Papers by Keyword: Resistivity

Abstract: A systematic investigation of neodymium-based manganite, Nd_0.7Sr_0.3MnO₃, was undertaken with a view to understand the influence of sintering temperature on various physical properties. The materials were prepared by the a soft chemical approach of co-precipitation method by sintering at four different temperatures starting from 700 to 1000 °C, with an interval of 100 °C. X-ray diffraction (XRD), transmission electron microscopy (TEM) and D. C. four-probe resistivity were employed to study the crystal structure, average particle size and electrical property respectively. Analysis of XRD patterns shows that all the samples exhibit single phase orthorhombic crystal structure. We followed William-son Hall approach to calculate the lattice stain (ε).These materials were found to exhibit different metal-insulator transition temperature (T_MI) for the different sintering temperature. The value of T_MI increases, as the sintering temperature increases, whereas ε decreases. TEM results show that with the increment of sintering temperature, the particle size of the NSMO samples also increases, which plays a key role on electrical transport. To understand the conduction mechanism in metallic and insulating regions of resistivity, various theoretical models are discussed in this communication.

Abstract: This paper developed a resistivity measurement system on the platform of in-situ detector which based on seafloor drilling machine. In order to precisely process the weak voltage signal which outputted by the resistivity probe, the paper carried out the cross-correlation algorithm theoretical derivation and MATLAB simulation, then ported the algorithm to TMS320F28069 DSP processor and designed hardware. A mass of contrast experiment shows that the cross-correlation algorithm is an effective method to process weak signal. It can improve accuracy and anti-jamming ability of the submarine sediment resistivity measurement system. The method of submarine sediment resistivity measurement can be widely used in fields of marine geological survey, marine environment research, etc.

Abstract: Copper-plated short carbon fiber/copper-plated Ti₃SiC₂-Cu-graphite composite, copper-plated short carbon fiber/Ti₃SiC₂-Cu-graphite composite with the same carbon fiber content and copper-plated Ti₃SiC₂-Cu-graphite composite were prepared by the powder metallurgy method. Physical and mechanical properties of these composites were tested. The dry friction tests of the composites under sliding velocity of 10m/s and load of 4.9N were conducted for 36 hours. The results show that the properties of the Cf-copper-plated Ti₃SiC₂-Cu-graphite composite such as electric conductivity, bending strength and wear resistance are remarkably increased than those of either Cf-Ti₃SiC₂-Cu-graphite or copper-plated Ti₃SiC₂-Cu-graphite composites.

Abstract: The paper analyzes the influence of structural parameters on the electrical performance of the microstructured environmentally-friendly electrical contact material Ag/SnO2 by using numerical simulation method.The numerical results show that the reisitivity of fiber-like electrical contact material Ag/SnO2 is significantly reduced compared with the resistivity of Ag/SnO2 adding reinforcing nanoparticles in the traditional way.So the fiber-like electrical contact material Ag/SnO2 exhibits higher conductivity in macro. On further analysis, we learn that the resistivity of fibrous electrical contact materials is related to weight percent of reinforced phase, and micro-structural parameter of length to diameter ratio. The resistivity increases as weight percent of reinforced phase increases,and decreases non-linearly with micro-structural parameter of length to diameter ratio increasing.This demonstrates that numerical simulation is one of effective methods for analysis of the electrical performance of the microstructured electrical contact material.

Abstract: To investigate the effects of the metallurgical route on the defects in mc-Si, various metallurgical routes were conducted. Dislocation formation and the resistivity of the mc-Si were also studied. The results showed that high inhomogeneity in dislocation distribution within individual grains and paralleled tacking faults could be observed when the ingot was grown by using the feedstock prepared by adopting the sequence of slag treatment, acid leaching and vacuum refining. Different grains have various dislocation density, which was showed in ingot grown by utilizing the feedstock prepared by adopting the sequence of vacuum refining, slag treatment and acid leaching, tacking faults could also be seen, as well as some dislocation clusters. The resistivity of this two ingots was detected at various height by using the a 4-point probe silicon tester, it was expected that the resistivity of these two ingots has the same tendency of the change, and the value of the resistivity of the ingot obtained using the previous technology was relatively higher than that of the ingot obtained using the latter technology.

Abstract: The scope of this work is based on the use of resistive method to quantify the water content in timber elements. For an in-depth mapping, we adapted a multiplexed technique derived from geophysics based on a maximum crossing of current lines to obtain topography of measures sweeping the space boundary conditions being defined by the sample. The calibration of these measures is completed by a gammadensimetry laboratory method which allows access to water profiles along a preferred direction. Nevertheless, the resistive method is penalized by logarithmic laws linking moisture and resistivity. So, we develop a hybrid method for coupling the data obtained to diffusion models: it will provide complementary information where resistivity and gammadensimetry are no longer effective. The developed experimental protocol allows employing the selected method and optimizing the diffusion properties (diffusion coefficient and convective exchange coefficient) injected into a characterization algorithm (Nelder-Mead’s simplex inversion method) based on a finite difference method for the Fick’s diffusion law determination integrating orthotropic and non- linear properties. Overlap between electric field and density measurements and the numerical simulation tool are possible.

Abstract: The microstructure, especially porosity, of PTC (positive temperature coefficient) thermistor based on BaTiO₃ was controlled with a forming pressure. The relationship between theirPTCR properties and microstructureswas investigated with an optical and SEM (Scanning Electron Microscope) images and digital multimeter. Disk samples were fabricated by pressinguniaxially at various pressures of 100~15000kg/cm² and sintering at 1265°C in reducing atmosphere and finally re-oxidizing at 700°C in air. The porosity of the samples decreased rapidly from 45% to 8% with increasing the forming pressure from 100 to 1000kg/cm²andbecame 4% at 15000kg/cm²with slowdecreasing of porosity in the pressure range of 1000~15000kg/cm².With increasing the forming pressure, the resistivity jump of samplesdecreased rapidlyfrom 0.5 to 2.9 at about1000kg/cm²that corresponds tothe porosity of 15% and was saturated above this pressure. It is considered that there is a critical amount of porosity for having PTCR effect, which was about 15% in our samples. In addition, the porosity of the sample has a greater influence on the resistivity jump than on theresistivity at room temperature, which is due to the oxidation of grain boundary through a favorable channel of oxygen such as a pore.

Abstract: Petrophysical study is playing an important role in oil and gas exploration. Shale gas and shale oil is blooming in recent years in many countries. Less rock physics knowledge is known about shale relatively to other rock type such as sandstone and limestone. In this paper, we carried out a rock physical study of shale core sample which is drilled from north China. The plan distribution of permeability, P wave velocity, S wave velocity and complex resistivity were acquired based on AutoScan-IIplatform. The results show that the permeability of the shale sample is basically low with values of 0.1 to several micro Darcy (mD) except some fracture areas in the surface, which has values of about several tens mD. The permeability can basically describe the distribution of the fracture. The complex resistivity has the similar characteristics with permeability, which is also roughly corresponding to the position of the facture. As for the Vp and Vs, although not very good correspondence with the surface, they are still approximately present the high and low velocity feature of the core sample as well. This result is significantly helpful for shale gas exploration and production.

Abstract: This paper presents a short review of research work on the development of synthesizing the colossal magnetoresistance materials through sol-gel method. Although there are a lot number of methods available, sol-gel method has been widely used and some excellent work has been reported. Two different manganite systems, which are LSMO and PSMO, that have been prepared through sol-gel method was choose for the discussion purpose. It was found that both systems were successfully prepared via the sol-gel method. Both systems showing better magnetoresistance properties compare to sample prepared through solid state reaction. X-ray diffraction technique was used to study the structural characteristic. Atomic force microscope and field emission scanning electron microscope were used in order to investigate surface morphology. Resistivity as a function of temperature was measured by a standard four-probe method.

Abstract: PbO-type structure β-FeSe superconductor ceramic were successfully prepared by solid state sinter method in high vacuum state. The structures of the ceramics were investigated by X-ray diffraction and scanning electron microscopy. X-ray diffraction indicates that the sample prepared by two-steps method exhibited a much improved crystallinity. And as sintering temperature increases to 700°C, secondary phase Fe₇Se₈ phase peak disappear and α-Fe peak weakened. Besides, the ceramic prepared in 700°C exhibited a denser surface morphology in comparison to that prepared in 410°C and its composition is closer to the chemical formula FeSe according to EDX compositional analyses. It was noted that the resistivity of the sample, sintered at 700°C using two-steps sinter method, shows a linear metallic behavior from room temperature and onset is around T = 7.5 K.