Ultrathin Tubes Research Articles

Alignment Controlled Aramid Nanofiber‐Assembled Films

AbstractAramid nanofibers (ANFs) are a strong and heat‐resistant nanomaterial that can be isolated from commercial para‐aramid fibers, which allow a bottom‐up self‐assembly to form ordered macroscale structures like ANF films. However, the anisotropic nature of high aspect ratio ANFs is not fully exploited when fabricating ANF films for the optimal mechanical properties. In this research, direct ink writing (DIW) is applied to produce ANF‐assembled films with arbitrary shapes, and the shear‐induced alignment of ANFs can follow the printing path direction. Therefore, controlled alignment of ANFs following the computer‐programmed printing pattern is achieved by DIW, which provides a path for the application of topology and nanofiber alignment optimization in nanofiber‐assembled films. In addition, the resulting DIW ANF films exhibit outstanding Young's modulus of 8.39 GPa, tensile strength of 198 MPa, and tensile toughness of 19.4 MJ m−3 in the alignment direction, together with a wide working temperature range up to 440 °C without losing 50% of its room temperature storage modulus. Moreover, the demonstrated self‐joining ability, rollability, and lamination processability of the DIW ANF films expand their potential applications toward high‐temperature ultrathin tubes, substrates for flexible printed circuit boards, and three‐dimensional all‐ANF lightweight structural parts in extreme environments.

Analysis of the properties and microstructure of ultra-thin tube

In order to satisfy the requirement of the engine heat exchangers, ultra-thin tubes with higher dimensional accuracy and better performance are required. Inconel 718, as the basic material of ultra-thin tube, is one of the materials that can meet the requirements of the engine heat exchanger. In this study, ultra-thin tubes with diameters and thicknesses of 1.50mm and 0.050mm were prepared by floating plug drawing process. The results showed that the yield strength increased and the corresponding elongation decreased with the increase of drawing passes. The wall thickness of the ultra-thin tube can be controlled by floating plug drawing. And the inner surface quality was greatly improved compared with the initial tube. The inner surface roughness can be controlled below 1.7μm. The average grain size after drawing can be reduced from 4.9μm to 2.1μm.

Natural torsion in chiral single-wall carbon nanotubes

Optimizations performed with two geometrical, molecular mechanical and density functional models show that the configuration of single-wall carbon nanotubes is slightly twisted with respect to that predicted by conventional techniques. Geometrical models are used to explain the effect by breaking of local symmetry of the equally distant neighbors in graphene in the course of rolling, which is minimized by torsion. The torsion angle is small, and decreases with nanotube diameter, being less than 1° Å−1 for ultrathin tubes. Therefore this effect can be hard to observe in experiments. Still, we single out features in diffraction patterns which can distinguish between twisted and non-twisted configurations. In addition, torsion makes a blue shift in the radial breathing mode, which for thin tubes can be seen by Raman measurement. The effect is slightly strengthened at room temperature.

Symmetry of chiral nanotubes: Natural torsion and diffraction evidence

AbstractOptimizations performed with geometrical, molecular mechanics, and density functional models show that chiral carbon nanotube configuration is slightly twisted with respect to the rolled‐up geometry. The torsion angle is small, <1° Å−1 for ultrathin tubes, and decreases with tube diameter. The effect can be explained through breaking of local symmetry of the equally distant neighbors in graphene, which is diminished by the torsion. Although, the twist is small, still, we single out features in diffraction patterns which can distinguish between twisted and non‐twisted configurations, at least for narrow single‐walled carbon nanotubes.

New Developments of Hydroforming in China

This paper reviews the recent developments of hydroforming technology in China. Limited corner radius, ring hoop tension test and tube bulging test were introduced on fundamentals of hydroforming. New hydroforming and hydro-bending process of ultra-thin tubes were investigated. Ultra-thin Y-shaped parts and complex section components were manufactured and applied in aerospace and aviation industry. Applications of tube hydroforming in automotive industry in China are also presented, including the hydroforming machines and production lines, typical automotive parts and potential market. New sheet hydroforming process with controllable radial pressure was proposed to increase the formability of sheets metals. Warm tube and sheet hydroforming were analyzed and discussed. [doi:10.2320/matertrans.MF201122]

Synthesis of nanotubes via catalytic pyrolysis of acetylene: A SEM study

Pyrolysis of acetylene over quartz plates coated with various metal catalysts resulted in the formation of all-carbon nanostructures which were observed directly by scanning electron microscopy (SEM). The nanotubes were studied in detail using transmission electron microscopy (TEM), and appear to grow as ultra-thin tubes with a central hollow core and considerable thickening due to secondary pyrolytic deposition. In nearly all samples the nanotube diameter was uniform. In some cases catalytic particles were entrapped within the tubes. The efficiency of the catalysts was evaluated semi-quantitatively.

The production and structure of pyrolytic carbon nanotubes (PCNTs)

The structures of pyrolytic carbon nanotubes (PCNTs), produced by thermal decomposition of hydrocarbon vapor (benzene at ca 1100°C) have been studied. Electron microscope images of the PCNTs “as-formed” and after various degrees of subsequent heat treatment are presented and discussed on the basis of elongated giant fullerene structures and a possible primary growth mechanism. The images indicate that some PCNTs show evidence of thickening due to secondary pyrolytic deposition whereas others appear to be essentially exposed nanotubes (without further carbon deposition) or have sections with negligible secondary deposition. The nanotubes appear initially to grow as ultra-thin tubes with a central hollow core (diameters ca2 nm or more). No catalytic particles are observed at the tips of the tubes shown by high resolution transmission electron microscope (HRTEM) studies to be composed of concentric graphite cylinders with consecutive radii increasing by a factor close to that of the standard graphite interlayer spacing. The further pyrolytic carbon thickening occurs at roughly the same time as longitudinal nanotube growth. This phenomenon can cause the diameters of the tubes to increase to micron sizes. Heat treatment of the “as-formed” PCNTs results in encapsulation of the hollow cores by polyhedral hemispherical fullerene-like caps. Single or multi-layered nodes are also generated, yielding “bamboo-like” structures. The PCNTs are similar to those obtained by d.c. arc techniques using graphite electrodes.