Graphene Nanoplatelets Content Research Articles

Investigating the Effects of Graphene Nanoplatelets and Al4C3 on the Tribological Performance of Aluminum-Based Nanocomposites

The study investigates the effects of graphene nanoplatelets (GNPs) on the tribological properties of aluminum-based nanocomposites, both annealed after extrusion and non-annealed. It also examines the role of nanosized Al4C3 (aluminum carbide), which forms in the annealed Al/GNPs nanocomposite, on the tribological performance of the nanocomposites. The nanocomposites were fabricated using the powder metallurgy method. The microstructure of the composite materials was characterized using SEM, EDS, XRD and TEM techniques. The coefficient of friction (CF) and mass wear of the composites were measured using a pin-on-disk test under dry sliding friction conditions. The results showed that adding GNPs increased the coefficient of friction (CF) of the nanocomposites by up to 44% at 0.1 wt.% GNP, but the CF decreased by 15% at 1.1 wt.% GNP. The optimal concentration of GNPs for minimizing the CF and mass wear of Al-based nanocomposites was 0.1 wt.%. Additionally, the presence of Al4C3 in the annealed Al/GNP nanocomposite had a positive effect on the CF at low GNP concentrations, with a 38% increases at 0.1 wt.% GNP, but this effect diminished as the GNP concentration increased. The study also found that the mass wear of the nanocomposites increased with the GNP concentration, with a 46% increase in the mass wear from 0.1 wt.% GNP to 0.5 wt.% GNP and a 202% increase from 0.1 wt.% GNP to 1.1 wt.% GNP. The presence of Al4C3 also affected the mass wear, with the effect diminishing as the GNP concentration increased. The study observed an increase in the mass wear with the increase in the GNP concentrations, but the mass wear of the annealed Al/GNPs with 1.1 wt.% GNP and Al4C3 was 52% lower than the Al composite with 1.1 wt.%. Overall, this study provides insights into the role of GNPs and Al4C3 on the tribological performance of aluminum-based nanocomposites.

Electrical Transport Mechanisms in Graphene Nanoplatelet Doped Polydimethylsiloxane and Application to Ultrasensitive Temperature Sensors.

The temperature effect on electronic transport mechanisms in graphene nanoplatelet (GNP) doped polydimethylsiloxane (PDMS) for temperature sensing applications has been investigated under electrical impedance spectroscopy (EIS) analysis. AC measurements showed a very prevalent frequency-dependent behavior in low filled nanocomposites due to the lower charge density. In fact, 4 wt % GNP samples showed a nonideal capacitive behavior due to scattering effects. Therefore, the standard RC-LRC circuit varies with the substitution of capacitive elements by CPEs, where a CPE is a constant phase element which denotes energy dissipation. In this regard, the temperature promotes a prevalence of scattering effects, with an increase of resistance and inductance and a decrease of capacitance values in both RC (intrinsic and contact mechanisms) and LRC (tunneling mechanisms) elements and, even, a change from ideal to nonideal capacitive behavior as in the case of 6 wt % GNP samples. In this way, a deeper understanding of electronic mechanisms depending on GNP content and temperature is achieved in a very intuitive way. Finally, a proof-of-concept carried out as temperature sensors showed a huge sensitivity (from 0.05 to 11.7 °C-1) in comparison to most of the consulted studies (below 0.01 °C-1), proving, thus, excellent capabilities never seen before for this type of application.

Mechanical properties of binderless tungsten carbide enhanced via the addition of ZrO2-20 wt% Al2O3 composite powder and graphene nanosheets

As an alternative to conventional tungsten carbide materials, binerless tungsten carbide (BTC) can be used in a variety of applications, such as high-speed cutting tools, rock drilling and extraction, and wear-resistant components. The absence of the metallic bonding phases solves the problems of oxidative corrosion and softening of the material during high-speed cutting process. However, the fabrication of high strength and toughness BTC ceramics remains a huge challenge. In this paper, ZrO2-20 wt% Al2O3 composite powder and graphene nanoplatelets (GNPs) were used as the reinforced phases to fabricate high performance BTC ceramics. The influence of GNPs contents on the densification, microstructure and mechanical properties of oscillatory pressure sintered BTC ceramics with 8 wt% composite powder was evaluated. The synergistic effect of ZrO2-20 wt% Al2O3 composite powder and GNPs exerted a critical role on the densification process and microstructural evolution. The produced BTC ceramics had the densest microstructure and optimal mechanical characteristics when the GNPs content reached up to 0.2 wt%; the flexural strength, Vickers hardness, fracture toughness and relative density were up to 1480 MPa, 23.72 GPa, 8.68 MPa·m1/2 and 99.8%, respectively.

The Effect of Graphene Nanoplatelets Content on the Hardness of Mg6%Zn0.2%Mn Composites

The effect of graphene nanoplatelets (GNPs) content on the hardness of magnesium-based composites was studied. A magnesium-based composite, Mg6%Zn0.2%Mn with graphene nanoplatelets (GNPs), was fabricated via powder metallurgy process at room temperature and compressive pressures of 50kN for 20 minutes, which was then sintered at 500°C for 2 hours. It produced significant grain refinement microstructure. The change in microstructure was examined by 3D microscope analysis, and the hardness value was evaluated using the Vickers microhardness apparatus. This study demonstrated the importance of GNPs reinforcement with zinc and manganese for microhardness analysis in the sintered Mg-based GNPs composites. It also portrayed their influence on grain refinement of the microstructure. The hardness results agreed with the microstructure results, proving that the presence of GNPs increases the hardness of the Mg-based composites.

Synthesis, stability, and heat transfer behavior of water and graphene nanoplatelet-based nanofluid for cool thermal storage applications

This study aims to synthesize stable nano-enhanced phase change materials (NEPCM) using deionized (DI) water and graphene nanoplatelets (GNPs) with the aid of three different surfactants (CTAB, SDBS, and GA). The study also investigates the dynamic behavior of the NEPCM during solidification and melting in a spherical encapsulation. GA-GNP dispersion showed prolonged stability based on zeta potential distribution (ZP) and UV–vis absorbance after 60 days of preparation. The effect of GNP concentration (0.25, 0.50, 0.75, and 1.00 wt%) on the heat transfer properties of the NEPCM was investigated using differential scanning calorimetry (DSC), temperature-time (T-t) profiles, and TC measurements. The maximum energy storage density decreased by 8.56 % and 15.3 % for 1.00 wt% GNPs added to DI-water during melting and crystallization, respectively, at a heating rate of 5 K/min. The thermal conductivity (TC) increased by 59.1 % and 10.8 % in the solid and fluid circumstances, correspondingly. Transient temperature results showed that GA significantly reduced super cooling (SC) by 47.6 % and eliminated it completely at a concentration of 1.00 wt% GNP-NEPCM. The maximum reduction in solidification rate was 26.4 % with 1.00 wt% GNP-NEPCM at a −7 °C constant heat transfer fluid (HTF) temperature. The melting duration was reduced by 33 % by adding 0.50 wt% GNPs, while the melting duration was prolonged at a concentration of 1.00 wt% due to the viscosity augmentation of molten layers. In conclusion, the proposed stable NEPCM formulation has great potential for use as an energy-efficient storage medium in the CTES system.

Microstructures and mechanical properties of Al nanocomposites hybrid-reinforced with B4C, carbon nanotubes and graphene nanoplatelets

To improve the mechanical properties of Al-30%B4C composites, modified carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) were added. The Al/B4C composites with different content of CNTs and GNPs were fabricated via ball milling and hot press. The B4C particles were homogeneously distributed, and the B4C/Al interface was tightly bonded due to AlB2 and Al3BC. With increase of CNTs content, the composites strength increased. The compressive strength of the Al-30%B4C-0.75%CNT-0.25%GNP composite was enhanced by 46% compared with that of the Al-30%B4C composite. The interface bonding and strengthening mechanisms of CNT-GNP hybrid were studied in detail. The reinforcements mainly reinforced the nanocomposites by Orowan, dislocation, grain refinement strengthening and load transfer. After calculation, CNT-GNP hybrid has lower contribution in thermal mismatch and Orowan strengthening due to the larger size. The load transfer efficiency of the CNT-GNP hybrid was significantly higher than that of the CNTs and GNPs, as the optimised interface structure and interconnected structure of the hybrids contributed to its high strength.

Sustainable Microfabrication Enhancement of Graphene Nanoplatelet-Reinforced Biomedical Alumina Ceramic Matrix Nanocomposites

Studies about adding graphene reinforcement to improve the microfabrication performance of alumina (Al2O3) ceramic materials are still too rare and incomplete to satisfy sustainable manufacturing requirements. Therefore, this study aims to develop a detailed understanding of the effect of graphene reinforcement to enhance the laser micromachining performance of Al2O3-based nanocomposites. To achieve this, high-density Al2O3 nanocomposite specimens were fabricated with 0 wt.%, 0.5 wt.%, 1 wt.%, 1.5 wt.%, and 2.5 wt.% graphene nanoplatelets (GNPs) using a high-frequency induction heating process. The specimens were subjected to laser micromachining. Afterward, the effects of the GNP contents on the ablation depth/width, surface morphology, surface roughness, and material removal rate were studied. The results indicate that the micro-fabrication performance of the nanocomposites was significantly affected by the GNP content. All nanocomposites exhibited improvement in the ablation depth and material removal rate compared to the base Al2O3 (0 wt.% GNP). For instance, at a higher scanning speed, the ablation depth was increased by a factor of 10 times for the GNP-reinforced specimens compared to the base Al2O3 nanocomposites. In addition, the MRRs were increased by 2134%, 2391%, 2915%, and 2427% for the 0.5 wt.%, 1 wt.%, 1.5 wt.%, and 2.5 wt.% GNP/Al2O3 nanocomposites, respectively, compared to the base Al2O3 specimens. Likewise, the surface roughness and surface morphology were considerably improved for all GNP/Al2O3 nanocomposite specimens compared to the base Al2O3. This is because the GNP reinforcement reduced the ablation threshold and increased the material removal efficiency by increasing the optical absorbance and thermal conductivity and reducing the grain size of the Al2O3 nanocomposites. Among the GNP/Al2O3 nanocomposites, the 0.5 wt.% and 1 wt.% GNP specimens showed superior performance with minimum defects in most laser micromachining conditions. Overall, the results show that the GNP-reinforced Al2O3 nanocomposites can be machined with high quality and a high production rate using a basic fiber laser system (20 Watts) with very low power consumption. This study shows huge potential for adding graphene to alumina ceramic-based materials to improve their machinability.

Modelling the anisotropic thermal conductivity of 3D logpile structures

Assessing and predicting the thermal conductivity (κ) of macroporous materials is particularly important for additive manufactured 3D structures, as they offer considerable potential for tuning architectures and properties. In this work, finite element methods (FEM) are used to simulate the transient plane source test in 3D logpile lattices, approaching the effect of interfacial thermal contact resistances on κ measurement. Besides, the influence of different geometrical parameters (rod diameter, macropore size and overlapping between rods in consecutive layers) and the κ of the strut material on the anisotropic thermal conductivity of 3D lattices are investigated. The models are validated using experimental data for 3D composite structures of γ-Al2O3 with graphene nanoplatelet contents up to 18 vol%, as well as with reported data for alike scaffolds, all printed by robocasting. Results have strong impact for the application of novel 3D structures in energy production and storage, catalysis and heat transfer-related fields.

Vibration damping properties of graphene nanoplatelets filled glass/carbon fiber hybrid composites

Abstract The present study investigates the effect of carbon fiber hybridization and graphene nanoplatelets inclusion on the vibration damping properties of glass fiber reinforced polymer composites. The hand layup method was utilized with hot press molding in hybrid/non-hybrid composite plate production. A total of sixteen laminates, eight containing pure glass/epoxy and pure carbon/epoxy, and the remainder containing glass/carbon, were stacked in four different arrays and impregnated with an epoxy matrix to provide a hybrid/non-hybrid configuration. In the first hybrid configuration, the glass fiber fabric is on the outer surface and the carbon fiber fabric is on the inside of the composite plate; in the second configuration, the opposite of this sequence was used. Graphene Nanoplatelets (GNPs) were added into the epoxy resin in different weight fractions (0, 0.1, 0.25, and 0.5 wt%). Experimental modal analysis was performed to evaluate the natural frequency and damping ratios of the GNPs modified/unmodified test samples. According to the results obtained, carbon fiber hybridization not only increased the natural frequency but also caused a decrease in the damping ratio of the glass fiber reinforced composite material. On the other hand, incorporating 0.5% by weight of GNPs into the epoxy matrix improved damping ratios by approximately 42.1, 51.6, 16.7 and 17.2% for the G05, GC05, CG05 and C05 samples, respectively, compared to the pure samples. Also, a decrease in natural frequency and loss storage values were observed at high GNPs content.

Graphene nanoplatelets composite resin curing and thermal diffusivity determination by photothermal techniques

In this work, the thermal diffusivity for graphene nanoplatelets (GNPs) incorporated into an acrylic resin with concentrations between 0.02 and 0.12 wt% were measured using the thermal wave resonant cavity (TWRC). An increased in this thermal parameter with increasing the concentration of the GNPs was observed. Moreover, the effect of the GNPs concentration on the curing time of resin nanocomposites was measured using the photoacoustic (PA) technique. The results showed that for higher GNPs concentrations, the curing time was higher for a fixed laser power. Samples were characterized by UV–Vis, TEM and FTIR techniques. On the other hand, the Shore hardness was measured for the cured resins, observing a hardness increase with GNPs concentration. The development of synthesis of new nanocomposites for curing (as 3D printing resins) will provide a better understanding of the physicochemical, thermal and mechanical properties of large-scale composite structures for applications in areas of medicine for implants and scaffolds.

Spray-coating of graphene nanoplatelets on sisal fibers and its influence on electromechanical behavior of biocomposite laminates

Spray coating and vacuum-assisted resin infusion processes were implemented in this work to develop multifunctional biocomposite laminates. The biocomposites were fabricated using a bio-based epoxy resin reinforced with natural sisal fibers coated with graphene nanoplatelets (GNPs). A systematic characterization of material properties was performed to evaluate the mechanical, thermomechanical, electrical, and piezoresistive behavior of biocomposites with different GNPs contents (0, 1, 4, 6, and 8 wt.%). The mechanical tests revealed that adding GNPs to biocomposites has a slight positive effect on their flexural properties compared to the neat biocomposites (without GNPs). The electrical and thermomechanical tests showed that the electrical conductivity and glass transition temperature of biocomposites containing GNPs were enhanced significantly, achieving average values of 5.19 x 10-4 S/m and 63.29°C (26%), respectively. Regarding electromechanical tests, the biocomposites with 8 wt.% GNPs exhibited an excellent piezoresistive behavior under monotonic loading conditions, achieving a gage factor (strain sensitivity) of 3.56. Bending tests with cyclic loading were also performed, and cyclic reproducibility of the piezoresistive response of the biocomposites after 10 cycles was demonstrated, evidencing that the incorporation of GNPs onto sisal fibers by spray-coating produces an effective formation of conductive networks into biocomposites suitable for sensing applications.

Enhancement of Bonding and Mechanical Performance of Epoxy Asphalt Bond Coats with Graphene Nanoplatelets.

Improving bonding and mechanical strengths is important for the application of bond coats used in the construction of steel deck bridges. Graphene nanoplatelets (GNPs) are attractive nanofillers for polymer modification because of their low cost, ultra-high aspect ratio, and extraordinary thermal and mechanical performance. In this paper, GNPs were used to reinforce the epoxy asphalt bond coat (EABC). The morphology, viscosity-time behavior, contact angle, dynamic mechanical properties, and mechanical and bonding strengths of GNP-reinforced EABCs were investigated using laser confocal microscopy, a Brookfield rotational viscometer, a contact angle meter, dynamic mechanical analysis, a universal test machine, and single-lap shear and pull-off adhesion tests. GNP dispersed non-uniformly in the asphalt phase of EABC. The viscosity of the neat EABC was lowered with the inclusion of GNPs and thus the allowable construction time was extended. The existence of GNPs enhances the hydrophobicity of the neat EABC. When adding more than 0.2% GNP, the storage modulus, crosslinking density and glass transition temperatures of both asphalt and epoxy of the neat EABC increased. The mechanical and bonding properties of the neat EABC were greatly enhanced with the incorporation of GNPs. Furthermore, the mechanical and bonding strengths of the modified EABCs increased with the GNP content. GNP-reinforced EABCs can be utilized in the pavement of long-span steel bridges with long durability.

Microcracking monitoring and damage detection of graphene nanoplatelets-cement composites based on acoustic emission technology

This study aims to identify the micro-cracking pattern and structural applications of cement composites replaced with 0 wt%, 0.04 wt%, and 0.08 wt% contents of graphene nanoplatelets (GNPs) over cement weight through acoustic emission (AE) monitoring under mechanical degradation. The ultraviolet-visible spectroscopy (UV–vis) results showed that at 60 min sonication period, GNP-4 showed maximum absorbance rate of 16.15% compared to the GNP-8. The microstructural characteristics revealed that during hydration of cement there was no apparent cracks appeared in GNPs-cement composites compared to the reference specimen (GNP-0) which was 1.44 mm. The cracking mode and damaged detection of the tested specimens resulted in three distinct stages i.e., (I) pre-peak, (II) peak, and (III) post-peak under mechanical degradation. GNP-4 achieved 780 N flexural capacity which was increased by 30% and 21.87% compared to the GNP-0 and GNP-8. Similarly, a compressive strength of 63.12 MPa, 57.5 MPa, and 56 MPa at 28 days was obtained by GNP-4, GNP-8, and GNP-0, respectively. Based on AE hits and amplitude analysis, the resistance to fracture, damping capacity, and ductility of GNP-4 was improved by 25.30%, 25.1%, and 22.47% respectively, to that of GNP-0. Shear failure (>35 kHz) was observed in GNP-0, while GNPs cement composites recorded tensile failure (<35 kHz) through RA-AF parameters. The cracking pattern through Ib value with a warning sign of 1.5 between micro and macro-cracks and severity of damages through historical index (HI) and severity index (Sr) of GNPs cement composites was determined. Lastly, it was concluded that GNPs contents can significantly improve bending strength and delay the cracks initiation in cement composites.

Study of the electroplating process parameters on the electrical resistance of an aluminium alloy with a Cu-graphene-based coating

ABSTRACT This study investigates the effects of the electroplating process parameters, such as temperature, graphene concentration in the bath and current density, on the electrical properties of a copper-coated aluminium alloy (AA6082). Based on previous experiences, a full factorial plan was developed and tested through the Design of Experiments (DOE) methodology to find a relation between parameters and properties. After validating the setup and the significance of the three input process parameters, a statistical model for copper electrodeposition is presented; the latter takes into account the physical interaction of the graphene nanoplatelets (GNP). From the results, the GNP amount is able to modify the electrical resistance of the copper coating; in detail, the resistance passes from 0.0319 to 0.02 mΩ, allowing a reduction of about 35% at the highest GNP content. Furthermore, an optimization following the new experimental model to decrease the electrical resistance of the graphene-based coating is presented.

Graphene nanoplatelets (GNPs): a source to bring change in the properties of Co-Ni-Gd-ferrite/GNP nanocomposites.

The nanocomposites of Co0.5Ni0.5Gd0.03Fe1.97O4/graphene nanoplatelets (CNGF/GNPs) were synthesized by a cost-effective sol-gel auto combustion (SGAC) route. The X-ray diffraction analysis confirmed the cubic structure of the as-prepared nanocomposites, and a crystallite size of 32.28 nm was observed for the 7.5 wt% GNPs. Irregular and unique nanoparticles consisting of short stacks of graphene sheets having a platelet shape were confirmed by the morphological analysis of the as-prepared nanocomposites. Raman analysis revealed a spinel crystal structure along with a new vibrational mode due to the GNPs. The energy bandgap was 3.98 eV for the composite with 7.5 wt% GNP concentration. It was observed that the percentage temperature coefficient of resistance (TCR%) rapidly decreased with an increase in temperature both in low- and high-temperature ranges. Dielectric studies carried out in the frequency range 104-107 Hz confirmed that the graphene-added composites had high values for both the real and imaginary parts of permittivity at low frequencies. A decrease in saturation magnetization with an increase in GNP concentration was observed compared with the pure CNGF samples. Hence, the as-prepared composites are useful for application in high-frequency devices as well as spintronics.

Calculation of the degree of crystallinity of HDPE/GNPs nanocomposites by using various experimental techniques: a comparative study

This work is a comparative study of four different techniques to determine the crystallinity of high-density polyethylene (HDPE) nanocomposites filled with different diameter sizes (5, 15 and 25 μm) of graphene nanoplatelets (GNPs) at various amounts (0.5–5 wt%). The structure of HDPE/GNPs nanocomposites was extensively studied by using different experimental methods, such as X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. To further provide a complete comparison, differential scanning calorimetry measurements were utilized to calculate the crystallinity values, while temperature-modulated DSC was employed to investigate the possible mechanism of the different crystalline structures. It was found that these methods can be used to estimate the crystallinity, but the sample parameters and experimental conditions must be taken into consideration. All the techniques showed that the crystallinity depends on GNPs size and content. The distance between dispersed platelets was substantial at low concentrations of GNPs, making it comparatively easy for additional nucleation sites to incorporate the polymer matrix, and the crystal nucleus was simply formed. However, at high concentrations of GNPs, the diffusion of polymer chains to the growing crystallites was hindered by large GNPs particles, despite the formation of additional nucleation sites.

Investigation of Dielectric, Magnetic and Electrical Behavior of BFO/GNPs Nano-Composites Synthesized via Sol-Gel Method

Nano composites of Ba0.5Bi0.5Nd0.05Fe0.95O3 multiferroic with graphene nano platelets (GNPs)x (x = 0, 0.125 %, 0.375 %, and 0.5 %) were synthesized using sol-gel auto ignition process. XRD analysis revealed a single rhombohedrally distorted phase of Ba0.5Bi0.5Nd0.05Fe0.95O3. The present study unfold the impact of GNPs on the structural, electrical, dielectric, and magnetic properties of Ba0.5Bi0.5Nd0.05Fe0.95O3 multiferroics. The substitution of Rare earth elements in pure BFO reduced the value of leakage current which is the basic drawback related with pure BFO. The prepared nanocomposites are then sintered at 800 °C for 7 hrs. The X-ray diffraction patterns showed the rhombohedral distorted perovskite crystal structure of the prepared samples including lattice constant, crystallite size, and X-ray density. The average crystallite sizes of the prepared nanocomposites are noticed in the range 28.14 -to 29.74 nm with increasing the GNPs concentration and lattice constant is found in the range 11.59 -to 11.61 Å. Temperature-dependent resistivity is first observed to increase with an increase in temperature then resistivity decreased with increasing the temperature which indicates a semi-conductor-like behavior as measured by two probe I-V characteristics. LCR technique showed that both the dielectric constant and the dissipation factor are decreased with an increase in frequency. VSM results indicated that saturation magnetization is noted to increase while remanent magnetization decreases with increasing concentration of GNPs.

Influence of Graphene Nanoplatelets on the Performance of Axial Suspension Plasma-Sprayed Hydroxyapatite Coatings.

Axial suspension plasma spraying (ASPS) is an alternative technique to atmospheric plasma spraying (APS), which uses a suspension of much finer powders (&lt;5-micron particle size) as the feedstock. It can produce more refined microstructures than APS for biomedical implants. This paper highlights the influence of incorporated graphene nanoplatelets (GNPs) on the behavior of ASPS hydroxyapatite (HAp) coatings. The characterization of the ASPS coatings (HAp + varying GNP contents) was carried out using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), confocal Raman microscopy (CRM), white light interferometry (WLI), and contact angle measurements. The evaluation of the mechanical properties such as the hardness, roughness, adhesion strength, and porosity was carried out, along with a fretting wear performance. Additionally, the biocompatibility of the Hap + GNP coatings was evaluated using cytotoxicity testing which revealed a decrease in the cell viability from 92.7% to 85.4%, with an increase in the GNP wt.%. The visualization of the cell's components was carried out using SEM and Laser Scanning Microscopy. Furthermore, the changes in the genetic expression of the various cellular markers were assessed to analyze the epigenetic changes in human mesenchymal stem cells. The gene expression changes suggested that GNPs upregulated the proliferation marker and downregulated the pluripotent markers by a minimum of three folds.

Effective Attenuation of Electromagnetic Waves by Synergetic Effect of α-Fe2O3 and MWCNT/Graphene in LDPE-Based Composites for EMI Applications.

In this study, a polymer nanocomposite is synthesized using magnetic and conducting fillers for enhanced electromagnetic interference (EMI) shielding. Alfa-ferrite (α-Fe2O3) nanoparticles with minimal multiwalled carbon nanotube (MWCNT) as low as 5 weight % in combination with variable concentrations of graphene nanoplatelets (GNP) are used as fillers in low-density polyethylene (LDPE) polymer matrix. Nanofillers and the polymer matrix are characterized by various techniques such as XRD, SEM, color mapping, EDAX, TGA, etc. The EMI shielding efficiency of the LDPE-based nanocomposites is tested using Vector Network Analyzer (VNA). The results showed that composite with LDPE:MWCNT:GNP:α-FO-50:5:40:5 displayed enhanced EMI shielding (in X-band (8.2-12.4 GHz) compared to other concentrations studied. This is due to the superior ohmic, dielectric, and magnetic losses at this particular composition and to the synergism amongst the filler. An attenuation of 99.99% was achieved for 5% α-Fe2O3. The mechanistic aspects of the shielding are discussed using permittivity, conductivity, and attenuation.

Electrical, Thermo-Electrical, and Electromagnetic Behaviour of Epoxy Composites Reinforced with Graphene Nanoplatelets with Different Average Surface Area.

The influence of the average surface area of different graphene nanoplatelets (GNP) on the thermo-electrical behaviour, associated with Joule heating, and the attenuation of electromagnetic signals of epoxy composites has been studied, analysing the effect of the morphology obtained as a function of the dispersion time by ultrasonication and the GNP content added. Gravity moulding was used as the first stage in the scaling-up, oriented to the industrial manufacture of multilayer coatings, observing a preferential self-orientation of nanoparticles and, in several conditions, a self-stratification too. The increase of sonication time during the GNP dispersion provides a decrease in the electrical conductivity, due to the GNP fragmentation. Instead, the thermal conductivity is enhanced due to the higher homogeneous distribution of GNPs into the epoxy matrix. Finally, the lower surface area of GNPs reduces the thermal and electrical conductivity due to a greater separation between nanosheets. Regarding the study of the attenuation of electromagnetic waves, it has been discovered that in the frequency range from 100 Hz to 20 MHz, this attenuation is independent of the direction of analysis, the type of graphene, the sonication time, and the state of dispersion of the nano-reinforcement in the matrix. Furthermore, it has also been observed that the conservation of the constant shielding values for the three types of GNPs are in a range of average frequencies between 0.3 and 3 MHz.