Effect Of Carbon Nanotubes Concentration Research Articles

CNT-Based Solar Thermal Coatings: Absorptance vs. Emittance

A novel approach for fabricating selective absorbing coatings based on carbon nanotubes (CNTs) for mid-temperature solar–thermal application is presented. The developed formulations are dispersions of CNTs in water or solvents. Being coated on stainless steel (SS) by spraying, these formulations provide good characteristics of solar absorptance. The effect of CNT concentration and the type of the binder and its ratios to the CNT were investigated. Coatings based on water dispersions give higher adsorption, but solvent-based coatings enable achieving lower emittance. Interestingly, the binder was found to be responsible for the high emittance, yet, it is essential for obtaining good adhesion to the SS substrate. The best performance of the coatings requires adjusting the concentration of the CNTs and their ratio to the binder to obtain the highest absorptance with excellent adhesion; high absorptance is obtained at high CNT concentration, while good adhesion requires a minimum ratio between the binder/CNT; however, increasing the binder concentration increases the emissivity. The best coatings have an absorptance of ca. 90% with an emittance of ca. 0.3 and excellent adhesion to stainless steel.

Molecular investigation into the effect of carbon nanotubes interaction with CO2 in molecular separation using microporous polymeric membranes

The use of nanofluids has been recently of great interest to separate acidic contaminants such as CO2. The main objective of this research is to assess the influence of carbon nanotubes (CNTs) addition to distilled water on enhancing the CO2 molecular separation through a porous membrane contactor (PMC). For this aim, a comprehensive model is developed based on non-wetted and counter-current operational modes to evaluate the principal mass and momentum transport equations in tube, membrane and shell compartments of PMC. Consequently, a CFD-based axisymmetrical simulation is implemented according to finite element technique (FET) to prognosticate the results. It is found from the results that the addition of 0.1 wt% carbon nanotubes (CNTs) particles to water significantly enhances the mass transfer and consequently the CO2 molecular separation efficiency from 38 to 63.3%. This considerable enhancement can be justified due to the existence of two momentous phenomena including Brownian motion and Grazing effect, which enhance the mass transport of CO2 molecules in the PMC. Moreover, the effect of CNTs concentration, some membrane's parameters such as number of hollow fibers and porosity and also some module's design parameters including module radius and length on the CO2 separation performance are investigated in this paper as another highlight of the current work.

Effect of Carbon Nanotube Concentration on the Corrosion Behavior of Electroless Ni-B-CNT Coating

In this study, Ni-B-CNT composite was deposited on AISI 4140 steel using different concentrations of CNTs ranging from 0.2 to 1 gr/lit in an electroless bath. The phase analysis and surface morphology of the samples were characterized using x-ray diffraction and FESEM. The corrosion behavior of the coated samples was investigated in a 3.5 wt.% NaCl solution through potentiodynamic polarization, EIS, and electrochemical noise (EN) analyses. The corroded surface of the samples was further analyzed via FESEM observation after 10 days of immersion in corrosive medium. It was found that although adding 0.2 gr/lit CNT in electroless solution improves corrosion resistance, increasing CNT concentration from 0.2 up to 1 gr/lit increases the corrosion rate. The FESEM observations and EN results imply that the formation of micro-galvanic cells in samples with high concentration of CNTs leads to nucleation and growth of the pits. The results revealed that no passive layer was formed on the surface of the Ni-B sample, and the corrosion occurred through ionic diffusion into the cracks and crevices. The results of potentiodynamic test show that adding CNTs into electroless bath facilitates the formation of passive layer. However, results of EN test imply that increasing CNT concentration causes repetitive breakdown and recovery of passive film.

A Meta-study on the Thermal Properties of Carbon Nanotubes in Thermal Interface Materials

Computer Integrated Circuit (IC) microprocessors are becoming more powerful and densely packed while cooling mechanisms are seeing an equivalent improvement to compensate. A significant limit to cooling performance is thermal transfer between die and heatsink. In this meta study we evaluate carbon nanotube (CNT) thermal interface materials (TIMs) in order to determine how to maximise thermal transfer efficiency. We gathered information from over 15 articles focused on the thermodynamic parameters of CNT TIMs from databases such as Scopus, IEEE Xplore and ScienceDirect. Articles were filtered by key words including ‘carbon nanotubes’ and ‘thermal interface materials’ to identify scientific articles relevant to our research on TIMs. From our meta study we have found that enhancing CNTs will provide the best improvement in TIMs. The parameters analysed to determine TIM performance included thermal resistance, thermal conductivity and the effect of CNT concentration on computer operation time. Through our investigation we understood that increasing the concentration of CNT from 0 to 2 wt % increases the operation time from 75 seconds at 66°C to 200s at 63°C as well as increasing the thermal conductivity by 1.82 times for the AS5 thermal paste with 2 wt % CNT. Furthermore, CNT TIM pastes with less thickness have a lower thermal resistance of 0.4 K/W. However not all these parameters have been tested with computer chips. This means that in order to increase current heat transfer efficiency limit, we must integrate these parameters into experimental models.
 Keywords: Thermal Interface Material; Thermal Paste; Carbon Nanotubes; Thermal Transfer Efficiency; Integrated Circuit; Heat Sink; Heat Dissipation.

Effect of CNTs concentration on the microstructure and friction behavior of Ni-GO-CNTs composite coatings

A kind of novel anti-wear and self-lubricating Ni-GO-CNTs composite coatings were deposited on the surface of AZ91D magnesium alloys substrates by an integrative method involved electrophoresis and electrodeposition with various CNTs (carbon nanotubes) concentration. The surface and cross-sectional morphologies of Ni-GO-CNTs composite coatings were studied by scanning electron microscope equipped with an energy dispersive spectroscope. The micro-indentation hardness as well as friction and tribological properties of Ni-GO-CNTs composite coatings were tested by micro-hardness tester, friction and wear tester separately. Results showed that the Ni-GO-CNTs composite coatings prepared successfully were strongly combined with the copper coating and the magnesium alloys substrates. The maximal micro-indentation hardness value of Ni-GO-CNTs composite coating was obtained with 0.04 g/L CNTs added. The wear resistance of Ni-GO-CNTs composite coating increased initially and then decreased with increasing the CNTs concentration. When the concentration of CNTs was 0.04 g/L, the friction coefficient and wear capacity of the composite coating exhibited the minimum value, which is mainly due to the cross-linking effect of CNTs and GO (graphene oxide) that enhanced the physicochemical properties of the CNTs and GO, indicating better mechanical properties of Ni-GO-CNTs coating.

Effect of carbon nanotube concentration on cooling behaviors of oil-based nanofluids during the immersion quenching

Oil-based nanofluids including 0.75%—1.75% (mass fraction) carbon nanotubes (CNTs) without any surfactants have been synthesized by a two-step process. The probes machined from 45# steel with 22mm diameter and 50mm length are quenched in the as-synthesized CNT nanofluids for testing the cooling behaviors of the nanofluids. The laser diffraction particle size analyzer, scanning electronic microscope (SEM), X-ray diffractometer and transmission electron microscope (TEM) are used to characterize the quality and distribution of CNTs in the nanofluids. The wettability and viscosity of 30# oil and oil-based CNT nanofluids are measured by a goniometer at 15 ◦C and a rotational type viscometer at 40 ◦C, respectively. The results show that the cooling efficiency of the oil-based CNT nanofluids is better than that of 30# oil. Moreover, the cooling rate of the naonofluids increases with the further increase of the CNT concentration. When the mass fraction of CNTs increases to 1.75%, the cooling rate of the naonofluids reaches a maximum at 760 ◦C and it is increased by 77.8% as compared to that of base oil. The improved cooling rate of oil by CNTs is mainly due to the uniform distribution and excellent thermal conductivity of CNTs.

Recent advances in understanding the reinforcing ability and mechanism of carbon nanotubes in ceramic matrix composites

Since the discovery of carbon nanotubes (CNTs), commonly referred to as ultimate reinforcement, the main purpose for fabricating CNT–ceramic matrix composites has been mainly to improve the fracture toughness and strength of the ceramic matrix materials. However, there have been many studies reporting marginal improvements or even the degradation of mechanical properties. On the other hand, those studies claiming noticeable toughening measured using indentation, which is an indirect/unreliable characterization method, have not demonstrated the responsible mechanisms applicable to the nanoscale, flexible CNTs; instead, those studies proposed those classical methods applicable to microscale fiber/whisker reinforced ceramics without showing any convincing evidence of load transfer to the CNTs. Therefore, the ability of CNTs to directly improve the macroscopic mechanical properties of structural ceramics has been strongly questioned and debated in the last ten years. In order to properly discuss the reinforcing ability (and possible mechanisms) of CNTs in a ceramic host material, there are three fundamental questions to our knowledge at both the nanoscale and macroscale levels that need to be addressed: (1) does the intrinsic load-bearing ability of CNTs change when embedded in a ceramic host matrix?; (2) when there is an intimate atomic-level interface without any chemical reaction with the matrix, could one expect any load transfer to the CNTs along with effective load bearing by them during crack propagation?; and (3) considering their nanometer-scale dimensions, flexibility and radial softness, are the CNTs able to improve the mechanical properties of the host ceramic matrix at the macroscale when individually, intimately and uniformly dispersed? If so, how? Also, what is the effect of CNT concentration in such a defect-free composite system? Here, we briefly review the recent studies addressing the above fundamental questions. In particular, we discuss the new reinforcing mechanism at the nanoscale responsible for unprecedented, simultaneous mechanical improvements and highlight the scalable processing method enabling the fabrication of defect-free CNT-concentered ceramics and CNT-graded composites with unprecedented properties. Finally, possible future directions will be briefly presented.

Effect of mechanical alloying time and rotation speed on evolution of CNTs/Al-2024 composite powders

Carbon nanotubes (CNTs) reinforced aluminum matrix composites were fabricated by mechanical milling followed by hot extrusion. The commercial Al-2024 alloy with 1% CNTs was milled under various ball milling conditions. Microstructure evolution and mechanical properties of the milled powder and consolidated bulk materials were examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and mechanical test. The effect of CNTs concentration and milling time on the microstructure of the CNTs/Al-2024 composites was studied. Based on the structural observation, the formation behavior of nanostructure in ball milled powder was discussed. The results show that the increment in the milling time and ration speed, for a fixed amount of CNTs, causes a reduction of the particle size of powders resulting from MM. The finest particle size was obtained after 15 h of milling. Moreover, the composite had an increase in tensile strength due to the small amount of CNTs addition.

An experimental investigation on the conductive behavior of carbon nanotube-reinforced natural polymer nanocomposites

It is well known that carbon nanotubes (CNTs) have excellent electrical properties and can be used as the nanofiller in natural polymers to produce conductive CNT/polymer nanocomposites. In this study, the conductive behavior of CNT-reinforced natural polymer nanocomposites was investigated. The effect of CNT concentration on the conductivity of CNT/natural polymer nanocomposites was also investigated. The natural polymers used were plasticized starch (PS) and chitosan (CS). FTIR spectroscopy was used to examine the interactions between PS, CS, and CNTs. TEM analysis on both nanocomposites were made to study the dispersion states of CNTs in both polymers. The results showed that the surface resistivities of both CNT/PS and CNT/CS nanocomposites decreased steeply with increasing CNT concentration. Particularly, the CNT/CS nanocomposites showed a better conductivity than the CNT/PS composites at the same CNT concentration. The TEM result showed that CNT/CS nanocomposites had better dispersibility and formation of fully connected, three-dimensional network structures between the CNTs than the CNT/PS nanocomposites, which results in the superior conductive property of CNT/CS nanocomposites compared to the CNT/PS nanocomposites.

Laser transmission welding of ABS: Effect of CNTs concentration and process parameters on material integrity and weld formation

This paper reports a study of the laser transmission welding of polymeric joints composed by two ABS (acrylonitrile/butadiene/styrene) sheets, one transparent (natural ABS) and the other absorbent (filled by different percentages of carbon nanotubes (CNTs)). The objective of this work is to analyze the effect of process parameters and CNTs concentrations on weld formation and mechanical resistance of the weld joints. Thermal and optical characterizations of natural and doped ABS sheets are studied. Microscopic characterization of the top and cross sections of the joining were carried out to study the corresponding weld widths and integrity. The mechanical resistance of the optimal welded joints was checked by mechanical shear tests. The welding capability was investigated as a function of the filler concentration. The results concerning weld formation and material integrity suggest a high sensitivity of the doped ABS with high concentration of CNTs to specific changes in the incident laser intensity. This sensitivity changes can be related with the changes in the optical properties of the doped polymer. • Glass transition temperature for doped ABS did not change with CNT concentration. • The optical properties for doped ABS change with the CNT concentration. • Laser transmission welding of ABS shows two regimens depending on the CNTs content. • More variable mechanical properties are observed for ABS with high CNTs content. • Neither CNTs content reveal clear correlation between weld width and shear force.

Poly(lactic acid)/Carbon Nanotube Fibers as Novel Platforms for Glucose Biosensors.

The focus of this paper is the development and investigation of properties of new nanostructured architecture for biosensors applications. Highly porous nanocomposite fibers were developed for use as active materials in biosensors. The nanocomposites comprised poly(lactic acid)(PLA)/multi-walled carbon nanotube (MWCNT) fibers obtained via solution-blow spinning onto indium tin oxide (ITO) electrodes. The electrocatalytic properties of nanocomposite-modified ITO electrodes were investigated toward hydrogen peroxide (H2O2) detection. We investigated the effect of carbon nanotube concentration and the time deposition of fibers on the sensors properties, viz., sensitivity and limit of detection. Cyclic voltammetry experiments revealed that the nanocomposite-modified electrodes displayed enhanced activity in the electrochemical reduction of H2O2, which offers a number of attractive features to be explored in development of an amperometric biosensor. Glucose oxidase (GOD) was further immobilized by drop coating on an optimized ITO electrode covered by poly(lactic acid)/carbon nanotube nanofibrous mats. The optimum biosensor response was linear up to 800 mM of glucose with a sensitivity of 358 nA·mM−1 and a Michaelis-Menten constant (KM) of 4.3 mM. These results demonstrate that the solution blow spun nanocomposite fibers have great potential for application as amperometric biosensors due to their high surface to volume ratio, high porosity and permeability of the substrate. The latter features may significantly enhance the field of glucose biosensors.

Characterization of Al 2024-CNTs composites produced by mechanical alloying

In the present work, the 2024 aluminum alloy (Al 2024) alloy has been produced by mechanical alloying (MA). The alloy was then strengthened by dispersion of carbon nanotubes (CNTs) during different times. Thus, the effect of CNTs concentration and milling time on the microstructure of the Al 2024-CNTs composites was studied. The results show a homogeneous dispersion of CNTs into the Al-matrix phase by mechanical milling (MM). It was observed that the increment in the milling time, for a fixed amount of CNTs, causes a reduction of the particle size of powders resulting from MA. The finest particle size was obtained at 20 h of milling. These observations were confirmed by scanning and transmission electron microscopy. After 10 h of milling, Cu, Mg and other alloying elements constituting the Al 2024 alloy, form a solid solution and only some remnant Mn particles were observed but not detected by X-ray diffraction.

Dispersion of CNTs in Aluminum 2024 Alloy by Milling Process

Elemental powders and carbon nanotubes (CNTs) were mixed and milled in a high energy shaker mill (SPEX-8000M), to produce 2024 aluminum (Al2024) matrix composites reinforced with CNTs. Milled products were consolidated by uniaxial load pressing followed by pressure-less sintering under argon atmosphere for 2 h at 773 K. The effect of CNTs concentration and milling time on Vickers microhardness (µHV) was studied. Scanning electron microscopy (SEM) micrographs show that by milling process it is possible to obtain a homogeneous dispersion of CNTs into the aluminum matrix. The mechanical properties of the composites show an important improvement with respect to reference samples. The possible strengthening mechanisms are discussed in the present work.

Effect of CNT concentration and agitation on surface heat flux during quenching in CNT nanofluids

In this article, the effect of Carbon Nanotube (CNT) concentration and agitation on the heat transfer rate has been studied during immersion quenching in CNT nanofluids. For this purpose, CNT nanofluids were prepared by suspending chemically treated CNTs (TCNT) at four different concentrations in deionized (D.I) water without using any surfactant. Quench probes with a diameter of 20 mm and a length of 50 mm were machined from 304L stainless steel (SS) and quenched in water and CNT nanofluids with the CNT concentration ranging from 0.25 to 1.0 wt.%. The heat flux and temperature at the quenched surface were estimated based on the Inverse Heat Conduction (IHC) method using the temperature data recorded at 2 mm below the probe surface during quenching. The computation results showed that the peak heat flux increased with an increase in the CNT concentration up to 0.50 wt.% and started decreasing with further increase in the CNT concentration. The enhanced heat transfer performance of CNT nanofluids during quenching at lower concentration of CNTs is attributed to their higher effective thermal conductivity. The reduced heat transfer performance of CNT nanofluids having higher concentration of CNTs is due to the increased viscosity of CNT nanofluids. The effect of agitation on heat transfer rate during quenching has also been studied in this work by stirring the CNT nanofluid prepared with 0.50 wt.% of CNTs which recorded the maximum peak heat flux among the four concentrations. The effect of CNT nanofluid agitation was counter-intuitive and resulted in decreased heat transfer rate with the increase in agitation rate.

Morphological and Dielectric Behavior of Carbon Nanotube-Ferroelectric Liquid Crystal Composite

The present study deals with the effect of dispersing Carbon Nano Tubes in Ferro-electric liquid crystal material. Carbon nanotube dispersed ferroelectric liquid crystals have high dielectric constant, fast switching response, large electro-optic coefficient which makes them ideal for memories, capacitors and display devices etc. An attempt has been made to understand the influence of carbon nanotubes on dielectric and morphological properties of ferro-electric liquid crystal. The effect of carbon nanotubes concentration on the transition temperature of ferro-electric liquid crystal is also studied. Hot Stage Microscope is used to investigate the texture and phase transformations in the composite. Differential Scanning Calorimetry also indicated the phase transformations. The results are compared with the original ferro-electric liquid crystal material which showed that the dielectric permittivity is increased to a great extent with the addition of carbon nanotubes.

Rheology and Electrorheology of Nanorod-Loaded Liquid Crystalline Polymers

AbstractThe effect of carbon nanotube concentration and dispersion on the rheology of liquid crystalline solutions of hydroxypropylcellulose (HPC) has been experimentally studied. The rheology of nanocomposites of HPC and multiwalled carbon nanotubes (MWCNT) in m-cresol was characterized in steady-state and transient dynamic tests. The rheology as particle loading increases shows a very distinct response in the magnitude and scaling of the steady-state viscosity, and the storage and loss modulus. The liquid crystalline phase was characterized by direct observations by reflected polarized light microscopy. Additionally, an electric-field effect was observed on the rheology of the HPC/MWCNT in m-cresol soft composites. The HPC in m-cresol matrix is non-responsive, thus the electrorheological effect is due to the presence of the carbon nanotubes. The mechanism for this effect is still uncertain, since it does not follow the scaling predicted by simple models for heterogeneous or homogeneous ER fluids.