CNTs Content Research Articles

Si/CNTs@melamine‐formaldehyde resin‐based carbon composites and its improved energy storage performances

AbstractIn this paper, Si/carbon nanotubes@melamine‐formaldehyde resin (MFR)‐based carbon (Si/CNTs@C) composites have been fabricated by surface modification, electrostatic self‐assembly, cross‐linking of MFR under hydrothermal treatment and further carbonization. The microstructure of the Si/CNTs@C composites was characterized, and the effects of CNTs content in Si/CNTs@C composites on their electrochemical performances were also investigated in detail. The results indicate Si/CNTs@C composites as anode materials of Li‐ion batteries exhibit better high‐rate and cycling performances compared to Si and Si@MFR‐based carbon composites. Notably, Si/CNTs@C composites with 10.4 wt% CNTs show specific capacities of 1900, 1879, 1,688, 1,394, 1,189 mAh·g−1 at 0.2, 0.5, 1, 2, and 3 A·g−1, respectively. Even at 4 and 5 A·g−1, their capacities still reach 970 and 752 mAh·g−1, respectively. Moreover, they deliver a reversible capacity of 1,184 mAh·g−1 at 0.5 A·g−1 after 100 cycles. Therefore, the reasonable structure is of great significance for enhancing the electrochemical performances of Si‐based composites.

Heat transfer of hybrid nanofluid in a shell and tube heat exchanger equipped with blade-shape turbulators

In the current study, the turbulent forced convection heat transfer of Fe3O4/-CNT/water hybrid nanofluid (HNF) in a heat exchanger (HE) equipped with blade-shape turbulators is studied. The 3D governing equations have been solved numerically with SIMPLEC algorithm and solution domain by employing the control volume method (CVM). The impact of Reynolds number (Re), volume concentration of Fe3O4 nanoparticles (φM) and CNTs (φCNT) and blade-rod diameter (dr) on the performance features of HE are evaluated. The results showed that the PEC of HNF augments with the augmentation of Re and φM, while with intensifying dr, the PEC first rises and then declines. The outcomes showed that the highest PEC occurs at Re = 9000, φM = 0.9%, φCNT = 1.35% and dr = 15mm.

Experimental investigation of the dependence of the thermoelectric performance of carbon nanotubes/polymer nanocomposites on the synthesis protocol

In this study, experiments were carried out to determine the mechanism of enhanced electron transport through segregated pathways formed using different synthesis protocols of nanocomposites obtained by the addition of nanocarbon-based fillers (i.e. CNTs) inside a polymer matrix. Studies of the different types of fillers and polymer matrices, filler concentrations, and the use of additional additives enabled an in-depth understanding of the effect of each factor on the thermoelectric performance of the nanocomposites. First, because of their intrinsic material characteristics, the use of TWCNTs as a filler and electrically conductive polymers (e.g. PEDOT:PSS) as a matrix instead of MWCNTs and insulating polymers (e.g. PVA), respectively, leads to the enhancement in the electrical conductivity. In addition, it has been demonstrated that higher concentrations of CNTs that are sufficient to form a percolation network and the use of additional additives (e.g. DMSO) make large contributions to the electron transport enhancement. It was also found that in addition to the influence of the intrinsic properties of the material, the dispersion during the synthesis process and the structural characteristics inside the material have a complex effect on the Seebeck coefficient.

Coupled electromechanical modeling of piezoresistive behavior of CNT-reinforced nanocomposites with varied morphology and concentration

In this first time effort, we developed a coupled electromechanical model of CNT-reinforced composites with realistic morphologies. First, a Monte-Carlo based algorithm was developed to generate representative volume elements (RVEs) reinforced with different concentrations of straight and wavy CNTs. The percolating CNT networks were identified and transformed into an equivalent electric circuit consisting of tunneling and intrinsic resistances. The effective conductivity of the composite was then obtained using the modified nodal analysis method. Second, the structural response of each RVE was obtained using a novel embedded finite element model, where the composite constituents are meshed independently but solved simultaneously by coupling their equilibrium equations. Third, the displacements of the deformed CNTs were updated in the electrical model to calculate the corresponding tunneling distances and the resistance of the deformed system. The gauge factor of the nanocomposite was calculated from the strain-resistance curve. The obtained results indicated that the gauge factor increases with the increase in the curvature of the CNTs. The highest gauge factor of the sensor was attained at concentrations near the percolation threshold. Finally, the gauge factor was found to increase with the decrease in Poisson's ratio of the matrix.

Study on Preparation and Properties of CNTs/Al2009 Composites by Cryogenic Milling

The CNTs/Al2009 composite powders were prepared by cryogenic milling. The CNTs were uniformly dispersed on the surface of Al2009 powders. And then the CNTs/2009Al composites were fabricated by hot extrusion/hot isostatic pressing method. The effects of CNTs content and cryogenic milling process on the dispersion of CNTs in Al2009 matrix, the microstructure of powders and the properties of composites were studied by Scanning electron microscopy, Raman spectroscopy and tensile strength testing at room temperature. The results showed that the dispersion of CNTs was improved with the extension of ball milling time (1h~4h), but the damage degree of CNTs was intensified. In comparison, CNTs had the highest damage rate at the beginning of ball milling. As the milling time increased, the mechanical properties began to increase slightly and then decreased. When the ball milling time was 2h, the mechanical properties reached the highest. Cryogenic milling could achieve good dispersion in the Al2009 matrix for mixed powders with low CNTs content. When the CNTs content increased to 1.0%, a small amount of agglomeration appeared, but for composites, the strengthening effect of CNTs was more dominant. When CNTs were further added, the dispersion was remarkably lowered and the performance was deteriorated. CNTs (1.0wt.%)/Al2009 composites had excellent mechanical properties. The tensile strength reached 560MPa, which was 25% higher than Al2009.

Dynamic Mechanical, Dielectrical, and Rheological Analysis of Polyethylene Terephthalate/Carbon Nanotube Nanocomposites Prepared by Melt Processing

The polyethylene terephthalate/carbon nanotube (PET/CNT) nanocomposites were prepared by melt mixing using a twin screw extruder. CNT content was varied up to 5 wt. %. Morphology as well as dynamic mechanical, calorimetric, and rheological properties of the PET/CNT nanocomposites was investigated. Morphological studies indicated that CNT bundles are regularly distributed within the polymer matrix creating a connected network structure which significantly affects the nanocomposite properties. Dynamic mechanical thermal analysis revealed increase in storage and loss modules of the investigated PET nanocomposites by increasing the content of CNTs. Differential scanning calorimetry results demonstrated increase in crystallinity of the investigated PET nanocomposites upon addition of the nanofiller. Rheological studies demonstrated that CNT addition up to 5 wt. % caused increment in complex viscosity and storage modulus. Rheological percolation threshold was observed to be 0.83 wt. % of CNT concentration, respectively.

Preparation and Characterization of Polypropylene/Carbon Nanotubes (PP/CNTs) Nanocomposites as Potential Strain Gauges for Structural Health Monitoring.

Polypropylene/carbon nanotubes (PP/CNTs) nanocomposites with different CNTs concentrations (i.e., 1, 2, 3, 5 and 7 wt%) were prepared and tested as strain gauges for structures monitoring. Such sensors were embedded in cementitious mortar prisms and tested in 3-point bending mode recording impedance variation at increasing load. First, thermal (differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA)), mechanical (tensile tests) and morphological (FE-SEM) properties of nanocomposites blends were assessed. Then, strain-sensing tests were carried out on PP/CNTs strips embedded in cementitious mortars. PP/CNTs nanocomposites blends with CNTs content of 1, 2 and 3 wt% did not show significant results because these concentrations are below the electrical percolation threshold (EPT). On the contrary, PP/CNTs nanocomposites with 5 and 7 wt% of CNTs showed interesting sensing properties. In particular, the best result was highlighted for the PP/CNT nanocomposite with 5 wt% CNTs for which an average gauge factor (GF) of approx. 1400 was measured. Moreover, load-unload cycles reported a good recovery of the initial impedance. Finally, a comparison with some literature results, in terms of GF, was done demonstrating the benefits deriving from the use of PP/CNTs strips as strain-gauges instead of using conductive fillers in the bulk matrix.

Effect of long-term mechanical cycling and laser surface treatment on piezoresistive properties of SEBS-CNTs composites

The piezoresistive behaviour of SEBS-CNTs nanocomposites was investigated to evaluate their.potential applications as strain sensors. Composites containing from 3%wt. to 7%wt. of CNTs were processed by injection moulding in order to evaluate the percolation threshold. The piezoresistive response under flexural strain of nanocomposites with a CNTs content above the percolation threshold was then studied. The nanocomposites showing the most promising performance were tested under cyclic conditions. Conductive tracks were then processed on nanocomposites surfaces (with 3 and 4% of CNTs) by means of a laser treatment. Samples with optimized laser tracks were then submitted to 1000 stretching/releasing cycles, showing improved piezoresistive performance.

Influence of Multiwall Carbon Nanotube on mechanical and wear properties of Copper – Iron composite

Multiwall Carbon nanotubes (MWCNTs) are frequently attractive due to their novel physical and chemical characteristics, as well as their larger aspect ratio and higher conductivity. Therefore, MWCNTs can allow tremendous possibilities for the improvement of the necessarily unique composite materials system. The present work deals with the fabrication of Cu-Fe/CNTs hybrid composites manufactured by powder metallurgy techniques. Copper powder with 10 vol. % of iron powder and different volume fractions of Multi-Wall Carbon Nanotubes (MWCNTs) were mixed to get hybrid composites. The hybrid composites were fabricated by adding 0.3, 0.6, 0.9, and 1.2 vol.% of MWCNTs to Cu- 10% Fe mixture using a mechanical mixer. The samples were compressed under a load of 700 MPa using a hydraulic press to compact the samples. Sintering was done at 900°C for 2 h at 5ºC/min heating rate. The microscopic structure was studied using a Scanning Electron Microscope (SEM). The effect of CNTs on the mechanical and wear properties, such as micro-hardness, dry sliding wear, density, and porosity were studied in detail. The wear tests were carried out at a fixed time of 20 minutes while the applied loads were varied (5, 10, 15, and 20 N). SEM images revealed that CNTs were uniformly distributed with relative agglomeration within the Cu/Fe matrix. The results showed that the hardness, density, and wear rates decreased while the percentage of porosity increased with increasing the CNT volume fraction. Furthermore, the wear rate for all the CNTs contents increased with the applied load.

Self-standing MWCNTs based gas sensor for detection of environmental limit of CO2

In this work, we have demonstrated multi walled carbon nanotubes (MWCNTs) based CO2 gas sensor using a reliable and low cost gel-cast method with MWCNT concentration of 0.6, 1.0, 1.5, 2.0 and 3.0 by wt% in alumina Al2O3 sol which acts as a host matrix for the composite. Sensing response of the as prepared highly uniform self-standing MWCNTs film was measured at room temperature by exposure to different CO2 concentrations, ranging from 50 ppm to 450 ppm. The adsorption effect of CO2 on the varying concentration of CNTs was investigated by measuring a significant change in the resistance. Upon exposure to CO2 molecules, the device shows a drastic increase in resistance attributed to the charge transfer between CNTs and CO2 molecules. High sensor response of 7.3% with a response time of 53.7 s exhibited by sensor S3 (1.5 wt% of MWCNTs) is reported when the concentration of CO2 is 450 ppm in ambient conditions. In addition, different recovery modes were examined and the results reveal that there is a significant decrease in the recovery time of sensor upon UV light exposure and heat application. Besides being fast recoverable with heat energy, the fabricated gas sensor shows favorable stability in response over multiple exposure of analyte gas.

The effect of carbon nanotubes on the mechanical and damping properties of macro-defect-free cements

Abstract The effect of CNTs on the mechanical and damping properties of macro-defect-free (MDF) cements was studied, and polyvinyl alcohol (PVA) fibers were also studied as a contrast. It was found that the compressive strength of MDF cements was not significantly affected by the two types of fibers. The CNTs enhanced the flexural strength of MDF, while PVA fibers made negative contribution. The strengthening mechanism of flexural strength of MDF cements by CNTs can be summarized as fiber bridging, crack deflection and fiber slippage. For the damping properties, the proper contents of CNTs and PVA fibers improved the loss factor significantly. The interface transition zone (ITZ) between the PVA fibers and matrix was large, which was favorable for fiber slippage. The damping property of MDF cements with CNTs was mainly due to the slippage between the inner tubes of the CNTs rather than the slippage between the CNTs and matrix.

Qualitative and Quantitative Investigation of As-Cast and Aged CNT/AZ31 Metal Matrix Composites

In this research, magnesium alloy AZ31 reinforced with CNTs (0 wt.%, 0.1 wt.%, 0.5 wt.%, 1 wt.%) was produced by a stir casting method followed by aged heat treatment. Composites were investigated using x-ray diffraction and scanning electron microscope techniques. The microstructure of the CNTs/AZ31 has been qualitatively and quantitatively evaluated. The results show that stir casting is a suitable method for uniformly distributing CNTs and maintaining the integrated structure. The concentration of CNTs and aged heat treatment affects the crystallite size, crystallinity degree, precipitates and phase composition of the CNT-reinforced AZ31 alloy. An increase in the concentration of CNTs results in a decrease in the degree of crystallinity and dissolution of the secondary phase. In 0.1 wt.% CNTs, the crystallite size decreases and then increases. The aged heat treatment affects the composition of the phase and creates a new secondary phase to refine the microstructure and grain size. The compressive strength is linearly related to the concentration of CNTs. Bramfitt disregistry and precipitation strengthening play an important role in qualitatively and quantitatively refining and altering the microstructure of CNTs/AZ31.

Nanocomposite starch graft copolymers with carbon nanotubes - synthesis and flocculation efficiency

Nanocomposite flocculants based on polyacrylamide-grafted starch copolymers with carbon nanotubes (PAM-St-CNT) were prepared using natural polymer – potato starch (St), acrylamide (AM) as monomer and CNTs by in situ polymerization process. The effect of monomer to starch molar ratio, dose of flocculants and content of CNTs in composition on flocculation efficiency were investigated. All materials were characterized by FT-IR (Fourier transform infrared spectroscopy), TGA (thermogravimetric analysis) and DSC (differential scanning calorimetry) methods. An aqueous suspension of kaolin was used for the flocculation studies. The flocculation effectiveness was evaluated on the basis of reduction of suspension absorption and the sludge volume. It was found that synthesized nanocomposites PAM-St-CNT exhibit satisfactory flocculating properties.

Synthesis of carbon nanotube reinforced aluminum composite powder (CNT-Al) by polymer pyrolysis chemical vapor deposition (PP-CVD) coupled high energy ball milling (HEBM) process

Carbon nanotube reinforced Aluminum (CNTAl) composite powder was prepared by polymer pyrochemical chemical vapor deposition (PP-CVD) at different temperatures with polyethylene glycol (PEG) as carbon source, cobalt nitrate as catalyst precursor and fine Al powder as starting material. The morphologies, structure, phase composition, and elemental content of the synthesized CNT-Al composite powders were investigated using scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD) and thermo-gravimetric analysis (TGA). The optimized CNT-Al was agglomerated with pure fine Al powder by a high energy ball milling (HEBM) method to obtain several kinds of CNT-Al composite powder with different content of CNTs. The results show that the CNTs in CNT-Al composite powder synthesized at 600 °C showed the highest crystallinity with a reinforcement content of 7 wt%. Although the HEBM process partly smashed the structure of CNTs, it increased the interfacial reaction between CNTs and Al particles. The resulting agglomeration helped to merge the small particulates to form larger particles, thus increasing the overall flowability of the composite powder. Therefore, the PP-CVD coupled HEBM procedure can be employed as an innovative process to prepare the CNT-Al composite powder with uniformly distributed CNTs. The powder manufactured in this investigation has excellent potential to be used in powder metallurgy, cold spraying of CNT-Al composite coatings, and additive manufacturing of composite free-forms.

Elucidating Hydrothermally Synthesized CNTs-MnO2 Composites through Electrochemical Scrutiny for Wielding Electrodes in Energy Storage

Search of materials with better electrochemical performance is currently one of the key interests around the globe. In this context, the electrochemical characteristics of MnO2/CNTs (manganese dioxide/carbon nanotubes) composites prepared in two simple steps have been reported. X-ray diffraction confirmed the structural purity of the composite contents revealing that the intensity of peaks first decreased and after the addition of more CNTs, the intensity of the peaks started to increase. Scanning electron microscope was utilized to examine the surface morphology of MnO2/CNTs composites which indicated that with increase of CNTs contents, the granular size of MnO2 particles slightly decreased. The conductivity was inspected by electrochemical impedance spectroscopy, which demonstrated that increase in CNTs concentration provided conducting channels for charge transportation. The energy density calculations revealed that maximum energy density was observed for the composition with 0.5% CNTs. These characteristics inferred that the composite material could be utilized as an electrode in electric batteries and energy storage devices.

Facile One-Step Dynamic Hydrothermal Synthesis of Spinel LiMn2O4/Carbon Nanotubes Composite as Cathode Material for Lithium-Ion Batteries.

Nano-sized spinel LiMn2O4/carbon nanotubes (LMO/CNTs) composite is facilely synthesized via a one-step dynamic hydrothermal approach. The characterizations and electrochemical measurements reveal that LiMn2O4 particles with narrow size distribution are well dispersed with CNTs in the composite. The LMO/CNTs nanocomposite with 5 wt % CNTs displays a high specific discharge capacity of 114 mAh g−1 at 1C rate, and the retention rate after 180 cycles at room temperature reaches 94.5% in the potential window of 3.3 to 4.3 V vs. Li/Li+. Furthermore, the electrochemical performance of the composite with 5 wt % CNTs at elevated temperature (55 °C) is also impressive, 90% discharging capacity could be maintained after 100 cycles at 1C. Such excellent electrochemical performance of the final product is attributed to the content of CNTs added in the hydrothermal process and small particle size inherited from pretreated MnO2 precursor.

Investigation of heating of nanomodified polymers under the action of microwave radiation

The article presents the study of heating nanomodified polymers under the action of microwave radiation. Modification of polyethylene was carried out using CNTs synthesized on Co-Mo / Al2O3-MgO catalysts. The influence of CNTs concentration on the temperature regime of polymer heating is investigated. The study of interaction with microwave radiation was carried out at the emitter power of 800 W in 2 minute increments for 8 minutes

Simple model for hydrolytic degradation of poly(lactic acid)/poly(ethylene oxide)/carbon nanotubes nanobiosensor in neutral phosphate-buffered saline solution.

In this study, the hydrolytic degradation of poly(lactic acid) (PLA)/poly(ethylene oxide) (PEO) blend and PLA/PEO/carbon nanotubes (CNTs) nanobiosensors in neutral phosphate-buffered saline (PBS) solution was investigated by experimental and theoretical approaches. A simple model was developed to estimate the degradation fraction by applying the average degradation rate (K) and time exponent. The predictions of the developed model were compared to the experimental results. Moreover, CNT concentration, CNT size, sample thickness, diffusion coefficient, and concentration of the PEO phase influenced the K value. The impacts of the parameters on the degradation rate were studied to confirm the developed equation. All samples were rapidly degraded during the first week, while the degradation slowly progressed in the following weeks. The experimental and theoretical results demonstrate that CNTs quicken the degradation of samples. The degradation fraction of a nanobiosensor depends directly on the values of K and the time exponent. Furthermore, a high concentration of PEO, small thickness of the sample, high concentration of thin CNTs, and high diffusion coefficient desirably improve the degradation rate.

Textile-based triboelectric nanogenerators with high-performance via optimized functional elastomer composited tribomaterials as wearable power source

Wearable power sources with high performance are attracting intensive attention, owing to their great potential in new-generation wearable electronics. Herein, we proposed a composited fabric with flexible functional elastomer layers (FEL@CF) and employed it as a negative tribomaterial in triboelectric nanogenerators (TENGs). The FEL@CF consists of a low-temperature vulcanized silicone (LTV) electrification layer, CNTs/Ecoflex nanocomposite layer, super-soft Ecoflex layer and conductive fabric substrate, which play critical roles on the output enhancement of FEL@CF-based TENG (abbreviated as FEL@CF-TENG). The effect of the thickness of the Ecoflex layer and CNTs content in the nanocomposite layer on the electrical performance of FEL@CF-TENG were systematically investigated. The FEL@CF with 180 μm thick Ecoflex layer and 1.6 wt% CNTs content was realized as an optimal sample to obtain optimum output signals. The high outputs (~490 V, ~43 μA, ~70 nC, 1.6 mW/cm2) were obtained from the optimal FEL@CF-TENG (2.5 × 2.5 cm2) under small force (~16 N) and low frequency (~1.5 Hz). The flexible FEL@CF-TENG can power for wearable electronics by harvesting biomechanical energy and operate in dual-electrodes mode (FEL@CF-DTENG) or single-electrode mode (FEL@CF-STENG). Especially, the power glove made of FEL@CF-STENG can contact with various daily-used objects for human motion energy harvesting. The durability and washability of FEL@CF-TENGs were also performed, exhibiting excellent stability even under harsh and complex conditions. All these merits of the FEL@CF-TENG not only provide a promising strategy for exploring high-performance wearable power source but also show great potential for applications in portable electronics and electronic textiles.

Studying changes in the electrical resistance of carbon-nanotubes-modified elastomers during their compression, stretching and torsion

Developing "smart" materials with improved both structural and functional characteristics is one of the promising areas of materials science. Measuring the electrical resistance of CNTs-modified (various mass contents) polymers and in particular, elastomers during performing several tests (compression, stretching, and torsion) at a constant current is relevant in electrical engineering, mechanical engineering, aviation, and space industry. Changes in the elastomer shape under different types of testing lead to the destruction of macromolecules and the structuring of the material as a whole. Therefore, it is important to study the effect of CNTsbased modifying fillers on the elastomer. When compressing, stretching or twisting the nano-modified elastomer, along with the mutual movement of its macromolecular fragments and aggregates, the modifier particles also move, which generally determines the transport of electrons in the resulting structure and affects the physical and mechanical parameters of the composite material. To conduct studies, elastomers containing different amounts of a CNTs-based modifying filler were prepared. To investigate and elucidate relevant dependencies, a measuring system (MS) was constructed, which makes it possible to determine electrical resistance values of the composite material with different CNTs contents in the polymer matrix composition exposed to various mechanical loads. Basing the research results, it was established that the electrical resistance of the elastomer composites modified with 1.0–2.5 wt.% CNTs decreases when compressing from 0 to 100 N, whereas when the compression force ranges from 100 to 350 N, the electrical resistance remains unchanged. When the elastomer composites modified with 2–2.5 wt.% CNTs were stretched by 30–40 %, the electrical resistance was found to increase from 5·103 to 1.9·107 Ω.