High temperature deformation of Mn-Zn ferrite single crystals

Compressive creep tests in a temperature region higher than 900° C were conducted on Mn-Zn ferrite single crystals of various compositions. The strain rates in the stationary creep vary with stress and temperature according to the well-known relation $$\mathop \varepsilon \limits^\cdot = A\sigma ^m \exp ( - H/kT)$$ The stress index,m, is nearly 3, independent of the composition, but the activation energy,H, depends on it. From TEM and etch pit observations the distribution of mobile dislocations were almost uniform and the effective stress index,m ^*, of the dislocation velocity was nearly 1. In the compression test with constant deformation velocity, the internal stress during the deformation was about 17% lower than the applied stress. From these experimental results the high temperature deformation of Mn-Zn ferrite crystals is concluded to be governed by the viscous movements of dislocations which drag the atmosphere of pinning atoms or ions. The chemical composition dependency of the activation energy is considered to be caused by the structural defects due to the deviation from stoichiometry which act as the obstacles for the diffusion of pinning atoms or ions.     

Combined effect of partial calcination and sintering condition on low loss Mn-Zn ferrite

In order to achieve highly densified lower loss Mn-Zn ferrite materials, various powder processing routes have been under investigation. In this report, a lower sintering temperature with lower oxygen partial pressure and proper attrition milling duration are suggested. From the previous study, a partial calcination procedure was studied and an optimum partial calcination level was found. Accordingly, Mn_0.71Zn_0.22Fe_2.07O₄ ferrite was prepared by calcination with small amounts of CaCO₃, SiO₂, Nb₂O₅ and SnO₂. The partially calcined ferrites were made by calcining the mixture of the whole amount of ZnO and amount of Fe₂O₃ and Mn₃O₄ and sintering the mixture of the calcined powders and the remaining of Fe₂O₃ and Mn₃O₄. Initially, from the 40 min secondary milling and the partial calcination, lower temperature (1300°C) sintered samples showed a power loss of 340 mW cm^–3 at 90°C. Secondly, several milling durations showed secondary milling had a more profound effect on magnetic properties than primary milling. The 20 min primary and 90 min secondary milling showed lower core loss around 320 mW cm^–3 at 1300°C and 1250°C, suggesting the sintering temperature could be reduced to 1250°C. Thus, the proper sintering condition of lower oxygen partial pressure at 1250°C was studied. As a result, lower loss with higher density was realized.     

热处理温度对纳米Mn-Zn铁氧体微粒的Ms、Hc的影响

采用柠檬酸盐自燃烧法制备纳米锰锌(Mn-Zn)铁氧体微粒,研究后续热处理温度对产物的饱和磁化强度(Ms)、矫顽力(Hc)的影响.结果表明,纳米Mn-Zn铁氧体微粒的Ms、Hc随着热处理温度的升高,变化趋势都是先增大后减小.Ms在热处理温度为450℃时,达到最大值(46.8Am2/g);Hc在热处理温度为400℃时,达到最大值(2.7×105A/m) .纳米Mn-Zn铁氧体微粒的单畴临界尺寸大约为58nm.     

Synthesis and properties of Mn-Zn ferrite ferrofluids

A Mn-Zn ferrite ferrofluid is produced by chemical synthesis. Two different types of ferrofluids, according to the type of carrier liquid, are synthesized: an aqueous cationic ferrofluid and a surfacted hydrocarbon-based one. Ferrite particles are characterized by using several techniques: X-ray diffraction, transmission electronic microscopy, IR-spectroscopy, thermogravimetry, magnetization measurements and chemical analysis. Particles size depends on the synthesis parameters and can be partly controlled by choosing the type of the coprecipitating base. Increasing of the Zn concentration leads to smaller size of synthesized particles, as well as effects the content of associated water. Magnetization of the ferrofluid significantly decreases when the degree of Zn substitution exceeds 0.5.     

Hot-pressed Mn-Zn ferrite for magnetic recording heads

Hot-pressed ferrites have been studied in connection with fabrication of a high quality head material. A two-step hot-pressing technique has enabled the preparation of hot-pressed ferrite with a porosity lower than 0.1 percent and an adjusted average grain size between 0.1 μm and 500 μm. The largest available ingot of hot-pressed ferrite is 120 mm in diameter and 20 mm in thickness. A hot-pressed Mn-Zn ferrite with an adjusted microstructure can be made with a μmof 40 000 and an Hclower than 0.02 Oe. A hot-pressed Mn-Zn ferrite of another composition will have a Bmgreater than 5000 G and a μ0of 700 at 10 MHz. The effect of mechanical working on magnetic properties of hot-pressed ferrites, single-crystal ferrites, and high-density ferrites is also described. The lapping characteristics and the wear problems in a ferrite head of hot-pressed, single-crystal, and high-density ferrite are also discussed.     

The effects of silica content,sintering temperature and sintering time on a Ni‐Zn ferrite

Abstract

In this experiment the effects of silica content, sintering time, and sintering temperature on the microstructure and magnetic properties of a ferrite, Ni₀₃₂Zn₀₆₈Fe₂O₄, were studied.

The initial permeability is reduced only slightly when the silica content is less than 0.2 wt %. The Q value is proportional to the silica content approximately. The peak value of μ _iQ product is about constant when the silica content is less than 0.2 wt %.

The best sintering temperature is between 1175°C and 1200°C. The addition of silica (<0.2 wt%) enhances the rate of densification, but the control of sintering time has to be more precise because the addition of silica makes the shape of μ _iQ product peak become sharper and narrower.     

锰锌铁氧体纳米粒子的制备和磁性能研究

以金属离子的硫酸盐溶液和氨水溶液为原料,采用水热法制备了粒径为6～16nm的锰锌铁氧体纳米粒子.采用XRD、TEM、TGA和VSM等方法对产物以及产物的磁性能进行了表征.结果表明,锰锌铁氧体(Mn1-xZnxFe2O4)的居里温度随着锌的相对含量x的增加而单调的降低.锰锌铁氧体的磁化强度先随着锌的相对含量x的增加而增大,当锌的相对含量＞0.6时,磁化强度随着锌的相对含量x的增加而减小.测量了锰锌铁氧体磁流体的饱和磁化强度,计算了锰锌铁氧体(Mn0.4Zn0.6Fe2O4)纳米粒子的磁矩,其值为1.01×10-19A·m2.     

Pulsed laser deposition of Mn-Zn ferrite thin films

Mn-Zn ferrite thin films were deposited on sapphire substrates by pulsed laser deposition from sintered Mn_{1 – x}Zn _x Fe₂O₄ ceramic targets. A full stoichiometric transfer from targets to substrates was achieved. Magnetic inplane measurements in two perpendicular directions were carried out and the macromagnetic properties of films were determined. The hysteresis loops obtained are rectangular and the values of the coercive force, the saturation, and the remanent magnetization are comparable to the same parameters of the bulk Mn-Zn ferrite. The films were characterized using a vibrating sample magnetometer (VSM), a scanning electron microscope (SEM) and by X-ray photoelectron spectroscopy (XPS).     

Rate of heating and sintering temperature effect on the electrical properties of Nd ferrite

The real part of the dielectric constant () and the dielectric loss angle (tan ) as well as the ac conductivity of ferrite Mg_1+x Ti _x Nd _y Fe_2–2x–y O₄ 0.1 x 0.9 at fixed Nd concentration of 0.025 were measured at different temperatures as a function of frequencies. The variation of activation energy as a function of the applied frequency was reported. The obtained data were discussed on the basis of the valence exchange between (Fe³⁺, Fe²⁺), (Fe²⁺, Nd³⁺) and (Fe²⁺, Ti⁴⁺). Also the effect of sintering temperature and heating rate of preparation were discussed.     

锰锌铁氧体制备工艺及其对磁性玻璃陶瓷性能的影响

采用氧化物煅烧法、共沉淀法和溶胶-凝胶法制备锰锌铁氧体前驱体,并将其与生物玻璃陶瓷复合,制备磁性玻璃陶瓷。研究了不同工艺制备的铁氧体对材料磁性、生物活性和细胞亲和性的影响。结果表明,充磁至7.96×105 A/m,材料的饱和磁化强度在7.49～6.46A.m2/kg之间,矫顽力在9.95×103～1.60×104 A/m之间。其中使用共沉淀法制备铁氧体前驱体使复合材料磁滞回线包围面积最大,预期有最好的生热能力。而各铁氧体的掺入均导致材料生物活性下降,但在浸泡入模拟体液21d后,各材料表面均能生成类磷灰石层。将ROS17/2.8细胞与共沉淀法制备的铁氧体复合材料共同培养7d,材料显示出良好的细胞亲和性。     

The production of Mn-Zn ferrite ceramics by injection moulding

A ceramic injection-moulding technique has been used for the preparation of bars and toroids of Mn-Zn ferrite. The binders were based on a combination of polypropylene, microcrystalline wax and stearic acid. Components up to 4 mm thick were fabricated; extended binder burn-out schedules, up to 8.5 days in duration, in a nitrogen atmosphere were required for the thicker parts. Sintered densities were typically 90% of the theoretical value. Initial permeabilities of the toroids were lower than expected (700–1600 rather than 4000) due to the smaller grain size (4–6 m) of the fired products. Optimization of the sintering schedule should enable the microstructure and magnetic properties to be improved.     

Low temperature sintering of MgCuZn ferrite and its electrical and magnetic properties

The low temperature sintering of MgCuZn ferrite was investigated using the usual ceramic method. The effect of Cu substitution on the properties of MgZn ferrites was also investigated and it was found that the densification of MgCuZn ferrite is dependent upon Cu concentration. The sintered ferrite with a density of 4.93 g/cm³ and electrical resistivity > 10¹¹ Ω-cm was obtained for the ferrite with 12 mol% Cu at relatively low sintering temperature (910° C). The magnetic properties of the ferrites also improved by the Cu substitution. The chip inductors made of the ferrite fired at 910 C with 12 mol% Cu exhibited higher d.c. resistance. From these studies it is concluded that the good quality chip inductor can be obtained using the MgCuZn ferrites.     

Reactive sintering of zinc ferrite

The reactive sintering of zinc ferrite, i.e. firing without previously calcining, has been studied using three types of iron oxide. The conversion into ferrite as well as the simultaneous densification were investigated upon variations in morphology and impurity content. The formation reaction is shown to be accompanied by a strong increase of the median pore size. This phenomenon appears responsible for the generally smaller density of the final material as compared with single-phase sintering. It is shown that reactive sintering is inevitably accompanied by expansion, irrespective of molecular volume variations. A calcining step appears indispensable for the preparation of the highest quality of ferrites.     

Reactive sintering of manganese ferrite

The reactive sintering of manganese ferrite, i.e. the concurrence of a chemical reaction with densification during firing, has been studied using several raw materials. It was shown that the formation reaction from the raw materials is always accompanied by expansion and that such processing invariably results in a less dense end product. After calcining the powder, these phenomena did not occur. This was shown to be related to an improved initial homogeneity rather than to the degree of conversion. On the other hand, calcining increased the change of excessive grain growth, which was further influenced by the porosity, the firing temperature and the presence of impurities.     

Low temperature sintering and microwave dielectric properties of zinc silicate ceramics

Effects of ZnO–B₂O₃–SiO₂ glass on the sintering behavior, the microstructure, and the microwave dielectric properties of Zn₂SiO₄ ceramics have been investigated. The ZnO–B₂O₃–SiO₂ glass lowered the sintering temperature of Zn₂SiO₄ ceramics effectively from 1300 to 900 °C. The X-ray diffraction results showed that the secondary phase of SiO₂ in the Zn₂SiO₄ ceramics could be dissolved in the glass. The dielectric constant decreased slightly, and the quality factor decreased with increasing glass content. Especially, when the glass content was chosen as 20 wt%, the ceramics sintered at 900 °C for 2 h exhibited a low dielectric constant of 6.85, a high quality factor of 31,690 and the temperature coefficient of the resonant frequency of −28 ppm/°C, which demonstrated a good potential for use in low temperature co-fired ceramics field.     

微波烧结Mn-Zn 铁氧体的微观结构演变特征

以传统氧化物法合成的Mn-Zn铁氧体前驱体和外购前驱体为实验原料,经压制成形后用频率为2.45 GHz的微波在1 200~1 400℃烧结制备Mn-Zn铁氧体软磁材料.对烧结过程样品的微观结构和形貌进行了研究,并探究了烧结过程致密化特性及微波加热温度对Mn-Zn铁氧体密度的影响.研究表明:微波烧结的Mn-Zn铁氧体具有典型的尖晶石结构,样品主体相为Mn0.4Zn0.6Fe2O4;用SEM观察样品形貌,发现在1 350~1 400℃烧结的样品结晶状况良好,晶界平直,烧结组织均匀;微波烧结温度对密度有较大影响,在1 200~1 400℃,随着烧结温度升高样品密度增高,密度为4.80~5.28 g/cm3,在1 400℃烧结样品比较致密.微波烧结可以实现样品的快速致密.