Papers by Keyword: Electrical Conductivity

Abstract: The microstructure of pre-aged AA7085 rolled plate was studied by means of hardness tests, optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction and electrical conductivity tests. The results show that supper refined and homogeneous precipitates were formed during pre-aging, but the hardness of the alloy was still relatively low. There occurred a large number of dislocations when the warm deformation was introduced, and the size of the intragranular precipitates firstly increases and then decreases and then increases with the dislocation density increasing, which was caused by the role of dislocations on inhibiting the formation of GP zone and promoting the nucleation and transformation of η phase. Meanwhile, the distribution of grain boundary precipitates also changed from continuous chain to coarsening interrupted distribution and the precipitate free zone (PFZ) broadened obviously.

Abstract: Aluminium alloys play an important role in overhead power transmission applications. All-aluminium alloy conductor cables require increasingly hard-to-achieve combinations of high tensile strength and high electrical conductivity. The problem is that a high strength is normally associated with a reduced electrical conductivity. Both heat-treatable 6xxx series aluminium alloys and work-hardening 1xxx series aluminium alloys are important contenders for these applications. By contrast, the addition of rare earths and/or transition metals to aluminium may provide further opportunities to achieve improved combinations of precipitation hardening, substructural hardening and elevated temperature stability. In this work, strength and electrical conductivity relationships are investigated for a range of 6xxx series aluminium alloys and an Al-Sc alloy. The Al-Sc alloy was produced by means of a direct laser metal deposition process that allowed more Sc to be placed into solid solution than by conventional casting or solution treatment. The paper explores the relative effects of composition, cold working and age hardening on the balance of strength and electrical conductivity, including examples of how improved combinations of both strength and conductivity can be achieved.

Abstract: The effect of different thermomechanical processes (hot extrusion and Properzi continuous rolling) on the electrical and mechanical properties of the Al-Fe aluminum conductor alloys was investigated. The microstructural evolution of the supply rods was characterized by an optical microscope, a transmission electron microscope and the electron backscatter diffraction technique (EBSD). Tensile tests and electrical conductivity measurements were carried out at room temperature on the supply rods. Results showed that, at the same Fe content, the continuously rolled rods demonstrated higher tensile strength but lower elongation and electrical conductivity compared with those of the extruded rods. A partially recrystallized structure along with a big subgrain size appeared in the extruded rods while only a dynamic recovery with a small subgrain size was found in the continuously rolled rods. The precipitation of iron-rich dispersoids was observed in the extruded rods and is associated with a depletion of the iron concentration.

Abstract: On the help of the atmosphere plasma spraying (APS) and suspension plasma spraying (SPS) conditions optimized previously, APS and SPS were both introduced to prepare the PEN (Positive- Electrolyte-Negative) of planar solid oxide fuel cells (SOFCs). Then the microstructure and material components of the PEN cells were analyzed. Experimental results show that the electrolyte layer fabricated by SPS represents higher densification, thinner thickness and more homogeneous component distribution than that manufactured by APS, and meets the microstructure and density requirements of SOFC. The porosities of cathode and anode layers by APS and SPS reached 25%-35%. Therefore, the SPS could be a better and suitable approach to fabricate PENs of SOFC stacks, and effectively improve the conductivity of electrodes.

Abstract: Undoped nanocrystalline ZnO thin films were deposited onto the glass substrates via the low cost sol-gel dip coating method. The as-grown ZnO films were annealed at the temperatures ranging from 400 °C to 550 °C. The X-ray diffraction (XRD) pattern revealed that the annealed ZnO films were polycrystalline with hexagonal wurtzite structure and majority preferentially grow along (002) c-axis orientation. Atomic force microscopy (AFM) micrographs showed the improvement of RMS roughness and grain size as annealing temperature increased. The ZnO films that annealed at 500 oC exhibited the lowest resistivity value.

Abstract: This work presents the study of the electrical conductivity in MWNT as a function of three different chemical functionalization conditions. Unmodified and chemically modified MWNT were characterized by microRaman spectroscopy, XPS and SEM whereas the electrical conductivity was determined by dust compression technique. MWNT were modified using three different oxidation conditions: (1) a mix of concentrated acids, H₂SO₄/HNO₃ (3:1, v/v) sonicated for 2 h; (2) same mixture as (1) but using mechanical stirring for 6 h and (3) a reflux of an aqueous solution of HNO₃ (20%, v/v) and mechanical stirring for 6 h. The characterization evidenced different functionalization degrees, based on the formation and detection of functional groups such as ether, carbonyl and carboxyl in different percentages. The unmodified CNT presented a conductivity of 510 S/m which decreased as the functionalization degree increased. For reactions (1) and (2) such conductivity was reduced by 8.8 and 15.5%, respectively, whereas for condition (3) it only decreased 0.98%.

Abstract: Polyaniline (PANI) Nanocomposites are potential materials for actuators, EMI shielding, Fuel cells and components in non volatile memory. Silver nanoparticles have wide range of applications such as catalysis, microelectronics, biotechnology and silver-oxide batteries. This work reports the effect of thermal alteration [lowhigh temperatur on the electrical conductivity of green synthesized silver (Ag) nanoparticles-polyaniline composite. A simple low cost green synthesis using Azadirachta indica [Neem] extract is employed for synthesis of silver nanoparticles; Polyaniline is prepared by redox polymerization of aniline using ammonium per sulphate. The silver nanoparticles are incorporated into Polyaniline during polymerization. PANI and PANI-Ag composites are characterized by FTIR, UV-Vis, TGA, XRD, TEM and DC conductivity. The DC conductivity and UV-Vis spectral response were recorded for the samples at low temperatures [263K, 273K, and 283 and high temperatures [353K, 433K, and 533. The effect of thermal alteration showed a significant change in both conductivity and UV-Vis spectral response. UV-visible spectra show the transition occurring in PANI Emeraldine salt phase to Pernigraniline with increase in temperature. TGA analysis confirms the improved thermal stability for PANI-Ag composite. The mechanism of electrical conductivity with temperature in the system is investigated and reported. Thus, this work deals with an approach to analyze the electrical behavior of green synthesized silver nanoparticles composited with a conducting polymer. The results show that these composites can be suitable for temperature dependent semiconductors, bio sensors and catalytic reactions.

Abstract: Recent studies showed that electrical conductivity is a valuable technique to identify the different zones of solid-state welded joints with a good correlation with the microstructure and hardness. This is a relevant result since this technique is expedite and, in some cases, non destructive. The concept was applied to other welding processes as the ones involving fusion and to a wide range of materials. For this, a comprehensive study was performed using friction stir welding, tungsten inert gas (TIG) and gas metal arc (MAG) welding processes in either bead on plate or butt joints in: carbon steel, magnesium and titanium. Eddy current non-destructive testing (NDT) was used to measure the electrical conductivity at different depths in transverse sections of the processed materials. The obtained profiles were compared to the hardness profiles in the same sections. As a result, a good correlation was observed in most materials welded by solid state and by fusion processes. The variation of the electrical conductivity closely follows the one detected in the hardness. Another interesting conclusion is that, even for fusion welding of carbon steels, the technique has potential to complement the hardness measurements and microstructural observations, allowing to identify the distinct zones of welds in materials commonly used in industry.

Abstract: 20vol% TiB₂ particle Al composites were fabricated by spark plasma sintering after blending TiB₂ and Al particles. The dispersibility of TiB₂ particles in composites was controlled by the blending method before sintering. Then the effect of the dispersibility on the electrical conductivity was estimated. As increasing the dispersibility, the electrical conductivity of the composites decreased. The dispersibility of TiB₂ particles in composites was estimated by two-dimensional local number (LN2D), quantitatively. The theoretical value of electrical conductivity considering LN2D was estimated by the simulation of finite volume method and the Laplace equation of electric potential distribution. The tendency of low electrical conductivity of the composite with uniform distribution of TiB₂ particles was confirmed by this simulation, but the experimental degradation of electrical conductivity for uniform distribution for clustering distribution was higher than that of theoretical value. The electrical conductivity of Al seems to be affected by the plastic deformation. There are the deformation regions around the interface between TiB₂ particle and Al because of the difference of thermal expansion. Therefore, the quantity of the deformation region is increasing for increasing the dispersibility, and then the electrical conductivity of the composites decrease.

Abstract: In this paper, the electrical properties of materials were evaluated using a microstrip patch sensor. The sensor was designed for the operating frequency in range of 1.5 to 3 GHz on a DiClad 880 substrate with the permittivity of 2.2. The resonant frequency of the design sensor ,as well as the magnitude of the reflection spectra S₁₁, were analyzed and then simulated three-dimensional finite element modeling when,. The result shows that the increase of the dielectric constant (ε_r) and conductivity (σ) of the material under test (MUT) led to the significant change of the resonant frequency. Thus, the resonant frequency may be used to evaluate the moisture content of the agricultural products.