Multi-walled Carbon Nanotubes Powder Research Articles

Multi-walled carbon nanotube-functional ionophore based composite potentiometric sensor for selective detection of lead in water

A functional ionophore (tetramethyl thiuram disulfide or TMTDS) and multi-walled carbon nanotubes (MWCNTs)-based composite paste was prepared by a novel and simple approach, to fabricate a two-electrode system for detection of lead ions in drinking water, by potentiometric method. Homogenous and properly dispersed paste was obtained by blending TMTDS and MWCNTs powder in silicon oil. The working electrode contained the ionophore and the potential between working and reference electrodes were used for assessing performance of the proposed sensor. Effect of various operating conditions, such as, concentration of TMTDS in working electrode, solution pH, temperature, inter-electrode distance and sensing time was carried out to obtain the best sensor. Highest sensitivity was achieved at 24 wt% TMTDS concentration, neutral pH, room temperature (298 K), 2-minute sensing time and 0.5 cm inter-electrode spacing. Following this, the best sensor was used for electrochemical characterization, such as, impedance spectroscopy, cyclic voltammetry, chronoamperometry and differential pulse voltammetry at different lead concentrations. Studies were also performed to show the content of different ions in the leachate solution from the prepared electrode. Compared to other conventional electrodes, synthesized composite paste-based electrode displayed significant enhancement in selective determination of lead. Proposed method offers scope for on-site detection of lead ions, even at trace levels, ranging from 0.2 μg/l till 150 μg/l. Sensitivity of the sensor toward lead ions was calculated and a detection limit of 31 μg/l was observed.

Effect of dry milling and MWCNTs content during fabrication of Fe-MWCNTs metal matrix composite by high energy planetary milling followed by conventional sintering

The present paper discusses about fabrication of iron-based composite using multi walled carbon nanotubes (MWCNTs) as reinforcing agent by using high energy planetary milling followed by conventional sintering. Composites containing iron and 0.5, 1.0, 2.0 and 4.0 vol. % MWCNTs powder mixtures are milled in dry (argon atmosphere) condition for 10 h in a dual drive planetary mill (DDPM). It has been observed that after 10 h of milling, average particle size decreases from 36 to 10 µm. The field emission-scanning electron microscopy (FESEM) images show that final powder is spherical in shape after milling. Raman spectroscopy reveals distortion and formation of defects in MWCNTs after 10 h of milling and MWCNTs are stable upto 900 °C and losses stability when consolidated at both 1200 and 1300 °C. The maximum value of relative density and hardness are 88 % and 252 VHN respectively for the Fe-0.5 vol. % MWCNT composite sintered at 1300 °C for 2 h. The maximum value of yield strength and compressive strength are also achieved for Fe-0.5 vol. % MWCNTs composite sintered at 1300 °C and the values are 350 MPa and 580 MPa respectively.

Development and characterization of iron (III) phthalocyanine modified carbon nanotube paste electrodes and application for determination of fluometuron herbicide as an electrochemical sensor

This study is the first electroanalytical study conducted for the determination of fluometuron herbicide. For this purpose, a new electrode was prepared by combining iron (III) phthalocyanine − 4.4′,4′′,4′′′-tetrasulfonic acid, oxygen monosodium salt hydrated compound (FePc) and multi-walled carbon nanotube powders (MWCNTP). The FePc/MWCNTP composite (hybrid) material prepared in this way was coated on glassy carbon electrode (GCE) and multi-walled carbon nanotube paste electrode (MWCNTPE) using the drop-dry method. Compared to both the bare GCE and MWCNTPE, the modified FePc/MWCNTPE increased the anodic peak current of fluometuron by approximately six fold. Calibration plots of the fluometuron were constructed using the standard addition method with differential puls stripping voltammetry (DPSV) and square wave stripping voltammetry (SWSV) under the optimum conditions. While the working range was determined as 0.4–15.0 mg/L in pH 6.0 Britton Robinson (BR) buffer solution on FePc/MWCNTP electrode with DPSV, this range was found to be 0.4–7.5 mg/L with SWSV. In addition, the limit of detection (LOD) and the limit of quantification (LOQ) values ​​were 69.8 µg/L and 233.0 µg/L, respectively, by DPSV. On the other hand, these two validation values ​​(LOD and LOQ) were 101 µg/L and 337 µg/L by SWSV, respectively. Subsequently, cyclic voltammetric (CV) studies were carried out to elucidate the electrochemical behavior and electrode mechanism of the fluometuron herbicide. In addition, the interference effects of some cations and pesticides in the determination of fluometuron were examined. Finally, studies of recovery of fluometuron herbicide from tap water and determination of fluometuron in Cottonex 500 SC® commercial pesticide formulation using the proposed DPSV method and modified FePc/MWCNTP electrode were performed with very low relative error.

The effect of MWCNT modification on structural and morphological properties of Li4Ti5O12

Lithium titanium oxide (Li4Ti5O12) particles were surface-modified with 1–5% wt. of multi-walled carbon nanotubes (MWCNT) using a new low temperature method (LTM). Subsequent techniques have been applied to characterize all materials: X-ray powder diffraction (XRD), Raman and X-ray photoelectron (XPS) spectroscopy, scanning electron (SEM), transmission (STEM), and atomic force (AFM) microscopy. The selected materials have been subjected to preliminary electrochemical analysis. The effect of the synthesis conditions on the obtained series of LTO/1–5% wt. MWCNT nanocomposites was analyzed. X-ray diffraction showed that the crystal structure of LTO is not affected by the multi-walled carbon nanotubes (MWCNT) modification. Raman spectroscopy confirms the XRD results that the MWCNTs do not affect the LTO structure and all nanocomposites show similar levels of defects and/or degree of graphitization. The XPS measurements showed the most intense line at the binding energy of 284.5 eV, which corresponds to the C=C/C-C bonding in carbon atoms in the graphitic structure on the surface of the LTO material. Additionally, the peak at 285.3 eV was attributed to aliphatic structures, edges, and defects in the graphitic nanotube structure, whereas the peaks at 286.1, 287.6, 289.0 and 290.1 eV, correspond to CO, CO, HO-C=O, and OCOO, carbon atoms attached to different oxygen-containing moieties, respectively. CNTs were well distributed between LTO particles, as revealed by STEM observations. Single CNTs or agglomerates by joining LTO particles created cross-links for electron transfer. The relationship and effect between the structural and morphological analysis of spinel Li4Ti5O12 structure modified with carbon nanotubes was examined for the first time in this work. The performed preliminary electrochemical measurements revealed that the best electrochemical properties was obtained for LTO powder modified with 1%wt. of MWCNT. After 50 cycles of charge/discharge processes at the current rate of 1 C, the LTO/1%wt. MWCNT powder retained more than 98% of its specific capacity.

Facile deposition of multiwalled carbon nanotubes via electrophoretic deposition in an environmentally friendly suspension

The present work focuses on the application of electrophoretic deposition (EPD) as a facile process to generate homogeneous layers of multi walled carbon nanotubes (MWCNTs) using water as an environmentally friendly solvent. The EPD process requires a pretreatment of the commercially available MWCNT powder to create a surface charge on the surfaces of the MWCNTs as well as to realize stable suspensions. After pre-treatment, the electrophoretic mobility of the MWCNTs was approximately μ ≈ − 4.3 · 10−4cm2V−1s−1 and the resulting ζ-potential is in the range of ζ ≈ −55 mV. The suspension showed no sedimentation over 50 days. The EPD was carried out at an applied voltage of 50 V. The MWCNTs were successfully deposited as open porous layers on gold as well as on aluminum. The specific double layer capacitance of the MWCNT-layers on gold amounts to C ≈ 11.9 Fg−1.However, on aluminum as substrate, the EPD of the MWCNTs is associated with the formation of a thin barrier like oxide film. In this case a major part of the applied voltage drops down across the oxide film and only a minor part across the suspension. Consequently, the field strength in the suspension decreases. Moreover, the capacitance of the oxide film dominates the whole capacitance of the electrode. The specific capacitance amounts to C = 0.3 mFg−1 related to the deposited mass of MWCNTs.

Potentiometric sensing platform for selective determination and monitoring of codeine phosphate in presence of ibuprofen in pharmaceutical and biological matrices

Recently, application of ion selective electrode field in pharmaceutical sciences has expanded due to the most interesting feature of the sensors, which is their remarkably selective recognition. In this work six electrodes were investigated for codeine phosphate (COD) determination including conventional liquid inner contact sensors (sensors 1–3) and solid state sensors (gold: sensor 4, modified screen-printed electrodes (SPE) with multi-walled carbon nanotubes powder (MWCNTs): sensor 5 and gold nanoparticles GNPs-SPE: sensor 6). Potassium tetrakis has proved to be the cationic exchanger of choice which was applied to all the solid contact electrodes with nitrophenyl octyl ether as a plasticizer in a polymeric matrix of polyvinyl chloride. Incorporation of GNPs presents a superior novel performance of the electrode regarding response and sensitivity. Sensors (3, 4 and 6) showed best Nernestian response slopes of 58.19 ± 1.09, 59 ± 0.95 and 62 ± 0.98 mV/decade, respectively over a wide COD concentration range. Those proposed sensors display useful analytical characteristics for determination of COD in bulk powder, combined pharmaceutical formulation with Ibuprofen and monitoring of COD concentration in human plasma. The method was validated according to ICH guidelines. Moreover, statistical evaluation of the results was carried out compared to a reported HPLC method where the null hypothesis was confirmed.

Preparation of MWCNT Microbeads for the Application of Bed Materials in a Fluidized Bed Heat Exchanger.

Fluidized beds have been utilized for various chemical and physical applications including heat transfer such as the gas–solid heat exchanger. It is advantageous to use carbon nanotubes (CNTs) with high thermal conductivity as bed materials for heat transfer enhancement in a direct gas–solid contacting heat exchanger. However, the poor fluidization of CNTs is the biggest challenge due to the strong cohesive force between the particles. A control over the macroscopic shapes of CNT powders is required for their application. A preparation method of CNT microbeads has been proposed to be suitable for fluidized bed applications. The method is characterized by using m-cresol known as processing solvents for fabrication of the CNT microbeads. Multiwalled CNT powders were directly mixed with m-cresol to yield a thick paste-like material. The paste droplets were rolled into round particles with in pure water with and without surfactant. The obtained particles were dried in a vacuum oven. The obtained microbeads have diameters ranging 300–2200 μm and apparent particle density of 350–400 kg/m3, which corresponds to Geldart group B in the fluidization classification. The micrograph of the CNT microbeads exhibited stacked nanotubes array on the surface, indicating obvious densification of the raw CNT powders. The microbeads prepared in water containing surfactant have better shape factor such as circularity and solidity. The thermal conductivity of the microbeads is about 1.18 W/mK in a bulk state, which is much higher than raw CNT powder (0.032 W/mK). The flowability and fluidization characteristics of the multiwalled CNT (MWCNT) microbeads showed a possibility as promising bed material suitable for the fluidized bed heat exchanger.

Electrochemical detection of calcium and magnesium in water bodies

The design, fabrication, and implementation of novel flexible sensors for electrochemical detection of multiple minerals such as calcium and magnesium in water bodies are presented in this paper. 3D printing technique was utilized to form the master moulds for developing the sensor prototype. The 3D printed moulds were developed initially using Poly Lactic Acid as the printing filament. Multi-Walled Carbon Nanotubes and Polydimethylsiloxane were used for forming the electrodes and substrates of the sensor patches, respectively. The casting of Multi-Walled Carbon Nanotubes powder and Polydimethylsiloxane were done on the 3D printed moulds. The electrodes were patterned in an interdigitated manner to operate on the impedimetric principle. The passive elements of the equivalent circuit of the interdigitated sensors were determined using Complex Non-Linear Least-Square Curve Fitting software. The total change in impedance concerning differently concentrated solutions was due to different resistive and reactive elements of the sensors. The resistance, reactance, and impedance values from the sensor patches were analysed during the experiment for calcium and magnesium solutions. Experimental outcomes proved that the sensor was able to differentiate various concentrations of calcium and magnesium ions between 1 ppm and 200 ppm solutions. The reproducibility, repeatability, and reusability of the sensors were also tested to propose the developed sensors as an alternative solution for the determination of calcium and magnesium ions from unknown samples.

Preparation and dispersion of multi-walled carbon nanotubes in Ti6Al4V metal matrix powders

Abstract This study investigated the preparation and dispersion of graphitized multi-walled carbon nanotubes (MWCNTs) into Ti6Al4V metal matrix powders. As-received MWCNTs powder was subjected to graphitization treatment for 5 h at 1800 °C in a vacuum atmosphere. 0, 1, 2 and 3 wt. % of the graphitized MWCNTs were dispersed by high energy ball milling (HEBM) into the Ti6Al4V matrices. The milled composite powders were thereafter characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques respectively. The results showed the optimized HEBM technique that was used for the MWCNTs dispersion achieved a relative homogeneous dispersion of the reinforcement powder into Ti6Al4V. There was minimal damage to the MWCNTs during the dispersion processing by milling, as interfacial reactions between defective MWCNTs and the metal matrix was effectively controlled

The electrochemical decoration of multi-walled carbon nanotubes with nickel oxide coating

In this paper, nickel coatings have been deposited on the multi-walled carbon nanotubes (MWCNT). In the first stage, MWCNT powder was ultra-wave mixed in the acid bath (H2SO4 and HNO3). The acid treating activates inert carbon surface introducing functional –OH and –COOH groups on the MWCNT surface. The mixture was diluted with distilled water and filtered for several times. The filtered sediment was dried in a plasma cleaner. The powder of such cleaned functionalized MWCNTs (fMWCNTs) was ultrasonicated with deionized water to produce stable colloid. Nickel atoms were injected into the colloid from a positive nickel electrode (with a negative graphite one). The Ni containing tubular nanostructures decorated the fMWCNTs at the specified regulated conditions (temperature, colloid concentration, electric current density). The electrochemically treated colloid was filtered and dried to a powder state (Ni-containing-fMWCNT powder). Hollow NiO nanotubes were produced by the annealing of the powder at 600°C (tubular nanostructured NiO powder). Both powders were examined by the Raman spectroscopy (RS), high-temperature X-ray diffraction (HTXRD), scanning electron microscopy (SEM), and thermal gravimetric analysis (TGA). The estimated high specific surface area of the nanostructured NiO powder is up to 97 m2/g at least and may be varied by time and the electric current of the electrochemical process.

Hydrogen Production and Subsequent Adsorption/Desorption Process within a Modified Unitized Regenerative Fuel Cell

For sustainable and incremental growth, mankind is adopting renewable sources of energy along with storage systems. Storing surplus renewable energy in the form of hydrogen is a viable solution to meet continuous energy demands. In this paper the concept of electrochemical hydrogen storage in a solid multi-walled carbon nanotube (MWCNT) electrode integrated in a modified unitized regenerative fuel cell (URFC) is investigated. The method of solid electrode fabrication from MWCNT powder and egg white as an organic binder is disclosed. The electrochemical testing of a modified URFC with an integrated MWCNT-based hydrogen storage electrode is performed and reported. Galvanostatic charging and discharging was carried out and results analyzed to ascertain the electrochemical hydrogen storage capacity of the fabricated electrode. The electrochemical hydrogen storage capacity of the porous MWCNT electrode is found to be 2.47 wt%, which is comparable with commercially available AB5-based hydrogen storage canisters. The obtained results prove the technical feasibility of a modified URFC with an integrated MWCNT-based hydrogen storage electrode, which is the first of its kind. This is surelya step forward towards building a sustainable energy economy.

Titanium dioxide protection against Al4C3 formation during fabrication of aluminum-TiO2 coated MWCNT composite

Aluminum and aluminum alloys have been very useful in the industry, mainly in the transport sector. So, is important to improve their mechanical properties to increase their applications. Carbon nanotubes (CNTs) could be an excellent reinforcing phase for metal matrix composites, specifically for composites with aluminum or aluminum alloy matrix. However, CNTs dispersion, wettability, and interaction with the matrix must be improved, without damaging their structure. In this work, multi-walled CNTs (MWCNTs) were coated by the sol-gel process with a titanium oxide (TiO2) layer with three different thickness and calcined at two different temperatures: 500 °C and 750 °C. The resultant powder was mixed by electrostatic adsorption method with aluminum powder and cold compacted. To simulate high temperature processing, the compacted disks were pressureless heated at 850 °C, aiming to check the effect of TiO2 in protecting the MWCNT when in contact with melted Al. The TiO2 coated MWCNT samples were characterized by a range of analytical techniques including Field-Emission Gun Scanning Electron Microscopy (FEG-SEM), X-ray diffraction (XRD), Z-Potential, Brunauer–Emmett–Teller (BET), Energy Dispersive X-Ray Spectroscopy (EDS) and Raman Spectroscopy (RS). The effect of the TiO2 layer as a protective barrier on the MWCNT against the Al4C3 formation during the heating process and the hardness of the Al/MWCNT (coated and uncoated) composite were studied. The results show that the MWCNT were successful coverage by a uniform amorphous TiO2 layer. After calcination at 500 °C and 750 °C, the layer was completely crystallized into a TiO2 film, with reduced surface area and pore volume. Electrostatic adsorption between TiO2 covered MWCNT and Al powders in aqueous suspension was found to disperse the reinforcing phase prior to consolidation. On the heat-treated discs, the formation of Al4C3 phase was observed to occur only for uncoated MWCNT samples, showing that the TiO2 layer effectively protected the nanotubes in presence of melted Al. The microhardness of the heated samples was increased up to 26% when reinforced with MWCNT and up to 46% when reinforced with TiO2 coated MWCNT, compared with pure aluminum.

The role of the attrition milling on the grain size and distribution of the carbon nanotubes in YSZ powders

The aim of present work was the examination of the role of the high efficient attrition milling on the structure and grain size of ZrO2 – 8mol.% Y2O3 (YSZ) and on the distribution of multiwall carbon nanotubes (MWCNTs) in these powder mixtures. The microstructure of YSZ/MWCNTs powder mixtures with 1, 5, 10wt.% MWCNTs was investigated. Detailed study confirmed the YSZ grain size decrease and simultaneously the non-destructive homogenization of MWCNTs in the ceramic powder mixtures. The best homogenization degree was achieved in the case of YSZ/1wt.% MWCNT powder. Raman scattering measurements were performed to investigate the atomic bonding and structural integrity of carbon nanotubes. The presence of the G and D bands in each samples at ∼1590 and ∼1355cm−1 confirmed the unaffected structural integrity of MWCNTs after the milling process. In addition to Raman measurements the high resolution transmission electron microscopy (HRTEM) studies have shown that the structure of MWCNTs remains intact after milling.

Assessment of nanofibre dustiness by means of vibro-fluidization

Dustiness testing probes for the propensity of a powdery material to release dust particles following agitation. For high aspect-ratio materials like nanotubes, the most important dust fraction is that of potentially carcinogenic fibres (WHO-fibres). We developed the fluidizer particularly for fibres that makes use of vibro-fluidization in order to effectively disentangle single fibres and agglomerates of multi-walled carbon nanotube powders. Counting rules for morphological characterization of collected particles by means of electron microscopy were established, allowing quantifying the WHO-fibre fraction. Dustiness tests on 15 different multi-walled carbon nanotubes were performed using two different levels of energy input for each material. The fluidizer accomplished bubbling fluidization for 13 out of the 15 multi-walled carbon nanotubes, resulting in continuous aerosol generation with stable particle number concentration and a high fraction of single fibres. Dustiness measurands like average particle number concentrations varied by three orders of magnitude. Morphological characterization of particles on aerosol samples proved to be essential to overcome the limitations of the applied aerosol instruments in quantifying the WHO-fibre fraction, therefore allowing material ranking based on associated risk. The materials showed strong ordering discrepancy when ranked based on total dustiness and WHO-fibre dustiness. Several multi-walled carbon nanotubes showed WHO-fibre concentrations high enough to potentially cause workplace exposure at hazardous concentration levels in case powders are handled carelessly.

Exposure assessment of carbon nanotubes at pilot factory focusing on quantitative determination of catalytic metals.

The application of multiwall carbon nanotubes (MWCNTs) currently extends to various fields. However, it has been reported that exposure to CNT causes hazardous effects on animals and cells. The purpose of this study was to quantify the exposure to MWCNT in MWCNT/polymer composites for exposure assessment. We focused on catalytic metals included in the MWCNT and the diameter of dust released during the working processes. Although the Co in MWCNTs is not a common catalyst, it was used as a tracer in this study. A field survey was conducted in a MWCNT/polymer composite pilot factory. Airborne MWCNTs were monitored using black carbon monitors (BCMs) and optical particle sizers (OPSs) and collected on a filter. The MWCNT powder, all polymer resins used during the working processes, and the filter were analyzed in our lab using inductively coupled plasma mass spectrometry (ICP-MS) and electron microscopic observation. The mean concentration of airborne MWCNT contained in the collected dust was 0.92 μg/m3 a few meters away from the extruder during the working processes (using elemental analysis). The maximum concentration measured using BCMs was shown to be seven times higher than the base concentration during the pelletizing process of polycarbonate (PC) and MWCNT composites. However, free, isolated, and unbound agglomerated MWCNTs were not detected using scanning electron microscopic (SEM) observation. The result obtained by elemental analysis indicated it was possible to quantify MWCNT in composites. The mean concentration at this factory was lower than the recommended exposure limit. However, additional studies during the pelletizing process are required in the future.

Modification of thin-film polyamide membrane with multi-walled carbon nanotubes by interfacial polymerization

Polyamide thin-film composite (TFC) was fabricated on polysulfone (PS-20) base by interfacial polymerization of aqueous m-phenylenediamine (MPD) solution and 1,3,5-benzenetricarbonyl trichloride (TMC) in hexane organic solution. Multi-wall carbon nanotubes (MWCNT) were carboxylated by heating MWCNT powder in a mixture of HNO3 and H2SO4 (1:3 v/v) at 70 °C under constant sonication for different periods. Polyamide nanocomposites were prepared by incorporating MWCNT and the carboxylated MWCNT (MWCNT–COOH) at different concentrations (0.001–0.009 wt%). The developed composites were analyzed by Fourier transform infrared spectroscopy-attenuated total reflection, scanning electron microscopy, transmission electron microscopy, contact angle measurement, determination of salt rejection and water permeate flux capabilities. The surface morphological studies displayed that the amalgamation of MWCNT considerably changed the surface properties of modified membranes. The surface hydrophilicity was increased as observed in the enhancement in water flux and pure water permeance, due to the presence of hydrophilic nanotubes. Salt rejection was obtained between 94 and 99% and varied water flux values for TFC-reference membrane, pristine-MWCNT in MPD, pristine-MWCNT in TMC and MWCNT–COOH in MPD were 20.5, 38, 40 and 43 L/m2h. The water flux and salt rejection performances revealed that the MWCNT–COOH membrane was superior membrane as compared to the other prepared membranes.

Two-electrode Sensor System for Rapid Detection of Sulfonamides by Applying the Nafion-Carboxyl Multiwalled Carbon Nanotubes Powder Microelectrode

Two-electrode Sensor System for Rapid Detection of Sulfonamides by Applying the Nafion-Carboxyl Multiwalled Carbon Nanotubes Powder Microelectrode

Freestanding Aligned Multi-walled Carbon Nanotubes for Supercapacitor Devices

We report on the synthesis and electrochemical properties of multi-walled carbon nanotubes (MWCNTs) for supercapacitor devices. Freestanding vertically-aligned MWCNTs and MWCNT powder were grown concomitantly in a one-step chemical vapour deposition process. Samples were characterized by scanning and transmission electron microscopies and Fourier transform infrared and Raman spectroscopies. At similar film thicknesses and surface areas, the freestanding MWCNT electrodes showed higher electrochemical capacitance and gravimetric specific energy and power than the randomly-packed nanoparticle-based electrodes. This suggests that more ordered electrode film architectures facilitate faster electron and ion transport during the charge–discharge processes. Energy storage and supply or supercapacitor devices made from these materials could bridge the gap between rechargeable batteries and conventional high-power electrostatic capacitors.

Mechanical properties, wear behavior and crystallographic texture of Al–multiwalled carbon nanotube composites developed by powder metallurgy route

Aluminum (Al)-based metal matrix composites reinforced with multiwalled carbon nanotubes were developed by powder metallurgy route. The Al and multiwalled carbon nanotubes powder mixtures were consolidated under a load of 565 MPa followed by sintering at 550℃ for 2 h in inert atmosphere. Al–1, 2, and 3 wt.% multiwalled carbon nanotube composites were developed. In the present study, the microstructure, mechanical properties, sliding wear behavior, and crystallographic texture of various Al–multiwalled carbon nanotube composites were investigated. The multiwalled carbon nanotubes produced by low-pressure chemical vapor deposition technique and the various sintered composites were characterized using scanning electron microscope, high-resolution transmission electron microscope, X-ray diffraction, differential scanning calorimetry and thermogravimetric analysis, Raman spectroscopy, and Fourier transform infrared spectroscopy. A significant improvement in relative density, Vickers microhardness, and wear resistance of the composites up to addition of 2 wt.% of multiwalled carbon nanotubes was observed. The deterioration in these properties beyond 2 wt.% of multiwalled carbon nanotubes was possibly due to the agglomeration of multiwalled carbon nanotubes in the Al matrix. The tensile strength of Al–multiwalled carbon nanotube composites continuously decreases with the addition of multiwalled carbon nanotubes. The decrease in tensile strength can be attributed to the detrimental effect of Al4C3 formed at the interface of the Al matrix and the multiwalled carbon nanotubes which will cause premature failure of the composite. The addition of multiwalled carbon nanotubes altered the crystallographic texture of the composites. The residual stresses in the various composites were found to be compressive in nature and also show improvement up to addition of 2 wt.% multiwalled carbon nanotubes in the Al matrix.

Occupational Exposure to Multi-Walled Carbon Nanotubes During Commercial Production Synthesis and Handling.

The world-wide production of carbon nanotubes (CNTs) has increased substantially in the last decade, leading to occupational exposures. There is a paucity of exposure data of workers involved in the commercial production of CNTs. The goals of this study were to assess personal exposure to multi-walled carbon nanotubes (MWCNTs) during the synthesis and handling of MWCNTs in a commercial production facility and to link these exposure levels to specific activities. Personal full-shift filter-based samples were collected, during commercial production and handling of MWCNTs, R&D activities, and office work. The concentrations of MWCNT were evaluated on the basis of EC concentrations. Associations were studied between observed MWCNT exposure levels and location and activities. SEM analyses showed MWCNTs, present as agglomerates ranging between 200 nm and 100 µm. Exposure levels of MWCNTs observed in the production area during the full scale synthesis of MWCNTs (N = 23) were comparable to levels observed during further handling of MWCNTs (N = 19): (GM (95% lower confidence limit-95% upper confidence limit)) 41 μg m(-3) (20-88) versus 43 μg m(-3) (22-86), respectively. In the R&D area (N = 11) and the office (N = 5), exposure levels of MWCNTs were significantly (P < 0.05) lower: 5 μg m(-3) (2-11) and 7 μg m(-3) (2-28), respectively. Bagging, maintenance of the reactor, and powder conditioning were associated with higher exposure levels in the production area, whereas increased exposure levels in the R&D area were related to handling of MWCNTs powder.