Thermal Analysis by Electrical Resistivity Measurement

Thermal analysis in the form of electrical resistivity measurement is reviewed. It is useful for studying phase transitions and electrical conduction mechanisms. The resistivity can be the volume resistivity or the contact resistivity, as illustrated for the case of continuous carbon fiber polymer-matrix composites.This revised version was published online in November 2005 with corrections to the Cover Date.     

特征值为二重根的压电材料异材界面端奇异性

横观各向同性压电材料的特征值的不同,其一般解的形式也不同,压电结合材料问题的求解,可以归结为寻找合适的调和函数,针对材料特征值为二重根（s1^2≠s2^2=s3^2)的情况,将变量分离形式的调和函数作特征展开,推导了横观各向同性压电材料轴对称异材界面端附近的奇民异应力场和奇异电位移场,给出院 决定奇异性的特性方程,结果表明,电位移场和应力场具有相同的奇异性,奇异性次数不仅与界面端形状以及材料的机械性质有关。也与材料的压电特性有关。     

基于$lt;i$gt;J$lt;/i$gt;积分的颗粒煤岩单轴压缩下裂纹扩展研究

颗粒煤岩是由众多离散的煤岩颗粒组成的固态多层次多结构物质,具有煤岩与颗粒物质的双重性质,其裂纹扩展规律可以从煤岩力学特性和颗粒物质多尺度特性进行研究. 首先,从能量角度对线弹性材料受压破坏,裂纹扩展产生原因进行了阐述,指出线弹性阶段裂纹的扩展动力源自应变能的释放. 然后,通过物理实验和数值试验从宏观和细观两方面对颗粒煤岩受压破裂过程中裂纹扩展做了进一步研究,结果表明:颗粒煤岩完全破裂后,底部会形成一个锥形堆,裂纹的扩展随着煤岩颗粒粒径的减小而减缓,部分裂纹扩展会出现突变点,且裂纹无光滑性;由于煤岩颗粒粒径等引起介质的非均匀性对裂纹扩展有重要的影响,均质度系数越大裂纹起裂时间越晚,声发射能量释放在裂纹扩展的轻度、中度和深度三个不同阶段逐渐变得频繁、剧烈. 研究结果将有利于进一步研究岩土类颗粒材料受压破裂过程的裂纹扩展规律. 关键词： J积分')" href="#">J积分 颗粒煤岩 单轴压缩 裂纹扩展     

Effect of Cu doping on the magnetic and electrical properties of n=2 Ruddlesden-Popper manganates

A series of polycrystalline Cu-doped n=2 Ruddlesden-Popper manganates La1.2Sr1.8CuzMn（2-x）O7 （x=0, 0.04, 0.13） were synthesized by the solid state reaction method. The effect of Cu doping on the magnetic and transport properties has been studied. It is found that Cu substitution for Mn greatly affects the magnetic and electrical properties of the parent phase La1.2Sr1.8Mn2O7. With the increase of Cu content, the system undergoes a transition from longrange ferromagnetic order to the spin glass state and further to an antiferromagnetic order. A little of Cu dopant can lead to the samples showing semiconductor or insulator behaviour in the whole observed temperature range while the parent phase has a metal-insulator transition. These samples show colossal magnetoresistance at low temperatures and the value of it decreases with increasing Cu content.     

Morphological,Thermal, and Electrical Characterization of Syndiotactic Polypropylene/Multiwalled Carbon Nanotube Composites

In this work, syndiotactic polypropylene/multiwalled carbon nanotubes (MWCNT) nanocomposites, in various concentrations, were produced using melt mixing. The influence of the addition of MWCNT on the morphology, crystalline form, and the thermal and electrical properties of the polymer matrix was studied. To that aim, scanning electron microscopy, Raman spectroscopy, X-ray diffraction, differential scanning calorimetry, and dielectric relaxation spectroscopy were employed. Significant alterations of both the crystallization behavior and the thermal properties of the matrix were found on addition of the carbon nanotubes: conversion of the disordered crystalline form I to the ordered one, increase of the crystallization temperature and the degree of crystallinity, and decrease of the glass transition temperature and the heat capacity jump. Finally, the electrical percolation threshold was found between 2.5–3.0 wt.% MWCNT. For comparison purposes, the results of the system studied here are also correlated with the findings from a previous work on the isotactic polypropylene/MWCNT system.     

DC Electrical Conductivity of the Direct Electrochemically Synthesized Polythiophene Metal Complexes

Electrochemical anodic oxidation of a metal anode in an acetone solution of 2,5-diamino-3,4-dicyanothiophene gave the polythiophene metal complexes of Co, Ni, Cu, Zn, Cd, and Sn. Chemical analyses, as well as FTIR and electronic spectral data, are presented to confirm the formulation of the isolated materials. DC electrical conductivity measurements of the polymer complexes were measured in the range 300–500 K in the annealed and 5% doped forms. The products gave electrical conductivity in the semi-conducting region that increased by heat.     

Reliability of flexible electrically conductive adhesives

Based on our previous work about electrically conductive adhesives (ECAs), a flexibilizer named 1,3‐propanediol bis (4‐aminobenzoate) was used to fabricate flexible ECAs (FECAs). ECAs, FECAs, and electronic devices connected by them were carried out the hot and humid aging test under constant humidity level of 85% relative humidity at 85 °C for 600 h. After aging, the bulk resistance change of ECAs was about 26%, that of FECAs was a little higher, about 29%. The contact resistance change of devices connected by ECAs and FECAs was very great, about 450% and 410%, respectively. The bonding area at connection interface between colloids and devices had delamination, even cracks. The delamination of ECAs was calculated about 60%, the average shear strength of ECAs was reduced about 45%, and those of FECAs were about 50% and 30%, respectively, so FECAs had a higher bonding stability in hot and humid environment. Copyright © 2012 John Wiley & Sons, Ltd.     

蜂窝结构吸波材料等效电磁参数和吸波特性研究

根据强扰动理论,在长波长近似条件下推导出蜂窝结构吸波材料等效介电常数和等效磁导率的计算公式.电磁参数计算结果表明,蜂窝结构吸波材料等效介电常数和等效磁导率均小于吸收层的介电常数和磁导率,但等效介电常数的降幅更大,从而使等效介电常数更接近于等效磁导率,这正是吸波材料波阻抗匹配设计所需要的.反射率计算结果表明,不同的蜂窝高度,吸收层对应一最优厚度,使蜂窝结构吸波材料的反射率最低.这些结果对于蜂窝结构吸波材料设计具有一定的意义. 关键词： 蜂窝结构吸波材料 等效介电常数 等效磁导率 反射率