Nanostructured lubricant additives for titanium alloy: Lubrication by
the solid-liquid interface with Coulomb repulsion
Abstract
In this work, the advantage of Coulomb repulsion in the intermolecular
forces experienced by molecules on the solid-liquid nanosized contact
interface is taken, and the superior friction-reducing property of
Cu3(PO4)2·3H2O (CuP) oil-based additives has been confirmed for titanium
alloy. 3D CuP nanoflowers (CuP-Fs) with a strong capillary absorption
effect are prepared to achieve the homogeneous mixing of solid CuP and
lubricating oil. Lubrication by CuP-Fs additives for titanium alloy,
friction coefficient (COF) can be reduced by 73.68%, and wear rate (WR)
reduced by 99.69%. It is demonstrated that the extraordinary
friction-reducing property is due to the repulsive solid-liquid
interface with low viscous shear force originating from Coulomb
repulsion between polar water molecules in CuP and non-polar oil
molecules. However, any steric hindrance or connection between this
repulsive solid-liquid interface will trigger the adhesion and increase
the viscous shear force, for example, dispersant, hydrogen bondings, and
shaky adsorbed water molecules. Besides, the lamellar thickness of CuP
and molecular size of lubricant both have a great influence on
tribological properties. Here the lubrication mechanism based on
interface Coulomb repulsion is proposed that may help broaden the scope
of the exploration in low-friction nanomaterial design and new lubricant
systems.