Publication:
Polyol synthesis and characterization of magnetic nanocrystalline cobalt and cobalt platinum
Polyol synthesis and characterization of magnetic nanocrystalline cobalt and cobalt platinum
Authors
Chávarri-Pajares, Erick E.
Embargoed Until
Advisor
Perales-Pérez, Oscar J.
College
College of Engineering
Department
Department of Mechanical Engineering
Degree Level
M.S.
Publisher
Date
2007
Abstract
The present work addresses the systematic study of the synthesis and characterization of
cobalt nanoparticles produced in polyol solutions. The kinetics of the metal forming
reaction strongly influenced the stability conditions of cobalt phases. The control of the
reaction kinetics was achieved through a suitable selection of the solution chemistry in
the Polyol–Co (II) system. The addition of hydroxyl ions into the cobalt polyol solution
under boiling conditions not only accelerated the formation of the magnetic phase but
also affected the stability conditions of the metallic precipitate. Depending on the OH-
/Co
mole ratio and the type of cobalt salt, hexagonal close packed (hcp), face centered cubic
(fcc), and metastable pseudo-cubic epsilon cobalt (ε-Co) phases were formed. Highly
monodisperse ε-Co nanoparticles were produced when cobalt acetyl-acetonate salt was
used instead of the acetate alone. Furthermore, the presence of Pt ions –added to promote
heterogeneous nucleation- caused a dramatic shortening of the time required for the
complete formation of the magnetic phase. The shortening in reaction time was
conducive to the formation of the ordered face centered tetragonal (fct)-CoPt
nanoparticles although co-existing with fcc and ε-Co structures. Excess of platinum was
present as fcc-Pt. The room-temperature saturation magnetization (Ms) and coercivity (Hc)
of the nanocrystalline cobalt powders ranged from 80 to 110 emu/g and 101 to 211 Oe,
respectively. The coercivity was as high as 248 Oe when CoPt was present. The coexistence
of Pt ions in starting solutions not only promoted the nucleation rate and accelerated the cobalt reduction but also induced the formation of ordered fct-CoPt nanocrystals at low temperature (487 K).
Keywords
synthesis and characterization
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Cite
Chávarri-Pajares, E. E. (2007). Polyol synthesis and characterization of magnetic nanocrystalline cobalt and cobalt platinum [Thesis]. Retrieved from https://hdl.handle.net/20.500.11801/707