Application of nitrogen doped bamboo-like carbon nanotube for development of electrically conductive lubricants

The aim of this work was to examine the applicability of nitrogen-doped bamboo-shaped carbon nanotubes (BCNTs) as conductive additive in bearing grease. To synthesize BCNTs, catalytic chemical vapour deposition (CCVD) method was used by applying butylamine as nitrogen containing carbon source. During the preparation of the polydimethylsiloxane (PDMS)-based lubricants BCNT (1.5 wt% or 3 wt%) and Li-soap (5 wt% or 10 wt%, lithium-stearate) or colloidal silicon dioxide (1 wt% and 1.5 wt% Aerosil 200) was added and mixed by using a highly efficient ultrasonic technique. By adding lithium-soap to the BCNT loaded greases their lubricity improved. The electrical conductivity of greases was measured in stationary state and in rotating bearing (during operation) by using an in-house developed instrument. The nanotube containing samples have shown good electrical conductivity (7–18.5 mS). The friction torque was also calculated based on the measurements of our in-house developed instrument. Efficient friction has been achieved with the 1.5 wt% BCNT loaded samples (6.1 and 5.1 Nmm). Thus, small amount of BCNT is enough to develop a conductive grease formula. All in all, the 3% BCNT and 1.0% colloidal SiO2 containing PDMS base-oil with 50 mm/s viscosity is well suitable for loading of ball bearings. Keywords: BCNT, Conductivity, Bearing, Friction