Investigation of 1-octanethiol capped ZnS nanoparticles as lubricant additives and tribological behavior of oil-based nanolubricant

1-Octanethiol (OT) capped ZnS nanoparticles (OT-ZnS) as lubricating oil additives were investigated by tribo-logical tests including wear tests and rheological measurements. The wear tests were performed on lubrication states using a custom design wear test device consisting of a rotating pin on a cylinder geometry. A rotating 1.2379 cylinder (steel counterpart) and a stationary C40 pin were used as a pair of test material for the wear test. The stationary pin was pressed against a rotating cylinder under lubrication conditions. It was observed that the synthesized OT-ZnS NP effectively improved the lubrication performance of 10W engine oil and the surface properties of the test materials. The addition of OT-ZnS NPs to the 10W base oil increased its viscosity and decreased the contact angle (CA) values. The results showed that the wear loss and the wear scar dimensions were both the lowest, while 0.0125 (wt.%) of OT-ZnS NPs were treated with the base oil. The mass loss of the pins was reduced to more than 6.3%. The wear reduction was observed at about 27% and the length of wear scar in the minor axis was reduced to 11.4% when a load of 100 kg was applied. The images of wear scars showed that the OT-ZnS NPs additives could prevent severe contact with the interacting surfaces. OT-ZnS NPs partially filled on the grooves and adhered on the wear scar surfaces and promote tribofilm formation, thereby it improve the tribological performance of 10W base oil, especially under extreme pressure conditions. Sulfide film (sulfuration layer) adhered to the wear scar surfaces and decrease the wear.