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Sinergia en la reducción catalítica selectiva de no x sobre ferritas Cu1-x co xFe2o4 Synergy in the selective catalytic reduction of no x over Cu1-x co xFe2o4 ferrites
Sarah Brice?o,Vicente Sagredo,Hector Del Castillo
Revista Latinoamericana de Metalurgia y Materiales , 2012,
Abstract: Nanopartículas de ferritas del tipo Cu1-X CoX Fe2O4, se sintetizaron utilizando el método sol-gel de auto-combustión y se caracterizaron usando las técnicas: Análisis termo gravimétrico (TGA), Análisis térmico diferencial (DTA), Difracción de rayos X (DRX), Microscopía electrónica de barrido (MEB), Microscopía electrónica de transmisión (MET), área superficial (BET), Espectroscopia de rayos X (XPS), Termo reducción a temperatura programada (TPR) y Termo desorción a temperatura programada (TPD). Las nanopartículas obtenidas con un tama o promedio de 100 nm y de forma esférica, mostraron formación de conglomerados. Las pruebas catalíticas revelaron que las ferritas Cu1-X CoX Fe2O4, son catalizadores eficientes para la Reducción catalítica selectiva de NOx (RCS-NOx), usando un hidrocarburo como agente reductor, alcanzando una conversión máxima de 40% de NO a 350°C y un 95% de selectividad hacia la formación de N2 debido a la influencia de los metales Cu2+ yCo2+ sugiriendo la presencia de un efecto sinérgico en el sistema Cu1-xCo xFe2O4. Ferrite nanoparticles of Cu1-X CoX Fe2O4, were synthesized by sol-gel auto-combustion method and characterized using the techniques: Thermo gravimetric (TGA), Differential Thermal Analysis (DTA), X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Surface area (BET), X-ray spectroscopy (XPS), Temperature programmed reduction (TPR) and Temperature programmed desorption (TPD). The obtained particles with an average size of 100 nm and spherical shape. The catalytic tests revealed that the Cu1-X CoX Fe2O4 ferrites are efficient catalysts for the Selective Catalytic Reduction of NOx (SCR-NOx), using a hydrocarbon as a reducing agent in the range of 250-450 oC, obtaining a maximum conversion of 40% NO and 95% selectivity towards the formation of N2, suggesting the presence of a synergistic effect between Cu2+ and Co2+ in the system Cu1-xCo xFe2O4.
Synthesis, Structural and Physical Properties of Cu1–xZnxFe2O4 Ferrites  [PDF]
Shahida Akhter, Deba Prasad Paul, Md. Abdul Hakim, Dilip Kumar Saha, Md. Al-Mamun, Alhamra Parveen
Materials Sciences and Applications (MSA) , 2011, DOI: 10.4236/msa.2011.211223
Abstract: Zn substituted Cu-Zn ferrites with a composition Cu1-xZnxFe2O4 have been synthesized by standard double sintering ceramic method and characterized by X-ray diffraction. The single-phase cubic spinel structure of all the samples has been confirmed from X-ray diffraction analyses. The lattice constant is found to increase linearly with the manganese content obeying Vegard’s law. This increase in lattice parameter is explained in terms of the sizes of component ions. It is well known that density plays a key role in controlling the properties of polycrystalline ferrites. The X-ray and bulk densities of the Cu-Zn ferrite is significantly decreased whereas porosity increased with increasing Zn concentration, thereby giving an impression that zinc might be helping in the densification of the materials. SEM micrographs exhibit a decrease in grain size with increasing Zn content. The real part of initial permeability, μ′ increase with increasing Zn contents upto x = 0.5 after that it decreases with higher Zn content.
International Journal of Engineering Science and Technology , 2012,
Abstract: Cobalt substituted Nickel-zinc ferrites of different compositions Ni0.95-xZn0.05CoxFe2O4 and Zn0.95- xNi0.05CoxFe2O4 (where x = 0.00, 0.01, 0.02,0.03, 0.04, 0.05 and 0.06).have been prepared by citrate precursor method involving concerned metals and mixing them in solution state. Parts of the sol-gel powder heated at elevated temperatures were characterized by X-ray diffraction (XRD), Particle size analyser and Scanning Electron Microscope (SEM) to reveal the crystallized single phase structure of the ferrite. In addition to that magnetic properties were measured. The initial magnetic permeability was found to increase with the increasing of the frequency as a result of the domain wall motion and the corresponding loss was small.
Synthesis, Structural and Magnetic Properties of Copper Substituted Nickel Ferrites by Sol-Gel Method  [PDF]
Gopathi Ravi Kumar, Katrapally Vijaya Kumar, Yarram Chetty Venudhar
Materials Sciences and Applications (MSA) , 2012, DOI: 10.4236/msa.2012.32013
Abstract: The Ni1–xCuxFe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0) ferrites have been prepared by sol-gel method in order to obtain homogeneous crystal structure and they are sintered at high temperature. The effect of copper doping on the structural and magnetic properties of nickel ferrites sintered at 1000°C has been examined. The X-ray diffraction measurements clearly showed the formation of single phase spinel ferrite structure in all the prepared ferrite compositions. Because of the high sintering temperature the particle size is observed beyond the nano-scale range in all the compositions. The lattice parameters are found to increase with increasing doping concentration of the copper content. Magnetization results exhibit a non-collinear ferrimagnetic structure for x = 0.0 to 0.5 and Neel’s collinear ferrimagnetic structure for x = 0.5 to 0.9 suggesting a change in magnetic ordering.
A Study on Waste-derived NiZn Soft Ferrites as EMI Suppressor
H. S. Woon,K. P. Lim,C. K. Ho,C. L. Cheah
International Journal of Electronics, Computer and Communications Technologies , 2011,
Abstract: Nickel-zinc soft ferrites with spinel structure are important electronic components popularly used as EMI suppressor, electromagnet core and transformer core. It contains nickel, zinc or manganese , and the raw material is mainly hematite. The most commonly use soft ferrites are NiZn ferrites and MnZn ferrites. NiZn ferrites exhibit higher resistivity than MnZn ferrites and are therefore more suitable for frequencies above 1 MHz. In this work, iron oxide waste generated from a local cold-rolling steel mill was purified and converted into hematite. The waste-derived hematite was used as the raw material in the synthesis of NiZn ferrites. The magnetic properties such as permeability, saturation magnetization and coercivity of the waste-derived NiZn ferrites was analyzed and compared to the industrial grade NiZn ferrites. Our results show that the waste-derived ferrite possesses excellent magnetic properties. The microstructure of the waste-derived NiZn ferrite is also discussed.
Structural and Physical Properties of Glasses  [PDF]
Virender Kundu,R. L. Dhiman,A. S. Maan,D. R. Goyal
Advances in Condensed Matter Physics , 2008, DOI: 10.1155/2008/937054
Abstract: The structural and physical properties of Fe2O3-(40-x) B2O3-60V2O5(0≤≤20) glass system have been investigated. The samples were prepared by normal melt-quench technique. The structural changes were inferred by means of FTIR by monitoring the infrared (IR) spectra in the spectral range 600–4000 cm?1. The absence of boroxol ring (806 cm?1) in the present glass system suggested that these glasses consist of randomly connected BO3 and BO4 units. The conversion of BO3 to BO4 and VO5 to VO4 tetrahedra along with the formation of non-bridging oxygen's (NBOs) attached to boron and vanadium takes place in the glasses under investigation. The density and molar volume of the present glass system were found to depend on Fe2O3 content. DC conductivity of the glass system has been determined in the temperature range 310–500 K. It was found that the general behavior of electrical conductivity was similar for all glass compositions and found to increase with increasing iron content. The parameters such as activation energy, average separation between transition metal ions (TMIs), polaron radius, and so forth have been calculated in adiabatic region and are found consistent with Mott's model of phonon-assisted polaronic hopping.
Structural and M?ssbauer Spectral Studies of Nanosized Aluminum Doped Manganese Zinc Ferrites  [PDF]
R. L. Dhiman,S. P. Taneja,V. R. Reddy
Advances in Condensed Matter Physics , 2008, DOI: 10.1155/2008/839536
Abstract: Nanoparticles of aluminum-substituted manganese zinc ferrites, Mn1.05Zn0.05AlFe1.9?O4 with 0.4≤≤1.0 were synthesized by solid-state reaction route and characterized by XRD, TEM, and Mössbauer spectroscopy measurements. The particle size is found to very from 46 to 28 nm with increase of aluminum ions concentration. The unit cell parameter ‘‘’’ is found to decrease linearly with aluminum ions concentration due to smaller ionic radius of aluminum. The cation distributions were estimated from X-ray diffraction intensities of various planes. The theoretical lattice parameter, bulk density, porosity, X-ray density, oxygen positional parameter, ionic radii, jump length, as well as bonds and edges lengths of the tetrahedral (A-) and octahedral (B-) sites were determined. 57Fe Mössbauer spectra recorded at room temperature were fitted with two sextets corresponding to Fe3
Magnetic and structural characterization of nanosized BaCo_xZn_{2-x}Fe_{16}O_{27} hexaferrite in the vicinity of spin reorientation transition  [PDF]
Alexander Pasko,Frédéric Mazaleyrat,Martino Lo Bue,Vincent Loyau,Vittorio Basso,Michaela Küpferling,Carlo Sasso,Lotfi Bessais
Physics , 2011, DOI: 10.1088/1742-6596/303/1/012045
Abstract: Numerous applications of hexagonal ferrites are related to their easy axis or easy plane magnetocrystalline anisotropy configurations. Certain W-type ferrites undergo spin reorientation transitions (SRT) between different anisotropy states on magnetic field or temperature variation. The transition point can be tuned by modifying the chemical composition, which suggests a potential application of hexaferrites in room temperature magnetic refrigeration. Here we present the results of structural and magnetic characterization of BaCo_xZn_{2-x}Fe_{16}O_{27} (0.7 \leq x \leq 2) doped barium ferrites. Fine powders were prepared using a sol-gel citrate precursor method. Crystal structures and particle size distributions were examined by X-ray diffraction and transmission electron microscopy. The optimal synthesis temperature ensuring complete formation of single W-phase with limited grain growth has been determined. Spin reorientation transitions were revealed by thermomagnetic analysis and AC susceptibility measurements.
Novel Applications of Ferrites  [PDF]
Raúl Valenzuela
Physics Research International , 2012, DOI: 10.1155/2012/591839
Abstract: The applications of ferrimagnetic oxides, or ferrites, in the last 10 years are reviewed, including thin films and nanoparticles. The general features of the three basic crystal systems and their magnetic structures are briefly discussed, followed by the most interesting applications in electronic circuits as inductors, in high-frequency systems, in power delivering devices, in electromagnetic interference suppression, and in biotechnology. As the field is considerably large, an effort has been made to include the original references discussing each particular application on a more detailed manner. 1. Introduction Ferrites are a large class of oxides with remarkable magnetic properties, which have been investigated and applied during the last ~50 years [1]. Their applications encompass an impressive range extending from millimeter wave integrated circuitry to power handling, simple permanent magnets, and magnetic recording. These applications are based upon the very basic properties of ferrites: a significant saturation magnetization, a high electrical resistivity, low electrical losses, and a very good chemical stability. Ferrites can be obtained in three different crystal systems by many methods, and the feasibility to prepare a virtually unlimited number of solid solutions opens the means to tailor their properties for many applications. For many applications, ferrites cannot be substituted by ferromagnetic metals; for other, ferrites often compete with metals on economic reasons. The possibility of preparing ferrites in the form of nanoparticles has open a new and exciting research field, with revolutionary applications not only in the electronic technology but also in the field of biotechnology. In this paper, the applications of ferrites developed in the last 10 years are briefly described. 2. Ferrites 2.1. Spinels Spinel ferrites possess the crystal structure of the natural spinel MgAl2O4, first determined by Bragg [2]. This structure is particularly stable, since there is an extremely large variety of oxides which adopt it, fulfilling the conditions of overall cation-to-anion ratio of 3/4, a total cation valency of 8, and relatively small cation radii. Spinel structure is shown in Figure 1. Cation valency combinations known are 2, 3 (as in Ni2+Fe3+2O4); 2, 4 (as in Co2GeO4); 1, 3, 4 (as in LiFeTiO4); 1, 3 (as in Li0.5Fe2.5O4); 1, 2, 5 (as in LiNiVO4); 1, 6 (as in Na2WO4). In ferrites with applications as magnetic materials, Al3+ has usually been substituted by Fe3+. An important ferrite is magnetite, Fe2+Fe3+2O4 (typically referred as Fe3O4),
Structural and Magnetic Properties of Cr3+ Doped Mg Ferrites  [PDF]
Faizun Nesa, A. K. M. Zakaria, M. A. Saeed Khan, S. M. Yunus, A. K. Das, S.-G. Eriksson, M. N. I. Khan, M. A. Hakim
World Journal of Condensed Matter Physics (WJCMP) , 2012, DOI: 10.4236/wjcmp.2012.21005
Abstract: The polycrystalline MgCrxFe2-xO4 ferrites (0.0 ? x ? 1.0) were prepared by conventional solid state ceramic sintering technique in air at 1300?C. X-ray diffraction experiments were carried out on all the samples in order to characterize the materials at room temperature. The X-ray diffraction patterns showed sharp peaks indicating the formation of single phased cubic spinel structure. The lattice parameters of the samples were determined from the X-ray diffraction data using Nelson-Riley extrapolation method. It was found that the lattice parameter decreased with increasing Cr concen- tration obeying Vegard’s law. Magnetic properties of the samples were measured using an Impedance Analyzer. Real and imaginary parts of the complex permeability, loss factor and quality factor were measured as the function of frequency at three different sintering temperatures 1250?C, 1300?C and 1350?C for all the samples in the frequency range 1 kHz to 13 MHz. Frequency stability of the real part of permeability increases with increasing Cr concentration and also with sintering temperature. Imaginary part of permeability decreases with increasing frequency and increased with increasing both of the Cr content and sintering temperature. Loss factor decreased with increasing frequency while the quality factor (Q) increased with increasing frequency for all the samples. The temperature de- pendence of initial permeability was measured for all the samples sintered at 1300?C. The Curie temperature (Tc) was determined from the -T curves. The values of Tc were found to be 733 K, 657 K, 583 K, 468 K, 400 K and 317 K for x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0, respectively.
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