Amount Of Graphene Nanosheets Research Articles

Tribological behaviour of ultra-thin stainless steel in micro deep drawing with graphene nanosheets

In this study, the micro deep drawing (MDD) experiments of an austenitic stainless steel with 40 μm in thickness were conducted using the lubricants containing different mass fractions of graphene nanosheets (GNS) in ethanol. Prior to the MDD tests, the lubricants with GNS concentrations of 5, 10, and 15 mg/ml were synthesised by mixing different amounts of GNS with pure ethanol, and then sprayed uniformly on the blank surface. The friction-reduction mechanisms of the GNS in the MDD were discussed by analysing the profile and surface roughness of the microcups. The results indicated that the GNS could reduce the friction and improve the surface quality of the micro products during the MDD process. In particular, the lubricant with 10 mg/ml GNS enabled the lowest drawing force, wrinkling, and surface roughness of the drawn microcup. These findings contribute to a better understanding of the friction-reduction mechanisms of using GNS in the MDD of materials.

Preparation and properties of Ti(C,N)-based cermets with graphene nanosheet addition by spark plasma sintering

The application of Ti(C,N)-based cermets remains limited due to their low toughness. The fracture toughness of cermets can be significantly improved by using advanced sintering methods and appropriate additives. Here, cermets were prepared by spark plasma sintering (SPS) technology with graphene nanosheets (GNSs) and nano-scale tungsten carbide (WC) as additives. The effects of GNSs and sintering conditions on the microstructure, mechanical properties, and magnetic properties of Ti(C,N)-based cermets were studied. The results show that the sample with 0.6 wt% GNSs fabricated at 1450 °C, 8 min, and 35 MPa has a denser microstructure and better mechanical properties. The cermet has a Vickers hardness of HV 2415.40 and fracture toughness of 10.6 MPa·m1/2. Compared with the specimen without GNSs, the hardness and fracture toughness are significantly improved by 44.58% and 92.73%, respectively. A certain amount of GNSs can increase the movement of hard phases in the liquid phase, inhibiting their solubility and grain growth, and greatly improving the fracture toughness of cermets. The addition of nano-WC is conducive to promoting the formation of a (Ti,W) (C,N) rim phase and improving properties of cermets. SPS can activate particle surfaces and promote the densification of cermets.

Low-threshold random lasers based on the DCM-DEG gain system with graphene nanosheets.

In this article, low-threshold random lasers based on DCM-DEG (DD) gain system with graphene nanosheets are studied. The experiment results show that the threshold of random lasers reduces rapidly when an appropriate amount of graphene nanosheets is added in DD solution. Meanwhile, the quantity and quality of random lasing modes raise significantly. We discussed the potential reasons why the graphene nanosheets can strengthen the sample's random lasing. And, the influence of the graphene nanosheet concentration on the radiation characteristics of random lasers is further studied. When the concentration of graphene nanosheets is 0.088wt%, the lasing threshold of DD samples with graphene nanosheets (GDD) is only about 31.8% of the lasing threshold of DD samples, and the quality of random lasing modes is five times higher than that of the DD sample. To further reduce the lasing threshold, the gold (Au) nanoparticles are added in the mixed solution to form the GDD solution with Au nanoparticles (GGDD). The results show that the lasing threshold of the GGDD sample is about 7.73 µJ/pulse, which is 5.2% of the lasing threshold of the DD sample. This experiment provides a new method to study low-threshold and high-quality random lasers based on graphene.

Mechanical and tribological characterization of nanostructured graphene sheets/A6061 composites fabricated by induction sintering and hot extrusion

An aluminum alloy (A6061) reinforced with graphene nanosheets (GNSs) was successfully fabricated by ultrasonic processing, high-frequency induction heat sintering (HFIHS), and hot extrusion. Harmful aluminum carbide (Al4C3) was not formed during HFIHS process as well as GNS particles were found to be able to stimulate recrystallization, restrict grain growth, and disturb the preferential texture in the present work. Enhancements in compressive strength of up to 50.4%, Vickers hardness of 13.3% as well as a 21.7% reduction in the friction coefficient along with a 17.2% reduction in the wear rate compared with those of as-extruded A6061 were measured. These improvements were due to the homogeneous dispersion of 0.25 wt% GNSs in the matrix. In addition, the yield strength predicted using modified model was in good agreement with the experimental results reported in this study. However, deterioration of the mechanical properties of the composites and a discrepancy between the theoretical prediction and experimental values occurred with the addition of 0.5 wt% GNSs owing to GNS agglomeration. This study demonstrated that the incorporation of an appropriate amount of GNSs can enhance the overall properties of a metal matrix, opening up an innovative design concept for fabricating bulk metal matrix composites (MMCs).

Microstructures and properties of Sn–0.3Ag–0.7Cu solder doped with graphene nanosheets

Low silver Sn–0.3Ag–0.7Cu (SAC0307) solders with different amounts of graphene nanosheets (GNSs) prepared by powder metallurgy were used to investigate the impacts of GNSs on the microstructures, melting temperature, wettability, and tensile strength of the SAC0307–xGNSs (x = 0, 0.01, 0.03, 0.05, 0.07, and 0.09 wt%) solders. The experimental results indicate that the wettability of SAC0307 solder can be improved significantly by adding GNSs and the melting temperature of the solder sample ranges from 219.6 to 222.7 °C. It is also revealed that with increasing GNSs content, the morphology of GNSs in the solder matrix changed from the initial dispersion distribution to the agglomeration, while the diameter and depth of the dimples of the solder joint fracture showed a tendency of increasing first and then decreasing. Doped with 0.07 wt% of GNSs, the solders showed the largest tensile strength. When GNS addition exceeds 0.07 wt%, it will induce negative effects on tensile property of the solder.

Effect of Laser Fluence on the Characteristics of Graphene Nanosheets Produced by Pulsed Laser Ablation in Water

The effect of laser fluence on the characteristics of carbon nanostructures produced by pulsed laser ablation has been investigated. The beam of a Q-switched Nd:YAG laser of 1064 nm wavelength at 7 ns pulse width and different fluences was employed to irradiate the graphite target in distilled water. The X-ray diffraction pattern, transmission electron microscopy, field emission scanning electron microscopy, Raman spectrum, and linear absorption properties of carbon nanostructures were used to characterize the ablation products. Carbon nanoparticles beside the graphene nanosheets were observed due to variation of laser fluence. The results show that under our experimental condition with increasing laser fluence the amount of carbon nanoparticles in suspensions was increased while the amount of graphene nanosheets was decreased.

Effect of fluence on carbon nanostructures produced by laser ablation in liquid nitrogen

Effects of laser fluence on the properties of carbon nanostructures produced by laser ablation method in liquid nitrogen have been studied experimentally. The beam of a Q-switched Nd:YAG laser of 1064-nm wavelength at 7 ns pulse width and different fluences is employed to irradiate the graphite target in liquid nitrogen. Properties of carbon nanostructures were studied using their UV–Vis–NIR spectrum, TEM images, and Raman scattering spectrum. Two categories of graphene nanosheets and carbon nanoparticles were observed due to variation of laser fluence. Results show that in our experimental condition there is a threshold fluence for producing carbon nanoparticles. With increasing the laser fluence from the threshold, the amount of carbon nanoparticles in suspensions was increased, while the amount of graphene nanosheets was decreased.

Crystallization, mechanical, and electromagnetic properties of conductive polypropylene/SEBS composites

Polypropylene (PP) and styrene–ethylene–butylene–styrene triblock copolymer (SEBS) are blended with a weight ratio of 70/30 to serve as the matrices. The prepared polymer blends were evaluated by tensile, flexural, and Izod impact tests, as well as by differential scanning calorimetry (DSC), optical microscopy, and scanning electron microscopy. The optimal PP/SEBS matrices were then combined with graphene nanosheets (GNs) and carbon fibers (CFs) by a melt compounding method to form conductive polymer composites. The crystallization properties, tensile properties, conductivity, and electromagnetic interference shielding effectiveness (EMISE) of the composites were evaluated by DSC and tensile strength and conductivity tests. In PP/SEBS blends, the SEBS acted as the nucleating agent of PP, thereby increasing the crystallization temperature and accelerating the crystallization rate, without significant influence on the degree of crystallinity. An increase in SEBS loading is inversely proportional to the tensile strength, tensile modulus, flexural strength, and flexural modulus of the PP/SEBS blends, but is highly proportional to the impact strength. In addition, the tensile strength of the conductive PP/SEBS/GN conductive composites decreased with the increase in the amount of GNs, with a percolating threshold of approximately 1.6 vol%. A distinct synergistic effect of the GNs and CFs on the conductive PP/SEBS/GN/CF composites was not achieved until the total loading level was 15 wt%. Optimal conductivity and EMISE of the conductive PP/SEBS/GN/CF composites were achieved at GN/CF ratios of 10/5 wt% and 5/10 wt%, respectively.

Sliding wear behavior of copper-based composites reinforced with graphene nanosheets and graphite

The mechanical and tribological properties of hot-pressed copper-based composites containing different amounts of graphene nanosheets (GNSs) are compared with those of copper–graphite (Gr) composites fabricated by the same method. The results show that the Cu–GNSs composites exhibit higher relative density, microhardness and bending strength compared with Cu–Gr composites with the same volume fraction of GNSs and Gr. Moreover, the friction coefficients and wear rates reduce significantly by the addition of GNSs, whereas the limited impact on reducing friction and wear is found on graphite. The abrasive and delamination wear are the dominant wear mechanisms of the composites. It is believed that the superior mechanical and tribological performances of Cu–GNSs composites are attributed to the unique strengthening effect as well as the higher lubricating efficiency of graphene nanosheets compared with those of graphite, which demonstrates that GNS is an ideal filler for copper matrix composites, acting as not only an impactful lubricant but also a favorable reinforcement.

Fabrication and mechanical properties of low‐loading graphene nanosheets encapsulated on the surface of graphene nanosheets/polypropylene composites

In recent years, numerous scientists have used graphene for reinforcing polymer-based composites because of its outstanding electrical, thermal and mechanical properties. Based on this present reported work, a simple manufacturing process is reported for the fabrication of low-loading graphene nanosheets (GNSs) coated on the surface of a polypropylene matrix. According to a scanning electron microscope micrograph, the GNSs were dispersed uniformly on the surface of polypropylene pellets. The mechanical properties and thermal stability of the GNSs /polypropylene composite plates were improved substantially by the addition of GNSs. X-ray diffraction was used to determine that the two-theta values of the GNSs /polypropylene composite plates correspond to the weight fraction of the added GNSs. Fourier transform infrared spectroscopy revealed that the vibration peak of the polypropylene methyl group decreased gradually when the amount of GNSs increased.

Highly sensitive electrochemical sensor for paeonol using NMP-exfoliated grapheme-modified electrode

Graphene nanosheets (GS) were easily prepared from graphite powder by one-step ultrasonic exfoliation in N-methyl-2-pyrrolidone (NMP). The resulting GS was used to modify the surface of glassy carbon electrode (GCE) via solvent evaporation. The electrochemical behaviors of paeonol were studied, and a sensitive oxidation peak of paeonol was observed on the GS-modified GCE (GS/GCE). Compared with the unmodified GCE, the GS/GCE greatly enhanced the oxidation signals of paeonol, showing remarkable signal enhancement effects. The influences of pH values, amount of GS, accumulation potential, and time were examined on the oxidation peak currents of paeonol. As a result, a highly sensitive electrochemical sensor was developed for paeonol. The linear range was over the range from 0.1 to 15 μM, and the detection limit was calculated to be 32 nM. The proposed method was used in the sample analysis of cortex moutan, and the detected results consisted with the values of that obtained by high-performance liquid chromatography.

Enhanced-oxidation and electrochemical determination of honokiol and magnolol using NMP-exfoliated graphene nanosheets

Using N-methyl-2-pyrrolidone (NMP) as the exfoliation solvent, graphite powder was easily exfoliated into graphene nanosheets (GS) via ultrasonication, which was characterized using transmission electron microscopy. The measurements of scanning electron microscopy and atomic force microscopy indicated that the modification of GS obviously increased the surface roughness of glassy carbon electrode, providing high accumulation efficiency and large response surface. As a result, the oxidation signals of honokiol and magnolol were increased greatly on the surface of GS. Moreover, the oxidation mechanisms were studied for honokiol and magnolol, and one electron was transferred in the oxidation process. After optimizing the parameters such as pH value, amount of GS, accumulation potential and time, a highly-sensitive electrochemical sensor was developed for the simultaneous determination of honokiol and magnolol. The values of detection limit were evaluated to be 0.2μgL−1 and 1.0μgL−1 for honokiol and magnolol. The application of this sensor was demonstrated using Chinese traditional medicines, and the accuracy and feasibility were tested to be good using high-performance liquid chromatography.

Improved microstructure and mechanical properties in gas tungsten arc welded aluminum joints by using graphene nanosheets/aluminum composite filler wires

In the present study, different amounts of graphene nanosheets (GNSs) were added to the 4043 aluminum alloy powders by using the mechanical alloying method to produce the composite filler wires. With each of the produced composite filler wires, one all-weld metal coupon was welded using the gas tungsten arc (GTA) welding process. The microstructure, mechanical properties and fracture surface morphology of the weld metals have been evaluated and the results are compared. As the amount of GNSs in the composition of filler wire is increased, the microstructure of weld metal was changed from the dendritic structure to fine equiaxed grains. Furthermore, the tensile strength and microhardness of weld metal was improved, and is attributed to the augmented nucleation and retarded growth. From the results, it was seen that the GNSs/Al composite filler wire can be used to improve the microstructure and mechanical properties of GTA weld metals of aluminum and its alloys.