Carbon nanotubes ( CNTs ) are carbon allotropes with cylindrical nanostructures. These carbon cylinder molecules have unusual properties, which are valuable for nanotechnology, electronics, optics and other fields of materials science and technology. Due to the immense power and rigidity of the material, the nanotubes have been built with a ratio of lengths to diameters of up to 132,000,000: 1, much larger than other materials.
In addition, due to their exceptional thermal conductivity, mechanics, and electrical properties, carbon nanotubes are finding applications as additives for a variety of structural materials. For example, nanotubes form a small part of the material (s) in some (especially carbon fiber) baseball bats, golf clubs, car parts or damaskus steel.
Nanotubes are members of the fullerene structural family. Their name comes from a long and hollow structure with walls formed by a sheet of carbon as thick as an atom, called graphene. These sheets are rolled at specific and discrete angles ("chiral"), and the combination of the rolling angle and the radius decides the properties of the nanotubes; for example, whether individual shell nanotubes are metals or semiconductors. Nanotubes are categorized as single-walled nanotubes (SWNTs) and multi-wall nanotubes (MWNTs). Nanotubes Individuals naturally align themselves into "ropes" held together by van der Waals forces, more specifically, pi-stacks.
Applied quantum chemistry, in particular, orbital hybridization best describes chemical bonds in nanotubes. The chemical bond of the nanotube involves a fully carbon atom sp 2 -hybrid. This bond, which is similar to graphite and stronger than that found in alkanes and diamonds (which use carbon atoms sp 3 -hybrid), provides nanotubes with their unique strength..
Video Carbon nanotube
There is no consensus on some terms that describe carbon nanotubes in the scientific literature: both "-wall" and "-walling" are being used in combination with "single", "double", "triple" or "multi", and the letter C is often ignored in abbreviation; for example, multi-wall carbon nanotubes (MWNT).
Single Wall
where a = 0,246Ã, nm.
SWNTs are an important variation of carbon nanotubes because most of their properties change significantly with values ​​( n , m ), and these non-monotonic dependencies (see Kataura plot). Specifically, their bandgap can vary from zero to about 2 eV and their electrical conductivity can indicate metallic or semiconducting behavior. Single-walled nanotubes are likely candidates for electronic miniaturization. The most basic building blocks of this system are power lines, and SWNTs with a diameter of a nanometer sequence can be excellent conductors. One useful application of SWNTs is in the development of the first intermolecular field effect transistor (FET). The first intermolecular logic gate using SWCNT FET was made in 2001. A logic gate requires both p-FET and n-FET. Since SWNTs are p-FETs when exposed to oxygen and n-FETs otherwise, it is possible to expose half of SWNT to oxygen and protect the other half of it. The SWNT result acts as a logical gate not with p and n-type FETs in the same molecule.
The price for single-walled nanotubes decreased from about $ 1500 per gram in 2000 to a retail price of about $ 50 per gram of production of 40-60% by weight of SWNTs as of March 2010. In 2016 the retail price of 75% of SWNTs weight was $ 2 per gram, cheap to use widely. SWNTs are forecast to make a big impact in electronics applications by 2020 according to a report Global Market for Carbon Nanotubes .
Multi-walled
The multi-walled nanotubes (MWNTs) consist of several layers of rolled (concentric tube) of graphene. There are two models that can be used to describe the multi-walled nanotube structure. In the model of Russian Dolls, graphite sheets are arranged in concentric cylinders, for example, (0.8) single-walled nanotubes (SWNTs) in larger single-walled nanotubes (0.17). In the Parchment model, a sheet of graphite is rolled around itself, resembling a roll of parchment or rolled newspaper. The interlayer distance in a multi-wall nanotube is close to the distance between graphene layers in graphite, about 3.4 ÃÆ'â € |. The structure of the Russian Dolls is observed more generally. The shells themselves can be described as SWNTs, which can be metallic or semiconducting. Due to statistical probabilities and restrictions on the relative diameter of the individual tubes, one of the shells, and thus the overall MWNT, is usually a zero-metal gap.
Double walled carbon nanotubes (DWNTs) form a special class of nanotubes because their morphology and properties are similar to SWNTs but they are more resistant to chemicals. This is especially important when it is necessary to transplant chemical functions to the surface of the nanotube (functionalization) to add properties to the CNT. The functionality of Covalent SWNTs will break some of the C = C double bonds, leaving "holes" in the structure on the nanotubes, and thus modifying both mechanical and electrical properties. In the case of DWNT, only the outer wall is modified. DWNT synthesis on a gram scale was first proposed in 2003 by the CCVD technique, from selective reduction of oxide solutions in methane and hydrogen.
The inner telescopic shell capability and unique mechanical properties will enable the use of multi-wall nanotubes as the main moving arm in upcoming nanomechanical devices. The retraction force that occurs in telescopic motion caused by Lennard-Jones interaction between the shell and its value is about 1.5 nN.
Pieces and cross crosses
The pause between 2 or more nanotubes has been widely discussed theoretically. Such intersections are quite often observed in samples made by arc discharges as well as by chemical vapor deposition. The electronic properties of the junction were first considered theoretically by Lambin et al., Which suggests that the relationship between the metal tube and the semiconductor would represent the hetero heteroscale. Therefore, such intersections may form nanotube-based electronic circuit components. The image on the right shows the intersection between two multiwalled nanotubes. The gap between nanotubes and graphene has been considered theoretically, but not much experimentally studied. Such intersections form the basis of pillared graphene, in which the parallel graphene sheets are separated by short nanotubes. Principled graphene represents a three dimensional carbon nanotube architecture class.
Recently, several studies have highlighted the prospect of using carbon nanotubes as building blocks to create three-dimensional macro (& gt; 100 jm in all three dimensions) of all carbon devices. Lalwani et al. has reported a newly started radical thermal crosslinking method for making carbonic, free-standing, porous scaffolds, all carbon using single, multi-wall carbon nanotubes as building blocks. The scaffold has macro, micro, and nano pores structured and porosity can be customized for special applications. All of these 3D carbon scaffolds/architectures can be used for the generation of next generation energy storage, supercapacitors, field emission transistors, high performance catalysts, photovoltaics, and biomedical and implant devices.
Other morphologies
Carbon nanobuds are the newly created ingredients combining two previously discovered carbon allotropes: carbon nanotubes and fullerenes. In this new material, fullerene-like "buds" are covalently bonded to the outer exterior of the underlying carbon nanotubes. This hybrid material has useful properties of fullerene and carbon nanotubes. In particular, they have been found as an excellent field emitter. In composite materials, attached fullerene molecules can serve as molecular anchors preventing the slipping of nanotubes, thereby enhancing the composite mechanical properties.
A carbon sequester is a new hybrid carbon material that traps fullerenes inside carbon nanotubes. It can have attractive magnetic properties with heating and irradiation. It can also be applied as an oscillator during investigation and theoretical prediction.
In theory, nanotorus is a carbon nanotube bending into a torus (a donut shape). Nanotori is predicted to have many unique properties, such as magnetic moment 1000 times greater than previously thought for a certain radius. Properties such as magnetic moment, thermal stability, etc. vary greatly depending on the radius of the torus and the radius of the tube.
Carbon nanotube graphenated is a relatively new hybrid that incorporates a graphite foliate grown along the side wall of a multiwalled or bamboo style CNT. The density of foliate may vary as a function of precipitation conditions (eg temperature and time) with structures ranging from several layers of graphene (& lt; 10) to thicker, more like graphite. The fundamental advantage of the integrated graphene-CNT structure is the high surface area of ​​a three-dimensional framework of CNT coupled with high-density graphene edges. Storing the high density of graphene foliata along the length of the lumped CNT can significantly increase total load capacity per unit of nominal area compared to other carbon nanostructures.
Capped nitrogen-carbon (CSCNTs) differ from other quasi-1D carbon structures, which usually behave as quasi-metallic electron conductors. CSCNTs exhibit semiconductor behavior due to the microstructure of layers of graphene layers.
Extreme carbon nanotubes
The longest carbon nanotube observations grown so far over 1/2 m (550 mm long) were reported in 2013. The nanotubes were grown on silicon substrates using an improved chemical vapor deposition method (CVD). and represents the electrical arrangement of single-carbon carbon nanotubes.
The shortest carbon nanotubes are the cycloparaphenylene organic compounds, which were synthesized in 2008.
The thinnest carbon nanotube is a seat (2.2) CNT with a diameter of 0.3Ã, nm. These nanotubes are grown in multi-walled carbon nanotubes. Determination of carbon nanotube type was done by a combination of high resolution transmission electron microscope (HRTEM), Raman spectroscopy and functional theory density calculation (DFT).
The thinnest freestanding single-walled carbon nanotube is about 0.43Ã, nm in diameter. The researchers suggest that it can be either (5,1) or (4,2) SWCNT, but the exact type of carbon nanotube remains questionable. (3.3), (4.3) and (5.1) carbon nanotubes (all about 0.4 nm diameter) are clearly identified using a high resolution transmission electron microscope correcting abnormalities within double walled CNTs.
The highest density of CNTs is achieved in 2013, grown on conductive titanium-coated copper surfaces coated with cobalt and molybdenum co-catalysts lower than typical temperatures of 450 ° C. The average tube height is 380 m and the mass density of 1.6 g cm < soup> -3 . The material shows the ohmic conductivity (lowest resistance ~ 22 k?).
Maps Carbon nanotube
Properties
Mechanical
Carbon nanotubes are the strongest and most rigid material yet found in terms of tensile strength and elastic modulus respectively. This strength results from the covalent bonds of sp 2 formed between individual carbon atoms. In 2000, multi-wall carbon nanotubes were tested to have a tensile strength of 63 gigapascals (9,100,000 psi). (For illustration, this translates into the ability to withstand tensions of weight equal to 6,422 kilogram-style (62,980 N; 14,160 lbf) on a 1-millimeter-square (0.0016 sq., In) cross-section cable.) Further studies, such as those performed in 2008, revealed that individual CNT shells have strengths of up to 100 gigapascals (15,000,000 psi), which correspond to quantum/atomistic models. Since carbon nanotubes have a low density for solids of 1.3 to 1.4 g/cm 3 , their specific strengths of up to 48,000 kNÃ, Â · mÃ, Â · kg -1 are the best known ingredient, compared to 154Ã, kNÃ, Â · mÃ, Â · kg -1 of high carbon steels.
Although the strength of individual CNT shells is very high, the weak shear interaction between adjacent shell and tube causes a significant reduction in the effective strength of double-walled carbon nanotubes and carbon nanotube collections to only a few GPa. This limitation has recently been addressed by applying high-energy electron irradiation, which binds cross-skins and deep tubes, and effectively increases the strength of these materials into? 60 GPa for double-walled carbon nanotubes and? 17 GPa for double-walled carbon nanotube bundles. CNT is not nearly as strong as compression. Because of the hollow structure and high-aspect ratios, they tend to buckle when placed under pressure, torsional or bending pressures.
On the other hand, there is evidence that in the radial direction they are rather soft. Observations of the first transmission electron microscope of radial elasticity suggest that even van der Waals forces can damage two adjacent nanotubes. Then, nanoindentations with atomic force microscopy were performed by several groups to quantitatively measure the radial elasticity of multiwalled carbon nanotubes and atomic force microscopy tapping/contact modes also performed on single-walled carbon nanotubes. Young's modulus on several GPa sequences shows that CNTs are actually very soft in the radial direction.
Electricity
Unlike graphene, which is a semimetal two-dimensional, carbon nanotube either metal or semiconductor along the tubular axis. For a given ( n , m ) nanotube, if n = m , nanotubes are metals; if n - m is a multiple of 3 and n? m and nm? 0, then the nanotube is quasi-metal with a very small bandgap, otherwise the nanotube is a moderate semiconductor. So all seats ( n = m ) nanotubes are metals, and nanotubes (6,4), (9,1), etc. Is a semiconductor. Carbon nanotubes are not semimetallic because of the degeneration point (the point at which bands meet the anti-bonding bands, where energy moves to zero) shifts slightly away from the K point in the Brillouin zone because of the curvature of the surface tubes, causing hybridization between band * * and * anti-bonding, modifying the tape dispersion.
Rules regarding the behavior of metal versus semiconductor have an exception, because the curvature effect in small diameter tubes can greatly affect the electrical properties. Thus, (5,0) The SWCNT of the supposed semiconductor is actually a metal according to the calculation. Likewise, zigzags and chiral SWCNTs with small diameters that should have metallic have limited gaps (fixed metallic arm nanotubes). In theory, metal nanotubes can carry an electric current density of 4 ÃÆ'â € "10 9 A/cm 2 , which is more than 1,000 times larger than metals such as copper, copper interconnect current density is limited by electromigration. Carbon nanotubes are thus being explored as interconnects, improving conductivity components in composite materials and many groups seeking to commercialize electric wires that conduct assemblies of individual carbon nanotubes. There are significant challenges to be overcome, however, such as unwanted saturation of undue currents under voltage, a much more resistive nanotube junction and impurities, all of which decrease the electrical conductivity of macroscopic nanotube wires by orders of magnitude, compared to the conductivity of individual nanotubes.
Because of the nanoscale cross-section, electrons spread only along the axis of the tube. As a result, carbon nanotubes are often referred to as single-dimensional conductors. The maximum electrical conductance of a single-walled carbon nanotube is 2 G 0 , where G 0 = 2 e 2 / h is the conductance of a single ballistic quantum channel.
Due to the role of electron-systems in determining the electronic properties of graphene, doping in carbon nanotubes differs from bulk crystal semiconductors from the same group of periodic tables (eg silicon). Graphitic substitution of carbon atoms in the walls of nanotubes by boron or nitrogen dopants leads to p-type and n-type behavior, respectively, as expected in silicon. However, some non-substitute doping (intercalated or adsorbed) is introduced to carbon nanotubes, such as alkali metals and metal-rich metallocene, producing n-type conduction because they donate electrons to nanotube electrons. In contrast, "electron acceptor such as FeCl 3 or electron-deficient metalocenes function as p-type dopants because they draw? -electrons away from the valence band tops.
Intrinsic superconductivity has been reported, although other experiments do not find this evidence, leaving the claim as the subject of debate.
Optics
Carbon nanotubes have useful absorption, photoluminescence (fluorescence), and Raman spectroscopic properties. The spectroscopic method offers the possibility of rapid and non-destructive characterization of a relatively large number of carbon nanotubes. There is a strong demand for such characterization from an industry point of view: many parameters of nanotube synthesis can be changed, intentionally or unintentionally, to change the quality of the nanotubes. As shown below, Raman absorption of optics, photoluminescence and spectroscopy enables rapid and reliable characterization of these "quality nanotubes" in terms of non-tubular carbon content, the structure (chirality) of the resulting nanotubes, and structural defects. These features determine virtually all other properties such as optical, mechanical, and electrical properties.
Carbon nanotubes are a unique "one dimensional" system that can be imagined as a single sheet of graphite roll (or rather graphene). These rolls can be performed at different angles and indentations resulting in different nanotube properties. The diameter usually varies in the range of 0.4-40 nm (ie "only" ~ 100 times), but the length can vary ~ 100,000,000,000 times, from 0.14 nm to 55.5 cm. The nanotube aspect ratio, or the ratio of length-to-diameter, can be as high as 132,000,000: 1, which is unequaled by other materials. Consequently, all the properties of carbon nanotubes relative to a typical semiconductor are highly anisotropic (directionally dependent) and melodic.
While the mechanical, electrical and electrochemical properties (supercapacitors) of carbon nanotubes are well established and have immediate applications, the practical use of optical properties is unclear. The tunability of the property is potentially useful in optics and photonics. In particular, light-emitting diodes (LEDs) and photo detectors based on single nanotubes have been produced in the lab. Their unique feature is not the efficiency, which is relatively low, but the narrow selectivity in emission wavelength and light detection and the possibility of fine tuning through the nanotube structure. In addition, bolometer and optoelectronic memory devices have been realized in single walled carbon nanotube ensembles.
Crystallographic defects also affect the electrical properties of the tubes. A common result is to decrease the conductivity through the damaged area of ​​the tube. Defects in seat-type tubes (which can conduct electricity) can cause the surrounding area to be semiconductor, and a single monatomic void induces magnetic properties.
Thermal
All nanotubes are expected to be excellent thermal conductors along the tube, showing a property known as "ballistic conduction", but a good insulator on the lateral axis of the tube. Measurements show that SWNT individuals have thermal conductivity of room temperature along its axis of about 3500 WÃ, Â · m -1 Ã, Â · K -1 ; compared with copper, a metal known for its excellent thermal conductivity, which transmits 385 Wm -1 Ã, Â · K -1 . Individual SWNT has a room-temperature thermal conductivity across its axis (in the radial direction) of about 1.52 W Â · m -1 Ã, Â · K -1 , which is about as thermally conductive as soil. Macroscopic assembly of nanotubes such as film or fiber has reached up to 1500 WÃ, Â · m -1 Ã, Â · K -1 so far. The stability of carbon nanotube temperature is estimated to be up to 2800 ° C in a vacuum and about 750 ° C in air.
The crystallographic defect greatly affects the heat properties of the tubes. Such defects cause phonon scattering, which in turn increases the rate of phonon relaxation. This reduces the mean free path and reduces the thermal conductivity of the nanotube structure. Phonon transport simulations show that substitution flaws such as nitrogen or boron will primarily cause high frequency optical phonon scattering. However, larger scale flaws such as the Wales Stone defect cause the phonon spreading at various frequencies, leading to greater decreases in thermal conductivity.
Synthesis
Techniques have been developed to produce large quantities of nanotubes, including arc discharges, laser ablation, chemical vapor deposition (CVD) and high pressure carbon monoxide disproportionation (HiPCO). Among them arc discharge, laser ablation, chemical vapor deposition (CVD) is batch by batch process and HiPCO is continuous process gas phase. Most of this process occurs in a vacuum or with process gas. CVD growth method is very popular, because it produces high quantity and has a degree of control over diameter, length and morphology. Using particulate catalysts, a large number of nanotubes can be synthesized by this method, but achieving repetition becomes a major problem with CVD growth. The advanced HiPCO process in catalysis and sustainable growth makes CNT more commercially viable. The HiPCO process helps in producing high-temperature, pure-walled carbon nanotubes in higher quantities. HiPCO reactors operate at high temperatures of 900-1100 Â ° C and high pressure ~ 30-50 bar. It uses carbon monoxide as a source of carbon and nickel/iron penta carbonyl as a catalyst. This catalyst acts as a nucleation site for growing nanotubes.
The vertically aligned carbon nanotube array is also grown by the deposition of thermal chemical vapor. Substrate (quartz, silicon, stainless steel, etc.) Coated with catalytic metal coating (Fe, Co, Ni). Usually the coating is iron, and is deposited through sputtering to a thickness of 1-5 nm. A 10-50m alumina bottom layer is often also placed on the first substrate. It instills controlled wetting and good interface properties. When the substrate is heated to a growing temperature (~ 700 Â ° C), continuous iron film breaks into small islands... each island then forms carbon nanotubes of nanotubes. The sputtered thickness controls the size of the island, and this in turn determines the diameter of the nanotube. The thin iron layer lowers the diameter of the island, and they decrease the diameter of the growing nanotubes. The amount of time it takes the metal islands to sit at a limited growth temperature, as they move, and can merge into larger (but less) islands. Annealing at the growth temperature reduces site density (number of CNT/mm 2 ) while increasing the catalyst diameter.
Carbon nanotubes prepared always contain impurities such as other carbon forms (amorphous carbon, fullerene, etc.) and non-carbon impurities (metal plates used for catalysts). These impurities need to be removed to use carbon nanotubes in the application.
Metrology
There are many metrology standards and reference materials available for carbon nanotubes.
For one-wall carbon nanotubes, ISO/TS 10868 describes measurement methods for the diameter, purity, and fraction of metal nanotubes through optical absorption spectroscopy, while ISO/TS 10797 and ISO/TS 10798 define methods for characterizing the morphology and composition of carbon nanotube elements of one- walls, using transmission electron microscopy and scanning electron microscopy respectively, coupled with analysis of energy dispersive X-ray spectrometry.
NIST SRM 2483 is carbon black carbon nanotubes used as reference material for elemental analysis, and characterized using thermogravimetric analysis, rapid gamma activation analysis, induced neutron activation analysis, inductively coupled plasma spectroscopy, Raman resonance scattering, UV - visible infrared fluorescence spectroscopy and absorption spectroscopy, scanning electron microscopy, and transmission electron microscopy. The Canadian National Research Council also offers certified SWCNT-1 reference materials for elemental analysis using inductively coupled inductive neutron activation and plasma mass spectroscopy analysis. NIST RM 8281 is a mixture of three long carbon nanotubes one-wall.
For multiwall carbon nanotubes, ISO/TR 10929 identifies the nature and contents of impurities, while ISO/TS 11888 describes morphology using scanning electron microscopy, transmission electron microscopy, viscometry, and light scattering analysis. ISO/TS 10798 also applies to multiwall carbon nanotubes.
Chemical modification
Carbon nanotubes can be enabled to achieve the desired properties that can be used in a wide range of applications. The two main methods of carbon nanotube functionalization are covalent and non-covalent modifications. Due to its hydrophobic nature, carbon nanotubes tend to clump to block their dispersion in a solvent or melt viscous polymer. The resulting or aggregated nanotube bundle reduces the mechanical performance of the final composite. Carbon nanotube surfaces can be modified to reduce hydrophobicity and improve interface adhesion to bulk polymers through chemical attachments.
Apps
Current
Current uses and applications of nanotubes have largely been limited to the use of bulk nanotubes, which is a rather disorganized mass of nanotube fragments. Bulk nanotube materials can never achieve tensile strength similar to individual tubes, but such composites can, however, produce sufficient power for many applications. Carbon bulk nanotubes have been used as composite fibers in polymers to improve the mechanical, thermal and electrical properties of bulk products.
- Easton-Bell Sports, Inc. has teamed up with Zyvex Performance Materials, using CNT technology in a number of components of their bikes - including flat handlebars and risers, cranks, forks, seatposts, rods and aero bars.
- Zyvex Technologies has also built a 54 'maritime ship, Piranha Unmanned Surface Vessel, as a technology demonstrator for what is possible using CNT technology. CNTs help improve the performance of ship structures, producing a boat weighing 8,000 pounds that can carry a weight of 15,000 pounds over 2,500 miles.
- Amroy Europe Oy produces Hybtonite carbon nanoepoxy resins whereby carbon nanotubes have been chemically activated to bind to epoxy, resulting in a composite material that is 20% to 30% stronger than other composite materials. It has been used for wind turbines, marine paints and a variety of sports equipment such as skiing, ice hockey sticks, baseball bats, hunting arrows, and surfboards.
- The Boeing Company has patented the use of carbon nanotubes for structural composite health monitoring used in aircraft structures. This technology will greatly reduce the risk of failure in flight caused by structural degradation of aircraft.
Other apps currently include:
- tips for atomic force microscope probes
- in tissue engineering, carbon nanotubes can act as scaffolds for bone growth
Recent research for modern applications includes:
- uses carbon nanotubes as scaffolds for a variety of microfabrication techniques.
- energy dissipation in a self-regulated nanostructure under the influence of an electric field.
- use carbon nanotubes for environmental monitoring because of their active surface area and their ability to absorb gas.
Potential
The strength and flexibility of carbon nanotubes keeps them from potential use in controlling other nanostructures, which suggests they will have an important role in nanotechnology engineering. The highest tensile strength of single-walled carbon nanotubes has been tested to 63 GPa. Carbon nanotubes found in Damascus steel from the 17th century, may help explain the legendary power of the swords made of it. Recently, several studies have highlighted the prospect of using carbon nanotubes as building blocks to create three-dimensional macro (& gt; 1mm all-dimensional) all-carbon devices. Lalwani et al. has reported a thermal binding method that starts with radical radicals to make macroscopic, free-standing, porous scaffolds, all carbon using single and multi-wall carbon nanotubes as building blocks. The scaffold has macro, micro, and nano pores structured and porosity can be customized for special applications. All of these 3D carbon scaffolds/architectures can be used for the generation of next generation energy storage, supercapacitors, field emission transistors, high performance catalysts, photovoltaics, and biomedical and implant devices.
CNTs are potential candidates for the future through wire and material at nanoscale VLSI circuits. Eliminating the concerns of electromigration reliability that interfere with current interconnections of Cu, isolated (single and multi-wall) CNTs can carry a current density of over 1000 MA/sq-cm without damage to electromigration.
A large number of pure CNTs can be made into free-standing sheets or films with surface-tape-casting fabric (SETC) fabrication techniques which are a scalable method for making flexible and folded sheets with superior properties. Another reported form factor is the CNT fiber (a.k.a. filament) by wet spinning. The fine fibers either directly rotate from the synthesis pot or spin from pre-made soluble CNTs. Individual fibers can be converted into threads. Regardless of its strength and flexibility, the main advantage is making electric threads. The electronic properties of individual CNT fibers (ie individual CNT bundles) are governed by a two-dimensional CNT structure. Fiber is measured to have a resistivity of only one order of magnitude higher than a metal conductor at 300K. By further optimizing the CNT and CNT fibers, CNT fibers with improved electrical properties can be developed.
CNT-based yarn is suitable for applications in energy and electrochemical water treatment when coated with ion exchange membranes. Also, the CNT-based yarn can replace copper as a winding material. PyrhÃÆ'¶nen et al. (2015) has built a motor using CNT reels.
Safety and health
The National Institute for Occupational Safety and Health (NIOSH) is a leading US federal agency that conducts research and provides guidance on the implications of occupational safety and health and nanotechnology applications. Early scientific research has shown that some of these nanoscale particles can pose a greater health risk than larger bulk forms of these materials. In 2013, NIOSH publishes the Current Intelligence Bulletin detailing the potential hazards and recommended exposure limits for carbon nanotubes and fibers.
As of October 2016, a single carbon nanotube tube has been registered under EU Registration, Evaluation, Authorization and Restriction of European Chemicals (REACH) regulations, based on an evaluation of the potentially hazardous properties of SWCNT. Based on this enrollment, commercialization of SWCNT is allowed in the EU to 10 metric tons. Currently, the SWCNT types listed under REACH are limited to the specific types of single wall carbon nanotubes manufactured by OCSiAl, which propose applications.
History
The true identity of the inventors of carbon nanotubes is the subject of some controversy. A 2006 editorial by Marc Monthioux and Vladimir Kuznetsov in the journal Carbon describes the origins of carbon nanotubes that are interesting and often misunderstood. Much of the academic and popular literature attributes the discovery of hollow tubes and nanometer-sized images composed of graphite carbon to Sumio Iijima of NEC in 1991. He published a paper describing his discovery that sparked busyness and can be credited with inspiring many scientists now studying carbon nanotube applications. Although Iijima has been given a lot of credit for finding carbon nanotubes, it turns out the carbon nanotube timeline goes back even further from 1991.
In 1952, L. V. Radushkevich and V. M. Lukyanovich published a clear picture of a 50 nanometer diameter tube made of carbon in the Soviet Physical Chemistry Journal. This discovery was largely unnoticed, because the article was published in Russian, and Western scientists' access to the Soviet press was limited during the Cold War. Monthioux and Kuznetsov are mentioned in their carbon editorial :
The fact is, Radushkevich and Lukyanovich [..] should be credited for the discovery that carbon filaments can be hollow and have a nanometer-sized diameter, meaning for the discovery of carbon nanotubes.
In 1976, Morinobu Endo of CNRS observed a vacuum tube of rolled graphite sheets that was synthesized by a chemical vapor growth technique. The first specimen observed will then be known as single-walled carbon nanotubes (SWNTs). Endo, in an earlier review of phase-growth carbon fiber (VPCF), also reminds us that it has observed a vacuum tube, which is linearly expanded with a parallel carbon layer facing the fiber core. This appears to be a multi-wall carbon nanotube observation in the fiber center. Mass-produced MWCNT is currently strongly associated with VPGCF developed by Endo. In fact, they call it "Endo-process", in honor of their work and initial patents.
In 1979, John Abrahamson presented evidence of carbon nanotubes at the 14th Biennial Conference of Carbon at Pennsylvania State University. Conference papers describe carbon nanotubes as carbon fibers produced on carbon anodes during arc discharge. The characterization of these fibers is given as well as the hypotheses for their growth in the nitrogen atmosphere at low pressure.
In 1981, a group of Soviet scientists published the results of chemical and structural characterization of the carbon nanoparticles produced by the proximal disproportion of carbon monoxide. Using TEM images and XRD patterns, the authors suggest that their carbon-fiber "multi-layer crystal" is formed by rolling the graphene layer into the cylinder. They speculate that by rolling the graphene layer into the cylinder, many different settings of the graphene hexagonal web are possible. They suggest two possible settings such as: circular arrangement (seat nanotube) and spiral, helical arrangement (chiral tube).
In 1987, Howard G. Tennent of Hyperion Catalysis issued a US patent for the production of "discrete carbon fiber cylinder" with a "diameter constant between about 3.5 and about 70 nanometers..., length of 10 2 times diameter, and outer region of several layers of regular carbon atoms and different nuclei in sequence.... "
Iijima's discovery of the multi-wall carbon nanotubes in the insoluble material of arc-burned graphite rods in 1991 and Mintmire, Dunlap, and White's independent prediction that if single-walled carbon nanotubes could be made, they would exhibit conduction properties which helps to create the initial buzz that is now associated with carbon nanotubes. Accelerated nanotube research strongly follows independent discoveries by Bethune at IBM and Iijima in NEC from carbon nanotubes and methods to specifically produce them by adding a transition metal catalyst to the carbon in arc discharge. The famous arc discharge technique for producing the famous fullerene Buckminster on the preparative scale, and these results seem to extend coincidence-related discoveries with fullerenes. The discovery of nanotubes remains a controversial issue. Many believe that the Iijima report in 1991 was crucial because it brought carbon nanotubes into the awareness of the scientific community as a whole.
See also
References
This article combines public domain text from the National Institute of Environmental Health Sciences (NIEHS) as cited.
External links
- Nanohedron.com image gallery with carbon nanotube
- Nanotube Site. Last updated 2009.05.03
- EU Marie Curie Network CARBIO: Multifunctional carbon nanotubes for biomedical applications
- Carbon nanotubes at arxiv.org
- C 60 and a short Carbon Nanotubes video that explains how nanotubes can be made from modified graphite sheets and three different types of nanotubes that are formed
- Carbon Nanotubes & amp; Buckyballs.
- The Extraordinary World of Carbon Nanotubes
- Learning module for Carbon Structure of Carbon Nanotube and Nanoribbons
- The durability of carbon nanotubes and their potential to cause inflammation by Dr. Megan Osmond and others. (SafeWork Australia, May 2011). This is a collaboration between the Institute of Occupational Medicine, the University of Edinburgh and CSIRO in Australia.
- NT06 Seventh International Conference on the Science and Application of Nanotubes
- NT05 Sixth International Conference on Nanotubes Science and Application
- Selection of a free nanotube carbon free article
- The first computer made of carbon nanotubes was launched (BBC News) 2013-09-25
- Research using carbon nanotubes for microfabrication and other applications
Source of the article : Wikipedia
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