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42625-AC10
Size Selection and Structure of Cuboctahedrally Faceted NiFe2O4 and (Ni,Zn)Fe2O4 Nanoparticles
Personnel and Expenditures
During the period between September 1, 2006 and August 31, 2007 ACS funds were expended to support the PI Michael McHenry. Ashfaque Habib (CMU) continued research on nanoparticles with internal CMU funding through the Institute for Complex Engineered Systems (ICES) and the ACS. Funds were expended to upgrade the RF plasma torch for further nanoparticle synthesis, as part of the training of graduate students Kelsey Miller (CMU) and Ashfaque Habib (CMU). This was accomplished during the Spring of 2007. Undergraduates Kelly Collier (CMU) and Kristina Breuer (Florida State Univ.) worked on the project during the Summer of 2007 through funding by the CMU Materials Research Science and Engineering Center (MRSEC) summer REU program. They continued work on facetted particles through the investigation of the structure and morphology of FeCo/Co-Ferrite core shell nanoparticles. Kristina won third prize and Kelly won honorable mention for their presentations of their summer research in the NSF REU symposium. Undergraduates Courtney Ondeck and Matt Ondeck worked on RF heating and EMI absorption of faceted magnetic nanoparticles, respectively.
Research Output
The work on (Ni,Zn)Fe2O4 nanoparticles was ostensibly completed with the publication of our article in Advances in Science and Technology. We have continued work aimed at elucidating the role of oxide thickness on determining the facet crystallography in metal/oxide nanoparticles produced by RF plasma torch synthesis. This work involved investigation of the oxidation of FeCo nanoparticles produced by RF plasma torch synthesis. These particles are more noble and as synthesized have a protective, adherent Co-ferrite coating. We have investigated the orientation relationships between the oxide shell and metal core. We have also performed high temperature oxidation experiments for which we are able to vary the thickness of the oxide shell and eventually produce Co-ferrite nanoparticles. This effectively reproduces the oxidation process that is achieved in one step in the plasma torch for our Ni- and (Ni,Zn)-ferrite nanoparticles. We plan on publishing this initial work in 2008 and use this as the subject of future proposed work.
CMU undergraduate Amber Fuller, returned from a summer REU program at the Naval Research Laboratory where she continued a project on sintering of (Ni,Zn)Fe2O4 nanoparticles. These sintered compacts were used to extend the understanding of the densification mechanisms of faceted nanoparticles and the phase and microstructural evolution of the same. Amber is a minority student who is (Fall 2006) funded by the ACS project. She reported on her work at the 2007 CMU Meeting of the Minds undergraduate research symposium.
A Materials Science and Engineering and subsequent Biomedical Engineering Capstone Design Project was used to leverage funds. This project investigated the functionalization of FeCo/Co-Ferrite core shell nanoparticles for use in ferrofluids for biomedical applications. The epitaxy of the ferrite with FeCo and the resulting exposed surfaces of the ferrite shells were examined by TEM. This work is considered publishable and a manuscript is in preparation.
While ferrite nanoparticles are most commonly used in RF heating applications, our group has predicted that FeCo nanoparticles would offer a great improvement in heating of ferrofluids. Ferrofluids are widely studied by the Petroleum industry with the author of the famous text Ferrohydrodynamics, R.E. Rosensweig, a distinguished researcher at Exxon Laboratories. FeCo alloys possess the highest saturation magnetization, which translates to higher heating rates. Since FeCo nanoparticles naturally form stable, protective cobalt-ferrite shell improving their biocompatibility, the FeCo system could also be a component of a biocompatible solution to several interesting biomedical applications. For these and other ubiquitous applications in RF heating it is important to understand the faceting and core shell morphologies.
We have thus initiated studies of the oxidation of plasma torch synthesized FeCo anoparticles to elucidate the faceting and interfacial crystallography in FeCo/Co-ferrite nanocomposites. This was an investigation not possible in the Ni- and (Ni,Zn)-ferrite system as the oxidation rates are too high and the as plasma torch synthesized nanoparticles are always completely oxidized. This new aspect of our work has allowed us to tailor the oxide thickness and thus continuously vary the oxide/metal ratio in the nanoparticles. The particles, like (Ni,Zn)Fe2O4 nanoparticles, are also faceted and the role of the oxide on faceting is an important new area of inquiry which will be pursued further in subsequent work.
