جستجوی مقالات مرتبط با کلیدواژه "هدایت الکتریکی" در نشریات گروه "مواد و متالورژی"

The present study aims to determine the scattering mechanism in two types of n- and p-type InSb single crystal semiconductors. For this purpose, the changes in the Hall constant, electrical conductivity, dynamics coefficient in the temperature range of 77K to 360K, and Hall effect with an intensity of 7900 Gauss were simultaneously measured and compared with the theoretical results. Additionally, Debye temperature and dispersion mechanism were determined from the curve of changes in the mobility coefficient with respect to temperature. Further, the energy of the forbidden band and overlapping temperature were calculated from the curve of changes in the electrical conductivity, and the density of the charged particles as well as the type of charge carriers were determined from the changes in the Hall constant with respect to temperature. From the change curve of the dynamic’s coefficient with respect to temperature, the dispersion mechanism was defined. In this experiment, for the n-type sample, the scattering mechanism was carried out by the optical mode at high temperatures and by impurity at low temperatures. In the p-type sample, scattering was done by the acoustic mode. Finally, in both samples, the dynamics coefficient was theoretically calculated that showed good agreement with the experimental values.

In this paper, the effects of the aging temperature on the microstructure, mechanical properties, and electrical conductivity of Cu-0.4% Cr are investigated. The solid solution treatment was performed at 950 ᵒC for 1 hour. Then the samples were aged 5 hours at 200, 300, 400, 500, and 600 ᵒC. The microstructure of the samples was surveyed using FESEM. An analytical model is also developed to predict the age-hardened samples yield stress and the precipitation of the alloying elements based on the microstructure images analysis and electrical conductivity of the samples. Increasing the aging temperature up to 500 ᵒC, the number of precipitates increases and their size decreases. Yield strength, tensile strength, and work hardening exponent at aging temperatures of 200 and 300 ᵒC decreases a little and increases at 400 and 500 ᵒC and then decreases at higher temperatures. In optimum precipitation hardening conditions, the yield strength and tensile strength are higher 51.7 and 21.7% than solid solution treatment, respectively. Electrical conductivity increases by the aging temperature increasing up to 500 ᵒC and then remains almost constant at higher temperatures. Comparison between the tensile test and the present model results shows that the model is capable to predict the yield strength of the age hardened samples by good accuracy.

Nowadays, various methods have been introduced for the fabrication of solid oxide fuel cells (SOFC). In this research, 3D printing technology has been used to produce oxide fuel cells. First, a 3D printer was constructed that has the ability to print the slurry of anode, cathode and electrolyte layers with the desired thickness and speed. Then a suitable slurry consisting of NiO-YSZ materials was produced for the anode layer, YSZ for the electrolyte layer and LSM for the cathode, with suitable solvents and additives. After cell formation, drying and then sintering of the layers were performed. The composition and microstructure characterization of layers has been performed by XRD, SEM, Mapping, EDS. The I-V-P curve showed the maximum power is around 0.84 W / cm2 at 800 OC with constant oxygen. The impedance curve values under open-circuit voltage were 0.23 Ωcm-2 and 1.25 Ωcm-2 at high and low frequencies, respectively. The tensile experiments indicated values 111 GPa for Young modulus and 137 MPa and 120 MPa values for the fracture toughness and the yield strength, respectively.

Due to low electrical conductivity of liquid fuels, electrostatic accumulation is a problem in production, transportation and storage of the fuels. Electrostatic accumulation more than ambient ionization energy leads to electrical spark which causes firing and/or fuel tank explosion. Therefore, the electrical conductivity is a key parameter in fuels or flammable solvents. In this research, the apparatus cell for electrical conductivity measurement of liquids was firstly manufactured based on DIN51412-1 standard. Due to some problems in standard cell such as dependency of electrical conductivity on sample volume, chemical leakage, high volume consumption of sample, difficult cleaning of the cell and carrying problems because of size and weight, a new cell was designed based on submerging method and manufactured. The new cell performance was calibrated with various solvents like toluene, hexane and also JP-8 and tetralin as aviation fuels. Then, the conductivity of each solvent and fuel was measured and compared via the standard and new cells in the presence of antistatic Stadis 450. The measuring error was less than 0.5%.

Liquid fuels usually have low electrical conductivity leads to accumulating in static electricity during transmission, mixing and spraying processes. This charge accumulation will spark and fire if it exceeds the air ionization energy. Therefore, one of the important parameters in fuels safety is their potential for static charge accumulation. In this manuscript, materials are classified into static electricity and the mode of generation, accumulation, discharge and distribution of electric charge in liquid fuels will be investigated. Then, solutions for static electricity control in low conductivity high energetic liquids presented. Finally, common methods of measuring the static electricity presented.

Bipolar plates are one of the most important components in a PEM fuel cell. In this study, a bipolar plate made of stamping method is developed to increase electrical conductivity and mechanical behavior and manufacturing productivity of the fuel cell and to decrease electrical resistance according to DOE. For fabrication these plates, phenolic resins were used as matrix and expanded graphite to increase electrical conductivity and graphite to filler and carbon fiber to increase flexural strength and optimize electrical conductivity. The electrical conductivity increased up to 40 percent respect to the DOE. The flexural strength and impact strength of the measured specimens were improved respect to the DOE about 11 and 170 percent, respectively. The experimental results are in accordance with DOE. According to SEM images and test curves, electric conductivity increases with expanded graphite filler. Finally, the results showed that expanded graphite weight gain did not affect the mechanical behavior of the composite and increased the electrical conductivity.

Copper-tin alloys with three tin contents of 0.18, 0.3, and 0.5wt.% was produced by continuous casting process at the temperature of 1150 and 1180 ℃ and speed of 3 and 5 m/min; then, microstructure, electrical, and mechanical properties of produced alloys were determined and compared with the pure copper. It was found that all casting samples have similar columnar grains, elongated radially from walls to the center. Also, the effect of Sn content on the columniation of grains is more sizeable than both other casting parameters. The results of scanning electron microscopy indicated that the produced alloys have a single-phase structure and Sn distribution is almost homogeneous in the copper. Additionally, electrical conductivity is slightly reduced by the increment of the alloying element whereas casting temperature and speed do not have a considerable effect.

In this work, commercial pure aluminum was subjected to friction stir processing (FSP) up to six passes, then, mechanical properties, electrical conductivity, and microstructure analysis of the processed samples were compared with the initial condition. Better yield strength, ultimate tensile strength, and hardness are achieved after imposing the process. Also, strengthening rate is reduced at the subsequent passes. It was found that hardness magnitude is decreased mildly by getting away from the center. Although material formability is reduced after the first pass, it is grown a little by adding the pass number. The microstructure analysis indicated that application of one pass FSP changes considerably grain size of the annealed aluminum and leads to extreme decrease of the high-angle grain boundaries density which plays the main role in the reduction of electrical conductivity. Addition of FSP pass number leads to increment of dislocations density, transformation of low-angle to high-angle grain boundaries, and the further intersection of shear micro bands, causing improvement of sample formability and electrical conductivity compared to the first pass. Therefore, this process has the capability for fabrication of pure aluminum with improved mechanical properties and acceptable electrical conductivity.

This present research was related to electrical conductivity of RGO-ZnO-TiO2 nanocomposite in comparison RGO-ZnO nanocomposite . In order to carry out this research, at first graphene oxide was synthesized by using modified Hummer method and reduction of graphene oxide (reduced graphene oxide(RGO), was done by UV light and temperature. TiO2 and ZnO nanoparticles were synthesized by sol-gel method.XRD,FTIR and DRSUV were used to investigate these nanoparticles.
For sample preparation ,dip coating method was used and all particles were coated on the surface of FTO respectively. for investigation of adding TiO2 nanoparticles on the electrical conductivity and amount of band gap of RGO-ZnO nanocomposite, electrochemical impedance spectroscopy and talc plot were used .
The results of comparison between these 2 samples showed that adding TiO2 nanoparticle to RGO-ZnO nanocomposite reduced band gap from 3.22 to 3.11 and increase resistance from 2.8*104Ω to 5.76*104Ω . with study of level energy of RGO, ZnO and TiO2 nanoparticles ,the reason of increasing resistance related to higher ZnO energy level in comparison to TiO2 energy level and electron Inability to overcome of this level energy in the absence of UV light .with putting this sample under UV light could be reduced this resistance.

The aim of current research was to examine the microstructure, mechanical properties and electrical conductivity of Al-7075 alloy that develops during Equal Channel Angular Pressing (ECAP) and Multi Directional Forging (MDF). The Annealed Al-7075 alloy was subjected up to 3 and 4 passes of MDF and ECAP deformation at room temperature, respectively. Followed by ECAP, Vickers microhardness and shear punch test were performed and microstructural observations were undertaken using transmission electron microscopy (TEM). The electrical conductivity was also measured by eddy current method. Microstructural investigations show that after 4 passes of ECAP very fine grains with average grain size of about 350 nm appear and most of the grains evolve into arrays of high angle boundaries. On the other hand, 3 passes of MDF leads to higher grain size (950 nm) and lower fraction of high angle boundaries compared with 4 pass of ECAP. Mechanical properties of specimens increase about 100 and 50 percent after 3 passes of MDF and 4 passes of ECAP, respectively. So, it can be concluded that the ECAP process is more effective than the MDF process in grain refinement and improvement of mechanical properties. The electrical conductivity measurement at room temperature showed that there was no significant change in the conductivity of the processed samples compared with the initial specimen. Finally, it can be deduced that grain refinement during ECAP and MDF processes can be considered as a strategy to improve mechanical strength of pure metals without sacrifice of their electrical conductivity.

In this study, amorphous silicon films were deposited by physical vapor deposition using electron beam (EBPVD). The process of deposition was carried out under high vacuum (torr 10-6) which led to the formation of an amorphous coating with controlled thicknesses. After sampling procedure, the samples were put under heat treatments at 800 oC under inert gas environment and their structural and electrical properties were analyzed before and after annealing conditions. The results obtained from microraman revealed the amorphous structure in the initial coatings which had been formed because of the increased thickness of the coating and due to the presence of more defects in nano-crystals. Moreover, we witnessed the development, growth, and integration of nano-crystals and formation of a poly crystal structure. Consequently, nano-crystals formation resulted in development of sp2 and sp3 bonds, which, in turn, increased the electrical conductivity of the coatings in that condition. Finally, as the thickness of the samples coatings increased, their electrical conductivity was also greatly enhanced.

In this work, fractal dimensions and electrical conductivity of carbon–nickel films deposited at deposition times from 50 to 600 second were investigated. Because of the existence of fractal components in the surface topographies, the power spectra densities (PSDs) of all films show inverse power law variation at the high spatial frequency region. The fractal dimensions and the topography carbon-nickel films from 50 to 180 second are increased however; at 600 second these characteristics are decreased. It was observed that with increasing deposition time from 50 to 180 second, the room temperature electrical conductivity (σRT) of films increases from 2.87x10-9 to 2.3x10-8 Ω-1 cm-1 and then decreases to 6.62x10-9 Ω-1 cm-1 for films deposited at 600 second. Fractal dimensions and the room temperature electrical conductivity are in consistent with field emission scanning electronic microscopy (FESEM) images.

In this study, it was aimed to investigate the super-hydrophobicity and conductivity properties of cotton fabrics coated with polypyrrole (PPy) through admicellar polymerization (AP) process and modified with alkyl silanes. Firstly, samples of cotton fabric were coated with PPy through AP process and also some samples were coated in the same condition without using sodium dodecyl sulfate (SDS) surfactant and then they were modified with HDTMS. Finally, their super-hydrophobicity and surface resistivity were studied and compared with each other. The samples were characterized by attenuated total reflectance FTIR spectroscopy. Their morphology and surface roughness were investigated by SEM and AFM respectively. Conductivity and hydrophobicity were also assessed by a standard two probe method and static and dynamic water contact angle measurements, respectively. Infrared spectroscopy and SEM images confirmed the existence of PPy on the treated samples. The agglomeration of PPy particles was more obvious on the surface of pristine sample. However, a uniform distribution of PPy films was observed for the admicellar polymerized cotton samples. After treating with HDTMS, the CA value for pristine sample was 115˚. But, it was reached to 153˚ for admicellar polymerized samples and their roughness increased up to up to 341%. It was concluded that AP process can be applied for fabrication a PPy layer on the rough and hydrophilic surface like cotton and consequently, it can be used for achieving to modified conductivity and superhydrophobicity properties.

In this research, three-dimensional graphene (3DG) was synthesized via thermal CVD method by using nickel foam in a tube furnace. This method consists of graphene growth on the nickel foam using Ar and H2 gases and ethanol carbon precursor, followed by removal of nickel foam by chemical etching. Finally, the synthesized graphene was characterized by XRD, SEM and Raman analyses. The electrical conductivity and work function of 3DG were determined by Van der Pauw method and UPS technique, respectively. The results indicated that the high porosity and good quality three-dimensional graphene was formed. The electrical conductivity and work function of 3DG were measured 4 s.cm-1 and 5 eV, respectively.

In present work a tested enamel coat for Ni-Cr wire-wound resistor is studied for its electrical and chemical properties. In the present work it is tried to find appropriate coating by testing different compounds. Results showed that the optimum enamel is the compound with 1 wt% cobalt oxide، 3 wt% chromium oxide and firing temperature 840˚C. Variation of the electrical conduction of the enamel with temperature is measured by an instrument designed by Rasch-Hinrichsen et al. Results indicate that with increasing the temperature to 275˚C electrical conduction reaches to 10-7. 60 Ω-1. cm-1. Dielectric strength test shows 100 KV/cm for breakdown voltage. Weight loss in different liquids with various pH shows that the most chemical resistance is yielded in water and for neutral pH.

The purpose of this study is the investigation of viscosity behavior and electrical conductivity of a copper enamel based on lead borosilicate. By using the dilatometeric measurements the characteristic temperatures of Tg (log η= 1012 Pa. s) and Ts (log η= 109. 25 Pa. s) obtained for the enamel (glaze) were found 478. 6 and 523. 9 °C respectively. Hot stage microscopy observations shows half sphere condition of the enamel around 800°C which correspond to a viscosity of log η= 103. 55 Pa. s. By using of these three obtained values and VFT equation، the dependency of viscosity verses temperature is investigated. Electrical conductivity of 10-8 Ω-1. cm-1 was calculated at 335°C for the enamel.

In this research, the properties and morphology development of gold nano-layer coat builds on fuel cell bipolar plates via Sputtering method were investigated. Morphology and surface microstructure of samples were investigated by scanning electron microscopy (SEM) and atomic force microscopy. Also in order to evaluate the electrical conductivity of the coated samples, electrical resistance were measured. Scanning electron microscopy results implies the formation of the gold nano-layer with appropriate and smooth morphology on surface. Also, according to test results of electrical resistance, resistance of samples coated with 20 nm thick layer of gold was about half the resistance of uncoated samples, And this issue represents a significant increase in the electrical conductivity of the coated samples.

Equal channel angular pressing (ECAP) is considered to be the most promising severe plastic deformation route to receive ultrafine grained materials with high strength and good physical properties. Mechanical properties, electrical conductivity and electrical erosion of commercial pure copper rod processed by ECAP were investigated. For this purpose a set of ECAP dies with the intersecting channel angle of 90 and an external arc of curvature of 37º and punch was design and manufactured. Commercially pure copper was processed through ECAP die up to 8 passes. The mechanical experiments indicated that the yield stress increased with increasing the number of passes till the 5th one, but beyond this pass a little decrease was observed. The trend of electrical conductivity changes is different from the yield stress of the material, in a way that electrical conductivity will gradually decrease to the fifth passes. After which electrical conductivity will increase slightly. Also for the first time electrical erosion of pure copper processed by ECAP during the electrical discharge processes were investigated. It was found that, with increasing the number of passes and finer grains of pure copper, electrical erosion decrease with respect to NON-ECAP copper in the same testing conditions.