Carbon is one of the most essential elements existing in the periodic table and chemistry itself. Due to the remarkability that carbon brings to the market, it has been in high demand ever since the market has understood the benefits of carbon. It is not only essential but also extremely beneficial as it provides benefits to the industry and market that it joins. Carbon nanotubes are the thin tubes of carbon having a very small diameter which is measured in nanometers as the size is so small that it cannot be measured in any other form. They are also written and known as CNTs. Carbon nanotubes are extremely important and the reason for them being important is the outclass properties that they have which eventually help in building up the potential applications which make them renowned in the market and different industries as well. The different industries that opt for the carbon nanotubes never face any difficulty in achieving what they aim for and the undying hard work that goes behind all these processes is so remarkable that success never leaves them. Due to all the progress that the carbon nanotubes are making in the industry, their potential is increasing day by day. All the properties and applications in-depth are mentioned in this article which elaborate on the best way of using these carbon nanotubes.
With their diameter in nanometer, the tubes are made of carbon, known as Carbon nanotubes (CNTs). Most often, carbon nanotubes are referred to as single-wall carbon nanotubes (SWCNTs). Fullerenes are produced in the carbon arc chambers, and the same chambers are the ones in which Iijima and lchihashi and Bethune et al. discovered carbon nanotubes independently in 1993. One of the carbon’s allotropes is Single-wall carbon nanotubes. They can be idealized as cutouts from a carbon atom’s 2-D hexagonal lattice rolled up along one of the Bravais lattice vectors of the hexagonal lattice for making a hollow cylinder. In this construction, for yielding a helical lattice of atoms of carbon that are seamlessly bonded on the surface of the cylinder, periodic boundary conditions are enforced over this roll-up vector’s length.
There are also multi-wall carbon nanotubes (MWCNTs). They consist of nested SWCNTs that are bonded together, weakly in a structure like that of a tree ring by van der Waals interactions. If we pay attention to the long parallel and straight carbon layers of Koyama, Endo, and Oberlin, cylindrically organized around a hollow tube, the MWCNTs are a lot like them if not identical. Sometimes, MWCNTs are also known as triple- and double-wall carbon nanotubes.
Carbon nanotubes are referred to as tubes with less than 100 nanometers diameter and undetermined structure of carbon wall. Lukyanovich and Radushkevich discovered such tubes in 1952. Most of the studies are focused on the nanotubes of carbon, as compared to other compositions. That’s why they are commonly referred to as MWNT, SWNT, and NT. When carbon nanotube is made from the general methods of production, the carbon nanotube’s length is much larger as compared to its diameter, therefore, the carbon nanotubes length is assumed as infinite for various purposes.
While other nanotubes are semiconductors, the carbon ones display excellent electrical conductivity. Their thermal conductivity and tensile strength are exceptional due to the bond-strength between the atoms of carbon and their nanostructure. Also, they are chemically modifiable. In many technological areas like nanotechnology, composite materials, optics, electronics, and other materials science applications, these characteristics are very useful and beneficial.
Along the tube axis, all these tubes have helical and translational symmetry too and possess nontrivial rotational symmetry. Also, most of them are chiral, therefore the tube and mirror image of the tube isn’t capable of being superimposed. A pair of integers labels the single-wall carbon nanotubes as the construction allows. Some of the specific single-wall carbon nanotubes are metallic whereas others are either moderate or small bandgap semiconductors. The rolling of hexagonal lattice whether it is from front to back or back to front doesn’t determine their electrical characteristics. Also, such characteristics don’t depend on the tube and its mirror image.
Various single-walled carbon nanotube’s characteristics majorly depend on the (n,m) type. It is non-monotonic dependence. The bandgap specifically, can range from 0 to almost 2 eV and semiconducting or metallic behavior can be displayed by the electrical conductivity.
When it comes to elastic modulus and tensile strength, the stiffest and strong material is the carbon nanotube. Its strength is because of the bonding between the individual atoms of carbon, covalent sp2 bonds. When tested, the multi-walled carbon nanotubes showed 63 gigapascals (9,100,000 psi) tensile strength, in 2000. Moreover, other researches showed in 2008 that the strength of 100 gigapascals (15,000,000 psi) is possessed by the individual CNT shells. In comparison with the specific strength of high-carbon steel (154 kNmkg−1), the carbon nanotubes have 48,000 kNmkg−1 specific strength which makes it a great and well-known material.
Reason for the specific strength of carbon nanotubes:
The reason for this specific strength of Carbon nanotubes is their low density for a solid of 1.3 to 1.4 g/cm3. Despite having very high strength, weak shear interactions between the tubes and adjacent shells result in a major lessening in the multi-walled carbon nanotubes’ effective strength, and the nanotubes of carbon bundles down to some GPa only, but this problem has been solved by implementing high-energy electron irradiation, crosslinking tubes and inner shells, resulting in an increase in these material’s strength to 17 gigapascals for double-walled carbon nanotube bundles and 60 gigapascals for multiwalled carbon nanotubes. When placed under bending, torsional, or compressive stress, they undergo buckling due to their high aspect ratio and hollow structure.
Along the tubular axis, carbon nanotubes are either semiconductors or metallic conductors as compared to a 2-dimensional semimetal, graphene. Due to the shifting of the degenerate point from the K point in the Brillouin zone due to the curvature of the surface of the tube, the nanotubes of carbon are not semimetallic. The curvature results in the modification of the band dispersion because of the hybridization between the π* and σ* anti-bonding bands as the curvature affects the electrical characteristics of the small diameter tubes, very strongly. According to the calculations, the single-walled carbon nanotube is metallic instead of semiconducting. The ones with small diameters have a finite gap. In comparison with metals like copper, the metallic nanotubes are capable of carrying 1000 times more electric current density (4 × 109 A/cm2), whereas in copper interconnects, electromigration limits the current densities. Therefore, carbon nanotubes are being studied as interconnects and in composite materials as the components to improve conductivity. The highly conducting electrical wire is being tried to be commercialized by many groups as it is assembled from the individual carbon nanotubes.
Beneficial characteristics of Raman spectroscopy, photoluminescence (fluorescence), and absorption are possessed by the carbon nanotubes. A chance, of non-destructive and quick characterization of carbon nanotube’s comparatively large amounts, is offered by the Spectroscopic methods. From an industrial perspective, such properties are demanded strongly. For changing the quality of nanotube, various nanotube synthesis parameters can be altered, unintentionally, or intentionally. Reliable and quick characterization is allowed by Raman spectroscopies, photoluminescence, and optical absorption, of this “nanotube quality” in terms of structural defects, produced nanotubes structure, and non-tubular carbon content.
Along the tube, all of the nanotubes are extremely good thermal conductors, displaying ballistic conduction, but lateral to the axis of the tube, they are good insulators.
Copper has a thermal conductivity of 385 Wm−1K−1 whereas the room temperature thermal conductivity of an individual SWNT along its axis is about 3500 Wm−1K−1. Like soil, the thermal conductivity of an individual SWNT is about 1.52 Wm−1K−1. In the air, the carbon nanotube’s temperature stability is 750 C and in a vacuum, their temperature stability is 2800 C.
The thermal characteristics of the tube are strongly affected by crystallographic defects. Phonon scattering is a result of such defects, as the phonon’s relaxation rate is increased, lessening the mean free path and lessening the thermal conductivity of the nanotube structures.
Best ways of utilizing the carbon nanotubes in Industry
There are many ways in which carbon nanotubes can be utilized in the industry however the best ones are explained further. It is due to their remarkable performance in every industry that their consumption is now increasing quite rapidly.
Potential applications of carbon nanotubes in the industry:
Firstly in metals, multi-walled nanotubes were utilized as electrically conductive fillers at 83.78 wt% concentrations. At 10 wt. percent loading, conductivities as high as 10,000 Sm−1 are achieved by multi-walled nanotube-polymer composites. Carbon nanotube plastics in the automotive industry are utilized in the electrostatic-assisted painting of mirror housings, also in the filter and fuel lines, which dissipate electrostatic charge. Silicon wafer carriers and electromagnetic interface (EMI)-shielding packages are included in other products. In order to improve toughness, strength, and stiffness, the Carbon nanotube powders are mixed with precursor resins or polymers for load-bearing applications. Carbon nanotube’s diameter, interfacial interaction, dispersion, alignment, and aspect ratio determines these improvements. Carbon nanotube loadings from 0.1 to 20 wt% are employed by the masterbatches and Premixed resins.
Utilization via sporting goods:
Sporting goods like bicycle frames, baseball bats, and tennis racquets can be enhanced and material damping can be increased by the Nanoscale stick-slip among carbon nanotubes and carbon nanotube-polymer contacts. The resins of carbon nanotube improve fiber composites, like hulls and wind turbine blades for maritime security boats, these are formed when carbon fiber composites are improved with the enhanced resin of carbon nanotubes. In the organic precursors of extremely strong carbon fibers of 1 μm, carbon nanotubes act as additives. The carbon’s arrangement in pyrolyzed fiber is affected by the carbon nanotubes.
Growth of aligned forests:
By growing aligned forests on carbon fibers, alumina, silicon carbide, and glass, the production of hierarchical fiber composites takes place. 69% enhanced crack-opening and in-plane shear interlaminar toughness is displayed by CNT-alumina fabric and Fuzzy epoxy CNT-SiC.
Applications include structural health monitoring, deicing, and lightning-strike protection for aircraft. Rheology faces change after loading of the nanotube, causing multi-walled nanotubes to be utilized as a flame-retardant additive to plastics. Halogenated flame retardants can be replaced by such additives. Lessened crack propagation and improved tensile strength are provided by carbon nanotube/concrete blends. Because of effective heat reflection, the resistance to fire can be majorly enhanced by the bucky paper (nanotube aggregate).
Due to their remarkable mechanical characteristics, CNTs are one of the building blocks in hierarchical composite materials. An in situ chemical vapor deposition spinning method was used by Windle et al. for producing from the CVD-grown Carbon nanotube aerogels, the continuous Carbon nanotube yarns.
In the form of bundles:
Take the bundles of a carbon nanotube from a carbon nanotube forest, that will make carbon nanotube yarns, and twisting those yarns subsequently results in the formation of the fiber. The Windle group at 1mm small gage lengths fabricated yarns of carbon nanotube with 9 gigapascal strengths, although, at 20 mm long gage length, there was only 1 gigapascal strength because of the failure of effectively transferring the load to the discontinuous (a constituent) carbon nanotubes within the fiber. To solve this complication, one promising way is through irradiation (or deposition) induced covalent inter-bundle and inter-Carbon nanotube cross-linking to join up the carbon nanotubes effectively.
Utilization in clothing:
Carbon nanotubes are currently being weaved into clothes for making bulletproof and stab-proof clothing due to the carbon nanotube’s high mechanical strength. It will stop the penetration of the bullet into the body, however, internal bleeding and broken bones are caused because of the kinetic energy of the bullet.
Films and Coatings:
Carbon nanotubes function as a multifunctional coating material too. For instance, the biofouling of ship hulls can be reduced by the paint/multi-walled nanotube mixtures by disheartening barnacles and algae’s attachment. To paints that contain biocide and are hazardous to the environment, carbon nanotubes are a promising alternative. The strength and stiffness of coating can be enhanced by the mixing of carbon nanotubes into the anticorrosion coatings for metals, it also gives a way to protect the cathode.
For many consumer devices, carbon nanotubes are a cheap alternative for ITO. When it comes to flexible displays, as compared to the brittle ITO coatings, the transparent and flexible conductors of carbon nanotubes despite the cost, provides a benefit.
Utilization via screen printing:
Methods like screen printing can pattern the carbon nanotube conductors, they can also be deposited from the solution. 100 ohm per square sheet resistivity and 90% transparency is provided by the single-walled nanotube films. To defrost sidewalks or windows as thin-film heaters, such films are under construction. Numerous different materials can coat carbon nanotubes foams and forests for changing their performance and functionality. For instance, the graphene coatings for producing highly elastic aerogels, silicon-coated carbon nanotubes for creating flexible energy-dense batteries, and silicon carbide coatings for producing a tough structural material for robust high-aspect-ratio 3D-micro architectures. There are many different methods to form carbon nanotubes into films and coatings.
Previously, the main purpose of the research on carbon nanotubes for textile functionalization was fiber spinning to enhance their mechanical and physical characteristics. Now. The main focus is on coating the textile fabrics with carbon nanotubes. To modify fabrics by the usage of carbon nanotubes, different methods have been used. Intelligent e-textiles are made by using a polyelectrolyte-based coating with carbon nanotubes for Human Biomonitoring.
Textile material was also dyed by immersing it in either a poly PMAS polymer solution or PMAS-SWNT dispersion with improved capacitance and conductivity with a durable behavior.
Single-walled carbon nanotubes can also be coated for energy storage applications and wearable electronics by just doing a simple process of “dipping and drying”.
Usage of elastomeric separator:
Recently, an elastomeric separator was used by Li and coworkers, they almost attained a fully stretchable supercapacitor. A sound mechanical stretchability is provided when the electrospun polyurethane was utilized. Remarkable discharge-charge cycling stability is achieved by the whole cell. A negative surface charge and an organized nanotube structure are possessed by the carbon nanotubes, having the same structures as direct dyes, so to coat and absorb carbon nanotubes on the surface of the fiber to prepare multifunctional fabric, including electromagnetic absorbance, flame retardant, electric conductive, and antibacterial characteristics.
Carbon nanotube yarns:
Later, for high-end applications, the carbon nanotube yarns and laminated sheets (made by drawing methods or forest spinning or direct chemical vapor deposition (CVD)) may compete with carbon fiber, particularly in applications that are weight-sensitive, and needs combined mechanical and electrical functionality.
A strength of 8.8 GPa and stiffness of 357 GPa for gauge length is possessed by the research yarns, composed of the few-walled carbon nanotubes. Like Kevlar, gravimetric strength of 2-GPa is offered by the centimeter-scale gauge lengths too.
Even at room temperature, carbon nanotube field-effect transistors (CNTFETs) can function and they use a single electron for digital switching. A carbon nanotube logic circuit was displayed in 2013 whose functions were very beneficial.
Absence of technology:
Technology absence for contact resistance, thermal budget, designed alignment, chirality, control over length, sample purity, individual electrical contact’s positioning, circuit density, and mass production are the main hurdles to nanotube-based microelectronics. Regulation of conductivity was a major challenge. A nanotube can function as a semiconductor or a conductor, it depends on the subtle surface characteristics. Using their random networks is another way of making carbon nanotube transistors. If it is done, then at the wafer level, it is capable of producing devices on a larger scale and can average all of their electrical differences. Nanomix used this approach first in 2002, enabling them for making the first transistor on a transparent and flexible substrate.
Near-ballistic transport properties:
Near-ballistic transport properties are displayed by long channel CNTFETs as in the single-walled carbon nanotubes, the electron means free path can exceed 1 micrometer, leading to high speeds. In hundreds of gigahertz frequency range, the carbon nanotube devices are supposed to be performing operations. On magnetic metal’s (Fe, Co) nanoparticles, nanotubes can grow, helping in producing electronic (spintronic) devices. For instance, in a single-tube nanostructure, control ofcurrent via a field-effect transistor by magnetic field has been displayed.
Optical power detectors:
An extraordinary capability of resisting the damage when the laser light is being absorbed is possessed by a spray-on mixture of ceramic and carbon nanotubes. Optical power detectors need such coatings that absorb the highly-powered laser’s energy without breaking down to measure such laser’s output. These are utilized in the equipment of the military to defuse the unexploded mines. The composite is made up of ceramic (composed of nitrogen, carbon, and silicon) and multi-walled carbon nanotubes. If boron is included, the breakdown temperature will be boosted by it. While damage resistance is boosted by the oxidation-resistant ceramic, heat is transmitted very well by the graphene-like carbon and the nanotubes.
Dispersion in toluene:
To create the coating, nanotubes should be dispersed in toluene. The mixture is added with a clear liquid polymer (containing boron) and then heated to 2,010 F (1,100 C). A fine powder results. It is then dispersed in toluene again and sprayed on the surface of copper in a thin coat. For 15 seconds, 15 kilowatts per square centimeter was tolerated by the coating while 97.5% of the light from a far-infrared laser was absorbed by the coating. As compared to similar coatings, for instance, carbon paint and nanotubes alone, the tolerance to damage is almost 50% higher.
In conclusion, Carbon nanotubes are thin elastic tubes made up of carbon and the reason that they are called nano is that the diameter of these tubes is very small and is measured in the nanoscale. They are an essential part of the industry and are highly used in the industry as they are capable of offering a lot of benefits and ease to the consumers and the industries that they are a part of. They have exceptional properties such as mechanical, electrical, optical, and thermal properties. All these properties are so strong that they are credited throughout the world in different industries.