Number Of Multi-walled Carbon Nanotubes Research Articles

Multi-scale design of MWCNT/glass fiber/balsa wood composite multilayer stealth structure with wide broadband absorption and excellent mechanical properties

In unmanned aircraft applications, electromagnetic wave (EMW) absorbers suffer from defects in narrow absorption bands and poor mechanical properties. To solve the problems, a lightweight multilayer stealth structure with wide broadband absorption performance and excellent mechanical properties was designed and prepared by adjusting microscopically the number of multi-walled carbon nanotubes (MWCNT) and modulating macroscopically the thickness-matching relationship of the structure to promote the absorption of EMW synergistically. Under the MWCNT of 30 wt% and the depletion layer with the thickness of 0.2 mm, the effective absorption bandwidth (EAB) covers the entire Ku-band while maintaining a minimum reflection loss (RL) of −15 dB. Besides, the radar cross-sectional area attenuation is as high as 23.1 dBm2, as well as the mechanical properties of the radar absorbing structures (RAS) were improved significantly due to the reducing structural density from balsa wood and the enhancement effect of glass fiber mats (GFM). The study constructed balsa-based RAS with excellent EMW absorbing and mechanical properties from both micro-nano scale and macro-structure, providing a research route for designing high-performance and lightweight stealth structures.

Enhanced microwave absorbing performance of Ni-containing SiCN ceramics by constructing multiple interfaces and in-situ generating MWCNTs

Ni-containing SiCN ceramics as microwave absorbing materials were successfully synthesized by facile polymer derived ceramics (PDCs) route using nickel acetates tetrahydrate (Ni(Ac)2·4H2O) and polysilazane (PSZ) as raw materials and pyrolyzing at 1200 °C. After introducing Ni(Ac)2·4H2O, a large number of multi-walled carbon nanotubes (MWCNTs) were in-situ formed in Ni-containing SiCN ceramics. Besides, some crystalline phases, such as Si3N4, β-SiC, Ni2Si, Si2N2O and turbostratic carbon, were observed. The 3D conductive network constructed by the MWCNTs and multiple heterogeneous interfaces formed by various phases were generated in SiCN matrix, which enhanced the electromagnetic wave (EMW) absorbing performance of Ni-containing SiCN ceramics. The morphology and electromagnetic parameters of Ni-containing SiCN ceramics could be effectively regulated by changing the addition content of Ni(Ac)2·4H2O. The Ni-containing SiCN ceramics with the Ni(Ac)2·4H2O addition content of 15 wt% presented the best electromagnetic wave absorption property. Its minimum reflection loss (RLmin) reached −60.71 dB at 9.44 GHz with the thickness of 2.20 mm and effective absorption bandwidth (EAB) broadened to 4.36 GHz (13.64–18 GHz) at 1.38 mm. The excellent properties should be mainly attributed to the synergistic effects of good impendence matching, conduction loss and polarization relaxation loss.

An Investigation on the Effect of High Temperatures on the Mechanical Properties and Microstructure of Concrete Containing Multiwalled Carbon Nanotubes

Abstract In this article, the effect of multiwalled carbon nanotubes on the properties of concrete was evaluated in the postheat-treated condition. For this, a number of cylindrical specimens (10 by 20 cm), including multiwalled carbon nanotubes in different percentages of 0.5, 1, and 1.5 % by weight of cement, were cast. Then, the concrete specimens were exposed to temperatures of 25°C, 100°C, 250°C, 500°C, and 700°C in an electric furnace, and after they cooled down, compressive and tensile strength tests were carried out on them. The results show that by increasing the number of multiwalled carbon nanotubes in concrete, the compressive and tensile strengths of concrete increase up to 138 and 88 %, respectively. In addition, the dissipation of energy and modulus of elasticity of the concrete specimens were up to two times greater than those of the control specimens. The scanning electron microscope test results indicated that a strong bond between concrete particles exists at room temperature and above.

Investigation of multiwalled carbon nanotube interconnection geometry and electrical characteristics of an CNT-filled aluminum microgap

In recent years a very large amount of data has been collected regarding devices formed by multiwalled carbon nanotubes (MWCNTs) in polymer matrix as well as single nanotubes. Conversely, very little investigation exists of nanotube networks composed of a small number of MWCNTs. A detailed investigation of the long time stability, adhesion to the surface, and topological structure of the interconnections between MWCNTs is reported here. Three different microscopy techniques, focused ion beam (FIB), scanning electron microscope (SEM), and atomic force microscope (AFM), were used to investigate the interconnection of MWCNTs deposited by electrophoresis on a thermally oxidized silicon wafer with aluminum microgap structures. SEM, AFM, and FIB imaging revealed an interesting interconnection morphology between the drop casted MWCNTs. In particular it was found that in some cases the MWCNTs were connected to each other in a geometry similar to a twisted structure. Furthermore a good stability of the sample in time has been found, proving a strong adhesion of the nanotubes to the oxide surface. Despite the fact that electrical contacts with aluminum to carbon nanotube - based devices are in general not very reliable, using the dielectrophoresis deposition technique with an adequate subsequent annealing procedure, long-term stable temperature sensors with carbon nanotube networks in the aluminum contact microgap were realized. Their temperature dependence can be explained by modeling the internanotube contact resistance.

Origin of the enhanced visible-light photocatalytic activity of CNT modified g-C3N4 for H2 production

Graphitic carbon nitride (g-C3N4) hybridized with a small number of multi-walled carbon nanotubes (CNT) was synthesized using cyanamide as precursor. The optimal CNT content is found to be ∼0.2 wt% in the composite, which displays a 2.4-fold enhancement in photocatalytic water splitting over pure g-C3N4. Characterizations by a series of joint techniques including Raman spectra, UV/vis diffuse reflectance spectra, steady and time-resolved fluorescence emission spectra, and photocurrent responses were carried out, aiming to reveal the determinative factor for the improved visible-light response. Our results indicate that the increased photoactivity originates from the enhanced charge-transfer effect due to the intimate interactions between g-C3N4 and conjugated CNT. The presence of CNT in the hybrids is beneficial for improving electron-hole separation on the excited g-C3N4 by prolonging the lifetimes of charge carriers and improving the population distribution of short-lived and long-lived charge carriers.

Analysis of propagation delay and power with variation in driver size and number of shells in multi walled carbon nanotube interconnects

PurposeThe purpose of this paper is to analyze the effect of driver size and number of shells on propagation delay and power for multi‐walled carbon nanotubes (MWCNT) interconnects at 22 nm technology node.Design/methodology/approachAn equivalent circuit model of MWCNT is used for estimation and analysis of propagation delay and power. The delay and power through MWCNT and Cu interconnects are compared for various driver sizes and number of MWCNT shells.FindingsThe SPICE simulation results show that the MWCNT interconnect has lower propagation delay than Cu interconnects. The delay ratio of MWCNT to Cu decreases with increase in length for different driver size and number of MWCNT shells. However, the delay ratio increases with reduction in number of MWCNT shells. The ratio of average power consumption (MWCNT/Cu) also decreases with the variation in driver size and numbers of shells with respect to the length of interconnect. The theoretical study proves CNTs to be better alternatives against copper on the ground of performance parameters.Research limitations/implicationsSeveral challenges remain to be overcome in the areas of fabrication and process integration for CNTs. Lowering of metal nanotube contact resistance would be vital, especially for local interconnect and via applications. Moreover, rigorous characterization and modeling of electromagnetic interactions in CNT bundles; 3‐D (metal) to 1‐D (CNT) contact resistance; impact of defects on electrical and thermal properties; and high‐frequency effects are being seen as additional challenges.Originality/valueThis paper investigates, assesses and compares the performance of carbon nanotubes (CNT) based interconnects as prospective alternatives to copper wire interconnects in future VLSI chips. Multi walled CNTs assure for long/global interconnect applications.

Extrapulmonary transport of MWCNT following inhalation exposure

BackgroundInhalation exposure studies of mice were conducted to determine if multi-walled carbon nanotubes (MWCNT) distribute to the tracheobronchial lymphatics, parietal pleura, respiratory musculature and/or extrapulmonary organs. Male C57BL/6 J mice were exposed in a whole-body inhalation system to a 5 mg/m3 MWCNT aerosol for 5 hours/day for 12 days (4 times/week for 3 weeks, lung burden 28.1 ug/lung). At 1 day and 336 days after the 12 day exposure period, mice were anesthetized and lungs, lymph nodes and extrapulmonary tissues were preserved by whole body vascular perfusion of paraformaldehyde while the lungs were inflated with air. Separate, clean-air control groups were studied at 1 day and 336 days post-exposure. Sirius Red stained sections from lung, tracheobronchial lymph nodes, diaphragm, chest wall, heart, brain, kidney and liver were analyzed. Enhanced darkfield microscopy and morphometric methods were used to detect and count MWCNT in tissue sections. Counts in tissue sections were expressed as number of MWCNT per g of tissue and as a percentage of total lung burden (Mean ± S.E., N = 8 mice per group). MWCNT burden in tracheobronchial lymph nodes was determined separately based on the volume density in the lymph nodes relative to the volume density in the lungs. Field emission scanning electron microscopy (FESEM) was used to examine MWCNT structure in the various tissues.ResultsTracheobronchial lymph nodes were found to contain 1.08 and 7.34 percent of the lung burden at 1 day and 336 days post-exposure, respectively. Although agglomerates account for approximately 54% of lung burden, only singlet MWCNT were observed in the diaphragm, chest wall, liver, kidney, heart and brain. At one day post exposure, the average length of singlet MWCNT in liver and kidney, was comparable to that of singlet MWCNT in the lungs 8.2 ± 0.3 versus 7.5 ± 0.4 um, respectively. On average, there were 15,371 and 109,885 fibers per gram in liver, kidney, heart and brain at 1 day and 336 days post-exposure, respectively. The burden of singlet MWCNT in the lymph nodes, diaphragm, chest wall and extrapulmonary organs at 336 days post-exposure was significantly higher than at 1 day post-exposure.ConclusionsInhaled MWCNT, which deposit in the lungs, are transported to the parietal pleura, the respiratory musculature, liver, kidney, heart and brain in a singlet form and accumulate with time following exposure. The tracheobronchial lymph nodes contain high levels of MWCNT following exposure and further accumulate over nearly a year to levels that are a significant fraction of the lung burden 1 day post-exposure.

Incorporation of multi-walled carbon nanotubes into the oxide layer on a 7075 Al alloy coated by plasma electrolytic oxidation: Coating structure and corrosion properties

The influence of incorporating multi-walled carbon nanotubes (MWCNTs) on the coating structure and the corrosion response of a 7075 Al alloy coated by plasma electrolytic oxidation (PEO) was investigated. For this purpose, a series of PEO coatings were prepared on 7075 alloy specimens in a silicate electrolyte with MWCNTs, and the results were compared to those without MWCNTs. Microstructure observations revealed that when MWCNTs were added to the electrolyte, the pore size and fraction of the oxide layer coated in the electrolyte incorporating MWCNTs were respectively smaller. Since the number of MWCNTs having negative potential within the present electrolyte moved into the oxide layer, which acts as an anode, some micro pores were filled effectively with MWCNTs, resulting in a denser coating layer. From the results of the electrochemical tests, the corrosion resistance of the present sample obtained by PEO coating in the electrolyte with MWCNTs was significantly improved. The electrochemical mechanism underlying the high corrosion resistance of the present sample was discussed based on the equivalent circuit model.

Growth of Carbon Nanotubes in Calcium Phosphate Matrix with Different Ca/P Molar Ratio

This paper reports that carbon nanotubes (CNTs) can be successfully grown from calcium phosphate matrix without additional catalysis of transition metal by chemical vapor deposition (CVD) using acetylene as carbon source. There is a great difference in the CNT growth from the matrix prepared with the different initial Ca/P molar ratio. The matrix prepared with lower initial Ca/P molar ratio is favorable for the growth of CNTs. A number of multi-walled CNTs with the diameter of 25~40 nm and 15~25 nm can be produced from the matrix with initial Ca/P molar ratio of 1.5 and 1.625, respectively, while no CNTs can be grown from the matrix with initial Ca/P molar ratio of 1.67. Tricalcium phosphate and hydroxyapatite crystallites with crystal size smaller than 50 nm besides carbon crystals are found in the as-obtained powders prepared with initial Ca/P molar ratio of 1.5 and 1.625. Compared with the growth of CNTs produced from all the matrixes, it is found that the CNTs grown from this matrix with Ca/P molar ratio of 1.5 have the longest tube length, cleanest and smoothest wall surface, and the content of CNTs is highest.

Controlled Dielectrophoretic Assembly of Multiwalled Carbon Nanotubes

The authors report on a real-time control method for assembly of a single or small number of multiwalled carbon nanotubes (MWNTs) onto microelectrodes by dielectrophoresis (DEP). On the basis of an impedance model and a real-time gap impedance monitoring method to evaluate and identify the number of MWNTs spanning an electrode gap, it has been demonstrated that a real-time gap impedance signal can be used to control the DEP process of MWNTs. The goal is controlled assembly with a connecting resistance of less than a defined limit or with a defined number of MWNT connections. With a control strategy designed for the DEP assembly of a small number of MWNTs, predefined numbers of connections from 1−3 have been achieved across an electrode gap.

Real-time gap impedance monitoring of dielectrophoretic assembly of multiwalled carbon nanotubes

We report on a real-time monitoring method for the assembly of a small number of multiwalled carbon nanotubes (MWNTs) by dielectrophoresis (DEP). A time-varying impedance model was developed to estimate the number of MWNTs which span an electrode gap indicated by the instantaneous decrease of gap impedance during DEP. Sudden decreases in gap impedance signals corresponding to tube deposition were measured. The impedance values agreed with the impedance model. Experiments confirmed that DEP assembly and measurement of gap impedance changes due to tube deposition can be accomplished with a single instrument, also providing a feedback signal for DEP process control.

Monitoring Multiwalled Carbon Nanotube Exposure in Carbon Nanotube Research Facility

With the increased production and widespread use of multiwalled carbon nanotubes (MWCNTs), human and environmental exposure to MWCNTs is inevitably increasing. Therefore, this study monitored the possible exposure to MWCNT release in a carbon nanotube research laboratory. To estimate the potential exposure of researchers and evaluate the improvement of the workplace environment after the implementation of protective control measures, personal and area monitoring were conducted in an MWCNT research facility where the researchers handled unrefined materials. The number, composition, and aspect ratio of MWCNTs were measured using scanning transmission electron microscopy with an energy-dispersive x-ray analyzer. The gravimetric concentrations of total dust before any control measures ranged from 0.21 to 0.43 mg/m3, then decreased to a nondetectable level after implementing the control measures. The number of MWCNTs in the samples obtained from the MWCNT blending laboratory ranged from 172.9 to 193.6 MWCNTs/cc before the control measures, and decreased to 0.018–0.05 MWCNTs/cc after the protective improvements. The real-time monitoring of aerosol particles provided a signature of the MWCNTs released from the blending equipment in laboratory C. In particular, the number size response of an aerodynamic particle sizer with a relatively high concentration in the range of 2 to 3 μ m in aerodynamic diameter revealed the evidence of MWCNT exposure. The black carbon mass concentration also increased significantly during the MWCNT release process. Therefore, the present study suggests that the conventional industrial hygiene measures can significantly reduce exposure to airborne MWCNTs and other particulate materials in a nano research facility.

Nanoelectromechanical switches with vertically aligned carbon nanotubes

Electromechanical switching devices have been fabricated successfully employing vertically grown multiwalled carbon nanotubes (MWCNTs) from the prepatterned catalyst dots on the patterned device electrodes. The devices show various interesting switching characteristics depending on the length and the number of MWCNTs used. The device design not only simplifies the fabrication process, but also improves the integration density greatly. The device has a great potential in realizing technically viable nanoelectromechanical systems, such as switch, memory, fingers, or grippers.