Stability Of Carbon Nanotubes Research Articles

Synergistic effect of carbon nanotubes and polyvinyl alcohol on the mechanical performance and microstructure of cement mortar

Abstract Herein, carbon nanotubes (CNTs) and polyvinyl alcohol (PVA) were used as hybrid modifiers to enhance the mechanical properties of cement mortar and overcome the limitations of modification methods based on only polymers and nanomaterials. The use of PVA latex as a bridging agent with the aid of ultrasound energy effectively improved the dispersion uniformity and stability of CNTs. The results indicate that doping an appropriate amount of PVA in CNT-modified cement mortar, especially those modified with hydroxylated CNTs (h-CNTs), could synergistically improve performance. Amongst the samples, the h-CNT-modified cement mortar incorporated with 1 wt% PVA showed the optimal mechanical properties. The compressive and flexural strengths of this cement mortar increased by 33 and 42%, respectively, compared with those of cement mortars modified with h-CNTs alone. The microscopic characterisation results showed that the formation of a uniformly distributed h-CNT/PVA film network in the matrix effective filling of pores and bridging of cracks were responsible for performance enhancement.

Carbon nanotubes anchored SiOx composite anode for high cyclic stability lithium-ion batteries

Silicon suboxide (SiOx, 0 < x < 2) is one of the most promising anode materials because of its high lithium-ion storage capacity. However, the poor intrinsic conductivity and large volume change during cycling limits its practical application as lithium-ion battery anode materials. Herein, we propose a novel strategy to introduce carbon nanotubes (CNTs) on the SiOx particles, forming a conductive network and relieving the volume expansion effect, which possess improved reversible capacity and robust structure for long cycling stability. The SiOx/CNT composite anode delivers reversible capacity of 1533.8 mAh g−1 at the first cycle and maintains 599.6 mAh g−1 after 500 cycles with a high coulombic efficiency of 99.7 %. In this paper, SiOx composite anchored by CNTs was prepared, which is a simple and effective strategy to improve the conductivity of SiOx, relieve the volume effect and further promote its electrochemical performance benefit from the high conductivity and structural stability of CNTs. This research provides a significant reference for constructing the delicate structure of SiOx-based composites to enhance cyclic performance.

Advance processing of cluster-free CNT reinforced 6082 Al matrix nanocomposites: influence of mechanical milling and cryomilling

ABSTRACT In the present study, lightweight high-strength carbon nanotubes (CNTs) reinforced aluminium-based composite was fabricated through powder metallurgical processing. The effect of planetary milling and cryogenic assisted milling on the structure, morphology, mechanical properties, phase composition, and thermal stability of CNTs reinforced Al6082 Al nanocomposites powders was investigated using X-ray diffraction (XRD), scanning electron microscope (SEM)- Energy dispersive spectroscopy (EDS), transmission electron microscope (TEM), and indentation techniques. The CNTs in the Aluminium (AL) matrix were distributed uniformly after 50 h of milling. Further, the cryomilling of 50 h milled Aluminium matrix composites (AMC) decreases agglomeration even more and was successful in cleaving the nanotubes as well as minimising entanglements. The broadening of diffraction peaks suggests a reduction in the crystallite size (from ~36 to ~20 nm) and an increase in induced strain. Milled powders were consolidated through the hot-press and spark plasma sintering technique. The mechanical properties of these AMCs were evaluated through indentation for hardness (>250 HV) and compressive testing techniques. SPSed samples reported better properties in comparison to hot-pressed samples. It is discovered that post-CM of Mechanical Milling (MM) powder aids in overcoming issues related to the agglomeration of Al/CNT composites, and the goal to fabricate tangle-free CNT reinforced composite was achieved. Moreover, it showed enhanced mechanical properties with a maximum yield strength of 210 MPa and good synergy between strength and ductility.

Dispersion Stability of Carbon Nanotubes and Their Impact on Energy Storage Devices

Carbon nanotubes (CNTs), with their extraordinary combination of mechanical, electrical, and thermal properties, have emerged as a revolutionary class of nanomaterials with immense potential in energy storage and harvesting devices. Realizing this potential hinges on a fundamental challenge: the dispersion stability of CNTs within various matrices. This review paper provides a comprehensive exploration of the critical interplay between CNT dispersion stability and its far-reaching implications for the performance of energy storage and harvesting technologies. By delving into the underlying mechanisms of dispersion, the strategies to achieve stability, and the direct effects on device functionality, this review sheds light on the intricate relationship between nanotube dispersion and the advancement of energy-related applications.

Influence of one-pot and two-step preparation on the quality of carbon nanotubes using pine sawdust as the catalyst support

In this paper, a novel low-cost process for preparing carbon nanotubes (CNTs) by loading transition metals (Fe, Co, Ni) on carbon materials (pine sawdust) is investigated. Among three metal catalysts, nickel catalyst exhibits the best catalytic performance including the highest carbon yield (23.8 wt%) and the best quality of the grown CNTs (ID/IG = 1.01). Meanwhile, the nickel content of 2.5 wt% was confirmed to be the most suitable metal content for CNTs growth. Based on the prepared CNTs with pine sawdust as the catalyst support, the two-step method and the one-pot method were proposed. In the two-step method, the Ca(OH)2 powder as a reactive assistant and the introduction of CO2 can obtain CNTs with the least defects and the highest purity. The comparative experiments show that the mere introduction of CO2 without any reactive assistants will cause greater damage to CNTs. In the one-pot method, the addition of Ca(OH)2 improves the quality and thermal stability of CNTs, which verifies the feasibility of the one-pot method reported in this study.

Rapid room temperature degradation of carbon nanotubes by sodium hypochlorite and UV-light irradiation

Due to their unique graphitic tubular structures, carbon nanotubes (CNTs) are chemically and mechanically stable, and thus not easily degradable, which is a major safety concern for their wide and environmentally friendly use. In this study, we report the rapid degradation of single-wall CNTs (SWNTs) into carbon dioxide at room temperature using sodium hypochlorite (NaClO) and UV-light irradiation (UV/NaClO). The results showed that SWNTs could be degraded within 1–2 h, compared with >1 week without light irradiation. No obvious light dependence was observed for SWNT degradation using monochromatic light sources at 245 nm, 365 nm, and 305 nm. Raman and Fourier-transform infrared spectroscopies and scanning electron microscopy with energy dispersive spectroscopy revealed that degradation of SWNTs involved a multi-step oxidation reaction. Irradiation of NaClO induced the formation of oxygen radicals, which reacted with SWNTs to generate epoxy and ether groups. These groups then reacted with the oxygen radicals to form carboxylic groups, which introduced defects into SWNTs. Carboxylic and/or ether groups were directly transformed to CO2, or into intermediate products such as ethylene glycols, as oxidation progressed. The findings improve our understanding of the stability of CNTs and demonstrate a potential route for the rapid treatment of CNT wastewater for safe handling, disposal, and risk management.

Numerical thermal analysis of armchair (6,6) and zig-zag (12,0) carbon nano-tubes (CNTs)

In this study, the thermal behaviour of small-sized single-atom CNTs was examined. CNTs are composed of crystals that form a nanostructure with different geometric shapes by arranging them in different ways according to the length-diameter ratio. Due to the mechanical, electrical, and thermal properties of CNTs, the thermal conduction of CNT materials is critical in controlling the performance and stability of CNTs. CNTs, which are low-dimensional materials with a single atomic layer thickness, have excellent thermal conductivity. According to the simulation technique in ANSYS, CNTs containing the same number of atoms and bonds were developed. The heat transfer of different structures of CNTs in armchairs (6,6) and zig-zag (12,0) were compared. A comparison of zig-zag and armchair CNTs thermal behaviour shows that zig-zag CNTs lattice structure has more advantages than armchair CNTs lattice structure by heat transfer. Highlights In this study, finite element-based thermal analysis of single and double-walled armchair and zig-zag carbon nano-tubes (CNTs) using the lattice method was investigated. A simulation technique was developed and applied in the ANSYS program for single and double-walled carbon nanotubes (CNTs). Armchairs (6,6) and zig-zag (12,0) CNTs in different lattice structures with equal atomic numbers and bond numbers are modelled according to different diameters and length ratios. The CNTs, which have the same material properties as the trays placed at both open ends of the pipes, are kept at different temperature values, and conduction heat transfer behaviour is investigated for certain temperature values. According to the investigated heat conduction behaviour of zig-zag and armchair CNTs, the lattice structure of the zig-zag carbon nano-tubes is more advantageous in terms of heat conduction than the cage structure of armchair CNTs, and it transmits heat faster than the armchair CNTs.

Carbon nanotubes doped with nitrogen, modified with platinum or platinum-free for alkaline H2-O2 fuel cell

A series of cathodic and anodic catalysts for alkaline H 2 -O 2 fuel cells (FC) deposited on the surface of functionalized and nitrogen-doped carbon nanotubes (CNT) was synthesized and studied by various structural and electrochemical methods. It was established that, due to the minor defect structure, CNT NaOH (functionalized in alkali) exhibit high corrosion stability. A further increase in the activity in the oxygen reduction reaction (ORR) and the stability of CNTs is observed following their doping with nitrogen. The high activity of CNT NaOH+N is attributed to pyridine groups and the increased electrical conductivity of this catalyst. It was shown that CNT NaOH comprise effective substrates for hydrogen oxidation reaction catalysts. The PtMo/CNT NaOH system containing 12 wt.% Pt at a molar ratio of PtMo=1:1 is characterized by the highest catalytic activity among investigated anode platinum and non-platinum catalysts. The use of this catalyst made it possible to reduce the content of platinum to 0.1-0.2 mg/cm 2 , while preserving the characteristics that significantly exceed those of the active layer containing 60Pt/C (HiSPEC 9100) catalyst (0.6 mgPt/cm 2 ).

The thermal conductivity improvements of phase change materials using modified carbon nanotubes

This paper describes a new method of modified carbon nanotubes (CNTs) by ethylene grafting or silicon coating. The thermal conductivity of paraffin is enhanced by the modified CNTs. The influence of modification on the dispersion stability of CNTs and the thermal conduction performance of paraffin are studied. Fourier transform infrared spectroscopy, scanning electron microscopy, thermal constant analyzer are used to analyze the composites. The results indicate that CNTs have been modified successfully. The dispersion stability of CNTs is significantly improved by polyethylene grafting or silicon coating. The thermal conductivity of paraffin phase change material is enhanced by 84.6% with the modified CNTs. The prepared paraffin/CNTs phase change materials show good thermal conductivity.

Novel Terahertz Spectroscopy Analysis for the Electrode with Carbon Nanotubes (CNTs) in Lithium-Ion Batteries

In this study, to use carbon nanotubes (CNTs) as a conductive material instead of carbon black in cathode electrodes, their dispersions were prepared in 1-Methyl-2-pyrrolidinone (NMP) solvent by using an ultrasonic horn, and their dispersion stability was analyzed using CNTs on the formation of the network between cathode electrode constituent materials comprised of cathode material, CNTs, and current collectors, and their correlation with electrochemical performance results were investigated using various analytical techniques. Particularly, in the analysis, terahertz time domain spectroscopy (THz-TDS), a new non-destructive analysis method, was used to analyze and compare the various optical properties of the cathode’s slurries that co-existed with CNTs and cathode material, suggesting the suitability of its analytical use in the field of materials dispersion and the slurry manufacturing process for lithium-ion batteries (LIBs). In the investigated results, the sample with the highest dispersion stability of CNTs uniformly formed the networks of CNTs and cathode material in the electrode, which results in the highest electrical conductivity among all samples, and as a result, the best performance in electrochemical evaluations.

Highly enhanced microwave absorption for carbon nanotube/barium ferrite composite with ultra-low carbon nanotube loading

• A facile approach for fabricated carbon nanotube (CNT)/barium ferrite (BaFe 12 O 19 ) composite with good dispersion of carbon nanotube was developed. • In view of the thermal stability of CNT in different atmosphere and the formation mechanism of BaFe 12 O 19 , uniform dispersion of CNT was achieved in the CNT-BaFe 12 O 19 composite. • The as-prepared CNT/BaFe 12 O 19 composite exhibits excellent microwave absorption ability. Barium ferrite (BaFe 12 O 19 ) is considered as potential microwave absorption (MA) material thanks to the large saturation magnetization, high Curie temperature, and excellent chemical stability. The integration of carbon nanotube (CNT) can improve the dielectric loss of BaFe 12 O 19 for further enhanced MA performance, nevertheless, the MA performance is still not desirable because of the poor CNT dispersion in the CNT/BaFe 12 O 19 composites, which usually prepared via the ball-milling method, unless high CNT loading was used. Herein, according to the thermal stability of CNT in different atmosphere and the formation mechanism of BaFe 12 O 19 from precursor, CNT was introduced in the precursor of BaFe 12 O 19 uniformly during auto-ignition process and calcined under different atmosphere. When CNT loading is only 2.0 wt%, the CNT/BaFe 12 O 19 composites obtained exhibits a minimum reflection loss ( R L min ) of -43.9 dB and effective bandwidth (with RL < -10 dB) of 3.9 GHz with the thickness of 1.5 mm, which are much superior to -10.2 dB and 2.2 GHz for pure BaFe 12 O 19 , and -13.6 dB and 2.5 GHz for CNT/BaFe 12 O 19 composite prepared by ball-milling method. These results may pave the way to design high-performance BaFe 12 O 19 based microwave absorbers.

Thermoelastic stability of CNT patterned conical shells under thermal loading in the framework of shear deformation theory

This study presents the thermoelastic stability of carbon nanotube (CNT) patterned composite conical shells in the framework of shear deformation theory (ST). The study includes two different boundary value problems. As the material properties are independent of temperature, the truncated conical shell is assumed to be under thermal load, and when the material properties are temperature dependent, the conical shell is assumed to be under axial compressive load. The modified Donnell-type shell theory is used to derive the basic equations for CNT patterned truncated conical shells. The Galerkin method is applied to the basic equations to find the critical temperature and critical axial load expressions of CNT patterned composite truncated conical shells in the framework of ST. The effect of changes in CNT patterns, volume fraction, radius-to-thickness and length-to-thickness ratios, as well as the half-peak angle on critical parameters within the ST, are estimated by comparison with classical shell theory (CT).

A low-temperature operated in situ synthesis of TiC-modified carbon nanotubes with enhanced thermal stability and electrochemical properties.

Carbon nanotubes (CNTs) with superior thermal and electrochemical properties are desirable for a large variety of applications. Herein, an in situ synthesis carried out at 1050 °C is proposed for the realization of titanium carbide (TiC) modified CNTs (TiC@CNTs) via a carbothermal treatment of the TiO2-coated CNTs deposited by a TALD technology, preserving the structural morphologies of CNT samples. Crystalline and amorphous TiC layers/nanoparticles are observed around the walls of CNTs, serving as a thermal insulation layer to enhance the thermal stability of CNTs. The TiC@CNT sample exhibits a minimal mass loss of 3.1%, which is 20.9% and 82.3% for the TiO2@CNT and pristine-CNT samples, respectively. In addition, the TiC@CNT electrode shows good energy storage performances, with a specific capacitance of 2.83 mF cm−2 at 20 μA cm−2, which is about 3.5 times higher than that of the pristine-CNT electrode, showing the potential of TiC@CNTs as next-generation electrode materials.

Effect of surfactant concentration on the evaporation-driven deposition of carbon nanotubes: from coffee-ring effect to strain sensing.

Carbon nanotubes (CNTs) as electrically conductive materials are of great importance in the fabrication of flexible electronic devices and wearable sensors. In this regard, the evaporation-driven self-assembly of CNTs has attracted increasing attention. CNT-based applications are mostly concerned with the alignment of CNTs and the density of CNT films. In the present work, we focus on the latter by trying to achieve an optimal evaporation-driven deposition with the densest CNT ring. Although surfactants are used for effective dispersion and colloidal stabilization of CNTs in the aqueous phase, their excessive usage induces Marangoni eddies in the evaporating sessile droplets, leading to poor ring depositions. Thus, there is an optimum surfactant concentration that contributes to CNTs deagglomeration and results in the densest ring-like deposition with relatively high thickness. We report that this optimum concentration for sodium dodecyl sulfate (SDS) as a surfactant can be approximately considered as much as the concentration of multi-walled carbon nanotubes (MWCNTs) as the colloidal nanoparticles. Optimal depositions show the lowest electrical resistances for each CNT concentration, making them suitable for electronic applications. We also propose the multiple depositions method in which a new droplet is printed after the complete evaporation of the previous droplet. This method can lead to denser rings with a higher conductivity using lower concentrations of CNTs. Lastly, we fabricate strain sensors based on the optimal evaporation-driven deposition of CNTs which show higher gauge factors than the commercial strain gauges, corroborating the applicability of our method.

Thermal-magneto-mechanical stability analysis of nanofluid conveying carbon nanotubes based on nonlocal couple stress theory

Carbon nanotubes (CNTs) have extensive biomedical applications in which a heat pulse is applied to the CNTs. The present study encompasses the novelty by focusing on the complicated effect of thermal loads and heat generation on the CNT stability with the aim of preserving and improving the stability. There is also a lack of research that evaluates the size-dependence using appropriate robust non-classic theory, which is incorporated by employing a hybrid method of nonlocal couple stress theory and nonlocal elasticity theory. Additionally, Euler–Bernoulli beam theory is employed for coupling the Navier–Stokes equation of magnetic-fluid flow with the CNT deformation. The CNT stability is evaluated by considering nonlocal and couple-stress sizing effect parameters, Knudsen number, magnetic field intensity, thermal effect, heat generation, and fluid flow velocity. Results indicate that, by rising the temperature gradient and the couple stress sizing effect parameter, the system stability is improved up to 19.07% and 16.58%. Whereas, by increasing the heat generation, the dimensionless critical velocity shows 6.91% decrease, which deteriorates the CNT stability. Results of the present study demonstrates that in CNT applications with the presence of thermal loads, neglect of thermal effects leads to misinterpretation of the system stability.

Sub‐micron calcium carbonate isolated carbon nanotubes/polyethylene composites with controllable electrical conductivity

AbstractThe dispersion and distribution of carbon nanotubes (CNTs) on/in the polymer composites are greatly affected by the molding technology progress, which results in different electrical conductivity. The uncontrollable electrical conductivity has limited the application of conductive polymer composites, for example, sensor components. In this work, to enhance the dispersion stability of CNTs in polyethylene (PE) matrix, sub‐micron calcium carbonate isolated CNTs (smCaCO3@CNTs) were selected based on the fact that smCaCO3 is much easier to disperse in polymer in comparison with CNTs. This good distribution of CNTs in smCaCO3@CNTs/PE was characterized by transmission electron microscope and Raman mapping. The electrical performance test results show that when 0.5 wt% of CNTs filled in smCaCO3@CNTs/PE, the percolation network begins to form; when CNTs filled increases to 1‐2 wt%, the surface resistance of smCaCO3@CNTs/PE ranges from 106 to 109Ω almost not affected by the molding technology process (compression molding or injection molding). The possible reason is that the isolated CNTs by smCaCO3 in polymer matrix are favorable for the formation of the stable conductive network.

Endohedral Fe3C decorated multi-walled CNTs as an efficient electrocatalyst for oxygen evolution

The design and fabrication of high-performance and low-cost electrocatalysts for the oxygen evolution reaction (OER) are highly desirable towards the next-generation energy storage and conversion technologies. Carbon nanotubes (CNTs), the typical non-precious metal-based catalyst, have drawn significant attentions in electrochemical OER, whereas their low catalytic performance and cumbersome synthesis route seriously prohibit the scalable applications in OER. In this study, a facile and economical strategy (namely, the simple one-step pyrolysis of Fe(C5H5)2) was dedicatedly exploited for successfully producing CNTs encapsulated with Fe3C nanoparticles (NPs). It is found that encapsulated Fe3C NPs significantly enhance the alkaline OER activity and the stability of CNTs. Our experimental investigations indicate the active sites of this Fe3C@CNTs electrocatalyst for OER are the oxygen-containing functional groups bonding to the surface of CNTs. The interaction between Fe3C NPs and CNTs boosts the OER activity and the stability of CNTs. In sum, the simple and low-cost synthetic strategy of Fe3C@CNTs combined with its excellent catalytic performances prompts it promising for future practical OER.

Analysis of the Storage Stability Property of Carbon Nanotube/Recycled Polyethylene-Modified Asphalt Using Molecular Dynamics Simulations.

Carbon nanotubes (CNTs) can improve the storage properties of modified asphalt by enhancing the interfacial adhesion of recycled polyethylene (RPE) and base asphalt. In this study, the interaction of CNT/RPE asphalt was investigated using molecular dynamics simulation. The base asphalt was examined using a 12-component molecular model and verified by assessing the following properties: its four-component content, elemental contents, radial distribution function (RDF) and glass transition temperature. Then, the adhesion properties at the interface of the CNT/RPE-modified asphalt molecules were studied by measuring binding energy. The molecular structural stability of CNTs at the interface between RPE and asphalt molecules was analyzed through the relative concentration distribution. The motion of molecules in the modified asphalt was studied in terms of the mean square displacement (MSD) and diffusion coefficient. The results showed that CNTs improved the binding energy between RPE and base asphalt. CNTs not only weakened the repulsion of RPE with asphaltenes and resins, but also promoted the interaction of RPE with light components, which facilitated the compatibility of RPE with the base asphalt. The change in the interaction affected the molecular motion, and the molecular diffusion coefficient in the CNT/RPE-modified asphalt system was significantly smaller than that of RPE-modified asphalt. Moreover, the distribution of the asphaltene component was promoted by CNTs, resulting in the enhancement of the storage stability of RPE-modified asphalt. The property indexes indicated that the storage stability was significantly improved by CNTs, and better viscoelastic properties were also observed. Our research provides a foundation for the application of RPE in pavement engineering.

Strong dark current suppression in flexible organic photodetectors by carbon nanotube transparent electrodes

• Carbon nanotube (CNT) transparent electrode enable high-performance flexible photodetectors. • The CNT-based photodetectors revealed high detectivity owing to high effective electron injection barriers. • Photoelectron yield spectroscopy was used for the analysis of injection model. • The devices demonstrate stable operation after 500 cyclic flex test, attributed to the mechanical stability of CNT. Carbon nanotubes possess outstanding mechanical, optical, and electronic properties and have been proposed as a replacement for indium–tin oxide in curved and flexible organic photodetectors to realize nearly 100% omnidirectional sensing. Because organic photodetectors require dense nanotube arrays to form suitable top layers, it is important to counterbalance their transmittance and packing density to achieve high performance. Carbon nanotubes are introduced as an electrode on a flexible substrate in this study. The carbon nanotube electrode, with an average visible transmittance of 90%, suppresses dark current considerably below the picoampere level, leads to a high detectivity of 2.07 × 10 14 Jones, which is 100 times larger than that of the indium–tin oxide-based devices. The deep work function of the carbon nanotube electrode induced a high electron injection barrier, which was investigated by photoelectron yield spectroscopy, considering the energy level bending caused by the electrode–semiconductor contact. The flexible organic photodetectors fabricated with the carbon nanotube electrode operated stably after a cyclic flex test of 500 bendings. This paper demonstrated the effective implementation of curved and flexible image sensors by developing an excellent flexible photodetector.

Wettability and reactivity between molten aluminum and randomly aligned carbon nanotubes

The wettability and reactivity between molten aluminum (Al) and carbon nanotubes (CNTs) are a key issue in the preparation of CNTs-reinforced Al-matrix composites using a solidification route. In this work, we measured the wettability of randomly aligned multi-walled carbon nanotubes (buckypaper) by molten Al at 973–1173 K in a high vacuum using a modified sessile-drop method and examined their interactions using a droplet-sucking technique. The wettability between Al and CNTs is even worse than that of the Al/graphite system. The contact angles are basically larger than 140° and show only a sluggish decrease with time during isothermal dwelling. The chemical stability of CNTs in contact with Al is closely related to their structural integrity. The CNTs with good crystallinity and structural integrity have relatively high chemical stability and exhibit only a weak interfacial reaction with Al at 973 K. However, the stability of structural defective parts is much lower. They are readily eroded by molten Al, leading to the fragmentation of the CNTs. These CNT fragments having an open tubular structure are then rapidly dissolved in molten Al along the axial and radial directions. Simultaneously, a large amount of Al4C3 is formed at the interfaces.