In: Book Name
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© 2008 Nova Science Publishers, Inc.

Chapter

APPLICATIONS OF CARBON NANOTUBES IN
NONTRADITIONAL MACHINING AND MICROSCOPY
Y.H. Guu1, C.C. Mai2 and H. Hocheng3,*
1

Department of Mechanical Engineering, National United University
Miaoli 360, Taiwan, R.O.C.
2
Department of Numerical Control Technology, Intelligent Machinery Technology
Division
Mechanical and Systems Research Laboratories, Industrial Technology Research
Institute
Taichung Industrial Area, Taichung 407, Taiwan, R.O.C.
3
Department of Power Mechanical Engineering, National Tsing Hua University
Hsinchu 300, Taiwan, R.O.C.

Abstract
Carbon nanotubes possess advantages over other materials due to their superior strengthto-weight ratios, tremendous stiffness, high conductivity, high flexibility, and low density.
Many promising applications have been proposed for carbon nanotubes, including miniaturized electronic and mechanical devices. In this chapter, the applications on nontraditional machining and microscopy are introduced. Electrical discharge machining
(EDM) is one of the most successful and widely accepted manufacturing processes for complicated shapes and tiny apertures with high accuracy including micro nozzle fabrication, drilling of composites and making of moulds and dies of hardened steels. This method is considered suitable for machining of materials with extremely high hardness, strength, wear resistance and thermal resistance. Carbon nanotube powder is mixed in the dielectric of EDM, where the powders continuously float and uniformly disperse throughout the entire dielectricfilled cavity with little agglomeration during EDM. Hence it reduces the insulating strength of the dielectric fluid and increases the spark gap between the tool and specimen. As a result, the
EDM becomes more stable, thereby improving the material removal rate, the surface characteristics and the machining efficiency. The surface characteristics play an important role in micro/nanofabrication as well as understanding the nature of workpiece. In recent years, atomic force microscopy (AFM) has been widely used to measure the surface at the
*

E-mail address: hocheng@pme.nthu.edu.tw

Author nanometer scale. AFM is also a powerful technique to conduct lithography on the substrates acquiring the desired nanostructures. AFM can act as a nanomanipulator to pick up and release nanoscale structures on surfaces. Carbon nanotubes show great potential for AFM applications due to their smaller diameters than Si or metal tips result in a high resolution. The high aspect ratios of carbon nanotubes are very suitable to observe a specimen with the precipitous features and their physical and chemical robustness lead to a high abrasion resistance. This work will review the mechanical and electrical properties of carbon nanotubes and the applications in EDM and AFM.

Introduction
Carbon nanotubes (CNTs) are composed of graphene sheet that is rolled up spirally into a seamless cylinder with diameters ranging from 0.5 to 50 nm and lengths of many microns.
The graphite sheet was constructed by the carbon atoms with honeycomb structure. There are two types of carbon nanotubes: single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs). SWNT is formed by rolling a grapheme sheet into a cylinder which have one atom thick and with diameters ranging from 0.6 to a few nm. MWNTs are made of a rolled-up stack of graphene sheets in concentric cylinders. MWNTs have diameters ranging from a few nm to 50 nm. Electron diffraction analysis showed that the graphene sheets had a helical arrangement relative to the tube axis [1-3]. In general, the SWNTs were put together to form bundles. In a bundle, it is hexagonally arranged to form crystal-like structure. The carbon nanotubes (both MWCNTs and SWCNTs) possess extraordinary mechanical combined with low density, unique electrical properties, and excellent thermal properties. The carbon nanotubes are the candidate with great potential as an application in nanoscale devices and can be widely used in electronic, mechanical, electromechanical, chemical and scanning probe, powder mixed EDM (PMEDM), and materials for macroscopic composites [1-2]. A number of reviews on the applications of CNTs in electronic and optoelectronic [3], energy storage devices [4], nano electro mechanical system (NEMS), sensors [5], reinforced polymer
[6], field emission and lighting [7], and biological [8]. Mechanical properties including excellent tensile strength and high Young’s modulus and extreme flexibility with elastic buckling without occurring catastrophic failure under large loads hence it is a promising material for AFM tips applications.
In this review article, the authors will focus on the major research of the properties of carbon nanotube and to review the emerging applications of carbon nanotubes in EDM and
AFM. This chapter is organized as follows. First, the properties of the carbon nanotubes are discussed. This includes the basic mechanical and electrical properties. A section is thus devoted to the applications in EDM after the description of the advantageous properties.
Finally, a survey of the status of applications in AFM is provided. The report ends with a conclusion. Mechanical Properties of Carbon Nanotubes
Carbon nanotube is composed of the discrete molecular structures linked by the carbon-tocarbon bonds. The carbon-carbon bond existed in graphite is one of the strongest structure in nature [9]. The carbon nanotubes possess the unique property: density lower than that of Al
[10]. In the past, researchers used experimental method to measure mechanical properties of
SWCNTs. The micro-Raman spectroscopy was used monitor the cooling-induced compressive deformation of carbon nanotubes embedded in an epoxy matrix. According to the measurement, the Young’s modulus of SWCNT was 2.8–3.6 TPa, while for MWCNT was

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1.7–2.4 TPa [11]. The values of the elastic moduli are consistent with the published experimental data from Treacy et al. [12]. The stiffness of SWCNTs is estimated by observation of their freestanding room-temperature vibrations in a transmission electron microscope. The average Young's modulus of SWCNTs, of 1.0-1.5 nm diameter, is 1.25 TPa
[13]. Using an atomic force microscope to measure the elastic and shear moduli of SWNT ropes, the values of elastic and shear moduli of SWNTs are the order of 1 TPa and 1 GPa, respectively [14]. The Young’s modulus of individual SWNTs under tensile load ranged from
0.32 to 1.47 TPa (mean 1.0 TPa). The breaking strength of SWNTs of 13 to 52 GPa (mean 30
GPa) was found on the perimeter of each rope. The mechanical properties of MWNTs surpassed those of any previously existing industry materials [15]. The correlation between the amplitude of the thermal vibrations of the free ends of anchored nanotubes as a function of temperature with the Young’s modulus showed that the elastic modulus of MWNTs have an average value of 1.8 TPa while its strength is approximately 10-100 times greater than that of the strongest steel [12]. The elastic moduli of multi-walled nanotubes are sensitive to both tube diameter and structure. The elastic modulus of MWNTs has also been obtained from the bending force measured by using AFM. The bending force was measured versus displacement along the unpinned lengths. An AFM was applied to record the profile of a
MWNT lying across an electrode array. The measured profile was found to be consistent with a Young’s modulus of approximately 1 TPa [16]. The mechanical properties of MWCNTs were determined with a "nanostressing stage" which located within a scanning electron microscope. Experimental results indicate that the tensile strength was 11 to 63 GPa for the
19 MWCNTs and the Young's modulus varied from 0.27 to 0.95 TPa [17]. MWCNTs possess a tensile strength of 0.15 TP and a Young’s modulus of 0.9 TPa when pulling and bending tests were conducted on MWCNTs in-situ in a transition electron microscope [18]. By tensile loading inside an SEM to study the mechanical properties of arc-grown MWCNT, the fracture strength of the outermost shell of 14 MWCNTs ranged from 10 to 66 GPa. The
Young’s moduli of the MWCNTs obtained from linear fit of the stress-strain curves were from 620 to 1,200 GPa with an average value of 940 GPa [19]. Furthermore, the mechanical properties of MWCNTs were performed in a SEM by nano-manipulator (Figure 1). The load response during the tensile test was obtained by the force sensor. The tensile strength of the
MWCNTs was about 41.01 GPa and the elastic modulus was 0.98 TPa [20].

Figure 1 The SEM images show (a) before and (b) after tensile test of MWCNTs, and (c) the force-displacement curves of MWCNTs with different growth methods during tensile tests.
The tensile loads of the MWCNT1 and MWCNT2 (produced by arc-discharge method) are
827 and 916 nN, respectively. The tensile loads of the MWCNT3 and MWCNT4 (grown with
CVD) are 755 and 557 nN, respectively [20].
The theoretical approaches play an important role in helping us to understand mechanical properties of CNTs. The mechanical properties of CNTs have been addressed by means of computational simulation in a number of publications. An empirical lattice dynamics model

Author was used to study the mechanical properties of single and mulyilayered nanotubes and found that Young’s modulus and the shear modulus are about 1.0 and about 0.45 TPa, respectively
[21]. A tight-binding (TB) total energy method was applied to calculate the elastic properties of SWNTs. The theoretical values for the Young’s modulus was approximately 1.26 TPa [22], conforming with results reported by Krishnan and coworkers [13] for SWNTs (1.25 TPa).
The mechanical properties of SWNTs are strongly dependent on the tube thickness. The theoretical Young’s modulus of SWNTs, of 0.25 nm thickness, is about 0.54-0.70 TPa. The shear modulus is 0.32-0.37 TPa [9]. MWCNTs produced by catalytic chemical vapour deposition (CCVD) weaken the Young’s modulus (E