Graphene systems are clean platforms for studying electron–electron (e–e) collisions. Electron transport in graphene constrictions is now found to behave anomalously due to e–e interactions: conductance values exceed the maximum free-electron value. Electron–electron (e–e) collisions can impact transport in a variety of surprising and sometimes counterintuitive ways1,2,3,4,5,6. Despite strong interest, experiments on the subject proved challenging because of the simultaneous presence of different scattering mechanisms that suppress or obscure consequences of e–e scattering7,8,9,10,11. Only recently, sufficiently clean electron systems with transport dominated by e–e collisions have become available, showing behaviour characteristic of highly viscous fluids12,13,14. Here we study electron transport through graphene constrictions and show that their conductance below 150 K increases with increasing temperature, in stark contrast to the metallic character of doped graphene15. Notably, the measured conductance exceeds the maximum conductance possible for free electrons16,17. This anomalous behaviour is attributed to collective movement of interacting electrons, which ‘shields’ individual carriers from momentum loss at sample boundaries18,19. The measurements allow us to identify the conductance contribution arising due to electron viscosity and determine its temperature dependence. Besides fundamental interest, our work shows that viscous effects can facilitate high-mobility transport at elevated temperatures, a potentially useful behaviour for designing graphene-based devices.

Superballistic flow of viscous electron fluid through graphene constrictions

Since their first synthesis, carbon nanotubes (CNTs) gained remarkable research interest owing to their astonishing mechanical properties and extensive range of potential applications in various sectors, such as aerospace, automobile, biomedical, defence, energy, etc. This paper covers numerous characterization techniques, synthesis approaches and properties of the CNTs, reported by earlier researchers in the past. The technological and industrial needs for the development of lightweight nanocomposites have led to the significant advancements in the preparation of CNT-reinforced composites. In preliminary sections, the properties and applications of the CNT-reinforced nanocomposites are elaborated along with the issues related to their preparation. Here, various nanotubes synthesis processes, such as arc discharge, laser ablation and chemical vapour deposition, are exemplified with the support of published works. Furthermore, we have also addressed the several surface modification techniques of CNTs, such as purification, functionalization and dispersion, which make this review novel and exhaustive. In order to address the limitations and challenges incurred during the preparation of various CNT-reinforced polymer/metal matrix composites, an extensive collection of the published literature is reported and discussed, thoroughly. Based on this exhaustive review, some specific observations are made which would facilitate upcoming researches to explore the research opportunities in the preparation of CNTs and CNT-reinforced composites and their potential applications for the high-performance structures/components.

A Comprehensive Review on CNTs and CNT-Reinforced Composites: Syntheses, Characteristics and Applications

Fabrication of high strength yet light and low cost composite materials with good mechanical properties at room and elevated temperatures is a challenge that metallurgy and materials science communities are facing for many years, and no “dream material” has been developed so far. The primary goal of this study was to fabricate, characterize, and to carry out tensile tests on Al-based composite materials strengthened with commercially-available BN nanoparticles (BNNPs). The composites were fabricated by spark plasma sintering (SPS) technique. The structures of powder mixtures and composite materials, as well as their fracture surfaces, were studied by scanning and transmission electron microscopy. The influence of BNNPs content (0.5, 1.5, 3, 4.5, 6, and 7.5 wt%) and holding times (5, 60, and 300 min) at 600 °C during SPS on the tensile strength was investigated. A maximum increase in strength was observed for Al-based composites with 4.5 wt% of BNNPs. The sample demonstrated a 50% increase in tensile strength compared with pristine Al. Although the tensile tests performed at 300 °C revealed that the tensile strength became 20% lower than the strength at room temperature, it was, however, still 75% higher compared with that of the pure Al at 300 °C. In addition, at 300 °C the Al–BNNPs composites demonstrated a much higher value of yield stress, about 115 MPa, which is 190% higher than that of pure Al at the same temperature. The damping properties of Al–BNNPs composites were evaluated by temperature dependent internal friction (TDIF) measurements. The obtained results are discussed based on structural analysis and the TDIF data.

Fabrication, characterization, and mechanical properties of spark plasma sintered Al–BN nanoparticle composites

Effect of ball milling time on the structural characteristics and mechanical properties of nano-sized Y2O3 particle reinforced aluminum matrix composites produced by powder metallurgy route

The elevated levels of electromagnetic (EM) radiation released by electronic instruments, communication devices, and information processing technologies are becoming a major concern nowadays. Consequently, great effort has been made to develop unique nanomaterials to enhance the electromagnetic absorption properties of microwave-absorbing materials. These materials should have superior reflection loss (RL), thin thickness, wide absorption bandwidth, low density, and light weightiness. This article discusses the electromagnetic microwave absorption basic theory, the materials and the performance will be highlighted. The strategies scheme to enhance the absorption properties of microwave absorbing materials (MAMs) will be elaborated. Metal-based composites often exhibit high efficiency to fulfill coveted magnetic and dielectric characteristics. This review provides a brief presentation of the useful theory of some selected microwave absorbers of ferrites and composites of carbon-based materials. In addition, the classifications of microwave absorbers according to important parameters for the fundamental microwave absorption property of the substance are discussed. The effect of great potential application in microwave absorbing materials (MAMs) with thin thicknesses was also investigated. Furthermore, this paper provides a comprehensive review study on several microwave absorption materials and their fundamental mechanisms of microwave absorption, dielectric loss, magnetic loss, dielectric/magnetic loss coupling, absorption bandwidth, and the reflection loss (RL) values of nanomaterials. The electromagnetic and microwave absorption properties of sandwich absorbers by the single- and double-layer microwave absorber, are studied intensively. 

A review on electromagnetic microwave absorption properties: their materials and performance

Fabrication and machinability analysis of squeeze cast Al 7075/h-BN/graphene hybrid nanocomposite

Influence of TiO2 and MWCNT nanoparticles dispersion on microstructure and mechanical properties of Al6061 matrix hybrid nanocomposites

The present work deals with the microstructure and mechanical characterization of the Al6061 based nanocomposites (2 wt% Graphene and 2 wt% Al2O3) and hybrid nanocomposites (2 wt% Al2O3 with 0.5, 1, 1.5, 2 and 2.5 wt% of Graphene) processed through ultrasonic-assisted melt-stirring technique. The combined effort of reinforcement processing (ball-milling) and ultrasonic-assisted melt stirring approach has been adopted for fabricating hybrid nanocomposites with uniformly dispersed ceramic nanoparticles and carbon nanomaterial. The grain structure, physical properties, fractured surfaces, microhardness, hardness, ultimate tensile strength (UTS), flexural and compressive strength of the Al6061, Al6061-based nanocomposites and hybrid nanocomposites were examined to understand the influence of ceramic and nanomaterial particles on the microstructure and mechanical characteristics of the fabricated specimens. Microstructure investigation employing optical microscopy (OM) images and scanning electron microscopy (SEM) revealed homogenous dispersal of nano-sized Al2O3 and Graphene particles in the prepared hybrid nanocomposite specimens. The mechanical properties of the hybrid nanocomposites enhance with the increase of graphene nanoparticles (up to 1 wt%) in the nanocomposite. The mechanical characteristics of the hybrid nanocomposites exhibited a decreasing trend with an increase in Graphene up to 2 wt%, and an increasing trend is observed with a further increase in Graphene after 2.5 wt%. Al6061-2 wt% Al2O3-1 wt% Graphene hybrid nanocomposite depicts enhancement in compressive strength, UTS, flexural strength, hardness and microhardness of about 105.55%, 171.70%, 37.86%, 71.11% and 34.78%, respectively as compared to casted Al6061 specimen.

Microstructure and Mechanical Characterization of Al2O3/Graphene Reinforced Al6061 Based Hybrid Nanocomposites

The present research article deals with the microstructure, mechanical properties and machinability investigation of squeeze-cast Al7075 and Al7075/SiC/h-BN hybrid nanocomposite The Al7075 alloy nanocomposite has been reinforced by micro-size SiC (1 wt%) particles and h-BN (05 wt%) nanoparticles, prepared via ultrasonic-assisted melt-stirring approach In order to achieve the better mixing of reinforcements, diminish the agglomeration effect of nanoparticles and improved wettability of the particles in the melt, SiC and h-BN powders have been ball-milled for the duration of 4 h The microstructural investigation of the prepared nanocomposite was carried out by using optical microscopy (OM), scanning electron microscopy (SEM) and x-ray mapping analysis The x-ray mapping and optical microscopic analysis show good dispersion uniformity of reinforcements and refinement in the grain sizes The investigation of mechanical properties of hybrid nanocomposite shows the significant improvement of about 3533 %, 2169 %, 1387 % and 1227 % in the offset yield strength, ultimate tensile strength, Rockwell hardness and microhardness (Vickers), respectively Furthermore, the machinability analysis has been performed to examine the influence of several machining parameters such as cutting speed, feed rate and depth of cut on the surface roughness, cutting force and chips length of the squeeze-cast hybrid nanocomposites under dry and minimum quantity lubrication (MQL) machining conditions The outcomes of the machinability analysis for hybrid nanocomposites are compared with the Al7075 specimen and discussed

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Microstructure, mechanical properties and machinability studies of Al7075/SiC/h-BN hybrid nanocomposite fabricated via ultrasonic-assisted squeeze casting

Benedict Thomas

Papers

A Comprehensive Review on CNTs and CNT-Reinforced Composites: Syntheses, Characteristics and Applications

Fabrication and machinability analysis of squeeze cast Al 7075/h-BN/graphene hybrid nanocomposite

Influence of TiO2 and MWCNT nanoparticles dispersion on microstructure and mechanical properties of Al6061 matrix hybrid nanocomposites

Microstructure and Mechanical Characterization of Al2O3/Graphene Reinforced Al6061 Based Hybrid Nanocomposites

Microstructure, mechanical properties and machinability studies of Al7075/SiC/h-BN hybrid nanocomposite fabricated via ultrasonic-assisted squeeze casting