Tribological properties of single-walled carbon nanotube solids.

Binder-free single-walled carbon nanotube (SWCNT) solids were evaluated for solid lubrication applications. The steady-state friction coefficients (mu) for the SWCNT solids were found to reach values as low as 0.22-0.24, according to unidirectional sliding friction tests using Si3N4 counterparts in air. The values were slightly higher than that of bulk graphite material (mu = 0.20). SEM and Raman analyses showed that most SWCNTs that existed in the friction surface transformed into SWCNT-derived transferred film made up of amorphous carbon during sliding. The resultant friction behavior may be related to the smearing of transferred film over the contact area, which was expected to permit easy shear and then help to achieve a lubricating effect during sliding.