Dispersion Of CNTs Research Articles

Simultaneous improvement of electrical conductivity and mechanical property of Cr doped Cu/CNTs composites

Acquiring high electrical conductivity and good mechanical property is a key issue for Cu/CNTs composites, which affects their potential applications in electrical material field. In this study, Cr was induced in the Cu matrix to enhance the interfacial bonding. Different amounts of Cr were chosen to thoroughly investigate their effect on the interface structure, the electrical conductivity and the mechanical property. By tailoring the combined effects of good densification, uniform dispersion of CNTs, moderate amount of carbide at the Cu/CNTs interface, strong interfacial bonding force and suitable Cu matrix microstructure, the good overall performance was obtained in a (Cu-0.07 wt.%Cr)-0.5 wt.%CNTs composite. The addition of trace amounts of Cr leads to in-situ formation of an appropriate amount of nano chromium carbide (Cr3C2) at the Cu/CNTs interface, which improves the interface wettability and benefits the current transfer and load transfer, and hence improves the conductivity while increasing the hardness.

A comparative review of Mg/CNTs and Al/CNTs composite to explore the prospect of bimetallic Mg-Al/CNTs composites

Lightweight materials characterized by low density, high strength to weight ratio, low porosity, high corrosion resistance with improved mechanical, thermal, electrical properties are now extensively used in many engineering applications ranging from the deep sea to aerospace. Besides, the materials must be multifunctional comprises a fast and economic manufacturing technique. Metallic matrix CNTs composites such as Mg/CNTs and Al/CNTs have such the aforementioned quality. However, Mg/CNTs and Al/CNTs has some specific advantages and disadvantages that restrict their applicability. To harvest the dual benefit of Mg/CNTs and Al/CNTs, bimetallic matrix Mg-Al/CNTs may be prospected. Mg-Al bimetallic combination for alloying has substantial mechanical properties with heavy amalgamation. Therefore, interdisciplinary research on reinforcement, compacting, bonding, dispersion of CNTs in the bimetallic matrix, microstructure and defect analysis will open the door for producing new class of composite materials. In this work, various Mg/CNTs, Al/CNTs, Mg-Al composites have been studied to find the prospect of Mg-Al/CNTs composites. The worthwhile accomplishment of the reviews will provide the knowledge of fabrication for CNTs reinforced bimetallic Mg-Al based lightweight composites and understand its mechanical behaviors.

Performance evaluation of bitumen with a homogeneous dispersion of carbon nanotubes

Nano-modified bitumen binders can be tailored to exhibit excellent properties for potential application in pavement engineering. However, a homogeneous dispersion of nano-materials in bitumen is still a challenge, which obscures the maximum property improvement of bitumen that can be achieved. In this study, a CNT sponge, which is a macroscopic assembly of nanotubes and represents one of the most promising lightweight carbon nanomaterials with homogeneous three-dimensional network and a high porosity, was used to reinforce bitumen. Bitumen can autonomously penetrate into the porous CNT sponge, and fill up all the pores, forming a bitumen/CNT nanocomposite with homogeneous CNT dispersion quality. We found that, the addition of CNTs significantly improves the performance of bitumen at elevated temperatures, as indicated by the much improved properties of stiffness, rutting resistance, creep and recovery behavior as well as high-temperature stability. Such effective modification of bitumen by CNT are ascribed to the highly uniform dispersion of CNTs, as well as the percolation structure formed throughout bitumen matrix. This study highlights the importance of CNT dispersion quality, and sheds light on the bitumen property improvement that could be achieved.

Thermal conductivity improvement of heat-storage composite filled with milling modified carbon nanotubes

ABSTRACTCarbon nanotubes (CNTs) were modified through ball milling. The influence of the ball milling time on the dispersion of CNTs was studied. CNTs composite phase change materials (PCMs) were prepared with paraffin and the modified CNTs. The influence of the ball milling time on the thermal properties of the modified CNTs/paraffin was studied. Functional groups of the modified CNTs were tested by a Fourier Transform Infrared (FTIR). The microstructure of the modified CNTss was characterized by a scanning electron microscopy (SEM). The dispersion of CNTs in the molten paraffin was tested by an UV-visible spectrophotometer. A thermal constant analyzer was used to test the thermal conductivity of CNTs/paraffin. The results showed that the optimum time of ball milling of CNTs is 3 h, the thermal conductivity of paraffin was increased by 61% when paraffin was compounded by 1 wt% modified CNTs that were milled for 3 h. With the prolongation of milling time, the increase rate of thermal conductivity decreases gradually. The reason for this phenomenon is that, CNTs were damaged seriously and the dispersion of CNTs was decreased if the ball milling time is too long.

Poly(methyl methacrylate)-induced Microstructure and Hydrolysis Behavior Changes of Poly(L-lactic acid)/Carbon Nanotubes Composites

Poly(L-lactic acid) (PLLA)-based composites exhibit wide applications in many fields. However, most of hydrophilic fillers usually accelerate the hydrolytic degradation of PLLA, which is unfavorable for the prolonging of the service life of the articles. In this work, a small quantity of poly(methyl methacrylate) (PMMA) (2 wt%–10 wt%) was incorporated into the PLLA/carbon nanotubes (CNTs) composites. The effects of PMMA content on the dispersion of CNTs as well as the microstructure and hydrolytic degradation behaviors of the composites were systematically investigated. The results showed that PMMA promoted the dispersion of CNTs in the composites. Amorphous PLLA was obtained in all the composites. Largely enhanced hydrolytic degradation resistance was achieved by incorporating PMMA, especially at relatively high PMMA content. Incorporating 10 wt% PMMA led to a dramatic decrease in the hydrolytic degradation rate from 0.19 %/h of the PLLA/CNT composite sample to 0.059 %/h of the PLLA/PMMA-10/CNT composite sample. The microstructure evolution of the composites was also detected, and the results showed that no crystallization occurred in the PLLA matrix. Further results based on the interfacial tension calculation showed that the enhanced hydrolytic degradation resistance of the PLLA matrix was mainly attributed to the relatively strong interfacial affinity between PMMA and CNTs, which prevented the occurrence of hydrolytic degradation at the interface between PLLA and CNTs. This work provides an alternative method for tailoring the hydrolytic degradation ability of the PLLA-based composites.

Fabrication of Al5083 surface hybrid nanocomposite reinforced by CNTs and Al2O3 nanoparticles using friction stir processing

In the present study, friction stir processing was adopted for surface treatment of Al5083 by incorporation of CNT and Al2O3 nanoparticles. Microstructural, mechanical and tribological properties of the surface of Al5083/CNT, Al5083/Al2O3 and hybrid Al5083/CNT/Al2O3 nanocomposite were investigated and compared. The friction stir processing yielded a nearly uniform dispersion of CNTs and Al2O3 nanoparticles, irrespective of nanoparticle reinforcements and their weight fraction. Microstructural observations revealed that Al2O3 nanoparticles have dispersed in different zones including intra-grain and grain boundary zones while, CNTs are pinned into grain boundaries during friction stir processing. From mechanical point of view, hybridization of CNT/Al2O3 enhances the hardness (126 HV at stirred zone), strength (UTS of ∼487 MPa) and also wear resistance of Al5083/CNT/Al2O3 nanocomposites. The enhancement is attributed to the presence and combination of features of both CNT and Al2O3 nanoparticles which are different in nature; one spherical oxide and one nanotube.

AC susceptibility investigation of YBCO superconductor added by carbon nanotubes

We report in this investigation the preparation as well as characterization of bulk YBa2Cu3O7-δ superconductor produced by solid state reaction route and added by various amount (x) of CNTs (x = 0.0, 0.1 and 1.0 wt%). The analysis of X-ray diffraction (XRD) indicated the achievement of orthorhombic structure of YBCO phase for various sintered samples. No relevant variations in the lattice parameters is observed with CNTs inclusion. The analysis of microstructure revealed a dispersion of CNTs into YBCO and presence of lattice defects for CNTs added samples. We evaluated the impacts of CNTs on inter-granular traits of YBCO using AC susceptibility measurements. Various superconducting parameter including critical temperature (Tc), inter-granular critical current density (Jc inter), grain volume fraction (fg), grains susceptibility (χg) and matrix susceptibility (χm) were estimated and deeply discussed. The obtained results confirm that the CNTs addition has a beneficial role on the inter-granular properties of YBCO system. Also, the critical current density Jcm was determined and its value has been shown to be greatly enhanced with the addition of CNTs in the existence of the applied magnetic field.

Effects of aligned carbon nanotube microcolumns on mechanical and thermal properties of C/SiC composites prepared by LA-CVI methods

Herein, C/SiC-CNTs composites were prepared by laser assisted chemical vapor infiltration (LA-CVI) method combined with vacuum impregnation. Density, mechanical property and thermal conductivity of as-prepared composites were then investigated by various analytical methods. Scanning electron microscopy (SEM) revealed good dispersion of CNTs in C/SiC-CNTs between composites layers and directional heat transfer channels. This formed unique three-dimensional connected networks, reinforcing multi-scale composites matrix. Average density and bending strength of composites were estimated to 2.35 g cm−3 and 598 MPa, respectively, which is 20.5% and 27.2% higher than those of CVI-C/SiC composites. The comparison between theoretical thermal conductivity and experiments revealed that the overall thermal conductivity of LA-CVI-C/SiC-CNTs composites (150.42 W m−1 K−1) was nearly 25 times higher than that of CVI-C/SiC composites.

Modeling of CNT-reinforced nanocomposite with complex morphologies using modified embedded finite element technique

In this article, we overcome the limitations of traditional finite element (FE) method in modeling CNT-reinforced nanocomposites with complex morphologies by developing a modified embedded finite element (mEFE) method. The composite constituents in the mEFE model are discretized independently but simulated simultaneously as a coupled system. The major advantage of this approach is discretizing the matrix as a regular grid, irrespective of the complex nature of the CNT network. The developed modeling approach allowed us to simulate realistic representative volume elements (RVEs) containing randomly dispersed CNTs of different curvatures, orientations, aspect ratios and volume fractions. An advanced Monte Carlo based algorithm was also developed to generate complex CNT networks. The proposed mEFE method requires a significantly shorter preprocessing effort and is more computationally efficient when compared to traditional FE method. It allowed us to study large scale RVEs reinforced with high CNT concentrations. The results of this idealised case showed that the elastic modulus of the nanocomposite increases with increasing the volume fraction of the CNTs; reaching 200 % improvement at 5 % volume fraction. However, the enhancement in the properties was not obvious at higher concentrations due to the poor dispersion and agglomeration of the dispersed CNTs.

Interdependence of carbon nanotubes agglomerations, its structural integrity and the mechanical properties of reinforced nickel aluminide composites

Spark plasma sintered NiAl-CNTs intermetallic composites were fabricated via two different ball milling processes. One comprising of an exclusive low energy ball milling (LEBM), and the other comprising of a two-stage milling, typically a prolonged LEBM with a short term high energy ball milling (HEBM). The differently milled powders were consolidated, and the resulting composites characterized. This was done to determine the individual effects of agglomerations vis-à-vis the structural integrity of the nanotubes. The composites were extensively characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy (RS), scanning electron microscopy (SEM) and nanoindentation techniques. The uniform dispersion of slightly impaired CNTs led to better mechanical properties as compared to the in-homogenous dispersion of higher structural integrity CNTs in the NiAl intermetallic matrices. Results showed that the sample with a two-stage milling exhibited superior mechanical properties in terms of hardness, elastic modulus and fracture toughness with 422.79 Hv, 50.5 GPa and 9 MPa√m respectively.

Conductive and flexible multi‐walled carbon nanotube/polydimethylsiloxane composites made with naphthalene/toluene mixture

ABSTRACTConventional conductive materials face challenges when utilizing them for flexible and wearable electronics and soft robotics. Carbon nanotube/polydimethylsiloxane (CNT/PDMS) composites are a promising alternative to the conventional hard conductors because they are light and can realize large deformation. To date, well dispersion of CNTs into PDMS to increase conductivity while maintaining flexibility remains challenging. We aimed at developing highly electrically conductive and flexible multi‐walled carbon nanotube/PDMS (MWCNT/PDMS) composites. To this end, we proposed a method to enhance the dispersion of MWCNTs into PDMS using naphthalene and toluene. Our results showed that the addition of naphthalene and toluene into the composites improved dispersion of the MWCNTs and increased the direct current (DC) electrical conductivity. We also found that the morphology of primary aggregates of the MWCNTs influenced the DC electrical conductivity of the composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48167.

A Comparison Study of Ag Composites Prepared by Spark Plasma Sintering and Hot Pressing with Silver-Coated CNTs as the Reinforcements.

In this study, carbon nanotube-reinforced silver composites (CNT/Ag) were prepared by the powder metallurgy process via spark plasma sintering (SPS) and hot pressing sintering (HP) with composite powders through an improved electroless plating method assisted by ultrasonic spray atomization. The dispersion of CNTs was effectively improved by ultrasonic spray atomization, and uniform silver layers were deposited on the surface of CNTs by electroless deposition. The property testing results showed significant improvements of the electrical conductivity, hardness, and tensile strength in the samples prepared by SPS, as compared to their HP sintered counterparts. When the volume fraction of CNTs reached 2.5%, the tensile strength reached a maximum value of 221 MPa, which was more than twice that of the pure silver samples. The structural analysis indicated different degrees of CNT agglomeration and matrix mean grain sizes in the composites prepared by SPS and HP, which are responsible for the differences in properties.

Al–CNT–Ni composite with significantly increased strength and hardness

In this study, aluminium–carbon nanotube–nickel (Al–CNT–Ni) composite was prepared by powder metallurgy from pure Al powder and Ni-encapsulated CNT. Previously, carbon nanotubes were coated with nickel following ultraviolet-assisted electroless deposition method. Tensile strength and hardness of the composites were found to increase in proportion to the CNTs addition. For an addition of 7 wt.% Ni-coated CNTs containing 2.5 wt.% nanotubes of 8–15 nm diameter (Ni to CNT ratio was 1–0.357), resultant tensile and yield strength were increased by 129.26% and 157.48% respectively compared to pure aluminium. Hardness was also increased by 171.39%. These results were obtained while conventional sintering was followed by further consolidation by Hot Isostatic Pressing (HIP). Enhanced mechanical properties are attributed to the well dispersion of CNTs in aluminium matrix and strong interfacial bonding between CNT and aluminium. Well dispersion of CNTs and strong interfacial bonding was resulted from the uniform Ni-encapsulation as verified by red shift in Raman Spectroscopy.

Tailoring and characterization of carbon nanotube dispersity in CNT/6061Al composites

The dispersity of carbon nanotubes in CNT/6061Al composites was tailored by varying the pre-dispersion state of CNTs on Al spherical powders, which was controlled by the high-shear pre-dispersion process. The difference in the dispersity and structural integrity of carbon nanotubes and the degree of interfacial reaction in the composites were analyzed by Raman spectroscopy mapping. The results show that Raman spectroscopy mapping is sensitive and can be used as a mesoscopic tool to evaluation of the overall status of CNTs in the composite. It also show that the slight adjust of the pre-dispersion state of the CNTs can achieve an improvement of tensile strength up to about 50 MPa. Specifically, under appropriate pre-mixing speed which makes CNTs partially embedded in the surface of Al powders, uniform dispersion of CNTs and good interface bonding can be simultaneously achieved, resulting in higher strengthening effect and good ductility.

Effect of CNT dispersion methods on the strength and fracture mechanism of interface in epoxy adhesive/Al joints

The tensile and shear strengths of adhesively bonded aluminum (Al) joints were inspected in the presence of amino functionalized multi-wall carbon nanotubes (MWCNTs). Tensile and shear tests were carried out using butt and lap-shear joints. The main goal was to compare the effects of dispersion methods of functionalized-CNT into epoxy on the mechanical performances and failure mechanisms of Al joints. Two different types of dispersion procedures, distributing CNT in the hardener (HH method) and distributing CNT in the resin (RR method), were applied. To identify the failure mechanisms, the morphology of fracture surfaces were analyzed using scanning electron microscopy (SEM). Comparing two dispersion methods against one another ascertained that following the RR method for dispersing CNTs in the adhesive displayed larger shear strength, while applying HH method offered fairly greater tensile strength. Moreover, dispersing CNTs in the resin induced more uniform dispersion of CNTs as compared to distributing nanofillers in the hardener. Following RR method, CNTs good dispersion as well as the presence of effective crack growth dissipating mechanisms, increased the shear strength of CNT reinforced adhesive joint. Incorporating CNTs using HH approach encouraged the plastic void formation of epoxy around the agglomerated CNTs, and as a consequence, promoted the plastic deformation under tension.

A study on the effect of carbon nanotube surface modification on mechanical and thermal properties of CNT/HDPE nanocomposite

In this article, the effect of carbon nanotube’s (CNT) surface modification on mechanical, thermal, and morphological properties of nanocomposite with different content of CNTs was studied. CNT/high-density polyethylene (HDPE) nanocomposites were prepared by a mini twin-screw extruder. To modify the dispersion of MWCNTs in HDPE, the surface of CNTs was functionalized by HNO3 and stearic acid (SA). The tensile tests results show that addition of 5% of acid-treated CNT in HDPE cause to increase in Young’s modulus and yield strength up to 4% and 6%, respectively; as compared to unmodified CNT/HDPE nanocomposite. The presence of the SA on CNTs can lead to slight decrease of the CNT-SA/HDPE strength properties; when compared to pure CNT/PE nanocomposite. However, there is a fracture toughness enhancement in CNT-SA/HDPE up to 10% compare to unmodified CNT/PE nanocomposite. Furthermore, the calculation of the stress whitening zone of all samples verifies the fracture toughness data of CNT/HDPE nanocomposites. Scanning electron microscopic images showed that the best dispersion of CNTs in the HDPE matrix was seen in CNT-SA/HDPE nanocomposite.

Hot rolling of MWCNTs reinforced Al matrix composites produced via spark plasma sintering

Aluminum/CNT nanocomposite sheets, with appropriate dispersion and interfacial bonding, were fabricated by a combination of powder metallurgy, spark plasma sintering (SPS), and hot rolling. The effects of CNT content as well as plastic deformation, on the microstructure and mechanical properties of the obtained nanocomposite, were investigated. The composite reinforced by 0.5 wt.% CNTs showed an optimal dispersion of CNTs into the aluminum matrix after both SPS and hot rolling. Minimum CNT damage and minimum carbide formation were observed after hot rolling. The best comprehensive mechanical properties corresponded to the sheet of Al-0.5 wt.% CNT nanocomposite thanks to the strong interfacial bonding between Al and CNTs, full densification of the nanocomposites as well as the uniform dispersion of the CNTs into the aluminum matrix. Hardness measurements showed that the maximum hardness was obtained for sheets containing 1.5 wt.% CNTs in both the as-SPS and the as-hot rolled conditions. Load transfer, Orowan, and grain size strengthening mechanisms could affect the increase of strength as well as the combination of strength and ductility of the sheets of Al-CNT nanocomposites.

Quaternized chitosan/functionalized carbon nanotubes composite anion exchange membranes

ABSTRACTNatural alkaline polyelectrolyte chitosan has been considered to be a promising anion exchange membrane (AEM) material due to its low cost and easy quaternization. To further improve the ionic conductivity and mechanical property of quaternized chitosan (QCS), QCS functionalized carbon nanotubes (QCS@CNTs) were prepared and used as a novel nanofiller to modify the membrane matrix. The QCS coating layer on the surface of CNTs can not only improve the dispersion of CNTs and thus promote the load transfer from the QCS matrix to stiff CNTs, but also endow CNTs with a certain hydroxide ions exchange ability. The results show that the addition of QCS@CNTs slightly decreased the ionic conductivity of the composite membranes while the tensile strength and alkaline stability of these membranes were significantly improved, indicating the potential application of these composite membranes in AEM fuel cells. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2019,136, 47778.

Defect detection of composite adhesive joints using electrical resistance method

Mechanical joint and adhesive bonding are two typical joining methods for composite materials. The bolt fastening method is reliable but increases the weight of the structure and cuts the composite fiber, which may cause stress concentration and strength degradation. The adhesive bonding method has a higher bonding strength than the mechanical fastening, but the bonding strength can deteriorate depending on the various parameters that influence the environmental conditions and manufacturing process. In addition, bonding defects due to the presence of foreign substances on the bonding surface or immature surface treatment is called a Kissing Bond, and can significantly reduce the bonding strength. The electrical resistance method is a very promising technique for detecting kissing bond defects by measuring the electrical characteristics after the dispersion of CNTs in the adhesive.In this study, composite-to-composite single-lap joint specimens with CNTs were fabricated and the defect detection capability and the static strength of composite joints were evaluated using the electrical resistance method. A carbon/epoxy composite was used as an adherend and the electrical resistance of the adhesive joint was measured by varying the content of CNTs to 0.5 wt%, 1.0 wt%, and 2.0 wt%. The AC and DC resistance values of composite adhesive joints with artificial defects were measured using an LCR meter and a high-resistance meter, and their lap shear strengths were evaluated.

A novel coupling of [formula omitted] hybrid nanofluid for improvements in heat transfer for flow in an asymmetric channel with dilating/squeezing walls

Hybrid nanofluid is an advanced version of a nanofluid, which significantly boosts the heat transport mechanisms. Therefore, this can be considered a new alternative source to the traditional ways (involving certain fluids or nanofluids) of heating or cooling. The main concern of this manuscript is to scrutinize the flow field and heat transfer phenomena, for the flow of a hybrid (CNT-Fe3O4/H2O) nanofluid, inside an asymmetric long channel, whose porous walls exhibit embracing or parting motion. The equations, corresponding to the mass, momentum and energy conservations, have been modeled accordingly and after this, by making use of similarity transformations, a relevant set of nonlinear ordinary differential equations have been successfully achieved. In order to devise a numerical solution of the consequent equations, shooting method coupled with Runge–Kutta–Fehlberg algorithm have been employed. Furthermore, a graphical aid, to interpret the influential behaviors of various emerging entities on the velocity and temperature distributions, have also been provided. The dispersion of CNTs in (Fe3O4/H2O) nanofluid, have a considerable impact on the flow, temperature and heat transport properties, and these variations can be clearly visible at the both walls. Moreover, it has been observed that the SWCNTs, in most of the cases, seem to have a greater impact on the temperature profile as well as on the heat transport phenomenon.