Wu, Jin Jwang (1987) Powder synthesis in aerosol reactors. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-06152006-074336
The onset of homogeneous nucleation of new particles from the products of gas phase chemical reactions has been explored using an aerosol flow reactor. Silicon seed particles were used as a probe to study the transition from seed growth by cluster deposition to runaway nucleation. This transition was found to be very abrupt. The mechanism of formation of solid particles from large excesses of low vapor pressure condensible species has been investigated by studying the microstructure of the product aerosol. A discrete - sectional solution of the aerosol general dynamic equation was derived in order to examine the aerosol evolution associated with fast chemical reactions. This kinetic model quantitatively predicts the aforementioned transition. Application of the understanding of aerosol generation and growth has led to the production of a high quality silicon powder suitable for ceramic applications. This powder was synthesized by the pyrolysis of silane in an aerosol reactor and has nearly ideal characteristics, i.e., controlled size distribution, spherically shaped, nonagglomerated submicron particles. A simple reaction coagulation model was developed to facilitate mapping of the nucleation and growth domains. This, in conjuction with the discrete-sectional model, was used to evaluate the various aerosol processes for powder synthesis. The influence of the initial reactant concentration, reaction rate, temperature profile, seed particle conditions, and residence time on the final powder characteristics were examined. The structure of the particles also depends on the way particles fuse together. Particle fusing was therefore, modeled along with the formation and growth processes to study the effects of coalescence on the extent of agglomeration of the product powder. A recipe for the synthesis of ideal powders was proposed.
|Item Type:||Thesis (Dissertation (Ph.D.))|
|Degree Grantor:||California Institute of Technology|
|Division:||Engineering and Applied Science|
|Major Option:||Environmental Science and Engineering|
|Thesis Availability:||Restricted to Caltech community only|
|Defense Date:||1 October 1986|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Imported from ETD-db|
|Deposited On:||29 Jun 2006|
|Last Modified:||26 Dec 2012 02:52|
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