Tribological properties and lubrication mechanism of manganese phosphate trihydrate as lubricant additives

Abstract

A deeper insight into two interacting frictional surfaces in nanosized spaces, especially the molecular groups at interfaces is considered to be important to friction reduction. In this paper, we report Mn3(PO4)2·3 H2O (MnP) nanosheets with loosely packed structure and high porosity as oil-base additives that can achieve good dispersion in oil because of their adsorption with strong capillary effect. Lubrication with MnP additives for titanium alloy, the average friction coefficient (COF) and wear rate (WR) can be reduced by 66.81 % and 98.78 %, respectively. It was confirmed that the extraordinary friction-reducing property was due to the solid-liquid interface with Coulomb repulsion between polar groups on MnP nanosheet and non-polar oil molecules, which resulted in a slip surface with low viscous shear force. The shear force of this solid-liquid interface was correlated with the different oxygen contents and the viscosity of lubricating oil, which showed different intermolecular forces. Additionally, any connectivity between this solid-liquid interface would increase the adhesion, for example, hydrogen bondings and dispersant. Our results establish a lubrication interface with Coulomb repulsion that can improve the tribological behavior of lubricating oil.