溶胶直接自蔓燃法制备NiZn铁氧体粉末研究

以柠檬酸铁或硝酸铁、硝酸锌、硝酸镍和柠檬酸为原料,利用溶胶直接自蔓延燃烧反应成功制备了尖晶石结构的NiZn铁氧体粉末.研究结果表明,溶胶直接自蔓延燃烧法形成的NiZn铁氧体粉末的颗粒尺寸总体较小,在含柠檬酸铁体系中晶粒平均尺寸仅为16～23nm,当柠檬酸量与金属盐总量的摩尔比为2时,形成的NiZn铁氧体粉末晶粒尺寸达最大.溶胶直接自蔓延燃烧法得到的NiZn铁氧体粉末的饱和磁化强度相对较小,约为10.54emu/g,矫顽力较大,约为412.5Oe .     

Effect of addition of the CuO-Fe2O3 system on the electromagnetic wave absorbing properties of sintered ferrite

The effects of the addition of the CuO-Fe₂O₃ system as a liquid former on the microstructure and electromagnetic wave absorbing property of sintered Ni-Zn ferrite were investigated. The CuO-Fe₂O₃ system, a spinel ferrite, has its own magnetic property, which enables it to be used as an electromagnetic wave absorber. The CuO-Fe₂O₃ system was preferentially located at the grain boundary in the matrix of an Ni-Zn ferrite. This resulted in an increase in the total loss and a decrease in matching thickness. The centre frequency shift is presumed to occur because Ni-Zn ferrite with CuO-Fe₂O₃ behaves like a mixture of two ferrites with loss characteristics at the different frequency ranges.     

Grain size effects on magnetic properties and core process of recording head Ferrites

A study has been made which correlates grain size with magnetic properties so that the proper range of grain size in ferrite materials can be determined for recording head applications. The effects of Ni-Zn and Mn-Zn ferrite grain size on 1) initial permeability, 2)B-Hloop, 3) density of ferrites, and 4) core processing, e.g., lapping and glass bonding, are described. Both experimental results and published research indicate that highly densified ferrites having larger grains are desirable for recording head applications. ASTM grain size Nos. 8-9 are therefore recommended for Ni-Zn ferrite R/W heads.     

Formation and magnetic properties of ultrafine spinel ferrites

Investigations of the formation and magnetic properties of MnδCo1-δFe2O4formed in alkaline aqueous solution by the coprecipitation method are covered. The lattice constant of these ferrites apparently reduced with decreasing average particle size below about 500 Å. The coercive force ratio of MnFe2O4and Co-Fe2O4is 1 to 50 and equal to that of the crystal magnetic anisotropy coefficient K1of sintered ferrites. As the average particle size became larger, the coercive force and the apparent remanence increased linearly, and superparamagnetic critical size was determined. The sizes range, for example, from 50 to 100 Å for CoFe2O4and from 150 to 200 Å. for MnFe2O4. From the correlation between the average particle size and their magnetization, the limit size of ferromagnetic critical particle was also determined. Results obtained in this experiment are approximately in accord with Néel's Version of the theory on thermal fluctuation aftereffect of magnetic fine particles.     

NiZnFe_2O_4包覆铁基软磁复合材料的制备及性能

采用溶胶-凝胶法制备的NiZnFe_2O_4作为绝缘剂包覆铁粉来制备铁基软磁复合材料,并研究了NiZnFe_2O_4含量和成型压力对复合材料磁性能的影响。采用SEM,EDX线扫描及元素面分布分析显示在铁粉颗粒表面存在一层均匀的NiZnFe_2O_4包覆层,绝缘包覆层的存在可以有效地提高软磁复合材料的电阻率。实验结果表明,随着NiZnFe_2O_4包覆剂含量的增加,软磁复合材料的复数磁导率实部值逐渐降低,与其他含量的样品相比,NiZnFe_2O_4含量为3%(质量分数,下同)的样品具有最低的复数磁导率虚部值和相对较高的复数磁导率实部值。NiZnFe_2O_4包覆剂的加入,可以大幅降低材料内部的磁损耗,在100kHz时其磁损耗仅为未包覆样品的16.2%。当NiZnFe_2O_4的含量为3%,成型压力为1000MPa时,软磁复合材料的密度达到7.14g/cm~3,饱和磁感应强度为1.47T。     

Effects of cobalt doping on nonlinearity of zinc oxide

The microstructures and electrical properties of ZnO–Bi₂O₃–CoO (ZBC), ZnO–Bi₂O₃ (ZB) and ZnO–CoO (ZC) ceramics were investigated. Cobalt oxide addition could reduce bismuth loss at high sintering temperature. The same amount of cobalt within ZnO grains was found in both specimens, ZBC and ZC, suggesting that bismuth had no effect on the dissolution of cobalt in ZnO and cobalt substitution for zinc in the ZnO structure. The highest nonlinear coefficient of about 19 was found in the ZBC varistor sintered at 1000–1100 °C. For the ZC specimens, nonlinear properties could also be obtained in this sintering temperature range.     

Magnetic properties of anisotropic Sr-La system ferrite magnets

An experiment was carried out to investigate the effect of La₂O₃ on the magnetic and physical properties of strontium ferrite magnets. It was found that the La₂O₃ addition to SrO-6Fe₂O₃ (stoichiometric composition) was very useful in stabilizing the magnetoplumbite structure and that these ferrites of the Sr-La system had excellent permanent-magnet properties. Various compositions were tested, and the optimum conditions for making magnets and some properties of typical specimens were determined. The semisintering condition was 1250°C for 1 h in oxygen, and the sintering condition 1300°C for 0.5 h in oxygen. Magnetic and physical properties are presented and discussed. The [(SrO)0.143(Fe₂O₃)_0.857]₉₈ (La₂O₃)₂ compound magnet exhibited the highest value of (BH)_max, and this value was equivalent to or higher than that of ordinary Ba and Sr ferrites     

Investigating the Characteristics of Cobalt-Substituted MnZn Ferrites by Equivalent Electrical Elements

We investigated the electrical and magnetic properties of cobalt-substituted manganese-zinc soft ferrite by using the equivalent lumped elements acquired from the appropriate equivalent electrical circuit of polycrystalline ferrite. We applied the equivalent lumped circuit, combined with equivalent lumped resistances and capacitance, to determine the effect of microstructure on electrical and magnetic properties of cobalt-substituted manganese-zinc ferrites. Both the hysteresis loss and the eddy-current loss of soft ferrites account for a major proportion of iron loss in high-frequency switching mode power supplies. Replacing a small portion of Fe²⁺ with Co²⁺ remarkably increases the bulk resistivity of the MnZn ferrite and decreases the core loss by lowering eddy-current loss. A longer isothermal duration causes grain growth and forms a larger equivalent capacitance, which leads to a reduction in hysteresis loss. However, excess substitution of Co²⁺ for Fe²⁺ is disadvantageous to magnetic permeability and raises core loss. We measured the dc resistivity by the four-probe method on sintered disks with both sides polished and coated with a thin layer of silver paste as a good contact material. We measured the magnetic permeability by an impedance analyzer at room temperature. The total loss of Mn_0.58Zn_0.37 Co_0.01Fe_2.04O₄ ferrite core does not exceed 420 mW/cm³ at 300 kHz/70 mT.     

Light modified switching properties of garnets and ferrites

The influence of light on the switching behavior of Si-doped Y3Fe5O12and Co-substituted Ni-Zn ferrites is investigated. After irradiation with light, YIG (Si) has an extremely square hysteresis loop, and the switching transients display anomalous behavior. When a step field is applied, there is a certain period of time during which no flux is switched irreversibly. After this delay, which depends on the amplitude of the applied step field, the material switches in the normal way. At 4.2 and 77°K these changes are permanent; at 200°K the effects disappear after illumination is terminated. The results are discussed in terms of a two-center model, which was proposed earlier to explain results for changes in permeability. Co-substituted Ni-Zn ferrites show similar behavior already in the nonirradiated state. Irradiation increases the coercive force and also the break-free behavior becomes more pronounced. These changes are still permanent at 200°K.     

Electrical conductivity studies of copper-substituted and non-substituted Ni-Zn mixed ferrites

The electrical conductivity of Ni-Zn and copper-substituted Ni-Zn ferrites is investigated in the range 300 to 1000 K. It is seen that the plots of log against 10³/T exhibit a linear relationship. There are four distinct regions exhibited by the Ni-Zn ferrite. However, with the substitution of copper there appears to be gradual disappearance of the fourth region. Also for the samples of Ni-Zn ferrite with more than 80% Zn, there are only three regions in the variation of log with 10³/T. The breaks and discontinuities are attributed to several sources. The electrical conduction in these ferrites is explained on the basis of a hopping mechanism. The activation energy in the paramagnetic region is found to be more than that for the ferri magnetic region. This is attributed to the effect of the magnetic ordering in the conduction process.     

Mechanical properties of barium hexaferrites

The mechanical properties of typical isotropic barium ferrites have been determined. A statistical analysis has shown that fracture toughness is the best quality parameter. It changes with variation of production operation conditions. The fracture statistics follows the Weibull distribution. A relationship is found between the influence of the Fe2O3/BaO molar ratio on mechanical and magnetic properties. A maximum of mechanical and magnetic properties has been observed when the SiO2content in sintered ferrites is about 0.9 percent.     

Stress relaxation phenomena in NiCuZn ferrites induced by annealing

The present study deals with the detection and correlation of the stress relaxation phenomena that are induced in NiCuZn ferrites, as an effect of an additional annealing process that takes place after sintering. The effect of annealing on the magnetic permeability and losses of NiCuZn ferrite materials is investigated and the microstructural changes of the samples are examined by transmission electron microscopy. The ferrite specimens were synthesized by the conventional ceramic method. Sintering temperatures between 1025 and 1100 °C were applied and the sintered samples were further annealed at temperatures 50 °C lower than the sintering ones. Results revealed an improvement of the power losses at low frequencies (50 kHz), while at the high frequency range (1 MHz) the relative loss factors increased. These results were in agreement with the detected microstructural changes in the polycrystalline microstructure that occurred due to the annealing process. The relation between the annealed microstructure, the specific resistivity and the magnetic losses of the NiCuZn ferrites specimens is discussed. It appears that the stress relaxation mechanism induced by annealing is attributed to the elimination of grain dislocations, which justifies the decrease of the specific resistivity of the specimens. The stress relaxation contributes to a reduction of the low frequency hysteresis losses while the decrease of the resistivity to an increase of the high frequency eddy current losses.     

含La~(3+)的Ni-Zn铁氧体的微观结构和电磁性能

本文通过在 Ni-Zn 铁氧体中掺入 La_2O_3后,材料的电磁性能、温度特性和微观结构所发生的变化,研究了 La~(3+)离子的掺杂效应和作用机制。实验表明:Ni_(0.41)Zn_(0.60)Sn_(0.01)Cu_(0.02)Fe_(2.04-X)La_xO_(4±δ)在x<0.010时,La~(3+)离子能细化晶粒;x>0.010时,La~(3+)离子使晶界模糊,晶粒尺寸增大;不同温度区域的电子激活能 E_ρ呈现出明显的差异。La~(3+)离子对电阻率ρ的贡献主要是提高了晶界电阻率。     

X-Ray Pole Figure Analysis and Magnetic Properties of Microwave Sintered Sr-M-type Hexagonal Ferrites

Sr-M-type sintered hexagonal ferrites were prepared by the conventional and microwave sintering method. X-ray diffraction and pole figure analysis, scanning electron microscopy (SEM), and Robograph 2 magnetic properties test instrument were applied to character the structure and magnetic properties of sintered ferrites. The XRD results reveal all the sintered samples are composed of SrFe₁₂O₁₉ single phase with obvious c-axis alignment. The sample with MS treatment at 1050 ^°C exhibits the optimum magnetic alignment, showing the optimum (0?0?8) and (1?0?7) pole figures with almost all circular lines focused on the center and at about 30^° of α, respectively. Few pores and optimal densification characters can be seen from the SEM image of strontium ferrites microwave sintered at 1050 ^°C, resulting in the optical magnetic properties as remanence (B _r) of 410.5 mT, coercivity (H _cj) of 372.2 kA/m, and maximum magnetic energy product ((BH)_max) of 31.53 kJ/m³, respectively.     

无铅压电陶瓷KNN常压烧结及其电学性能

用常压烧结法制备K_0.5Na_0.5NbO₃陶瓷。研究烧结温度与陶瓷密度和电学性能的关系。研究表明在1065℃~1120℃范围内, 温度对陶瓷的密度有显著影响。当烧结温度为1100℃时, 密度达到4.35 g/cm³ (占理论密度的95%); 1100℃烧结的陶瓷表现出最好的电学性能, 压电常数最大118 pC/N, 相对介电常数最大达538, 介电损耗最小仅4.7%, 剩余极化强度为15.37 μC/cm², 矫顽场为13.16 kV/cm。陶瓷样品在206℃从正交结构转变到四方结构, 居里温度为410℃。     

Effect of dopants on the magnetic properties of MnZn ferrites forhigh frequency power supplies

The effect of additions on the magnetic properties of MnZn ferrites for high frequency power supplies was studied. The investigation revealed that various combinations of dopants added to the ferrite modify the grain boundary resistivity and the magnetic permeability spectra at constant microstructure. Particularly, the combined effect of Sn⁴⁺, Ti⁴⁺ and Ta⁵⁺ was found to increase the grain boundary resistivity in the ferrites studied and remarkably decrease the power loss at higher frequencies     

Simultaneous substitution of Co2+and Zn2+ions in submicronic acicular γ - Fe2O3particles

In iron sesquioxide of acicular shaded γ-Fe2O3simultaneous substitution of Co²⁺and Zn²⁺ions leads to the formation of mixed-defect ferrites and modulation of magnetic properties is of interest for their application to high density magnetic recording. It is shown that the coercive force, remanent magnetization and saturation-magnetization are controlled by a judicious choice of the contents of Co²⁺and Zn²⁺, while it is indispensable to optimize the morphological features like the average size of the crystallites, the shape, the size and texture of the particles. A high value of coercive force (650-700 Oe) and of the remanent magnetization (35-45 emu/g) had been obtained with a minimal content of cobalt ions (Co²⁺= 2.5 to 3% by wt.) permitting limits to the magnetocrystalline anisotropy of these compounds and their thermal variation near the ambient temperature. The influence of the zinc content had been systematically studied notably in relation to its effect on the structural, morphological and magnetic properties of the ferrites.     

Size variation and magnetic dilution effects on the structure and magnetic properties of cobalt zinc ferrite

Nanocrystalline cobalt zinc ferrites Co_1?xZn_xFe₂O₄ (x?=?0.0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0), have been prepared by employing a precursor combustion method via decomposition of the metal carboxylato hydrazinate precursors. This synthesis technique yields nanoparticles with particle size between 12 and 15 nm as determined from transmission electron microscopy (TEM) studies. The nanoferrites were then sintered at 1000 °C for 15 h to obtain micrometer size ‘bulk’ ferrites in the range of 0.3–0.8 μm. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) Spectroscopy confirmed the formation of the mixed ferrites without any impurities. Addition of non-magnetic ion like Zn²⁺ into the crystal structure of cobalt ferrite leads to a prominent change in the size, structure and properties. The saturation magnetization values (M_S) increases upto x?=?0.4 and then decreases with further increase in Zn concentration. A maximum M_S value of 90.85 emu/g and 79.59 emu/g for x?=?0.4 was obtained for the sintered and nanoferrite sample, respectively. The lower M_S and higher coercivity (H_C) values for nanoferrites than the sintered ferrites exhibited a strong dependence on the particle size due to the cation distribution and surface effects. The Curie temperature (T_C) was found to decrease appreciably with the reduction in particle size and with increasing concentration of Zn. The room temperature Mössbauer spectra showed a transition from ferrimagnetic to a paramagnetic state with increasing zinc concentration along with superparamagnetic features which was in corroboration with VSM studies.

     

Effect of W ion doping on magnetic and dielectric properties of Ni-Zn ferrites by “one-step synthesis”

W-doped Ni-Zn ferrites with a nominal composition of Ni_0.5Zn_0.5W_xFe_2−xO₄ (where x = 0, 0.02, 0.04, 0.06, and 0.08) were prepared by one-step synthesis through the incorporation of WO₃ into the raw powders. The magnetic and dielectric properties of the as-prepared Ni-Zn ferrites were investigated. All samples have a typical spinel cubic structure. With increasing amount of W ions doped, the lattice constant decreases, while the grain size increases. The density and diameter shrinkage of the samples raise with small amount of W ions doped, but drop down with large amount of W ions doped. However, an uneven abnormal growth and closed pores were observed when too much of WO₃ was added. The saturation magnetization of the samples increases with small amount of W ions doped, but decreases with large amount of W ions doped, and the coercivity shows an opposite trend. The Curie temperature raises with increasing amount of W ions doped. Both the real and imaginary parts of permeability of the ferrites decrease with increasing amount of W ions doped, while the natural resonance changes very little. Both the dielectric constant and dielectric loss present a decrease with small amount of W ions doped, but increase with large amount of W ions doped.     

自蔓延高温合成Ni-Zn铁氧体的研究

采用SHS方法合成Ni0.35Zn0.65Fe2O4铁氧体 ,取代了传统铁氧体工艺耗能、耗时的预烧环节。以XRD、SEM、阻抗分析仪等对铁氧体的微观结构、磁性能进行表征,并与传统工艺对比,获得了性能优良的铁氧体。