Effect of (Mn + Cr) addition on the microstructure and thermal stability of spray-formed hypereutectic Al–Si alloys

This study aims to investigate the tensile mechanical behavior and fracture toughness of vinyl-ester/polyester hybrid nanocomposites containing various types of nanofillers, including multi- and double-walled carbon nanotubes with and without amine functional groups (MWCNTs, DWCNTs, MWCNT-NH₂ and DWCNT-NH₂). To prepare the resin suspensions, very low contents (0.05, 0.1 and 0.3 wt.%) of carbon nanotubes (CNTs) were dispersed within a specially synthesized styrene-free polyester resin, conducting 3-roll milling technique. The collected resin stuff was subsequently blended with vinyl-ester via mechanical stirring to achieve final suspensions prior to polymerization. Nanocomposites containing MWCNTs and MWCNT-NH₂ were found to exhibit higher tensile strength and modulus as well as larger fracture toughness and fracture energy compared to neat hybrid polymer. However, incorporation of similar contents of DWCNTs and DWCNT-NH₂ into the hybrid resin did not reflect the same improvement in the corresponding mechanical properties. Furthermore, experimentally measured elastic moduli of the nanocomposites containing DWCNTs, DWCNT-NH₂, MWCNTs and MWCNT-NH₂ were fitted to Halphin–Tsai model. Regardless of amine functional groups or content of carbon nanotubes, MWCNT modified nanocomposites exhibited better agreement between the predicted and the measured elastic moduli values compared to nanocomposites with DWCNTs. Furthermore, Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) were used to reveal dispersion state of the carbon nanotubes within the hybrid polymer and to examine the CNT induced failure modes that occurred under mechanical loading, respectively. Based on the experimental findings obtained, it was emphasized that the types of CNTs and presence of amine functional groups on the surface of CNTs affects substantially the chemical interactions at the interface, thus tuning the ultimate mechanical performance of the resulting nanocomposites.     

Process and mechanical properties of carbon/carbon–silicon carbide composite reinforced with carbon nanotubes grown in situ

A hierarchical C_f/C–SiC composite was fabricated via in situ growth of carbon nanotubes (CNTs) on fiber cloths following polymer impregnation and pyrolysis process. The effects of CNTs grown in situ on mechanical properties of the composite, such as flexural strength, fracture toughness, crack propagation behavior and interfacial bonding strength, were evaluated. Fiber push-out test showed that the interfacial bonding strength between fiber and matrix was enhanced by CNTs grown in situ. The propagation of cracks into and in fiber bundles was impeded, which results in decreased crack density and a “pull-out of fiber bundle” failure mode. The flexural strength was increased while the fracture toughness was not improved significantly due to the decreased crack density and few interfacial debonding between fiber and matrix, although the local toughness can be improved by the pull-out of CNTs.     

Atomistic simulations of shearing friction and dynamic adhesion of double-walled carbon nanotubes on Au substrates

Functional gecko-mimetic adhesives have attracted a lot of research interest in recent years. In this paper, the physical adhesion behavior of (5, 5)@(10, 10) double-walled carbon nanotubes (DWCNTs) on an Au substrate is investigated by performing detailed, fully atomistic molecular dynamics (MD) simulations. The effects of adhesion temperature, tube length, and peeling velocity on the binding energy, normal adhesion force, lateral shearing friction, and adhesion time are thoroughly analyzed. The simulation results indicate that the binding energy (per unit length) of the DWCNT–Au adhesive system is −26.7 × 10⁻² eV/Å, which is 7.2% higher than that of single-walled counterparts. The tip-surface adhesion force for a single DWCNT is calculated to be 1.4 nN, and thus the adhesive strength of a DWCNT array is about 1.4 × 10¹–1.4 × 10³ N/cm² (corresponding to an aerial density of 10¹⁰–10¹² tubes/cm²). Two distinctive friction modes, namely (i) sliding friction (by the nanotube wall) and (ii) sticking friction (by the nanotube tip), are elucidated in term of the phase relationship of atomic friction forces. Moreover, the effective Young’s moduli of double- and single-walled CNTs are obtained using MD simulations combined with Euler–Bernoulli beam theory. The calculation results show good agreement with previously reported numerical and experimental results.     

Improvement of mechanical properties in aluminum/CNTs nanocomposites by addition of mechanically activated graphite

Carbon nanotubes reinforced aluminum nanocomposite was prepared by ball milling route. CNTs were initially mixed with mechanically amorphized graphite. Specimens were analyzed by X-ray diffractometry and Raman spectroscopy. Crystallite size and dislocation density were calculated by modified Warren–Averbach method. Carbide formation was semi-quantitatively investigated via Raman spectroscopy. A band located in 950 cm⁻¹ was considered to be corresponded to Al₄C₃. Hardness of the samples was also evaluated using a Vickers micro-hardness tester. The hardness strengthening contributions were modeled to evaluate interfacial bonding between CNTs and the aluminum matrix. In specimens, including amorphized graphite, hardening was due to both work hardening and second phase strengthening otherwise, only due to work hardening. It was deducted that the amorphized graphite has a major role for mechanical properties improvement. This seems to be due to the formation of aluminum carbide at the interface which consequently increases adhesion of CNTs to aluminum.     

Synthesis of fullerene nanowhiskers using the liquid–liquid interfacial precipitation method and their mechanical,electrical and superconducting properties

Abstract

Fullerene nanowhiskers (FNWs) are thin crystalline fibers composed of fullerene molecules, including C₆₀, C₇₀, endohedral, or functionalized fullerenes. FNWs display n-type semiconducting behavior and are used in a diverse range of applications, including field-effect transistors, solar cells, chemical sensors, and photocatalysts. Alkali metal-doped C₆₀ (fullerene) nanowhiskers (C₆₀NWs) exhibit superconducting behavior. Potassium-doped C₆₀NWs have realized the highest superconducting volume fraction of the alkali metal-doped C₆₀ crystals and display a high critical current density (J_c) under a high magnetic field of 50 kOe. The growth control of FNWs is important for their success in practical applications. This paper reviews recent FNWs research focusing on their mechanical, electrical and superconducting properties and growth mechanisms in the liquid–liquid interfacial precipitation method.     

Mechanical reinforcement while remaining electrical insulation of glass fibre/polymer composites using core–shell CNT@SiO2 hybrids as fillers

Carbon nanotubes (CNTs) have been widely used as mechanical reinforcement agents of composites. However, their aggregations, weak interfacial interaction with polymer, as well as high electrical conductivity limit their use in some especial applications. In this paper, the silicon oxide (SiO₂)-coated (CNT@SiO₂) core–shell hybrids with different SiO₂ thickness were prepared and employed to reinforce glass fibre-reinforced bismaleimide–triazine (BT) resin (GFRBT) composites. The results indicated the mechanical properties, including tensile strength and Young’s modulus increased with the increase of SiO₂ thickness and CNT@SiO₂ loading. Such enhanced mechanical properties were mainly attributed to the intrinsically nature of CNTs, homogeneous dispersion of the hybrids, as well as improved interfacial interaction. Meanwhile, the composites remained high electrical insulation (9.63 × 10¹² Ω cm) due to the existence of SiO₂ layer on CNT surface. This study will guide the design of functionalized CNTs and the construction of high-performance composites.     

Synthesis of fullerene nanowhiskers using the liquid–liquid interfacial precipitation method and their mechanical,electrical and superconducting properties

Fullerene nanowhiskers (FNWs) are thin crystalline fibers composed of fullerene molecules, including C₆₀, C₇₀, endohedral, or functionalized fullerenes. FNWs display n-type semiconducting behavior and are used in a diverse range of applications, including field-effect transistors, solar cells, chemical sensors, and photocatalysts. Alkali metal-doped C₆₀ (fullerene) nanowhiskers (C₆₀NWs) exhibit superconducting behavior. Potassium-doped C₆₀NWs have realized the highest superconducting volume fraction of the alkali metal-doped C₆₀ crystals and display a high critical current density (J_c) under a high magnetic field of 50 kOe. The growth control of FNWs is important for their success in practical applications. This paper reviews recent FNWs research focusing on their mechanical, electrical and superconducting properties and growth mechanisms in the liquid–liquid interfacial precipitation method.     

热轧对搅拌摩擦加工制备CNTs/Al复合材料微结构与性能的影响

在搅拌摩擦加工制备碳纳米管增强铝基复合材料(CNTs/Al)的基础上,研究了热轧对复合材料微结构与性能的影响。结果表明,热轧使基体晶粒沿轧制方向拉长,同时有利于CNTs的取向并在一些CNTs-Al界面形成Al4C3相;基于CNTs取向等微结构的变化以及界面反应引起界面结合力增强的因素,沿轧制方向复合材料的抗拉强度、导电性明显提高,热膨胀率降低。     

Self-Powered Integrated Sensing System with In-Plane Micro-Supercapacitors for Wearable Electronics

Self-powered integrated sensor with high-sensitivity physiological signals detection is indispensable for next-generation wearable electronic devices. Herein, a Ti₃C₂T_x/CNTs-based self-powered resistive sensor with solar cells and in-plane micro-supercapacitors (MSCs) is successfully realized on a flexible styrene–ethylene/butylene–styrene (SEBS) electrospinning film. The prepared Ti₃C₂T_x/CNTs@SEBS/CNTs nanofiber membranes exhibit high electrical conductivity and mechanical flexibility. The laser-assisted fabricated Ti₃C₂T_x/CNTs based-MSCs demonstrate a high areal energy density of 52.89 and 9.56 µWh cm⁻² with a corresponding areal power density of 0.2 and 4 mW cm⁻². Additionally, the MSCs exhibit remarkable capacity retention of 90.62% after 10 000 cycles. Furthermore, the Ti₃C₂T_x/CNTs based-sensor exhibits real-time detection capability for human facial micro-expressions and pulse single under physiological conditions. The repeated bending/release tests indicate the long-time cycle stability of the Ti₃C₂T_x/CNTs based-sensor. Owing to the excellent sensing performance, the sensing array was also fabricated. It is believed that this work develops a route for designing a self-powered sensor system with flexible production, high performance, and human-friendly characteristics for wearable electronics.     

Hard and superhard carbon phases synthesized from fullerites under pressure

A review has been presented on the structural and mechanical properties of hard carbon phases synthesized from fullerite C₆₀ under pressure. The density and nanostructure have been recognized as the key parameters defining the mechanical properties of hard carbon phases. By suggesting a version of the transitional high-pressure diagram of C₆₀ (developed up to 20 GPa), the three areas of the formation of hard carbon phases have been highlighted. The corresponding phases of superhard carbon are (1) disordered sp₂-type atomic structures at moderate pressures and high temperatures (> 1100 K), (2) three-dimensionally polymerized C₆₀ structures at moderate temperatures and high pressures (> 8 GPa), and (3) sp₃-based amorphous and nanocomposite phases at high pressures and temperatures. First region can be in turn separated into 2 subparts with different peculiarities of sp² structures and properties: low pressure part (0.1–2 GPa) and high-pressure part (2–8 GPa). Temperature can be recognized as a factor responsible for the formation of nanostructures by the partial destruction of molecular phases, whereas pressure is a factor responsible for stimulating the formation of rigid polymerized structures consisting of covalently bonded C₆₀ molecules, whereas the combination of both factors leads to the formation of atomic-based phases with dominating sp³ bonding.     

Structural modification and enhanced electron emission from multiwalled carbon nanotubes grown on Ag/Fe catalysts coated Si-substrates

Multiwalled carbon nanotubes and carbon nano-filaments were grown using Fe as the main catalyst and Ag as a co-catalyst by microwave plasma enhanced chemical vapour deposition. In this work we demonstrate the growth behaviour of carbon nanotubes (CNTs) grown on pure Fe-film and Ag–Fe films. We find that using Ag film beneath Fe film significantly abate the catalyst–substrate interactions by acting as a barrier layer as well as enhances the nucleation sites for the growth of CNTs due to the limited solubility with Fe and silicon. Scanning electron microscopy and transmission electron microscopy studies were carried out to image the microstructures of the samples. It was observed that the length of Fe catalyzed CNTs was ∼500 nm and Ag–Fe catalyzed CNTs varied from ∼600 nm to 1.7 μm. Micro Raman spectroscopy confirmed the improved crystalline nature of Ag–Fe CNTs. It was found that I_D/I_G ratio for Fe catalyzed CNTs was ∼1.08 and for Ag–Fe catalyzed CNTs was ∼0.7. The Ag–Fe catalyzed CNTs were found to be less defective as compared to Fe catalyzed CNTs. Field emission measurements using diode configuration, showed that electron emission from Ag–Fe catalyzed CNTs was much stronger as compared to Fe catalyzed CNTs. The threshold field for Ag–Fe catalyzed CNTs was (2.6 V μm⁻¹) smaller as compared to Fe catalyzed CNTs (3.8 V μm⁻¹) and thus shows better emission properties. This enhancement in electron emission mechanism as a result of introduction of Ag underlayer is attributed to the increased emitter sites and improved crystallinity.     

Mechanical behavior of self-assembled carbon nanotube reinforced nylon 6,6 fibers

The versatile electrospinning technique was used to successfully align and disperse multiwalled carbon nanotubes (MWCNT) in nylon 6,6 matrix to obtain composite fibers. The morphology of the composite fibers and the dispersion of the CNTs within the fibers were analyzed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. TEM analysis revealed that the CNTs were well-dispersed, separated and aligned along the fiber axis. The thermal and mechanical properties of the composite fibers were characterized as a function of weight fraction of the CNTs. Incorporation of the CNTs in the fibers resulted in an increase in glass-transition temperature (T_g) by ∼7 °C, indicating that the addition of CNTs has restricted the mobility of the polymer chains and provided confinement to neighboring molecular chains. Tensile and nanoindentation experiments were performed to investigate the mechanical deformation behavior of the composite fibers. The results suggested that incorporation of high strength and high aspect ratio CNTs into the fiber matrix enhanced significantly the stiffness and strength of nylon 6,6 fibers. An understanding of the structure–property relationships can provide fruitful insights to develop electrospun fibers with superior properties for miniaturized and load-bearing applications.     

Influence of carbon nanotube-polymeric compatibilizer masterbatches on morphological, thermal, mechanical, and tribological properties of polyethylene

Study was made of the effect of multiwall carbon nanotubes (MWCNTs) and polymeric compatibilizer on thermal, mechanical, and tribological properties of high density polyethylene (HDPE). The composites were prepared by melt mixing in two steps. Carbon nanotubes (CNTs) were melt mixed with maleic anhydride grafted polyethylene (PEgMA) as polymeric compatibilizer to produce a PEgMA-CNT masterbatch containing 20 wt% of CNTs. The masterbatch was then added to HDPE to prepare HDPE nanocomposites with CNT content of 2 or 6 wt%. The unmodified and modified (hydroxyl or amine groups) CNTs had similar effects on the properties of HDPE-PEgMA indicating that only non-covalent interactions were achieved between CNTs and matrix. According to SEM studies, single nanotubes and CNT agglomerates (size up to 1 μm) were present in all nanocomposites regardless of content or modification of CNTs. Addition of CNTs to HDPE-PEgMA increased decomposition temperature, but only slight changes were observed in crystallization temperature, crystallinity, melting temperature, and coefficient of linear thermal expansion (CLTE). Young’s modulus and tensile strength of matrix clearly increased, while elongation at break decreased. Measured values of Young’s moduli of HDPE-PEgMA-CNT composites were between the values of Young’s moduli for longitudinal (E₁₁) and transverse (E₂₂) direction predicted by Mori-Tanaka and Halpin-Tsai composite theories. Addition of CNTs to HDPE-PEgMA did not change the tribological properties of the matrix. Because of its higher crystallinity, PEgMA possessed significantly different properties from HDPE matrix: better mechanical properties, lower friction and wear, and lower CLTE in normal direction. Interestingly, the mechanical and tribological properties and CLTEs of HDPE-PEgMA-CNT composites lie between those of PEgMA and HDPE.     

Antibacterial activity of carbon nanoparticles isolated from chimney soot

Carbon nanoparticles (CNPs) are isolated from chimney soot and characterised by various tools such as X‐ray diffraction, scanning electron microscopy, transmission electron microscopy and ultraviolet–visible spectroscopy. The X‐ray diffraction studies confirm the presence of C₆₀ nanoparticles in the isolated sample. The thermal properties of the prepared CNPs are recorded using thermogravimetric analysis and differential thermal analysis. The analysis of the antibacterial activity of the synthesised CNPs against selected Gram‐positive and Gram‐negative bacterial strains is also investigated. The systematic study confirms that CNPs collected from chimney soot exhibit good antibacterial potency against Staphylococcus aureus, Streptococcus pyogenes, Klebsiella pneumoniae, and Proteus mirabilis.Inspec keywords: ultraviolet spectra, scanning electron microscopy, visible spectra, differential thermal analysis, thermal analysis, antibacterial activity, nanoparticles, X‐ray diffraction, nanofabrication, transmission electron microscopy, carbonOther keywords: chimney soot, transmission electron microscopy, ultraviolet–visible spectroscopy, thermal properties, thermogravimetric analysis, differential thermal analysis, antibacterial activity, carbon nanoparticles, X‐ray diffraction study, gram‐positive bacterial strains, gram‐negative bacterial strains, antibacterial potency, scanning electron microscopy, C₆₀      

Improvements in mechanical and thermo-mechanical properties of e-glass/epoxy composites using amino functionalized MWCNTs

The prime objective of this work is to optimize the mechanical and thermo-mechanical properties of e-glass/epoxy composites by utilizing amino-functionalized multi-walled carbon nanotubes (MWCNTs–NH₂) through a combination of dispersion method. At first, 0.1–0.4 wt.% of MWCNT–NH₂ was integrated into SC-15 epoxy suspension using a combination of ultra-sonication and calendaring techniques. E-glass/epoxy nanocomposites were than fabricated at elevated temperature with the modified resin using hand layup and compression hot press. 3-Point flexural and dynamic mechanical analysis (DMA) results demonstrated a linearly increasing trend in properties from 0 to 0.3 wt.% loading. Micrographs of MWCNTs incorporated epoxy and e-glass/epoxy samples revealed uniform dispersion of MWCNTs in epoxy, good interfacial adhesion between CNTs and polymer, and improved interfacial bonding between fiber/matrix at 0.3 wt.% loading. An improved dispersion and hence an improved crosslink interaction between MWCNT–NH₂ and epoxy lead to the stronger shift of the mechanical and thermo-mechanical properties of the composites.     

The interface electronic structure of thiol terminated molecules on cobalt and gold surfaces

The bonding strength and interfacial electronic properties of biphenyldimethyldithiol (HS–CH₂–C₆H₄–C₆H₄–CH₂–SH) adsorbed on Au(111) and polycrystalline cobalt are identified from combined photoemission and inverse photoemission. In order to develop a better understanding of the thiol functional group to metal surface interaction, the stable orientation, bonding site, bonding strength and interfacial electronic properties of methylthiol (S–CH₃) adsorbed on Au(111) and Co(0001) have been determined by ab initio density functional calculations. Both experiment and theory suggest that thiol bonding to cobalt surfaces is stronger compared to gold surfaces. The transfer of charge toward the adsorbed sulfur is greater for the thiols on cobalt than on gold.     

Properties of carbon nano-tubes–Cf/SiC composite by precursor infiltration and pyrolysis process

Carbon nanotubes (CNTs) were introduced into the precursor infiltration and pyrolysis (PIP) carbon fiber reinforced silicon carbide matrix (C_f/SiC) composite via the infiltration slurry. The weight fraction of CNTs in the composite was 0.765‰. The fiber–matrix interface coating was prepared through chemical vapor deposition (CVD) process using methyltrichlorosilane (MTS). Effects of the CNTs on mechanical and thermal properties of the composite were evaluated by three-point bending test, single-edge notched beam (SENB) test, and laser flash method. Attributed to the introduction of the small quantity of CNTs, flexural strength and fracture toughness of the C_f/SiC composite both increased by 25%, and thermal conductivity at room temperature increased by 30%.     

Evolution of interfacial nanostructures and stress states in Mg matrix composites reinforced with coated continuous carbon fibers

Magnesium (Mg) matrix composites reinforced with 45 vol.% continuous carbon fibers (C_f) were fabricated using a pressureless infiltration process in vacuum. In order to modify the interface between the C_f and the Mg matrix, the C_f were coated with 5.0 mol.% yttria stabilized zirconia (YSZ) in sol–gel route. The C_f/Mg composite exhibited a tensile strength of 1.08 GPa which reached 90% of the theoretical prediction by means of the rule of mixture. Microstructural examinations revealed the occurrence of interfacial reaction between the YSZ coating and the Mg matrix, producing a ∼20 nm thick interfacial reaction layer consisting of nanocrystalline particles, which include MgO particles, remaining ZrO₂ particles and a small quantity of ZrC particles. Interfacial reaction could induce a large compressive stress in the interfacial layer. As a result, some nanostructured defects, such as edge dislocations, were formed in interfacial layer due to the compressive stress. In the cooling process of fabricating the composite, the phase transformation of the remaining ZrO₂ from tetragonal to monoclinic could relax the thermal residual stress of interfacial layer.     

Multicolor luminescent carbon nanoparticles: Synthesis, supramolecular assembly with porphyrin, intrinsic peroxidase-like catalytic activity and applications

Luminescent carbon nanoparticles (CNPs) are newcomers to the world of nanomaterials and have shown great impact in health and environmental applications as well as being promising building blocks for future nanodevices because of their fascinating photoluminescence and potential to serve as nontoxic replacements for traditional heavy-metals-based quantum dots. Herein, fluorescent CNPs have been prepared from candle soot by refluxing with HNO₃ and subsequently separated by a single centrifugation. The CNPs can be represented by the empirical formula C₁H_0.677O_0.586N_0.015Na_0.069, and have a size of 20–100 nm, height of 3.0 nm, lifetime of 7.31 ns ± 0.06 ns and quantum yield of ∼1.7%. Further studies demonstrate that: (1) the as-prepared CNPs exhibit excellent stability in biological media and their luminescence intensity does not change with ionic strength or pH in the physiological and pathological range of pH 4.5–8.8; (2) CNPs can act as electron donors and transporters and porphyrin can assemble onto CNPs through electrostatic and π-stacking interactions to form porphyrin-CNPs supramolecular composites; (3) CNPs have strong intrinsic peroxidase-like activity. Based on this intrinsic peroxidase activity, a simple, cheap, and highly selective and sensitive colorimetric and quantitative assay has been developed for the detection of glucose levels. This assay has been used to analyze real samples, such as diluted blood and fruit juice.      

Multi-barrier layer-mediated growth of carbon nanotubes

Variation in the height of carbon nanotubes (CNTs) grown has been co-related to the type of multi-barrier-layer used. Initially, various types of barrier-layers such as Al, Al₂O₃, Al/SiO₂, Al₂O₃/SiO₂ were prepared onto a n-type Si (100) substrate. The thickness of SiO₂ was ∼ 550 nm, where as, Al₂O₃ and Al were ∼ 15 nm thick. These samples were covered with ∼ 1 nm thick Fe catalyst layer. The coated samples were subjected to the thermal chemical vapor deposition (T-CVD) process. SEM analysis showed that, for Al₂O₃/SiO₂ barrier layers, the average height of the CNTs was ∼ 10 μm, where as, for other types of samples it was less than ∼ 1 μm. To investigate this, multi-barrier layers were characterized by dynamic secondary ion mass spectrometry (D-SIMS). The observed variation in height of CNTs is attributed to the variation in diffusivity of Fe atoms into multi-barriers-layers. The results showed that, diffusion of Fe catalyst atoms could severally affect height of CNTs.