Carbon Nanotubes: Synthesis, Properties and Applications

*Aravind Kumar Jagadeesan, Krithiga Thangavelu and Venkatesan Dhananjeyan*

### **Abstract**

Recent discoveries of salient carbon nanoforms have paved tremendous interest among research and also toward their discrete applications in scientific fields. Various generation methods for carbon nanotubes (CNTs) involve chemical deposition of vapor, discharge using electric arc and laser ablation mechanism which were driven by functionalization, chemical addition, doping, and filing such that in-depth characterization and manipulation of CNTs were possible. The in-built elasticity, electromechanical, chemical, and optical properties of CNTs have a notable impact on its stability and reactivity. Perhaps, the flexibility along with its determined strength makes them to validate its potential application in diverse fields which enables that these CNTs will definitely procure a prominent role in nanotechnology.

**Keywords:** nanotechnology, nanotubes, synthesis, electromechanical, nanosensor

#### **1. Introduction**

Carbon materials can be grouped into three classifications based on their period of advancement: classical carbons, nano ones and new carbons. Cracking carbons incorporate engineered graphite squares principally utilized as anodes, carbon blacks, what are more, enacted carbons, for which creation systems were created before [1] the 1960s. During the 1960s, carbon materials not quite the same as these great carbons were designed: carbon filaments from different forerunners, including fume developed carbon filaments; pyrolytic carbons delivered by means of concoction fume testimony forms; glasslike carbons with high hardness and gas impermeability; high-thickness isotropic carbons created by isostatic squeezing; intercalation mixes with various functionalities, for example, high electrical conductivity; and precious stone like carbons as straightforward carbon sheets. These recently evolved carbon materials are grouped as new carbons [2]. Since the 1990s, different fullerenes with shut shell structure, carbon nanotubes with nanometer distances across, and graphene pieces of just a couple molecules' thickness has stood out from nanotechnology; these are ordered as nanocarbons.

On the off chance that these carbon materials are considered from the perspective of their surface, be that as it may, they might be ordered into two gatherings: nano-textured and nano-sized carbons [3]. Most carbon materials in the new carbon classification are delegated nano-textured carbon, in light of the fact that their nano texture is controlled by means of various procedures in their creation, notwithstanding the basic control. Then again, fullerenes, carbon nanotubes, and graphene can be delegated nano-sized carbon, the shell size of fullerenes, breadth of carbon nanotubes, and thickness of graphene, drops are on the nanometer scale [4]. Carbon blacks in great carbon are made out of nano-sized particles, yet they are not typically named nanocarbons since they have different applications as a mass, not as individual nano-sized particles [5].

Carbon, a basic chemical substance containing 6 as atomic number with 6 electrons tend to occupy s and p orbitals. It can able to undergo hybridization through three different forms such as sp/sp2 or sp3 means. Recent inventions of compact structured carbon materials such as fullerene [6], graphene [7], and carbon nanotubes [8] have envisaged prompt enquiries into this emerging field. Various physical properties of carbon nanotubes were mostly derived from base material (graphene). Such graphene involves the dense packing arrangement of carbon atoms in a regular sp2 pattern bonded to honeycomb based atomic scale structure and especially this pattern is most suitable as a primary structure for other sp2 materials [9]. Based on theoretical judgment, this CNT is explicitly distinct in the cylinder form fabricated of swirled up graphene thick sheet, which can delineate itself to single or multiple well. The single well nanotubes were known as single walled carbon tubes which were investigated during 1993 whereas multi-walled ones were found during 1991 itself [10].

CNTs have outstanding mechanical, thermal, electrical, and optical properties that are being used exclusively or in mix to deliver keen sensors or on the other hand multifunctional materials [11, 12]. They have high angle proportions that are perfect for long and persistent detecting. Their high surface region, for example, can be misused for storing materials to make half breed useful materials or functionalized to make cathodes for an assortment of uses [13]. CNTs are additionally known to display ballistic conductivity because of insignificant electron dispersing in their 1D structure with mean free-ways of the request of several microns [14, 15].

Mechanical strain may cause reproducible changes in the electrical properties of CNT filaments, making it conceivable to misuse them as electromechanical sensors [16, 17]. The partner changes incorporate inductance, capacitance, and obstruction which can be associated to the strain. Of incredible significance is that CNT filaments are receptive to elastic, compressive, flexural, and torsional strain [18].

The working standards of sensors produced using a CNT plainly visible get together incorporate difference in their electrical resistivity or obstruction because of mechanical strain known as piezoresistivity, change of their inductance and capacitance because of mechanical strain, change of their electrical resistivity because of variety in temperature known as thermoresistivity [19], change of their electrical obstruction because of variety in an attractive field known as magnetoresistance [20], and change in their electrical opposition with change of their mechanical thunderous recurrence because of variety of temperature, weight, mass, and strain [11]. The adjustment in conductance or obstruction is substantially more predominant than other variety in electrical properties. This is somewhat in light of the fact that charge transporters are handily isolated under simultaneous deformation prompting an expansion in obstruction. For extremely little strains, the total deformation has demonstrated to be flexible and the conductive system is completely recouped when the strain is evacuated, prompting an abatement in opposition [21]. Thus, the presented chapter highlights the synthesis details, associated properties and current applications of carbon nanotubes.

#### **2. Discussion**

#### **2.1 Synthesis of carbon nanotubes**

There are many methods to synthesize CNTs, but these three methods are most important and commonly used methods. They are as follows.

**29**

**Figure 1.** *CVD method.*

*Carbon Nanotubes: Synthesis, Properties and Applications*

such as acetylene, ethylene, methane, etc. [22].

**Chemical vapor deposition (CVD):** CVD is a technique in which the vaporized reactants react chemically and forms a nanomaterial product that is deposited on

**Sources for carbon:** The precursor for carbon nanotubes are hydrocarbon gases

**Substrate used:** Substrates are materials on which the CNTS are grown. The commonly used substrates in CVD method are zeolite, silica, silicon plate coated

**Catalyst used:** To produce single-walled carbon nanotubes metal catalyst nanoparticles such as iron, cobalt, nickel, molybdenum, iron-molybdenum alloys,

**Sources for CVD used:** Based on the heating source, the CVD can be:

• Plasma assisted CVD which is heated by microwave radiation, etc.

• Thermal activated CVD which is heated by IR radiation, RF heater, etc.

• Photo assisted CVD which is heated by Arc lamps, CO2 laser, Argon ion laser,

**Conditions maintained:** The following conditions are maintained inside the

CNTs are synthesized by thermal CVD method by using hydrocarbon gas as carbon source. In this method, a quartz tube is placed inside a furnace maintained at high temperature (500–900°C) heated by RF heater. A crucible containing the substrate coated with catalyst nanoparticles is placed inside quartz tube filled with inert gas

*DOI: http://dx.doi.org/10.5772/intechopen.92995*

*2.1.1 Chemical vapor deposition method*

the substrate **Figure 1**.

with iron particles, etc.

Nd:YAG laser, etc.

• Temperature: 500–900°C.

• Inert gas atmosphere: Argon gas.

*2.1.2 Procedure for synthesis of CNTs by thermal CVD method*

etc. are used.

furnace.
