Various Amounts Of Multi-walled Carbon Nanotubes Research Articles

Characterization of airborne dust emissions from three types of crushed multi-walled carbon nanotube-enhanced concretes

Dispersing Multi-Walled Carbon Nanotubes (MWCNTs) into concrete at low (<1 wt% in cement) concentrations may improve concrete performance and properties and provide enhanced functionalities. When MWCNT-enhanced concrete is fragmented during remodelling or demolition, the stiff, fibrous and carcinogenic MWCNTs will, however, also be part of the respirable particulate matter released in the process. Consequently, systematic aerosolizing of crushed MWCNT-enhanced concretes in a controlled environment and measuring the properties of this aerosol can give valuable insights into the characteristics of the emissions such as concentrations, size range and morphology. These properties impact to which extent the emissions can be inhaled as well as where they are expected to deposit in the lung, which is critical to assess whether these materials might constitute a future health risk for construction and demolition workers. In this work, the impact from MWCNTs on aerosol characteristics was assessed for samples of three concrete types with various amounts of MWCNT, using a novel methodology based on the continuous drop method. MWCNT-enhanced concretes were crushed, aerosolized and the emitted particles were characterized with online and offline techniques. For light-weight porous concrete, the addition of MWCNT significantly reduced the respirable mass fraction (RESP) and particle number concentrations (PNC) across all size ranges (7 nm – 20 μm), indicating that MWCNTs dampened the fragmentation process by possibly reinforcing the microstructure of brittle concrete. For normal concrete, the opposite could be seen, where MWCNTs resulted in drastic increases in RESP and PNC, suggesting that the MWCNTs may be acting as defects in the concrete matrix, thus enhancing the fragmentation process. For the high strength concrete, the fragmentation decreased at the lowest MWCNT concentration, but increased again for the highest MWCNT concentration. All tested concrete types emitted <100 nm particles, regardless of CNT content. SEM imaging displayed CNTs protruding from concrete fragments, but no free fibres were detected.

Improving the lithium-ion diffusion and electrical conductivity of LiFePO4 cathode material by doping magnesium and multi-walled carbon nanotubes

This paper reports a co-modification approach to improve both electronic conductivity and lithium-ion diffusion of lithium iron phosphate (LiFePO4) via doping magnesium (Mg2+) and multi-walled carbon nanotubes (MWCNTs). A series of LiFe1−xMgxPO4 composites consisting of various amounts of MWCNTs were synthesized by using a facile hydrothermal method which involves an in-situ MWCNTs embedding process. The structure and morphology of prepared composites were investigated by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical performance was tested via cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge tests. All composites exhibit good crystallinity without any impurity phases. Besides, a slight shrinkage in the crystal lattice was observed after Mg2+ doping. Mg2+ is uniformly dispersed in the composites in which the formation of a three-dimensional conductive network enhances electronic conductivity and lithium-ion diffusion especially at high current densities. Among LiFe1−xMgxPO4/yMWNT composites, LiFe0.98Mg0.02PO4 with 1.5 wt% MWCNTs displays the highest electrochemical performance, offering a discharge capacity of 142 mA h g−1 at 0.1 C and exhibiting a good rate capability with a capacity of 120 mA h g−1 at a high rate of 2 C and a stable long cycle life (94.5 % capacity retention over 150 cycles). The co-modified composite cathode displays high discharge capacity, good rate capability, and excellent cycling stability compared to pure LiFePO4, rendering the co-modification approach a promising strategy for the preparation of high-performance electrode materials.

Thermal‐Insulation, Electrical, and Mechanical Properties of Highly‐Expanded PMMA/MWCNT Nanocomposite Foams Fabricated by Supercritical CO2 Foaming

AbstractFoaming behavior of poly(methyl methacrylate) (PMMA)/multi‐walled carbon nanotubes (MWCNTs) nanocomposites and thermally‐insulating, electrical, and mechanical properties of the nanocomposite foams are investigated. PMMA/MWCNT nanocomposites containing various amounts of MWCNTs are first prepared by combining solution and melt blending methods, and then foamed using CO2. The foaming temperature and MWCNT content are varied for regulating the structure of PMMA/MWCNT nanocomposite foams. The electrical conductivity measurement results show that MWCNTs have little effect on the electrical conductivity of foams with large expansion ratio. Thermal conductivities of both solid and foamed PMMA/MWCNT nanocomposites are measured to evaluate their thermally insulating properties. The gas conduction, solid conduction, and thermal radiation of the foams are calculated for clarifying the effects of cellular structure and MWCNT content on thermal insulation properties. The result demonstrates that MWCNTs endowed foams with enhanced thermal insulation performance by blocking thermal radiation. Moreover, the compressive testing shows that MWCNTs improve the compressive strength and rigidity of foams. This research is essential for optimizing environmentally friendly thermal insulation nanocomposite foams with enhanced thermal‐insulation and compressive mechanical properties.

Mechanical Properties and Durability of Ultra High Strength Concrete Incorporating Multi-Walled Carbon Nanotubes.

In this work, the effect of the addition of multi-walled carbon nanotubes (MWCNTs) on the mechanical properties and durability of ultra high strength concrete (UHSC) is reported. First, the MWCNTs were dispersed by a nano sand-mill in the presence of a surfactant in water. The UHSC specimens were prepared with various amounts of MWCNTs, ranging from 0% to 0.15% by weight of cement (bwoc). Results indicated that use of an optimal percentage of MWCNTs (0.05% bwoc) caused a 4.63% increase in compressive strength and a 24.0% decrease in chloride diffusion coefficient of UHSC at 28 days curing. Moreover, the addition of MWCNTs also improved the flexural strength and deformation ability. Furthermore, a field-emission scanning electron microscopy (FE-SEM) was used to observe the dispersion of MWCNTs in the cement matrix and morphology of the hardened cement paste containing MWCNTs. FE-SEM observation revealed that MWCNTs were well dispersed in the matrix and no agglomerate was found and the reinforcing effect of MWCNTs on UHSC was thought to be pulling out and microcrack bridging of MWCNTs, which transferred the load in tension.

Preparation and properties of ethylene propylene diene rubber/multi walled carbon nanotube composites for strain sensitive materials

Conducting rubber composites of ethylene propylene diene M-class rubber (EPDM) were prepared with multi walled carbon nanotubes (MWCNTs) and organo-clay, Cloisite® 15A to develop flexible strain sensitive materials. The composites were prepared with a constant amount of organo-clay and various amounts of MWCNTs from 5 to 50 wt.%. Organo-clay led to improved dispersion of MWCNTs in the rubber matrix. Upon increasing the MWCNT contents, the tensile strength, stiffness and electrical conductivity of the composites increased significantly but the elongation at break decreased in the EPDM/MWCNT composites. The organo-clay was able to improve tensile strength, stiffness, elongation at break and electrical conductivity of the composites. The non-symmetric linear resistance change was observed by the composites under deformation.

A membrane actuator based on an ionic polymer network and carbon nanotubes: thesynergy of ionic transport and mechanical properties

There is a growing interest in the development of ionic polymer–metal composites(IPMC) as sensors and actuators for biomedical applications due to their largedeformation under low driving voltage. In this study, we employed poly(vinylalcohol)/poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PVA/PAMPS)blend membranes as semi-interpenetrating polymer networks for ion exchange inIPMC construction. To improve the mechanical and electrical properties of theIPMC, multi-walled carbon nanotubes (MWNT) were added into PVA/PAMPSmembranes. The actuator performance of the membranes was measured as a function oftheir water uptake, ion exchange capacity, ionic conductivity and the amount ofMWNT in the membrane. The dispersion quality of the modified MWNT in thePVA/PAMPS membrane was measured using transmission electron microscopy. Thecantilever-type IPMC actuator bends under applied voltage and its bending angle andthe generative tip force were measured. Under an applied voltage, IPMC with∼1 wt% MWNT showed the largest deflection and generated the largest blocking tip forcecompared with those of IPMC with other various amounts of MWNT. These results showthat a small addition of MWNT can optimize the actuation performance of IPMC. Theresult indicates that IPMC with MWNT shows potential for use as biomimetic artificialmuscle.

The Study on the Microstructures and High Performances of Melt Blending Polyurethane/Multiwalled Carbon Nanotubes Composites

A melt blending process was employed to prepare nanocomposites based on thermoplastic polyurethane (TPU) and multiwalled carbon nanotubes (MWNT). The content of MWNT filled in TPU was increased till 40 phr (parts per hundreds of rubber). The morphological, structural and mechanical properties of the resulting TPU nanocomposites were systematically investigated using scanning electron microscope (SEM), transmission electron microscope (TEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD), dynamic mechanical thermal analysis (DMTA) and tensile testing. The results indicated that the unmodified MWNT were dispersed finely and uniformly in the TPU matrix beyond expectation, and the microphase separation structures of the TPU nanocomposites were slightly affected by the presence of MWNT. The mechanical properties of the TPU nanocomposites containing various amounts of MWNT at both room temperature and 120 °C were studied, which demonstrated that the modulus of TPU were greatly increased and the high temperature tensile strength of TPU was also prominently improved when MWNT content is higher. Moreover, the TPU nanocomposites exhibited improved thermal and electrical conductivities that might mean the TPU/MWNT nanocomposites have potential application as multifunctional materials.

In situ synthesized composite thin films of MWCNTs/PMMA doped with KOH as a resistive humidity sensor

In situ synthesized multi-walled carbon nanotubes (MWCNTs), methyl methacrylate (MMA) and KOH composite thin films on an alumina substrate were used to fabricate resistive humidity sensors. The thin films were analyzed by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and Fourier transform infrared spectroscopy (FT-IR). The electrical characteristics of PMMA to which various amounts of MWCNTs were added were measured in detail as a function of relative humidity (RH), to elucidate the contribution of MWCNTs to the humidity-sensing capacity. The humidity-sensing mechanism of the MWCNTs/PMMA composite thin films with various amounts of MWCNTs were explained by considering the composition and microstructures. The charge-transportation by the ions formed by electrolytic dissociation, their interactions with polymers, and the dimensions of the channels through which ions migrated were used to explain the sensing mechanism of the composite thin films of MWCNTs/PMMA doped with KOH. Other sensing characteristics, including linearity, sensitivity, response and recovery time, hysteresis and stability, were also investigated.