Electrical Conductivity Of Specimens Research Articles

Effect of Alloy Elements on the Corrosion Resistance and Electrical Conductivity of Austenitic Stainless Steel for MCFC

Bipolar plate and current collector are important stainless steel components of the molten carbonate fuel cell (MCFC) because they supply the pathway of the electron flow between each unit cell. However, these stainless steel components are prone to corrosion in the hot corrosion environment and corrosion products forming on the surface increase the ohmic resistance. In addition, hot corrosion reduces the mechanical strength of the current collector, accelerates electrolyte loss, and finally leads to degradation in cell performance. Therefore, corrosion of stainless steel components is one of the main problems in MCFC systems. To solve these problems, various methods have been studied, such as addition of alloy elements, surface coatings and replacement with higher grade materials. Corrosion resistance of stainless steels is evaluated by potentiodynamic polarization test and weight loss measurements. Electrical conductivity of specimens is measured in molten carbonate at 650 oC. Results from electrochemical tests show that high Cr content causes the formation of a dense and thin oxide layer, subsequently improving the corrosion resistance. However, high Cr content gives rise to inner oxide penetration. Mn enrichment occurs in the oxide layer and may lead to an increase in electrical conductivity. In addition, minor elements such as Si, Nb and N may contribute to the improvement of corrosion resistance and electrical conductivity.

A First Report of Photoemission in Experiments Related to Flash Sintering

A highly nonlinear increase in electrical conductivity and concomitant photoemission occurs not only during “flash sintering” but also in presintered, dense specimens. We report results from experiments with dense specimens that show a strong correspondence between the intensity of photoemission and electrical conductivity of specimens under a variety of conditions of the electrical parameters. It is proposed that both properties are related to the concentration of electron–hole pairs generated in such experiments.

Characterization of Heat Treated Titanium-Based Implants by Nondestructive Eddy Current and Ultrasonic Tests

This study presents nondestructive characterization of microstructure and mechanical properties of heat treated Ti, Ti-Cu, and Ti-6Al-4V titanium-based alloys and 17-4 PH stainless steel alloy for biomedical implant applications. Ti, Ti-Cu, and 17-4 PH stainless steel based implants were produced by powder metallurgy. Ti-6Al-4V alloy was investigated as bulk wrought specimens. Effects of sintering temperature, aging, and grain size on mechanical properties were investigated by nondestructive and destructive tests comparatively. Ultrasonic velocity in specimens was measured by using pulse-echo and transmission methods. Electrical conductivity of specimens was determined by eddy current tests. Determination of Young’s modulus and strength is important in biomedical implants. Young’s modulus of specimens was calculated by using ultrasonic velocities. Calculated Young’s modulus values were compared and correlated with experimental values.

Preparation and Electrical Properties of Interconnect Material Made by Substituting Mixed Rare Earth Oxides (Sm<sub>2</sub>O<sub>3</sub>, Gd<sub>2</sub>O<sub>3</sub>, Eu<sub>2</sub>O<sub>3</sub> and CeO<sub>2</sub>) for La<sub>2</sub>O<sub>3</sub> in La

La1-xCaxCrO3 (0.1≤ x ≤ 0.4) is usually used as interconnect material for solid oxide fuel cells (SOFCs). In this paper, composite material, the two-phase mixtures of face-centered cubic fluorite structure CayCe1-yO2-y (0 ≤ y≤ 0.2) and orthorhombic perovskite structure [Sm(Eu,Gd)]1-zCazCrO3 (0 < z < 0.3), was prepared by an auto-ignition process in which mixed rare earth oxides (Sm2O3, Gd2O3, Eu2O3 and CeO2) are substituted for La2O3 in La1-xCaxCrO3. The direct current (DC) four-probe technique measurement indicated that the electrical conductivities of specimens increased along with the increase of Ca2+ content (x), especially when x=0.3 and 0.4. The material (x=0.4, about 94% relative density) showed excellent electrical conductivities of 48 Scm-1 in air and 13 Scm-1 in H2 (purity 99.999%) at 700°C respectively, which is about 3 times as high as that of La0.7Ca0.3CrO3.

Effect of High-Energy Ball-Milling and TiB<sub>2</sub> Content on Microstructures and Properties of Cu-TiB<sub>2</sub> Composites Sintered by SPS

The microstructure and properties of Cu-TiB2 composites produced by high-energy ball-milling of TiB2 powders and spark-plasma sintering (SPS) were investigated. TiB2 powders were mechanically milled at a rotation speed of 1000rpm for short time in Ar atmosphere, using a planetary ball mill. To produce Cu-xTiB2 composites( x = 2.5, 5, 7.5 and 10wt.% ), the raw and milled TiB2 powders were mixed with Cu powders by means of a turbular mixer, respectively. Sintering of mixed powders was carried out in a SPS facility under vacuum. High-energy ball-milling resulted in refinement of TiB2 particles. XRD patterns of milled TiB2 powders indicated broader TiB2 peaks with decreased intensities. After sintering at 950 for 5min using the raw and milled TiB2 mixture powders, the sintered density decreased with increasing TiB2 content regardless of milling of TiB2. In the case of raw TiB2, hardness rapidly increased from 4 to 44 HRB with increasing TiB2 content. The electrical conductivity changed from 95.5 to 80.7 %IACS. For mixtures of Cu powders with milled TiB2 powders, hardness increased from 38 to 67 HRB as TiB2 content increased, while the electrical conductivity varied from 88% to 51 % IACS. When compared to compacts sintered with raw and milled TiB2 powders, the electrical conductivity of specimens with raw TiB2 powder was higher than that of specimens with milled TiB2 powder, while hardness was slightly lower.

Estimation by Electrical Conductivity for Elastic Modulus of Carbon-fiber Filled Epoxy Resin Composites Moulded under Centrifugal Force.

Samples of carbon-fiber filled epoxy resin composites were moulded under centrifugal force. The gradient distribution of fiber content of samples was derived in direction of centrifugal force. Rectangular solid specimens were made from samples and surfaces of specimens were polished by sand papers. The electrical conductivity of specimens was measured by four-point probe method in both directions parallel to and parpendicular to the centrifugal force direction. The elastic modulus was derived from strain measurements during compression test in same directions as conductivity measurements. The correlation between conductivity and elastic modulus was found in both directions parallel to and parpendicular to the centrifugal force direction.

Electrical conduction in sintered SiC containing BN.

Electrical properties of SiC sintered with 0.34wt%6.89wt% boron nitride and 2.0wt% carbon in the temperature range of 1900°C2100°C for 30min in vacuum were investigated. Specimens containing 1.15wt% boron nitride (0.5t% boron) showed the most remarkable densification independent of the sintering temperature. The electrical conductivity of specimens containing 1.15wt% boron nitride was the lowest, and the value depended strongly on the frequency and measuring temperature. In order to explain the experimental results, a microstructure model, charge distribution model and energy band model were proposed. The electrical conduction mechanism was discussed based on these models.

Electrical properties of high purity tin dioxide doped with antimony

The electrical conductivity of high purity tin dioxide doped with antimony was studied at temperatures of 900 to 1200° C and partial pressures of oxygen between 10−8 and 1 atm. For specimens having a dopant concentration over 1 × 1019Sb cm−3, the electrical conductivity decreased slightly with temperature and independent of oxygen partial pressure. The electrical conductivity of specimens having a dopant concentration under 1 × 10−8Sb cm−3 increased with temperature and with decreasing partial pressure of oxygen. The significance of the dopant and the thermally created defects is discussed.

Some features of the sintering behavior of pure and technical boron carbide

1. At temperature below 1500°C specimens from pure and technical boron carbide powders experience no shrinkage. An investigation into the variation of the strength and electrical conductivity of specimens has shown that sintering in this temperature range is due to processes of surface self-diffusion. 2. At temperatures above 1800°C an important part in the sintering process is played by the mechanism of mass transport through the vapor phase. This conclusion is arrived at on the basis of data yielded by measurements of the strength properties of specimens sintered under different partial vapor pressures. 3. Diffusion-controlled densification processes take place at temperatures above 2000°C in pure boron carbide and above 1500° C in technical boron carbide. The active behavior of technical boron carbide may be ascribed to its reaction with the impurities present in it and to the formation of a liquid phase at its grain boundaries. These phenomena promote densification by the mechanism of activated sliding and lead to the appearance of structural defects activating diffusion processes.

The electrical properties of plastically bent p-type indium antimonide between 50 and 200� k

A special technique of plastic bending at elevated temperatures was applied to introduce, into a pair of simultaneously deformed, weakly p-doped, InSb single crystal bars, an excess, of indium and antimony dislocations, respectively. Hall coefficient and electrical conductivity of specimens containing an excess of In or Sb dislocations, of annealed control specimens, and of the Ge-doped starting material were measured between 50 and 200° K. Indium dislocations in Ge-doped InSb show not only an acceptor, but also a donor action; Sb dislocations show only an acceptor action. The electrostatic charge of the dislocations due to dislocation-impurity interaction has more influence on the measured energy level of indium dislocation states than on those of antimony. These results may be explained by assuming an energy level scheme in which the energy level of the indium dislocation states lies above and that of the antimony dislocation states below the acceptor level of the Ge impurity atoms.

Study by the electrical conductivity method of the process of metallic contact formation between powder particles during sintering

1. Copper powders of different origin display different activity during sintering. The process of metallic contact formation and growth between the particles is more pronounced in electrolytic powder. 2. The electrical conductivity of specimens from electrolytic powder as a function of sintering temperature obeys Arrhenius' equation. The calculated value of the energy of activation is 5.5 kJ/mole, which is one whole order of magnitude smaller than the energy of activation of the surface self-diffusion process of copper. The value obtained for the energy of activation is in agreement with reports according to which the propagation of diffusion processes is more active in metals of electrolytic origin [4]. 3. On the example of the sintering of atomized copper powder it is shown that the electrical conductivity method is not always suitable for following the growth of metallic contacts between powder particles. It should be combined with other methods (measurement of density, strength, etc.) permitting the determination of properties which depend on the quality of metallic contacts between the powder particles.