6 Key excerpts on "Carbon Structures"

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  eBook - ePub

  Introduction to Nanoscience and Nanotechnology

  • Chris Binns(Author)
  • 2021(Publication Date)
  • Wiley

    (Publisher)

  3 Carbon Nanostructures : Bucky Balls and Nanotubes

  This chapter focuses on nanostructures produced by carbon. It may seem strange to devote a chapter to a single element, but there is such a plethora of nanostructures composed of carbon that it is easy to justify several books, never mind a chapter on them. Here we will pass lightly over the subject and discuss how and why these structures form and their basic properties. Some technological applications will also be presented, but carbon nanostructures are ubiquitous in nanotechnology and references to them can be found throughout the rest of this book.

  3.1 Why Carbon?

  Carbon is a light simple element, its atoms containing just six electrons, two of them being core (1s) electrons and the remaining four (2sp) available for bonding with other atoms. It is the slightly schizophrenic nature of the chemical bonding by these four that naturally gives carbon a diversity of forms. The details of the environment in which the atoms come together (pressure, temperature etc.) determine the types of bonds. For example, we are familiar with the two very different bulk forms (allotropes) of carbon, that is, graphite, and diamond that result from different types of bonds. The bonding in diamond and graphite and why they adopt their particular crystal structures are illustrated in Figure 3.1 .

  The diagrams on the left show the charge distribution associated with the four bonding electrons for the two crystal structures. It is important to realize that these have no meaning out of the context of bonding to other atoms (see advanced reading Box 3.1 ). They are the charge distributions that would be found if we suddenly plucked a carbon atom out of its crystal and somehow kept the electronic charge distribution associated with the atom frozen. In the case of diamond, the four bonding electrons produce a tetrahedral charge distribution around each atom and so the atoms come together along these mutual bonds forming a tetrahedral arrangement. The bonds (covalent σ

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  eBook - ePub

  Nanotechnology in Textiles

  Theory and Application

  • Rajesh Mishra, Jiri Militky(Authors)
  • 2018(Publication Date)
  • Woodhead Publishing

    (Publisher)

  3

  Carbon-based nanomaterials

  Rajesh Mishra; Jiri Militky    Department of Material Engineering, Faculty of Textile Engineering, Technical University of Liberec, Liberec, Czech Republic

  Abstract

  Carbon is an extremely versatile material exhibiting a large number of unique properties. It exists as several different allotropes that range from 1-D to 3-D structures that are used in numerous applications. The characterization and applications of single carbon allotropes are extremely large, and many of the fundamental properties of the various allotropes have been extensively characterized. Carbon nanoparticles and nanotubes are extensively studied in recent times for their multifunctional applications. The current chapter discusses various carbon-based nanomaterials and their specific characteristics. Selected applications are also described in some detail.

  Keywords

  Nanoporous carbon; Single-walled carbon nanotube (SWCNT); Multiwalled carbon nanotube (MWCNT); Fullerenes; Graphene

  3.1 Introduction

  Carbon is very unique material with many allotropes having quite different behavior from amorphous (charcoal and carbon black) to crystalline (diamond and graphite) structures. The properties of Carbon Structures vary uniquely with allotrope type. For example, there are huge differences between diamond and graphite. Diamond is highly transparent and very hard (microhardness of 100 GPa), with highest thermal conductivity but extremely low electric conductivity. Graphite is opaque and black, relatively soft, and a very good electric conductor.

  Nanocarbon materials play a critical role in the development of new or improved technologies and devices for sustainable production and use of renewable energy. This perspective paper defines some of the trends and outlooks in this exciting area, with the effort of evidencing some of the possibilities offered from the growing level of knowledge, as testified from the exponentially rising number of publications and putting bases for a more rational design of these nanomaterials.

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  eBook - ePub

  Carbon Nanotubes

  Properties and Applications

  • Michael J. O'Connell(Author)
  • 2018(Publication Date)
  • CRC Press

    (Publisher)

  chapter one The element carbon Frank Hennrich

  Institut für Nanotechnologie

  Candace Chan

  Stanford University

  Valerie Moore

  Rice University

  Marco Rolandi

  Stanford University

  Mike O’Connel

  Theranos, Inc.

  Contents

  1.1	Allotropes of carbon
  1.2	History
  1.3	Structure
  1.4	Progress of single-walled carbon nanotube research
  References

  Carbon is the most versatile element in the periodic table, owing to the type, strength, and number of bonds it can form with many different elements. The diversity of bonds and their corresponding geometries enable the existence of structural isomers, geometric isomers, and enantiomers. These are found in large, complex, and diverse structures and allow for an endless variety of organic molecules.

  The properties of carbon are a direct consequence of the arrangement of electrons around the nucleus of the atom. There are six electrons in a carbon atom, shared evenly between the 1s, 2s, and 2p orbitals. Since the 2p atomic orbitals can hold up to six electrons, carbon can make up to four bonds; however, the valence electrons, involved in chemical bonding, occupy both the 2s and 2p orbitals.

  Covalent bonds are formed by promotion of the 2s electrons to one or more 2p orbitals; the resulting hybridized orbitals are the sum of the original orbitals. Depending on how many p orbitals are involved, this can happen in three different ways. In the first type of hybridization, the 2s orbital pairs with one of the 2p orbitals, forming two hybridized sp1 orbitals in a linear geometry, separated by an angle of 180°. The second type of hybridization involves the 2s orbital hybridizing with two 2p orbitals; as a result, three sp2 orbitals are formed. These are on the same plane separated by an angle of 120°. In the third hybridization, one 2s orbital hybridizes with the three 2p orbitals, yielding four sp3 orbitals separated by an angle of 109.5°. Sp3

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  eBook - ePub

  Nanocarbon and Its Composites

  Preparation, Properties and Applications

  • Anish Khan, Mohammad Jawaid, Abdullah M. Asiri, Inamuddin(Authors)
  • 2018(Publication Date)
  • Woodhead Publishing

    (Publisher)

  10] .

  CNTs and fullerenes are the allotropes of carbon characterized by a hollow structure and extraordinary thermal, electrical, and mechanical properties. Spherical fullerenes are also called buckyballs whereas cylindrical ones are known as nanotubes. The walls of these structures consist of a single layer of carbon atoms called graphene [11] . Although carbon is ubiquitous in nature, CNTs are a man-made form of carbon [12] . Among them, CNT possess better structural and fascinating properties which attracted it utilization and opened up a broad range of possible studies and functional applications [13 ,14] . The development and characterization of inorganic hybrids consisting of metal oxide (MO) and CNTs are gaining attention, in terms of superior electronic, optical, and mechanical properties [9 ,15 ,16] .

  The discovery of CNTs perhaps contributed to the nanotechnology revolution, owing to their superior thermal, physical, optical, and electrical properties as well as a remarkably high thermal conductivity [17] . A Japanese scientist Iijima is known for his discovery of CNTs. However, according to Monthioux and Kuznetsov [18] , CNTs were discovered much earlier than the 1990s. Conceptually, CNTs are classified as single-walled carbon nanotubes (SWCNTs), and are made by rolling a graphene sheet into a seamless cylinder. CNTs with a multiwalled configuration are called multiwalled carbon nanotubes (MWCNTs), and are formed by more rolled-up graphene sheets [19] . MWCNTs were first discovered in 1951 by Russian scientists Radushkevich and Lukyanovich [20] . Forty years after the discovery of MWCNTs, another type of CNT with a single wall, also known as an SWCNT, was discovered by Iijima and Ichihashi [21] in 1993 [17] . CNTs classified as SWCNTs and MWCNTs are displayed in Fig. 9.1 [22] . Arc discharge, laser ablation, and chemical vapor deposition (CVD) as well as diffusion and premixed flame methods are the major synthesis methods for SWCNTs and MWCNTs [23 ,24]

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  eBook - ePub

  Understanding the Nanotechnology Revolution

  • Edward L. Wolf, Manasa Medikonda(Authors)
  • 2012(Publication Date)
  • Wiley-VCH

    (Publisher)

  L of the quantum dot, the color of the emitted light can be adjusted from red to blue.

  7.4 Carbon Nanotubes

  Recently, smaller self-assembly forms of carbon, mainly based upon graphite, have been discovered and are in the inventory for materials engineering. We will focus on “buckyballs” (carbon C60 molecules, ∼0.5 nm) and carbon nanotubes that are hollow cylindrical shells of carbon, with diameters of a few nanometers. An experimental image of a single-wall carbon nanotube is shown in Figure 7.2 .

  Figure 7.2 An STM (scanning tunneling microscope) image of a single-walled carbon nanotube. Individual sp2 -bonded carbon atoms are shown. This is a “chiral” nanotube because its atoms do not line up perfectly along the axis of the structure. (See the cover of this book.) The carbon–carbon bond length is 0.144 nm

  (http://www.ncnr.nist.gov/staff/taner/nanotube/types.html ).

  To understand these useful building blocks of nanotechnology, we have to understand graphite. While we have explained earlier, the diamond structure of silicon and carbon have tetrahedral bonding. Carbon is able to bond in other ways. An “sp2 ” bonding allows carbon to form sheets in which each carbon has three nearest neighbors forming a triangular lattice. This lattice is a sheet in graphite, called graphene . Graphite is a layered compound. It is a pure crystal of carbon made up of individual layers that are s–p bonded triangular lattices of carbon. The separate layers are called graphene layers and these have also recently become interesting from the point of view of patterning and nanoelectronics. Graphite forms in nature and probably the best crystals of graphite are mined from the earth. However, the same structure, the triangular lattice of sp2 -bonded carbon appears in smaller structures.

  The easiest one of the materials to think about is the carbon nanotube. If we think of the graphene layer, we can imagine rolling this sheet around a variety of crystalline directions. One can imagine a family of cylinders having variable radius and also variable orientation, and all of these are carbon nanotubes. They are found in nature rarely but can be produced in controlled fashions, principally by chemical vapor deposition. The carbon nanotubes with moderately controlled properties, the properties being radius and the index that controls the rolling direction of underlying graphene layer can be made in the following way. Let’s imagine a chemical vapor deposition (CVD) system with a heated substrate at ∼500 °C and a flow of methane gas CH4

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  eBook - ePub

  The Science For Conservators Series

  Volume 1: An Introduction to Materials

  • The Conservation Unit Museums and Galleries Commission(Author)
  • 2008(Publication Date)
  • Routledge

    (Publisher)

  n can be used to show that a large but uncertain number of units is repeated. A great many materials used in conservation are composed of giant covalent molecules; wool, silk, cotton, polyester thread, wood, leather, PVA, nylon, Perspex (Plexiglass), etc. The molecules of cellulose in cotton are composed of about 3000 repeated units each containing 21 atoms. Here is part of its structure:

  Figure 4.20 Part of the structural formula for cellulose (C6 H10 O5 ) , showing how the units repeat.

  Materials with such big molecules cannot evaporate easily. The long chains may actually become physically tangled. When the material is heated the primary bonds are eventually broken and chemical changes such as charring are frequently observed.

  The properties of a substance composed of large covalent molecules will depend very much on their size and shape. If the molecules are relatively compact, they will stack together neatly and regularly in the solid and will form hard crystals (like sugar). If they are long twisting string-like molecules, they will tend to lie lengthways alongside one another but not necessarily in any orderly fashion. In this case, the solid may be very flexible and have strong directional properties. Examples are the fibres of wood and silk.

  lattice

  Diamond is a poor conductor of electricity and is not at all volatile. It can be burned at extremely high temperatures in oxygen to form carbon dioxide and nothing else. This expensive experiment shows that diamond is composed of nothing but carbon atoms and is chemically identical to the black carbon we are familiar with in charcoal and carbon inks. If the carbon atoms were not joined to one another in any way, we would expect it (with molecular mass as low as 12) to be very volatile, even gaseous, at room temperature (compare nitrogen which has a molecular mass of 28); but diamond is hard and crystalline with a melting point in excess of 3500°C. The molecule of diamond must be very big; what is its structure? If it contains covalent bonds the diamond molecule will contain carbon atoms with a valency of 4. There are several ways that large numbers of carbon atoms could be joined together so that each has four bonds attached to it. (Try to see how many you can find.) The rigidity and symmetry of diamond suggests that there are not long flexible strings of carbon atoms or large flat sheet-like molecules that could slide over one another. The actual structure in some ways resembles that of methane, where the C-H bonds point to the corners of an imaginary tetrahedron. The diamond “molecule” is an infinite three-dimensional lattice

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