Resistance Of Multiwalled Carbon Nanotubes Research Articles

Quasi-static puncture shear loading behaviour MWCNT/glass fibre epoxy laminates with various indenters

Investigation was performed to evaluate the puncture resistance of multi-walled carbon nanotubes (MWCNTs)/glass fibre epoxy laminate composites using different indenters (conical, elliptical, flat, and hemispherical). For the puncture tests, MWCNT weight percentage and indenter type were varied. Furthermore, the impact of MWCNT on tensile, flexural, and interlaminar shear strength was evaluated. Ultrasonic C-scan provided insights into the damage evolution and failure mechanisms of the laminates under puncture. The results indicate that the flat indenter exhibits prolonged indentation time and enhanced energy absorption, resulting in a disc-shaped failure pattern. On the other hand, the conical indenter demonstrates rapid penetration due to its smaller contact surface area. The elliptical indenter generates higher frictional energy, leading to bulging damage. The hemispherical indenter showed an even distribution of force across the impacted surface, minimizing force concentration and reducing the extent of damage. These findings shed light on the puncture mechanisms of MWCNT/Glass fibre epoxy laminate composites, paving the way for more precise glass fibre laminate composite design and optimisation in practical applications such as aerospace, automotive, and sporting goods, where puncture loading is a critical consideration.

Transport properties of carbon nanotubes with different degrees of structural perfection

The resistivity and magnetoresistance of multi-walled carbon nanotubes with different degrees of structural perfection in the temperature interval from 4.2 K to 293 K and in the magnetic field up to 2 T are investigated. The revealed anomalies of the temperature and field dependences of resistivity of multi-walled carbon nanotubes are analyzed in the terms of charge carrier’s weak localization and interaction effects for two-dimensional systems. For carbon nanotubes with different degrees of structural perfection diffusion coefficient, charge carrier’s interaction parameter and the value of the Fermi energy are estimated. It is shown that the anomalies found in the resistivity and magnetoresistance for the defective multi-walled carbon nanotubes are related with the manifestation of the weak localization effect, while for the multi-walled carbon nanotubes of the perfect structure these anomalies are explained by the charge carriers interaction effect.

Enhanced mechanical properties and thermal shock resistance of Si2BC3N ceramics with SiC coated MWCNTs

Bulk Si2BC3N ceramics were reinforced with SiC coated multi-walled carbon nanotubes (MWCNTs). The phase compositions, mechanical properties, and thermal shock resistance, as well as the oxidation resistance of the designed Si2BC3N ceramics were comparatively investigated. The results show that nano SiC coating can be formed on MWCNTs through pyrolyzing polysilazane, which improves the oxidation resistance of MWCNTs. A stronger chemical bonding is formed between the SiC coated MWCNTs and SiC particles, contributing to improved flexural strength (532.1 MPa) and fracture toughness (6.66 MPa·m1/2). Besides, the 2 vol% SiC coated MWCNTs reinforced Si2BC3N ceramics maintains much higher residual strength (193.0 MPa) after thermal shock test at 1000 °C. The enhanced properties should be attributed to: (1) the breaking of MWCNTs and the debonding between MWCNTs and SiC interfaces, which leads to more energy dissipation; (2) the rough surfaces of SiC coated MWCNTs increase the adhesion strength during the “pull out” of MWCNTs.

Enhanced thermal shock and oxidation resistance of Si2BC3N ceramics through MWCNTs incorporation

Multi-walled carbon nanotubes (MWCNTs) reinforced Si2BC3N ceramics were prepared through mechanical alloying (MA) and following spark plasma sintering (SPS). The thermal shock resistance of Si2BC3N ceramics was evaluated comparatively through ice water quenching test and theoretical prediction. Furthermore, the oxidation resistance of MWCNTs incorporated Si2BC3N ceramics was evaluated under high temperature. The results show that the calculated parameters such as the critical thermal shock temperature (R) and the thermal stresses resistance (Rst), as well as the toughness (R″″) are improved with addition of 1 vol% MWCNTs. In addition, the crack propagation resistance of 1 vol% MWCNTs incorporated Si2BC3N ceramics is obviously improved through generating more tortuous crack propagation paths attributing to the “crack bridging”, “pull-out”, and “crack deflection” mechanisms of MWCNTs. Therefore, the residual strengths of 1 vol% MWCNTs containing specimens remained the highest after the thermal shock tests. Besides, the present work also reveals that the oxidation resistance is more sensitive to relative density than MWCNTs addition.

Work function and electrical properties of individual multiwalled carbon nanotube: influenced by nature of catalyst and substrate

To employ the multiwalled carbon nanotubes (MWCNTs) in electronic devices, their growth on conductive substrates is a prerequisite. Since electronic properties of MWCNT might be influenced by catalyst and substrate, therefore, to understand their influence on the work function and electrical resistance, individual MWCNT needs to be studied. In this report, we have demonstrated the growth of MWCNTs on conducting substrates such as copper, stainless steel, and insulating SiO2 using thermal CVD technique. First, as-grown MWCNTs on different substrates have been characterized with scanning electron microscopy and Raman spectroscopy. Furthermore, electrical measurements on as-grown individual MWCNT has been performed using electrostatic force microscopy and conductive atomic force microscopy. Performed measurements reveal that work function and electrical resistance of MWCNT vary from 4.32 to 5.32 eV and 4–498 kΩ, respectively, depending on the nature of catalyst as well as substrates. We envision that performed study might boost the on-going research activity in the area of MWCNT-based nanoelectronic devices.

Core/Shell Structure of TiO2‐Coated MWCNTs for Thermal Protection for High‐Temperature Processing of Metal Matrix Composites

The production of metal matrix composites with elevated mechanical properties depends largely on the reinforcing phase properties. Due to the poor oxidation resistance of multiwalled carbon nanotubes (MWCNTs) as well as their high reactivity with molten metal, the processing conditions for the production of MWCNT‐reinforced metal matrix composites may be an obstacle to their successful use as reinforcement. Coating MWCNTs with a ceramic material that acts as a thermal protection would be an alternative to improve oxidation stability. In this work, MWCNTs previously functionalized were coated with titanium dioxide (TiO2) layers of different thicknesses, producing a core‐shell structure. Heat treatments at three different temperatures (500°C, 750°C, and 1000°C) were performed on coated nanotubes in order to form a stable metal oxide structure. The MWCNT/TiO2 hybrids produced were evaluated in terms of thermal stability. Thermogravimetric analysis (TGA), X‐ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy (RS), and X‐ray photoelectron spectroscopy (XPS) were performed in order to investigate TiO2‐coated MWCNT structure and thermal stability under oxidative atmosphere. It was found that the thermal stability of the TiO2‐coated MWCNTs was dependent of the TiO2 layer morphology that in turn depends on the heat treatment temperature.

A theoretical study on the piezoresistive response of carbon nanotubes embedded in polymer nanocomposites in an elastic region

Herein, we report a theoretical study of polymeric nanocomposites to provide physical insight into complex material systems in elastic regions. A self-consistent scheme is adopted to predict piezoresistive characteristics, and the effects of the interface and of tunneling on the effective piezoresistive and electrical properties of the nanocomposites are simulated. The overall piezoresistive sensitivity is predicted to be reduced when the lower interfacial resistivity of multi-walled carbon nanotubes (MWCNTs) and the higher effective stiffness of nanocomposites are considered. In addition, thin film nanocomposites with various MWCNT weight percentages are manufactured and their electrical performance capabilities are measured to verify the predictive capability of the present simulation. From experimental tests, the nanocomposites show clear piezoresistive behaviors, exhibiting a percolation threshold at less than 0.5 wt% of the MWCNTs. Three sets of comparisons between the experimental data and the present predictions are conducted within an elastic range, and the resulting good correlations between them demonstrate the predictive capability of the present model.

Effect of multi-walled carbon nanotubes on the electrochemical performance of LiVPO4F cathode material for rechargeable lithium-ion batteries

A novel network cathode material for lithium-ion batteries, pristine and multi-walled carbon nanotubes modified LiVPO4F composites have been successfully synthesized via a microwave assisted sol–gel route. The crystalline structure and morphology of as-synthesized samples are investigated systematically by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Their electrochemical performances are also studied and compared in detail. The achieved results indicate that the multi-walled carbon nanotube modified LiVPO4F sample has excellent C-rate performance, and delivered discharge capacities of 137.6, 131.2, 120.5 and 108.9mAhg−1 at 0.5, 1, 2 and 5C in the voltage range of 3.0–4.5V at room temperature, respectively. Moreover, the capacity retention is 96.2% with the discharge capacity of 132.4mAhg−1 at 0.5C after 100cycles. Electrochemical impedance spectroscopy results reveal that the charge-transfer resistance of multi-walled carbon nanotube modified LiVPO4F is much smaller than that of the pristine LiVPO4F. The outstanding features are desirable and enable the multi-walled carbon nanotube modified LiVPO4F to be an excellent cathode material for lithium-ion batteries.

Compressive strength, chloride permeability, and freeze-thaw resistance of MWNT concretes under different chemical treatments.

This study investigated compressive strength, chloride penetration, and freeze-thaw resistance of multiwalled carbon nanotube (MWNT) concrete. More than 100 cylindrical specimens were used to assess test variables during sensitivity observations, including water-cement ratios (0.75, 0.5, and 0.4) and exposure to chemical agents (including gum arabic, propanol, ethanol, sodium polyacrylate, methylcellulose, sodium dodecyl sulfate, and silane). To determine the adequate sonication time for MWNT dispersal in water, the compressive strengths of MWNT concrete cylinders were measured after sonication times ranging from 2 to 24 minutes. The results demonstrated that the addition of MWNT can increase the compressive strength of concrete by up to 108%. However, without chemical treatment, MWNT concretes tend to have poor freeze-thaw resistance. Among the different chemical treatments, MWNT concrete treated with sodium polyacrylate has the best compressive strength, chloride resistance, and freeze-thaw durability.

Enhanced dispersion for electrical percolation behavior of multi-walled carbon nanotubes in polymer nanocomposites using simple powder mixing and in situ polymerization with surface treatment of the fillers

The electrical conductivity of nanocomposites with a Cyclic Butylene Terephthalate (CBT) matrix and multi-walled carbon nanotubes (MWCNTs) was investigated. Uniform dispersion of the incorporated MWCNTs in the nanocomposites was achieved using a novel preparation method that involved powder mixing and in situ polymerization. Promoted and retarded results at the percolation threshold were observed, and the trend strongly depended on the surface treatment of the MWCNTs, such as acid, hydrogen peroxide and heat treatments. The electrical percolation behavior of nanocomposites with surface treated MWCNTs has been a controversial topic in the literature. The defect and resistivity of MWCNTs, which were expected to be important physical factors that influence the electrical conductivity of the nanocomposites, were found to have only a minor influence. Different functionalities of the MWCNTs after surface treatments altered the dispersion state of the incorporated MWCNTs in the nanocomposites, and the dispersion state was the dominant physical factor that governed the electrical percolation behavior of the nanocomposites.

Microstructural Evolution and Oxidation Resistance of Multi-walled Carbon Nanotubes in the Presence of Silicon Powder at High Temperatures

The microstructural evolution and oxidation resistance of multi-walled carbon nanotubes (MWCNTs) by directly heating silicon powder and MWCNTs in a coke bed from 1000 to 1500 C are investigated with the aid of X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and thermogravimetry-differential scanning calorimetry (TG-DSC). The results showed that the morphology and microstructure of MWCNTs did not change much after being treated from 1000 C to 1200 C. An obvious SiC coating was formed on the surface of MWCNTs from 1300 to 1400 C. Up to 1500 C, nearly all the MWCNTs transformed into SiC nanowires. The oxidation resistance of the treated MWCNTs was improved compared with as-received ones. Non-isothermal kinetics showed that the oxidation activation energy of the treated MWCNTs reached 208 kJ/mol, much higher than 164 kJ/mol of as-received ones.

Oxidation resistance of multi-walled carbon nanotubes coated with polycarbosilane-derived SiC xO y ceramic

Multi-walled carbon nanotubes (MWCNTs) have been successfully coated with a thin SiC x O y coating when polycarbosilane (PCS) was used as precursor and pyrolyzed in a coke bed. Meanwhile, effect of PCS concentration on oxidation resistance of the coated MWCNTs is studied. The results showed that the pyrolysis products of PCS were composed of amorphous SiC x O y as the main phase, together with β-SiC and SiO 2 as the minor phases whose amount increased a little with the increase of temperature from 1000 °C to 1500 °C. The thickness of SiC x O y coating on the surface of MWCNTs increased a little from 1 wt.% to 5 wt.%, but decreased dramatically with PCS concentration in the range of 10–30 wt.%. The oxidation resistance of the coated MWCNTs was greatly improved in comparison with as-received ones. The oxidation peak temperature of the coated MWCNTs reached 783.7 °C, much higher than 652.2 °C for as-received ones.

An atomistic study of thermal conductance across a metal-graphene nanoribbon interface

This paper presents an atomistic Green’s function study of phonon transport through a heterogeneous interface between bulk TiC substrates and graphene nanoribbons (GNRs). The force constants that govern the lattice dynamical equations are obtained from first-principles density functional theory (DFT) calculations and then optimized for the Green’s function formulation. Phonon vibrational properties of TiC and GNRs are investigated by lattice dynamics calculations with optimized force constants that correlate well to direct DFT results. Thermal conductances of TiC-GNR-TiC systems are studied together with TiC-GNR structures. The conductances of TiC-GNR interfaces are normalized by ribbon width and are found to converge. The converged value is used to estimate the interface resistance of multiwalled carbon nanotubes (MWCNTs) grown on metal catalyst support substrates and is found to be consistent in an order of magnitude sense with experimental results on MWCNT arrays. The results reveal that covalent bonds may be formed during CNT synthesis and quantify the resulting thermal impedance caused by phonon mismatch.

Measurement of contact resistance of multiwall carbon nanotubes by electrical contact using a focused ion beam

Carbon nanotubes (CNTs) have found many potential applications but using CNTs as building blocks for nanoelectronics is still challenging. Various micro- and nanofabrication techniques including focused ion beam (FIB) are therefore being developed for combining CNTs into a nanodevice or to help assess the electrical properties of integrated CNTs. In this paper, multiwall carbon nanotubes (MWNTs) are assembled between a pair of gold (Au) electrodes by dielectrophoresis (DEP). Contact resistances of MWNT-Au and, in particular, MWNT-MWNT are measured with the help of making electrical connections between a MWNT and electrodes by FIB induced tungsten deposition. A method for resistance calculation is presented which considers the contact length of MWNTs. Under the conditions of this research, measured conducting resistances of MWNTs were from 1–10 kΩ/μm and the contact resistance of MWNTs with Au was around 100 kΩ μm. The contact resistance between MWNTs varied depending on contact configurations and could be as low as 50 KΩ. The effect of FIB parameters on the measurement results is discussed.

Effects of carboxyl radical on electrical resistance of multi-walled carbon nanotube filled silicone rubber composite under pressure

The piezoresistance of a multi-walled carbon nanotube filled silicone rubber composite under uniaxial pressure was studied. The experimental results show that the active carboxyl radical on multi-walled carbon nanotubes can effectively improve the homogeneous distribution and alignment of conductive paths in the composite. As a result, the composite presented positive piezoresistance with improved sensitivity and sensing linearity for pressure, both of which are key parameters for sensor applications.

PREPARATION OF FUNCTIONALIZED MWCNTs COATING WITH MgO VIA SIMPLE PRECIPITATION METHOD

Multiwalled carbon nanotubes (MWCNTs) were coated with MgO nanoparticles using simple precipitation method. The nanometer-sized Mg(OH)2 particles were precipitated on the surface of functionalized MWCNTs by reaction between MgSO4 solution and NH4OH as an alkaline agent. The growth of Mg(OH)2 particles was controlled by adjusting the alkaline concentration, salt concentration and feed rate in simple precipitation method. The samples have been characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), X-ray diffraction (XRD) and thermal gravimetric analysis (TG). The results showed a nominally complete coating over the entire outer surface of MWCNTs and the oxidation resistance of MWCNTs was improved by the MgO coating significantly.

Oxidation resistance of multi-walled carbon nanotubes purified with sulfuric and nitric acids

Oxidation resistance of multi-walled carbon nanotubes purified with sulfuric and nitric acids

Correlating electrical resistance to growth conditions for multiwalled carbon nanotubes

A correlation between growth temperature and electrical resistance of multiwalled carbon nanotubes (MWNTs) has been established by measuring the resistance of individual MWNTs grown by microwave plasma-enhanced chemical vapor deposition (PECVD) at 800, 900, and 950°C. The lowest resistances were obtained mainly from MWNTs grown at 900°C. The MWNT resistance is larger on average at lower (800°C) and higher (950°C) growth temperatures. The resistance of MWNTs correlated well with other MWNT quality indices obtained from Raman spectra. This study identifies a temperature window for growing higher-quality MWNTs with fewer defects and lower resistance by PECVD.

Electric resistivity of multi-walled carbon nanotubes at high temperatures

The electric resistivity of a clean multi-walled carbon nanotube (MWNT) mat sample was studied at temperatures T between 300 and 1900 K. We found that the resistivity ρ decreases monotonously with increasing temperature without showing any sign of turn up. Our results can be well fitted with a power law of T − α within the framework of one dimensional Luttinger liquid theory with α = 0.13 or with a simple thermally activated inter shell hopping model.

Oxidation Resistance of Multiwalled Carbon Nanotubes Coated with Silicon Carbide

Multiwalled carbon nanotubes (MWCNTs) were coated with a SiC layer using SiO vapor. The growth mechanism of SiC and the oxidation resistance of the SiC-coated MWCNTs were studied. The growth of the SiC layer was controlled by adjusting the partial pressure of CO2 using carbon felt placed in a crucible. The nanometer-sized SiC particles were deposited onto the tubes by the reaction between SiO(g) and CO(g). On the other hand, the thin surface of the MWCNTs was converted to the SiC layer when the carbon felt was not used. The oxidation durability of MWCNTs was improved by the SiC coating. MWCNTs were oxidized completely in air at 650°C for 60 min. However, about 90 mass% of the SiC-coated MWCNTs remained after the same oxidation test.