Papers by Keyword: Ferrite

Abstract: A series of xBiFeO₃-(1-x) NiCuZn ferrite multiferroic composites have been prepared by solid state reaction method, in which x is 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0. Composites are densified at 700 °C for 3 h. XRD results show that ferroelectric phase and ferromagnetic phase can be co-existed in the composites. The density of composites increases with an increase of BiFeO₃ content. SEM results reveal that the bigger grains are BiFeO₃ and the smaller grains are NiCuZn ferrite. Composites exhibits the typical magnetic hysteresis loops. Increasing x, the saturation magnetization of composites linearly decrease. The real part of permeability for composites decreases with increasing x. Meanwhile, the peak of imaginary part of permeability shifts toward higher frequency.

Abstract: A suitable match of annealing process parameters is critical for obtaining the fine microstructure of material. Low carbon low alloy steel (20CrMnTi) was heated for various durations near Ac temperature to achieve fine pearlite and ferrite grains. Annealing temperature and time were used as independent variables, and material property data were acquired by orthogonal experiment under intercritical annealing followed by subcritical annealing process (IASAP). The weights of plasticity (hardness, yield strength, section shrinkage, and elongation) of annealing material were calculated by analytic hierarchy process, and then the process parameters were optimized by using the grey theory system. The results observed by SEM images show that the optimized material microstructure consists of refining and distributing uniformly ferrite-pearlite grains, and smaller lamellar cementites. Morphologies on tension fracture surface of the optimized material indicates that the numbers of dimple fracture show more finer toughness obviously comparing with other annealing materials. Moreover, the yield strength value of the optimized material decreases apparently measured by tensile test. Thus, the new optimized strategy is accurate and feasible.

Abstract: With the advancement of meteorology modernization, automatic weather station had become an important means of atmospheric sounding. Collecting data and information security were basic requirements for meteorological monitoring and forecasting. When lightning struck large scale and very large scale integrated circuits, the automatic station can be damaged or its data collector can be interrupted. Two-level SPD lightning protection system and three-level ferrite lightning protection system can compensate for the lack of lightning protection board and power protector. MATLAB simulation analysis shows that the three level lightning protection circuits with ferrite are better than the two level SPD circuits in guaranteeing the automatic station operation. Putting the ferrite rings around the power lines or communication lines, along with the common lightning protection devices, can make the load terminal voltage limit to 500V. The lightning current is significantly reduced by using the simple method in the collector.

Abstract: CoCr_xFe_2-xO₄ samples with x = 0.0 to 2.0 were prepared by air oxidation of aqueous suspension containing Co²⁺, Cr³⁺ and Fe³⁺ ions and characterized by x-ray diffraction. Positron lifetime and coincidence Doppler broadening (CDB) measurements indicated three distinct stages of positron trapping in defects. Initially the vacancy-type defects located at the A-sites (tetrahedral) trapped positrons but, with the substitution of Fe by Cr in low concentrations (x <= 0.7), positrons are trapped by defects at the B-sites (octahedral). Mossbauer spectroscopic results indicated the cationic distribution at B-sites to be stoichiometry-dependent and, till x = 0.7, the deficiency of Fe³⁺(B) ions was compensated by interchange of Fe³⁺(A) ions with Co²⁺(B) ions. Between x = 0.9 and 1.7, the substitution resulted in continued decrease of Fe³⁺(B) ions and the structure got fully transformed into a normal spinel configuration during x = 1.8 to 2.0.

Abstract: We report in this work about the inversion of the spinel structure of ZnFe₂O₄ induced by the substitution of Zn²⁺ by Ni²⁺ ions. Positron lifetimes were measured in Zn_1-xNi_xFe₂O₄ with different concentrations (x) of doped Ni²⁺ ions and a drastic change across x = 0.4 – 0.6 was observed, which is attributed to this transformation. The interchange of positions of the cations on doping leaves a fraction of them unoccupied and these vacancies act as positron trapping centres. Since Ni²⁺ is smaller in size than Zn²⁺, defects due to non-stoichiometry are less in NiFe₂O₄ than in ZnFe₂O₄. The increase in positron lifetime implies the trapping of positrons being shifted from A- to B-sites and is an indication of the transformation from inverse to normal spinel configuration. Coincidence Doppler broadening measurements supported these findings.

Abstract: Effect of the laying head temperature and controlled cooling process on microstructure and mechanical properties of 72LXA wire rod were investigated．The results show that under the same cooling process，with the raising laying temperature and increasing sorbitizing rate and decreasing proeutectoid ferrite，the steel rod strength is improving，proeutectoid ferrite and sorbitizing rate are the critical impact factors on steel rod properties；indentifying cooling after perlite forming can restrain the dissolve of lamellar cementite；the mechanical properties of whole rod coil are improved by the proper rolling rate and air cooling．The high strength of 1050 MPa of steel rod was obtained，that shows the defined hot rolling process can conform to the steel rod properties requirement．

Abstract: This work proposes to study the influence of dilution on the synthesis of ferrites Mn_0.65Zn_0.35Fe₂O₄ using glycine. It was used the reactants/H₂O proportions of 1:0; 1:3.5; 1:7; 1:10, and 1:14 (100 mL of H₂O). During the synthesis were measured the time and temperature of combustion. The samples were characterized by X-ray diffraction and X-ray fluorescence. The dilution in the samples increased with the increasing of the reaction time and flame temperature. For samples synthesized with 1:0, 1:3.5; and 1:7 ratio were observed traces of hematite, and to the remaining samples only the single phase of the Mn_0.65Zn_0.35Fe₂O₄ spinel. The crystallite sizes ranged from 32 to 42 nm.

Abstract: Abstract: Manganese zinc ferrite/barium ferrite composite materials were prepared with various content of Z type barium ferrite (0, 10, 20 wt%) using solid state reaction method. The effect of the compositon on the microstructure and electromagnetic properties of the composites are investigated by means of X-ray diffraction, scanning electron microscope and impedance analyzer. The X-ray diffraction patterns reveal that W phase of barium ferrite instead of Z phase appears in the composite sintered as well as the spinel phase. Some small hexagonal grains were observed in the SEM images and the proportion increases with increasing content of barium ferrite. The cut-off frequencies of the composite systematically shift towards high frequency from 2.5 MHz to 32.6 MHz which is attributed to the increasing of W phase. The composites show a higher frequency for the maximum of the impedance as well as a higher value of the impedance at certain frequency which may be benefit for the application at GHz frequency range.

Abstract: Ni-Zn ferrite nanoparticles with Cr doping, having the general formula Ni_0.5Zn_0.5Cr_xFe_2-xO₄ (x = 0.1, 0.3, 0.5) were prepared by simplified sol-gel method and sintered at 750±5°C. The structural and magnetic properties of the samples sintered at 750±5°C were studied. From X-ray diffraction (XRD) patterns, it was confirmed that the samples have single phase spinel structure. The crystallite size was calculated from the most intense peak (3 1 1) using the Debye Scherrer formula and was found to be in the range of 29-34 nm. The scanning electron microscope images showed that the particle size of the samples were in the range 60-120nm. Quantum design PPMS model 6700 was used to study magnetic properties of these samples. The effect of Cr doping on the magnetic properties was explained on the basis of cations distribution in the crystal structure.

Abstract: Samples of Cr doped cobalt ferrite were prepared by co-precipitation route. These particles were characterized by X-ray diffraction (XRD) at room temperature. The structural properties were observed before and after sintering. The FCC spinel structure was confirmed by XRD patterns of the samples. The crystallite sizes lie in the range of 37-60 nm. DC electrical properties as a function composition were measured. Scanning electron microscopy was used in order to investigate the surface morphology of the prepared samples. The system for thermoelectric power measurement was designed, developed and calibrated in the laboratory. The room temperature thermoelectric power was measured for the prepared samples. The magnitude of Seebeck coefficient depends on the composition and resistivity of the samples. The obtained values of Seebeck coefficient for CoFe₂O₄ are in good agreement to the reported values. Determined values of Seebeck coefficient for other studied compositions are an addition to the literature.