Orientador: Miguel Jafelicci Junior / Banca: Hercílio Rodolfo Rechenberg / Banca: Luiz Antonio Andrade De Oliveira / Banca: Paulo César De Morais / Banca: Younès Messaddeq / Resumo: Neste trabalho, nanopartículas metálicas (NPM) aciculares e monodispersas de FeCo, FeTR (TR = Nd, Eu, Sm e Tb) e FeCoTR (TR = La-Tb), com ~60 nm de comprimento, razão axial de ~6 e estáveis frente à oxidação e sinterização foram obtidas pela redução em atmosfera de hidrogênio de NP de goetita contendo Co ou Co/TR e recobertas com alumina. O precursor na forma de NP de goetita monodispersas (60±5 nm de comprimento e razão axial de ~6) foi obtido por uma nova rota sintética baseado na hidrólise alcalina de íons Fe(III) em solução na presença de íons carbonato em três estágios: (i) formação de ferrihidrita, (ii) dissolução da ferrihidrita e nucleação de goetita, e (iii) crescimento dos núcleos de goetita. Duas temperaturas distintas foram utilizadas para a nucleação e o crescimento das partículas de goetita e o mecanismo de formação das NP monodispersas de goetita pode ser proposto. NP aciculares e monodispersas de hematita (210±20 nm de comprimento e razão axial de ~5) também foram sintetizadas por reações de hidrólise ácida forçada, e o mecanismo de transformação de -Fe2O3 a -Fe foi avaliado. NP de hematita foram recobertas com agentes antisinterizantes (sílica ou alumina), reduzidas a metal em atmosfera de hidrogênio (450 °C/12 h) e passivadas utilizando uma nova metodologia de passivação: uma mistura de vapores de etanol e gás nitrogênio passada pela amostra durante 15-20 min (processo comercial: nitrogênio:oxigênio (1:1) durante 4-6 h). NP recobertas com sílica apresentaram pequenas partículas esféricas metálicas encapsuladas em um molde acicular de sílica, conduzindo a perda da forma elipsoidal da fase metálica. NP recobertas com alumina resultaram em partículas aciculares metálicas recobertas com uma fina camada do agente anti-sinterizante (alumina) e estabilizadas pela formação ...(Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Acicular monodispersed, metallic nanoparticles (MNP) of FeCo, FeRE (RE = Nd, Eu, Sm and Tb) and FeCoRE (RE = La-Tb), ~60 nm in the length and axial ratio ~6, stabilized against oxidation and sintering, obtained by reduction of alumina-coated goethite NP containing either Co or Co/RE under hydrogen flow were reported. Monodispersed goethite NP precursor (60±5 nm in length, axial ratio ~6) was obtained by a new synthetic route based on the hydrolysis of alkaline Fe(III) solutions in the presence of carbonate ions by a three step-procedure: (i) ferrihydrite formation, (ii) ferrihydrite dissolution and goethite nucleation, and (iii) goethite nuclei growth. Two different temperatures to promote goethite nucleation and growth were used and the formation mechanism of monodispersed goethite NP was proposed. Monodispersed and acicular hematite NP (210±20 nm in length, axial ratio ~5) were also synthesized by forced acid hydrolysis reaction, and the transformation mechanism from -Fe2O3 to -Fe was evaluated. Hematite was covered with anti-sintering agents (silica or alumina), reduced to metal in hydrogen atmosphere (450 °C/12 h) and passivated using a new methodology: ethanol vapors and nitrogen gas mixture for 15-20 min (commercial procedure: nitrogen:oxygen (1:1) gas mixture for 4-6 h). Silica-coated NP showed small metallic spherical particles encapsulated in an acicular silica template, leading to ellipsoidal-shape metallic phase loss. Alumina-coated particle showed an acicular metallic particle with thin layer anti-sintering alumina agent stabilized by maghemite thin layer on particle surface. The influence of the temperature, hydrogen flows and reduction time on the magnetic properties, crystallite size, crystallographic structure and phases were also investigated. A topotatic ...(Complete abstract, click electronic access below) / Doutor

Thesis (Ph. D.)--Florida State University, 2003. / Advisor: Dr. L.P. Gorʹkov, Florida State University, Dept. of Physics. Title and description from dissertation home page (viewed Nov. 24, 2003). Includes bibliographical references.

No description available.

No description available.

Thesis (Master)--İzmir Institute of Technology, İzmir, 2006. / Keywords: Magnetic materials, structural properties, spintronics, magnetic multilayers. Includes bibliographical references (leaves 57-61).

I performed first principles studies of the site occupancy and magnetic properties of zinc-tin-substituted strontium hexaferrite by using density functional theory. In this study, I determined the site preference of zinc and tin atoms when they are restricted to occupy the same sublattice in strontium-hexaferrite. I found that Zn and Sn atoms prefer to replace Fe ions at 2a sublattice under this restriction and caused the saturation magnetization to decrease.

published_or_final_version / abstract / toc / Physics / Master / Master of Philosophy

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A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science WITS University, Johannesburg, 2013 / Occurring parallel to the developments in imprinting technology are magnetic materials which are being applied increasingly in environmental remediation, medicine, biotechnology and many other fields. Combining the imprinting effects of the polymer and nano magnetic particles yields composite materials which are both selective to the template and magneto responsive for easy polymer removal from aqueous solutions. In this study, magnetic ion imprinted polymers with high recognition for uranyl ion (UO2 2+) in the presence of competing ions were synthesized by bulk and precipitation polymerizations. The uranyl template was removed from the magnetic polymer matric by 1M HCl and 1M NaHCO3 leachants to form cavities which were complimentary in shape and size to the template. Full characterization of the magnetite and magnetic polymers was achieved by use of the following characterization techniques: Raman spectroscopy (RS), Transmission electron microscopy (TEM), Energy dispersive spectrometry (EDS), Powder X-ray diffraction (PXRD) analysis, Brunauer, Emmett and Teller (BET) analysis, Ultraviolet visible (UV-vis) spectroscopy, Fourier-transform infrared (FTIR), Thermo-gravimetric analysis (TGA), Carbon, hydrogen, nitrogen and sulphur (CHNS) analysis, Diffuse reflectance spectroscopy (DRS) and Atomic force microscopy (AFM). Parameters which were optimized included sample pH, which gave an optimum value of 4. Magnetic IIP and NIP amounts which gave maximum adsorption capacities were found to be 50 mg for both of these adsorbents. The optimum contact time was found to be 45 minutes. The performance of all magnetic ion imprinted polymers (IIPs) was expectedly superior to that of the corresponding non imprinted polymers (NIPs) in all adsorption studies. The first rate constant (k1) and correlation coefficient (R2) values evaluated for the pseudo first order were found to be between 0.048-0.093 min-1 and 0.602-0.991 min-1, respectively. For the pseudo second order, second rate constant (k2) and correlation coefficient (R2) were found to be between 0.273- 0.678 and 0.9811-0.9992, respectively. The selectivity order observed was as follows: UO2 2+ > Fe3+ > Pb2+ > Ni2+ > Mg2+. The magnetic polymers selective to Cr(VI) were also synthesized and were leached with HCl to remove the template. The synthesized Cr(VI) magnetic polymers, the optimum pH obtained was 4 for both the magnetic IIP and the corresponding NIP. The amount of the adsorbent which gave the maximum adsorption was determined to be 20 and 65 mg for the magnetic IIP and NIP, respectively. A Cr(VI) concentration which was adsorbed maximally was from 5 mg L-1 which was therefore taken as the optimum. The maximum adsorption capacities for the magnetic polymers were 6.20 and 1.87 mg g-1 for the magnetic IIP and NIP, respectively. The optimum time for the adsorption of the Cr(VI) analyte was determined as 40 minutes. Investigation of the order of selectivity of anions followed the trend: Cr2O7 2- SO4 2- F- NO3- -.