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Triboelectric Series and its Effect

Posted on Apr 10, 2009

Triboelectric Series

There are many different kinds of thermocouple wire insulations. Is there an ESD concern using these?

To understand the ESD threat, one must first understand that all insulators can be an ESD threat, yet electronic circuits cannot function without insulators. Electrons are what “charge” a material and conductors allow the charges to be carried away removing the potential difference, NOT the electrons, but the difference in the number of electrons between the conductors. In other words, conductors let electrons even out so current (electrons) has no reason to flow and risk damage to sensitive parts. Insulators can build up electrons and because they are insulators, they stay there and huge potential differences can build. One source of this build up is caused by mechanical moving of different materials against each other, called "triboelectric" charging.

Triboelectric charging takes place when two materials come together, or rubbed together and then are separated. "Tribo" means to rub. This process of charging is caused when one material loses electrons, thus making it more positive, and the other gains electrons, thus making it more negative.

The triboelectric series is a list that ranks materials according to their propensity to gain or lose electrons. Steel is near the middle of the list and these materials do not show strong tendency to behave either way. Note that the propensity of a material to become more positive or more negative after charging has nothing to do with the level of conductivity of the material.

These tests are not exact science and are not easy to do, so different tests sometimes yield different results in determining the placement of a material on the triboelectric series. The triboelectric series shown in the table is a product of a merging of several triboelectric series I found on the web.

Conclusion and Recommendation

The charging that can occur with these materials only happens when they are different and somewhat distant from each other in the series. So materials near the middle of the series will help generate a charge on those either positive or negative, while somewhat uncharged themselves. Also remember, the charging does not happen unless there is some mechanical action, like rubbing, between the two. That is why the attraction between a balloon and your hair gets stronger with rubbing.

These materials by themselves are threat unless they are in the presence of others at opposite ends of the series and there is mechanical action between them. So don’t run out and get rid of all the Teflon or Kapton tape. Just know that good ESD practices should be employed when working with these materials. And keep this at opposite ends of the series away from each other.

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