جستجوی مقالات مرتبط با کلیدواژه « گرافن » در نشریات گروه « مواد و متالورژی »

Nowadays, energy storage has become a crucial challenge for humanity. Supercapacitors have emerged as a promising option for energy storage due to their numerous advantages. In this study, Co3O4/RGO nanocomposite electrode materials with high specific capacity and favorable electrochemical performance and cycling stability for electrochemical applications were synthesized via a one-step hydrothermal method on a nickel foam substrate and compared with cobalt oxide nanoparticles. The synthesized samples were characterized using various techniques, including X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and Fourier-transform infrared spectroscopy. For electrochemical evaluation, the synthesized nanostructures were examined in a three-electrode system with a 6 M KOH electrolyte. Cyclic voltammetry and galvanostatic charge-discharge tests were performed. The obtained specific capacity for the hybrid sample was 634.8 F/g at a current density of 1.5 A/g. In contrast, the specific capacity for the cobalt oxide nanoparticle sample was obtained to be 206.1 F/g, indicating a significant capacity enhancement for the hybrid sample. The demonstrated favorable electrochemical performance could be attributed to the nanoscale morphology and hybrid composition.

Tracking military structures and equipment is one of the parameters to create superiority in military battles. Camouflage has long been used to reduce the possibility of detection of military structures and equipment. Development of knowledge in the field of tracking and discovering military structures and equipment followed by the necessity of using the concealment in order to reduce vulnerability in war, has enhanced the importance of using new camouflage and radar evasion methods. The use of nanotechnology in the field of radar evasion of military facilities was developed by introducing graphene as a very strong absorber of electromagnetic waves. Graphene coating on the military installations causes the absorption of electromagnetic waves and as a result, these installations are not detected by the enemy's radar.  Referring to the fact that there is a functional relationship between the diameter of the graphene oxide used and the radar evasion of the equipment, an attempt has been made in this article for the first time to find a solution to control and monitor the radar evasion quality using graphene oxide (with the scientific name of RGO/NiFe2O4) in the microwave spectrum of 7GHZ by the profile approach and presentation of a regression relationship. This model can be used to monitor the quality of radar evasion products (cheaper and faster than existing methods). Finally, sensitivity analysis of the model showed that the ability to detect non-conformity in the manufactured products can be detected quickly (between 1 and 20 samples) with the change in the parameters of the regression model.

In this research, Ni-Co/Gr nanocomposite coating was applied on a low carbon steel substrate based on electrodeposition method under pulse-reverse current using watt plating solution in the presence of saccharin with 0.05 g/L graphene. For better graphene distribution, the plating solution was sonicated. The microstructure of the coating was examined by scanning electron microscopy, atomic force microscopy, and X-ray diffraction, and its corrosion resistance was assessed by polarization and Electrochemical Impedance Spectroscopy (EIS) analysis. The results showed that the coating included Ni-Co/Gr alloy with a smooth surface morphology and contained about 26 % by weight of cobalt. Graphene reinforcing particles were co-deposited on the surface. The average grain size of the Ni-Co/graphene composite coating was obtained as about 7 nm, indicating the formation of a very fine-grained structure. The hardness value of the sample increased from 220 HV (microhardness of the substrate) up to 496 HV followed by nanocomposite coating application. The results of the corrosion tests showed that the corrosion resistance of the coated sample was much higher than that of the uncoated steel. As a result of applying this coating, the corrosion rate decreased from 0.611 mm/y to 0.0029 mm/y.

In this study, in order to investigate the graphene effect on the oxidation resistance, at first two laminates TaCTiC/ TaC-TiC-graphene composite was sintered via spark plasma sintering (SPS) at the temperature of 1850 ˚C, for 8 min sintering time,under the pressure of 35 MPa. For investigation the oxidation resistance, the samples were putted in the box furnace at the temperatures of 400, 500, 600 and 700 ˚C for 30 min under the air atmosphere. For oxidation resistance evaluation, X-ray diffraction (XRD), thermal analysis and scanning electron microscopy were applied. It was revealed increasing the temperature resulted to reduce mass of samples which indicates oxidation of Tantalum carbide, Titanium carbide, silicon carbide and graphene. XRD result showed phases such as Ta2O5 and SiO2 formed during oxidation process and the amount of them increases with temperature ascent. The grain growth is negligible up to 600˚C but in higher temperatures, the noticeable growth is occurred. Also, it was disclosed all reactions are exothermic below the 900˚C and at the higher temperature are endothermic and occurred in one step.

In this research, the structure and mechanical properties of aluminum 6061 composite with graphene reinforcing nanoparticles produced by friction stir method (FSP) were investigated. The rotation speed of the tool was set from 112 to 280 rpm, the speed of the tool movement in the range of 31.5 to 20 mm/min and the slope of the conical tool was set at 2, 2.5 and 3 degrees.

Characterization was done by tensile tests, microhardness, field emission scanning electron microscope (FESEM) along with X-ray energy spectroscopy (EDS) and optical microscope (OM). The results show that in the presence of graphene as a reinforcement, the mechanical properties are improved.

By increasing the ratio of rotation speed to tool movement speed (advance per revolution) from 0.07 to 0.28 and increasing the tool angle from 2 to 3 degrees, tensile strength enhanced from 338 to 396 MPa, yield strength from 319 to 383 MPa and the elongation increase has increased from 10.9 to 12.3 percent. Also, the micro-hardness in the nugget area increased from 273 to 400 Vickers.

In recent years, utilizing two-dimensional materials has attracted much attention due to the exclusive features like high specific area and high surface activity. Among the diverse 2D materials like graphene and disulfides, Mxene is a newly developed material that could be achieved from MAX phases. These materials contain a metallic element mainly from transitional metals like titanium, molybdenum, niobium, or chromium, with carbon or nitrogen and groups like fluoride, oxygen, or hydroxide. Considering their unique properties, the range of applications of the Mxene is developing. Therefore, it is essential to understand better these newly developed two dimensional materials, their structures, synthesis methods and the parameters that could optimize the achieved properties. Furthermore, more Mxenes could be achieved by designing and synthesizing more MAX phases, which could be used in more applications. In this study, we tried to introduce a history of the Mxene and emphasize its features, synthesis methods, and application.

In recent scientific studies, the use of graphene has been considered due to its positive effect on the properties of composites, including mechanical, electrical and thermal properties. In this research, the microstructural and mechanical properties of pure aluminum nanocomposite cast reinforced with 0.5 wt% graphene with mechanical-electromagnetic stirrer and then hot extrusion and finally annealing, in two methods of using ball milling and without using ball milling process, was investigated. By applying both mechanical and electromagnetic stirring techniques, combining both shear and body forces can cause more turbulence in the molten metal that lead to as well as distribute reinforcing particles, decreasing the dendritic structures and refining the grains during solidification. The microstructural studies showed that in the ball mill method, the distribution of graphene nanoparticles and reduce grain size in the matrix phase is significantly better than the non-ball mill method. Also, in the method of ball mill, hardness, tensile strength and compressive strength increased by 19.7, 142.8 and 11.7%, respectively, and in the method without mill, 9, 85.2 and 13.5%, respectively, compared to pure aluminum. The elongation decreased by 6.8% in the ball mill method and 35.4% in the non-ball mill method.

Graphene, as the first presented two-dimensional material, is undergoing a growing trend in various industries. In this study, some effective parameters on the structural and microstructural properties of graphene synthesized by wet milling, in the presence of N-methyl-2-pyrrolidone (NMP) as a solvent were investigated. These variable parameters consist of the amount of graphite, solids to solvent ratio, weight ratio of pellets to solids, and the time of milling. The results of field emission scanning electron microscopy (FESEM), Raman spectroscopy and Fourier-transform infrared spectroscopy (FT-IR) analysis showed that the optimal parameters are 25 for the weight of pellets to graphite, concentration of 20 g/ml of graphite in NMP, and milling time of 6 hours. However, the application of a mixture of melamine and urea was evaluated for the exfoliation and functionalization of graphene by the planetary mill, according to the results, this mixture, showed a promising result as a promising composition for the simultaneous exfoliation and functionalization of graphene.

In this research, the effect of graphene oxide (GO) and reduced graphene oxide (RGO) nanosheets on the mechanical and microstructural properties of AISI 304 stainless steel welded joints produced by the flux-cored arc welding (FCAW) method was investigated. Light microscope, field emission scanning electron microscope (FE-SEM) equipped with energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD), Raman spectroscopy, and tensile strength test were used to characterize the samples. GO was synthesized by modified Hummers’ method and reduced by hydrazine. Accordingly, the pastes of GO and RGO in different concentrations of 1, 3, and 10 mg/ml were applied in the groove. The results demonstrated that increasing the RGO concentration up to 10 mg/ml improves the tensile strength and hardness values of welded joints up to 23% and 43%, respectively. It seems that RGO nanosheets have a significant effect on the mechanical properties of the welded joints by pinning of dislocations.

In this study, the plasma etching of a graphene layer (in order to make it porous) deposited on a SiO2 substrate was investigated. Therefore, for the first time, the process of the graphene layer bombardment with the oxygen ions was simulated by molecular dynamics simulation using LAMMPS. Moreover, the effect of the bombarding ion energies on the etching process was studied. Our results showed that with increasing the oxygen ion energies from 3 eV to 12 eV, the number and size of the created holes in the graphene layer increase. Investigation of the radius distribution function of the graphene layer before and after the bombarding process also showed that the etching process has caused some sort of irregularities in the graphene layer. In addition, the average number of C-C bonds in the graphene layer decreased with the oxygen ion energies which is the indicator of the fact that the C-C bonds have been broken with increasing energy. Moreover, the results showed that at the energy of 3 eV for the oxygen ions, the graphene layer remains almost undamaged. It is noteworthy that the Reax force field is used in the simulation which predicts the formation of O2, CO, CO2, C2O2 and CO3 species.

One of the methods to improve and achieve superior properties, is to modify and optimize the Manufacturing Process and to consider the use of nanoparticles as reinforcements in these materials. In this regard, stir casting method is considered as one of the methods of distribution of refractory particles in the melt and three percent by weight of 0.01, 0.05 and 0.1% of graphene nameplates and carbon nanotubes as reinforcements particles added to The primary alloy A356, due to the properties of carbon based nanoparticles. The optimum conditions, including the rotational speed of the graphite mixer, 500 RPM, were obtained for one-minute mixing in a row, at 740⁰C. The results of elemental, phasic and microstructural analysis, confirmed, the distribution correctly of reinforcements nanoparticles in the composite matrix. The tensile test showed, an increase in yield, ultimate and fracture strength, and also strain, so that the maximum increase in strength and strain using 0.1 wt.% graphene, was 28% and 2.6%, respectively. Also, by using 0.1 wt.% carbon nanotube, the nanocomposite hardness increased to 88.4 Vickers, indicating a 33% improvement in the ratio of non-reinforced alloy.

In this study, using Hydrothermal method, electrodes were synthesized to be used as supercapacitors. Using the alteration ratio of Al+3/Co+2/Ni+2 metal ions, Al0.5Co0.5Ni2O4 electrode with a molar ratio of 1:1:2 for Al+3/Co+2/Ni+2 ions, the highest capacitance was obtained, which was called the NiCoAl electrode. With the change of time (2, 5 and 20 hours) and the temperature of the hydrothermal process (150 and 180 °C), the performance of the manufactured electrodes changed, and as a result, the NiCoAl electrode synthesized at 150 °C for a period of 5 h, the capacity of 1473 F g-1 in the current density of 8 A g-1 was obtained as the best electrode made. By adding graphene to the electrode's constituent materials, the NiCoAl-rGO electrode, synthesized at 150 °C showed a maximum capacity of 2364 F g-1 at a current density equal to 8 A g-1. With the help of structural analysis of X-ray diffraction test (XRD) and infrared spectrum (FTIR), the presence of constituent materials in the structure was confirmed, and the presence of graphene in the NiCoAl-rGO electrode structure was observed. In order to determine how electrochemical performance works, the electrodes were subjected to cycles (CV), Galvanostatic charge and discharge (CD), and electrochemical impedance (EIS) tests.

In the present study, Graphene oxide (GO) was deposited using inexpensive and environmentally-compatible methods on the nickel oxide foam. Then, GO thin films have been reduced by Cyclic Voltammetry (CV), Chronoamperometry and Chronopotentiometry modes of electrodeposition. The effects of different modes on structural, surface morphological and supercapacitive properties of ERGO thin films have been investigated by X-ray diffraction (XRD), Scanning electron microscope (SEM), Raman spectroscopy, Cyclic Voltammetry, and Galvanostatic charge and discharge (GCD). Formation of ERGO by all three modes is confirmed by X-ray diffraction (XRD) patterns. A Significant change in the surface morphologies of the ERGO thin film due to different modes has been observed. The supercapacitive properties of ERGO thin films have been studied in 1 M KOH electrolyte. The maximum supercapacitance obtained for potentiodynamic, potentiostatic, and galvanostatic modes is 1380, 1259, and 1995 F/g, respectively which is completely in agreement with the special level and impedance results. The results showed that the constant current method is the best way for the electrochemical reducing of graphene oxide. In this way, most functional groups have been reduced. In addition, a high density of the defects and wrinkling of the sheets is observed. Consequently, the method can replace chemical methods for the reducing of graphene oxide and eliminate the major weakness of chemical methods that use toxic substances.

Hybrid nano-biocomposite of Mg-0.5Ca-0.8Mn (wt%) magnesium alloy reinforced by 2 wt% fluorapatite (FA) nanoparticles and 0.3 wt% graphene nanoplates (GNPs) were prepared via mechanical stir casting process. In order to eliminate the casting defects, remelting process was carried out under argon atmosphere. Mechanical and biocorrosion properties were investigated by tensile testing and electrochemical impedance spectroscopy in simulated body fluid (SBF) solution, respectively. Microstructural development including the size and distribution of the reinforcement particles, and matrix grain size were studied by optical microscopy and scanning electron microscopy (SEM). Mechanical test results revealed an increase of 27% in the ultimate tensile strength. Biocorrosion behavior approved the lower corrosion rate of the composite samples in comparison with unreinforced alloy. Optical micrographs confirmed the effect of reinforcement particles on twinning formation and reduction of composite grain size (175 μm) compared to that of unreinforced alloy (484 μm). SEM observations exhibited the formation of graphene scaffolds and their positive effect on the mechanical and biocorrosion properties.

One of the materials used in the manufacture of sensors is nanocomposites. Nanocomposite components have better properties than other materials due to the surface interaction between the base material and the filler. The aim of this study was to synthesize nanocomposites including graphene and polytechnic as a conductive polymer for use in electrochemical sensors. Electropolymerization method was used to synthesize nanocomposite. Graphene was chosen as the phase and poly catechol phase as a reinforcing phase and this polymer material was distributed on a wide range of graphene. SEM images of synthesized nanocomposites showed that this composition has a very porous morphology consisting of a sheet-like structure. Sodium nitrite and barium sulfate were used for oxidation on the modified electrode surface. The results showed that the electrochemical sensor made in a wide range of concentrations of nitrite has a linear response and can be used for quantitative measurement of these two species. Using calibration curve slope for the two studied species, the detection limit of this electrochemical sensor for nitrite was calculated to be 0.741 μM for nitrite. The results showed that synthesized nano sensor could be used as an anesthetic due to high sensitivity, optimal linear response, acceptable stability and not interference with interference. The use of graphene nanoscopes, which has the most effective properties to reduce electron transfer resistance and increase conductivity at the electrode surface, has been able to provide a very suitable surface with a high surface area for use in nanosized composites.

In this paper a new multi-scale method was presented to calculate the elastic modulus of graphene/polymer nano composites. Macro, micro and nano scales were considered within this hierarchical multi-scale method. In macro scale, a nanocomposite was modeled with a cubic representative volume element (RVE) which was constructed by several small cubic elements in micro scale. Each element in micro or nano scale, is made of aligned graphenes which were oriented in three dimensional space via a random algorithm. The stiffness tensor of each element was obtained by Mori-Tanaka micromechanical method and the elastic modulus of the RVE was calculated using a new analytical approach. In fact this method is a development of the laminated analogy, in to a three dimensional version which is in better accordance with the physics of real nanocomposites. It has been shown that the results of the present approach are in good agreement with several experimental works in the literature.

The electrochemical exfoliation of graphite is a method to obtain graphene. Despite the important role of electrical power in this process, it hasn’t been investigated extensively. In this research, the effect of electrical power in an extensive range on the amount of exfoliated graphene and oxygen functional groups was studied. Transmission electron microscopy, weighing, UV-vis spectroscopy and electrical conductivity were used for characterization of the products. According to the results, by decreasing the power, the amount of exfoliated graphene and its functional groups increased.

High conductivity and high level of electrolyte availability are the main requirements of active materials used in supercapacitors (SCs) to achieve high electrochemical efficiency. In recent years, metal-organic frameworks (MOFs) have been used as electrode materials for SCs due to their suitability of porosity and high surface area. However, using single-component MOFs in supercapacitors results in poor electrical conductivity, insufficient stability, and poor mechanical properties, and neutralize the effect of high capacity and efficient performance. In this paper, using a hydrothermal synthesis method, Cu-based MOFs were fabricated and graphene was added during synthesis to enhance the conductivity of these materials.  To investigate the structure of nanocomposites were used XRD, FTIR, and FESEM analyze. To investigate the electrochemical behavior of electrodes, cyclic voltammetry, electrochemical impedance and repeatability behavior were performed. The Cu based MOFs had a capacity of 372 F.g-1, while its composite capacity with graphene is 570 F.g-1. In these composites, graphene enhances electrical conductivity, porosity accessibility, and charge storage through a non-Faradic mechanism and metal-organic frameworks increase the total capacity with high porosity, porosity adjustable, and charge storage through the Faradic Mechanism.