Superlubricity of silicone oil achieved between two surfaces by running-in with acid solution

In this paper, we showed that the superlubricity of silicone oil can be achieved between friction surfaces (Si3N4/glass) by running-in with an acid solution. The friction coefficient of silicone oil can be reduced to about 0.004, which is only one-thirtieth of its original value (mu = 0.13). Experimental results indicate that the formation of a circular plane under the action of hydrogen ions on the worn region of the ball is closely linked to superlubricity, while the topography of the track on the glass substrate has no obvious effect on the superlubricity. In addition, the tribochemical reaction between Si3N4 and water can lead to the reduction of the friction coefficient in mixed lubrication, but it has no effect on the friction coefficient in hydrodynamic lubrication. According to these results, a superlubricity mechanism was proposed, in which the two friction surfaces form a micro-slope plain bearing, owing to the effect of hydrogen ions, and the silicone oil forms a hydrodynamic film at a certain speed.