Surfactant-decorated graphite nanoplatelets(GNPs) reinforced aluminum nanocomposites: sintering effects on hardness and wear

The exceptional properties of graphene make it ideal as a reinforcement to enhance the properties of aluminum matrices and this critically depends on uniform dispersion. In this study, the dispersion issue was addressed by sonication and non-covalent surface functionalization of graphite nanoplatelets（GNPs） using two types of surfactant： anionic（sodium dodecyl benzene sulfate（SDBS）） and non-ionic polymeric（ethyl cellulose（EC））. After colloidal mixing with Al powder, consolidation was performed at two sintering temperatures（550 and 620°C）. The structure, density, mechanical and wear properties of the nanocomposite samples were investigated and compared with a pure Al and a pure GNPs/Al nanocomposite sample. Noticeably, EC-based 0.5 wt% GNPs/Al samples showed the highest increment of 31% increase in hardness with reduced wear rate of 98.25% at 620°C, while a 22% increase in hardness with reduced wear rate of 96.98% at 550°C was observed, as compared to pure Al. Microstructural analysis and the overall results validate the use of EC-based GNPs/Al nanocomposites as they performed better than pure Al and pure GNPs/Al nanocomposite at both sintering temperatures.

Development of Cu-Exfoliated Graphite Nanoplatelets (xGnP) Metal Matrix Composite by Powder Metallurgy Route

In the present investigation the possibility of using exfoliated graphite nanoplatelets (xGnP) as reinforcement in order to enhance the mechanical properties of Cu-based metal matrix composites is explored. Cu-based metal matrix composites reinforced with different amounts of xGnP were fabricated by powder metallurgy route. The microstructure, sliding wear behaviour and mechanical properties of the Cu-xGnP composites were investigated. xGnP has been synthesized from the graphite intercalation compounds (GIC) through rapid evaporation of the intercalant at an elevated temperature. The thermally exfoliated graphite was later sonicated for a period of 5 h in acetone in order to achieve further exfoliation. The xGnP synthesized was characterized using SEM, HRTEM, X-ray diffraction, Raman spectroscopy and Fourier transform infrared spectroscopy. The Cu and xGnP powder mixtures were consolidated under a load of 565 MPa followed by sintering at 850°C for 2 h in inert atmosphere. Cu-1, 2, 3 and 5 wt% xGnP composites were developed. Results of the wear test show that there is a significant improvement in the wear resistance of the composites up to addition of 2 wt% of xGnP. Hardness, tensile strength and strain at failure of the various Cu-xGnP composites also show improvement upto the addition of 2 wt% xGnP beyond which there is a decrease in these properties. The density of the composites decreases with the addition of higher wt% of xGnP although addition of higher wt% of xGnP leads to higher sinterability and densification of the composites, resulting in higher relative density values. The nature of fracture in the pure Cu as well as the various Cu-xGnP composites was found to be ductile. Nanoplatelets of graphite were found firmly embedded in the Cu matrix in case of Cu-xGnP composites containing low wt% of xGnP.

GNPs改性环氧3D编织复合材料导热特性研究

石墨烯纳米片(Graphene nanoplatelets,GNPs)改性3D编织复合材料将GNPs与编织物有机融合,有望协同提高材料导热特性。然而,3D编织复合材料内胞和表胞呈现出不同的导热特性,加之GNPs的协同改性作用,增加了材料导热特性研究难度。本文紧扣GNPs改性3D编织复合材料细观结构特征,以GNPs改性树脂等效热导率表征为基础,基于周期性温度边界条件,构建材料的多胞有限元热物理分析模型,详尽研究了GNPs含量、编织角和纤维体积分数等对各胞元热导率的影响规律。分析表明:随着GNPs含量增加,3D编织复合材料导热特性逐步提升。随着编织角增加,GNPs改性3D编织复合材料横向热导率迅速增加而纵向热导率下降;同时,GNPs改性3D编织复合材料热导率随纤维体积分数增加而提升。上述规律为GNPs改性3D编织复合材料导热性能设计提供了坚实的理论基础。

Curing Kinetics, Mechanical Properties and Thermal Stability of Epoxy/Graphene Nanoplatelets(GNPs) Powder Coatings

Epoxy/graphene nanoplatelets（GNPs） powder coatings were fabricated using ultrasonic predispersion of GNPs and melt-blend extrusion method. The isothermal curing kinetics of epoxy/GNPs powder coating were monitored by means of real-time Fourier transform infrared spectroscopy（FT-IR） with a heating cell. The mechanical properties of the epoxy/GNPs cured coatings had been investigated, by evaluating their fracture surfaces with field-emission scanning electron microscopy（FE-SEM） after three-point-bending tests. The thermal stability of the epoxy/GNPs cured coatings was studied by thermo-gravimetric analysis（TGA）. The isothermal curing kinetics result showed that the GNPs would not affect the autocatalytic reaction mechanism, but the loading of GNPs below 1.0 wt % additive played a prompting role in the curing of the epoxy/GNPs powder coatings. The fracture strain, fracture toughness and impact resistance of the epoxy/GNPs cured coatings increased dramatically at low levels of GNPs loading（1 wt %）, indicating that the GNPs could improve the toughness of the epoxy/GNPs powder coatings. Furthermore, from FE-SEM studies of the fracture surfaces, the possible toughening mechanisms of the epoxy/GNPs cured coatings were proposed. TGA result showed that the incorporation of GNPs improved the thermal stability of the cured coatings. Hence, the GNPs modified epoxy can be an efficient approach to toughen epoxy powder coating along with improving their thermal stability.

Graphite Nanoplatelets Composite Materials: Role of the Epoxy-System in the Thermal Conductivity

Polymers typically have intrinsic thermal conductivity much lower than other materials. Enhancement of this property may be obtained by the addition of conductive fillers. In this research, epoxy nanocomposites with exfoliated graphite nanoplatelets are prepared and characterized. The chosen approach requires no surface treatment and no sophisticated equipments allowing one to produce composites on a pilot scale. A significant increase of the thermal conductivity with the increasing of the graphite fillers content is nevertheless observed on 4 mm thick specimens. Our results viewed in the latest scientific findings suggest that the choice of resin is an important parameter to move towards composite materials with high thermal conductivity.

Scalable preparation of functionalized graphite nanoplatelets via magnetic grinding as lubricity-enhanced additive

Graphite nanoplatelets were prepared by a novel magnetic-grinding method using self-made equipments. Under a variant magnetic field, magnetic needles collided at a high rotating speed and exfoliated pristine graphite into graphite nanoplatelets with high efficiency. The obtained graphite nanoplatelets are highly crystalline, and the thickness is less than 10 nm. Moreover, the surface area could reached 738.1 m^2/g with a grinding time of 4 h. Silanized graphite nanoplatelets can disperse well in SG 15W-40 engine oil and serve as lubricant additive. Tribological results indicate that the friction coefficient and wear-scar of the friction pairs are lower than 76% and 41%, respectively, by adding 1.5‰(mass fraction) of silanized graphite nanoplatelets. Notably, the functionalized graphite nanoplatelets can realize large-scale production and commercial application.

Characterization of Nanocomposite Membrane Based Bacterial Cellulose Made of Pineapple Waste Reinforced by Graphite Nanoplatelets

Waste is the main problem for the environment.Handling waste for various useful applications has a benefit for the future.This work has been studied for handling pineapple peel waste to make composite film bacterial cellulose nanocomposite membrane(BCNM)with addition graphite nanoplatelet(GNP).The concentration of GNP in the membrane influence the membrane properties.The bacterial cellulose(BC)pellicle was synthesized by using media from pineapple peel waste extract.BC pellicle is cleaned with water and NaOH solution to be free from impactors.BCNM is synthesized through the mechanical disintegration stage.The results of disintegration using high pressure homogenizer at 150 bar and five cycles.BCNM/GNP is synthesized with varying addition of GNP of 2.5,5.0,10 and 100 wt%of dry bacterial nanocellulose(BNC).The BC and GNP solution were dried in an oven for 14 h at 80℃.BCNM morphology was observed using SEM.GNP is dispersed and distributed in the BC matrix as reinforcement.FTIR analysis shows many peaks of BNC less pronounced with increasing of GNP.The higher concentration of GNP,the rougher of BCNM.The optimum tensile strength of BCNM was achieved after addition GNP of 2.5 wt%.

High-Density Polyethylene Based on Exfoliated Graphite Nanoplatelets/Nano-Magnesium Oxide: An Investigation of Thermal Properties and Morphology

In this study, high-density polyethylene (HDPE)/exfoliated graphite nanoplatelet (xGnP) composites reinforced with a 2 wt.% concentration of nano-magnesia (n-MgO) were fabricated using an injection moulding machine. The thermal properties and morphological structures of the composites were investigated. The XRD results showed the peaks of xGnP and n-MgO, where the intensity of the xGnP peaks became stronger with adding increasing amounts of xGnP into the polymermatrix. In terms of morphology, some agglomeration of particles was observed within the matrix, and the agglomeration decreased the thermal properties of the composites. The nanocomposites showed less thermal stability than the pristine polymer. The reduction in the onset temperature compared to that of neat HDPE was attributed to less adhesion between the fillers and the matrix. In addition, the crystallinity was reduced by the addition of fillers.

Effective thermal and electrical conductivity of graphite nanoplatelet composites

The relationship between the thermal/electrical conductivity enhancement in graphite nanoplatelets （GNPs） composites and the properties of filling graphite nanoplatelets is studied. The effective thermal and electrical conductivity enhancements of GNP-oil nanofluids and GNP-polyimide composites are measured. By taking into account the particle shape, the volume fraction, the thermal conductivity of filling particles and the base fluids, the thermal and electrical conductivity enhancements of GNP nanofluids are theoretically predicted by the generalized effective medium theory. Both the nonlinear dependence of effective thermal conductivity on the GNP volume fraction in nanofhiids and the very low percolation threshold for GNP-polyimide composites are well predicted. The theoretical predications are found to be in reasonably good agreement with the experimental data. The generalized effective medium theory can be used for predicting the thermal and electrical properties of GNP composites and it is still available for most of the thermal/electrical modifications in two-phase composites.

Fabrication of graphene nanoplatelets reinforced Mg matrix composites via powder thixoforging

A powder thixoforging route combined with slurry based mixing process was proposed to fabricate graphene nanoplatelets(GNPs) reinforced magnesium matrix composites(MgMCs). The originally spherical and ball-milled ZK60 powders were used as matrices, respectively.The mixing of 0.05 wt.% GNPs with the spherical powder led to GNPs clusters and degraded the mechanical properties of the composite.In contrast, with the addition of an optimal content(0.1 wt.%) of GNPs, the composite fabricated from ball-milled powder achieved a joint enhancement in tensile yield strength(52%) and fracture toughness(19%), demonstrating a pronounced strengthening efficiency of 650% and a good balance between strength and toughness. The ball-milled powder endowed the composite with a homogenous distribution of GNPs and a denser microstructure with reduced Mg-Zn eutectics, and the thixoforging process offered a well-bonded Mg/GNP interface, making full use of the strengthening and toughening potential of GNPs. Theoretical predication based on a modified shear-lag model suggested that load transfer dominated the strengthening mechanisms. In-situ tensile tests verified that crack deflection, secondary cracks and GNPs bridging mainly accounted for the toughening mechanisms. A numerical model with consideration of GNPs orientations was also established to understand the toughening effect from GNPs bridging.

PP/POE/GNP导电复合材料的制备与性能研究

用油酸钠/乙醇溶液、邻二氯苯、N-甲基吡咯烷酮对膨胀石墨进行表面处理和分散改性并制备了纳米石墨微片(GNP),研究了其效果,确定了油酸钠/乙醇溶液作为分散介质和表面改性剂。将由该处理剂制得的GNP以不同添加量添加到聚丙烯/聚烯烃弹性体共混树脂(PP/POE)中,制得PP/POE/GNP复合材料。测试表明,GNP在基体中分散均匀,大部分达到纳米尺寸,与基体结合良好,复合材料的室温渗滤阈值为9%左右(对应GNP质量份数为10份),GNP质量份数超过10份之后复合材料成为半导体,最低体积电阻率为3.6×107Ω.cm。当GNP质量份数为20份时,复合材料仍然保持较佳力学性能,材料破坏方式为脆性断裂。

Ameliorating the Strength-Modulus Synergy in GNPs Reinforced Mg-Zn-Zr Composites via Multidirectional Forging and Hot Extrusion Deformation

The integration of lightweight and high-modulus magnesium-based materials is becoming increasingly valued as structural materials due to the complexity and intelligence of industrial products like automobiles and electronics.In this study,the graphene nanoplatelets(GNPs)/Mg-Zn-Zr composites with 0.5 wt%GNPs were successfully prepared by the combination of multidirectional forging(MDF)and hot extrusion(Ex).The newly-developed composites after multi-step deformation possessed excellent strength and modulus,with a tensile strength exceeding 375 MPa and an elastic modulus reaching 54 GPa.The results revealed that the stripping and thinning of GNPs bands parallel to the extrusion direction occurred after MDF+Ex,which promoted the dynamic recrystallization and the formation of numerous fine grains.The significant improvement in comprehensive mechanical performances of the composites could be primarily ascribed to the refinement of grain size caused by the optimized distribution of GNPs,and efficient load transfer facilitated by the tight interface.

GNP/Al_2O_3填充聚丙烯导热复合材料研究

以聚丙烯(PP)为基体,以石墨纳米片(GNP)和Al_2O_3为主、辅导热填料,通过熔融共混法制备导热复合材料,考察了填料含量和填料复配对复合材料结构和性能的影响。结果表明,随着GNP含量的增加,PP/GNP二元复合材料的导热系数和电导率均不断上升。GNP在PP基体中发生了取向,导致复合材料的面内和面间导热系数产生差异,并且这种差异随GNP含量的提高而增大。在上述复合材料中加入辅助填料Al_2O_3后产生了显著的体积排除效应,使复合材料的导热系数和电导率进一步提升。在固定GNP含量为30%的情况下,当Al_2O_3含量为20%时,复合材料的面间和面内导热系数分别达到1.01 W/(m·K)和3.68 W/(m·K)。增容剂PP-g-MAH的加入改善了基体和填料的界面粘结作用,使复合材料保持了较高的力学性能。

石墨纳米片的原位分散及对聚丙烯力学性能的影响

石墨纳米片(GNP)在聚合物基体中的分散状态和界面相互作用是决定GNP/聚合物复合材料力学性能的关键因素。文中采用与聚丙烯(PP)共球磨剥离石墨得到GNP均匀包覆PP的母粒,进一步与PP熔融共混制备了PP/GNP复合材料。结果表明,与纯石墨和石墨烯相比,GNP与PP基体之间的界面相互作用更强,扫描电镜分析显示GNP分散更均匀,添加0.7%GNP的复合材料经差示扫描量热分析后发现,其结晶温度(Tc)显著提高。PP/GNP复合材料的拉伸强度和冲击强度相对于纯PP分别提升了33.34%和33.47%。该分散方法在开发其他高性能多功能GNP/聚合物复合材料方面具有巨大潜力。

Facile production of ultrathin graphitic carbon nitride nanoplatelets for efficient visible-light water splitting

Ultrathin graphitic carbon nitride nanoplatelets （UGCNPs） are synthesized by a facile manner via an efficient and eco-friendly ball milling approach. The obtained UGCNPs are 2-6 nm in size and 0.35-0.7 nm in thickness, with improved specific surface area over that of bulk graphitic carbon nitride. Photochemical experiments show that the UGCNPs are highly active in visible-light water splitting, with a hydrogen evolution rate of 1,365 μmol·h^-1·g^-1, which is 13.7-fold greater than that of their bulk counterparts. The notable improvement in the hydrogen evolution rate observed with UGCNPs under visible light is due to the synergistic effects derived from the increased specific surface area, reduced thickness, and a negative shift in the conduction band concomitant with the exfoliation of bulk graphitic carbon nitride into UGCNPs. In addition to metal- free visible-light-driven photocatalytic hydrogen production, the UGCNPs find attractive applications in biomedical imaging and optoelectronics because of their superior luminescence characteristics.

Tribological properties of Al-GNP composites at elevated temperature

Lighter and more powerful next generation vehicles and other rotary machinery demand bearings to operate in harsher conditions for higher efficiency,and the continuous development of advanced low-wear and friction materials is thus becoming even more important to meet these requirements.New aluminium composites reinforced with high performance lubricate phases such as graphene nanoplatelets(GNPs)are very promising and have been vigorously investigated.By maintaining a low coefficient of friction(COF)and offering great strength against wear due to their self-lubricating capability,the solid lubricant like GNPs protect the bearing surface from wear damage and prevent change in metallurgical properties during temperature fluctuations.This paper first studies the high-temperature tribological performance of aluminium matrix composites reinforced with GNP,consolidated via powder metallurgy,then elucidates their tribological mechanism.We report that the best tribological performance is achieved by the composite containing 2.0 wt%GNP,with an extraordinarily low COF of 0.09 and a specific wear rate of 3.5×10^(−2)mm^(3)·N^(−1)·m^(−1),which represent 75%and 40%reduction respectively,against the plain aluminium consolidated under identical conditions.The in-track and out-of-track Raman analysis have confirmed the role of GNPs in creating a tribofilm on the counterpart surface which contributed to the excellent performance.

掺纳米石墨烯片的水泥基复合材料的压敏性

研究了掺入少量纳米石墨烯片(GnPs)的水泥基复合材料的力学性能、电学性能和压敏性,结果表明,GnPs的掺入显著提高了水泥砂浆的早龄期抗压强度,但对后期抗压强度的影响不大。GnPs表面积较大,将阻塞离子移动通路,故少量GnPs(体积掺量低于0.15%)对改善水泥砂浆导电性的作用效果不明显。GnPs水泥基复合材料能感知应力、应变,GnPs的掺入提高了其灵敏度和重复性。

石墨烯纳米片的制备和表征

以鳞片石墨为原料,采用氧化插层和微波膨化制备膨胀石墨,对膨胀石墨进行二次酸化膨胀处理,利用超声剥离法制备石墨烯纳米片,并借助XRD、SEM、RAMAN和AFM等分析其微观结构和形貌。结果表明:微波膨化处理可快速高效得到膨胀石墨;通过对膨胀石墨超声剥离可破坏其原有网络结构并将石墨晶片剥离为大量的石墨薄片;对二次膨胀处理的膨胀石墨进行超声剥离可得到石墨烯纳米片,其中包含大量的3-5层石墨烯。

混合填充复合材料热导率方程的推导

混合填充复合材料的导热特性好于单一填充。根据碳纳米管与纳米片状石墨在高分子基材中的分布形态,将碳纳米管与纳米片状石墨的"桥状搭接"结构作为等效基材,未搭接的"游离态"碳纳米管作为填料,利用串并联热阻模型和Maxwell-Garnett等效介质法建立了混合填充复合材料的导热模型,并通过数量级分析对热导率方程进行了简化。结果表明,在混合填料质量分数不变的情况下,等效热导率随纳米片状石墨的增多呈现先增加后减少的趋势,表现出明显的协同效应;在质量分数配比不变的情况下,等效热导率随混合填料的质量分数增大而增大。

碳纳米材料在导热聚合物复合材料中的应用

介绍了三种具有较高热导率的碳纳米材料:碳纳米管、纳米石墨片及纳米碳纤维的结构与导热性能,概述了三种碳纳米材料在改善聚合物复合材料导热性能方面的应用,重点分析了碳纳米材料的种类、用量、表面改性方法及复合材料的制备方法对聚合物复合材料热导率的影响,并对含碳纳米材料的导热聚合物复合材料未来的发展方向进行了分析与展望。