The surface potential measurement is applied to make clear the behavior of molecules that-e are adsorbed on a metal surface and cause the boundary lubrication.
When spindle oil with or without the addition of stearic acid is spread on a cuprous-oxide-surfaced copper plate, the surface potential increases for 10 to 20minutes. This seems to tell the process of polar molecules in the oil being adsorbed and oriented on the metal surface. The increase of the potential is augmented with the concentration of the acid and is stopped at the concentration of about 0.4%, which suggests the completion of the first monomolecular layer.
When a lubricated surface of steadied surface potential is rubbed with care not to originate frictional electricity, the potential undergoes a temporary change, the change being larger as the concentration of the acid is lower, suggesting desorption of adsorbed molecules and re-adsorption. of the acid molecules. When a surface lubricated with pure spindle oil alone is rubbed, the po-tential decreases remarkably recovering very slowly. In this case, even the cuprous oxide layer-seems to be rubbed off.
In general, the extent of wear on the surface can be estimated by surface potential measure-ment from the difference between the velocities of adsorption of polar molecules and oxidation of the metal surface.
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