Thermal Stability Of Carbon Nanotubes Research Articles

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.

Elastic Moduli of Non-Chiral Singe-Walled Silicon Carbide Nanotubes: Numerical Simulation Study.

Silicon carbide nanotubes (SiCNTs) have generated significant research interest due to their potential use in the fabrication of electronic and optoelectronic nanodevices and biosensors. The exceptional chemical, electrical and thermal properties of SiCNTs are beneficial for their application in high-temperature and harsh-environments. In view of the limited thermal stability of carbon nanotubes, they can be replaced by silicon carbide nanotubes in reinforced composites, developed for operations at high temperatures. However, fundamentally theoretical studies of the mechanical properties of the silicon carbide nanotubes are at an early stage and their results are still insufficient for designing and exploiting appropriate nanodevices based on SiCNTs and reinforced composites. In this context, the present study deals with the determination of Young's and shear moduli of non-chiral single-walled silicon carbide nanotubes, using a three-dimensional finite element model.

Improving the thermal stability of carbon nanotubes and their field emission characteristics by adding boron and phosphorus compounds

Adding boron and phosphorus compounds substantially improved the thermal stability of carbon nanotubes (CNTs), increasing their oxidation temperature by 37–173 °C. Analysis of the B1s and P2p X-ray photoelectron spectral peaks suggested that the boron and phosphorus compounds chemically poisoned active sites of CNTs by forming C–O–B, C–O–P and C–P–O bonds. These interactions drove away oxygen from the active sites and delayed their oxidative reactions. Incorporation of these compounds in CNT pastes followed by high-temperature heat treatment in a vacuum considerably enhanced their field emission characteristics, evaluated by measuring current–voltage (I–V) curves and long-term stability, for an X-ray tube application.

Inherent and interfacial evaluations of carbon nanotubes/epoxy composites and single carbon fiber at different temperatures

Abstract In order to develop an improved processability for machines and equipment operating at high temperatures, thermal degradation resistance of a high temperature epoxy network became a hot issue. Nanocomposites were not only used for improving mechanical and electrical properties. In here, the thermal stability of carbon nanotube (CNT)/epoxy nanocomposite was investigated by mechanical and interfacial evaluation. The dispersion state was monitored and observed by electrical resistance measurements as well as by using a scanning electron microscope (SEM). At low concentration of 0.3 vol%, the CNT reinforcement significantly improved the mechanical and interfacial properties of nanocomposites. At 150 °C, the CNT/epoxy nanocomposites exhibited much better thermal stability than neat epoxy resin as a result of the thermal resistance of CNTs. Microstructural studies revealed that the uniformity of the CNT dispersion played an important role in this thermal resistance. Addition of low concentration CNT could improve both mechanical properties and thermal stability of epoxy resin for high temperature applications.

Thermal stability of compound stucture of silicon nanowire encapsulated in carbon nanotubes

To guide the experiment research, the thermal stability of composite silicon nanowire encapsulated in carbon nanotubes is investigated by computer simulation. The cubic-diamond-structured silicon nanowires with the same diameter and [111] orientationt are filled in some armchaired single-walled carbon nanotubes. The heat process of compound structure of silicon nanowire encapsulated in carbon nanotubes is simulated by classical molecular dynamic method. Through the visualization and energy analysis method, the thermal stability of composite structure is studied. The changes in the thermal stability of silicon nanowires and carbon nanotubes are explained by the relationship between carbon nanotube space constraint and van der Waals force. It is found that the diameter of the carbon nanotubes is closely related to the thermal stability of silicon nanowires inside. When the nanotube diameter is small, thermal stability of silicon nanowires increases; when the nanotube diameter increases up to a certain size, the thermal stability of silicon nanowires will suddenly drop significantly: until the distance between silicon nanowires and the wall of carbon nanotube is greater than 1 nm, the thermal stability of silicon nanowires will be restored. On the other hand, silicon nanowires filled into the carbon nanotubes have an effect of reducing the thermal stability of carbon nanotubes.

The fabrication and tribological behavior of epoxy composites modified by the three-dimensional polyurethane sponge reinforced with dopamine functionalized carbon nanotubes

Three-dimensional (3D) interpenetrating network structure epoxy composites were fabricated based on the modified carbon nanotube (CNT) reinforced flexible polyurethane (PU) sponge. CNTs were first functionalized with polydopamine (PDA) as revealed by TEM imaging, which is formed via the oxidative self-polymerization of dopamine. Then the functionalized CNTs (CNT–PDA) were successfully anchored on the skeleton surfaces of sponge, forming a continuous 3D carbon network. The interfacial interaction between modified PU sponge and epoxy (EP) matrix was significantly enhanced due to the covalent linkage of PDA. Improvement in the thermal stability of CNT–PDA/PU3D/EP composites was observed by TG analysis and related to the CNTs anchored on the skeleton of sponge. The tribological properties of pure EP, PU3D/EP and CNT–PDA/PU3D/EP composites were comparatively investigated in terms of different loads and velocities. Results demonstrated that CNT–PDA/PU3D/EP composites exhibited the best tribological performance owing to the strong interfacial interaction and the 3D carbon network structure. In particular, the wear resistance of CNT–PDA/PU3D/EP composites was 6.2 times and 3 times higher than those of pure EP and PU3D/EP composites under the applied load of 1.6MPa, respectively.

Effect of Magnetic Field on the Growth of Aligned Carbon Nanotubes Using a Metal Free Arc Discharge Method and their Purification

Multiwalled Carbon Nanotubes (MWCNTs) have been synthesized using a low cost arc discharge method without using metal catalyst and vacuum devices. Effect of magnetic field on the synthesis of MWCNTs and their purity has been scrutinized. A magnetic field of 310 gauss has been found to give better purity of carbon nanotubes as confirmed by Raman spectroscopy. However, the removal of amorphous carbon from the surface of so prepared multiwalled carbon nanotubes has been achieved by different oxidizing conditions. It has been observed that the maximum removal of amorphous carbon found by using the strong oxidizing agent HNO3/H2O2. This strong oxidizing agent HNO3/H2O2removes most of the carbonaceous impurities leading to thermal stability of carbon nanotubes suggested by thermo gravimetric analysis. X-ray diffraction show the formation of carbon nanotubes having a peak indexed at (002) as the fingerprint for multiwalled carbon nanotubes. Fourier Transform Infrared (FTIR) spectra confirmed the formation of the multiwalled carbon nanotubes showing a characteristic stretching band at 1615 cm-1corresponding to the C=C bonds of tubular carbon. Raman spectroscopy revealed invaluable insights into the purification of nanotubes. G-band (1577 cm-1) corresponds to the confirmation of MWCNTs. Defect induced D-band (1355 cm-1) has been minimized after purifying CNTs with HNO3/H2O2for 24 hrs. Transmission Electron microscopic (TEM) studies indicate the formation of CNTs with controlled alignment having diameter in the range 2-8 nm.

Carbon Nanotube/Polymer Nanocomposites: Improved or Reduced Thermal Stabilities?

The effects of carbon nanotubes (CNTs) on the thermal stability of CNT/polymer nanocomposites are discussed using CNT/silicone composites as a model compound. Pristine CNTs can improve the thermal stability of polymer composites due to the high thermal stability of CNTs, their network structure and free radical scavenging capabilities. However, impurities such as metal catalyst residues and defects such as carboxylic acid functional groups in CNTs can lead to decreased thermal stability of CNT/silicone nanocomposites. Acid purification is an efficient way to remove metallic impurities and can enhance free radical scavenging capabilities. However, controlling the amount of oxidation is important to avoid acid catalyzed thermal degradation induced by carboxylic acid groups on CNT surfaces.

Thermal stability of carbon nanotubes probed by anchored tungsten nanoparticles

The thermal stability of multiwalled carbon nanotubes (CNTs) was studied in high vacuum using tungsten nanoparticles as miniaturized thermal probes. The particles were placed on CNTs inside a high-resolution transmission electron microscope equipped with a scanning tunneling microscope unit. The setup allowed manipulating individual nanoparticles and heating individual CNTs by applying current to them. CNTs were found to withstand high temperatures, up to the melting point of 60-nm-diameter W particles (∼3400 K). The dynamics of W particles on a hot CNT, including particle crystallization, quasimelting, melting, sublimation and intradiffusion, were observed in real time and recorded as a video. Graphite layers reel off CNTs when melted or premelted W particles revolve along the tube axis.

Thermal stability of carbon nanotubes, fullerene and graphite under spark plasma sintering

The thermal stabilities of carbon nanotubes, fullerene and graphite were investigated under spark plasma sintering (SPS). Results were compared with data from synchrotron radiation in situ high temperature X-ray diffraction of these materials. Part of the nanotubes and fullerene transformed into diamond under SPS, but graphite kept stable. There was no diamond conversion in the in situ X-ray diffraction experiments under the same condition. Their phase transitional mechanism indicated the presence of plasmas during the SPS operation.

Compact AC Modeling and Performance Analysis of Through-Silicon Vias in 3-D ICs

This paper introduces the first comprehensive and accurate compact resistance-inductance-capacitance-conductance ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RLCG</i> ) model for through-silicon vias (TSVs) in 3-D ICs valid from low- to high-frequency regimes, with consideration of the MOS effect in silicon, the alternating-current (ac) conduction in silicon, the skin effect in TSV metal, and the eddy currents in the silicon substrate. The model is verified against electrostatic measurements as well as a commercial full-wave electromagnetic simulation tool and subsequently employed for various performance (delay) analyses. The compact model is also applicable to TSVs made of carbon nanotube (CNT) bundles, once a slight modification (making the effective conductivity complex) is made. Various geometries (as per the International Technology Roadmap for Semiconductors) and prospective materials (Cu, W, and single-walled/multiwalled CNTs) are evaluated, and a comparative performance analysis is presented. It is shown that CNT-bundle-based TSVs can offer smaller or comparable high-frequency resistance than those of other materials due to the reduced skin effect in CNT bundle structures. On the other hand, the performance (delay) analysis indicates that the performance differences among different TSV materials are rather small. However, it is shown that CNTs provide an improved heat dissipation path due to their much higher thermal conductivity. In addition, the improved mechanical robustness and thermal stability of CNTs also favor their selection as TSV materials in emerging 3-D ICs.

The effect of thermal stability of carbon nanotubes on the flame retardancy of epoxy and bismaleimide/carbon fiber/buckypaper composites

Single-walled carbon nanotube (SWCNT) and multi-walled carbon nanotube (MWCNT) membranes (buckypaper) were incorporated onto the surface of epoxy and bismaleimide (BMI) carbon fiber composites. Their flammability behaviors were investigated by a cone calorimeter. The composites with buckypaper reduced the heat release rate (HRR) by more than 60% peak and smoke generation by 50% during combustion. The effects of different buckypaper on the flame retardancy of epoxy and BMI were compared and discussed. Our research team found that buckypapers acted as an effective flame-retardant shield to dramatically reduce the fire hazards of composites if they survived during fire combustion. Thermogravimetric analyses was used to compare the thermo-oxidation stability of the resins and buckypapers to explain the different effects of SWCNT and MWCNT buckypaper on flammability of epoxy and BMI carbon fiber composites.

Thermal stability of carbon nanotubes

Heat capacities of the carbon nanotubes (CNTs) with different sizes have been measured by modulated temperature differential scanning calorimetry (MDSC) and reported for the first time. The results indicated the values of C p increased with shortening length of CNTs when the diameters of CNTs were between 60 and 100 nm. However, the values of C p of CNTs were not affected by their diameter when the lengths of CNTs were 1–2 um, or not affected by the length of CNTs when their diameters were below 10 nm. The thermal stabilities of the CNTs have been studied by TG-DTG-DSC. The results of TG-DTG showed that thermal stabilities of CNTs were enhanced with their diameters increase. With lengths increase, the thermal stabilities of CNTs increased when their diameters were between 60 and 100 nm, but there is a slight decrease when their diameters were less than 60 nm. The further DSC analyses showed both released heat and T onset increased with the increase of CNTs diameters, which confirms the consistency of the results from both TG-DTG and DSC on CNTs thermal stability.

Study on the thermal stability of carbon nanotubes by simulation

Tight-binding molecular dynamics was used to simulate the thermal behavior of carbon nanotubes （CNTs） in this paper. A few kinds of single wall CNTs （SWCNTs） and double wall CNTs （DWCNTs） were studied during the simulation experiment at temperatures of 300—4000 K and the pressure of 1 atm. The results showed that the chiral SWCNTs have higher thermally stability than the armchair and zigzag type, and that the bigger the nanotube diameter is, the more stable the nanotube stucture is for those with the same chiral angles. The DWCNTs with at least one chiral structured wall are more stable than the others, but that with two zigzag walls were damaged badly, which also gives support to the study about SWCNT thermo-stability. One factor to describe CNTs in connection with their thermo-stability was proposed, and some data were theoretically analyzed based on carbon bond structures.

Enhanced thermal stability of carbon nanotubes by plasma surface modification in Al2O3 composites

A plasma polymerization method was employed to deposit an ultrathin pyrrole film of 3 nm onto the surfaces of single wall carbon nanotubes (SWCNTs) and Al2O3 nanoparticles for developing high-strength nanocomposites. The surfaces of plasma coated SWCNTs and Al2O3 nanoparticles were studied by high resolution transmission electron microscopy (TEM) and time-of-flight secondary ion mass spectroscopy. After sintering the SWCNTs-Al2O3 composites at different temperatures (maximum of 1200 °C), the thermal stability of plasma-coated SWCNTs was significantly increased, compared to their uncoated counterparts. After hot-press sintering, the SWCNTs without plasma coating were essentially decomposed into amorphous clusters in the composites, leading to degraded mechanical properties. However, under the same sintering conditions, the plasma surface modified SWCNTs were well preserved and distributed in the composite matrices. The effects of plasma surface coating on the thermal stability of SWCNTs and mechanical behavior of the nanocomposites are discussed.

Effects of MeV Ions on Thermal Stability of Single Walled Carbon Nanotubes

AbstractThe properties of carbon nanotubes (CNTs) are closely dependent on their structures, and therefore may be tailored by controllably introducing defects in the nanotube systems. In this work, we have investigated the effects of energetic ions (H+ and He+) on the thermal stability of single wall nanotubes (SWNTs) against oxidation in air. SWNTs were irradiated with MeV ions to various doses in the range 1013-1016 cm−2. Thermogravimetric analysis (TGA) was used to determine the loss of CNT masses as a result of oxidation processes. As opposed to the case of pristine SWNTs for which the temperature (Tmax) corresponding to maximum oxidation rate was found to be ∼ 495 °C, ion beam processing significantly enhanced the thermal stability of nanotubes, e.g., Tmax increased by about 30 °C after H+ implantation (dosage: 1015 cm−2) and 17 °C after He+ implantation (dosage: 1013 cm−2). The activation energies for thermal oxidation under various conditions were also extracted from TGA data, with values ranging from 1.13 eV (for pristine SWNTs) to 1.37 eV, depending on ion doses and species. Raman spectroscopy was used to determine the characteristics of the G band (C-C stretching mode) and D band (disorder induced mode) in CNTs. The work suggests that the SWNTs modifies to more stable structure (may be cross-linked SWNTs) at small doses. Once the number of defects exceeds some critical value (depending on the type and dosage of bombarding ion) the bonding energy in CNTs weakens, leading to the reduced thermal stability of CNTs against oxidation.