The correlation among the tribological characteristic parameters of rare earth trifluorides and their electron structures, bond parameters, and thermodynamic parameters

Abstract

Compared with other metal fluorides, the rare earth trifluorides (mainly refers to the trifluorides of light rare earths such as La, Ce, Gd, etc.) are more thermally and chemically stable. Therefore, some rare earth trifluorides have been used as high temperature solid lubricants. For example, LaF 3 and CeF 3 have been applied in lubricating greases and bonded films recently. But the related research work was confined to LaF 3, CeF 3, and NdF 3. Moreover, the friction and wear behaviours of rare earth trifluorides as lubricating additives need to be disclosed. Especially the correlation among the tribological characteristic parameters of rare earth trifluorides and their electron structures, bond parameters, and thermodynamic parameters need to be revealed. In addition, more work should be done so as to realize the action mechanisms of the rare earth trifluorides as lubricating additives. Because the measurement of some thermodynamic parameters of heavy rare earth trifluorides is confined owing to the experimental difficulties related to the chemistry of fluorine, so in this work, the light rare earth trifluorides such as LaF 3, CeF 3, PrF 3, SmF 3, EuF 3, GdF 3, and the mixtures of these rare earth trifluorides were selected as the additive samples. The antiwear and extreme pressure properties of these compounds as additives in lithium grease were evaluated on a four-ball friction and wear tester and an Optimol SRV friction and wear tester. Meanwhile, the correlation among the tribological characteristic parameters of these rare earth trifluorides and their electron structures, bond parameters, and thermodynamic parameters were investigated as well.