Tribological Properties of Carbon Nanotube Thin Films by using Electrodynamic Spraying Method

전기 분사 증착 방식을 이용한 탄소 나노 튜브 박막의 트라이볼로지적 특성에 관한 연구

Abstract

Carbon-based coatings, including carbon nanotubes (CNTs), graphene, and buckyball ($C_{60}$), receive much interest because of their outstanding mechanical and electrical properties for a wide range of electromechanical component-based applications. Previous experimental results demonstrate that these carbon-based coatings are promising solid lubricants because of their superior tribological properties, and thus help prolong the lifetime of silicon-based applications. In this study, CNT coatings are deposited on a bare silicon (100) substrate by electrodynamic spraying under different deposition conditions. During the coating deposition, the applied voltage, CNT concentration of the solution, distance between the injecting nozzle and the substrate and diameter of the injecting nozzle are optimized to control the thickness and surface roughness of the CNT coatings. The surface morphology and thickness of the coatings are characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. The friction and wear properties of the coatings are investigated by using a pin-on-reciprocating-type tribotester under various experimental conditions. The friction coefficient of the CNT coating is as low as 0.15 under high normal loads. The overall results reveal that CNT coatings deposited by electrodynamic spraying provide relatively uniform with superior lubrication performance.

Fig. 4. Schematics of the sliding test and mechanism of the friction behaviors during the tests under relatively (a) low load and (b) high load.

Fig. 4. Schematics of the sliding test and mechanism of the friction behaviors during the tests under relatively (a) low load and (b) high load.

Fig. 1. (a) MWCNTs dispersed in the mixture of EtOH/H₂O (v:v=7:3) solution for the electrodynamic spraying process. (b) TEM image of a MWCNT.

Fig. 1. (a) MWCNTs dispersed in the mixture of EtOH/H₂O (v:v=7:3) solution for the electrodynamic spraying process. (b) TEM image of a MWCNT.

Fig. 2. (a) SEM image of the resulted CNT coating by using the electrodynamic spraying method. (b) Surface morphology (up) and thickness (down) of the resulted CNT coating by using a confocal microscope.

Fig. 2. (a) SEM image of the resulted CNT coating by using the electrodynamic spraying method. (b) Surface morphology (up) and thickness (down) of the resulted CNT coating by using a confocal microscope.

Fig. 3. (a) Friction force and corresponding friction coefficient of the 300 nm-thick CNT coating under different normal loads. Optical microscope images of the steel ball and the wear track under (b) 10 mN and (c) 400 mN normal loads.

Fig. 3. (a) Friction force and corresponding friction coefficient of the 300 nm-thick CNT coating under different normal loads. Optical microscope images of the steel ball and the wear track under (b) 10 mN and (c) 400 mN normal loads.

Fig. 5. (a) Friction coefficient of the 100 nm (black square) and 300 nm (blue circle) thick CNT coating under different normal loads. (b) Optical microscope images of the steel ball and the wear track under 400 mN normal loads.

Fig. 5. (a) Friction coefficient of the 100 nm (black square) and 300 nm (blue circle) thick CNT coating under different normal loads. (b) Optical microscope images of the steel ball and the wear track under 400 mN normal loads.

Table 1. Parameters used for the electrodynamic spraying method for CNT deposition on Si wafer

Table 1. Parameters used for the electrodynamic spraying method for CNT deposition on Si wafer