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dc.contributor.advisorPerales Pérez, Oscar
dc.contributor.authorChávarri Pajares, Erick Edgardo
dc.date.accessioned2018-06-03T23:20:51Z
dc.date.available2018-06-03T23:20:51Z
dc.date.issued2007
dc.identifier.urihttp://hdl.handle.net/20.500.11801/707
dc.description.abstractThe 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).en_US
dc.description.sponsorshipNational Science Foundation under Grant No. 0351449 and NSF-Start Up Program.en_US
dc.language.isoenen_US
dc.subjectsynthesis and characterizationen_US
dc.subject.lcshCobalt--Synthesis.en_US
dc.subject.lcshNanocrystals--Synthesis.en_US
dc.subject.lcshNanoparticles.en_US
dc.subject.lcshMagnetism.en_US
dc.subject.lcshPolyols.en_US
dc.subject.lcshNanostructured materials--Magnetic properties.en_US
dc.titlePolyol synthesis and characterization of magnetic nanocrystalline cobalt and cobalt platinumen_US
dc.rights.licenseAll rights reserveden_US
dc.rights.holder(c) 2007 Erick E. Chávarri Pajaresen_US
dc.contributor.committeeGutiérrez, Gustavo
dc.contributor.committeeSundaram, Paul A.
dc.contributor.representativeRinaldi, Carlos
thesis.degree.levelM.S.en_US
thesis.degree.disciplineMechanical Engineeringen_US
dc.type.thesisThesisen_US
dc.contributor.collegeCollege of Engineeringen_US
dc.contributor.departmentDepartment of Mechanical Engineeringen_US
dc.description.graduationYear2007en_US


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  • Theses & Dissertations
    Items included under this collection are theses, dissertations, and project reports submitted as a requirement for completing a degree at UPR-Mayagüez.

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