Multilayer Graphene Platelets Research Articles

Polyaniline-derived amorphous carbon conformally coated multilayer graphene platelets as anode for lithium-ion batteries

Materials made of amorphous carbon that includes nitrogen have been extensively researched for use as negative electrodes in systems that store energy like lithium-ion batteries (LIBs). Graphene platelets (GP) covered with polyaniline (PANi) were effectively created through polymerization and utilized as anode material for lithium-ion batteries. The prepared AGP composite material, utilized in lithium-ion batteries as an anode material (AM), was evaluated for its electrochemical properties. It produced a specific capacity (SC) of 450 mAhg−1 for 160 electrochemical cycles at a current density (CD) of 100 mAg−1 and 256 mAhg−1 for 500 cycles at a high current density (CD) of 1 Ag−1. These suggest that it could be a good option for the anode material (AM) in lithium-ion batteries (LIBs).

Contactless Scanning Near‐Field Optical Dilatometry Imaging at the Nanoscale

AbstractTo date, there are very few experimental techniques, if any, that are suitable for the purpose of acquiring quantitative maps of the thermal expansivity of 2D materials and nanostructured thin films with nanoscale lateral resolution in spite of huge demand for nanoscale thermal management, for example in designing integrated circuitry for power electronics. Besides, contactless analytical tools for determining the thermal expansion coefficient (TEC) are highly desirable because probes in contact with the sample significantly perturb any thermal measurements. Here, ω‐2ω near‐field thermoreflectance imaging is presented as a novel, all‐optical, and contactless technique to map the TEC at the nanoscale with precision. Testing of this technique is performed on nanogranular films of gold and multilayer graphene (ML‐G) platelets. With ω‐2ω near‐field thermoreflectance, it is demonstrated that the TEC of Au is higher at the metal‐insulator interface, with an average of (17.12 ± 2.30) ×10−6 K−1 in agreement with macroscopic techniques. For ML‐G, the average TEC is (−5.77 ± 3.79) x10−6 K−1 and is assigned to in‐plane vibrational bending modes. A vibrational‐thermal transition from graphene to graphite is observed, where the TEC becomes positive as the ML thickness increases. The nanoscale method here reported demonstrates results in excellent agreement with its macroscopic counterparts, as well as superior capabilities to probe 2D materials and interfaces.

Buckling analysis of stiffened functionally graded multilayer graphene platelet reinforced composite plate with circular cutout embedded on elastic support subjected to in-plane normal and shear loads

Buckling analyses of orthogonally stiffened functionally graded graphene platelet reinforced composite plate with circular cutout supporting on Winkler elastic foundation is conducted according to the third order shear deformation plate theory and the finite element method to achieve the desired solutions. Material properties of the composite plate are evaluated using Rule of mixture and Halpin-Tsai approach. Graphene platelet reinforcements and Poly methyl methacrylate matrix are considered as the two components of the composite media. The material of the stiffeners is selected the same as that of the polymer matrix. In one efficient case, adding a set of stiffeners increased the critical buckling load by 41.8 % with only a 10.3 % increase in weight of the structure. Influence of broad range of factors such as GPLs nanofillers distribution pattern and weight fraction, Winkler-type elastic foundation, uniaxial and biaxial normal and shear loads, plate thickness and aspect ratio, width, height and number of longitudinal and transverse stiffeners are reported in several tabular and graphical data in detail.

Thermal buckling and postbuckling of functionally graded multilayer GPL-reinforced composite beams on nonlinear elastic foundations

Under the influence of axial forces and uniform temperature variations, the thermal buckling and postbuckling of composite beams reinforced of functionally graded multilayer graphene platelets (GPLs) resting on nonlinear elastic foundations are examined. The Halpin-Tsai model is used to calculate the elastic modulus of each layer of GPL-reinforced composite (GPLRC). According to the virtual work principle, the nonlinear governing equations for the beam are obtained from the first-order shear deformation beam theory. The impact of axial force and nonlinear elastic foundation on thermal buckling and postbuckling is discussed using the differential quadrature method (DQM), and the analytical expression is given by the two-step perturbation method (TSPM). The effects of axial force, boundary conditions, slenderness ratio, GPL geometry, GPL weight fraction, GPL distribution pattern, and elastic foundation coefficient on thermal buckling and postbuckling are examined through parameter analysis.

Effect of stirring on characteristics of electrochemically exfoliated graphene

Electrochemical exfoliation of graphite is a promising technique for the synthesis of graphene at a commercial scale. Electrochemical synthesis of graphene at high voltage (∼10 V) is widely reported. However, at high voltage, multilayer graphene platelets with high defect concentration are produced. In this study, high quality graphene nanoplatelets consisting of 1–5 layers were produced at low voltage (3–4 V) using KOH solution as electrolyte. The effect of electrolyte stirring on the characteristics of graphene was studied. The stirring of electrolyte during electrolysis showed profound effect on the characteristics of graphene. The scanning electron microscopic (SEM) analysis showed that the stirring of electrolyte increased the average size of graphene nanoplatelets to 360 nm from 253 nm (without stirring). Raman spectroscopy indicated the presence of 1–5 layers of carbon atoms and the same was confirmed by transmission electron microscopy (TEM). A decrease in the defect concentration was noted with the increase in number of layers of carbon atoms in graphene produced with stirring.

Surface roughness and morphology evaluation of bearing steel after grinding with multilayer graphene platelets dispersed in different base fluids

Bearings are widely used in different industries which demand different quality requirements to ensure a long life with low wear rates. In this sense, bearing components should present combination of low surface roughness and tight dimensional deviations, as well as good lubricant retention capacity. So, grinding is an alternative to achieve this combination, however, one of the challenges is the large amount of heat generated in the grinding wheel-workpiece interface when using conventional abrasives grinding wheels, which can lead to surface finish deterioration and thermal damages, thereby reducing the component's life. Thus, several cooling-lubrication techniques have been tested in the past decades to enhance the cooling-lubrication properties of cutting fluids, with a highlight in recent years for the benefits of adding solid particles with good tribological properties to improve grinding efficiency. In this context, this work sought to evaluate the roughness and surface morphology of the bearing steel SAE 52100 (60 ± 2 HRC) after grinding with multilayer graphene (MLG) platelets dispersed in two different cutting fluids (synthetic and semi-synthetic). Tests with traditional MQL (without solid particles) and conventional techniques (flood) were also carried out for comparison. The output variables investigated were surface roughness parameters Ra, Rz, Rku, Rsk, Rk, Rpk, and Rv, images of machined surfaces through a scanning electron microscope (SEM), and the specific grinding energy. The results indicated that the base fluid type significantly affected the grinding performance. Tests with semi-synthetic fluid having MLG decreased the Ra parameter of the ground surface by 9% compared to the traditional MQL technique, with a higher Rvk and negative skewness. For the synthetic fluid also with MLG, about 29% increase in the Ra parameter was observed compared to MQL without nanoparticles, although it resulted in higher values of Rpk with more positive skewness. Presence of MLG in semi-synthetic and synthetic fluids reduced the specific grinding energy by 7% and 14%, respectively. Also, less intense plastic deformation and material adhesion was observed when grinding with MLG.

Improvements of the MQL Cooling-Lubrication Condition by the Addition of Multilayer Graphene Platelets in Peripheral Grinding of SAE 52100 Steel

In most grinding processes, the use of cutting fluid is required, and research has been carried out to reduce the amount of fluid used due to costs and environmental impacts. However, such a reduction of fluid can result in thermal damage to the machined component because the amount of cutting fluid may not be sufficient to lubricate and cool the system. One way of improving the cutting fluid properties is to add micro or nanoparticles of solid lubricants. This paper aims to evaluate the performance of multilayer graphene platelets dispersed in cutting fluid and applied through the technique of minimum quantity of lubrication (MQL) during the peripheral surface grinding of SAE 52100 hardened steel. In this sense, the influence of these solid particles with respect to the surface and sub-surface integrity of the machined components was analyzed, performing the roughness and microhardness measurement and analyzing the ground surfaces. The results showed that the cooling–lubrication conditions employing graphene could obtain smaller roughness values and decreases of microhardness in relation to the reference value and components with better surface texture compared to the conventional MQL technique without solid particles.

Study on grinding of inconel 625 and 718 alloys with cutting fluid enriched with multilayer graphene platelets

Nickel-based superalloys present excellent thermo-mechanical properties that can be maintained at high temperatures, making them suitable for application in aerospace and nuclear industries. Such components require a combination of superior surface finish and tight dimensional tolerances, thus grinding is the first option. However, these properties demand high specific energy during grinding and cause rapid grinding wheel wear, that adversely affects the ground surface hence leading to poor grindability. Thus, a proper selection of a cooling-lubrication technique is indispensable to reduce the friction and cool the grinding wheel-workpiece interface, thereby avoiding thermal damage that compromises workpiece surface integrity. In contrast, the use of cutting fluids in high volumes must be discouraged due to their harmful impact to environmental and human healthy. In this sense, research for improving eco-friendly techniques such as minimum quantity lubrication (MQL) in grinding have been increased, and the application of cutting fluids with solid particles dispersed on it have shown promising results. In this context, this work aims to analyze the surface finish and morphology of two nickel-based superalloys (Inconel 625 and Inconel 718) after grinding with semi-synthetic environmentally friendly oil enriched with multilayer graphene (MLG) platelets delivered via MQL technique. Surface roughness (Ra, Rz, Rsk and Rku parameters), images via scanning electron microscope (SEM), cutting power and grinding force ratio were the output parameters analyzed. The results for Inconel 718 showed that presence of the MLG promoted reduction in Ra and Rz, a better surface morphology and negligible effect on the other output parameters. With respect to the Inconel 625, on the other hand, the use of MLG platelets did not show any benefits in terms of surface finish, with evidence of occurrence of intense plastic deformation at machined surface (micro-plowing wear mechanism), although significant reduction in grinding force ratio was observed.

One pot facile transformation of CO2 to an unusual 3-D nano-scaffold morphology of carbon

An electrosynthesis is presented to transform CO2 into an unusual nano and micron dimensioned morphology of carbon, termed Carbon Nano-Scaffold (CNS) with wide a range of high surface area graphene potential usages including batteries, supercapacitors, compression devices, electromagnetic wave shielding and sensors. Current CNS value is over $323 per milligram. The morphology consists of a series of asymmetric 20 to 100 nm thick flat multilayer graphene platelets 2 to 20 µm long orthogonally oriented in a 3D neoplasticism-like geometry, and appears distinct from the honeycomb, foam, or balsa wood cell structures previously attributed to carbon scaffolds. The CNS synthesis splits CO2 by electrolysis in molten carbonate and has a carbon negative footprint. It is observed that transition metal nucleated, high yield growth of carbon nanotubes (CNTs) is inhibited in electrolytes containing over 50 wt% of sodium or 30 wt% of potassium carbonate, or at electrolysis temperatures less than 700 °C. Here, it is found that a lower temperature of synthesis, lower concentrations of lithium carbonate, and higher current density promotes CNS growth while suppressing CNT growth. Electrolyte conditions of 50 wt% sodium carbonate relative to lithium carbonate at an electrolysis temperature of 670 °C produced over 80% of the CNS desired product at 85% faradaic efficiency with a Muntz brass cathode and an Inconel anode.

Post-buckling analysis of functionally graded multilayer graphene platelet reinforced composite cylindrical shells under axial compression.

Axially compressed composite cylindrical shells can attain multiple bifurcation points in their post-buckling procedure because of the natural transverse deformation restraint provided by their geometry. In this paper, the post-buckling analysis of functionally graded (FG) multilayer graphene platelets reinforced composite (GPLRC) cylindrical shells under axial compression is carried out to investigate the stability of such shells. Rather than the critical buckling limit, the focus of the present study is to obtain convergence post-buckling response curves of axially compressed FG multilayer GPLRC cylindrical shells. By introducing a unified shell theory, the nonlinear large deflection governing equations for post-buckling of FG multilayer GPLRC cylindrical shells with wide range of thickness are established, which can be easily changed into three widely used shell theories. Load-shortening curves for both symmetric and asymmetric post-buckling modes are obtained by Galerkin's method. Numerical results illustrate that the present solutions agree well with the existing theoretical and experimental data. The effects of geometries and material properties on the post-buckling behaviours of FG multilayer GPLRC cylindrical shells are investigated. The differences in the three shell theories and their scopes are discussed also.

Large-amplitude dynamical behavior of multilayer graphene platelets reinforced nanocomposite annular plate under thermo-mechanical loadings

For the first time, the nonlinear forced vibration analysis of graphene nanoplatelets reinforced composite (GPLRC) annular plate under hygro-thermal environment and subjected to mechanical loading is presented. The GPLRC imperfect annular plate’s displacement fields are determined using third-order shear deformation theory (third-order SDT) and nonlinearity of vibration behavior of this structure is taken into account considering von Karman nonlinear shell model. Energy method known as Hamilton principle is applied to create the motion equations governed to the shell structures, while they are solved using generalized differential quadrature method (GDQM) as well as perturbation method (PM). Ultimately, the research’s outcomes reveal that increasing the value of the moisture change () and orientation angle parameter (), and the rigidity of the boundary conditions lead to an increase in the structure’s frequency. Besides, whenever the values of the nonlinear parameter () are positive and negative, the dynamic behavior of the plate tends to have hardening and softening behaviors, respectively, and could not be seen any effects from parameter on the maximum amplitudes of resonant vibration of the GPLRC imperfect annular plate. Last but not the list by decreasing the structure’s flexibility, the plate can be susceptible to have unstable responses.

Experimental study of the influence of graphene platelets on the performance of grinding of SAE 52100 steel

The use of coolant during grinding process is indispensable to avoid and/or attenuate any possible thermal damages on the workpiece. However, the conventional cooling-lubrication technique (flood system) has some drawbacks, especially regarding the fact that most of the coolants are harmful to environment and human healthy, besides higher costs, maintenance, and disposal. Therefore, not only the search for new methods that contribute in reducing the amount of coolant in grinding process is crucial, but also the search to improve techniques consolidated in machining processes, such as the minimum quantity lubrication (MQL). In this sense, the improvement of the thermal properties and lubrication of the coolants by nanoparticles has been one of the promising alternatives. The present work brings a contribution for bearing manufacturing industry by analyzing the effect of the concentration of multilayer graphene platelets (MLG) dispersed in coolant on the surface finish and morphology of the SAE 52100 bearing steel after grinding under various conditions. MLG were dispersed in an environmentally friendly cutting fluid (semi-synthetic vegetable based) and delivered via the MQL technique. Tests with the traditional MQL technique (oil without graphene) were also carried out for comparisons. Electric power was also monitored. The results showed that the low concentrations of MLG improved the tribological conditions in the cutting zone that resulted in better surface finish and morphology, but no influence on the electrical power was observed. The MLG proved to be a practical alternative in relation to traditional MQL technique in grinding of the SAE 52100 bearing steel.

Study of the mechanical-electrical-magnetic properties and the microstructure of three-layered cement-based absorbing boards

Abstract In this paper, a three-layered cement-based wave-absorbing board is designed and prepared by mixing wave-absorbing fillers such as nano-Si3N4, multi-layer nano graphene platelets (NGPs), nano-Ni, carbon fiber (CF) and carbon black (CB) into cement slurry. The effect of the amount of wave-absorbing fillers on the mechanical properties, resistivity and wave-absorbing reflectivity of cement slurry is studies. The microstructure of NGPs, nano-Si3N4 and the wave-absorbing board are characterized by TEM and SEM. Research shows that low content of NGPs and other wave-absorbing fillers can significantly reduce the resistivity of cement slurry and improve its mechanical strength, and dense massive crystals are precipitated in the cement hydration products. The reflectivity test reveals that in the frequency range of 2~18 GHz, the minimum reflectivity of the three-layered cement-based wave absorbing board reaches −18.8 dB, and the maximum bandwidth less than −10 dB reaches 15.3 GHz. This study can serve as reference for the preparation of new three-layered cement-based wave absorbing boards.

Investigations on Graphene Platelets as Dry Lubricant and as Grease Additive for Sliding Contacts and Rolling Bearing Application

In recent years, graphene-based lubrication was in the focus of nano- and microtribological studies. While the sliding properties of graphene based dry lubrication were previously investigated on the nano- and micro-scale, few studies can be found in the literature for the application of graphene as an additive to oil and grease in rolling contacts. In order to apply graphene platelets as dry lubricants and as grease additives in machine elements, tests were carried out on a rolling bearing test rig under typical load conditions. For these investigations, multilayer graphene platelets of varied staple thickness were functionalized on angular contact ball bearing surfaces as a dry lubricant, which forms a thin film. In addition, bearings were lubricated with grease containing graphene platelets. In this case, a small ratio of graphene was dispersed with grease. The graphene platelets were divided into three groups of different thickness: 2 nm, 6–8 nm, and 11–15 nm. Additionally, the tests were compared to graphite nanoparticles (spheres with a size of 3–4 nm) as dry lubricant and graphite-containing grease. The experimental studies were carried out under oscillating motion. The respective load in the tribological contact was 1.5 GPa. During the tests, the pivoting angle was measured by utilizing a rotary encoder. In addition, the friction torque was recorded under a frequency of 0.2 Hz. As the balls’ velocity at the reversal point is zero, the lubrication conditions are critical. The dry lubricated bearings were compared to grease lubricated bearings. Additionally, the frictional properties of the respective greases were investigated by applying a sliding tribometer. In this case, a ball rotates against three contact planes, which causes a tribological contact under a contact pressure of 1 GPa. It was shown that applying graphene as a dry lubricant and as a grease additive under rolling contact conditions reduces friction significantly.

Torsional Buckling of Functionally Graded Multilayer Graphene Nanoplatelet-Reinforced Cylindrical Shells

Exact solutions for the torsional bifurcation buckling of functionally graded (FG) multilayer graphene platelet reinforced composite (GPLRC) cylindrical shells are obtained. Five types of graphene platelets (GPLs) distributions are considered, and a slope factor is introduced to adjust the distribution profile of the GPLs. Within the framework of Donnell’s shell theory and with the aid symplectic mathematics, a set of lower-order Hamiltonian canonical equations are established and solved analytically. Consequently, the critical buckling loads and corresponding buckling mode shapes of the GPLRC shells are obtained. The effects of various factors, including the geometric parameters, boundary conditions and material properties on the torsional buckling behaviors are investigated and discussed in detail.

Wrinkle networks in exfoliated multilayer graphene and other layered materials

We describe a method to obtain networks of wrinkles in multilayer graphene flakes (and other layered materials) by thermal contraction of the underlying PDMS substrate they are deposited on. The exfoliated flakes on PDMS are dipped into liquid nitrogen and after removal networks of wrinkles are found. The density of wrinkles can be controlled to some degree by sequential dipping into liquid nitrogen. Atomic force microscopy shows that wrinkles form preferentially along the armchair direction of the graphene lattice in such multilayer graphene platelets. Raman spectra show that the interlayer coupling at a wrinkle in multilayer graphene differs from, and is weaker than, that in undeformed regions. High resolution transmission electron microscopy measurements show that the interlayer distance increases in strained regions, which results in the interlayer coupling being decreased in particular regions of the wrinkles in these multilayer graphenes.

Free vibration and buckling analyses of edge-cracked functionally graded multilayer graphene nanoplatelet-reinforced composite beams resting on an elastic foundation

This study investigates the linear free vibration and elastic buckling behaviors of functionally graded (FG) multilayer graphene platelet (GPL)-reinforced composite beams containing a single edge crack and resting on a Pasternak-type elastic foundation. GPLs are randomly oriented, and their concentration varies layer-wisely through the beam thickness. A modified Halpin-Tsai model is employed to estimate Young’s modulus of the GPL-reinforced composite (GPLRC). The first-order shear deformation beam theory is applied in structural modeling. The bending stiffness of the cracked section is assumed to be equivalent to that of a massless rotational spring, which is related to the stress intensity factor (SIF) at the crack tip. SIFs of the cracked FG multilayer GPLRC beams are calculated by the finite element method. The differential quadrature method is used to discretize the equations of motion of the cracked beams. A parametric study is performed after a validation study for the present approach to illustrate the effects of crack location, crack length, boundary condition, GPL weight fraction, GPL distribution pattern, GPL size and geometry, and foundation stiffnesses on the fundamental frequencies and critical buckling loads.

Influence of multilayer graphene platelet concentration dispersed in semi-synthetic oil on the grinding performance of Inconel 718 alloy under various machining conditions

Coolant plays an important role in grinding, as it preserves the workpiece integrity by reducing the friction, as well as cooling the surface. In grinding, the coolant is generally applied at high flow rates, through the flooding technique, which can cause health and environmental damage and moreover high costs. An alternative is to use less coolant with the addition of solid lubricant particles, which improve the tribological behavior of the fluid, such as multilayer graphene that is a small solid lubricant with high thermal conductivity. The aim of this present study is to investigate the influence of a multilayer graphene concentration (0.05 wt% and 0.10 wt%) dispersed in semi-synthetic oil applied using the Minimum Quantity of Lubrication (MQL) technique on the grinding performance of Inconel 718 alloy under various machining conditions. Graphene-free oil, flooding and dry conditions were also tested for comparison. The output parameters evaluated were: surface roughness, microhardness, residual stresses, grinding power and SEM images. The cooling-lubrication fluid properties (viscosity and thermal conductivity) were also obtained. The results showed that grinding with the lowest graphene concentration in the milder condition provided the lowest roughness values and microhardness variation, required about 50% less grinding power, inhibited surface crack generation, led to smoother surfaces and resulted in compressive residual stress.

A novel ‘bottom-up’ synthesis of few- and multi-layer graphene platelets with partial oxidation via cavitation

The transient cavitation of diaromatic components such as 1-methylnaphthalene has been used to produce graphene platelets in a ‘bottom-up’ synthesis via the high temperature (>5000 K) conditions that are generated inside collapsing bubbles. Acoustic cavitation produced yields of 5.7 × 10−11 kgJ−1 at a production rate of 2.2 × 10−9 kgs−1. This can be improved by generating cavitation hydrodynamically, thus making commercial scale production viable. Hydrodynamic cavitation produced platelets with larger lateral dimensions (≥2 µm) than those formed by acoustic cavitation (10–200 nm). The partially oxidised nature of the platelets enables their covalent chemical functionalisation, which was achieved by combining suitable molecules in the reaction medium to affect a one-pot formation and functionalisation of graphene.

Adsorption-assisted transport of water vapour in super-hydrophobic membranes filled with multilayer graphene platelets.

The effects of confinement of multilayer graphene platelets in hydrophobic microporous polymeric membranes are here examined. Intermolecular interactions between water vapour molecules and nanocomposite membranes are envisaged to originate assisted transport of water vapour in membrane distillation processes when a suitable filler-polymer ratio is reached. Mass transport coefficients are estimated under different working conditions, suggesting a strong dependence of the transport on molecular interactions. Remarkably, no thermal polarization is observed, although the filler exhibits ultrahigh thermal conductivity. In contrast, enhanced resistance to wetting as well as outstanding mechanical and chemical stability meets the basic requirements of water purification via membrane distillation. As a result, a significant improvement of the productivity-efficiency trade-off is achieved with respect to the pristine polymeric membrane when low amounts of platelets are confined in spherulitic-like PVDF networks.