Abstract
The aim of the paper is to investigate the effect of size of multiwalled carbon nanotubes (MWCNTs) as additives for dispersion in gear oil to improve the tribological properties. Since long pristine MWCNTs tend to form clusters compromising dispersion stability, they are mildly processed in a ball mill to shorten the length and stabilized with a surfactant before dispersing in lubricant. Investigations are made to assess the effect of ball milling on the size and structure of MWCNTs using electron microscopy and Raman spectroscopy. The long and shortened MWCNTs are dispersed in EP 140 gear oil in 0.5% weight. The stability of the dispersed multiwalled carbon nanotubes is evaluated using light scattering techniques. The antiwear, antifriction, and extreme pressure properties of test oils are evaluated on a four-ball wear tester. It is found that ball milling of MWCNTs has a strong effect on the stability and tribological properties of the lubricant. From Raman spectroscopy, it is found that ball milling time of up to 10 hours did not produce any defects on the surface of MWCNTs. The stability of the lubricant and the antiwear, antifriction, and extreme pressure properties have improved significantly with dispersion shortened MWCNTs. Ball milling for longer periods produces defects on the surface of MWCNTs reducing their advantage as oil additives.
Highlights
Gear oils used in industries and automotive engines are often subjected to heavy loads, due to which they experience high temperatures and pressures causing higher friction and surface damage leading to failure of the system
The most common and frugal method to reduce the size of multiwalled carbon nanotubes (MWCNTs) is ball milling which shortens the length of MWCNTs and obtaining open ends
The results indicate that the extreme pressure behavior of lubricant with nano particles is strongly dependent on the size and hardness of the nanoparticles
Summary
Gear oils used in industries and automotive engines are often subjected to heavy loads, due to which they experience high temperatures and pressures causing higher friction and surface damage leading to failure of the system. Chen et al [5] first studied the effect of dispersed of ball-milled and stearic acid modified multiwalled carbon nanotubes (MWCNTs) on the stability and thereby improvement in the lubricating properties of liquid paraffin base oil. The present study is aimed at investigating improvements in antiwear, antifriction, and extreme pressure properties of formulated EP 140 grade gear engine oil dispersed with surface-modified and ball-milled MWCNTs. Ball milling is performed in inert gas medium and at a low intensity to prevent damage to the structure of MWCNTs. A simpler surface modification technique is used to stabilize the MWCNTs in oil medium and the stability of the suspensions is investigated over a period of 2 months. The paper compares chemical and physical routes for dispersion of MWCNTs in lubricant by comparing performance of surface-modified pristine MWCNTs and surface-modified ball-milled MWCNTs, respectively
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