Fabrication of homogeneously dispersed graphene/Al composites by solution mixing and powder metallurgy

Graphene-reinforced aluminum （AI） matrix composites were successfully prepared via solution mixing and powder metallurgy in this study. The mechanical properties of the composites were studied using microhardness and tensile tests. Compared to the pure Al alloy, the graphene/Al composites showed increased strength and hardness. A tensile strength of 255 MPa was achieved for the graphene/Al com- posite with only 0.3wt% graphene, which has a 25% increase over the tensile strength of the pure Al matrix. Raman spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy were used to investigate the morphol- ogies, chemical compositions, and microstructures of the graphene and the graphene/A1 composites. On the basis of fractographic evidence, a relevant fracture mechanism is proposed.

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.

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.

Structure-dependent re-dispersibility of graphene oxide powders prepared by fast spray drying

The graphene oxide powder(GOP)obtained from the spray drying process often exhibits poor redispersibility which is considered due to the partial reduction of GO sheets.The reduction of drying temperature can effectively increase the redispersibility of GOP,but result in a decreased drying efficiency.Herein,we found that the redispersibility of GOP is strongly affected by its microstructure,which is determined by the feed concentration.With the increase of feed concentration,the GO nanosheet assembly varies from the disordered stacking to relatively oriented assembly,making the morphology of the GOP transform from balllike(the most crumpled one)to flakelike(the least crumpled one),and the 0.8 mgml 1 is the threshold concentration for the morphology,structure,and redispersibility change.Once the feed concentration reaches 0.8 mg ml 1,the appearance of the nematic phase in droplet ensures the relatively oriented assembly of GO sheets to form the layered structure with a low crumpling degree,which greatly improves the polar parts surface tension of the solid GOP,making the GOP easier to form hydrogen bonding with water during the redispersion process,thus stabilizing dispersion.This work provides useful information for understanding the relationships between the morphology,microstructure,and final redispersibility of GOPs.

Buckling analysis of embedded graphene oxide powder-reinforced nanocomposite shells

In this study,the buckling analysis of a Graphene oxide powder reinforced(GOPR)nanocomposite shell is investigated.The effective material properties of the nanocomposite are estimated through Halpin-Tsai micromechanical scheme.Three distribution types of GOPs are considered,namely uniform,X and O.Also,a first-order shear deformation shell theory is incorporated with the principle of virtual work to derive the governing differential equations of the problem.The governing equations are solved via Galerkin’s method,which is a powerful analytical method for static and dynamic problems.Comparison study is performed to verify the present formulation with those of previous data.New results for the buckling load of GOPR nanocomposite shells are presented regarding for different values of circumferential wave number.Besides,the influences of weight fraction of nanofillers,length and radius to thickness ratios and elastic foundation on the critical buckling loads of GOP-reinforced nanocomposite shells are explored.

A Green and Mild Approach of Synthesis of Highly-Conductive Graphene Film by Zn Reduction of Exfoliated Graphite Oxide

We report a simple and green approach to synthesize reduced graphene oxide （RGO） nanosheets at room temperature based on Zn reduction of exfoliated GO. The evolution of GO to RGO has been characterized by X-ray diffraction, UV-Vis absorption spectroscopy and Raman spectroscopy. The results of X-ray photoelectron spectroscopy reveal that the atomic ratio of carbon to oxygen in the RGO can be tuned from 1.67 to 13.7 through controlling the reduction time. Moreover, the conductivity of the RGO is measured to be 26.9±2.2 kS/m, much larger than those previously obtained by chemical reduction through other reducing agents. More importantly, the resistance of the RGO film with 20 nm thickhess can be as low as 2 kΩ/square, while a high transparency over 70% within a broad spectral range from 0.45 pm to 1.50 p.m can be retained. The proposed method is low-cost, eco-friendly and highly-eiffcient, the as-prepared thinner RGO films are useful in a variety of potential application fields such as optoelectronics, photovoltaics and electrochemistry by serving as an ultralight, flexible and transparent electrode material.

Effect of graphene nanoplatelets(GNPs)addition on strength and ductility of magnesium-titanium alloys

Effect of graphene nanoplatelets(GNPs)addition on mechanical properties of magnesium–10wt%Titanium(Mg–10Ti)alloy is investigated in current work.The Mg-(10Ti+0.18GNPs)composite was synthesized using the semi powder metallurgy method followed by hot extrusion.Microstructural characterization results revealed the uniform distribution of reinforcement(Ti+GNPs)particles in the matrix,therefore(Ti+GNPs)particles act as an effective reinforcing filler to prevent the deformation.Room temperature tensile results showed that the addition of Ti+GNPs to monolithic Mg lead to increase in 0.2%yield strength(0.2%YS),ultimate tensile strength(UTS),and failure strain.Scanning Electron Microscopy(SEM),Energy-Dispersive X-ray Spectroscopy(EDS)and X-Ray Diffraction(XRD)were used to investigate the surface morphology,elemental dispersion and phase analysis,respectively.

Preparation and properties of graphene nanoplatelets reinforced aluminum composites

5.0 vol.% graphene nanoplatelets(GNPs) and aluminum powders were mixed to prepare GNPs/Al composites via high-energy ball milling(HEBM). The mixed powders were subjected to spark plasma sintering(SPS) and subsequent hot extrusion. The microstructure and mechanical properties of extruded composites were investigated by X-ray photoelectron spectroscopy(XPS), transmission electron microscopy(TEM) and tensile tests. In the extruded composites, 5.0 vol.% GNPs were dispersed homogeneously and no serious GNP-Al interfacial reaction occurred. As a result, the yield strength and ultimate tensile strength of the extruded GNPs/Al composites reached 462 and 479 MPa, which were 62% and 60% higher than those of the extruded Al matrix, respectively. The enhanced mechanical properties were attributed to the effective load transfer capacity of dispersed GNPs. This demonstrated that it may be promising to introduce dispersed high-content GNPs via HEBM, SPS and hot extrusion techniques and GNP-Al interfacial reaction can be controlled.

Effect of graphene oxide on the corrosion,mechanical and biological properties of Mg-based nanocomposite

This study investigates the effect of graphene oxide(GO)on the mechanical and corrosion behavior,antibacterial performance,and cell response of Mg–Zn–Mn(MZM)nanocomposite.MZM/GO nanocomposites with different amounts of GO(i.e.,0.5 wt%,1.0 wt%,and1.5 wt%)were fabricated by the semi-powder metallurgy method.The influence of GO on the MZM nanocomposite was analyzed through the hardness,compressive,corrosion,antibacterial,and cytotoxicity tests.The experimental results showed that,with the increase in the amount of GO(0.5 wt%and 1.5 wt%),the hardness value,compressive strength,and antibacterial performance of the MZM nanocomposite increased,whereas the cell viability and osteogenesis level decreased after the addition of 1.5 wt%GO.Moreover,the electrochemical examination results showed that the corrosion behavior of the MZM alloy was significantly enhanced after encapsulation in 0.5 wt%GO.In summary,MZM nanocomposites reinforced with GO can be used for implant applications because of their antibacterial performance and mechanical property.

Synthesis and Characterization of Mass Produced High Quality Few Layered Graphene Sheets via a Chemical Method

Graphene is a two-dimensional crystal of carbon atoms arranged in a honeycomb lattice. It is a zero band gap semimetal with very unique physical and chemical properties which make it useful for many applications such as ultra-high-speed field-effect transistors, p-n junction diodes, terahertz oscillators, and low-noise electronic, NEMS and sensors. When the high quality mass production of this nanomaterial is still a big challenge, we developed a process which will be an important step to achieve this goal. Atomic Force Microscopy, Scanning Electron Microscopy, Scanning tunneling microscopy, High Resolution Transmission Electron Microscopy, X-Ray Diffraction, Raman spectroscopy, Energy Dispersive X-ray system were investigated to characterize and examine the quality of this product.

Microstructure and Thermal Conductivity of Al–Graphene Composites Fabricated by Powder Metallurgy and Hot Rolling Techniques

The objective of this research is to improve the thermal conductivity and mechanical properties of Al/GNPs（graphene nanoplatelets） nanocomposites produced by classical powder metallurgy and hot rolling techniques. The microstructural evaluation confirmed the uniform dispersion of GNPs at low content and agglomeration at higher contents of GNPs. The structure of graphene was studied before and after the mixing and the Raman spectrum proofs that the wet mixing has a great potential to be used as a dispersion method. There was no significant peak corresponding to the Al_4C_3 formation in both the differential scanning calorimetry curves and X-ray diffraction patterns. The microstructural observation in both fabrication techniques showed grain refinement as a function of the GNPs content. Moreover, the introduction of the GNPs not only improved the Vickers hardness of the composites but also decreased their density. The thermal conductivity investigations showed that in both the press-sintered and hot-rolled samples, although the thermal conductivity of composites was improved at low GNPs contents, it was negatively affected at high GNPs contents.

Mechanical and tribological properties of graphene nanoplatelets-reinforced titanium composites fabricated by powder metallurgy

Titanium matrix composite reinforced by graphene nanoplatelets(GNPs)was fabricated via powder metallurgy route.Hot isostatic pressing and hot extrusion were used to consolidate the mixed powder of GNPs and TC4 titanium(Ti)alloy.The microstructures,mechanical properties and sliding wear performance of Ti/GNPs composite had been researched to evaluate the rein forcing effect of GNPs on tita nium matrix.Microstructure observation indicates that GNPs could restrain grai n growth slightly in titanium matrix.Titanium matrix and graphene exhibit a clean and firm interface formed by means of metallurgical bonding on atomic scale.Compared with the monolithic titanium alloy,the composite with 1.2 vol.%GNPs exhibits significantly improved elastic modulus and strength.The sliding wear test shows that there is an obvious enhancement in the tribological performance of Ti/GNPs composite with 1.2 vol.%GNPs.The results of this work indicate that GNP is an efficient reinforcenient material in titanium matrix.The strengthening mechanism including precipitates strengthening,load transfer and grain refinement mechanism of GNPs in titanium matrix was discussed.A modified shear-lag model was used to analyze the reinforcement contribution of the stress transfer mechanism.The calculation shows that the stress load mechanism constitutes the main strengthening mechanism in Ti/GNPs composite.

An approach to prepare uniform graphene oxide/aluminum composite powders by simple electrostatic interaction in water/alcohol solution

The homogenous dispersion of graphene in Al powders is a key challenge that limits the development of graphene-reinforced metal matrix composites with high performance.Here,uniform distribution of graphene oxide(GO)coated on flake Al powders were obtained by a simply stirring and ultrasonic treatment in the water/alcohol solution.The effect of water volume content on the formation of GO/Al composite powders was investigated.The results showed that GO adsorbed with synchronous reduction on the surface of Al powders,but when the water content was higher than 80%in the solution,Al powders were totally changed into Al(OH)3.With optimizing the water content of 60%in the solution,reduced GO was homogenously coated onto the surface of flake Al powders.The formation mechanism can be ascribed to the balance control between the liquid/solid interaction and the hydrolysis reaction.

Characterization of Interfacial Bonding Mechanism for Graphene-Modified Powder Metallurgy Nickle-Based Superalloy

A modified FGH96 superalloy using 0.1 wt% graphene was successfully prepared using the wet mixing method. The interracial bonding mechanism between the graphene and the superalloy matrix was characterized using optical micro- scope, scanning electronic microscope, transmission electronic microscope and X-ray tomography. The results revealed that the graphene could be dispersed uniformly inside the matrix of the superalloy, and the bonding interface between graphene and the superalloy showed a rather diffusion instead of abrupt distinction, suggesting that the interface was formed via chemical fusion rather than a mechanical combination. The uniform dispersity of the graphene inside the superalloy matrix could improve the tensile properties significantly, including tensile strength, plasticity and yield strength. The existence of the graphene at the fracture surface further verified that the graphene could increase the effective bearing force of the material during the tensile test.

Enhancing kinetics of Li-S batteries by graphene-like N,S-codoped biochar fabricated in NaCl non-aqueous ionic liquid

Graphene-like N,S-codoped bio-carbon nanosheets(GNSCS) were prepared by a facile and environment-friendly NaCl non-aqueous ionic liquid route to house sulfur for lithium-sulfur battery. The natural nori powder was calcined at 900°C for 3 h under Ar, in which NaCl non-aqueous ionic liquid can exfoliate carbon aggregates into nanosheets. The structural characterization of GNSCS by a series of techniques demonstrates the graphene-like feature.When evaluated as the matrix for sulfur cathode, GNSCS/S exhibits more prominent cycling stability and rate capability.A discharge capacity of 548 mA h g-1 at a current density of 1.6 A g-1 after 400 cycles was delivered with a capacity fade rate of only 0.13% per cycle and an initial Coulombic efficiency(CE) as high as 99.7%. When increasing the areal sulfur loading up to 3 mg cm-2, the discharge capacity can still be retained at 647 mA h g-1 after more than 100 cycles with a low capacity degradation of only ~0.30% per cycle. The features of N/S dual-doping and the graphene-like structure are propitious to the electron transportation, lithium-ion diffusion and more active sites for chemically adsorbing polysulfides. It is anticipated that other functional biochar carbon can also be attained via the low-cost, sustainable and green method.

石墨烯锌粉涂料技术和应用进展

石墨烯锌粉涂料体现了新材料、新机理和卓越性能的特征,成为涂料行业的一个突破性创新。文章综述了石墨烯锌粉涂料的技术发展和应用现状。石墨烯独特的原子片层结构和不可渗透性,以及优异的力、热、电性能,贡献了石墨烯锌粉涂料新的防护机理。石墨烯的物理屏蔽作用、活化锌粉作用以及增强力学强度作用,在高性能石墨烯锌粉涂料中发挥了主导作用。石墨烯锌粉涂料优先物理屏蔽主导防护机理,与传统环氧富锌涂料优先阴极保护机理有着本质差异。石墨烯锌粉涂料在防腐性能、力学性能、施工性能以及节约锌粉和节能降碳等方面,均体现出明显优势,石墨烯低锌和石墨烯锌粉双涂层更具有创新优势。总结了近期石墨烯锌粉涂料在桥梁、风电、化工、水电、建筑、集装箱等领域的应用案例和现状。最后,指出石墨烯锌粉涂料技术和替代传统环氧富锌涂料的应用发展趋势,以及对钢结构长效保护的技术创新价值。

冷涂烯锌涂料的制备与性能研究

首先研究了不同环氧树脂(E20、E44和E51)对环氧含锌涂层基本性能的影响,其次探究了纯薄石墨烯的添加对涂层防腐蚀性和力学性能的影响,确定了锌质量分数30%涂料体系中纯薄石墨烯的最佳添加量,最后考察了膨润土、聚脲、聚酰胺钠作为防沉体系对冷涂烯锌涂料贮存稳定性的作用。通过中性盐雾试验,并结合扫描电镜、表面电阻率、剩余锌含量和力学性能测试,制备出符合T/CHTS 10105—2023标准要求的冷涂烯锌涂料。结果表明:采用环氧树脂E44所制备的涂层基本性能最佳;加入质量分数0.5%纯薄石墨烯后,涂层的力学性能均有提升,表面电阻率≤10^(6)Ω,锌粉利用率超过80%,耐中性盐雾时间可达3000 h;添加质量分数0.9%膨润土、0.6%聚脲和1%聚酰胺钠防沉体系后,冷涂烯锌涂料可在50℃下稳定贮存60 d。

电爆法制备石墨烯及其铜基复合涂层的性能研究

石墨烯与金属粉末混合后容易团聚,不能有效均匀分散,无法充分发挥其优异特性。为解决石墨烯在复合材料中的团聚问题,采用自主研制的电爆设备制备了石墨烯气溶胶,将其与铜粉混合得到石墨烯/铜复合粉体,并制备出石墨烯/铜复合涂层。使用扫描电子显微镜(SEM)、透射电子显微镜(TEM)和原子力显微镜(AFM)对石墨烯气溶胶及复合材料进行表征分析,并测试涂层的硬度和耐磨性。结果表明,电爆法制备的石墨烯主要为小片径石墨烯,片径尺寸为5~40 nm,层数为3~7层。在浓度0.875 mg/L的石墨烯气溶胶中,衬底放置时间少于10 min时,单个的小片径石墨烯片碰撞吸附在衬底上,未发现凝并后的石墨烯气溶胶凝胶;衬底放置时间超过10 min后,许多小片径石墨烯堆叠在一起,形成石墨烯气溶胶凝胶,且衬底放置时间越长,凝并越严重,石墨烯气溶胶凝胶团也在不断长大。石墨烯/铜复合粉体中小片径石墨烯均匀吸附在铜粉表面,制备出的复合涂层其表面C元素分布均匀,有效解决了团聚问题。0.5 wt.%石墨烯/铜涂层平均硬度为74.8 HV0.05、摩擦系数为0.18,与纯铜涂层相比均有不同程度的提升。结果表明,电爆法制备的石墨烯气溶胶可用于制备石墨烯/铜复合涂层,提高涂层的硬度和耐磨性。该方法有望为制备高性能石墨烯/金属复合材料提供新的途径。

一种新型Al-2.5GNPs细化剂制备及其对AZ31镁合金的细化作用

镁合金因自身强度低和塑性较差限制了其在工业领域的应用,向镁合金中添加晶粒细化剂的方法能够改善其组织并提高材料的强度和塑性,是提升镁合金性能的最有效方法之一。本文利用球磨工艺结合粉末冶金的方法制备出一种含有GNPs(石墨烯纳米片)的新型镁合金细化剂。采用拉曼光谱分析法探究了不同球磨参数对GNPs的质量影响规律,得出较优球磨工艺参数为:转速300 r/min、球磨时间2 h,可以保证球磨后GNPs的高质量。将其混合粉体进行冷压,并在400℃烧结2 h,得到含有GNPs且组织致密、成型良好的Al-2.5GNPs细化剂。采用OM、SEM、XRD、TEM等表征手段初步分析了细化剂中Al4C3和GNPs对AZ31镁合金中的细化及强化机理。在720℃下加入质量分数为1.5%的Al-2.5GNPs细化剂,可以使AZ31镁合金的晶粒尺寸从228.8μm细化至65.6μm,抗拉强度从112.6 MPa提升至178.2 MPa,伸长率从8.9%提升至16.7%,分别提高了58.3%和87.6%。

多频谱干扰剂研究进展

针对部分精确制导弹药主要使用对抗光电红外类的干扰剂进行有效对抗的情况,对配置多频谱干扰剂所用材料的主要成分铜粉、金属箔条、膨胀石墨、石墨烯、碳纤维的干扰原理与研究进展进行了介绍,在此基础上对多频谱干扰剂的3种实现方式研究进展进行了综述,分析了当前对组合装药技术、复合配药技术、材料改性技术研究的局限性,着眼新材料具有较强的结构设计性特点进行研发,能够有效克服现有多频谱实现技术的内在矛盾与缺点,对多频谱干扰剂发展前景进行了展望。