Papers by Keyword: Electrical Resistance

Abstract: This work involved fabrication of an efficient thin film heater from 100 μm thick polyimide (PI) sheet by scribing it using a carbon dioxide lasing machine through optimizing laser power (P), scanning speed (SS), and pulses per inch (PPI). A 15 mm × 15 mm square pattern was designed using CorelDRAW software and scribed in a rastering mode on top of PI with the help of Universal Control Panel (UCP) software of the laser machine. Laser power of 8 %, SS of 4 % and PPI of 1000 were obtained as optimal parameters for producing laser induced graphene (LIG). This LIG exhibited a low sheet resistance of approximately 16.64 Ω/sq and was thermally stable on the PI substrate even after 30 cycles of repeated heating and cooling. The LIG was found to be highly porous with the aid of scanning electron microscope (SEM) and its structure was crystalline from XRD patterns. FTIR was conducted and showed disappearance of functional groups in PI after treatment with the laser beam. Our developed LIG heater showed great electrothermal performance with maximum temperature of approximately 288.7 °C, rate of temperature rise of 107.06 °Cs^-1, and time of 1.85 s to reach 63 % of temperature difference at a low input voltage of 6 V with homogeneous temperature distribution seen in the thermal images taken using FLIR camera. This LIG heating element can be placed in confined spaces because of its flexibility, thinness, and lightness. Additionally, its efficient joule heating effect attracts many applications such as seat warmers, anti-fogging equipment, food shelf displays, etc.

Abstract: Sustainable development requires green energy and low carbon footprint in manufacturing sector of photovoltaic systems. The electrical connections of photovoltaic cells need to have low electrical resistance in order to reduce the electrical losses and therefore to improve the performance of the photovoltaic panels. This paper aims to present researches related to bonding of wires that connect solar cells by using microwave technology. The microwave bonding has the main advantage that offers fast bonding but, in the same time, this technology does not offer stability of the thermal heating. Two different unwanted phenomena like thermal runaway and plasma arc discharge often lead to the damaging of copper and aluminum wires used in electrical connection. The study presented in this paper is focused on simulation of the thermal field developed in copper wires in order to optimize the bonding process and increase the quality of products. The simulation of the thermal field has been done using Fourier equations for conducting heating in copper materials and eutectic alloys. The simulation model has been validated through experimental heating using a 6 kW water-cooled microwave generator controlled by a matching load auto-tuner for best transfer of the power from generator to copper wires. The temperature has been measured in real time using an infrared pyrometer for metals with 2.3 μm spectral range and measurement range between 0o C and 7000 C. The study is finalized with elaboration of mathematical model for microwave-injected power as function for temperature developed in copper wires that can be applied with success in further microwave bonding applications of copper wires. In addition, the electrical resistance of bonded wires was measured in order to collect feedback for improving the microwave bonding process.

Abstract: Research of alkali-activated materials and geopolymers suggests their increased ability to transfer the electric charge thus indicating their suitability for self-sensing and other multifunctional composites. In this paper, the electrical properties of metakaolin geopolymer are enhanced by the incorporated steel microfibres that also improve the mechanical and fractural properties of the composite. Selected electrical properties of metakaolin geopolymer mortars with steel microfibres (up to 30 % of metakaolin wt.) were assessed via impedance spectroscopy analysis and followed by testing their compressive and flexural strength. Mercury intrusion porosimetry and SEM imaging enabled to characterize the binder microstructure and quality of fibre-matrix bonding.

Abstract: The paper presents the results of studies of the structure and properties of a fluorohydrite binder modified by a chrysotile nanotubes dispersion in a medium of calcium nitrate solution. It is shown that addition of this modifier into the anhydrite composition leads to a 106-fold decrease in electrical resistance. Microstructural analysis of the fluorohydrite composition showed changes in the morphology of new formations with the creation of crystalline hydrates of increased density. The presence of elongated nanocrystals on the surface of the hardened matrix was noted. In addition, IR spectrum absorption lines, prove the presence of calcium nitrate in the pore space of the composition, which contributes to a significant decrease in the electrical resistance of the developed composite.

Abstract: It has been established that external uniaxial tensile stresses influence the character and kinetics of the g®a-transformation in cold-rolled martensite steel at sub-zero temperatures (down to -60 °C).

Abstract: The superconductivity phenomenon and the method of preparing the superconductingmercury-based (HgSr2-xYxCa2Cu3O8+δ with x=0 to 0.15) compound were presented in this paper. The physical properties of the compound are presented at a high temperature, with a special focus on the effect of partial substitution of strontium with Yttrium (Y). The effect on structural and electrical properties were investigated. All the samples in the present investigation were subjected to gross structural characterization by X-ray diffraction. The XRD data collected from various have the Hg1223 phase and the analysis showed that all samples correspond to the tetragonal structure. The electrical resistance uses the four probe technology to find the critical temperature and found that it drops from 116 K to 81K by increase the yttrium concentration.

Abstract: In the article, the authors examined the technological aspects of obtaining a functional alloy based on silver alloyed with chromium, zirconium, rhenium and rare earth elements (cerium, lanthanum, yttrium). A technology has been developed for producing powder from this alloy and nanostructured functional coatings based on it using the method of cold gas-dynamic spraying.

Abstract: Polymer composite materials based on polypropylene matrix and carbon nanoparticles of various shapes: spherical particles - carbon black and anisotropic nanoparticles - carbon nanofibers, were obtained by the melt technology. A character of the dependences of the electrical conductivities on the concentration of carbon nanofillers has been revealed. A simulation of the electrical conductivity of the polymer composite in the region of the concentration of the filler at the threshold of the flow of electric current and below it was carried out.

Abstract: On the CCDS2000 installation, detonation spraying of coatings from M28 and METCO 6103 aluminum oxide powders on steel substrates was carried out, and the dependence of the electrical resistivity of coatings on the atmosphere humidity was studied. It is shown that when the relative humidity changes from 14 to 80%, the specific electrical resistance of the coating decreases by 2-3 orders of magnitude from ρ ˃10¹³ Ω·cm to ρ ≈ 10¹¹ Ω·cm. On the base of obtained data, the model of coating microstructure is proposed, according to which alumina layer contained through defects in a form of nanochannels with diameter in the range 1-10 nanometers. In a coating cross section, the area of nanochannels sums up to 1%. In presence of high atmospheric humidity, these nanochannels can be filled with absorbed water, increasing drasticcaly the coating electrical conductivity.

Abstract: The aim was to investigate the relation between micromorphology of porosity and electrical resistance of dental luting cements. Five dental luting cements were evaluated: zinc phosphate, glass ionomer, and three types of resin luting cements. Porosity of the specimen was analyzed by micro-CT and electrical resistance of cement was measured at voltage of 125 V up to 30 days and solubility of each specimen was calculated. It showed that the resin luting cements provided the highest electrical resistance regardless of amount of porosity. Zinc phosphate and glass ionomer had high porosity and the lowest resistance (14 and 3 kΩ, respectively). It was found that the electrical resistance of luting cement was not directly affected by the amount of porosity, but it seems to be related to pore connection. There is no correlation between electrical resistance and percentage of porosity but the morphology of porosity may have an influence on the electrical property of luting cement. Models of pore connection were proposed to explain the electrical resistance of luting cement.