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.

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%.

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.

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.

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.

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.

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.

Raman spectra of coal-based graphite

Graphite formed in response to thermal contact metamorphism of coal bodies with magmatic intrusion is referred to as coal-based graphite. The first-order Raman spectrum of all the coal-based graphite taken from the Lutang area, Hunan Province exhibits a single Raman band near 1585cm-1, which comes directly from in-plane vibration of aromatic layer assigned to the E2g mode. Their Raman band of the structural defect in-plane can be divided into 2 types: one is the defect band (D peak) caused by the primary structural delect of the graphite in graphitization process, which is called D2-peak located at 1 360 cm-1; the other is the defect bank caused by the secondary structural defect in the graphite subject to tectonic shearing stress, which is called D1 peak located at 1370cm-1. The second Raman spectrum of the coal-based graphite shows three-dimensional lattice degree in the coal-based graphite. If the three-dimensional lattice of graphite is not well developed, it exhibits only a band of 2700cm-1; if the three-dimensional lattice of the coal-based graphite has been formed, the band of 2700cm-1 is split into two Raman bands, which are respectively located near 2681 cm-1 and near 2726cm-1, Raman band intensity ratio increases synchronously as the ordering degree of three-dimensional lattice increases regularly.

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.

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。

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。

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。

聚乙烯醇/纳米石墨微片复合膜的制备与性能研究

以聚乙烯醇(PVA)和石墨为原料,先以水为介质通过超声剥离膨胀石墨制备了纳米石墨微片(GNP)悬浮液,再直接加入到PVA中经溶液共混后流延成膜,制备了PVA/GNP复合膜;借助扫描电子显微镜、电阻测量仪和万能材料试验机等对复合膜进行了表征,研究了GNP含量及其在PVA基体中的分散状态对复合膜结构与性能的影响。结果表明,石墨片层被剥离成具有较大径厚比的GNP分散在PVA基体中;随着GNP含量的增加,复合膜的体积电阻率明显降低,力学性能先增大后降低,同时其耐水性和热稳定性均有所改善;GNP的含量为2%(质量分数,下同)时,复合膜的体积电阻率达到渗流阈值并下降到108数量级,拉伸强度提高了7.34 MPa,水接触角从56.3°提高至97.9(°)。

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。

球形容器内复合相变材料的约束熔化传热过程

为评估高导热填料对复合相变材料熔化传热过程的影响,采用实验方法定量分析典型球形容器中添加石墨纳米片的十二醇基复合相变材料的约束熔化传热过程.以熔化过程中的瞬时质量熔化率为比较对象,对石墨纳米片的质量分数和恒温加热边界条件进行参数化研究.实验结果表明,随着质量分数的增加,复合相变材料的熔化传热过程从以自然对流为主导逐渐转变为以导热为主导.在所研究的工况范围内,虽然复合相变材料的导热系数有一定程度的提高,但不足以弥补黏度增长所引起的自然对流削弱效应,反而使得熔化过程有所减缓.通过数据拟合得到了熔化率随傅里叶数、斯蒂芬数和格拉晓夫数等特征无量纲数变化的实验关联式,其预测结果的误差小于15%.

纳米石墨微片对无卤阻燃聚苯乙烯阻燃性能的影响

本文以纳米石墨微片(Graphite Nanoplatelets,GNP)作为协效剂,与膨胀阻燃剂(聚磷酸钱和季戊四醇)复配,考察了GNP在无卤阻燃聚苯乙烯中的协同作用与阻燃机理。采用粉末复合法制备聚苯乙烯阻燃复合材料,固定膨胀阻燃剂用量为25wt.%,探究了不同GNP用量(Owt.%、0.5wt.%、1.Owt.%、2.0wt.%)对复合材料阻燃性能的影响,以及GNP对阻燃复合材料的协同效果。通过极限氧指数(LOI)、垂直燃烧表征了复合材料的阻燃性能,采用扫描电镜研究了GNP对炭层形貌的影响,锥形量热仪研究了GNP对复合材料热释放速率的影响。PS/IFR阻燃复合材料中阻燃剂用量超过25wt.%时,复合材料的阻燃性能显著提高,阻燃剂用量达到30wt.%时,极限氧指数达到37.3,垂直燃烧达到V-0级。GNP的引入可显著降低膨胀阻燃剂的用量。GNP/IFR/PS阻燃复合材料中膨胀阻燃剂用量为24.5wt.%、GNP添加量为0.5wt%时,极限氧指数可达到36,垂直燃烧达到V-0级。探究了阻燃剂中引入GNP对于复合材料的协效阻燃机理,结果显示GNP引入后可促使燃烧后炭层致密,且热释放速率降低,从而表现出较好的协同阻燃效果。

纳米石墨片/炭黑/氯醋树脂复合导电膜的制备及性能研究

以氯醋树脂P(VC-Co-VAc)为基体,采用原位还原萃取分散技术制备了纳米石墨片复合导电膜,通过与炭黑填料的对比,考察了导电填料的几何形状以及两相导电填料之间的协同作用对复合膜导电性能的影响。结果表明:纳米石墨片在基体中分散良好,其复合膜的导电性能明显优于炭黑导电膜;当纳米石墨片和炭黑的体积比为4∶6时,二者的协同作用最佳,其导电性明显优于相同含量下的单相填料复合导电膜。

石墨纳米片快速制备及增强树脂导热性能

石墨纳米片由于其优异的导热性能受到广泛关注,但现有的制备过程耗时长。本研究以膨胀石墨为原料,利用硝酸剥离法实现了石墨纳米片的快速制备,并采用多种手段对材料进行了表征。研究结果表明,经过0.5h的硝酸处理,石墨纳米片平均尺寸降至20μm左右,且其层状石墨烯堆叠结构未发生改变。同时,将制得的石墨纳米片加入到环氧树脂中,当掺杂量为20wt.%时,复合材料热导率较纯环氧树脂提升了506%。

以天然石墨为原料制备纳米石墨片在有机溶剂中的分散液

以天然石墨为原料,采用球磨法制备纳米石墨片在有机溶剂中的分散液。考察了球磨时间、不同分散剂和分散剂含量以及树脂含量对纳米石墨片分散效果的影响。研究发现以天然石墨为原料,采用球磨工艺可以制备直径为5μm,厚度小于30nm的纳米石墨片。纳米石墨片分散液的稳定性随着球磨时间的延长、分散剂的增加先增大后减小;随着树脂含量的增加先显著增加,达到最高之后,略有降低。

三辊剥离微纳米石墨薄片及其对环氧树脂性能的影响

为改善环氧树脂(EP)的使用性能,以尺寸约2mm、厚度约100μm的膨胀石墨(EG)和EP为原料,创新性地采用三辊研磨(TRM)技术连续剥离得到尺寸1~10μm、厚度10~20nm的大纵横比微纳米石墨薄片(GNPs),并进一步制备得到GNPs原位强化EP的复合材料。结果表明,制得的GNPs/EP复合材料的弯曲和拉伸性能随EG含量的增加呈现先升后降的变化,且当EG在EP中含量为1.0wt%时复合材料的性能最佳。与纯EP材料相比,该复合材料的弯曲强度、拉伸强度分别平均提高了31.9%、53.4%,这可能是由于GNPs与EP界面的紧密结合。本研究为进一步制备GNPs强化EP基碳纤维高强度航空复合材料奠定技术依据。