Proportion Of Carbon Nanotubes Research Articles

Influence of pyrolysis temperature on carbon deposition from the perspective of volatile evolution during the ex-situ pyrolysis-catalysis of plastic

To better understand the mechanism of carbon deposition, the ex-situ catalytic pyrolysis of polyethylene (PE) was explored over a FeNi/Al2O3 catalyst, and the evolution of volatiles as well as the yield and structure of carbon products at different temperatures were analyzed in depth by an in-situ atmospheric pressure photoionization high-resolution mass spectrometry (APPI HRMS) combined with a fixed-bed reactor. The results show that raising the pyrolysis temperature (from 500 to 800 °C) reduces carbon product yield and H2 production, and the proportion of carbon nanotubes (CNTs) in the carbon products decreases. The source of carbon products gradually shifts from liquid-phase carbon sources to gaseous-phase carbon sources. Below 700 °C, both the outer diameter and carbon interlayer spacing of CNTs decrease, while above 700 °C, they both increase along with increased distortion of carbon layers. It is also observed that the carbon layers are connected to the catalyst lattice stripes, and the interlayer spacing of carbon layers is greater than the catalyst lattice spacing. In situ mass spectrometry reveals a significant increase in the carbon number and double bond equivalent (DBE) values of volatiles with increasing pyrolysis temperature, but the rate of increase slows down after 700 °C. Volatiles from lower pyrolysis temperatures undergo severe polymerization, upon entering the catalytic zone at higher temperatures, minimizing temperature-induced distinctions. Nevertheless, it remains evident that volatiles from lower pyrolysis temperatures exhibit less pronounced polymerization when exposed to higher catalytic temperatures.

Molecular dynamics simulation of the effect of carbon nanotubes on liquid argon phase transition behavior on the platinum plate

The effect of varying single-walled carbon nanotubes (SWCNTs) volume fractions on the phase transition behavior exhibited by liquid argon was investigated in this study. The thermodynamic behavior of SWCNTs/Ar nanofluid was performed by molecular dynamics simulation realized through the LAMMPS computational package. Physical parameters (e.g., thermal conductivity, heat flow, total energy, fluid temperature, gas phase atomic number, and density) were examined to investigate the atomic characteristics exhibited by nanofluid with volume fractions of carbon nanotubes (CNTs) ranging from 0 vol% (pure liquid) to 2.28 vol%. As revealed by the result of the simulation analysis, the rate of temperature rise can be increased, and the transition period can be shortened through the incorporation of CNTs into the base fluid. When the CNTs volume fraction ranged from 0.57 vol% to 1.14 vol%, the thermal conductivity was enhanced by a maximum of 75 %, from 0.0507 W/mK for pure liquid argon to 0.089 W/mK for CNTs/Ar nanofluid. The thermal conductivity was reduced under CNTs volume fraction of over 1.71 vol%. Lastly, a conclusion was drawn in this study, i.e., introducing a proper proportion of CNTs into Ar fluid can lead to the effective improvement of the thermodynamic performance of the nanofluid.

Doping Effects of Carbon Nanotubes and Graphene on the Flexural Properties and Tribological Performance of Needle-Punched Carbon/Carbon Composites Prepared by Liquid-Phase Impregnation.

The main goal of this study is to investigate the doping effects of carbon nanotubes (CNTs) and graphene on the needle-punched carbon/carbon (C/C) composites that are prepared by liquid-phase impregnation. In order to achieve, for the C/C composites, the purposes of high flexural strength, stable friction coefficient, low weight loss, and high thermal conductivity, our primary concern is to examine the flexural properties and the tribological performance, and then to explore a little further into the influence on thermal conductivity. In this study, carbon fiber preforms were first fabricated by needle-punched carbon-fiber cloth, and then liquid-phase phenolic resin, doped with different proportions of carbon nanotubes and graphene, was used as the impregnation solution to carry out multiple densification (impregnation-carbonization) cycles and fabricate various C/C composites. The main purpose was to probe into the doping effects of the CNTs and graphene, added to the impregnation solution, on the properties of C/C composites. The experimental results show that the addition of CNTs and graphene can improve the heat conductivity, flexural properties, and tribological performance of C/C composites, and the impact on these properties is more significant with the addition. Furthermore, the properties of graphene-doped C/C specimens are better than those of CNT-doped C/C specimens.

Utilization of carbon nanotubes and steel fibers to improve the mechanical properties of concrete pavement

BackgroundRigid pavements have become an urgent demand in recent years, as these pavements need less maintenance and renovation than other types. However, traditional rigid pavement faces various challenges and difficulties over its lifetime. It has a much higher initial erection cost than asphalt pavements, a greater sensitivity to dynamic stresses, and a highly susceptible to temperature variations causing cracking. Previous works dealt with these drawbacks by using effective materials as alternatives to cement and/or aggregates in pavements mixtures. In the last few years, much interest has been carried out in nanomaterial applications to improve the mechanical performance of construction materials, which can also be used for rigid pavement constructions. This improvement is due to nanomaterials' role in concrete as nanoreinforcements and nanofillers. On the other hand, various types of fibers have been used to improve the performance of concrete constructions. This study investigates the effect of adding carbon nanotubes (CNTs) and steel fibers (SFs) to concrete mixtures. A series of experiments on concrete mixes with various weight percentages of CNTs (0%, 0.025%, 0.050%, and 0.075%) were added to the mixtures to determine the best cost and amount of CNTs to add to a concrete mix. Compressive, tensile, and flexure strength characteristics are investigated. In the second experimental stage of this work, the effect of adding steel fibers to the mixture was investigated.ResultsAccording to the results, the optimal carbon nanotube content in concrete is 0.05%. Compared to other concrete combinations with varying proportions of CNTs, this quantity offers the maximum compressive, tensile, and flexural strength. Additionally, SFs can improve the mechanical properties of the mix as well as enhance its post-cracking and fatigue behavior. Adding both CNTs with SFs increased compressive, tensile, and flexural strength by 22.7%, 29.3%, and 70.8%, respectively, more than the traditional pavement.ConclusionThis work found that combining SFs with CNTs improves the mechanical properties of the concrete mortar, resulting in a stronger mortar that can withstand more loads than the traditional one.

Insight into dynamic compressive response of carbon nanotube/carbon fiber-reinforced concrete

The dynamic compressive properties of concrete reinforced with the carbon nanotubes (CNTs) and carbon fibers (CFs) were investigated in this paper. For both single and hybrid addition, the CNTs and CFs enhanced the dynamic compressive strength of the concrete, but the hybrid addition showed a higher enhancement effect. Hybrid CNTs and CFs were more conducive to improve the strain-rate effect of the dynamic compressive strength, and when the content of hybrid CNTs and CFs was constant, a higher proportion of CNTs led to a more significant improvement. However, the addition of CNTs alone reduced the strain-rate effect. The addition of CNTs increased the content of hexagonal prismatic Ca(OH)2, the proportions of gel pores and harmless capillaries, and decreased the porosity of the concrete, thus enhancing the dynamic compressive strength of the concrete. The addition of CFs increased the porosity of the concrete and the probability of large pores. But the crack-inhibition action of the CFs still led to the increase of the dynamic compressive strength. The hybrid synergistic effect of CNTs and CFs was more conducive to enhance the dynamic compressive strength and its strain-rate effect, and also to enhance the impact resistance of the concrete.

Experimental Testing on Mechanical, Durability, and Adsorption Dispersion Properties of Concrete with Multiwalled Carbon Nanotubes and Silica Fumes

The major goal of this research is to see how carbon nanotubes and silica fume affect the durability and mechanical qualities of high-performance concrete (HPC). Mechanical properties, such as split tensile strength, compressive strength, elasticity modulus, and flexural strength, and durability properties like water absorption, abrasion, chloride penetration, acid, and sea water resistance, impact resistance of HPC consisting silica fume (SF), and carbon nanotubes (CNT) were examined in this study. Varied trail combinations with different proportions of CNT and SF admixtures were created for this reason. Portland cement was partially replaced with 1 percent, 1.5 percent, 2 percent, and 3 percent CNT, while SF was substituted with 5 percent, 7.5 percent, and 10 percent. Both CNT and SF outperform conventional concrete in terms of mechanical and durability attributes, according to the findings. CNT produces superior results than SF due to its smaller size.

Experimental investigation of thermal performance for pulsating flow in a microchannel heat sink filled with PCM (paraffin/CNT composite)

A novel microchannel heat sink, which includes a heat exchange cavity with pyramid pin-fins and a PCM (phase change material) cavity with square pin-fins, is designed. The CNT (carbon nanotube) is added to paraffin to enhance thermal conductivity. GOPs (Graphene oxide particles) nanofluids pulsating flow driven by square wave are used to improve the thermal performance. The PCM cavity is filled with CNT/paraffin composite material to absorb and store the heat on the heating surfaces and to transfer the heat through the exchange chamber to achieve cooling. The results show that the microchannel heat sink’s thermal performance can be significantly improved using PCM composite and GOPs nanofluids. Under steady flow conditions, the total thermal resistance decreases significantly when the proportion of carbon nanotubes is approximately 20%; and, the maximum increase of Nusselt number reaches 34.9%. The thermal performance reaches the maximum enhancement under pulsating flow as the pulsating frequency is around 6 Hz. The total thermal resistance decreases by 19%, and the Nusselt number increases by 15.2%. The enhanced effects of pulsating flow and PCM composite on thermal performance are also affected by pump power and heating load. The higher heating power plays an active role in the enhancement effect, whereas the higher pump power has the opposite effect.

Effect of silica fume-enhanced carbon nanotube dispersion on the strength and damping properties of cement composites

Carbon nanotubes (CNTs) tend to agglomerate in cement paste, which impedes the effect of performance reinforcement. This paper applies silica fume as an active factor to enhance the dispersion of CNTs and investigates the influence of silica fume on the strength and damping properties of CNT-reinforced cement composites. Mechanical strength tests and dynamic mechanical analysis on specimens with different contents of CNTs (0%, 0.1% and 0.2%) and silica fume (0%, 5%, 10% and 15%) are conducted. The microstructure is characterized by Scanning Electron Microscopy (SEM), and the pore size distribution is measured by Mercury Intrusion Porosimetry (MIP). Due to the CNT dispersion enhancement, both the number of gel pores and the size of microcapillary pores are reduced. The incorporation of silica fume also facilitates the interfacial friction between CNTs and cement hydration products and promotes heat generation, when reciprocating loads are applied. The result indicates that the mixture proportion of CNTs and silica fume strongly influences the extent of the dispersion enhancement, which is optimized at 0.1% and 5%, respectively. Excessive addition of either CNTs or silica fume will hinder CNT dispersion and subsequently reduce the strength and damping properties of the material, which should be avoided in practical applications.

Enhanced magnetic properties of aluminum oxide nanopowder reinforced with carbon nanotubes

Magnetic carbon nanotubes (CNTs)/alumina (Al2O3) nanocomposites were synthesized by the direct growth of CNTs on alumina by chemical vapor deposition (CVD) process. X-ray diffraction studies show that the crystalline structure of alumina nanoparticles remains preserved during the CVD process. Electron microscopy studies reveal the uniform distribution of CNTs within the alumina matrix. CNTs of average diameter 20 nm are spread around alumina particles of size 120 nm. The proportion of CNTs in alumina composites is determined to be approximately 10% from the thermogravimetric analysis. CNT-reinforced alumina nanocomposites demonstrate a significant improvement of the magnetic properties as compared with pristine alumina powder. The diamagnetic property of alumina nanopowder is transformed into a strongly pronounced ferromagnetic response upon the incorporation of CNTs. The saturation magnetization increased by ~ 2500%, and a pronounced coercivity of 68 Oe was observed in the nanocomposites. It is suggested that the encapsulation of cobalt inside the CNTs constrains the magnetic moments to result in higher saturation magnetization. Hence, the CNTs/Al2O3 system synthesized in this work can be employed to engineer novel ceramic composites with enhanced magnetic properties.

Micro-/macro-level optimization of phase change material panel in building envelope

Recently, improving heat transfer performance and latent heat utilization ratio of phase change materials (PCMs) and products is a key focus for energy saving in building. In present study, a PCM panel was optimized at the micro-level (mixing carbon nanotubes) and macro-level (integrating metal fins) simultaneously. Firstly, thermo-physical properties of the composite PCM with different proportions of carbon nanotubes (CNTs) were compared (based on 256 cooling/heating cycles). The optimal proportion was obtained toward improving thermal conductivity, which was used as the input of following numerical simulation. Then, geometric parameters of the fin in the PCM panel were optimized with numerical simulation, by comparing complete melting time of the PCM and temperature difference in the PCM panel’s heating surface. Finally, thermal performance of the composite walls with non-optimized and optimized PCM panels were compared based on the interior surface temperature and heat flux. The results show that the wall with optimized PCM panel had the optimal performance for heat storage and release. The proposed two-level optimization method has been successfully applied for thermal performance improvement of building envelope in Shenzhen (China), which could also provide references for other regions.

Mechanical Characterization of PC-ABS Reinforced with CNT Nanocomposites developed by Fused Deposition Modelling

Fused Deposition Modeling (FDM), a category of Additive Manufacturing (AM) is a versatile form of manufacturing technology that enables the development of the part layer by layer, of any complex geometry. The development and utilization of polymer nanocomposites for has seen a wide range of implementation. The development of polymer nanocomposite by fused deposition technology and evaluation of its mechanical propertieshave been carried out in this study. Polycarbonate (PC) and Acrylonotrile Butadiene Styrene (ABS) are compounded together with carbon nanotubes. Different proportion of Carbon Nano Tubes (CNT) was added as reinforcement at to PC-ABS matrix. Two variations of samples were developed with incremental addition of CNT to PC-ABS. Ultimate tensile strength and impact strength were analyzed for the developed nano composite FDM parts. It was observed that, with the addition of CNT the ultimate tensile strength of the parts increased significantly. Similar trend was seen for impact strength as well.

Effectiveness of polycarboxylate as a dispersant of carbon nanotubes in concrete

Excellent multifunctional properties of Carbon Nanotubes (CNTs) have brought interest of concrete analyst towards the use of nano materials in concrete. One of the most conventional problems accompany the usage of CNTs in concrete is spreading of the material which is known as dispersion in concrete which significantly affect the mechanical properties of concrete and results in large size of combined CNTs. To achieve dispersion of CNTs in cement concrete, many ways have been adopted. In this paper a study is considered to check the dispersion of CNTs into the concrete with the use of chemical process by considering polycarboxylate as a dispersant. To compare the observations samples with and without polycarboxylate were considered. Mechanical properties like compressive strength, indirect tensile strength and flexural strength were considered with proportions of CNTs as 0.1%, 0.2%, 0.3%, 0.4% and 0.5% of total cementitious materials. Results suggest the effectiveness of polycarboxylate as a dispersant.

Controlled Layer-By-Layer Deposition of Carbon Nanotubes on Electrodes for Microbial Fuel Cells

Carbon nanotubes (CNTs) and polyelectrolyte poly(allylamine hydrochloride) (PAH) composite modified indium tin oxide (ITO) electrodes, by a layer-by-layer (LBL) self-assembly technique, was evaluated as an anode for microbial fuel cells (MFCs). The bioelectrochemistry of Shewanella loihica PV-4 in an electrochemical cell and the electricity generation performance of MFCs with multilayer (CNTs/PAH)n-deposited ITO electrodes as an anode were investigated. Experimental results showed that the current density generated on the multilayer modified electrode increased initially and then decreased as the deposition of the number of layers (n = 12) increased. Chronoamperometric results showed that the highest peak current density of 34.85 ± 2.80 mA/m2 was generated on the multilayer (CNTs/PAH)9-deposited ITO electrode, of which the redox peak current of cyclic voltammetry was also significantly enhanced. Electrochemical impedance spectroscopy analyses showed a well-formed nanostructure porous film on the surface of the multilayer modified electrode. Compared with the plain ITO electrode, the multilayered (CNTs/PAH)9 anodic modification improved the power density of the dual-compartment MFC by 29%, due to the appropriate proportion of CNTs and PAH, as well as the porous nanostructure on the electrodes.

Adsorption of Heavy Metal Ions by Carbon‐Nanofibers‐Blended Carbon Nanotubes

AbstractBy spinning different proportions of carbon nanotubes (CNTs) and polyacrylonitrile into filaments, discussing the structure of CNTs exposed on the surface of nanofibers after carbonization treatment at different temperatures, and the relationship between CNTs and pores in carbon nanofibers. Different pH, dosage, initial concentration of pollutants and adsorption time on the adsorption of Cr(VI) was studied on carbon nanofiber porous materials with carbon nanotubes. The results showed that the specific surface area of carbon nanofibers blended with CNTs increased to 37.627 m2/g and the pore volume reached 3.832cc/g. The porous adsorption material can reach the adsorption capacity of 25.17mgg−1 within 20 min. When the adsorption reached equilibrium, the adsorption capacity reached 76.62mgg−1.

Preparation of carbon nanotube-activated carbon hybrid electrodes by electrophoretic deposition for supercapacitor applications

This study examines the possibility of preparing activated carbon (AC) and carbon nanotubes (CNT) based electrodes for supercapacitors by a facile electrophoretic deposition (EPD) method. The EPD method is able to deposit AC and CNTs on a stainless steel substrate, fabricating a three dimensional porous structure. The weight proportions of CNT to AC in the as-prepared electrodes are estimated by thermogravimetric analysis. The amount of CNTs in the electrodes can be easily controlled by tuning the solution bath composition before the EPD process. The effects of the presence of CNTs in the AC electrode on supercapacitor performance are also examined in this work. The addition of CNTs not only increases the specific capacitance but also enhances the rate capability of the AC electrodes. After a cyclic stability test for 11,000cycles, the as-prepared AC/CNT electrode shows capacitance retention of 85%, clearly demonstrating the commercial applicability of the electrodes fabricated by EPD process.

Acetone Sensing Properties of a Gas Sensor Composed of Carbon Nanotubes Doped With Iron Oxide Nanopowder.

Iron oxide (Fe2O3) nanopowder was prepared by a precipitation method and then mixed with different proportions of carbon nanotubes. The composite materials were characterized by X-ray powder diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. A fabricated heater-type gas sensor was compared with a pure Fe2O3 gas sensor under the influence of acetone. The effects of the amount of doping, the sintering temperature, and the operating temperature on the response of the sensor and the response recovery time were analyzed. Experiments show that doping of carbon nanotubes with iron oxide effectively improves the response of the resulting gas sensors to acetone gas. It also reduces the operating temperature and shortens the response recovery time of the sensor. The response of the sensor in an acetone gas concentration of 80 ppm was enhanced, with good repeatability.

Creep Behavior Study for Carbon Fiber Nano-Composites

The surface modification of carbon nanotubes (CNTs) has been recently observed to influence the distribution of CNTs in epoxy resin and the mechanical properties and electrical conductivities of these CNTs. Accordingly, the treatment of CNTs to with organic acids to oxidize them generates functional groups on the surface of CNTs. This investigation studies the consequent enhancement of the mechanical properties and electrical conductivities of CNTs. The influence of adding various proportions of CNTs to the epoxy resin on the mechanical properties and electrical conductivities of the composites thus formed is investigated, and the strength of the material is tested at different temperatures.The test results also indicate that mechanical strength and electrical conductivity increase with the amount of CNTs added to the composites. Different coefficients of expansion of the matrix, fiber and CNTs, are such that overexpansion of the matrix at high temperature results in cracking in it.Moreover, the creep behaviors of carbon fiber (CF) /epoxy resin thermosetting composites and CNTs/CF/ epoxy resin composites were tested and analyzed at different stresses, orientations of fiber, temperatures and humidities. The creep exhibits only two stages-primary creep and steady-state creep. The effects of creep stress, creep time, and humidity on the creep of composites that contain various proportion of CNTs were investigated at various temperatures.Additionally, increasing the number of cycles in cyclic creep tests at room temperature resulted in a decrease in creep strain even at a high temperature of 55°C. Possible room temperature creep mechanisms have been proposed and discussed. With increasing number of creep tests, the creep strain decreased due to strain hardening which occurred during creep. Creep strain is believed to increase with applied stress, creep time, humidity, temperature and degree of the angle θ between the orientation of fiber and the direction of the applied stress.Finally, the test results of creep strain of CF/epoxy resin composites and CNTs/CF/epoxy resin composites tested under various conditions can be smoothly fitted by the fitting curves of Findley power law.

Preparation of graphene–carbon nanotube–TiO2 composites with enhanced photocatalytic activity for the removal of dye and Cr (VI)

Graphene–carbon nanotubes (CNTs)–TiO2 composites were successfully synthesized by a one-pot solvothermal method. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and diffuse reflectance UV–vis spectra. The photocatalytic activity of as-prepared composite photocatalysts was tested by degradation of dye methylene blue (MB) and photoreduction of Cr(VI) in aqueous solution under UV light irradiation. The experiment results showed that the composites exhibited enhanced photocatalytic performance compared to binary one (i.e. graphene–TiO2) and pristine TiO2. The effect of CNTs content on the photocatalytic activity was also studied. It showed that the photocatalytic performance of the graphene–CNTs–TiO2 hybrids was dependent on the proportion of CNTs in the composite. The mass ratio of CNTs:TiO2=5% was proved to be the optimal ratio. The apparent rate constants k for MB degradation and Cr(VI) reduction were 2.2 and 1.9 times as graphene–TiO2 composite, respectively. The enhanced activity can be ascribed to the addition of CNTs, which can be severed as charge transmitting paths thus decrease the recombination rate of photoinduced electron–hole pairs. This mechanism for the enhanced photoactivity was further confirmed by measuring the hydroxyl radical and transient photocurrent.

Synthesis of porous carbon nanotubes/activated carbon composite spheres and their application for vitamin B12 adsorption

AbstractIn this paper, carbon nanotubes (CNTs) were added to activated carbon to enhance the mesopores. At first, different amounts of CNTs were added to phenolic resin and composite spheres were synthesized by suspension polymerization. Then, by carbonizing these spheres at 600°C followed by steam activation at 850°C for more than 90 min, we prepared highly developed porous CNTs/activated carbon composite spheres. The composite spheres were characterized by a laser particle size analyzer, scanning electron microscopy, Raman spectrum, and nitrogen adsorption-desorption isotherms. Results showed that the composite spheres had good sphericity even with high proportion of CNTs (45 wt.%). Analysis also showed that the pore size distribution of the composite spheres containing CNTs was “multi-peak”, especially with 20–100-nm pores. The improved 20–100-nm porous structures in the composite spheres can be ascribed to aggregated pores of CNT bundles. The amount of vitamin B12 adsorbed on the 45 wt.% CNT composite spheres was as high as 32.38 mg/g. The spheres could be used as adsorbents for middle-molecular-weight toxins or large molecules in hemoperfusion.

In situ preparation and mechanical properties of CNTs/MCMBs composites

By adding carbon nanotubes (CNTs) into medium temperature coal tar pitch, mesocarbon microbeads (MCMBs) were obtained via thermal condensation, then CNTs/MCMBs composites were in situ prepared using compression molding. The morphology, structure and mechanical properties of CNTs/MCMBs composites were characterized by optical microscope, digital camera, scanning electron microscope (SEM) and mechanical test machine. Results showed that CNTs were used as the nucleating agent and could inhibit the growth and coalescence of MCMBs. The optical textures of CNTs/MCMBs composites showed similar characteristics to the thermal condensation products from coal tar pitch with CNTs. The mass ratio of CNTs to coal tar pitch played an important role in the mechanical properties of CNTs/MCMBs composites. The density and bending strength of CNTs/MCMBs composite first increased and then decreased with the increase of the proportion of CNTs. When the proportion of CNTs was 5wt%, the density of the composite reached the maximum (1.76g/cm3). In addition, the bending strength of the composite reached the maximum (79.6MPa) as adding 2wt% CNTs into coal tar pitch.