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The effect of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) addition on the phase formation and the superconducting properties of GdBa₂Cu₃O${}_{7-\delta }$ phase has been studied. Therefore, composite superconductor samples of type (CNTs)${}_x$ GdBa₂Cu₃O${}_{7-\delta }$, 0.0 $\le x\le$ 0.1 wt.% have been synthesized by a standard solid-state reaction technique. The samples have been characterized using X-ray powder diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results of XRD show an enhancement in the phase formation up to 0.06 wt.% and 0.08 wt.% for SWCNTs and MWCNTs, respectively. SEM and TEM reveal that CNTs form an electrical network resulting in well-connected superconducting grains. The electrical properties of the prepared samples have been examined by electric resistivity and I–V measurements, and their results reinforce the XRD, SEM and TEM. Consequently, both $T_c$ and $J_c$ improve as the addition percentage increases up to 0.06 wt.% and 0.08 wt.% for SWCNTs and MWCNTs, respectively.

Conductive and transparent thin film structures are useful in flexible electronics. In this paper, we report multi-walled carbon nanotubes (MWCNTs) patterning into gradient regular patterns with large area of about several square centimeters on silicon or wafer glass slide via thermally enhanced evaporative self-assembly under wedge-shaped geometric confinement. The morphologies, electrical and optical properties of the MWCNTs thin film were characterized. The findings reveal that the conductance would increase with depositing times, meanwhile the transparency would decrease. The resistance of the grid patterning films of MWCNTs has a nearly linear relation to the transmittance in a relatively large range. The MWCNTs can be easily transferred to flexible substrate such as PET films or an adhesive tape. In comparison, SWCNTs could hardly be deposited into stripes or grid patterns, but the continuous thick films and discontinuous thin films could demonstrate better electrical and mechanical performance.

The objective of this paper is to analyze the unsteady incompressible flow of the viscous nanofluid on a contracting surface with viscous dissipation effects. Presented and contrasted are analyses of both multi-wall carbon nanotubes (MWNTs) and single-wall carbon nanotubes (SWNTs). As the common (or base) fluids, kerosene oil and water are utilized. In the existence of first-order thermal and velocity slip conditions, mathematical modeling and analysis are performed. Using the MATLAB software’s bvp4c solver tool, numerical solutions to the governing nonlinear modeled problems were obtained. This technique is particularly effective for developing many solutions to highly nonlinear differential equations. In addition, a comparison is done between this study and previously published works. The temperature, velocity, skin friction coefficient and heat-transfer rate have been explored for various significant factors included in the problem statements. In the unsteadiness parameter regime, dual solutions can be found. As the velocity slip parameter is increased, the flow slows down. In comparison to SWCNTs kerosene, MWCNTs kerosene oil has a greater velocity curve for the nanoparticles volume fraction. Increases in volume fraction decrease skin friction, whereas increases in the unsteadiness parameter speed up the drag force. Furthermore, as the Eckert number intensity increases, so do the temperature profiles in both solutions. Finally, the stability study revealed that the initial solution is robust, whereas the breakage in the second solution in the Nusselt number shows singularity, and thus the second solution is considered unstable.

In order to arrange directionally, multi-wall carbon nanotubes (MWCNTs) are functionalized with ferromagnetic cobalt on the surface via the electroless plating method. The uniform and continuous cobalt coating was received in pH $=$ 9 at 45${}^{\circ }$C for 30min. It is found that the hydroxyl and carbonyl groups could be successfully introduced on the surface of raw MWCNTs after treated in boiling nitric acid that would provide the active points for cobalt deposition. The diameters of the cobalt (Co)-coated MWCNTs increase to 20–50nm from 8–15nm of purified ones. As a result of nanoscale cobalt coating, MWCNTs show strong ferromagnetism at room temperature. The Co-coated MWCNT respond to magnetic field susceptibly in the distilled water and arrange themselves in the direction of the applied magnetic field up to 1T. The hysteresis curve results show that the coercivity of Co-MWCNTs is 1285.2 Oe, which is about four times that of cobalt powder itself.

This paper investigates the steady sliding behavior of multiwalled carbon nanotubes (MWCNTs) mixed lubricants at the metal–metal interface in direct shear tests. Slide-free-slide (SFS) experiments were performed to understand dynamic frictional stress of the sliding surfaces above the critical velocity. The experimental observations show that the dynamic stress decreases with increase in sliding velocity, but the same increases with normal stress. Further, in the case of change in concentration of the MWCNTs in the lubricant, the dynamic stress increases initially and then decreases to a minimum value and then further increases with addition of more nanoparticles in the lubricant. Dynamic stress and corresponding critical velocity are found to be minimum about 1.6% (wt./vol.) of MWCNTs concentration. Magnitude of cohesion as well as the coefficient of friction were also determined experimentally with the Coulomb friction law. The friction results are discussed in terms of the scaling laws in three regimes, namely viscous, rolling and sliding. These laws are justified on the basis of the mixed lubrication regime of Stribeck curve. Surface morphology of the test specimens before and after the experiment was also examined using SEM and EDS tests. No evidence of surface damage owing to motion of the nanoparticles was observed.

Titanium dioxide (TiO₂) and iron oxide (Fe₂O₃) nanoparticles (NPs) were successfully deposited on multiwall carbon nanotubes (MWCNTs) films using a low-cost and simple sparking process. The as-deposited film was annealed at $350^{\circ }$C for 2h to improve their crystallinity. The results show the anatase TiO₂ and hematite Fe₂O₃ NPs with the size of 5–10nm are coated on MWCNTs. The bandgap energy of the as-prepared and the annealed films were 2.3eV and 2.7eV. Photocatalytic activity of the annealed films under visible irradiation is greater than the as-prepared films. Moreover, TiO₂:Fe₂O₃ with the ratio of 3:1 was the optimized condition. Interestingly, the relative current of the annealed films increased to 0.75 when increasing the irradiation time for 5h. This result confirmed that the excited electron from photocatalytic activity can be transferred through the MWCNTs. This is an alternative way to produce the electric current from photocatalysis in the future.

After micro-arc oxidation, the surface properties of AZ31 magnesium alloy have been improved. However, micro-arc oxidation treatment leads to high insulation, which limits its application in electronic devices. To increase conductivity, a conductive coating was developed by adding multi-walled carbon nanotubes (MWCNTs) to the epoxy resin. The microstructure and performance of the coating were tested by SEM, thermogravimetric analyzer, four-probe conductivity meter, high-temperature friction and wear tester, and electrochemical workstation. The results indicate that the optimal conductivity with a resistivity of 303$\mathrm{\Omega }\cdot$m is obtained when the MWCNT content is at 4wt%. In addition, MWCNTs are filled with a network structure of epoxy resin, which increases the density of the coating and enhances their wear and corrosion resistance.

In this paper, we present a novel hybrid material consisting of multiwalled carbon nanotubes (MWCNTs) and molybdenum disulfide (MoS${}_2)$ with enhanced photoresponsivity in the near-infrared (NIR) region. MoS₂ nanosheets are obtained through chemical exfoliation in NMP solvent, and MWCNTs are grown on these nanosheets using the chemical vapor deposition (CVD) technique. The combination of the NIR transparency of MWCNTs and the high UV light absorption of MoS₂ leads to a substantial increase in the photoresponsivity ($R)$ of the MoS₂@MWCNTs hybrid compared to bare MoS₂ specifically in the NIR region. Experimental results demonstrate a remarkable enhancement of $R$ from 18.6 $\mu$A/W to 155.7 $\mu$A/W in the hybrid material, whereas the opposite trend is observed in the case of bare MoS₂.

In this work, nanocrystalline hexagonal tungsten oxide was prepared by acidic precipitation from sodium tungstate solution. TEM studies of nanopowders showed that the average size of the hexagonal nanoparticles is 30–50 nm. Novel nanocomposites were prepared by embedding a low amount of gold-decorated carbon nanotubes into the hex-WO₃ matrix. The addition of MWCNTs lowered the temperature range of sensitivity of hex-WO₃ nanocomposites to NO₂ hazardous gas. The sensitivity of hex-WO₃ with Au-decorated MWCNTs to NO₂ is at the temperature range between 25°C and 250°C.

The effect of carbon nanotubes on the kinetics of free radical polymerization of methyl methacrylate (MMA) was investigated. To do this, pristine, acid treated, alcoholic and methacrylate-modified carbon nanotubes with different loadings were used and Conversion, molecular weight and polydispersity index (PDI) of all samples were monitored during polymerization. The results show that carbon nanotubes induce an induction time to polymerization system which is independent of modification system while decrease in monomer conversion can be improved by developing organic moieties on surface. Molecular weight and polydispersity index for free and attached-on-surface chains were studied separately and different kinetics behaviors were observed for them. Molecular weight of free chains was increased by adding carbon nanotubes while more modified nanotubes resulted in much increased molecular weight. On the other hand, more system stability of more modified nanotubes, which was tested using UV-Visible spectra, resulted in higher molecular weights. Adding more nanotubes in the case of MMA-modified nanotubes caused to determine an optimum loading value to reach maximum molecular weight of free chains which was ascribed to system stability according to UV-Visible results. In this optimum loading value, free chains had minimum PDI value. However, increasing carbon nanotubes content led to decreased molecular weight of attached chains while PDI values increased because of shielding effect as physical phenomenon.

Electromagnetic (EM) wave absorption materials have drawn a lot of attention because they can effectively reduce EM wave pollution from electronic equipment. In this work, we combined ZrO₂ nanoparticles with multi-walled carbon nanotubes (MWCNTs) and explored applications of MWCNT/ZrO₂ composites in EM wave absorbing field. ZrO₂ nanoparticles with a high crystalline were synthesized by one-step hydrothermal method. Adding MWCNTs in this hydrothermal process, ZrO₂ nanoparticles aggregated together to form uneven lumps and wraps on MWCNTs surfaces. MWCNTs improved the conductivity loss and electron polarization capability of composites. The minimum reflection loss (RL) of MWCNT/ZrO₂ composites reached $-$39.73 dB at a thickness of 2mm. Such excellent EM wave absorption properties are attributed to the dielectric loss, dipole polarizations and interfacial polarizations. This composite can be a promising candidate as high efficiency EM wave absorption material and used for commercial production because of the simple synthesis methods.

Multi-walled carbon nanotubes (MWCNTs) were grown on Silicon (Si) substrate by using low-pressure chemical vapor deposition (LPCVD) technique where iron (Fe) and silver (Ag) colloidal solution act as a catalyst were prepared by chemical route. The as-prepared solutions in varied concentrations were deposited on a Si substrate using a spin coating process at 700rpm. The purpose of Fe in composite catalysts is to have high carbon solubility and diffusion rate, and Ag utilization can change catalyst activity temperature and enhance carbon yields. In this work, we demonstrate the growth of carbon nanotubes (CNTs) on different catalyst concentrations (${}_{0.025\text{M}}$Fe/${}_{0.100\text{M}}$Ag), (${}_{0.050\text{M}}$Fe/${}_{0.100\text{M}}$Ag), (${}_{0.075\text{M}}$Fe/${}_{0.100\text{M}}$Ag) and (${}_{0.100\text{M}}$Fe/${}_{0.100\text{M}}$Ag) catalytic films. Field Emission Scanning Electron Microscopy (FESEM) was used to image the morphologies of various catalyst concentrations MWCNTs. The natures of the synthesized CNTs were determined using Raman spectroscopy and it was revealed that as-prepared CNTs are MWCNTs due to the absence of radial breathing mode (RBM). Raman spectroscopy demonstrated the lower I_D/I_G ratio (Ratio of the intensity of D-Raman peak and G-Raman peak) of (${}_{0.025\text{M}}$Fe/${}_{0.100\text{M}}$Ag) MWCNTs. The I_D/I_G ratio for (${}_{0.025\text{M}}$Fe/${}_{0.100\text{M}}$Ag) catalyzed MWCNTs was 0.76, while the I_D/I_G ratio for (${}_{0.100\text{M}}$Fe/${}_{0.100\text{M}}$Ag) catalyzed MWCNTs was 0.89. The (${}_{0.100\text{M}}$Fe/${}_{0.100\text{M}}$Ag) catalyzed MWCNTs were found to be more defective as compared to other. Electron Emission from (${}_{0.025\text{M}}$Fe/${}_{0.100\text{M}}$Ag) catalyzed MWCNTs were much stronger than from other samples, as demonstrated by Field Emission measurement using diode configuration. The turn-on field for (${}_{0.025\text{M}}$Fe/${}_{0.100\text{M}}$Ag) catalyzed MWCNTs was (0.92 V/$\mu$m) which is slightly lower than that of (${}_{0.100\text{M}}$Fe/${}_{0.100\text{M}}$Ag) catalyzed MWCNTs (1.83 V/$\mu$m), indicating superior enhancement.

This research work describes the cost-effective synthesis and purification of multiwall carbon nanotubes (MWCNTs). Synthesis of CNTs was carried out in distilled water between two electrodes using the electric arc discharge (EAD) method. EAD is a simple and straightforward route in which an electric arc is generated between graphite electrodes through DC power source to produce soot which contains MWCNTs along with impurities. The deposited soot containing MWCNTs was then chipped off and purified. In this case, multistep purification scheme was opted to remove unwanted impurities from produced MWCNTs. Purification route comprised thermal treatment, chemical treatment and a combination of both to yield pure MWCNTs. Thermal treatments were carried out in normal air and under controlled flow of oxygen at different temperatures whereas chemical treatment was performed using acidic solution. Thermo gravimetric analysis (TGA), field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) were carried out before and after purification treatments to investigate the outcome of employed treatments. Results showed that the thermal or chemical treatment alone is not sufficient to remove impurities from soot. Moreover, the introduction of an oxide group through chemical treatment reduces the oxidization temperature of graphitic particles. It was found that the chemical treatment followed by thermal annealing under the controlled flow of oxygen is the most appropriate method for successful purification of MWCNTs synthesized via EAD method.

The hybrid nanomaterials of platinum/cerium oxide/multi-walled carbon nanotubes (Pt/CeO₂/MWCNTs) are synthesized successfully via impregnation and polyol processes. MWCNTs serve as an excellent supporter where CeO₂ nanoparticles are decorated with well-distributed Pt nanoparticles. Images show the average particle size of crystalline Pt and CeO₂ on MWCNTs are 3–7 and 20–30 nm, respectively. In electrochemical reaction, the redox peak of Pt/CeO₂-700°C/MWCNTs reveals lower potential and higher current density in methanol electro-oxidation than those of other Pt-based ones. The study indicates that the cerium oxide in Pt/CeO₂-700°C/MWCNTs catalyst will enhance significantly the oxygen ions transportation between the interface of Pt and MWCNTs to eliminate the CO poison effect on Pt catalyst.

A three-phase composite film was produced by inserting multi-walled carbon nanotubes (MWCNTs) and BaTiO₃ nanoparticles into polyimide (PI). The combination of in-situ polymerization and water-based preparation involved in the experiment ensured fillers’ homogeneous dispersion in the matrix, which led to flexible shape of the composite films. The dielectric properties of composite films as a function of the frequency and the volume fraction of MWCNTs were studied. Such composite film displayed a high dielectric constant (314.07), low dielectric loss and excellent flexibility at 100Hz in the neighborhood of percolation threshold (9.02 vol%) owing to the special microcapacitor structure. The experimental results were highly consistent with the power law of percolation theory.