Lubrication modes solid-film

In examining the action of boundary lubricant compounds in reducing friction or wear or both between sohds in shding contact, it may be helpful to consider at least the foUowing five modes of film formation on or protection of surfaces (1) physisorption, (2) chemisorption, (3) chemical reactions with the solid surface, (4) chemical reactions on the solid surface, and (5) mere interposition of a solid or other material. These modes of surface protection are discussed in more detail in Reference 2. 

Elastohydrodynamic lubrication (EHD) occurs when the extent of surface deformation is comparable with the lubricant film thickness, so that a heavy load causes local elastic deformation of the contacting surfaces, but without any significant a.sperity interaction. Taking into account the low lubricant thickness (typically from 0.01 to 10 pm) and the high contact pressures (typically in the GPa range), the lubricant properties differ from tho.se of a traditional bulk liquid. since a strong viscosity increase may occur, when the lubricant behaves more like a solid than a liquid. Moderate temperature rises may occur, thus inducing some thermochemical reactions between the surfaces and the lubricant additives, but no tribochemical phenomena are involved, unlike the next lubrication mode. 

There are several basic modes of lubrication. In all modes, contact surfaces are separated by a lubricating medium, which may be a solid, a semisolid, or a pressurized liquid or gaseous film. 

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