The objective of this study is to investigate hydrogen storage capability of heat welded random carbon nanotube (CNT) network structures. To achieve this objective, different three-dimensional random ...CNT network structures are generated by using a stochastic algorithm and molecular dynamic simulations. The interaction of CNT networks with hydrogen molecules is then examined via grand canonical Monte Carlo calculations. Hydrogen adsorption capacity of CNT networks having an arbitrarily natured morphology, adjustable porous structure and large surface ratio is investigated. The results show that if cross link density of random CNT networks decreases, hydrogen storage capability of CNT networks increases in terms of the gravimetric capacity. It is observed that random CNT networks could uptake 8.85 wt.% hydrogen at 77 K and this result is very comparable with the results reported in literature where generally ideal ordered nanostructures having no topological irregularities are considered.
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•Random CNT network structures are generated using a stochastic algorithm.•Molecular dynamics method is employed to simulate heat welding.•Interaction of CNT networks with hydrogen is examined via GCMC calculations.•Effects of cross-link density on hydrogen storage properties are investigated.
In this study, we examined the effect of increasing the diameter of the CFRP strand on the structural performance of the end fixing structure with the aim of further expanding the application of the ...end fixing structure in the CFRP strand (6φ). For verification, the end fixing structure of CFRP strand (9φ) was formed, and a pull-out test and cross-sectional observation by X-ray CT were performed. As a result, 9φ and 6φ showed the same structural performance by increasing the shortest distance from the through hole of the CFRP socket to the outermost end of the socket.
Carbon nanotubes (CNTs) have excellent electrical properties. However, it is challenging to demonstrate these properties in actual electrochemical measurements fully. Previous research has improved ...the electrical properties of CNTs through welding experiments. But the mechanism of the conductivity enhancement is still unclear. The welding process lacks adequate mechanistic studies and theoretical models. This article presents a theoretical model of a CNT circuit with staggered electrodes, which considers the effect of twist angle on a CNT bundle. A welding model of the CNT bundle circuit is also developed based on the structural changes of CNTs after welding and characterized by the resistance ratio of the CNT circuit pre- and post-welding. The welding model is analyzed to explore how the quantity, diameter, and length of CNTs in the bundle affect the welding effect. An electrical measurement system for CNTs was established to validate the welding model using a nanomanipulation system compatible with a scanning electron microscope. Then, a constant voltage and long-duration electric welding experiment was performed, which showed that the conductivity was enhanced about 1.5–4 times after welding. The results also demonstrated that longer and fewer CNTs in the bundle could improve the electrical conductivity by the welding process more significantly. These findings were consistent with the trend of the welding model. This article establishes a welding theoretical model of the CNT bundle with staggered electrodes, which effectively accounts for the electrical conductivity enhancement during CNT welding and will help more fully express excellent performance in carbon-based nanoelectronic devices, nanoelectromechanical systems, and electrocatalysts in its manufacturing stage.
In this study, we proposed a method to determine the frictional resistance by pushing the CFRTP socket at a temperature above Tg and changing its shape without heating it to the melting temperature. ...Since the surface of the strand and socket were heated to a temperature above Tg, it was confirmed that they were bonded, and the initial behavior was adhesive resistance. However, pull-out tests and observations using CT and digital microscope have confirmed that the frictional resistance after yielding does not cause brittle fracture.
In this study, we examined the effect of increasing the diameter of the CFRP strand on the structural performance of the end fixing structure with the aim of further expanding the application of the ...end fixing structure in the CFRP strand (6φ). For verification, the end fixing structure of CFRP strand (9φ) was formed, and a pull-out test and cross-sectional observation by X-ray CT were performed. As a result, 9φ and 6φ showed the same structural performance by increasing the shortest distance from the through hole of the CFRP socket to the outermost end of the socket.
The thermoelectromotive force due to the Seebeck effect is governed by the Seebeck coefficient of the thermoelectric circuit and the temperature gradient in the circuit. Thus for enhancing the ...thermoelectromotive force, not only selecting the materials but also inducing a large temperature gradient in a small space is very important in order to realize an efficient space-saving thermoelectric device. This paper describes a method by which the thermoelectric circuits can be fabricated by joining metallic microwires with Joule heat. Minor metal-free, Fe and Al microwires with diameters of 100 μm and various lengths were used in the circuits, and the effect of the wire length on the thermoelectromotive force developed in the circuit was investigated. We observed the Seebeck effect in the circuit by controlling the temperature gradient in the circuit. It was found that the temperature at each end of the microwire depended on the temperature at the high temperature end and the wire length. We describe this phenomenon with a heat conduction model and analyze the dependency of the temperature gradient on the wire length. Finally, we were able to estimate the suitable length of the microwires for getting the largest thermoelectromotive force in the smallest possible space.
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•Thermoelectric circuits were created by joining metallic microwires with Joule heat.•Bi-metal junctions were heated locally using a heater wire with a current supply.•A technique to measure the Seebeck coefficient of the circuit is described.•A method to determine the suitable wire length for a small device is described.
In this study, we proposed a method to determine the frictional resistance by pushing the CFRTP socket at a temperature above Tg and changing its shape without heating it to the melting temperature. ...Since the surface of the strand and socket were heated to a temperature above Tg, it was confirmed that they were bonded, and the initial behavior was adhesive resistance. However, pull-out tests and observations using CT and digital microscope have confirmed that the frictional resistance after yielding does not cause brittle fracture.
•3D carbon nanotube networks with controlled cross-linked density are generated.•Molecular dynamics method is employed to simulate heat welding and tensile simulations.•Constitutive behaviors of the ...networks are computed.•Effects of cross-link density on numerical results are investigated.
In this study, a computational investigation on the mechanical properties of random carbon nanotube (CNT) networks is reported. For this purpose, atomistic models of 3-D CNT network structures are generated by an automated stochastic algorithm that is capable of randomly inserting CNTs into a design space while controlling several topological parameters including cross-link density, distance between cross-links, as well as length and chirality of CNTs. During the atomistic model generation process, heat welding is applied to the close contacts to form a welded CNT network with covalently-bonded junctions. Following the generation of atomistic models, molecular dynamics (MD) simulations of uniaxial tensile loading experiments are performed to investigate the basic deformation mechanisms of CNT networks as well as to obtain mechanical properties such as the Young’s modulus, yield strength and ultimate strain values. The effects of cross-link density on the mechanical performance of CNT network materials are obtained by employing network specimens with different cross-link densities.
Effect of REM (Ce, La, Nd) addition on the austenite grain refinement of heat affected zone in Fe-0.07/C-0.05/Si-1.5/Mn-0.003/S (mass%) steel has been investigated by microstructural observation of ...SEM/EDS and thermodynamic analysis. It is observed that the 30 ppm of REM addition is most effective for reducing the austenite grain size annealed at 1450 °C for 10 sec, but the grain size increases with increasing REM contents more than 30 ppm. Since the total numbers of precipitates of oxide, sulfide and oxysulfide increase with increasing REM contents, the austenite grain growth can not be explained by Zener’s pinning model. Thermodynamic calculation shows that REM-oxide and MnS in oxysulfides are formed by the miscibility gap in the 30 ppm REM steel, which results in the formation of the liquid MnS-rich precipitates due to eutectic reaction. On the other hand, the melting temperature of MnS-rich precipitates increases with increasing REM amount in oxysulfide, which is not effective for inhibiting grain growth. It is suggested that the austenite grain growth is suppressed by liquid phase pinning effect of MnS-rich precipitates.
Effect of REM (Ce, La, Nd) addition on the austenite grain refinement of heat affected zone in Fe-0.07/C-0.05/Si-1.5/Mn-0.003/S (mass%) steel has been investigated by microstructural observation of ...SEM/EDS and thermodynamic analysis. It is observed that the 30 ppm of REM addition is most effective for reducing the austenite grain size annealed at 1450 °C for 10 sec, but the grain size increases with increasing REM contents more than 30 ppm. Since the total numbers of precipitates of oxide, sulfide and oxysulfide increase with increasing REM contents, the austenite grain growth can not be explained by Zener’s pinning model. Thermodynamic calculation shows that REM-oxide and MnS in oxysulfides are formed by the miscibility gap in the 30 ppm REM steel, which results in the formation of the liquid MnS-rich precipitates due to eutectic reaction. On the other hand, the melting temperature of MnS-rich precipitates increases with increasing REM amount in oxysulfide, which is not effective for inhibiting grain growth. It is suggested that the austenite grain growth is suppressed by liquid phase pinning effect of MnS-rich precipitates.
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