1,720,992 research outputs found
Stabilization of the high coercivity epsilon-Fe 23 O phase in the CeO2 - Fe2O3-SiO 2 nanocomposites
No full textWe have investigated the processes leading to the formation of the Fe2O3 and CeO2 nanoparticles in the SiO2 matrix in order to stabilize the Ïμ-Fe2O3 as the major phase. The samples with two different concentrations of the Fe were prepared by sol-gel method, subsequently annealed at different temperatures up to 1100 °C, and characterized by the Mössbauer spectroscopy, Transmission Electron Microscopy (TEM), Powder X-ray Diffraction (PXRD), Energy dispersive X-ray analysis (EDX) and magnetic measurements. The evolution of the different Fe2O3 phases under various conditions of preparation was investigated, starting with the preferential appearance of the Î3-Fe2O3 phase for the sample with low Fe concentration and low annealing temperature and stabilization of the major Ïμ-Fe2O3 phase for high Fe concentration and high annealing temperature, coexisting with the most stable α-Fe2O3 phase. A continuous increase of the particle size of the CeO2 nanocrystals with increasing annealing temperature was also observed. The graphical abstract displays the most important results of our work. The significant change of the phase composition due to the variation of preparation conditions is demonstrated. As a result, significant change of the magnetic properties from superparamagnetic Î3-Fe2O3 phase with negligible coercivity to the high coercivity Ïμ-Fe2O3 phase has been observed. âo Research of the stabilization of the high coercivity Ïμ-Fe2O3 in CeO2-Fe2O3/SiO2. âo Samples with two different concentrations of Fe and three annealing temperatures. âo Phase transition Î3→Ïμ→(Î2)→α with increasing annealing temperature and particle size. âo Elimination of the superparamagnetic phases in samples with higher content of Fe. âo Best conditions for high coercivity Ïμ-Fe2O3 - higher Fe content and
Hydrothermal synthesis, characterization, and magnetic properties of cobalt chromite nanoparticle
No full textThe CoCr2O4 nanoparticles were prepared by hydrothermal treatment of chromium and cobalt oleates in a mixture of solvents (water and ethanol or pentanol) at various temperatures. The samples were further annealed at the temperatures from 300 to 500 C. The obtained nanoparticles were characterized using powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), high-resolution TEM, scanning electron microscopy, thermogravimetric analysis, Raman and infrared spectroscopy, and magnetic measurements. The particle size, ranging from 4.4 to 11.5 nm, was determined from the TEM and PXRD methods. The tendency of particles to form the aggregates with the increasing annealing temperature has been observed. The magnetic measurements revealed that the typical features of the CoCr 2O4 long-range magnetic order are suppressed in the nanoparticles
Hierarchical formation mechanism of CoFe2O4 mesoporous assemblies
No full textThe development of synthetic hybrid organic-inorganic approaches and the understanding of the chemico-physical mechanisms leading to hierarchical assembly of nanocrystals into superstructures pave the way to the design and fabrication of multifunction microdevices able to simultaneously control processes at the nanoscale. This work deals with the design of spherical mesoporous magnetic assemblies through a surfactant assisted water-based strategy and the study of the formation mechanism by a combined use of transmission electron microscopy, X-ray diffraction, and time-resolved small angle X-ray scattering techniques. We visualize the hierarchical mechanism formation of the magnetic assemblies in the selected sodium dodecylsulfate (SDS)-assisted water-based strategy. At the first stage, an intermediate lamellar phase (L) represented by β-Co(OH)2 and FeOOH hexagonal plates is formed. Then, the nucleation of primary CoFe2O4 (N1) nanocrystals of about 6-7 nm occurs by the dissolution of FeOOH and the reaction of FeIII ions coordinated to the SDS micelles, at the reactive sites provided by vertices and edges of the β-Co(OH)2 plates. The intermediate phase consumes as the primary crystalline nanoparticles form, confined by the surfactant molecules around them, and assembly in spherical mesoporous assemblies. The key role of the surfactant in the formation of porous assemblies has been evidenced by an experiment carried out in the absence of SDS and confirmed by the pore size diameter of the assemblies (about 2-3 nm), that can be correlated with the length of the surfactant dodecylsulfate molecule
Bifunctional FePt@MWCNTs/Ru nanoarchitectures: Synthesis and characterization
No full textThe synthesis of novel nanoarchitectures is an important way to combine several properties into the same nanometric object. Magnetic, catalytic, optical, and electrical properties can be embedded and used for heating, moving, or monitoring the nanocomposite. Following this approach, smart materials exhibiting remarkable properties could be obtained. Several nanocomposites are based on carbon nanotubes (CNTs). Because of the presence of empty cavities and very large surface external area, this allotropic form of carbon is especially suitable for this purpose and particularly for catalytic applications. In this work, a new general strategy to synthesize by a wet method three-block, smart nanocomposites based on MWCNTs is described. The new bifunctional material is shortly referred to as FePt@MWCNTs/Ru(NPs) to point out that nanoparticles (NPs) of a magnetically soft alloy (FePt fcc) fill the MWCNTs cavity, whereas catalytic Ru NPs decorate the external wall. In this way well separated catalytic and magnetic NPs are obtained. All the synthetic steps are described in detail. TEM, HRTEM, XRD, and magnetic measurements by VSM are used to monitor all the steps and to prove the effectiveness of the metho
Photoelectrochemical Properties of TiO2 nanotubes as anodes for the electrically enhanced water splitting
No full textOleate-Based Solvothermal Approach for Size Control of MIIFe2IIIO4 (MII ═ MnII, FeII) Colloidal Nanoparticles
No full textThe versatility of a promising and repeatable oleate-based solvothermal approach has been explored through the synthesis of MnFe2O4 and gamma-Fe2O3/Fe3O4 nanoparticles in form of colloidal dispersions and the tuning of the particle and crystallite sizes. Spinel ferrite nanoparticles with controlled-size in the range 7-14 nm with dispersity below 15% was reached for both MnFe2O4 and gamma-Fe2O3/Fe3O4. The size-tuning was obtained with three different pathways: (i) direct approach by changing the solvent polarity or the precursor concentration; (ii) post-synthesis solvothermal treatment in the presence of metal oleates; (iii) post-synthesis solvothermal treatment in the absence of metal oleates
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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