AVS 56th International Symposium & Exhibition
    Tribology Focus Topic Tuesday Sessions
       Session TR+SS-TuA

Paper TR+SS-TuA1
Effect of the Surrounding Gas Pressure on Charge Separation Caused by Friction between Insulators

Tuesday, November 10, 2009, 2:00 pm, Room B2

Session: Surface Science for Tribology
Presenter: T. Miura, Gakushuin University, Japan
Authors: T. Miura, Gakushuin University, Japan
E. Hosobuchi, Gakushuin University, Japan
S. Ueno, Gakushuin University, Japan
I. Arakawa, Gakushuin University, Japan
Correspondent: Click to Email
Friction between insulators induces charge separation at the interface. The surface electrification after sliding contact yields electric field in the gap near the contact and results in gas discharge if the friction is carried out in a gas ambience. This gas discharge reduces the charge that was once induced at the frictional interface. It has been believed that the initial charge separation was not affected by a surrounding gas and was determined solely by the frictional materials. We have investigated the charge separation rate before the gas discharge under various gas conditions and found that it linearly decreased with the logarithm of the pressure from 10 Pa to atmospheric pressure for Ne, Ar, and Kr.

The friction experiment was performed by means of pin-on-disk equipment. The pin was made of natural diamond and was gold coated. The disk was quartz or sapphire. The charge accumulated on the gold-coated pin was measured by an electrometer. The diameter of a contact area between the bare diamond tip and the disk was about 10 μm and the sliding velocity was 11 μm/s. The charge on the pin increased at a constant rate during sliding and fell to zero when the gas discharge occurred. The charge accumulation and the gas discharge were repeated during sliding friction in a gas ambience. The initial charge density at the interface of the sliding contact was calculated from the accumulation rate, the track width and the sliding velocity.

The charge density was typically the order of 1 mC/m2 for sliding friction in a vacuum (10 Pa). It was found that the initial charge separation under the atmospheric gas pressure is one order of magnitude smaller than that at 10 Pa. This reduction of the charge separation rate was observed for Ne, Ar, and Kr gas at almost the same efficiency. It is likely that the gas molecules penetrate into the frictional interface and interrupt or relax the charge separation. It should be necessary to investigate the surrounding gas effect on the initial charge separation in detail in order to reveal the origin of triboelectricity.