Electrical Properties of Polycrystalline Nickel Zinc Ferrites

The electrical properties of three ferrites of composition (Ni_0.36Zn_0.64)_{1– x} Fe_{2+ x} O₄, x =−0.03, 0, 0.13, were investigated by impedance spectroscopy. The observed impedance responses corresponded to that of a highly resistive grain-boundary component in series with a less resistive bulk component. Bulk resistances gave linear Arrhenius conductivity plots ( E _a ≤0.25 eV) that were independent of thermal cycling. Grain-boundary resistances changed greatly on cycling between room temperature and 200°C, probably because of changes in the extent of oxidation at the grain boundaries.     

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.     

Microstructure and Properties of Ferrites

Microstructure significantly affects the magnetic and electrical properties of ferrites. Domain behavior and its relation to microstructure of magnetic materials are reviewed, and the critical grain size necessary to maintain a single domain in nickel ferrite is calculated. Experimental data are given for BaO. 6Fe₂ O₃ and NiFe₂O₄ to show the relations among grain sue, coercive force, permeability, ferromagnetic resonance line width (ΔH) , and dielectric losses. Predictions are made for the role of ferrites in the future of ceramic research.     

Magnetic Properties of Dense Lithium Ferrites

Dense lithium ferrite ceramic bodies prepared by hot-pressing exhibited rectangular hysteresis loops. A number of physical properties of technical interest were evaluated and results given. These include initial permeability, dc resistivity, resonance Une width, g_eff factor, and saturation magnetization. The effect of 3–1 octahedral site ordering is discussed. Investigation was extended to the preparation of solid solutions of lithium ferrite and zinc ferrite (Lio._0.5Feo._0.5)_1-xZn_x-Fe₂O₄, where 0 ≤ x ≤ 0.7. Methods of separate control of remanent induction, B _r, and coercive force, H _c, are described.     

Influence of Milled Powder Particle Size Distribution on the Microstructure and Electrical Properties of Sintered Mn-Zn Ferrites

The grain growth and densification rates of Mn-Zn ferrites during sintering are closely linked to the characteristics of the calcined and milled powders used. Long milling times enlarge powder particle size distributions and tend to promote discontinuous grain growth during sintering. For fixed sintering conditions, an optimum milling time, which corresponds to minimal eddy current and hysteresis losses, exists. The electrical properties of overmilled powders deteriorate greatly because duplex structure occurs. Theoretical analysis of the probability of discontinuous grain growth occurring during sintering in relation to powder particle size distribution agrees with the experimental results.     

Magnetic and Magnetostrictive Properties of Magnesium-Nickel Ferrites

The purpose of this study was to determine whether or not the magnetic and magnetostrictive properties of mixed Ni-Mg ferrites having various compositions were superior to those of a simple Ni ferrite. The preparation of the ferrites and the test methods are described briefly. The properties tested were Young's modulus, the remanence, the coercivity, the reversible permeability, the static magnetostriction, the electromechanical coupling coefficient, and the dynamic magnetostrictive constant. The results of the tests showed that the Ni ferrite was superior to the Ni-Mg ferrites as far as magnetic and magnetostrictive properties were concerned.     

Electrical Properties of the Ta-RuO2 Diffusion Barrier for High-Density Memory Devices

The electrical properties of a Ta layer prepared with and without RuO₂ addition were investigated. The Ta + RuO₂/TiSi₂/poly-Si/SiO₂/Si contact system exhibited lower total resistance and ohmic characteristics up to 800°C. Meanwhile, the Ta/TiSi₂/poly-Si/SiO₂/Si contact system showed higher total resistance and nonohmic behavior after annealing at 650°C, attributed to the oxidation of both Ta and TiSi₂ layers. In the former case, a Ta + RuO₂ diffusion barrier showed an amorphous Ta microstructure and embedded RuO _x nanocrystals in the as-deposited state. The conductive RuO₂ crystalline phase in the Ta + RuO₂ film was formed by reaction between the nanocrystalline RuO _x and oxygen indiffused from air during annealing. When the Ta layer was deposited with RuO₂ addition, therefore, both the electrical properties and the oxidation resistance of the Ta + RuO₂ diffusion barrier were better than those of TiN, TaN, and Ta-Si-N barriers.     

Some Physical Properties of High-Density Thorium Dioxide

The values for a number of physical properties are reported for a very high density form of thorium dioxide. When specimens of a mixture of 99½% ThO² and ½% CaO, by weight, were hydrostatically pressed at 30,000 lb. per sq. in. and heat-treated for 1 hour at 1800°C., they attained 99.0% of theoretical density. All the test specimens were extremely brittle. Physical-property values determined at room tempera- ture were the following: lattice constant; bulk and theoretical (X-ray) densities; compressive and impact strengths; Knoop hardness; modulus of rupture and Young's modulus, determined by a static method; Young's modulus and the shear modulus, determined by a dynamic method; Poisson's ratio and the bulk modulus, calculated from the dynamic-test data; and the velocity of sound through the material. The properties determined at elevated temperatures were the following : linear thermal expansion modulus of rupture and Young's modulus, determined by a static method; Young's modulus and the shear modulus, determined by a dynamic method; and Poisson's ratio, calculated from the elevated-temperature dynamic-test data. "Martin's diameter" grain counts were taken for the material both before and after heat-treatment.     

Growth and Properties of Single Crystals of Hexagonal Ferrites

Single crystals of hexagonal ferrites up to 1/2 in. long were grown from the system NaFeO₂-Fe₂O₃-BaO-MeO, where Me = divalent Zn, Co, Ni, or Mg. NaFeO₂ was the flux from which crystals were grown in platinum crucibles from a maximum temperature of 1250° to 1375°C. More than 150 single-crystal growth experiments were attempted and the reaction products were studied by X-ray diffraction and optical microscopy. Stability data for the principal single-crystal products are given for initial compositions lying in quaternary planes. Such planes were considered for BaO/MeO ratios corresponding to the compounds 1/1 for Ba₂Me₂Fe₁₂O₂₂ (Y) and Ba₂Me₂Fe₂₈O₄₆ (X) , 3/2 for Ba₃Me₂Fe₂₄O₄₁ (Z) , 2/1 for Ba₄Me₂Fe₃₆O₆₀ (U) , and 1/2 for BaMe₂-Fe₁₆O₂₇ (W) (Me = Zn, Co, Ni, or Mg). A number of adjoining planes were also considered. All the five known structure types were grown as single crystals. A series of four new hexagonal ferrite structures was discovered. These were derived from Z by systematically adding blocks of Y. Magnetization as a function of temperature and field was investigated for crystals of two structure types. The room-temperature ferromagnetic resonance and effective anisotropy were studied for substituted crystals of the same two structure types.     

Magnetic Properties and Associated Microstructure of Zinc-Bearing Square-Loop Ferrites

Zinc oxide was added to square-loop ferrite compositions in order to obtain a lower coercive force and higher magnetic saturation induction than that usually possible from standard commercial square-loop ferrites. Curie temperatures, hysteresis loops, initial permeabilities, magnetization curves, and switching times for these zinc-bearing square-loop ferrites were determined, and representative curves of these parameters are given. Grain structure and etchpit density were also studied, and typical photomicrographs are presented. Zinc oxide can be added to square-loop ferrites to great advantage, but if too much is added, the useful magnetic properties degenerate completely.     

导电聚苯胺/钡铁氧体复合材料性能研究

对采用柠檬酸溶胶–凝胶法和共沉淀法两种方法制备的钡铁氧体粒子进行了对比,采用原位聚合的方法合成了聚苯胺/钡铁氧体复合材料。用X射线衍射仪、扫描电子显微镜、四探针测试仪、振动样品磁强计对产物的结构和性能进行了表征和测试。实验结果显示,柠檬酸溶胶-凝胶法所制得的产物主要为钡铁氧体,纯度较高。钡铁氧体结构主要为M型六角晶系片状结构,平均粒径在20~60μm。电磁测试结果显示,钡铁氧体的比饱和磁化强度与矫顽力均随焙烧时间的延长呈上升趋势,随着时间从3 h延长到5 h,比饱和磁化强度从36.9 emu/g增加到44.9 emu/g,矫顽力也从5 198.0 Oe增加到5 339.1 Oe;聚苯胺/钡铁氧体复合材料的电阻率随钡铁氧体含量的增加呈上升趋势。     

Structure and Properties of Vibrating Extruded High-Density Polyethylene Sheet

Summary The effect of vibration frequency and vibration amplitude on the microstructure and mechanical properties of high-density polyethylene (HDPE) sheets, obtained through electromagnetic dynamic plasticating extruder, were studied systematically. The mechanical properties, characterized by tensile and impact strengths, have been tested along the flowing and transverse directions (MD&TD). The mechanical tests show that the tensile strength and impact toughness, especially in TD, were much improved under the reciprocating axial vibration. Differential scanning calorimetry (DSC), scanning electron microcopy (SEM) and wide angle X-ray diffraction (WAXD) were executed to analyze the microstructure of the samples. The results indicate that the vibration extrudate has higher crystallinity, perfect crystallite, and strong inter-spherulite ties, which account for enhancement of the mechanical properties of sheets, compared to conventional static extrusion.     

预烧温度对锶铁氧体的微结构和磁性能的影响

采用传统陶瓷工艺法,在相同配方、相同实验条件情况下制备了不同温度预烧的锶铁氧体,分析了预烧温度(1180℃,1200℃,1210℃,1250℃,1270℃,1290℃,1300℃,1310℃)对锶铁氧体微结构和磁性能的影响.X射线衍射分析表明,随着预烧温度的上升,锶铁氧体主体仍为六角锶铁氧体结构.预烧温度较低时,反应不完全,有Fe2O3杂相存在.通过扫描电镜对样品的形貌结构进行分析,测试结果显示铁氧体晶粒呈六角锶铁氧体片状结构,随着预烧温度的上升出现熔融甚至出现全部熔融;磁性能测试显示,样品的Br随预烧温度的上升先增大后减小,当预烧温度达到1290℃时,Br和(BH)max达到最大值,Br为422.85 mT,(BH)max为34.99 kJ/m3.Hcj先下降,预烧温度到1250℃时上升;Hcb先上升至1290℃时达到最大值,之后下降.综合各方面的性能,最佳的预烧温度确定为1290℃.     

Ni1-xZnxFe2O4铁氧体的制备及其性能研究

通过化学共沉淀法制备了颗粒较细、粒度分布较均匀、团聚较少的Ni1-xZnxFe2O4前驱体。通过TG-DSC分析、XRD测量、激光粒度分析和形貌观察确定了Ni1-xZnxFe2O4前驱体的优化煅烧温度。以活性Ni1-xZnxFe2O4前驱体为原料,通过固相反应法制备Ni1-xZnxFe2O4陶瓷。不同温度烧结的、不同组成的Ni1-xZnxFe2O4陶瓷均呈现纯尖晶石结构。Zn2+含量、烧结温度对Ni1-xZnxFe2O4陶瓷的结构、密度、物理性能产生重要影响。在相同的烧结温度下,随着Zn2+含量的增加,Ni1-xZnxFe2O4陶瓷的密度、方块电阻、饱和磁化强度呈现增大的趋势。随着烧结温度的升高,Ni1-xZnxFe2O4陶瓷的密度、方块电阻、饱和磁化强度明显增大。     

Electrical Properties of Woodceramics

Woodceramics have recently attracted much attention as ecomaterials at low cost. Electrical properties of the woodceramics (WCM hereafter) have been characterized in the range 10–70% relative humidity and for temperatures from –20 to 100°C. The WCM bulk has been prepared by burning MDF board impregnated with phenolic resin at 650 and 750°C. Electrical resistance decreased linearly with increasing temperature, indicating the negative temperature coefficient like semiconductor. Relative humidity dependence of the resistance also indicated excellent linear characteristics between 10 and 70% RH measured here. Activation energies of 0.21, 0.15, 0.05, and 0.01 eV have been revealed from van der Pauw method. The excellent linearity for humidity and temperature is prominent advantages of WCM which may be useful as a new humidity and also temperature sensor.