Three-Dimensional Solution and Experimental Confirmation for the Electric Resistivity Testing of Surface-Breaking Defects in Green-State Powder Metallurgy Compacts

This paper investigates electrostatic voltage distributions around a surface-breaking flaw due to an injected current of known strength. The direct 3-D solution of the voltage behavior over the flawed surface is obtained numerically by the use of a boundary integral formulation. A novel iteration method is applied to solve the resulting electrostatic integral equation for the unknown surface voltage distribution. In addition to investigating the sensitivity of different flaw sizes to the observed surface voltage distribution, important issues such as suitable probe spacing and current flow orientation are studied. For sufficiently small surface-breaking flaws, a simple image source model is developed to evaluate the voltage response of hairline cracks. The model is tested by comparing it with the developed numerical solution. Experiments aimed at establishing the validity of the modeling approach show remarkable agreement with the theoretical model.     

Thermophysical Properties of W–Re Alloys Above the Melting Region

In earlier experiments we have studied pure elements with a fast pulse heating technique to obtain thermophysical properties of the liquid state. We report here results for thermophysical properties such as specific heat and dependences among enthalpy, electrical resistivity, and temperature, for four W–Re alloys (3.95, 21.03, 23.84, and 30.82 at % of Re) in a wide temperature range covering solid and liquid states. Thermal conductivity is calculated using the Wiedemann–Franz law for the liquid alloy, as.well as data for thermal diffusivity for the beginning of the liquid phase. Additionally, data for the entire temperature range studied have been analyzed in comparison with those of the constituent elements, tungsten and rhenium, since both metals have been studied previously with the same experimental technique. Such information is of interest in the field of metallurgy since W–Re alloys of low Re content in the region of mutual component solubility in the solid state are widely used as thermocouple materials for the purposes of high-temperature thermometry.     

一个低电阻率油气藏的测井评价

根据J油田大量岩芯分析资料,应用油藏流体分布理论和毛管压力计算方法,研究该油田低电阻率油气层的形成原因认为:地层水矿化度高(多数>20万ppm);微细孔隙发育,束缚水含量高;粘土矿物含量高且分布在碎屑颗粒表面等是形成低电阻率油气层的主要原因.一般常规测井评价时,对这种低电阻率油气层容易误释而丢弃.依据油气藏流体分布原理,应用毛管压力方法计算原始含油饱和度,可准确地识别出这种低电阻油气层,并可预测其产能.     

High-temperature properties of the Bi-Sr-Ca-Cu-O system: Simultaneous occurrence of melting, oxygen desorption, and a metal-insulator transition

We have investigated the temperature dependence of the electrical transport and the thermogravimetric properties, from -200°C to +1000, of the Bi-Sr-Ca-Cu-O high-temperature superconductor. We conclude that this system has a cooperative, simultaneous-melting/oxygen desorption/metal-insulator transition that occurs near 900°C. We speculate on its nature and on its relationship to phenomena found in other high-T _c superconductors.     

A universal dependence for thermal conductivity of metals and dilute alloys

A universal curve relating the maximum of thermal conductivity and its respective temperature with the residual electrical resistivity has been proposed for metals and dilute alloys. Based on the equation of that curve, a comparative analysis of selected literature data of thermal conductivity of metals, which have residual electrical resistivity in the range 10^–11<₀<10^–5. cm, have been performed. Using the data for 33 metals, confirmation of the Wiedemann-Franz law for the impurity component/T of thermal conductivity was obtained, which means that _th/_el1, where _th and _el are the parameters of the electron-lattice defect interaction obtained from measurements of thermal and electrical conductivity, respectively. Examples of the failure of the Wiedemann-Franz law are also presented, exhibiting the values of _th/_el in the range 0.16 to 25. Measurements of thermal conductivity in the range 2 to 20 K and determination of the residual electrical resistivity for the samples of Cd doped with Zn and quenched were performed, resulting in values _th/_el1.     

Structure and electronic properties of SiC thin-films deposited by RF magnetron sputtering

SiC thin-films were prepared by RF-magnetron sputtering technique(RMS) with the target of single crystalline SiC and then annealed. The surface morphology of thin-films was characterized by AFM. The result shows that the surface of the thin-films is smooth and compact; XRD analysis reveals that the thin-films are amorphous. The thickness, square-resistance and curves of resistance—temperature were measured. The results show that the curves of lnR versus 1/kT both before and after annealing satisfy the expression of lnR∝△W/kT, where ?W is electron excitation energy in the range of 0.014 2-0.018 5 eV, and it has a trend of increasing when the temperature is increased. After synthetical analysis we get the conclusion that the electronic mechanism of the thin-films is short distance transition between the localized states in the temperature range of 25-250 ℃. The resistivity is in the range of 2.4×10-3-4.4×10-3 Ω·cm and it has the same trend as electron excitation energy when annealing temperature is increased, which further confirms the electronic mechanism of thin-films and the trend of electron excitation energy versus annealing temperature.     

熔体快淬Cu100-xCrx合金过饱和固溶体的时效分解及对电阻率的影响

用熔体快淬法制备了C11100-xCrx(x=2～35)合金带.研究表明:熔体快淬带的组织由Cr在Cu中的过饱和固溶体、富Cr溶质偏聚区、富Cr液相分解粒子组成;含Cr量增加,液相分解粒子体积分数增加,电阻率提高;过饱和固溶体在等温时效过程中短时间内(10 min)快速分解完毕,合金带的电阻率大幅下降,延长时效时间,富Cr沉淀相尺寸长大缓慢;时效温度升高,富Cr沉淀的尺寸略有增大,电阻率在600℃时效达到最小值.     

工程物探在温泉区域断层调查的效果分析

温泉区域地质构造一般比较复杂、埋深浅,高精度工程物探方法在此类区域进行地质调查能够取得很好的效果。本文以青岛沧口-温泉断裂带调查为实例,通过高密度电法和浅层地震方法的综合运用,来查明断裂带以及地下水在该区域的分布情况。     

降温速率对Ba0.92Ca0.08TiO3 PTCR陶瓷室温电阻率"反常"现象的影响

通过系统研究烧结工艺对BaO92Ca0.08TiO3电阻正温度系数(possitive temperature coefficient resistance，PTCR)陶瓷的影响，在晶粒生长过程中分析液相在晶界中的分布。着重研究降温速率对PTCR室温电阻率的影响。发现在1300～1150℃温区内，当降温速率大于15℃／min时，出现随降温速率增加，室温电阻率增大的“反常”现象。根据液相在晶界区分布随降温速率的变化规律，对这种“反常”进行解释。     

掺锰BaTiO3 PTCR陶瓷的电子顺磁共振研究

利用电子顺磁共振（EPR）方法对Mn掺杂的BaTiO3 PTCR陶瓷在120－450K的温度范围内进行了研究，研究结果表明：高自旋Mn^2 离子的6重谱线非常明显，表征谱线位置的g因子为2．009 9,Mn^2 离子信号弱弱与BaTiO3晶体结构密切相关，Mn^2 离子信号的温度分布呈U型，即在三方相和立方相时，信号强度较强，而在四方相和斜方相时信号很弱，这是因为在四方相和斜方相中，由于BaTiO3晶体结构的扭曲和畸变，导致Mn^2 和Vo空位缔合生成Mn^2 -Vo复合缺陷，未成对电子的消失以及复合缺陷n^2 -Vo的生成最Mn^2 在四方相和斜方相（200－380K）消失的主因，实验中没有发现Mn^3 和Mn^4 的信号，而与实验的环境条件一致，掺Mn后样品Curie点的漂移可能是Mn进入晶格的一个判据，此外，由于试样的n(Ba)/n(Ti)=1，因而没有发现钡空位VBa及其它的复合缺陷（如：VBa-Mn^2 ,Mn^3 -Vo,La^3 -Mn^3 等），Mn^2 离子等电子陷阱的生长是Curie温度处电阻骤然增加的主要原因。