Increasing Carbon Nanotubes Content Research Articles

Nanocomposites of ultrahigh molar mass polyethylene and modified carbon nanotubes

ABSTRACTIn this work, the use of a laboratory twin‐screw extruder was evaluated to process ultrahigh molar mass polyethylene and composites with carbon nanotubes (CNTs). Commercial polymer samples with lubricant (1%) and different percentages (0.01%, 0.05%, and 0.1%) of pure, oxidized, and chemically surface treated multi‐walled carbon nanotubes (MWCNTs) were evaluated. The results showed that polymer melting and crystallization temperatures were not affected by CNTs, although an increase in the degree of crystallinity in all nanocomposites was observed along with a decrease in crystal size. Therefore, CNTs behaved as nucleating agents. All ultrahigh molar mass polyethylene (UHMWPE)/CNT samples showed increased initial degradation temperature, although this was not very great when introducing acetylated and stearic acid modified CNTs. Both oxidized CNTs and stearic acid CNTs did not markedly improve the composites' mechanical properties. Therefore, the nanocomposites containing pure CNTs and most of those with acetylated CNTs resulted in higher reinforcement for UHMWPE. The addition of the lubricant allowed the polymer matrix to be processed in the extruder, whereas the increase in CNT content in UHMWPE improved the stiffness of the material. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47459

Synthesis and Properties of Silica and Alginate Hybrid Aerogel Particles with Embedded Carbon Nanotubes (CNTs) for Selective Sorption.

The manuscript describes methods for producing hybrid silica microparticles and hybrid alginate beads with carbon nanotube (CNT) contents up to 4.5 and 30 wt.%, respectively. Silica hybrid aerogel microparticles with embedded nanotubes were obtained using a two-stage sol–gel method with a gelling process in an oil-emulsion. Alginate hybrid aerogels with embedded nanotubes were obtained using cross-linking reactions. The following methods were used to measure the structural characteristics of obtained materials: nitrogen adsorption porosimetry, scanning electron microscopy (SEM), and others. It is shown that specific surface area and pore volume increase with the increase of CNT content in silica aerogel microparticles. Obtained aerogels were tested as adsorbents for argon–oxygen separation. The alginate hybrid aerogel with 30 wt.% CNT content has the best argon adsorption selectivity.

Mechanical and Tribological Behavior of Multiwalled Carbon Nanotubes-Reinforced AA7075 Composites Prepared by Powder Metallurgy and Hot Extrusion

Carbon nanotubes (CNT) are synthesized using arc discharge method in an open air. Various amounts of carbon nanotubes-reinforced AA7075 composites are prepared by powder metallurgy route and then hot extrusion at 450 °C. Hot-extruded composites are characterized, and mechanical properties are measured. Dry sliding wear properties of hot-extruded samples were evaluated using a pin-on-disk method for various loads (5-20 N) at room temperature and for various temperatures (100-400 °C) at the applied load 10 N as a function of CNT amount. Grain size of the composites is decreased compared with Al alloy matrix. Transmission electron microscopy of the composites revealed that the CNT are uniformly distributed in the composites. Mechanical properties of the hot-extruded composites are enhanced with an increase in CNT content. The wear performance is improved with an increased CNT amount, but decreases with an increase in the applied load and temperature as well. The wear damage is mild at lower applied loads and temperatures, whereas the damage is severe at 400 °C. The wear mechanism was plowing in the initial stages which is transformed to severe sliding and chipping with increasing load and temperature. The enhanced wear behavior of composites is attributed to self-lubricating nature of carbon nanotubes.

Cyclic high temperature corrosion studies of carbon nanotubes-Cr2O3 composite coatings on boiler steel at 900°C in molten salt environment

PurposeMolten sulphate-vanadate induced hot corrosion is the main reason of failure of boiler tubes used at high temperatures in thermal power plants. The hot corrosion can be encountered by applying thermal spray coatings on the alloy steels. In this perspective, this paper aims to attempt to investigate the effect of carbon nanotubes reinforcement on Cr2O3 composite coatings on hot corrosion behaviour of ASTM-SA213-T22 steel in a corrosive environment of Na2SO4 – 60%V2O5 at 900°C for 50 cycles.Design/methodology/approachThe coatings have been deposited with high velocity oxy fuel process. The samples were exposed to hot corrosion in a Silicon tube furnace at 900°C for 50 cycles. The kinetics of corrosion behaviour were analysed by the weight gain measurements after each cycle. Corrosion products were analysed with X-ray diffraction, scanning electron microscopy, energy dispersive and cross-sectional analysis techniques.FindingsDuring investigations, the carbon nanotubes (CNT) reinforced Cr2O3 composite coatings on T22 steel were found to provide better corrosion resistance in the molten salt environment at 900°C. The coatings showed lower weight gain along with formation of protective oxide scales during the experiment. Improvement in protection against hot corrosion was observed with increase in CNT content in the coating matrix.Research limitations/implicationsThe addition of CNT has resulted in reduction in porosity by filling the voids in chromium oxide coating, with interlocking of particle and has blocked the penetration of corroding species to enhance the corrosion resistance of the composite coatings. The corrosion rate was found to be decreasing with increase in CNT content in coating matrix.Originality/valueIt must be mentioned here that high temperature corrosion behaviour of thermally sprayed CNT-Cr2O3 composite coatings has never been studied, and it is not available in the literature. Hence, present investigation can provide valuable information for application of CNT-reinforced coatings in high temperature fuel combustion environments.

Hot corrosion behaviour of carbon nanotubes reinforced chromium oxide composite coatings at elevated temperature

The present work aims to investigate the hot corrosion resistance of HVOF (high velocity oxy fuel) sprayed CNT (Carbon nanotubes) reinforced Cr2O3 coated ASTM-SA213-T22 (T22) steel at 800 °C temperature in molten salt environment. The coatings have been deposited with high velocity oxy fuel process. The samples were exposed to hot corrosion in a Silicon tube furnace at 800 °C for 50 cycles. The kinetics of corrosion behaviour were analysed by the weight gain measurements after each cycle. Corrosion products were analysed with x-ray diffraction, scanning electron microscopy, energy dispersive and x-ray analysis techniques. During investigations, the CNT reinforced Cr2O3 composite coatings on T22 steel were found to provide better corrosion resistance in the molten salt environment at 800 °C. The coatings showed lower weight gain along with formation of protective oxide scales during the experiment. Improvement in protection against hot corrosion was observed with increase in CNT content in the coating matrix. The addition of CNT has resulted in reduction in porosity by filling the voids in chromium oxide coating, with interlocking of particle and has blocked the penetration of corroding species to enhance the corrosion resistance of the composite coatings. The corrosion rate was found to be decreasing with increase in CNT content in coating matrix.

Polyethylene Glycol-Carbon Nanotubes/Expanded Vermiculite Form-Stable Composite Phase Change Materials: Simultaneously Enhanced Latent Heat and Heat Transfer.

Polyethylene glycol (PEG)-carbon nanotubes (CNTs) with expanded vermiculite (EVM) form-stable composite phase change materials (PCE-CPCMs) were constructed via the efficient synergistic effect between EVM and CNTs. The resultant material demonstrated simultaneously enhanced latent heat and heat transfer. The unique EVM pore structure and CNTs surfaces contributed to the form stability of PCE-CPCMs. The adsorption capacity was 77.75–81.54 wt %. The latent heat of the PCE-CPCMs increased with increasing CNTs content due to the decreasing inhibition effect of EVM and the increasing adsorption capacity of PEG, which was 83.9 J/g during melting and 104.2 J/g during solidification for PCE7.09. The pore confinement and surface EVM interactions inhibited the heat storage capacity of the PCE-CPCMs. Moreover, the inhibition effect on the heat storage capacity of PCE-CPCMs during the melting process was stronger than during solidification due to the crystallization-promoting effect. The heat transfer of PCE-CPCMs was significantly enhanced by the CNTs filler (0.5148 W/(m·K) for PCE7.09) due to the decrease in interfacial thermal resistance and the formation of rapid thermally conductive pathways. Fourier transform infrared spectroscopy, thermogravimetric analysis, and thermal cycles test results confirmed that the PCE-CPCMs exhibited excellent chemical compatibility, thermal stability, and reliability.

Promoting Helix-Rich Structure in Silk Fibroin Films through Molecular Interactions with Carbon Nanotubes and Selective Heating for Transparent Biodegradable Devices

Tunability of the properties of regenerated silk fibroin (RSF) films is required for use as flexible substrates in many applications aimed at exploiting their unique mechanical, optical, and degradation properties, such as bioelectronic and biomedical devices. Here, a new approach for programing these properties is demonstrated based on molecular interactions between fibroins and functionalized carbon nanotubes (CNTs), combined with microwave heating. RSF-CNT composite films were irradiated with microwaves, resulting in local heating and local structural transition of amorphous silk fibroin molecules to stable helical structures. Upon microwave irradiation, a significant increase of helix secondary structure between 18.9% and 35.5% was observed with increasing CNT content. By further methanol vapor-treatment, the composite films with different helical content exhibited controllable mechanical and degradation properties combining the higher extensibility and faster degradation of α-helix structures with th...

Preparation and properties of CNT reinforced Fe–Ni–P composites fabricated by liquid phase sintering

The Fe–Ni–P matrix composites reinforced with carbon nanotubes (CNTs) were prepared by means of liquid phase sintering at 950[Formula: see text]C. The effects of the mass fraction of CNTs on the microstructures and properties of the composites were investigated. It is noteworthy that the structures of CNTs were hardly damaged during the sintering process via evaluation of microstructures on as-sintered composites. The strength and ductility increased gradually with the increase of CNT content while the saturation magnetization decreased gradually. The sample containing 1 wt.% CNTs showed a good combination of a compression ratio of 60% and a compressive strength of approximately 3800 MPa, which indicated its potential application in modern power generation systems.

Catalytic cracking of light naphtha over hierarchical ZSM-5 using rice husk ash as silica source in presence of ultrasound energy: Effect of carbon nanotube content

Hierarchical structured ZSM-5 was prepared by sonochemical assisted carbon nanotube templated method and their catalytic activity was examined in catalytic cracking of light naphtha. Different amounts of carbon nanotubes (5, 15, 30 wt%) was introduced into the synthesis gel, as a hard template, for mesopore creation. The rice husk ash was used as a silica source. In order to analyse physicochemical properties of synthesized catalysts, multi-techniques such as XRF, XRD, BET, FE-SEM, NH3-TPD and TGA were used. The obtained results revealed that by adjusting the amount of carbon nanotube, catalyst properties can be favorably tuned. The XRD analysis confirmed successful synthesis of high crystalline ZSM-5 zeolite. According to the FE-SEM analysis, small rough spheres of ZSM-5 were synthesized in all samples. The use of carbon nanotube led to creating new mesopores in the ZSM-5 structure. However, increase in carbon nanotube content led to destruction of micropores of ZSM-5. The acidity of ZSM-5 slightly changed. Results from catalytic activity test showed that high catalyst stability can be achieved in presence of mesopores along with the micropores. The highest olefin yield (54 wt%) and the best catalytic stability were obtained over the synthesized ZSM-5 with 15 wt% carbon nanotube.

A comprehensive in vitro study of the carbon nanotube enhanced chitosan scaffolds for cancellous bone regeneration

It is well known that chitosan composites are good candidates for novel orthopedic applications. Herein, a comprehensive in vitro comparison between neat and carbon nanotube (CNT) containing chitosan scaffolds will be reported for the first time. Functionalized multiwalled carbon nanotubes (f-MWCNTs) prepared by the acid treatment of CNTs were used as reinforcement agents. In this study, a group of chitosan scaffolds was manufactured reinforced by different amounts of the f-MWCNTs. Analysis of the FTIR spectra of the scaffolds confirmed the presence and functionalization of MWCNTs in polymer matrices. A high degree of crystallinity in the engineered scaffolds was noted in XRD patterns. Further, XRD results were used to study the structural properties. In order to survey the morphology of the chitosan/MWCNT scaffold, a FESEM micrograph was taken. The values of porosity ranged between 93.6 and 94.5%. The mechanical characteristics of the chitosan scaffolds were boosted by introducing f-MWCNTs. As expected, pore size on crystallinity index (CrI) of the scaffolds were decreased after introducing the f-MWCNTs. PBS was used to investigate the water uptake and water stability of the products. MTT assay results of the scaffolds’ cell viability shows the non-toxicity and satisfactory biocompatibility of the CNT enriched scaffolds. The electrical conductivity test showed stepwise increases in electrical conductivity with the increase in CNT content. This work demonstrates that f-MWCNTs can improve the capabilities of the chitosan scaffolds in low concentrations without endangering cell proliferation on the scaffolds.

Influence of the morphological structure of carbon nanotubes on the viscoelasticity of PMMA‐based nanocomposites

ABSTRACTThe rheological behavior of polymeric nanocomposites provides major determination for their processability. In this work, three carbon nanotubes (CNTs) with varied geometries were adopted as nanofiller and then were introduced into poly(methyl methacrylate) (PMMA) matrix with different loadings (0.07–1.0 wt %). The different preparation routine led to varied CNTs dispersion states, on which the shear viscosity and the compressibility of their melts were proved to be sensitive. The technology for the preparation of their nanocomposites played a crucial role in controlling their rheological behavior. With melting blended bare CNTs, the dynamic shear viscosity of PMMA/CNTs increased with the increase of CNTs content, accompanied by aggregated CNTs in which no polymer matrix was entrapped. With the help of surface modification and pre‐mixing, well dispersed CNTs were obtained and a rather low aggregation rate ca. 0.029% was revealed. The well dispersed CNTs with an organic layer which was constructed by small molecules and presented lower viscosity. Such CNTs led to no remarkable clusters within polymer host and played the role of lubricant with an increased‐mobility layer, which can be reflected from the weighted relaxation time spectra. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46444.

Effects of carbon nanotubes additions on flash ignition characteristics of Fe and Al nanoparticles

ABSTRACTThe influences of carbon nanotubes (CNTs) additions on the flash ignition characteristics of Iron (Fe) and aluminum (Al) nanoparticles (NPs) were presented. CNTs can be used as the additive to these metal nanoparticles for improving the flash ignition and burning processes. Different mass fractions of CNTs additions were considered. The mixture of Al and CNTs could combust in air with obvious giant flame, whereas the mixture of Fe and CNTs combusted under a relative stable condition with slight red light. The temperature distributions were measured using non-contact optical method and showed that Al NPs mixed with CNTs were burning at a higher temperature level than Fe NPs. Although different mass fractions of CNTs cannot significantly change the overall flash ignition phenomenon, CNTs additions influenced the minimum ignition energy (MIE) of mixtures. The appropriate content of CNTs addition can decrease the Fe NPs MIE significantly. However, the Al NPs MIE decreased all along with the increase of CNTs content. The micro- and nano- structures of Fe and Al NPs with CNTs additions before and after ignitions were examined by scanning electron microscope and high-resolution transmission electron microscopy. It was found that the special thermal conductive characteristics of CNTs and the cross-connected features for metal particles with CNTs caused the enhancement of flash ignition.

Preparation of Aluminum–Carbon Nanotubes Composite Material by Hot Pressing

A hot pressing method is developed for aluminum powder with preliminary sample and die heating to 600°C. The effect of modifying aluminum with carbon nanotubes in an amount of 0.01–1 wt.% is studied. The microstructure, phase composition, and mechanical and electrical properties of the specimens obtained are determined. It is established that the best uniformity and mechanical strength applies to aluminum specimens containing small additions of nanotubes, i.e., 0.01–0.05 wt.%. An increase in carbon nanotube content above 0.1 wt.% is a reason for the occurrence of inhomogeneity formed as a result of nanotube conglomerates.

Preparation and mechanical properties of carbon nanotube-silicon nitride nano-ceramic matrix composites

Carbon nanotube–silicon nitride nano-ceramic matrix composites were fabricated by hot-pressing nano-sized Si3N4 powders and carbon nanotubes. The effect of CNTs on the mechanical properties of silicon nitride was researched. The phase compositions and the microstructure characteristics of the samples as well as the distribution of carbon nanotube in the silicon nitride ceramic were analyzed by X-ray diffraction and scanning electron microscope. The results show that the microstructure of composites consists mainly of α-Si3N4, β-Si3N4, Si2N2O and carbon natubes. The addition of proper amount of carbon nanotubes can improve the fracture toughness and the flexural strength, and the optimal amount of carbon nanotube are both 3wt.%. However the Vickers hardness values decrease with the increase of carbon nanotubes content.

Characterization of solution casting derived carbon nanotube reinforced poly(vinyl alcohol) thin films

Carbon nanotube (CNT) reinforced polyvinyl alcohol (PVA) composite thin films have been prepared by a solution casting process at room temperature using gum acacia as a surfactant. CNT contents in the composites were varied from 5 to 10% by weight to increase its electrical conductivity. Electrical properties, such as conductivity, capacitance, dielectric constant and loss tangent, of the composites were investigated. All the electrical properties were found to be improved with the incorporation of CNTs. The absorbance and transmittance of light were determined by UV–visible spectroscopy and from the transmittance data, band gaps were calculated. The smallest band gap, of 1.18 eV, was found for the 10% CNT containing composite while the 0% CNT containing composite had a band gap of 2.4 eV. Thermal properties of the films were characterized by a thermo mechanical analyzer. The experimental results revealed that the blended films exhibited higher stability and improved thermal properties, which suggests the occurrence of an interaction, detected by FTIR, among PVA, CNT and water molecules in the films. The mechanical properties, tensile strength, elongation at break and Young modulus, were found to be improved. Water absorption properties of the composites were found to decrease with the increase of CNT content. The lowest water uptake properties and highest thermal stability were demonstrated by 10% CNT containing film. All of the results indicated that the developed PVA/CNT composite might be promising for use in optoelectronic application.

Effect of carbon nanotubes and aluminum oxide on the properties of a plasma sprayed thermal barrier coating

To protect the structural components of a power generating unit from the corrosive environment, thermal spray coatings are applied to the components. In the present work, four different types of thermal barrier coating (TBC) viz. partially stabilised zirconia (8YSZ), zirconia-20% alumina (ZA) composite coating without carbon nanotube (CNT) reinforcement, and ZA with 1% and 3% CNT reinforcement. The coating was deposited on NiCrAlY coated P91 steel using a plasma spraying process. The coating microstructure and phases were characterised using field emission scanning electron microscope (FE-SEM) with energy dispersive spectroscopy (EDS). The phases of the coating were analyzed using X-ray diffraction technique. The effect of CNT reinforcement on the thermal conductivity, porosity, and hardness of the composite coatings was investigated. The protective behavior of the coatings was characterised by potentiodynamic polarization testing and electrochemical impedance measurements. The thermal conductivity of the composite coating was found to be increased with increasing CNT content. Hardness was found to be highest for 3% CNT reinforcement and the thermal conductivity was found to increase with decreasing porosity. The electrochemical measurements indicate that reinforcement of CNT in zirconia alumina composite coating improved its corrosion resistance.

Nanoindentation and wear behaviour of copper based hybrid composites reinforced with SiC and MWCNTs synthesized by spark plasma sintering

In this study, copper based hybrid composites comprising of multiple reinforcements like silicon carbide and multiwalled carbon nanotubes were synthesized via mechanical milling followed by spark plasma sintering. The weight fraction of silicon carbide was fixed to 4 wt.% and that of multiwalled carbon nanotubes was varied from 1 to 4 wt.% in the steps of 1 wt.%. Microstructural observations carried using scanning and transmission electron microscopy showed uniform dispersion of both silicon carbide and multiwalled carbon nanotubes. Hardness behaviour was analysed using microindentation and nanoindentation at various local regions of the hybrid composites. The experimental results showed that the multiple reinforcements were effective in improving the hardness and elastic modulus. In addition to this tribological properties were evaluated using pin on disc tribometer under variable normal loads. The wear rates of all hybrid composites were low compared to that of pure copper revealing significant strengthening by both the reinforcements. However the electrical conductivity of hybrid composites were found to decrease with the increase in carbon nanotubes content.

Investigating the performance, chemical, and microstructure properties of carbon nanotube-modified asphalt binder

Carbon nanotubes (CNT) hold the potential to enhance the performance of construction materials such as asphalt binders and mixtures. With the goal of designing long-life asphalt pavements, this research report investigates the laboratory performance of CNT-modified asphalt. Mixing combination conditions including shearing time and shearing rate are studied in the first step. Then modified asphalts with different CNT contents are evaluated by penetration, softening point, and ductility indexes. Storage stability of modified asphalt is accessed using the separation test. After that, aged asphalts are obtained by using the thin film oven test (TFOT). Samples of base and CNT-modified asphalts before and after ageing are characterised by running the rotational viscosity (RV) test, dynamic shear rheometer (DSR) test, and bending beam rheometer (BBR) test. Furthermore, Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM) are employed to characterise the functional groups and microstructures of base and modified asphalt binders before and after ageing. It is shown that shearing rate and shearing rate*shearing time interaction have a profound influence on the property of modified asphalt whereas shearing time does not. Conventional test results indicate that increasing CNT content would decrease penetration and ductility while increasing the softening point. The separation test shows that CNT may settle down during the storage process. Rheological test results show that the addition of CNT can improve the high temperature performance and ageing resistance while decreasing the low temperature performance. The functional groups in base and modified asphalt are found to be similar which indicates that there are no chemical reactions during modification. It demonstrates that CNT-modified asphalt has better anti-ageing property with a lower increase in sulphoxide index after ageing. AFM characterisation provides details of the CNT modification mechanism. This research provides useful guidance and potential problems on the use of CNT as a high performance modifier.

Mechanical and electrical properties of ethylene-1-octene and polypropylene composites filled with carbon nanotubes

In the present work, the effect of carbon nanotubes (CNTs) addition on the electrical conductivity and mechanical properties of thermoplastic polymers was investigated. CNTs were incorporated into the polymer matrix either in high concentrations (masterbatch) or as an additive in small quantity (dilution source of masterbatches in a polymeric binder). Masterbatches containing a 5–20% by weight of CNTs and composites obtained through their addition in polypropylene - the actual content of CNTs in polymer 0.1 and 0.01 wt% - were synthesized and characterized by mechanical tests and scanning electron microscopy. Also, the frequency dependence of the AC electrical conductivity of masterbatches and dilute composites were measured. It has been shown that the introduction of masterbatches containing 10 wt% of CNT provides a more efficient reinforcement of the composite than those using masterbatches with 5 and 20 wt% of CNTs. It is also found that the alternating current (AC) conductivities display two or three regions: regions of constant conductivity and regions where the conductivity increases with increasing frequency (following the percolation scaling law). It was also observed that the conductivity increases drastically with increasing CNT content in the investigated concentration range (from 0 to 20 wt%).

Characterization of plasma-sprayed carbon nanotube (CNT)-reinforced alumina coatings on ASME-SA213-T11 boiler tube steel

In this research work, carbon nanotube (CNT)-reinforced Al2O3 coatings were prepared and successfully deposited on ASME-SA213-T11 boiler tube steel. Coatings were deposited by the plasma spray process. Ni-Cr was also used as a bond coat before applying CNTs-Al2O3 coatings. The coatings were subjected to metallography, XRD, SEM/EDAX, and X-ray mapping analysis. The porosity of CNT-Al2O3 mixed coatings was decreasing with increase in CNT content. The CNTs were found to be uniformly distributed within the Al2O3 matrix. The CNTs were chemically stable during the spray forming. It did not react to form oxides or aluminum carbides even at the very high processing temperature.