Using Electrochemical and Spectroscopic Techniques as Probes for Investigating Metal-Lubricant Interactions

Abstract

The interactions between three representative lubricant additives and iron are characterized using AC impedance and surface infrared spectroscopies, fast-scan cyclic voltammetry, and laboratory friction measurements. The experimental results provide an increased understanding of the mechanisms by which each additive reduces friction. At 50°C, oleic acid adsorbs on iron to form a friction-reducing layer. This friction-reducing layer becomes less effective at elevated temperatures (100° and 150°C) due to de-sorption of the oleic acid molecules. A mixed acid phosphate is characterized by a relatively high electrochemical reactivity as compared to that for oleic acid and fatty amine, which correlates with its ability to form a reaction film on iron. The formation of this reaction film is accelerated by increasing the temperature from 50° to 150°C. Therefore, an acid phosphate is more effective in reducing friction at elevated temperatures. A fatty amine is characterized by intermediate electrochemical reactivity, with insignificant amounts of oxide forming on the iron surface.