Degree Type

Thesis

Date of Award

2010

Degree Name

Master of Science

Department

Physics and Astronomy

First Advisor

Ruslan Prozorov

Abstract

The purpose of this study is to demonstrate the capability of a single process, heterogenous sonochemistry, as a tool to produce two very different nanocomposites with tunable properties: a superconductor, MgB2 with nano-inclusions, and iron/iron oxide (Fe/Fe2O3) in an alumina (Al2O3) matrix. By modifying the sonochemical parameters, one is able to tune the magnetic properties and enhance the superconducting properties of MgB2 and the superparamagnetic (SPM) properties of the Fe/Al2O3 system. This tuning is done through the ability of sonochemical irradiation, “)))” or the exposure to high intensity ultrasound (HIU), to produce extreme environments where chemical and physical processes can occur due to acoustic cavitation. ))) has been shown to reduce particle size, increase reactivity, act as a catalyst, and improve powder homogeneity. These are the effects of ))) which are exploited in this study.

For the MgB2 study, B powder (both with and without dopants/inclusions) is exposed to HIU in a decane solution before reaction with Mg to form MgB2 nanocomposites. MgB2 is produced by encapsulation of stoichiometric amounts of B and Mg in a Ta pouch, which is then reacted and pressed using hot isostatic press (HIP). The result is a dense MgB2 pellet that is then cut, polished, and measured using a SQUID MPMS magnetometer. Critical current, Jc, values are calculated using the Bean critical state and compared at 25K and 30K. Samples, post-))), show an increase in grain connectivity, as seen by SEM, leading to an enhancement of Jc.

The SPM study utilized ))) to create SPM nanocomposites through the irradiation with HIU of the carrier matrix material, Al2O3 in the presence of a volatile organometallic precursor, Fe(CO)5. ))) results in nanosized Fe and Fe2O3 being uniformly dispersed throughout the Al2O3 matrix. Magnetic properties of these materials are measured using the SQUID MPMS magnetometer and the nanosized Fe and Fe2O3 can be seen in SEM images. Analysis of the data shows a SPM component and a general trend of the data with the adjustment of slurry loading, V% of sample to medium, and mass percentage, M% of Fe to Fe+Al2O3. The trends suggest that an increase in M% results in an increased number of SPM particles, but the V% has a optimized value where the magnetization peaks, corresponding to a peak in the moment per SPM particle.

Copyright Owner

Brett Alan Mccarty

Language

en

Date Available

2012-04-30

File Format

application/pdf

File Size

97 pages

Included in

Physics Commons

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