Influence of rare earth Ce on structural, electrical and magnetic properties of Sr based W-type hexagonal ferrites

A series of single phase W-type Sr_3−xCe_xFe₁₆O₂₇ (x=0, 0.02, 0.04, 0.06, 0.08, 0.10) hexagonal ferrites prepared by the Sol-Gel method was sintered at 1050 °C for 5 h. The X-ray diffraction analysis reveals that all the samples belong to the family of W-type hexagonal ferrites. The c/a ratio falls in the range of W-type hexagonal ferrites. The grain size was measured by SEM varies from 0.7684 to 0.4366 μm which shows that the Ce³⁺ substituted samples have smaller grain size than pure ferrite Sr₃Fe₁₆O₂₇ which results from the difference in ionic radii of Ce³⁺ (1.034 Å) and Sr²⁺ (1.12 Å). The room temperature resistivity of the present samples varies from 6.5×10⁸ to 272×10⁸ Ω-cm. The coercivity increases from 1370 to 1993 Oe which is consistent with the decrease in grain size. The coercivity values indicate that the present samples fall in the range of hard ferrites. The large value of H_c may be due to domain wall pinning at the grain boundaries.     

A New Method for Calculating Two-Phase Relative Permeability from Resistivity Data in Porous Media

Many resistivity data from laboratory measurements and well logging are available. Papers on the relationship between resistivity and relative permeability have been few. To this end, a new method was developed to infer two-phase relative permeability from the resistivity data in a consolidated porous medium. It was found that the wetting phase relative permeability is inversely proportional to the resistivity index of a porous medium. The proposed model was verified using the experimental data in different rocks (Berea, Boise sandstone, and limestone) at different temperatures up to 300°F. The results demonstrated that the oil and water relative permeabilities calculated from the experimental resistivity data by using the model proposed in this article were close to those calculated from the capillary pressure data in the rock samples with different porosities and permeabilities. The results demonstrated that the proposed approach to calculating two-phase relative permeability from resistivity data works satisfactorily in the cases studied.     

金属W阴极电阻率随温度变化的实验研究

本文给出了温度在300K到2500K范围内,金属W的电阻率随温度变化的实验曲线,对实际工作具有一定的指导意义．     

基于有限元数值模拟的直流电阻率激电找矿探测技术

为提高直流电阻率激电探测成果地质解释准确性,促进直流电阻率激电在找矿勘查中的应用,采用有限元数值模拟对直流电阻率激电探测中低阻高极化体、直立板状体、低阻盖层、高阻盖层、地表不均匀体、地形起伏及实测数据反演解释几个主要方面进行了对比分析。研究结果表明,对于实际勘查中的反演解释结果,根据异常特征构建地质体模型并进行有限元数值模拟,能快速判别探测目标体异常属性、区分虚假异常,提高定量解释水平及找矿勘查效率。研究结果为直流电阻率激电找矿探测定量解释提供了参考。     

半导体小圆形薄片电阻率四探针测量的修正因子

本文推导了任意形状排列四探针测量小圆形薄片电阻率时同时考虑厚度和半径影响的修正因子表达式:作为特例,计算了直线和方形两种常用的探针排列情况下的修正因子,并用直线四探针对硅单晶片进行实验测量.结果表明所推导的公式可较准确地测量任意厚度小圆形薄片的电阻率.     

Electric transmission behavior of self-assembled Cu–W nano multilayers

Metallic nano multilayers were usually prepared by dual targets alternating deposition method. In this paper, a series of self-assembled Cu–W nano multilayers with different modulation periods were deposited on single crystal silicon substrate by dual targets confocal magnetron sputtering technique. The self-assembled film presented an alternation of W-rich layer and Cu-rich layer. The degree of coherence of the layered interface can be adjusted by controlling both the solid solubility of W-rich...     

基于丝网印刷技术的碳纳米管场发射冷阴极制作

制备了一种新型碳纳米管浆料,并总结了一套阴极制作工艺.实验表明,质量比约为10%的纯化碳纳米管、5%的纳米金属粉末和有机材料混合形成的印刷浆料,其阴极具有较好的发射均匀特性.在浆料制备过程中通过加入表面活性剂使碳纳米管分散更加均匀.用丝网印刷技术制作阴极,并用机械刀刻的办法制作阴、栅两极之间的沟槽,经烧结后分析阴极膜的电阻率和粘附性随阴极材料组分和制作工艺的变化关系,确定较为合适的升温曲线及丝网目数,阴极碳纳米管的均匀性、导电性的提高改善了发射均匀性.该阴极开启场为2.5 V/μm,在电场强度为3.3 V/μm下,阳极电流为5.6 μA,场发射电流稳定,波动小于5%.     

Electrical transport, magnetic and thermal properties of icosahedral Al–Pd–Mn quasicrystals

We report measurements of electrical resistivity (ρ), Hall coefficient (R_H), magnetization (M) and specific heat (C_p(T)) of high-quality icosahedral Al_70.4Pd_20.8Mn_8.8 phases with different thermal treatment. An improvement in the quasi-crystallinity upon the annealing treatment caused a drastic increase in ρ up to 7000 μΩ cm accompanied by a very small electronic specific heat coefficient γ. The low temperature ρ(T) data has been analyzed in terms of weak localization and electron–electron interaction effects. The Hall resistivity (ρ_H) is found to be strongly temperature-dependent and varies linearly with the magnetization (M) for the same field and temperature. Magnetization measurement reveals that more conductive samples are more magnetic and vice versa. Magnetic susceptibility (χ) data of all the annealed samples agrees with the Curie–Weiss-like behavior implying the existence of localized moments. The negative Curie–Weiss temperature (θ) indicates strong antiferromagnetic coupling between individual Mn atoms. The magnetic Mn concentration is found to be small, ranging from 1.73×10^-4 for the less magnetic sample studied up to 3×10^-3 for the more magnetic one. The small electronic specific heat coefficient obtained for all the samples suggests a significant reduction in the electronic density of states (DOS) at the Fermi level (E_F) upon thermal annealing treatment.     

红粘土土洞的形成及其电探异常特征的研究

通过对土洞及形成条件的初步探讨，认为红粘土土洞是由于红粘土的胀缩性和地下水、溶隙等潜蚀作用造成的，模型断面上电测探曲线形态与实际工作结果有较好的统一，对评价地基的稳定性，预防水土流失等均有较好的指导意义。     

ZrO2—SiC复合材料的制备及导电特性的研究

ＺｒＯ２－ＳｉＣ复合材料的制备及导电特性的研究许小红任引哲（山西师范大学化学系临汾０４１００４）宋波毛裕文（北京科技大学物化系北京１０００８３）关键词氧化锆碳化硅复合材料热压烧结电阻率中图分类号Ｏ６１４．４１２近十几年来，电热体材料的研制开发和利用已...