Carbon nanotubes (CNTs) were first officially named in 1991. Scientific-grade carbon nanotubes are seamless nanotube crystals formed by curling graphite layers. According to the number of graphite layers, they can be divided into single-walled tubes, double-walled tubes and multi-walled tubes. Due to the different "curling" angles of graphite, carbon nanotubes can form chair-shaped, Z-shaped or chiral structures.
Scientific-grade carbon nanotubes have unique physical and chemical properties. For example, in terms of conductivity, carbon nanotubes can be metallic or semiconducting. Even different parts of the same carbon nanotube will show different conductivity due to different structures. Moreover, the conductivity of carbon nanotubes is closely related to their diameter and chirality. Carbon nanotubes are considered to be a 7-dimensional conductor. Studies have shown that the current carrying capacity of carbon nanotubes is one thousand times that of copper wires. Another example is that carbon nanotubes have excellent mechanical properties. Although its specific gravity is 1/6 of that of steel, its strength is 100 times that of steel. Because carbon nanotubes have extremely high strength, they are considered to be the ultimate form of fiber and reinforcement phase with a high strength-to-weight ratio. Due to its special structure, it also has good flexibility, resilience and anti-distortion ability.
In addition, scientific research-grade carbon nanotubes have many properties such as good chemical stability, high thermal stability, good axial thermal conductivity, low-temperature superconductivity, electromagnetic wave absorption characteristics and good adsorption. The results of applied research show that based on the excellent electrical and mechanical properties of carbon nanotubes, carbon nanotubes can be widely used in high-tech fields such as energy, materials, and life sciences. For example, it can be used as a new type of reinforcement material, electronic components, stealth materials, new hydrogen storage materials, catalyst carriers and electrode materials, etc., among which it has potential in the application of electronics and composite materials. The advantage of using carbon nanotubes to prepare composite materials is that they are easy to process and shape, and because carbon nanotubes have a low density and a high aspect ratio, their volume content can be reduced a lot compared with spherical fillers.
Carbon nanotubes are another variant of elemental carbon besides graphite, diamond, amorphous carbon and fullerene. Here, carbon atoms are arranged in a hexagonal shape. This structure is equivalent to a rolled-up monoatomic or polyatomic graphite layer, so that a hollow cylinder with a diameter of usually a few nanometers and a length of a few millimeters at most is formed. In principle, a distinction is made between multi-walled carbon nanotubes and single-walled carbon nanotubes, which are also usually abbreviated to MWNTs and SWNTs in the literature (from English: multi walled nanotubes and single walled nanotubes). Due to van der Waals forces, carbon nanotubes show a strong tendency to aggregate into bundles, so they must be untied/dispersed by high shear forces during the extrusion process without causing them to be severely shortened.
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