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1.
Z-type Sr3Co2Fe24O41 hexaferrites (Co2Z hexaferrites) were synthesized with sol–gel method and were mechanically mixed with spherical Fe88Si7Cr2.5B2.5 (FeSiCrB) amorphous powders, and then compacted to form toroidal Co2Z hexaferrites/FeSiCrB amorphous soft magnetic composites (Co2Z/FeSiCrB SMCs). The compositions, morphology and soft magnetic performance were characterized through SEM, XRD, VSM, EDS, B-H analyzer and impedance analyzer. All results reveal that Co2Z hexaferrites in Co2Z/FeSiCrB SMCs should mainly exist in air gaps between spherical FeSiCrB amorphous powders, leading to the increasing density. Saturation magnetization decreases a little for magnetic dilution and coercivity increases for the stronger magnetic interaction of Co2Z/FeSiCrB SMCs. The introduction of Co2Z hexaferrites in air gaps increases the conduction area of magnetic circuits and decreases the demagnetization effect, leading to the higher effective permeability of 27.4 for Co2Z/FeSiCrB SMCs, much higher than 25.0 for FeSiCrB SMCs. Furthermore, Co2Z/FeSiCrB SMCs present the smaller core loss and more stable DC bias characteristics owing to the insulating Co2Z hexaferrites.  相似文献   

2.
In order to reduce the sintering temperature of Ba3Co2Fe24O41 (Co2Z), fluorine containing glass powder was added as a sintering aid to ferrite powder with a Co2Z stoichiometric composition prepared by a solid-state reaction, and dense sintered specimens could be obtained at 1000°C in air. The densification was achieved by liquid-phase sintering which was induced by the melting of the additive glass at 800°C. The main crystalline phase was Co2Z, and spinel ferrite appeared as the impurity phase. By sintering in a sealed container, the densification was accelerated still more, and in addition to spinel ferrite, Ba-M also appeared as the impurity phase. The Ba-M contained some Co instead of Fe, and grew to discontinuously large hexagonal plate-like grains. In a fluorine and/or fluorides rich atmosphere, Co2Z was discomposed to Ba-M and spinel ferrite, and large hexagonal plate-like grains appeared. These results suggest that fluorine and/or fluorides evaporated from the additive glass decomposed Co2Z to Ba-M and spinel ferrite, and induced the discontinuously grain growth of Ba-M. The initial permeability was lower than that of the specimen with no additive glass but remained almost constant in the frequency regions up to 1 GHz.  相似文献   

3.
The static, dynamic and attenuation properties of Co2Z barium ferrites and Co2Z composites have been studied. The results showed that both static and dynamic magnetic properties are significantly different for large particles and nanoparticles. As compared to large particles, Co2Z nanoparticles have a small saturation magnetization Ms, large coercivity Hc, small permeability 0 and max, but high resonance frequency fR. The maximum reflection loss predicted is much smaller for nanoparticles than for large particles. Therefore, Co2Z barium ferrite with large particle is more suitable for EM materials with high attenuation and broad bandwidth at microwave frequency.  相似文献   

4.
Synthesis of single-phase Sr3Co2Fe24O41 Z-type (Sr3Co2Z) ferrite was realized by adopting the polymerizable complex method. Crystal structure of samples has been investigated by powder X-ray diffraction (XRD). Single-phase Sr3Co2Z ferrite was obtained by heating at 1473 K for 5 h in air. Magnetic properties were discussed by measurements of M-H curves with vibrating sample magnetometer (VSM). Sr3Co2Z ferrite prepared by polymerizable complex method showed typical M-H curve of soft ferrite, with a saturation magnetization of 21.5μB/formula unit (50.5 emu/g) and a coercive force of 0.014 T at room temperature.  相似文献   

5.
The magnetic properties, especially the high frequency magnetic mechanism, of Ni-substituted Co2Z hexagonal ferrite were studied. The polycrystalline Z-type hexagonal ferrite of Ba3NixCo2−xFe24O41 (0 ≤ x ≤ 2) were prepared by solid-state reaction. The results indicate that Ni-substituted Co2Z samples all exhibit typical soft magnetic character. Substitution of Ni for Co will turn the planar magnetocrystalline anisotropy of Co2Z to uniaxial anisotropy when x ≥ 1, so that the permeability drops dramatically and domain wall resonance appears in the frequency spectra. With the rise of Ni amount or sintering temperature, domain wall resonance strengthens gradually.  相似文献   

6.
The nickel cobalt ferrite (Co0.5Zn0.5Fe2O4) nanopowders were synthesized by a sol–gel method and a hydrothermal method. Polyethylene glycol (PEG-4000) and carboxymethyl cellulose (CMC) were used as the templating agents for controlling the anisotropy and the microstructure of the Co0.5Zn0.5Fe2O4 nanopowders. The microstructure and magnetic property of the synthesized powders were comparatively studied. The results indicated that the synthesis technique and the template had remarkable dependence on the microstructure and the magnetic property of the nanopowders. The powder synthesized by the sol–gel method without any template had a maximum saturation magnetization of 73.6 emu g−1 closing to the value of the bulk material (80 emu g−1), while the PEG-4000 and CMC decreased the magnetization to 54.0 and 60.9 emu g−1. The three powders showed almost same coercivity (314–343 Oe). However, the PEG-4000 and CMC in the hydrothermal process obviously decreased and increased the coercivity respectively from 1,464 Oe to 5 Oe and 4,304 Oe but had small effect of the magnetization (55.5–59.0 emu g−1).  相似文献   

7.
This study reports that NiCoMn ferrite [Ni(1?x)Co x Mn y Fe(2?y)O4 with (x=y=0.01,0.02)] powders are prepared by using the sol-gel combustion method. The effect of various calcination temperatures on their structural and magnetic properties is also investigated. Structural properties of the powders are carried out by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). According to XRD analysis, all samples of two compositions have cubic spinel structure, with an enlargement in crystalline size is observed with increasing of calcination temperature. The crystallite size of the nanopowders is estimated from (311) peaks using Scherrer’s formula. Spherical particles of nanocrystalline ferrite powders are shown in TEM photographs. The room temperature magnetic properties of particles are studied by using a vibrating sample magnetometer (VSM). The magnetization measurements also indicated that the saturation magnetization (M s) increases as the calcinations temperature increases for both A and B samples in the range of 31.69 to 47.77 and 21.81 to 48.89 emu/gr, respectively. The value of coercivity fields (H c) decrease with increasing the calcinations temperature. Furthermore, the properties of two samples synthesis at the optimum calcinations temperature (800 °C) compared together.  相似文献   

8.
In this research work, magnetic and microwave absorption loss and other response characteristics in cobalt zinc ferrite composite has been studied. Cobalt zinc ferrite with the composition of Co0.5Zn0.5Fe2O4 was prepared via high energy ball milling followed by sintering. Phase characteristics of the as-prepared sample by using XRD analysis shows evidently that a high crystalline ferrite has been formed with the assists of thermal energy by sintering at 1250 °C which subsequently changes the magnetic properties of the ferrite. A high magnetic permeability and losses was obtained from ferrite with zinc content. Zn substitution into cobalt ferrite has altered the cation distribution between A and B sites in spinel ferrite which contributed to higher magnetic properties. Specifically, Co0.5Zn0.5Fe2O4 provides electromagnetic wave absorption characteristics. It was found that cobalt zinc ferrite sample is highly potential for microwave absorber which showed the highest reflection loss (RL) value of ??24.5 dB at 8.6 GHz. This material can potentially minimize EMI interferences in the measured frequency range, and was therefore used as fillers in the prepared composite that is applied for microwave absorbing material.  相似文献   

9.
Nanocrystalline Cu0.5Co0.5Fe2O4 powders were prepared via a metal-cellulose precursor synthetic route. Cellulose was used as a fuel and a dispersing agent. The resulting precursors were calcined in the temperature range of 450–600 °C. The phase development of the samples was determined by using Fourier transform infrared (FT-IR) spectroscopy and powder X-ray diffraction (XRD). The field-dependent magnetizations of the nanopowders were measured by vibrating sample magnetometer (VSM). All XRD patterns are of a spinel ferrite with cubic symmetry. Microstructure of the ferrites showed irregular shapes and uniform particles with agglomeration. From XRD data, the crystallite sizes are in range of 16–42 nm. Saturation magnetization and coercivity increased with increasing calcining temperature due to enhancement of crystallinity and reduction of oxygen vacancies.  相似文献   

10.
In order to improve the rheological properties of the zirconia/polypropylene system for ceramic injection moulding, the zirconia powder was surface-treated with aluminate (A), silane (S) and titanate (T) coupling agents dissolved in toluene. 2% additions of these coupling agents decreased the torque,T h, for compounding the zirconia filled-polypropylene after 1 h at 180°C. The surface treatment also reduced the viscosity, ηa, of the compound, the effectiveness of the coupling agents on viscosity reduction being T > S > A. On the contrary, the apparent activation energy,E a, for flow of the compound increased when fluidity was promoted by surface treatment. Rheological measurements in systems with different titanate concentrations showed that the three parameters,T h, ηa, andE a, remained nearly constant for coupling agent additions of over 2%. This critical concentration of 2% showed good correspondence to the optimum concentration evaluated from thermogravimetric analysis of the powders.  相似文献   

11.
Ultrafine oxide powders were produced by CO2 laser evaporation of coarse ZrO2 powder or compact stabilized ZrO2 material The 10.6μm radiation in the power range 1–4kW was generated by a transversal flow Co2 laser which can oscillate in cw and pw operation The vaporization rate depends on the relative position of the focal plane to the surface of the ZrO2 powder, the laser intensity and the supplied energy input. At a laser intensity of 4.2 · 105 Wcm−2 the optimum vaporization rate is 130 g · h−1 (cw-operation of the laser). The produced powders consist of spherical particles; their diameters vary in the range from 5 to 200 nm can be controlled by the process conditions. The surface area (BET) is adjustable from 10 to 30 m2 · g−1. The powders of unstabilized zirconia show an unusual high content of the tetragonal phase. In case of chemically stabilized zirconia the composition can change during the process of evaporation and recondensation.  相似文献   

12.
In this work, the physical and the magnetic properties of cobalt-zinc ferrite nanoparticles, synthesized via high-energy ball milling (HEBM), were examined. X-Ray diffraction (XRD), field emission scanning electron microscopy (FeSEM), and scanning transmission electron microscopy (STEM) were used to study changes of the powder structure and morphology analyses. Hysteresis and permeability measurement were carried out using a BH hysteresisgraph system and an impedance analyzer, respectively. The results suggested improved magnetic properties of Co0.5Zn0.5Fe2O4 with increasing sintering temperature from 950 °C up to 1200 °C. However, the variations of the magnetic responses were consistent with the varying volume concentration of the ferrite composites. Unlike the highly crystalline pure ferrite which showed magnetic resonance within the measured frequency, the crystallineamorphous composites showed no visible resonance peak. This proved that the resonance peak shifted to higher frequency as a result of the single domain spin behavior in the absence of domain walls movement.  相似文献   

13.
The effect of glass addition on the magnetic properties of 3Ba0.5Sr0.5O·2CoO·12Fe2O3 (Co2Z) ferrites was investigated. The densification of Co2Z ferrites was enhanced by addition of glass due to the liquid phase sintering. Although the initial permeability decreased slightly, the quality factor was improved over a wide frequency range with the addition of glass. The resonant frequency shifted to a higher frequency range with increasing the addition of glass. Therefore, the addition of glass in Co2Z ferrites is an effective method to improve the magnetic properties for application in the radio frequency range.  相似文献   

14.
Nanostructured Na0.5Bi0.5TiO3 particles have been synthesized by a hydrothermal synthesis method using a layered titanate H1.07Ti1.73O4·nH2O as a Ti precursor. The obtained Na0.5Bi0.5TiO3 particles showed different morphologies including plate-like, wire-like, and cubic-like structures in different hydrothermal conditions. The effect of the NaOH concentration on the growth and morphology evolution of hydrothermally derived Na0.5Bi0.5TiO3 powders were investigated. It was found that alkaline concentration had a great effect on the phase and morphology of the resultant powders. The dissolution–recrystallization and in situ topotactic transformation mechanisms were suggested in different alkaline concentrations according to the evolution process.  相似文献   

15.
采用机械球磨的方法扁平化处理气雾化Fe-Cr-Si-Al软磁合金(SMSS)粉末,并以柠檬酸溶胶-凝胶法合成六角铁氧体Ba3Co2Fe24O41(C02Z)粉末.运用SEM、XRD表征粉末的表面形貌和晶体结构,并测试不同质量比的片状SMSS磁粉与Co2Z粉末混合组分在2.0-8.2GHz范围的复介电常数和复磁导率.结果表明,随着Co2Z粉末质量分数的增加,样品的复介电常数和复磁导率减小;同时计算得到的反射系数曲线显示样品的匹配频率移向高频,当SMSS磁粉与Co2Z粉末的质量比为4/1时,样品具有最小的反射系数峰值.  相似文献   

16.
Ba3Co2Fe24O41 nanocrystals are synthesized through a stearic acid sol-gel method. The reaction temperatures are dramatically lower than that of the conventional ceramic method. The nanocrystalline powders obtained at 750°C were spherical in shape with grain sizes in the range 15–25 nm and become a plate-like form when the heat-treatment temperature increased. The magnetic properties of these samples are different from those of the bulk Z-type hexagonal ferrite with a lower specific saturation magnetization. This phenomenon can be attributed to the existing of a nonmagnetic layer existing on the surface of the particles. The higher value of the coercivity force is obtained when the particle sizes approximately are equal to 90 nm and assume a single-domain character. The surface composition of the nanocrystalline Co2-Z hexagonal ferrite is different from that of the bulk counterpart material with a higher content of the Ba element and Co element.  相似文献   

17.
Abstract

High magnetic field was applied to fabricate novel lead-free piezoelectric ceramics with a textured structure. A compact of crystallographically oriented grains was prepared by dry forming in a high magnetic field from a mixed slurry of bismuth titanate and barium titanate powders. Bismuth titanate particles with a size of about 1 μ m were used as the host material. In the forming process, the slurry was poured into a mold and set in a magnetic field of 10 T until completely dried. Bismuth titanate particles were highly oriented in the slurry under the magnetic field. The dried powder compact consisted of highly oriented bismuth titanate particles and randomly oriented barium titanate particles. Barium bismuth titanate ceramics with a- and b-axis orientations were successfully produced from the dried compact by sintering at temperatures above 1100 ° C.  相似文献   

18.
19.
The X and U phases of hexagonal ferrites are notoriously difficult to make as pure materials, and what little data there is published regarding their physical or magnetic properties relates only to single crystals. Stoichiometric Co2X and Co2U fibres were made from a sol-gel based process, and the characteristics of the sols and fibres were studied using PCS, XRD, SEM and VSM. The evolution of the X and U fibres was studied, and shown to be similar that of the W and Z fibres whose structures they respectively resemble. Co2X and Co2U had been formed at 1200°C, and the morphology of the fibres was different from those of the W and Z phases. The magnetic properties, again while resembling the W and Z phases, were different to any of the other hexagonal ferrite fibres. The magnetic hysteresis loops of both fibres were magnetically as was, the Co2X fibres having M s = 45.0 emu g–1 and H c = 0.085 T, and the Co2U fibres having M s = 51.5 emu g–1 and H c = 0.059 T.  相似文献   

20.
High magnetic field was applied to fabricate novel lead-free piezoelectric ceramics with a textured structure. A compact of crystallographically oriented grains was prepared by dry forming in a high magnetic field from a mixed slurry of bismuth titanate and barium titanate powders. Bismuth titanate particles with a size of about 1 μ m were used as the host material. In the forming process, the slurry was poured into a mold and set in a magnetic field of 10 T until completely dried. Bismuth titanate particles were highly oriented in the slurry under the magnetic field. The dried powder compact consisted of highly oriented bismuth titanate particles and randomly oriented barium titanate particles. Barium bismuth titanate ceramics with a- and b-axis orientations were successfully produced from the dried compact by sintering at temperatures above 1100 ° C.  相似文献   

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