2022 年 67 巻 1 号 p. 61-67
We characterized the adsorption and desorption behavior of a sulfur-type extreme-pressure (EP) agent in a mixture of dodecane and methyl oleate (MO) as a model polar oil. The solid material used in this study was iron oxide or steel. The quartz crystal microbalance with dissipation monitoring technique revealed that the residual mass of the EP agent, measured after rinsing the adsorption film by dodecane or the mixture of dodecane and MO, was smaller in the mixed oil than in dodecane. This indicates the lesser adsorption ability of the EP agent in the mixed oil, resulting from the facts that (i) the solubility of the EP agent in the mixed oil is larger than that in dodecane, and (ii) the competitive adsorption between the EP agent and MO occurs on the iron oxide surface. We also analyzed the surface composition of the steel substrate, followed by thermal treatment of the adsorption film. The addition of MO required higher temperatures to yield a reaction film of the EP agent. Although the residual mass of the EP agent in the mixed oil was smaller than that in dodecane, no significant difference in a lubrication ability was observed between the two reaction films.
