Adsorption and Desorption Characteristics of Sulfur-Type Extreme Pressure Agents on Aluminum-Based Substrates and Surface Composition Analysis of Their Thermally Treated Films

Abstract

We have characterized the adsorption and desorption behavior of a sulfur-type extreme-pressure (EP) agent at an aluminum-based substrate/dodecane interface by means of quartz crystal microbalance with dissipation monitoring (QCM-D) technique. We have also analyzed the surface composition of an aluminum plate, followed by thermal treatment of the adsorption film. The EP agent used in this study was synthesized from oleic acid and has a double-chain structure with two carboxylic acid headgroups. The QCM-D results suggested that the EP agent formed a monolayer film on the aluminum-based substrate. In addition, the adsorption film still remained on the substrate even after rinsing by the solvent. After thermal treatment of the adsorption film, the EP agent yielded a decomposed product on the aluminum plate. Ball-on-plate type friction measurements suggested that this product reduced significantly a dynamic friction coefficient. On the basis of these results, we suggest that it is important to see the adsorption and desorption behavior as well as the reactivity in order to understand the friction reducing mechanism of the sulfur-type EP agent on the aluminum plate.