Examinando por Materia "Magnetite"
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Ítem Dipolar interactions among magnetic dipoles of iron oxide particles dispersed in mili-size hydrogel beads(Elsevier B.V., 2020-01-01) Actis, D.G.; Muñoz Medina, G.A.; Velásquez, A.A.; Pereda, C.; Sanchez, L.M.; Alvarez, V.A.; Muñetón Arboleda, D.; Mendoza Zélis, P.; Sánchez, F.H.; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)The recently published Mean Field Interacting Superparamagnet Model (MFISP model), which introduces the effective demagnetizing factor NE, is tested in specimens having a random-like spatial distribution of magnetic nanoparticles, where different hierarchies of clustering are present. These specimens are ferrogel PVA/iron oxide beads synthesized by a one-pot route, having spheroidal shapes and sizes of about 1 mm, and chain and disk-like arrays (superstructures) of beads. Raman analyses indicated that magnetic nanoparticles are composed by a mixture of magnetite and maghemite. Beads swell 208% by hydration in about 40 min. The increase of the ac susceptibility as a function of hydration time closely reflects the effect of bead swelling, in agreement with the expected diminution of dipole–dipole interactions. Measured susceptibility is analyzed in terms of the susceptibility ? of non-interacting particles and the effective demagnetizing factor NE of the specimen, which depends on swelling. The Specific Absorption Rate of electromagnetic power by the beads grows with the hydration time in agreement with ac susceptibility behavior. For long hydration times susceptibility and high field magnetization decrease. This is explained by the occurrence of oxidation of magnetite/maghemite to hematite. Isothermal magnetization experiments are performed on each superstructure in two perpendicular principal directions each. Results are consistently described with the MFISP model by considering two hierarchies of clustering: beads themselves and clusters within the beads. From the whole set of experiments, it is possible to estimate values for the volume fractions of particles in clusters and clusters in beads, given by xpc=0.46(15) and xcb=0.16(5). The susceptibility of non-interacting particles, ?=13(4), is also obtained, which results about five times larger than the measured (apparent) one. The MFISP model proves to be a convenient and efficient tool for the analysis of magnetization studies of complex 3d dispersions of magnetic nanoparticles, allowing an experimental determination of relevant physical information, otherwise not accessible by magnetic measurements. © 2020 Elsevier B.V.Ítem Green synthesis of magnetic nanoparticles using leaf extracts of Aloe vera and Kalanchoe daigremontiana to remove divalent mercury from natural waters(IOP PUBLISHING LTD, 2019-01-01) Morales G.; Campillo G.; Vélez E.; Osorio J.; Urquijo J.; Velásquez Á.A.; Morales G.; Campillo G.; Vélez E.; Osorio J.; Urquijo J.; Velásquez Á.A.; Universidad EAFIT. Departamento de Ciencias; Electromagnetismo Aplicado (Gema)In this study, magnetic nanoparticles of magnetite were prepared by an eco-friendly method using aqueous leaf extracts of Aloe vera and Kalanchoe daigremontiana. These vegetal extracts have suitable characteristics such as high availability, low cost, and serve as good colloidal stabilizers. Synthetized products were characterized by Transmission Electron Microscopy (TEM), Room Temperature Mossbauer Spectroscopy (RT-MS), and their potential use as adsorbents for Hg (II) removal in natural waters was evaluated by Atomic Absorption Spectroscopy (AAS). Size distribution and morphology of the products obtained by TEM show spherical nanoparticles composites, with sizes between 3 and 10 nm for both extracts. Mossbauer spectra are consistent with superparamagnetic particles for both samples. Moreover, particles from both extracts showed mercury removal efficiencies above 75%. © Published under licence by IOP Publishing Ltd.Ítem Growth and characterization of magnetite-maghemite thin films by the dip coating method(SPRINGER, 2017-03-07) Velásquez, A.A.; Arnedo, A.; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)We present the process of growth and characterization of magnetite-maghemite thin films obtained by the dip coating method. The thin films were deposited on glass substrates, using a ferrofluid of nanostructured magnetite-maghemite particles as precursor solution. During the growth of the films the following parameters were controlled: number of dips of the substrates, dip velocity of the substrates and drying times. The films were characterized by Atomic Force Microscopy, Scanning Elelectron Microscopy, four-point method for resistance measurement, Room Temperature Mössbauer Spectroscopy and Hall effect. Mössbauer measurements showed the presence of a sextet attributed to maghemite (?-Fe2O3) and two doublets attributed to superparamagnetic magnetite (Fe3O4), indicating a distribution of oxidation states of the iron as well as a particle size distribution of the magnetic phases in the films. Atomic force microscopy measurements showed that the films cover quasi uniformly the substrates, existing in them some pores with sub-micron size. Scanning Electron Microscopy measurements showed a uniform structure in the films, with spherical particles with size around 10 nm. Voltage versus current measurements showed an ohmic response of the films for currents between 0 and 100 nA. On the other hand, Hall effect measurements showed a nonlinear response of the Hall voltage with the magnetic flux density applied perpendicular to the plane of the films, however the response is fairly linear for magnetic flux densities between 0.15 and 0.35 T approximately. The results suggest that the films are promising for application as magnetic flux density sensors. © 2017, Springer International Publishing Switzerland.Ítem Growth of magnetite films by a hydrogel method(Elsevier B.V., 2017-06-15) Velásquez, A.A.; Marín, C.C.; Urquijo, J.P.; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)Magnetite (Fe3O4) films were grown on glass substrates by formation and condensation of complex of iron oxides in an agarose hydrogel. The obtained films were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), Room Temperature Mössbauer Spectroscopy (TMS), Vibrating Sample Magnetometry (VSM), Atomic Force Microscopy (AFM) and Voltage vs. Current measurements by the four-point method. FTIR and TGA measurements showed that some polymer chains of agarose remain linked to the surface of the magnetic particles of the films after heat treatment. SEM measurements showed that the films are composed by quasi spherical particles with sizes around 55 nm. Mössbauer spectroscopy measurements showed two sextets with broaden lines, which were assigned to magnetite with a distributed particle size, and two doublets, which were assigned to superparamagnetic phases of magnetite. For the specific dimensions of the films prepared, measurements of Voltage vs. Current showed an ohmic behavior for currents between 0 and 200 nA, with a resistance of 355 kO. © 2017 Elsevier B.V.Ítem Preliminary geochemical study of thermal waters at the Puracé volcano system (South Western Colombia): An approximation for geothermal exploration(Universidad Industrial de Santander, 2018-01-01) Gómez-Díaz E.; Marin-Cerón M.I.; Gómez-Díaz E.; Marin-Cerón M.I.; Universidad EAFIT. Departamento de Ciencias; Geología Ambiental y TectónicaThe Puracé Volcano is located in the Cauca department, SW of Colombia, along the Coconucos volcanic chain. This volcano is an interesting target for geothermal exploration, because it is a young caldera-type volcano, with thermal activity (e.g. hot springs and fumaroles). Using hydro-geochemical analyses of hot springs, we determine the type of water, origin and relation with the geothermal system, reservoir temperature, mixing process and finally the potential areas for future exploration. The analyzed water-types are bicarbonate, dilutechloride, sulphate-chloride, acid-sulphate and heated steam-acid sulfated. The conservative elements, allow to identify the correlation between different springs and to infer commune sources. Moreover, the applied solutes geothermometers for each suitable thermal-water group were used to estimate the reservoir temperature. The Silica geothermometers resulted within a range of 120°C -170°C while those the Cation geothermometers are above these temperatures reflecting values from 160°C to 220°C. However, the Cation geothermometer of low temperature clearly identify another zone of lower temperature. Mixing and recharge processes, were identified through of stable isotopes. Finally, the preliminary geothermal model shows two zones of high enthalpy system ( > 150°C). © 2018, Boletín de Geología.Ítem Síntesis y caracterización de nanocompositos obtenidos a base de nanopartículas de magnetita-maghemita recubiertas con un polímero biocompatible(Universidad EAFIT, 2024) Páez Pinzón, Johan Sebastián; Velásquez Torres, Álvaro Andrés; Gómez Ramírez, Luis Alejandro; Urquijo Morales, Jeaneth PatriciaÍtem Synthesis and characterization of Cu2+ substituted magnetite(SPRINGER, 2011-11-01) Morales, A. L.; Velasquez, A. A.; Urquijo, J. P.; Baggio, E.; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)Samples of magnetite, both pure and doped with divalent copper, Fe3-xCuxO4, with x = 0, 0.05, 0.10 and 0.20 atm.%, were synthesized hydrothermally. The samples were characterized by Atomic Absorption Spectroscopy, Mössbauer Spectroscopy, X-ray diffraction, Scanning Electron Microscopy and SQUID magnetometry. The analyses made by the above techniques showed that as the Cu2+ concentration increases, a simultaneous reduction in the magnetic and structural parameters takes place, namely: magnetic hyperfine interactions at octahedral sites, particle size and lattice constant. Degradation in the particles morphology as well as a distribution of their size were also observed. Our study points two important effects of Cu2+ in magnetite, the first one is its incorporation within the structure, replacing Fe2+ ions and decreasing both the magnetic hyperfine interactions at octahedral sites and the bulk magnetization, the second one is the contraction of the crystalline lattice of magnetite, because incorporation of Cu2+ within the structure, generation of vacancies or both simultaneous effects. © 2011 Springer Science+Business Media B.V.Ítem Synthesis and characterization of magnetite-maghemite nanoparticles obtained by the high-energy ball milling method(Springer Netherlands, 2018-03-13) Velásquez, A. A.; Marín, C; Urquijo, P; Universidad EAFIT. Departamento de Ciencias Básicas; Electromagnetismo Aplicado (Gema)We present the process of synthesis and characterization of magnetite-maghemite nanoparticles by the ball milling method. The particles were synthesized in a planetary ball mill equipped with vials and balls of tempered steel, employing dry and wet conditions. For dry milling, we employed microstructured analytical-grade hematite (a-Fe2O3), while for wet milling, we mixed hematite and deionized water. Milling products were characterized by X-ray diffraction, transmission electron microscopy, room temperature Mössbauer spectroscopy, vibrating sample magnetometry, and atomic absorption spectroscopy. The Mössbauer spectrum of the dry milling product was well fitted with two sextets of hematite, while the spectrum of the wet milling product was well fitted with three sextets of spinel phase. X-ray measurements confirmed the phases identified by Mössbauer spectroscopy in both milling conditions and a reduction in the crystallinity of the dry milling product. TEM measurements showed that the products of dry milling for 100 h and wet milling for 24 h consist of aggregates of nanoparticles distributed in size, with mean particle size of 10 and 15 nm, respectively. Magnetization measurements of the wet milling product showed little coercivity and a saturation magnetization around 69 emu g-1, characteristic of a nano-spinel system. Atomic absorption measurements showed that the chromium contamination in the wet milling product is approximately two orders of magnitude greater than that found in the dry milling product for 24 h, indicating that the material of the milling bodies, liberated more widely in wet conditions, plays an important role in the conversion hematite-spinel phase. © 2018, Springer Science+Business Media B.V., part of Springer Nature.