抄録
Boundary lubrication is one of the most interesting topics in the field of tribology. Under the boundary lubrication, oiliness additives mixed in a base oil are expected to form adsorption layers on a sliding surface and then achieve low friction and high wear durability. Many classical reports confirmed that the adsorptive performance of an additive to the surface greatly affects the friction coefficient of surface. However, quantitative analysis for the physical and chemical properties of adsorption layers had not been done until recent years because the adsorption layers are very thin, less than several nanometers. To clarify the phenomena under boundary lubrication, thickness and density of an adsorption layer of oiliness additives formed on a metal surface under the lubricating oil were directly measured by neutron reflectometry that is one of in-situ analytical methods. A copper surface on ultra-flat silicon block was formed by physical deposition. The poly-alpha-olefin was used as base oil, and some kinds of deuterated acids were used as additives. The reflectivity profiles for such sample were acquired by neutron reflectometer in air, in PAO and in PAO mixed with additive. Fitting operation based on Parratt's theory showed that the thickness of the additive adsorption layer on the metal surface was very thin, approximately 2.3-2.4 nm and its density was 42-100% of bulk acid. Neutron reflectometry is a quite useful tool for in-situ analysis for the interface between the metal surface and lubricant.
