Tribological synergy between classical ZDDP and innovative MoS2 and MoO3 nanotube additives at elevated temperatures

Abstract

One of the most important drawbacks limiting the application of MoS2 nanotubes (NTs) as an oil additive is their temperature sensitivity. Recent studies showed that MoS2 NTs can be substituted by MoO3 NTs in conjunction with S-containing lubricants by exploiting a novel approach of in-situ tribochemical sulphurization. The objective of this work was to investigate the temperature influence on tribological properties of innovative lubricant additives in the form of MoS2 and MoO3 NTs. The NTs were mixed in base oil with and without the presence of S-containing additives. The tribological performance was investigated using a SRV reciprocating sliding testing machine in a steel ball on a steel disc configuration under temperature ramping conditions. The results showed very positive synergy between the traditional anti-wear additive and the innovative MoO3 and MoS2 NTs, causing superb tribological performance up to temperatures of 200 °C. The presented findings show that the in-situ sulphurization of MoO3 NTs was promoted by using the traditional zinc dialkyl dithiophosphates (ZDDP) anti-wear additive, which ensured the stability of this additive combination at severe oil temperature and tribotest conditions. The tribochemically formed tribofilm derived from ZDDP and in-situ sulphurized MoO3 was much thicker compared to other lubricating blends investigated in our research so far.