Date of Award

Fall 2007

Document Type

Thesis

Degree Name

Master of Science in Chemical Engineering - (M.S.)

Department

Chemical Engineering

First Advisor

Rajesh N. Dave

Second Advisor

Piero M. Armenante

Third Advisor

Norman W. Loney

Abstract

Mixing of nanoparticles of different compositions offers wide opportunities in manufacturing new nanocomposite materials with unique electronic, optical, mechanical, and chemical properties. However, due to large cohesive forces between nanoparticles, they often form large micron-sized agglomerates, thus losing their main advantage of small size and high surface area. Therefore, breaking of these agglomerates is necessary prior to mixing. One of the techniques to achieve deagglomeration and mixing of nanoparticles is based on rapid depressurization/expansion of supercritical suspensions. where the suspension of initially premixed agglomerates in supercritical CO2 pass through the nozzle undergoing deagglomeration as a result of rapid expansion of CO2 and subsequently passing through a shockwave. This technique requires the agglomerates of different constituents to be premixed before passing through the nozzle, and this can achieved in a stirred tank. Study of the stirred mixing of nanoparticles in supercritical CO2 is the main goal of this work. Binary suspension of silica/alumina and silica/titania powders with the average primary particle sizes 16 nm (silica). 13 nm (alumina), and 21 nm (titania) was mixed in a 300 ml pressurized stirred tank at 45°C, both in supercritical and gaseous CO2. The obtained nanopowder mixture was pressed into a pellet. Mixture homogeneity was determined by means of composition variance analysis of the surface of the pellet using energy-dispersive spectroscopy (EDS). Effect of pressure in the range of 400 to 2000 psi, mixing time, and mixing speed on mixture homogeneity was studied.

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