Magnetic Ceramics: VI, Evaluation of Some Methods of Nickel Ferrite Formation

The extent of nickel ferrite formation, as affected by four preparatory techniques, was investigated by determining the magnetic moment of the reacted powder with a vibrating-coil magnetometer. The oxide, carbonate, hydroxide, and oxalate methods were used. At low temperatures the hydroxide and oxalate techniques were found to give the greatest yield of ferrospinel. The hydroxide method yielded a magnetic material by precipitation. Weight-loss measurements were correlated to the magnetic data.     

Magnetic Ceramics: III, Effects of Fabrication Techniques on Magnetic Properties of Magnesium Ferrite

Magnesium ferrite specimens made of unreacted (mixed oxides) and reacted (ground ferrite) materials were prepared to determine the effects of forming pressure, firing temperature, time at peak temperature, firing atmosphere, and quenching treatment on their magnetic and electrical properties. High firing temperatures (1450°C.), long holding times (8 hours), and quenching from the highest temperature (1200°C.) produced the highest μ_i, and B _m, the lowest H _c, and a decrease in B _r. These changes were related to the change in the void volume and particle size of the specimens brought about by the fabrication techniques and to the alterations in the degree of inversion in the spinel lattice during quenching. Oxygen loss or gain from the stoichiometric amount caused a loss of magnetic properties. X-ray and microstructure studies aided in the interpretation of the experimental data.     

软磁铁氧体纳米粉的制备

介绍了一种制备纳米级软磁铁氧体的新方法——催化相转化水热法。     

Magnetic Ceramics: II, Properties of Magnetite and Manganese Ferrite Fired in Various Atmospheres

Magnetite and manganese ferrite, fired in various atmospheres, were tested for initial a.-c. permeability, for quasi-static hysteresis characteristics of B_m, B_r , and H_c , and for resistivity. Optimum properties were obtained for magnetite made under exactly controlled oxygen pressures and for manganese ferrite fired in a CO₂ atmosphere. These data are discussed with reference to the resistivity as affected by probable cation distribution.     

Magnetic Ceramics: IV, Development of a Complex Ferrite with a Rectangular Hysteresis-Loop Characteristic

A complex ferrite composition was investigated to ascertain how much the magnetic properties of the final product were affected by body preparation, forming pressure, firing temperature, and time at peak temperature. One reducing and three oxidizing atmospheres, in addition to a quenching cycle, were investigated. The magnetic parameters μ_i and B_m increased with density, whereas H_c decreased. The specimens fired at the maximum peak temperature, or quenched from above 800°C, gave markedly diminished B_T values. The maximum loop rectangularity followed the same pattern.     

Magnetic Ceramics: VII, Effect of Iron Oxide Particle Size on Nickel Ferrite Formation

Five iron oxides of increasing particle-size distribution, mixed with nickel oxide of a constant-size range, were heated at various temperatures and time intervals. The extent of nickel ferrite formation, as influenced by particle-size distribution of the iron oxide constituent, was measured with a compensating-coil magnetometer. Using the Jander relation for this type of reaction, activation energies ranging from 54 to 70 kcal. were computed for increasing particle size. These results are examined and compared with current procedures for the production of ferrite powders.     

钡铁氧体磁粉的热处理方式

对生产钡铁氧体磁粉的不同热处理方式进行了研究．以化学共沉淀得到的合成料粉为原料,分别在循环流化床和马弗炉中进行了对比实验,考察了不同热处理方式对磁粉磁性能、晶体结构和表面形态的影响,特别是温度的影响,以及适宜的热处理条件;讨论并分析了循环流化床设备在粉体材料热处理中具有的优势和特点,提出了动态热处理的概念．     

泡沫陶瓷的制备方法

本文综述了泡沫陶瓷的几种制备方法,指出了各种方法的工艺关键及其优缺点。通过分析认为目前泡沫陶瓷最理想的制备方法是有机前驱体浸渍法;在陶瓷粉料中适当加入陶瓷纤维,会改善发泡反应法制品性能;将注凝成型技术移植到泡沫陶瓷制备工艺中可望取得较理想的效果。     

Magneto-Dielectric Properties of Mg–Cu–Co Ferrite Ceramics: II. Electrical, Dielectric, and Magnetic Properties

DC resistivity, dielectric, and magnetic properties of Mg-ferrite ceramics (Mg_1−xCu_xFe_1.98O₄, with x=0.10–0.30, and Mg_0.90−xCo_xCu_0.10Fe_1.98O₄, with x=0.05–0.20) were investigated. A primary objective is to develop magneto-dielectric materials with almost equal values of permeability and permittivity, as well as low magnetic and dielectric loss tangent, for miniaturization of antennas. The MgFe_1.98O₄ ceramic sintered at 1125°C possessed values of permeability and permittivity of ∼6.5, and relatively low magnetic and dielectric loss tangents of <10⁻², with a sintered density of only ∼70% of the theoretical density. Incorporation of Cu was found to be able to not only improve the densification and grain growth but also alter the electrical and magnetic properties of MgFe_1.98O₄. Further modification by Co resulted in promising magneto-dielectric materials, with an almost equal permeability and permittivity of ∼9.5 over 3–30 MHz (HF band). Together with their low magnetic and dielectric loss tangents and good sinterability, this class of magneto-dielectric materials could be potential candidates for the design of small antennas in the HF band (3–30 MHz). The DC resistivities and complex relative permittivities of the ferrite ceramics were discussed with respect to their microstructure, grain size, and the formation of Fe²⁺ ions. The variation of high-frequency magnetic properties of the ferrite materials with sintering temperature can be quantitatively understood by the magnetic circuit model and the Snoek-like law.     

纳米锰锌软磁铁氧体的制备及其产品表征

以氯化铁、二价金属离子(锰、锌、镍)的硫酸盐为原料,在微量FeSO4催化剂的作用下,通过沸腾回流反应制备出前驱体,再经140℃干燥得到纳米锰锌软磁铁氧体产物。然后运用TG-DTA、XRD、SEMF、T IR等检测手段对前驱体及产物的物性和结构进行表征,结果表明该法具有工艺简单、生产效率高、反应时间短、条件温和、产品矫顽力小等优点,产物是理想的纳米级软磁性锰锌铁氧体材料。     

Preparation,Dielectric, and Magnetic Characteristics of LuFe2O4 Ceramics

Preparation of LuFe₂O₄ ceramics under vacuum environment was investigated together with the structural, dielectric, and magnetic characterization. Single‐phase LuFe₂O₄ could be obtained by the present process and the crystal structure was identified to be rhombohedral in space group . An obvious dielectric relaxation with activation energy of 0.29 eV was observed between 175 and 275 K. The Néel temperature of the present ceramics was ~250 K, and a reentrant spin glass transition was indicated at ~216 K. Two anomalies were observed in the DSC curve, which were relative with the ferrimagnetic transition and 2D–3D charge ordering transition of LuFe₂O₄. Meanwhile, a remarkable decrease appeared in the dielectric constant of the as‐magnetized LuFe₂O₄ sample, implying the magnetodielectric effect in the present ceramics.     

铁氧体橡塑磁条的新型制备方法探索

采用取向充磁取代传统的脉冲充磁制备了铁氧体橡塑磁条,可以得到相同质量的磁条,而且生产成本降低,应用掏空设计的新方法可以进一步节约成本,且不影响磁条的质量。     

Characterization of the Free-Carbon Phase in Precursor-Derived Si-C-N Ceramics: I, Spectroscopic Methods

Polyvinylsilazane, as a precursor for Si-C-N ceramics, was prepared by ammonolysis of functionalized chlorosilanes. Pyrolysis under inert atmospheres at T _p= 1000°C led to an amorphous Si-C-N-(H) ceramic. Further heat treatment caused the transformation to the thermodynamically stable crystalline phase assemblage. The structural changes, especially those of the excess carbon, were studied by characterizing the solid intermediates via solid-state magic angle spinning nuclear magnetic resonance spectroscopy. Moreover, Raman spectroscopy, electron spin resonance spectroscopy, and chemical analysis were used. Based on these methods, a comprehensive picture of the formation and behavior of the free-carbon phase present in polymer-derived ceramics was obtained.     

多孔陶瓷的制备方法及研究现状

近年来,多孔陶瓷材料在保温、气体过滤、催化载体、分离膜、窑具、骨和牙齿的生物医学替代品,以及传感器材料等领域应用越来越广泛.针对多孔陶瓷制备工艺和性能的研究呈现快速发展的趋势,并取得了大量的研究成果.本文以多孔陶瓷的制备工艺为主线,综述了部分烧结法、牺牲模板法、复制模板法、直接发泡法和3D打印法等5种主要多孔陶瓷制备方...     

浅谈干法生产软磁铁氧体陶瓷颗粒料的松装密度

阐述了干法生产软磁铁氧体陶瓷颗粒料松装密度的测试方法,从工艺角度讨论了松装密度的影响因素,并提出了松装密度的调整方法。     

多孔陶瓷制备工艺及其孔结构检测方法研究进展

多孔陶瓷由于具有特殊的渗透率、热传导率、强度、捕获效率和电导率等性能而受到越来越多关注。在环境保护方面,它有减少污染、吸收有毒气体和净化污水等绿色环保功能。本文综述了多孔陶瓷制备工艺的最新进展,并对多孔陶瓷孔结构的常见检测方法进行了比较,最后展望了多孔陶瓷的发展前景。     

Nickel-Zinc Ferrites: I, Effect of Composition on the Magnetic Properties of a Nickel-Zinc-(Cobalt) Ferrite

By varying the mole percent of Fe₂O₃ in a nickel-zinc-(cobalt) ferrite in very small increments, it was found that an optimum composition exists. Deviations from this composition as small as 0.1% can cause a decrease in resistivity by e.g. a factor of 1000. The ferrite is stoichiometric at the optimum composition, and its resistivity has a narrow, sharp maximum; the μ_o Q product is also maximal. Such a coincidence has not been previously observed. The usual eddy-current relation between resistivity and ac losses fails to explain this phenomenon because of the very high resistivities involved.     

Magneto-Dielectric Properties of Mg–Cu–Co Ferrite Ceramics: I. Densification Behavior and Microstructure Development

The densification, grain growth, and microstructure development of Mg–Cu–Co ferrite ceramics (MgFe_1.98O₄, Mg_{1− x} Cu _x Fe_1.98O₄, with x =0.10–0.30 and Mg_{0.90− x} Co _x Cu_0.10Fe_1.98O₄, with x =0.05–0.20) were studied. The primary objective was to develop magneto-dielectric materials for miniaturization of high frequency and very-high frequency antennas. It was found that magnesium ferrite (MgFe_1.98O₄) is a promising magneto-dielectric material. However, due to its poor densification, it could not be fully sintered at a temperature below 1200°C. High-temperature sintering resulted in undesirable electrical and dielectric properties, due to the formation of Fe²⁺ ions. The poor densification and slow grain growth rate of MgFe_1.98O₄ can be considerably improved by incorporating Cu, due to the occurrence of liquid-phase sintering at a high temperature. A critical concentration of Cu was observed for Mg_{1− x} Cu _x Fe_1.98O₄, above which both densification and grain growth were maximized or saturated. The presence of Co did not have a significant influence on the densification and grain growth of the Mg-based ferrite ceramics.     

碳化硅多孔陶瓷的制备工艺比较

多孔碳化硅陶瓷由于具有优良的高温强度、耐磨性、耐腐蚀性以及抗热震性而得到越来越广泛的关注.随着科技的发展,其已在环境保护、过滤分离、尾气吸收、吸声降噪、生物医学、航空航天和能源化工等方面发挥着重要的作用.本文着重分析了多孔碳化硅陶瓷的传统制备工艺与先进制备工艺的优缺点,并对其未来的制备工艺作出展望.     

Effect of TiO2 Doping on the Sintering Process,Mechanical and Magnetic Properties of NiFe2O4 Ferrite Ceramics

TiO₂‐doped NiFe₂O₄ samples were prepared via ball‐milling and two‐step sintering processes. Besides NiFe₂O₄ phase, two new phases, NiTiO₃ and Fe₂TiO₅, formed in TiO₂‐doped samples. The temperature of sintering onset for 1.0 wt% TiO₂‐doped samples is 230°C lower than that of undoped samples. Early‐stage synthesis process of TiO₂‐doped NiFe₂O₄ ceramics is controlled by grain boundary diffusion mechanism. Increasing TiO₂ content from 0 to 1.0 wt%, the apparent activation energy decreased from 813.919 KJ/mol to 639.361 KJ/mol. The values of relative density and bending strength reached their maximum value with 1.0 wt% TiO₂. Saturation magnetization, residual magnetization ratio and coercivity decrease with increasing TiO₂ content.