Tribological properties of lanthanum perrhenate as lubricating additive over a wide temperature range

Abstract

Lanthanum perrhenate for use as a lubricating additive was prepared via the aqueous solution method in this study, and was dispersed into a pentaerythritol ester (PETE) base oil accompanied by surface active agents. The thermal stability of the complex oil with/without lanthanum perrhenate and surface active agents was evaluated by thermogravimetry. The influences of lanthanum perrhenate as a solid lubricating additive on the extreme pressure performance and friction-reducing property of the complex lubricants in a wide temperature range were investigated by four-ball tests and ball-on-disc frictional tests with a silicon nitride ball and Ni-base superalloy frictional pair. The results suggested that the added lanthanum perrhenate did not significantly affect the thermal stability and anti-oxidation properties of PETE, and improved the extreme pressure performance of the base oil. Additionally, it decreased the friction coefficient and wear scar diameter to a certain degree. The complex oil had a similar lubricating performance to the base oil below the decomposition temperature point; within the scope of 350 °C to 600 °C, the friction coefficients of oil containing the lanthanum perrhenate additive were markedly lower than that of the base oil, and this was attributed to lanthanum perrhenate's intrinsic shear susceptibility and resistance to phase transformation under high temperature conditions, enabling it to form an effective antifriction layer with native oxides of the superalloy matrix, thus reducing the friction in high-temperature environments.