What are Carbon Nanotubes Essay - 543 Words

Carbon nanotubes are long cylindrical structures of small nano-scale diameters formed only by carbon atoms. These structures can be understood as rolled sheets of graphene into a tube. The interactions between carbon atoms are mostly deï ¬ ned as Van der Waals forces. If we categorize CNTs by their structure, the following division can be obtained: - single-walled nanotubes (SWNTs) - multi-walled nanotubes (MWNTs) The above structures differ in the arrangement of graphene cylindrical structures . SWNTs have only one single layer of graphene tubes, whereas MWNTs have many. There are three geometrical types of nanotubes: armchair, zig-zag and chiral. Between these types there is a difference of how the graphene is formed into a†¦show more content†¦The latter is the most popular one as it has many advantages from large area deposition to low costs. What is more, it enables aligned CNTs growth at moderate temperatures. There are various conï ¬ gurations of CVD reactor used in the synthesis of CNTs such as horizontal, vertical or barrel. The vertical one is commonly used for large-scale CNTs production in which catalyst is ï ¬â€šuidized with high carrier gas ï ¬â€šow rates. The other method in CNTs growth uses a horizontal quartz reactor. It relies on the following carbon sources: gaseous hydrocarbons, e.g. methane or acetylene, or liquid ones such as alcohol, benzene or toluene. The most widely used carrier gases are argon and nitrogen. To prevent the oxidation of catalyst particles and production of various carbon impurities, in the process of CNTs catalytic synthesis hydrogen is used with the carrier gas [4]. In this method a non-uniform growth is observed as a result of the position dependent chemical reaction kinetics in the reactor. The growth rate, hybrid structure, diameter and number density of CNTs varies greatly, depending on the temperature and hydrogen ratio of the process. On the other hand spray pyrolysis CVD enables CNTs synthesis without the presence of hydrogen and at low carrier gas ï ¬â€šow rates. Here the growth rate and other signiï ¬ cant features of CNTs is also highly dependent on the parameter of the reaction, i.e. temperature,Show MoreRelatedCarbon Nanotubes : What Are They?1157 Words   |  5 PagesCarbon Nanotubes, What Are They? The growth of carbon nanotubes is an intricate process that has many challenges. It is important to understand what carbon nanotubes are, there history, what their potential applications are and how they will be able to accomplish these task. Carbon nanotubes (CNTs) are one of a multitude of tiny materials that will help to define the future. Carbon nanotubes have an unparalleled history. The first publication about these was written in 1952 by Raduskevich and LukyanovichRead MoreNanotechnology: What are Carbon Nanotubes? 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