Powder production in aerosol reactors : particle structure and reactor optimization

Citation

Nguyen, Hung Viet (1990) Powder production in aerosol reactors : particle structure and reactor optimization. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/qk6a-e067. https://resolver.caltech.edu/CaltechETD:etd-03122007-105616

Abstract

Powders consisting of dense, nonagglomerated, roughly spherical particles with a controlled size distribution are thought to be ideal for engineering applications of ceramic materials. The production of such powders in aerosol reactors is difficult due to the extreme difficulty of controlling particle formation by homogeneous nucleation of condensible vapors produced by gas phase chemical reactions. To generate the quality of powders necessary for engineering applications, one needs to understand the processes governing particle formation and growth in aerosol reactors.

Homogeneous and heterogeneous nucleation were studied in a laminar flow aerosol generator using dibutylphthalate vapor. Seed particles were found to suppress homogeneous nucleation to an extent depending on their concentration. With additional insights on nucleation and nucleation suppression, aerosol physics was applied to an effort to generate dense, spherical silicon particles in a single stage multi-zone externally heated aerosol reactor. Subsequent experiments revealed that the dense silicon particles generated resulted from the sintering of aggregates formed by coagulation of like-sized particles. While the production of dense particles by sintering of low density agglomerates are feasible for low melting materials, it is not practical for refractory materials due to the high sintering temperatures required for complete coalescence in the available residence time. To produce ideal refractory powder materials, growth must be limited to vapor and small cluster deposition. An optimization technique was applied to the highly nonlinear aerosol reactor system to directly derive optimal temperature profiles that maximizes seed growth while minimizing the amount of fine particles formed.

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