Papers by Keyword: Ni-Zn Ferrite

Abstract: Research with emphasis on substitution of energy sources used in worldwide for renewable energy undoubtedly indicates that the use of biodiesel would be an option to increase the income in rural areas, reduction in oil derivatives spending and also new opportunities for job creation. Soon, in purpose to contribute with the research growth, this research proposes to evaluate the new catalysts performance as nanoferrites Ni_0,5Zn_0,5Fe₂O₄ (pure) and Ni_0,1Cu_0,4Zn_0,5Fe₂O₄ (doped with 0.4 mol of Cu²⁺) in transesterification reactions of soybean oil methyl. For both samples were synthesized by chemical method in the stoichiometry of the combustion reaction, using urea as a fuel source and a resistance heating coil. During synthesis were measured time and combustion temperature. Later they were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), textural analysis (BET) and subjected to catalytic tests bench. The reaction conditions used in the transesterification were: 10 g of oil, 2 h reaction time, molar ratio of 1:20 oil and alcohol, 4% (w/w) of catalyst and reaction temperature of 160°C. Finally, the reaction product was characterized for conversion into methyl esters by gas chromatography. Results has shown only the presence of the inverse spinel phase, characteristic of Ni-Zn ferrite for both samples, with crystallite size of 26 and 29 nm, respectively. The thermogravimetric analysis has shown that samples are thermally stable, with a weight loss of 4.9 and 3.7%, respectively. The surface area and particle size were 48.89 m²g^-1 and 23 nm, and 18.06 m²g^-1 and 62 nm, respectively. The conversion results obtained by the transesterification reaction were 13 and 50% Ni_0,5Zn_0,5Fe₂O₄ and Ni_0,1Cu_0,4Zn_0,5Fe₂O₄, respectively, indicating that sample with presence of copper was 26% more effectively, thus being one promising catalyst for the transesterification reaction, which aims to obtain biodiesel.

Abstract: This study proposes to evaluate the influence of the variation of sintering temperature on microstructural characteristics and magnetic ferrite Ni_0,5Zn_0,5Fe₂O₄ sintered by microwave energy. The samples were sintered at 900, 1000, 1100 and 1200°C for exposure time of 10 minutes, with rate 50°C/minutes and characterized by density and porosity, X-ray diffraction, scanning electron microscopy and magnetic measurements. The results indicate that the values of density and apparent porosity were 4.2, 4.5, 4.4 and 4.5 g/cm³ and 3.4, 2.1, 2.2 and 2.4% for the sintering temperatures of 900, 1000, 1100 and 1200°C respectively. The formation of the ferrite phase Ni_0,5Zn_0,5Fe₂O₄ been identified for all conditions of sintering, with grain sizes of 52, 62, 71 and 58nm and saturation magnetization values of 63, 68, 69 and 27 emu/g to temperatures sintering 900, 1000, 1100 and 1200°C respectively.

Abstract: Ferrites are ceramic materials whose magnetic properties are very interesting used in various applications. This study evaluates the calcination on the characteristics of Ni_0.5Zn_0.5Fe_1.97Al_0.3O₄ ferrites synthesized by combustion reaction. The samples as synthesized and after calcination at 700 oC/1h in a muffle type furnace were characterized by X-ray diffraction, infrared spectroscopy, scanning electron microscopy, magnetic measurements and determination of carbon content. The results showed the formation of the Ni_0.5Zn_0.5Fe₂O₄ ferrite phase for samples with and without calcination. The infrared spectra showed characteristic vibrations of HO and NO bonds, possibly attributed to the adsorbed water and residual nitrate. Morphologically there was the formation of soft agglomerates with interparticule porosity for both samples. The Ni-Zn ferrite doped with 0.3 mol of Al³⁺ showed superparamagnetic behavior without calcination and after calcination observing its behavior as a soft magnetic material (easy magnetization and demagnetization). Samples showed very low carbon content, indicating that urea used as a fuel was nearly completely consumed in the reaction and after calcination it wasnt observed the presence of carbon.

Abstract: This paper reports the preparation of ferrite Ni_0,5Zn0,5Fe₂O₄ by combustion reaction in a microwave oven, and its structural, morphological and magnetic characterization. The influence of microwave power and the fuel type was investigated. The samples were characterized by: XRD, BET, SEM and AGM. The results showed the formation of phase ferrite Ni_{0, 5}Zn_0,5Fe₂O₄ in all conditions evaluated. The presence of secondary phase hematite and nickel were observed only in samples with glycine. The microwave oven power and the fuel type altered the structure, morphology and magnetic behavior of the samples. In general, the samples synthesized with urea are promising for applications in catalysis, ferrofluids, magnetic sensors and the samples synthesized with glycine are promising for use as absorber electromagnetic radiation, due to the large particle size and good magnetic characteristics observed.

Abstract: This paper proposes to assess the sintering of Ni-Zn ferrites synthesized by combustion reaction in advance to procure materials for applications as soft magnetic devices. The samples used for sintering have different morphological characteristics and were previously synthesized by microwave energy. The samples were uniaxially pressed and sintered in a microwave oven at 1200°C/2h with a heating rate of 5°C/min, and characterized by XRD, SEM and magnetic measurements. The results show that for all samples have the formation of Ni-Zn phase and traces hematite as secondary phase. The resulting microstructure after sintering was different and was influenced by previous morphological characteristics of the synthesized samples. As for the magnetic parameters, all samples were characteristic of soft magnetic material with saturation magnetization between 57 and 62 emu.g^-1, indicating are promising materials for the fabrication of soft magnetic devices.

Abstract: This paper assesses the sintering in a conventional oven and microwave oven of Ni-Zn ferrite. The samples were previously synthesized by combustion reaction in the microwave, and then sintered in a conventional oven and microwave oven 1200°C/2h with a heating rate of 5°C/min. The samples were characterized by: XRD, SEM and magnetic measurements by AGM. The results indicate the formation of inverse spinel crystalline phase of Ni-Zn ferrite, with inter-and intergranular porosity and average grain size of 0.15 µm and 0.30 µm, respectively for the samples sintered in a conventional oven and microwave oven. The sample sintered in conventional furnace showed a pattern characteristic of superparamagnetic materials with saturation magnetization of 7.6 emu.g^-1, while in the microwave sintered sample showed a typical behavior of soft magnetic materials with saturation magnetization of 70 emu.g^-1.

Abstract: Ni_0.5Zn_0.5Fe_1.97Al_0.3O₄ ferrites were synthesized by combustion reaction method and after calcined at 700°C/1 h, with the aim to investigate how the Al³⁺ ions substitution byNi²⁺ ions can influence the magnetic properties. The results from X-ray diffraction showed the formation of a unique Ni-Zn ferrite phase with average crystallite size of 8 and 22nm, before and after calcination, respectively. The synthesize samples presented a superparamagnetic behavior, with saturation magnetization of 0.9 emu/g, and coercive field of 0.05 kOe, and after calcination the samples presented soft magnetic behavior with saturation magnetization of 40.0 emu/g and coercive field of 0.04 kOe.

Abstract: In order to get high microwave absorbing properties, a new kind of three-layer structure composite absorption material was designed and prepared for optimal attenuation. Manganese Oxide was used as the absorbent in the matching layer. Nickel-Zinc ferrite (Ni-Zn ferrite) was used as the absorbent in the dielectric layer and Graphite was used as the absorbent in absorbing layer. The effects of different proportions of absorbents on the microwave absorbing properties were investigated. The results shows that the maximum wave absorbing peak of the 11# sample with the thickness of 5mm is −38.54dB at 14.35GHz and had a bandwidth of 7.1GHz (R<−10dB). This is very important in the design and application of absorbing material.

Abstract: Magnetic composites, especially ferrite composites, are of great interest for embedded inductor applications. In this paper, the Ni-Zn ferrite particles (Ni1-xZnxFe2O4, x=0.2～0.8) with different zinc contents were synthesized via chemical coprecipitation method followed by modification with γ-glycidoxypropyl trimethoxysilane (KH-560). The particles were investigated by X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The results show that the prepared Ni1-xZnxFe2O4(x=0.2～0.7) have good spinel structures, higher saturation magnetization (35.18～77.69 emu/g) and smaller hysteresis hoops, while Ni0.2Zn0.8Fe2O4 grains exhibit some paramagnetic behaviors, such as almost zero hysteresis and non-saturated magnetization. Next Ni1-xZnxFe2O4 magnetic/epoxy composites with different volume fraction of ferrite were prepared and their magnetic performances at high frequencies were characterized by an Agilent E4991A impedance analyzer (USA). It is found that with zinc content in Ni1-xZnxFe2O4 increasing from 0.2 to 0.7, the real part of the complex permeability (μ′) of these composites increase first and then decrease with the frequency increasing gradually from 10 MHz to 1 GHz. Of all, the epoxy composites with filler of Ni0.6Zn0.4Fe2O4 or Ni0.5Zn0.5Fe2O4 ferrite show good frequency stability, and the composites including Ni0.4Zn0.6Fe2O4 ferrite have the highest permeability, and the maximal value at the frequency of 100 MHz is 5.55 when the volume faction is 42.75%. The imaginary part of the complex permeability (μ′′) of all magnetic composites is low For the Ni0.2Zn0.8Fe2O4/epoxy composites, they have very low real permeability (μ′～1) and imaginary permeability (μ″≤0.2).

Abstract: In order to design a ferrite absorber that can be used at frequencies of several GHz, the frequency dependences of the relative complex permeability μ_r^*, the relative complex permittivity ε_r^*, and return loss were investigated for a composite made of Ni-Zn ferrite and SiO₂. When ferrite particles were dispersed and isolated in an SiO₂ medium, the frequency dependence of μ_r^* was different from that for a composite made of SiO₂ particles dispersed and isolated in the ferrite medium. Moreover, when ferrite particles were isolated and a suitable mixture ratio of ferrite and SiO₂ was selected, the return loss was less than −20 dB at frequencies of several GHz. The dispersion states of ferrite and SiO₂ particles are thus important factors to design an absorber, and improvement in the absorption characteristics of the ferrite tile which is used as a practical absorber could be achieved using a composite made of Ni-Zn ferrite particles dispersed and isolated in an SiO₂ medium.