is investigated. A scaling law is found between average aggregate projected area and equivalent number of constituent primary particles during sintering: from fractal-like agglomerates to aggregates and eventually compact particles (e.g. spheres). This is essentially a relation independent of time, material properties and sintering mechanisms. It is used to estimate the equivalent primary particle diameter and number in aggregates. The evolution of aggregate morphology or structure is quantified by the effective fractal dimension (Df) and mass-mobility exponent (Dfm) and the corresponding prefactors. TheDfmincreases monotonically during sintering converging to 3 for a compact particle. ThereforeDfmand its prefactor could be used to gauge the degree or extent of sintering of agglomerates made by a known collision mechanism. This analysis is exemplified by comparison to experiments of silver nanoparticle aggregates sintered at different temperatures in an electric tube furnace.
authors: Particle Technology Laboratory, Institute of Process Engineering, Department of Mechanical and Process Engineering, ETH Zurich, Sonneggstrasse 3, CH-8092 Zürich, Switzerland.
authors: Max L
authors: ML
authors: Eggersdorfer
authors: Dirk
authors: D
authors: Kadau
authors: Hans J
authors: HJ
authors: Herrmann
authors: Sotiris E
authors: SE
authors: Pratsinis
keywords: Aggregate; fractal dimension; grain boundary diffusion; mass-mobility exponent; primary particle size
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