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High concentration agglomerate dynamics at high temperatures
1Particle Technology Laboratory, Institute of Process Engineering, Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zürich, Switzerland.
Langmuir : the ACS Journal of Surfaces and Colloids
|November 17, 2006
Summary
High concentrations in aerosol manufacturing significantly impact soft-agglomerate dynamics, leading to gelation. Primary particle size is unaffected, but agglomerate structure and volume fraction are dominated by these conditions.
Area of Science:
- Aerosol science and particle technology
- Chemical engineering
- Materials science
Background:
- Industrial production of fine particles often involves high solids concentrations.
- Understanding aerosol dynamics at these concentrations is crucial for controlling product characteristics.
- Existing models like Smoluchowski theory have limitations in describing agglomeration under such conditions.
Purpose of the Study:
- To investigate the dynamics of agglomerate aerosols at high solids concentrations typical in industrial fine particle manufacturing.
- To simulate the formation and growth of fumed silica under nonisothermal conditions.
- To compare simulation results with experimental data and commercial product specifications.
Main Methods:
- Simulation of fumed silica formation and growth using recent chemical kinetics for SiCl4 hydrolysis.
- Nonisothermal modeling of aerosol dynamics, considering chemical reaction, coagulation, and sintering.
- Neglecting aerosol polydispersity to focus on agglomerate evolution (primary particle diameter, SSA, hard- and soft-agglomerates, effective volume fraction).
Main Results:
- High solids concentrations minimally affect primary particle diameter and specific surface area (SSA).
- These concentrations significantly influence soft-agglomerate diameter, structure, and volume fraction.
- Simulations predict gelation, consistent with experimental observations at high concentrations.
Conclusions:
- Classic Smoluchowski theory is inadequate for describing soft-agglomerate Brownian coagulation at high solids concentrations.
- Restructuring and fragmentation are critical factors influencing product characteristics during high-temperature synthesis of nanostructured particles at high concentrations.
- The study highlights the importance of considering agglomerate dynamics for optimizing industrial aerosol processes.
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