• Journal of the Korean Ceramic Society
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• v.55 no.6
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• pp.556-561
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• 2018

In this study, we performed a microwave sintering (MWS) of $Al_2O_3$ ceramic and $Al_2O_3$-based composites with nominal contents of graphene nanoplatelets (GPLs) of 0.2, 0.4, 0.6, and 0.8 vol%. The GPL dispersion in N-methyl pyrroleketone was optimized to deagglomerate the GPLs without damaging their structure. Dense composites were then obtained by MWS at $1500^{\circ}C$ for 30 min. The effects of different GPL contents on the phase compositions, microstructures, and mechanical properties of the composites were investigated. The microstructures of the composites became finer with the incorporation of the GPLs. The well-dispersed GPL fillers led to higher sintered densities in the composites. The optimal mechanical properties were achieved with 0.4 vol% GPLs. For this sample, the hardness, fracture toughness, and bending strength were $2000kgf/mm^2$, $6.19MPa{\cdot}m^{1/2}$, and 365.10 MPa, respectively. The addition of GPL could improve the microstructure of the $Al_2O_3$ ceramic and has potential to improve the fracture toughness of the ceramics.

• Steel and Composite Structures
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• v.37 no.1
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• pp.27-35
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• 2020

This study examines the wave propagation of the functionally graded polymer composite (FG-PC) nanoplates reinforced with graphene nanoplatelets (GNPs) resting on elastic foundations in the framework of the nonlocal strain gradient theory incorporating both stiffness hardening and softening mechanisms of nanostructures. To this end, the material properties are based on the Halpin-Tsai model, and the expressions for the classical and higher-order stresses and strains are consistently derived employing the second-order shear deformation theory. The equations of motion are then consistently derived using Hamilton's principle of variation. These governing equations are solved with the help of Trial function method. Extensive numerical discussions are conducted for wave propagation of the nanoplates and the influences of different parameters, such as the nonlocal parameter, strain gradient parameter, weight fraction of GNPs, uniform and non-uniform distributions of GNPs, elastic foundation parameters as well as wave number.

• Carbon letters
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• v.11 no.4
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• pp.316-324
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• 2010

The effects of geometrical parameters on mechanical properties of graphite-vinylester nanocomposites and their constituents (matrix, reinforcement and interface) are studied using molecular dynamics (MD) simulations. Young's modulii of 1.3 TPa and 1.16 TPa are obtained for graphene layer and for graphite layers respectively. Interfacial shear strength resulting from the molecular dynamic (MD) simulations for graphene-vinylester is found to be 256 MPa compared to 126 MPa for graphitevinylester. MD simulations prove that exfoliation improves mechanical properties of graphite nanoplatelet vinylester nanocomposites. Also, the effects of bromination on the mechanical properties of vinylester and interfacial strength of the graphene.brominated vinylester nanocomposites are investigated. MD simulation revealed that, although there is minimal effect of bromination on mechanical properties of pure vinylester, bromination tends to enhance interfacial shear strength between graphite-brominated vinylester/graphene-brominated vinylester in a considerable magnitude.

• Advances in nano research
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• v.13 no.3
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• pp.233-245
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• 2022

Resently, the use of smart structures has been heightened up rapidly. For this issue, vibration analysis related to a graphene nanoplatelet composite (GPLRC) nanodisk which is attached to a piezoelectric layer and is subjected to thermal loads is explored in the current paper. The formulation of this study is obtained through the energy method and nonlocal strain gradient theory, and then it is solved employing generalized differential quadrature method (GDQM). Halpin-Tsai model in addition to the mixture's rule are utilized to capture the material properties related to the reinforced composite layer. The compatibility conditions are presented for exhibiting the perfect bounding between two layers. The results of this study are validated by employing the other published articles. The impact of such parameters as external voltage, the radius ratio, temperature difference, and nonlocality on the vibrational frequency of the system is investigated in detail.

• Advances in concrete construction
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• v.15 no.2
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• pp.97-114
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• 2023

The nonlocal strain gradient theory for the static bending analysis of graphene nanoplatelets (GPLs) reinforced the nanoplate is developed in this paper. The nanoplatelet is exposed to thermo-mechanical loads and is also supposed to stand on an elastic foundation. For computing impressive composite material characteristics, the Halpin-Tsai model is selected for various sectors. The various distributions are propounded including UD, FG-O, and FG-X. The represented equations are acquired based on the virtual work and sinusoidal shear and normal deformation theory (SSNDT). Navier's solution as the analytical method is applied to solve these equations. Furthermore, the effects of GPL weight fraction, temperature parameters, distribution pattern and parameters of the foundation are presented and discussed.

• Structural Engineering and Mechanics
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• v.90 no.4
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• pp.403-415
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• 2024

We looked at how the damping qualities of epoxy composites changed when different amounts of graphite nanoplatelets (GNP) were added, from 0% to 6% by weight. A mix of free and forced vibration tests helped us find the key GNP content that makes the damper ability better the most. We also created a Representative Volume Element (RVE) model to guess how the alloys would behave mechanically and checked these models against testing data. An Artificial Neural Network (ANN) was also used to guess how these compounds would react to motion. With proper hyperparameter tweaking, the ANN model showed good correlation (R²=0.98) with actual data, indicating its ability to predict complex material behavior. Combining these methods shows how GNPs impact epoxy composite mechanical properties and how machine learning might improve material design. We show how adding GNPs to epoxy composites may considerably reduce vibration. These materials may be used in industries that value vibration damping.

• Composites Research
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• v.36 no.3
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• pp.167-172
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• 2023

The manufacturing technology of composite material is applicable with filler characteristics maintaining low cost, flexibility, and easy process to develope the various functional composite materials. To realize functional composites, various researches on the high performance of composite materials using graphene as a filler is being actively conducted. In this study, physical and chemical properties were investigated using graphene to improve high functional properties. Graphene oxide (GO) was prepared using graphane nanoplatelet (GNP), and reduced graphene oxide (R-GO) was formed by reducing GO. The physical properties of GO and R-GO were analyzed, and the reliability of the manufactured method was reviewed by comparing that of GNP results. As a result of analysis by Raman spectroscopy, in the case of R-GO, it was confirmed that the intensity of D-peak and G-peak decreased compared to GO, and an increase of 0.08 was observed through the ratio of ID/IG. For the FTIR results, GO and RGO has a repeating C-C and C=C connection structure unlike GNP. GO and R-GO show clear peaks for C-O bond, C=C bond, C=O bond, and O-H bonding. As a result of X-ray diffraction analysis, GNP showed a wide diffraction peak at 25.86° of (002) plane characteristics, whereas GO and R-GO showed peaks corresponding to (001) and (100) planes. It was also found that the interlayer distance of GO increased by about 2.6 times compared to GNP.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.79-79
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• 2012

A high temperature and a low temperature plasma process technologies were developed and demonstrated for synthesis, hybrid formation, surface treatment and CVD engineering of nano powder. RF thermal plasma is used for synthesis of spherical nano particles in a diameter ranged from 10 nm to 100 nm. A variety of nano particules such as Si, Ni, has been synthesized. The diameter of the nano-particles can be controlled by RF plasma power, pressure, gas flow rate and raw material feed rate. A modified RF thermal plasma also produces nano hybrid materials with graphene. Hemispherical nano-materials such as Ag, Ni, Si, SiO2, Al2O3, size ranged from 30 to 100 nm, has been grown on graphene nanoplatelet surface. The coverage ranged from 0.1 to 0.7 has been achieved uniformly over the graphene surface. Low temperature AC plasma is developed for surface modification of nano-powder. In order to have a three dimensional and lengthy plasma treatment, a spiral type of reactor has been developed. A similar plasma reactor has been modfied for nano plasma CVD process. The reactor can be heated with halogen lamp.

• Bulletin of the Korean Chemical Society
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• v.34 no.7
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• pp.2041-2043
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• 2013

A layered perovskite of Dion-Jacobson phase, $RbLaTa_2O_7$, was successfully exfoliated into colloidal suspension via successive ion-exchange and intercalation reaction. The pristine perovskite $RbLaTa_2O_7$ was synthesized by conventional solid-state reaction, and then, it was ion-exchanged with hydrochloric acid to obtain a protonic form of perovskite. The resulting proton-exchanged perovskite was reacted with ethylamine to increase interlayer spaces for further intercalation reaction. Finally, the ethylamine-intercalated form was exfoliated into nanosheets via an intercalation of bulky organic cations (tetrabutylammonium). According to X-ray diffraction (XRD) analysis, the TBA-intercalated form showed remarkably increased interlayer spacing (${\Delta}d$ = 1.67 nm) in comparison with that of the pristine material. Transmission electron microscopic image of exfoliated perovskite clearly revealed that the present exfoliated perovskite were composed of very thin layers. This exfoliated perovskite nanosheets could be applicable as building blocks for fabricating functional nanocomposites.

• Carbon letters
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• v.17 no.1
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• pp.33-38
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• 2016

In the present study, exfoliated graphite nanoplatelets (xGnP) with different particle sizes were coated onto polyacrylonitrile-based carbon fibers by a direct coating method. The flexural properties, interlaminar shear strength, and the morphology of the xGnP-coated carbon fiber/phenolic matrix composites were investigated in terms of their longitudinal flexural strength and modulus, interlaminar shear strength, and by optical and scanning electron microscopic observations. The results were compared with a phenolic matrix composite counterpart prepared without xGnP. The flexural properties and interlaminar shear strength of the xGnP-coated carbon fiber/phenolic matrix composites were found to be higher than those of the uncoated composite. The flexural and interlaminar shear strengths were affected by the particle size of the xGnP, while the particle size had no significant effect on the flexural modulus. It seems that the interfacial contacts between the xGnP-coated carbon fibers and the phenolic matrix play a role in enhancing the flexural strength as well as the interlaminar shear strength of the composites.