Increasing Carbon Nanotubes Content Research Articles

Study on Thermal-Oxidative Aging Properties of Ethylene-Propylene-Diene Monomer Composites Filled with Silica and Carbon Nanotubes.

In this work, a small amount of carbon nanotubes (CNTs) was used to partially replace the silica in ethylene-propylene-diene monomer (EPDM) to prepare EPDM composites via mechanical blending. The mechanical properties, thermal-oxidative aging properties and thermal stability of the composites were systematically investigated. The results showed that with the increase of CNTs content, the Shore A hardness and stress at 100% strain of the composites increased, while the elongation at break decreased. With the aging time increasing, the aging coefficient and elongation at break of composites decreased while hardness increased due to the raise of crosslinking density. In addition, evidences were found to demonstrate the improved aging resistance by adding CNTs in the EPDM composites, including the less change in Shore A hardness, the smaller change ratio of elongation at break and the lower aging coefficient. When the content of CNTs reached 10 phr, the aging coefficient of the EPDM composite aged for 168 h was nearly twice that of the composite without CNTs, and the thermal stability of the EPDM composite with CNTs was improved as demonstrated by thermal analysis.

Vertically aligned carbon nanotubes/graphene/cellulose nanofiber networks for enhancing electrical conductivity and piezoresistivity of silicone rubber composites

The directional arrangement of a conductive filler is an effective method to improve electrical conductivity of composites. In this paper, aqueous dispersions of carbon nanotubes and graphene were prepared by high-pressure microfluidization technology. After mixing cellulose nanofiber into these dispersions, vertically aligned carbon nanotubes/graphene network foams were prepared using an ice-template assembly method, to which liquid silicone rubber was filled to obtain carbon nanotubes/graphene/silicone rubber composites. Polymethylhydrosiloxane was grafted with 3-(trimethoxysilyl) propyl methacrylate and the resultant copolymer was used as a coupling agent to improve interface interaction between silicone rubber and filler. With increasing carbon nanotubes content, the electrical conductivities of the foams and composites increased. The composite prepared with 4 g CNT and 1 g graphene aqueous dispersions had the conductive percolation threshold of 0.08% and exhibited high conductivity at low filler content. The addition of the copolymer increased the compressive strength of the composites. The composite prepared with 1 g CNT and 4 g graphene aqueous dispersions was encapsulated in an insole as a piezoresistor to effectively detect the number of pedestrian steps, and had a stable output of electrical signal. This work provides a method for preparing conductive silicone rubber composites with low conductive percolation threshold and excellent piezoresistivity.

Superior high-temperature tensile properties of aluminum matrix composites reinforced with carbon nanotubes

The relatively low strength of aluminum (Al) alloys and Al matrix composites at high temperatures has greatly limited their applications in aerospace and automobile areas. In this study, high-performance carbon nanotubes (CNTs)/Al composites with high room-temperature tensile strength over 500 MPa were tested at elevated temperatures up to 400 °C. Results showed that the strength of CNTs/Al composites increased with increasing CNT content up to 5 vol%. CNTs/Al composites showed improved reinforcing effects at elevated temperatures compared with those at room temperature. Consequently, the 5 vol%CNTs/Al composite achieved high tensile strength of 205 MPa when tested at 400 °C, which was superior to those values (less than 100 MPa) of most available Al matrix composites. The underlying mechanism was thoroughly discussed from the grain sizes, phase compositions, interface reaction and strengthening mechanisms at different testing temperatures. The results have revealed the excellent high-temperature properties of CNTs/Al composites and their potential use at elevated temperatures.

Study on carbon nanotube/shape memory polymer composites and their applications in wireless worm actuator

Abstract In this study, the surface of the carbon nanotubes was modified by chemical functionalization. The carbon nanotubes were placed in a mixed acid solution with a nitric acid-to-sulfuric acid volume ratio of 1:3. The results of the functionalization of the carbon nanotubes were investigated by controlling the reaction time. From the experimental results, the functionalized carbon nanotubes with a reaction time of 12 hours show good dispersibility. In the study of the essential characteristics of composite materials, it was observed that the tensile strength decreased with increase of carbon nanotube content. Compared with the result of the tensile strength test, it can be found that with increasing carbon nanotube content, the microwave heating and shape recovery speed are greatly improved. The experimental results show that the shape memory polymer composite with 4 wt% carbon nanotubes has the fastest microwave heating rate, so it takes only 2 minutes to achieve complete shape recovery. Finally, this study used shape memory polymer composites doped with 4 wt% carbon nanotubes as the driving end, combined with an elastic structure made of polyimide (PI) film using origami techniques to form a worm actuator. In the test, the system could move a distance of 6 mm forward during a microwave time of 1 minute. In addition, this research also constructed a physical model of shape memory polymer and explored the simple movement mechanism of the system.

Environmental-friendly three-dimensional carbon nanotubes grown by soil clay and graphene oxide nanosheets for energy storage

Environmental-friendly three-dimensional (3D) multiwalled carbon nanotubes (CNTs) grown from the montmorillonite (MMT) and graphene oxide (GO) without adding metal catalysts are the first investigation for the supercapacitor electrode application, which dramatically reduces the noble and rare metal needs. Growth mechanisms of as-synthesized CNT-based MMTs (MCNTs) and CNT-based GOs- (GCNTs) via thermal chemical vapor deposition are suggested that the Ni ion nuclear seeds are self-arranged and intercalated spontaneously into the substrate surfaces and template layers. In addition, the maximum energy densities of MCNT and GCNT electrodes are 63.8 Wh/kg at 0.02 kW/kg and 147 Wh/kg at 0.09 kW/kg, respectively. The electrochemical impedance spectroscopy spectrum exhibits the charge transfer resistance significantly decreases with fabricating 3D active composite materials, indicating the mass transfer limitation in the low-frequency area and the charge transfer of kinetic controlling in the high-frequency domain. The Bode-phase angle at 78.6° of the GCNT electrode indicates ideal capacitive behavior. Frequencies of MCNT and GCNT electrodes at a phase angle of 45° are 0.27 and 0.11 Hz, corresponding to the calculated time relaxation constants of 3.70 and 9.09, respectively. MCNT and GCNT composites are clear to enhance a more surface accessible region for electrolyte ions and electron conductivity with the increasing CNT content. After 2000 continuous cyclic voltammetry and galvanostatic charge-discharge cyclic experiments, specific capacitance retentions with a 5% error bar of 3D MCNT and GCNT electrodes achieve 122.3 and 75.2%, 127.6 and 85.3%, respectively. As both electrodes, less metal usage is friendly to the environment, and in addition, layered fabrication is beneficial for production and further follow-up recycle separation of energy devices. Non-blending 3D MCNT and GCNT composites possess the potential to be the prospective materials for further energy storage application.

Thermal and electrical dual‐triggered shape memory Eucommia ulmoides gum derived from renewable resources

AbstractThermal and electrical dual‐triggered shape memory composites were prepared by introducing multi‐walled carbon nanotubes (CNTs) into the Eucommia ulmoides gum (EUG) matrix. The morphology of the composites was investigated by scanning electron microscope, and the CNTs exhibited good dispersion in the EUG matrix. The well‐dispersed CNTs built a conductive network in the EUG matrix, generating electric current induced heat. The composites showed the shape memory effect upon stimulation by heat and electricity. The composites exhibited increased shape recovery speed with the increase in CNTs content and applied voltage. Furthermore, the composites recovered to 90% of their initial length within 36 V (AC), which is safe for humans. This work provides a feasible material with dual‐triggered shape memory characteristics, which can find potential applications in medicine devices.

Hot corrosion behaviour of CNT-reinforced ZrO2-Y2O3 composite coatings on boiler tube steel at 900°C

PurposeIn Indian thermal power plants, the main cause of boiler tube failure is the presence of molten sulphates and vanadates, which deteriorate the tube material at high temperatures. To combat the hot corrosion failure of metals, thermal spray technology is adopted. This study aims to investigate and study the effect of hot corrosion behaviour of carbon nanotube (CNT)-reinforced ZrO2-Y2O3 composite coatings on T-91 boiler tube steel in a molten salt environment at 900 °C for 50 cycles.Design/methodology/approachA plasma spray technique was used for development of the coatings. The samples were exposed to hot corrosion in a silicon tube furnace at 900 °C for 50 cycles. After testing, the test coupons were analysed by X-ray diffraction, scanning electron microscopy/energy dispersive spectroscopy and cross-sectional analysis techniques to aid understanding the kinetics of the corrosion reaction.FindingsCNT-based reinforced coatings showed lower weight gain along with the formation of protective oxide scales during the experimentation. Improvement in protection against hot corrosion was observed with increase in CNT content in the coating matrix.Originality/valueIt is pertinent to mention here that the high temperature behaviour of CNT-reinforced ZrO2-Y2O3 composite on T-91 steel at 900°C temperature in molten salt environment has never been studied. Thus, the present research was conducted to provide useful results for the application of CNT-reinforced composite coatings at elevated temperature.

The Effect of Carbon Nanotubes on the Strength of Sand Seeped by Colloidal Silica in Triaxial Testing.

Colloidal silica can quickly seep through sand and then form silica gels to cement sand particles. To improve the strength of sand seeped by colloidal silica, carbon nanotubes were dispersed in the colloidal silica to form carbon-nanotube-reinforced sand-gel composites. Then triaxial tests were performed to explore how carbon nanotube content affects shear strength. The test results showed that: (1) with the increase of colloidal silica concentration, the shear strength significantly increased with the same carbon nanotube content (especially the low concentration of 10 wt. % colloidal silica, which showed almost no reinforcing effect with carbon nanotubes) while 40 wt. % colloidal silica plus 0.01 wt. % carbon nanotube caused the maximum increase of shear strength by up to 93.65%; (2) there was a concentration threshold of colloidal silica, above which the shear strength first increased to the peak value and then decreased with increasing carbon nanotube content (and we also established a formula to predict such phenomenon); and (3) SEM images showed that carbon nanotubes were connected as several ropes in the micro-cracks of the silica gel, resulting in greater macroscopic shear strength. Our new method of mixing carbon nanotubes and colloidal silica to seep through sand can contribute to sandy ground improvement.

Influence of Ultrasonication of Functionalized Carbon Nanotubes on the Rheology, Hydration, and Compressive Strength of Portland Cement Pastes.

The functionalization process usually increases the localized defects of carbon nanotubes (CNT). Thus, the ultrasonication parameters used for dispersing non-functionalized CNT should be carefully evaluated to verify if they are adequate in dispersing functionalized CNT. Although ultrasonication is widely used for non-functionalized CNT, the effect of this dispersing process of functionalized CNT has not been thoroughly investigated. Thus, this work investigated the effect of ultrasonication on functionalized CNT + superplasticizer (SP) aqueous dispersions by ultraviolet-visible (UV-Vis) spectroscopy, dynamic light scattering (DLS), and Fourier transform infrared spectroscopy (FTIR). Furthermore, Portland cement pastes with additions of 0.05% and 0.1% CNT by cement weight and ultrasonication amplitudes of 0%, 50% and 80% were evaluated through rheometry, isothermal calorimetry, compressive strength at 1, 7 and 28 days, X-ray diffraction (XRD), and thermogravimetric analysis (TGA). FTIR results from CNT + SP dispersions indicated that ultrasonication may negatively affect SP molecules and CNT graphene structure. The increase in CNT content and amplitude of ultrasonication gradually increased the static and dynamic yield stress of paste but did not significantly affect its hydration kinetics. Compressive strength results indicated that the optimum CNT content was 0.05% by cement weight, which increased the strength of composite by up to 15.8% compared with the plain paste. CNT ultrasonication neither increases the degree of hydration of cement nor the mechanical performance of composite when compared with mixes containing unsonicated CNT. Overall, ultrasonication of functionalized CNT is not efficient in improving the fresh and hardened performance of cementitious composites.

Wetting behavior of AgCu-4.5Ti filler reinforced by carbon nanotubes on C/C composite

The effect of Carbon Nanotubes (CNTs) content on the wettability of AgCu-4.5Ti + x CNTs (wt%) composite filler alloys on C/C composite was investigated. The results show that the added CNTs reacted with element Ti in the filler and produced the dispersed fine in situ synthesized TiC particles, which increased the consumption of element Ti and provided the nucleus for the growth of Ti-Cu compounds simultaneously. The above effects of introducing CNTs, inhibited the formation of Ti-Cu compounds, also changed the distribution of compounds, which dramatically influenced the interfacial microstructure and characteristics of wetting behavior. The increase of CNTs content refined and dispersed coarse Ti-Cu compounds, decreased the initial spreading temperature, and improved the wettability, but high content of CNTs (more than 0.3wt%) decreased the wettability of the filler alloy. The wetting interfacial microstructure of corresponding composite filler alloys were analyzed by Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectrometer (EDS) and Transmission Electron Microscope (TEM), which consisted of TiC, TiCu, TiCu2 and TiCu4 compound. The typical wetting behavior of AgCu-4.5Ti + 0.3wt% CNTs composite filler on C/C composite was divided into four stages. The effect mechanism of CNTs content on the wetting behavior was proposed.

Elucidation of high permeability water among VACNFs using molecular dynamics

The cause of the high permeability in the flow of water in CNT (carbon nanotube)-based nanoscale materials remains to be elucidated. In this study, water impregnation simulations outside the VACNFs were performed using the molecular dynamics method to investigate the factors that cause high permeability by virtually changing the force field parameters. As a result, the permeability coefficient increased with increasing CNT content (VC) in the slip flow region. For the constant VC, the smaller the intermolecular force between water and CNTs, the higher the permeability coefficient. Because the intermolecular forces between water and CNTs are smaller than those between water and water, it may have an effect on the high permeability phenomenon. Furthermore, in the present VC change, the arrangement structure of the water molecules changed from a disordered structure, such as bulk flow, to a chain structure in the impregnation direction, which is also considered a factor for the increase in the permeability. Therefore, both the intermolecular forces between water and CNTs and structural change in the arrangement of water molecules were factors in the high permeability phenomenon.

Microstructure and compression behavior of in-situ synthesized Ti2AlC reinforced Ti-48Al-2Cr alloy with carbon nanotubes addition

Different contents of carbon nanotubes (CNTs) were added into Ti-48Al-2Cr alloys (at%) to obtain in-situ synthesized Ti2AlC particles by vacuum arc melting. The effect of the CNT content in the range of 0–1.5 wt% on the microstructure and compression behavior were systematically investigated, especially the controlling mechanism of the Ti2AlC phase. The experimental results showed that the volume fraction of the Ti2AlC phase increases with increasing CNT content. The lamellar spacing of the microstructure and the length-diameter ratio of the Ti2AlC phase decreases as the CNT content increases. The compressive strength and strain first increase and then decrease with increasing CNT content. When the mass fraction of CNT is 1.0, the maximum compressive strength is 1904.25 MPa and the maximum strain is 9.84%, respectively, which is 37.9% and 53.9% higher than that of the Ti-48Al-2Cr alloy. The controlling mechanism of mechanical properties of Ti-48Al-2Cr-xCNT alloy is the combination of fine grain strengthening and γ phase weakening.

Self-sensing cement-based sensor with carbon nanotube: Fabrication and properties – A review

Structural health monitoring is currently becoming more and more vital as it detects damage and warns users early. Since metallic sensors are less reliable and incompatible with concrete, their use in structural health monitoring is limited. This leads to the development of a nanomaterial embedded cement-based sensor. Cement composite is converted to a cement-based sensor due to its piezoresistive property. Thus, the paper examines the use of carbon nanotubes (CNT) in the development of cement-based sensors. The properties and optimum dosage of the CNT are also investigated to prepare the cement-based sensor. The manufacturing process determines the cement-based sensor properties, which is carefully examined and a manufacturing process is also proposed. The review explored that the sensor shows greater elongation capacity, compressive and flexural strength due to the CNT reinforcing capability, CNT properties, and stable interface connection with O–H bond formation. The cement-based conductive properties increase with an increase in CNT content due to contact conduction and tunnelling conduction. The analysis shows that the CNT disperses and distributes favourably in the composite through the acid treatment and sonication process, resulting in improved mechanical, conductive and piezoresistive properties. The cement composite exhibits stable piezoresistive properties with hybrid embedment due to pore filling capability, contact point increase, fiber spacing shortening and tunnelling effect. The reason for property enhancement was validated with the help of SEM investigations. This review gives a detailed insight into the material properties, sensor fabrication, mechanical, conductive and piezoresistive properties of the developed cement-based sensor.

Experimental investigation on sealing efficiency of CNT composite grouts in inclined fractures with flowing water

A series of physical simulation tests were conducted to investigate performance of carbon nanotube (CNT) composite grouts in inclined fracture grouting with flowing water. The viscosity of grouts increases with an increase of CNTs content. Silica fume can improve the dispersion of CNTs and maximal fluid pressure of CNT composite grouts. Orthogonal experimental results shows that sealing efficiency (SE) of CNT composite grouts increases with an increase of CNTs and a decrease of initial flowing rate. Slight inclination can improve the SE of CNT composite grouts and superfluous silica fume has limited effects on SE.

Highly Compressible Polymer Composite Foams with Thermal Heating-Boosted Electromagnetic Wave Absorption Abilities.

Polymer composite foams are desirable materials for electromagnetic (EM) energy attenuation. However, a number of challenges limit improvement in the EM energy attenuation properties of foams. In this study, a simple microcellular injection molding method was used to fabricate highly compressible thermoplastic urethane (TPU)/carbon nanotube (CNTs) composite foams, which also had increased conductivity with an increase in CNT content. Compared to unfoamed composites, foamed composites exhibited higher conductivity and EM attenuation properties because of the presence of a microcellular structure. Moreover, the TPU/CNT foam with 4 wt % CNTs (F(4)) demonstrated strong EM dissipation and an optimal reflection loss (RL) value of -30.4 dB. Furthermore, stimulated by thermal heating and cyclic compression, EM attenuation was observed to increase because of the higher conductivity. Note that F(4) foam having a small thickness of 1.3 mm when treated at 333 K had the highest EM dissipation and the lowest RL value of -51.8 dB. Enhanced polarization and ohmic losses and multiscattering were responsible for the increased EM absorption. This behavior is attributed to the movement of CNTs within the TPU elastomer walls via thermal or compression stimulation. For designing stimulation-dependent multifunctional materials, composite foams with response to thermal heating were proved to be an alternative approach.

Impedance characterization and microwave permittivity of multi-walled carbon nanotubes/BaTiO3/epoxy composites

Polymer composite materials with mixed fillers are widely investigated due to potentially superior properties they provide compared to a composite with a single filler. In this work, the electrical properties of multi-walled carbon nanotubes (MWCNT)/BaTiO3/epoxy composites are investigated using impedance measurements, modeling with equivalent circuit model, determining of alternating current conductivity in the range 10 Hz–2 MHz, permittivity measurements at frequencies 1–67 GHz, and temperature dependencies (77–290 K) of direct current conductivity. Measurements were processed to define the influence of filler combination (carbon nanotubes and BaTiO3) on dielectric properties of the epoxy composites. Nyquist diagrams indicate that all investigated composites have extensive conductive clusters. Permittivity increases monotonically with carbon nanotubes content with a steeper increase of the real part at lower frequencies. Alternating current conductivity has been determined to increase significantly at frequencies over 1 GHz. Temperature dependencies of direct current conductivity in the range 77–293 K exhibit a maximum near 180–220 K, which is shifted to the higher temperatures with the increase of carbon nanotubes content. The observed enhanced values of complex permittivity and electrical conductivity of three-phase MWCNT/BaTiO3/epoxy composites lead to a comparatively high microwave attenuation constant, which may be tuned by the carbon nanotubes content in the composite. It suggests that these composites might be perspective shielding and absorbing materials used for microwave applications.

Chloride-induced corrosion behavior of reinforced cement mortar with MWCNTs

Abstract The use of multi-walled carbon nanotubes (MWC-NTs), as excellent mechanical and conductive fibers, for making self-sensing cementitious composites has attracted great interest. However, few researches have focused on the durability of mortar with MWCNTs. This paper attempts to explore the corrosion of embedded steel rebar in cement mortar with different contents of MWC-NTs. Tests for compressive strength, chloride migration coefficient, conductivity, and corrosion behaviors of MWCNT-cement mortar were carried out. The results show that the addition of MWCNTs to the cement mortar accelerated the development of the steel corrosion under chloride environment. The migration behavior of chlorine ions and steel corrosion rate were related to the carbon nanotube content. The increase in carbon nanotube content resulted in higher steel corrosion intensities. Moreover, the rates of chloride transport into the mortar increased with the nanotube content under both accelerated and natural chloride conditions.

Radio-frequency transparent carbon nanotube electrothermal film for radome de-icing application

As an aircraft faces a hostile environment during the flight, ice can easily form on the surface, especially on a radome, which is a dielectric housing that protects the radar system. Communication disruption and change in aerodynamic shape features are common problems that ice accumulation causes, which are responsible for significant performance degradation. Even though several de-icing methods have shown exceptional heating performance, obtaining radio-frequency (RF) transparency still remains challenging. Therefore, a new de-icing strategy is necessary to effectively remove ice without affecting the communication system. In this study, we fabricated a highly RF transparent electrothermal film based on carbon nanotube (CNT) by a simple spin-coating method and found that the decreased sheet resistance of the film associated with an increase in CNT content resulted in deterioration of RF transmission despite improved heating performance. In particular, the CNT film with optimized characteristics was prepared, which exhibited both high RF transmittance (>80% in the given frequency range) and good heating performance (160 °C at 80 V). Effective de-icing capability was also demonstrated, which confirmed that CNT-based electrothermal films have great promise for practical application to radomes with improved operational efficiency and less weight burden for the aircraft.

The role of multiwall carbon nanotubes on physical, mechanical and rheological properties of poly(lactic acid)/natural rubber/CNT hybrid systems

The main objective of the present work was to study the role of carbon nanotube (CNT) on the microstructure development and physical, mechanical, and rheological properties of poly(lactic acid) (PLA)/natural rubber (NR)/CNT hybrid nanocomposites. The PLA/NR blend samples with constant blend ratio (90/10) were prepared by melt mixing in a laboratory internal mixer at a temperature of 190°C. The behavior of the PLA/NR blend was examined depending on the CNT content (0.5–6 wt%). The droplet size and droplet size distribution of the NR phase decreases with the increase in CNTs content. This could be explained in terms of compatibilizing effect of CNT and the changing of the viscosity ratio of the blend phases. The development of the microstructure and the physical properties of the blend were also investigated according to the CNT contents by measuring the linear viscoelasticity. The elongational behavior and mechanical properties of the blends were strongly dependent on the location of the CNT. The CNT worked as an efficient compatibilizer and also it worked as a reinforcing filler making the matrix more rigid.

Carbon nanotubes to enable autonomous and volumetric self-heating in epoxy/polycaprolactone blends

Carbon nanotubes (CNT) were added to epoxy/polycaprolactone (PCL) blends in order to get electrically conductive blends. As it was expected, an increase of CNT content promotes a higher electrical conductivity due to the creation of more electrical pathways. Furthermore, it was observed that the enhancement is also observed with increasing PCL content, reaching values of around 0.2 S/m for 0.2 wt % CNT and 20 wt % PCL samples, due to its effect on rheological properties of the mixture, which affect positively to the CNT dispersion process, thus leading to more homogeneous and well dispersed nanocomposites, as observed by microstructural analysis. Thermal conductivity also increases with CNT content but decreases with PCL addition due to its insulating properties. A study of the voltage required to reach the above-mentioned self-healing temperature for each material has been performed by thermography monitoring. It has been observed that the samples with the highest amount of both CNT and PCL, have the best resistive heating capabilities due to a higher thermoresistive efficiency of the electrical network, reaching temperatures above 100 °C, at voltages below 150 V.