Increasing Carbon Nanotubes Content Research Articles

Microwave absorption and infrared stealth capabilities of hot-pressed Si3N4/CNT ceramics tailored by CNT content

Current research on radar and infrared dual stealth in dense Si3N4-based ceramic materials is limited. This study investigates the influence of carbon nanotubes (CNTs) on the composition, microstructure, electromagnetic wave absorption (EMA) capabilities, and infrared emissivity of hot-pressed Si3N4-based ceramics. The addition of CNTs resulted in the formation of numerous heterogeneous interfaces and the CNTs conductive network, initially enhancing the ceramics’ EMA capabilities before gradually decreasing. Si3N4-based ceramics loaded with 0.5 wt% and 1 wt% CNTs exhibited significant EMA capabilities, with a minimum refection loss of -60.95 dB at thickness of 7.49 mm. However, with an increase in CNT content, the increasing heterogeneous interfaces and pores in ceramics enhanced the absorption of the electromagnetic wave in the infrared band, resulting in a rise in total infrared emissivity from 0.584 to 0.679. To optimize radar and infrared stealth performance, a two-layered structure can be designed, with Si3N4 and Si3N4/CNT ceramics serving as the outermost and second layers, respectively. This study provides a way to design high density Si3N4-based ceramics with infrared and radar stealth.

Effects of conductive phase content on magnetic sensitivity of spiral conductive polymer composite

Flexible magnetic field sensors are essential for small dimensions, excellent precision, and flexibility in narrow gap or pipe environments. A spiral conductive polymer composite has been proposed for magnetic field detection. To investigate how conductive phase content impacts its magnetic sensitivity, the relationship between magnetic flux density and voltage difference/magnetic sensitivity was examined with different carbon nanotube contents (1 wt%∼20 wt%). From the perspectives of the equivalent network and magnetic susceptibility, the voltage difference /magnetic sensitivity of the composite was analysed by varying its carbon nanotube content. The addition of carbon nanotubes creates a contradiction in the magnetic sensitivity caused by internal equivalent impedance or induced current. The experiments demonstrate that the interpolar voltage difference /magnetic sensitivity first increases and then sharply decreases with increasing carbon nanotube content within composites. The optimum carbon nanotube content is about 8 wt%, which can be an optimal sensitive material choice for a flexible magnetic sensor.

Concurrent effect of shear flow and CNT presence on crystallization behavior and electrical properties of polypropylene based nanocomposites: A comprehensive structure-property investigation

The loading of nanoparticle in the polymer matrix affects their response to shear flows applied during the fabrication process. With this in mind, in the present study, the concurrent effect of carbon nanotube (CNT) presence and shear application on the rheological and electrical properties as well as on the crystallization behavior of polypropylene (PP) based nanocomposites has been investigated. The results of rheological analyses showed that the solid-like behavior increases in proportion to the CNT content, and a remarkable increase in the solid-like behavior is obtained at a CNT content of 2 wt%. The isothermal crystallization results corroborated that crystallization temperature increases proportionally with the CNT content, however does not change with shearing. The non-isothermal crystallization findings confirmed that crystallization kinetics promotes with increasing CNT content, and this effect becomes more pronounced with shearing. The results of thermal analysis confirmed that the melting temperature decreases slightly, and the crystallinity remains almost unchanged with increasing CNT content up to 2%. However, when the CNT content rose up to 4%, the crystallinity decreased significantly due to confined crystallization. When this nanocomposite was subjected to shearing, the crystallinity increased. The results of electrical conductivity measurement revealed that the conductivity increases with increasing CNT content, while it decreases with shearing and the vulnerability of nanocomposites to shearing decreases with increasing CNT content.

Evolution of surface oxide chemistry and its effect on the electrochemical degradation behaviour of AlCoFeCuNi high entropy alloy coating incorporated with multiwalled carbon nanotubes

AlCoFeCuNi high entropy alloy (HEA) coatings containing different volume fractions of carbon nanotubes (CNTs) were electrodeposited over mild steel substrate. Phase constitution, morphological evolution, electrochemical corrosion properties and surface oxide chemistry of the coatings were investigated as a function of their CNT content and correlated. With initial incorporation of the CNTs, the surface morphology of the composite coatings became progressively finer and compact till an optimum CNT volume fraction. Higher volume fractions of CNTs led to their agglomeration which yielded rougher and defective coating morphology. Corrosion rate of the HEA coating was highly sensitive to the CNT content and at an optimum CNT volume fraction HEA-CNT composite coatings (HEA_CNT-3 coating produced from electrolyte with 10 mg/L of CNT) with lowest corrosion rate was obtained (polarization resistance: Rp = 1178.85 Ω-cm2) while the highest corrosion rate was observed for the pristine HEA coating (Rp = 225.84 Ω-cm2). The coating with highest CNT volume fraction (HEA_CNT-6 coating produced from electrolyte with 35 mg/L of CNT) exhibited the polarization resistance value of 281.80 Ω-cm2. Contact angle measurement revealed that with increase in CNT content, coating hydrophobicity increased monotonically. Analysis of the surface oxide layer of the exposed samples exhibited increase in the relative content of Co3O4, CuO, NiO, AlO(OH) oxides with the presence of CNTs. This work shows that an optimum volume fraction of CNT which produces relatively compact morphology and facilitates evolution of stabler surface oxides leads to significant enhancement in the corrosion resistance of AlCoFeCuNi HEA-CNT composite coating.

The Impact of Carbon Nanotube on the Thermal Properties of Polypropylene

This research paper investigates the effect of the addition of carbon nanotubes (0.5 and 1.0% by weight) on crystallisation procedure in isotactic polypropylene. The study found that the crystallisation temperature increased with increasing nanotube content, while the crystallisation of polymers did not substantially change. The critical cooling speed, at which PP does not crystalize, increases with the increase in carbon nanotube content. Using the critical cooling speed and nanotube content, a nucleation effectiveness parameter was developed, that is not dependent on the crystallisation temperature or the CNT load. The study also found that carbon nanotubes only speed up the development of α-phase in isothermal crystallisation experiments. The control fibers had a shrinkage of 27% to 160°C, while the shrinkage of the composite fibers was less than 5%. The melting temperature of PP and its nanocomposites was approximately 150 to 152°C. However, the values for the degree of crystallinity of the nanocomposites rose along with the CNT content.

Molecular dynamics simulation of mechanical and tribological properties of nitrile butadiene rubber with different length and content carbon nanotubes

Nitrile butadiene rubber is attracting attention as an essential elastic material in the automobile, aviation, petroleum, and printing industries. However, the effects of carbon nanotubes (CNTS) with different contents and lengths on mechanical and tribological properties of nitrile butadiene rubber are rarely reported. Therefore, we aim to elucidate the microscopic strengthening mechanism of NBR matrix by changing the content and length of CNTS from an atomic perspective. Specifically, the effects of CNTS (5 wt%, 9 wt%, 13 wt% and 17 wt%) and CNTS (2.130 nm, 2.556 nm and 2.982 nm) on mechanical and tribological properties of butadiene rubber composites are investigated by molecular dynamics simulation. The experimental results show that the mechanical properties of the composites increase first and then decrease with the increase of CNTS content. In addition, the shear resistance of the composites is improved with the increase of CNTS content, and the composites containing 13 wt% CNTS showed relatively excellent friction properties. Moreover, the mechanical and frictional properties of the composites are improved with the increase of the length of CNTS. It is determined that the increasing length of CNTS also enhances the interaction between CNTS and the molecular chains of nitrile butadiene rubber, which improves the compactness and shear deformation resistance of the composite.

Formation of a conductive network in urea−formaldehyde/carbon nanotube composite foams for electromagnetic shielding

AbstractDue to advantages of low cost and intrinsic flame retardancy, urea−formaldehyde (UF) foams with electromagnetic shielding function present a promising application prospect in the fields of construction, transportation and electronics. In this study, by using carbon nanotubes (CNTs) as conductive filler and thermo‐expandable microspheres (EMs) as physical foaming agent, a series of UF/CNT composite foams with perfect and polygonal closed cellular structure were prepared for electromagnetic shielding. By adding 6 wt% EMs, the composite foam exhibited a uniform cell wall thickness, while the local accumulation of CNTs was inhibited and CNTs were distributed evenly within the cell walls. With increasing CNT content the dispersion of CNTs transformed from a scattered and ‘island‐like’ structure to an interconnected structure, and for samples with CNT content higher than 1.34 vol% a continuous conductive network was constructed within the cell walls, thus significantly improving the electrical conductivity and electromagnetic shielding effectiveness for the foams, which reached 34.5 dB and satisfied the requirement of commercial applications. Moreover, the contribution of absorption to the electromagnetic shielding effectiveness was much larger than that of reflection for composite foams, indicating that absorption was the dominant shielding mechanism. © 2023 Society of Industrial Chemistry.

Microstructures and mechanical properties of Al nanocomposites hybrid-reinforced with B4C, carbon nanotubes and graphene nanoplatelets

To improve the mechanical properties of Al-30%B4C composites, modified carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) were added. The Al/B4C composites with different content of CNTs and GNPs were fabricated via ball milling and hot press. The B4C particles were homogeneously distributed, and the B4C/Al interface was tightly bonded due to AlB2 and Al3BC. With increase of CNTs content, the composites strength increased. The compressive strength of the Al-30%B4C-0.75%CNT-0.25%GNP composite was enhanced by 46% compared with that of the Al-30%B4C composite. The interface bonding and strengthening mechanisms of CNT-GNP hybrid were studied in detail. The reinforcements mainly reinforced the nanocomposites by Orowan, dislocation, grain refinement strengthening and load transfer. After calculation, CNT-GNP hybrid has lower contribution in thermal mismatch and Orowan strengthening due to the larger size. The load transfer efficiency of the CNT-GNP hybrid was significantly higher than that of the CNTs and GNPs, as the optimised interface structure and interconnected structure of the hybrids contributed to its high strength.

Effect of carbon nanotubes additives on mechanical properties of WC–6Co cemented carbide

AbstractIn order to increase the toughness of WC–6Co cemented carbide, different contents of carbon nanotubes (CNTs) were added to the WC–6Co alloy powder to prepare cemented carbide by low‐pressure sintering. The results showed that some of the CNTs were embedded between the grains of WC–6Co cemented carbide, which would hinder the growth of WC grain boundary, thus leading to grain refinement. In addition, CNTs inhibited the formation of decarbonized phase and guided the deflection and bridge of crack to hinder the crack extension. With the increase of CNTs content, the density increased at first and then decreased, and the transverse fracture strength increased at first and then decreased. When the content was 0.2 wt.%, the alloy had the best performance. The density of the alloy was 99.67%; the transverse fracture strength was up to 2937.5 MPa, which is about 100% higher than that of cemented carbide without CNTs. The fracture toughness was 9.84 MPa m1/2, and the hardness was 1924.8HV30.

Effect of carbon nanotube content on the microstructure and mechanical properties of CNTs/TiAl alloys

TiAl alloys are ideal high-temperature structural materials for aerospace applications. However, their ductility, bending strength and machinability are poor at room temperature, thus severely limiting their practical application. In this study, carbon nanotubes (CNTs) were used as additives, and Ti–48Al–2Cr–8Nb was used as the original powder to prepare CNTs/TiAl alloys by employing spark plasma sintering. The effects of different CNT contents on the microstructure, hardness and bending strength of CNTs/TiAl alloys were investigated. The results indicated that CNTs reacted with the matrix to generate granular TiC and Ti2AlC reinforced phases stacked into bands at the grain boundaries, limiting grain growth. The Ti2AlC phase content increased with increasing CNT content. When the contents of the TiC and Ti2AlC phases were high, agglomeration occurred, leading to defects such as pits and cracks on the surface, which explains the weakened mechanical properties of the CNTs/TiAl alloys at room temperature. When the CNT content was 0.4 wt%, the average grain size was approximately 32 μm under the effects of fine grain strengthening and second phase strengthening. Moreover, the mechanical properties of the composite were the best at room temperature. The Vickers hardness and bending strength at room temperature were 377 HV and 879 MPa, respectively, and the compressive strength and strain were 2554 MPa and 31.86%, respectively. The fracture mode was mainly transgranular.

Effect of CNT Content on Microstructure and Properties of CNTs/Refined-AZ61 Magnesium Matrix Composites.

Carbon nanotubes (CNTs) reinforced magnesium matrix composites have great application potential in the transportation industry, but the low absolute strength is the main obstacle to its application. In this paper, copper-coated CNTs and AZ61 powder were used as raw materials to prepare CNTs/refined-AZ61 composites with good interfacial bonding, uniformly dispersed CNTs and fine grains by the process of ball milling refinement of AZ61 powder, ball milling dispersion and hot-pressing sintering. When the volume fraction of CNTs is less than or equal to 1 vol.%, CNTs can be uniformly dispersed and the yield strength and compressive strength of composites increase with higher CNT content. When the volume fraction of CNTs is 1 vol.%, the compressive strength and yield strength of composites reach 439 MPa and 361 MPa, respectively, which are 14% and 9% higher than those of matrix composites with nearly the same value of fracture strain. When the volume fraction of CNTs is greater than 1 vol.%, with the increase in CNT content, CNT clustering becomes more and more serious, resulting in a decrease in the strength and fracture strain of composites.

Film casting of polycarbonate/multi-walled carbon nanotubes composites using ultrasound-assisted twin-screw extruder: experiment and simulation

Abstract A one-step ultrasonic film casting process to manufacture nanocomposite films was developed, in which polycarbonate (PC) was mixed with multi-walled carbon nanotubes (CNT) and cast into films in one process. Numerical and experimental investigations of necking phenomenon were carried out for film casting of PC/CNT composites. Experimental results revealed that the necking along film line decreased with imposition of ultrasound and increasing CNT content, indicating that incorporation of CNT and imposition of ultrasound restrained the elongational flow behavior of melt, resulting in film of a larger width. Isothermal and nonisothermal numerical simulations of the process were performed. In isothermal simulations, the polymer melt was assumed to be maintained at the die temperature. In nonisothermal simulations, the temperature change along the film line was determined from heat transfer calculations with the WLF temperature-dependent viscosity. The simulated and experimental results on normalized film width, defined as a ratio of cast film width to die width, as a function of the distance from the die at various extension ratios were compared. The comparison indicated that changes in film width and thickness along the stretching direction in the nonisothermal process were in better agreement with experimental results than that in the isothermal process. Both experimental and simulated results showed a decrease of film width with take-up speed. Due to the presence of edge effect, the film width in experiment was lower than the simulated one. With incorporation of CNT, a better agreement between experimental and simulated results was obtained, due to a reduced edge effect in the film.

Comparative study on the effect of carbon nanotubes and carbon black on fatigue properties of natural rubber composites

Fatigue property is of great importance for the security and reliability of rubber products. The fatigue performance of natural rubber (NR) filled with carbon nanotube (CNT) and carbon black (CB) with different content but similar hardness was investigated. Results indicated that CNT/NR exhibited the best fatigue performance at low CNT content and fatigue strain, while the crack growth was accelerated with the increase of CNT content and strain. As for CB/NR, the fatigue resistance increased with CB content and strain. The different fatigue performance of NR composites was discussed from the perspective of hysteresis, strain-induced crystallization, and stress concentration effect.

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.