Microstructure Of Multiwalled Carbon Nanotubes Research Articles

Effect of pretreatment on the microstructure of multiwalled carbon nanotubes

Four kinds of multi-walled carbon nanotubes pretreated by different methods were studied. Chemically functionalized (hydroxylation and carboxylation) CNTs were prepared by oxidizing original CNTs in H2SO4 solutions of different temperatures and concentrations by KMnO4. Graphitized CNTs were prepared by heat-treating original CNTs in an inert gas at 2800°C for 20 hours. CNTs Nickel plating on the surface was obtained by electroless plating. The effect of pretreatment on the surface state and microstructure of carbon nanotubes was also studied. The results showed that Chemical functionalization could form some functional groups on the surface of CNTs, which could not only improve the compatibility of CNTs with some solvents, but also purified CNTs, which had a positive effect on the preparation of composite materials. High-temperature graphitization treatment could significantly increase the degree of crystallization of carbon nanotubes and reduce structural defects. After electroless nickel plating, evenly distributed nano-sized metal particles were formed on the surface of the CNTs, and the interface between the two was well bonded.

The influence of heating rate on the microstructural evolutions and mechanical properties of spark plasma sintered multi-walled carbon nanotubes reinforced NiAl intermetallic matrix composites

The effect of heating rate on the mechanical characteristics and microstructures of multi-walled carbon nanotubes (MWCNTs) reinforced nickel aluminide (NiAl) was studied. Powder synthesis was carried out by the use of the planetary ball milling and the admixed powders were fabricated by spark plasma sintering (SPS) technique to promote homogeneity. Three values of the heating rate was used namely 50, 100 and 150 °C/min to evaluate the effect of heating rate on the resulting microstructures and mechanical properties of the sintered composites. The microstructures of the sintered composites revealed the presence of porosity as the heating rate was higher, due to lack of contact area between particles. The densifications of the composites were observed to decrease as the heating rate was increased. Furthermore, results showed that a heating rate of 50 °C/min gave the best combination of properties among the composite batches with nanohardness of 9.6 GPa, microhardness of 371.2 HV, elastic modulus of 107.7 GPa, and relative density of 95.7%.

Mechanical properties and microstructure of multi-walled carbon nanotube-reinforced cementitious composites under the early-age freezing conditions

This research investigated mechanical properties and microstructure of multi-walled carbon nanotube (MWCNT) reinforced cementitious composites. Different cement mixes containing MWCNT-to-cement weight fractions of 0, 0.05, 0.1 and 0.2 wt% were prepared. After demolding, the samples were immediately cured in the deep freezer (−15 °C) for 7 days and then stored in the standard curing room (+20 °C) until the testing age. The strength results showed that the addition of MWCNTs can effectively enhance flexural and compressive strengths. With the incorporation of 0.05 wt% MWCNTs, the early flexural and compressive strength increased by 70.7% and 25.6%, respectively. And the late flexural and compressive strength were also improved by the addition of MWCNTs, with the maximum enhancement reaching 16.9% and 11.6% respectively. Mercury intrusion porosimetry (MIP) results showed that MWCNTs can reduce the total porosity and improve pore size distribution, especially a reduction in the number of mesopores. Thermogravimetric (TG) analysis and scanning electron microscopy (SEM) observations indicated that MWCNTs can accelerate the hydration process through the nucleating effect. Due to these effects, MWCNTs can effectively enhance the mechanical properties of cement pastes suffered from early-age freezing. Moreover, the crack bridging, filling, and bonding between MWCNTs and cement matrix are also observed in SEM images, which have a positive influence on the mechanical properties of cement pastes.

New insight on the interfacial interaction between multiwalled carbon nanotubes and elastomers

We studied the effect of the microstructure of multiwalled carbon nanotubes (MWCNTs) on interfacial interaction in seven kinds of MWCNT/natural rubber (NR) composites. Unexpectedly, the degree of defects (ID/IG) of MWCNTs was found to play a key role in the interfacial interaction of MWCNT/NR composites. The content of bound rubber (BR) of the composites almost linearly increased with the increase in the ID/IG of MWCNTs. Then we studied the interfacial interaction between MWCNTs with high degree of defects and NR. Interestingly, the BR of the composites consisted of loosely adsorbed BR (LBR) and tight BR (TBR). TBR occupied about half of the total BR, and cannot be removed by extraction in hot toluene for 48 h. Meanwhile, the mobilities of macromolecules in TBR were more restricted than those in LBR. We discussed in depth the molecular origin of the interfacial interaction between defected MWCNTs and NR, and then proposed that LBR was topologically confined by the steps-like structure of defected MWCNTs whereas TBR was principally chemically bonded to MWCNTs. This study provided new insight on the interfacial interaction between MWCNTs and NR and thus provides guidance for the preparation of high-performance elastomer composites with strong interfacial interaction.

Effect of high-temperature heat treatment duration on the purity and microstructure of MWCNTs

The effect of high-temperature heat treatment on purity and structural changes of multiwalled carbon nanotubes (MWCNTs) were studied by subjecting the raw MWCNTs (pristine MWCNTs) to 2600∘C for 60 and 120 min. Thermogravimetric analysis (TGA), X-ray diffraction, Raman spectroscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to study the effect of heat-treatment duration on the purity and structural changes of MWCNTs. Results show that high-temperature heat treatment can be used to purify MWCNTs with proper optimization of treatment time. It was observed that 60 min heat treatment of raw MWCNTs imparts high purity and structural perfection to MWCNTs, while 120 min heat treatment imparts structural degradation to MWCNTs with collapse of the innermost shells. The present study indicates that metal impurities act as moderators in controlling the degradation of MWCNTs up to certain duration, and once the metal impurities escape completely, further heat treatment degrades the structure of MWCNTs.

Rheology and thermal conductivity of calcium grease containing multi-walled carbon nanotube

ABSTRACTRecently, nanofluids attract considerable interest for enhanced rheological behavior and thermal performance. The aim of this research is to study the influence of additives Multi-Walled Carbon Nanotubes (MWCNTs) on the rheological behavior and its structure, thermal conductivity, and the influence of shear thinning rate on oil separation at different temperatures for calcium grease. Various concentrations of MWCNTs (0.5, 1, 2, 3, and 4%) have been added to the grease to obtain the best percentages that improve the properties of nanofluid. The microstructure of MWCNTs and nanofluid were examined by X-ray diffraction (XRD), Transmission Electron Microscope (TEM), and Scanning Electron Microscope (SEM). These experimental investigations were evaluated with a Brookfield programmable Rheometer DV-III ULTRA. The results indicated that the optimum concentration of MWCNTs was 3%, and the dropping point increasing about 11%. The rheological behaviors of the nanofluids show that the grease with various concentrations of MWCNTs demonstrates non Newtonian behaviors and the results indicated that the shear stress, apparent viscosity and thermal conductivity increase with the increase of volume concentration of MWCNTs to 65%, 52%, and% 56, respectively.

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.

Optimization of Synthesis of Carbon Nanotubes Using Chemical Vapor Deposition Method

Multi walled carbon nanotubes (MWCNTs) were synthesized using floating catalyst-chemical vapor deposition (FC-CVD) with ferrocene and benzene as catalyst and carbon source, respectively. Argon was used as a purging gas while hydrogen was used as a carrier gas. Hydrogen flow rate, reaction time and reactor temperature were varied to obtain high yield and purity of MWCNTs. The morphology and microstructures of MWCNTs produced were studied using Scanning Electron Microscopy (SEM). It was found that the maximum yield and purity of MWCNTs were produced at hydrogen flow rate of 300 ml/min with reactor temperature of 900°C and reaction time 45 minutes. It was observed that the MWCNTs are film-like, randomly oriented and in some cases entangled with uniform diameter.

Compressive Strength and Microstructure of Multi-Wall Carbon Nanotubes Reinforced Cement Composites

Advancement in the study of carbon nanotube has enabled its application in civil engineering as constitutive materials or additives. In this study, the availability of applying multi-walled carbon nanotube to improve the characteristics of cement composites was investigated with experiments on more than 30 specimens. The multi-walled carbon nanotubes (MWCNTs) were effectively dispersed in the water with surfactant, which can keep stable for over 3 months. Specimens with MWCNTs of 0.025%, 0.05% and 0.1% of cement (by weight) were tested with a loading machine and then analyzed with a SEM. It was found that the compressive strength of the samples increased with the increasing MWCNTs, it can improve the 7-day compressive strength by 22% . Microscopic analysis (SEM) revealed that carbon nanotubes were surrounded with hydration products. The bridging and debonding of carbon nanotubes in cement pastes was observed as well.

Compressive Strength and Microstructure of Multi-Wall Carbon Nanotubes Reinforced Cement Composites

Advancement in the study of carbon nanotube has enabled its application in civil engineering as constitutive materials or additives. In this study, the availability of applying multi-walled carbon nanotube to improve the characteristics of cement composites was investigated with experiments on more than 30 specimens. The multi-walled carbon nanotubes (MWCNTs) were effectively dispersed in the water with surfactant, which can keep stable for over 3 months. Specimens with MWCNTs of 0.025%, 0.05% and 0.1% of cement (by weight) were tested with a loading machine and then analyzed with a SEM. It was found that the compressive strength of the samples increased with the increasing MWCNTs, it can improve the 7-day compressive strength by 22% . Microscopic analysis (SEM) revealed that carbon nanotubes were surrounded with hydration products. The bridging and debonding of carbon nanotubes in cement pastes was observed as well.

Effect of hydrogen plasma treatment on the growth and microstructures of multiwalled carbon nanotubes

Effect of hydrogen plasma treatment on the growth and microstructures of multiwalled carbon nanotubes

Effect of hydrogen plasma treatment on the growth and microstructures of multiwalled carbon nanotubes

Abstract The effect of hydrogen plasma treatment of iron oxide films on the growth and microstructure of carbon nanotubes (CNTs) by microwave plasma enhanced chemical vapor deposition process has been investigated. Microwave plasma was characterized in-situ using optical emission spectrometer. Morphology of the films was examined by scanning electron microscopy. Structural analysis was carried out by high resolution transmission electron microscopy (HRTEM) equipped with energy dispersive X-ray spectroscopy (EDS) and micro-diffraction attachments. It is found that oxide films without H2 plasma pretreatment or treated for lesser time resulted in CNT films with high percentage of carbonaceous particles and with embedded particles/nanorods distributed discontinuously in the cavity of the nanotubes. The embedded particles were found to be of iron carbide (Fe-C) as confirmed by HRTEM, EDS and micro-diffraction analysis. Experimental observations suggested that the iron oxide particles had poor catalytic action for CNT growth and in-situ reduction of oxide clusters to Fe by hydrogen plasma plays a key role in discontinuous filling of the nanotubes by the catalytic particles.

Aggregation, percolation and phase transitions in nematic liquid crystal EBBA doped with carbon nanotubes

Electrical conductivity, optical transmittance and microstructure of multiwalled carbon nanotubes (MWCNTs) dispersed in nematic liquid crystal 4-ethoxybenzylidene-4′-n-butylaniline (EBBA) were studied in the temperature range between 287 and 363 K. The concentration C of MWCNTs was varied within 0.01–1% wt. The percolation threshold with a noticeable increase in electrical conductivity (by many orders of magnitude) was observed in the vicinity of C ≈ 0.1% wt. The heating–cooling hysteretic behaviour of electrical conductivity and optical transmittance thermal pre-history effects were studied. These effects reflected strong agglomeration and rearrangement of nanotubes during the thermal incubation. The estimates show that transient behaviour during the thermal incubation can be caused by Brownian motion of MWCNTs. The solidification of MWCNT + EBBA composite in the nematic range extended by conditions of supercooling was also studied as a function of temperature using electrical conductivity measurements. The solidification lag-time dependence on supercooling temperature followed the classical heterogeneous nucleation law, with MWCNTs serving as centres of EBBA solidification.

Effect of Electro-Optical Memory in Liquid Crystals Doped with Carbon Nanotubes

The electro-optical response and the microstructure of multiwalled carbon nanotubes dispersed in nematic liquid crystals with negative dielectric anisotropy are investigated. In contrast to undoped liquid crystals, the liquid crystal dispersions of carbon nanotubes are characterized by the irreversible electro-optic response or the so-called electro-optical memory effect. This effect is that the light transmittance through the sandwiched layer of the dispersion placed between two crossed polarizers considerably increases after the electric field application cycle. The state of memory persisted over months of our observation. The memory is caused by the incomplete relaxation of liquid crystal molecules from the random planar to the initial homeotropic state after the field is off. It is pointed out that the stabilization of the planar state is due to the network of small nanotube aggregates formed in the liquid crystal disturbed by electro-hydrodynamic flows. It is revealed that the efficiency of electro-optical memory depends on the network morphology and the efficiency of electro-hydrodynamic flows in a liquid crystal.

The effects of synthesis procedures on the morphology and photocatalytic activity of multi-walledcarbon nanotubes/TiO2 nanocomposites

This study investigates the microstructures of multi-walled carbon nanotubes(MWNTs)/TiO2 nanocomposites, obtained by sol–gel and hydrothermal processes. The synthesizednanocomposite materials were characterized by x-ray diffractometry (XRD),Brunauer–Emmett–Teller (BET) adsorption analysis, transmittance electronmicroscopy (TEM), scanning electron microscopy (SEM), photoluminescence(PL) spectroscopy, and x-ray photoelectron spectroscopy (XPS). The effects ofthe synthetic procedures and MWNTs on the morphology and photocatalyticactivity of the nanocomposites were studied. The photocatalytic activity of theMWNTs/TiO2 nanocomposite was elucidated based on the photooxidation ofNOx under UV light illumination. A fleck-like and well dispersedTiO2 microstructure on the surface of the MWNTs was observed in the sol–gel system, whilecompact and large aggregated particles were found in the hydrothermal procedure. Thenanocomposite prepared by the sol–gel system exhibits better photocatalytic activity forNO oxidation (from 20.52 to 32.14%) than that prepared by the hydrothermal method(from 22.58 to 26.51%) with the same MWNT loading (from 0 to 8 wt%), respectively.The optimal MWNT content in the nanocomposite was considered at 8 wt%.Additionally, results confirm that the introduction of MWNTs will cause theNO2 to be more consumed than NO in the photocatalytic experiments, leading to more completeNOx photooxidation. These observations indicate that the differentTiO2 distributions on the MWNT surfaces and MWNT contents in the materials woulddetermine the morphology, the physicochemical and photocatalytic characteristics for thenanocomposite materials.

Etching effects of ethanol on multi-walled carbon nanotubes

The morphology and microstructure of multi-walled carbon nanotubes (MWCNTs) were modified using ethanol as a mild gas reactant. The etching by OH radicals and deposition of C radicals on the carbon nanotubes were considered to be responsible for the modification of the MWCNT structures and the formation of new carbon nanostructures. The effects of etching and deposition on the MWCNTs were confirmed by using methanol as another gas reactant; this molecule has a higher ratio of hydroxyl radicals to carbon atoms than ethanol. In addition, water vapor, containing no carbon atoms in the molecule, was also applied to etch the MWCNTs as a weak oxidant which resulted in stronger etching effects on the MWCNTs than methanol and ethanol.

05/00022 A computational fluid dynamics based study of the combustion characteristics of coal blends in pulverised coal-fired furnace: Sheng, C. et al. Fuel, 2004, 83, (11–12), 1543–1552

Multiwall carbon nanotubes (MWNTs) were synthesized using chemical evaporation deposition (CVD). The morphology and microstructure of MWNTs were observed via HRTEM. The multiwall carbon nanotubes are entangled to bundles with a diameter of several tens of nanometers. Electrochemical properties of MWNTs were examined via a variety of electrochemical testing techniques. The MWNTs electrode demonstrated a reversible lithium storage capacity of 340 mAh/g with good cyclability at moderate current density. The kinetic properties of lithium insertion in MWNTs electrodes were characterized via ac impedance measurements. It was found that the lithium diffusion coefficient DLi decreases with an increase of Li-ion concentration in MWNTs electrodes.

Preparation and characterization of carbon nanotubes for energy storage

Multiwall carbon nanotubes (MWNTs) were synthesized using chemical evaporation deposition (CVD). The morphology and microstructure of MWNTs were observed via HRTEM. The multiwall carbon nanotubes are entangled to bundles with a diameter of several tens of nanometers. Electrochemical properties of MWNTs were examined via a variety of electrochemical testing techniques. The MWNTs electrode demonstrated a reversible lithium storage capacity of 340 mAh/g with good cyclability at moderate current density. The kinetic properties of lithium insertion in MWNTs electrodes were characterized via ac impedance measurements. It was found that the lithium diffusion coefficient D Li decreases with an increase of Li-ion concentration in MWNTs electrodes.

Characterization of Co-catalyzed Multiwalled Carbon Nanotubes by High-Resolution Transmission Electron Microscopy

ABSTRACTThe dependence of characteristics of multiwalled carbon nanotubes (MWCNT) on the microstructure of cobalt catalysts are intensively investigated by high-resolution transmission electron microscopy (HREM). The cobalt catalysts are prepared by either molecule beam epitaxy (MBE) or by DC magnetron sputtering, followed by MWCNT growth by microwave plasma CVD. The MBE-grown Co thin films consist of large epitaxial grains, whereas the Co nanoparticles of FCC or HCP crystal structures can be directly grown on Si(001) substrates by sputtering. Various HREM technologies are applied to completely characterize the microstructures of those Co catalysts and MWCNT. The results reveal that the morphology and microstructures of MWCNT are greatly controlled by the characteristics of Co catalysts. Better quality of carbon nanotube can be grown by FCC cobalt rather than HCP cobalt. The different effects of cobalt catalysts on MWCNT are discussed in this paper.