Importance of the triboemission process for tribochemical reaction

Abstract

Chemical reactions under boundary lubrication conditions are distinct from those of thermochemical ones. Flash temperature is very short and holding in esteem the mechanically triggered chemistry and thermally triggered chemistry at the contact of asperities caused by the flash temperature effect, the following question arises. ‘Can this reaction initiation process be considered in terms of overcoming the activation energy by heat or by another form of energy’? The purpose of this paper is to discuss that question in terms of the hypothesis: The common denominator of tribochemical reactions is that they might be initiated by low-energy electrons. This is consistent with the negative-ion-radical action mechanism (NIRAM) approach assuming that tribochemical reactions are initiated by electrons in the energy-range of 1–4 eV. The hypothesis is also relevant to the next author's hypothesis saying that the intermediate reactive species of both tribochemical reactions and some heterogeneous catalytic reactions are produced by the same mechanism, governed by the NIRAM approach. The catalyst effect on a chemical reaction is to increase its rate. The reaction rate is further increased when the catalyst is under friction (tribocatysis). The primary objective of this work is to better understand mechanisms of tribochemical reactions and catalytic processes. To initiate thermochemical reactions, heat should be supplied. The same is due to heterogeneous catalytic reactions, however, the catalyst lowers the reaction activation energy. Even a very high calculated flash temperature is short lived, thus, it rather cannot initiate tribochemical reactions by heat. The present author assumes that flash temperature can be expressed in the form of the thermionic emission. Bearing this in mind, it is possible to hypothesize that heterogeneous catalytic reactions are also initiated by thermal electrons. Accordingly, the tribocatalytic process might be initiated and/or enhanced by triboelectrons. Important objective of this work is to better understand both tribochemical reactions and catalytic/tribocatalytic processes. Tribochemistry of simple environment friendly lubricant compounds and examples of water synthesis catalytic and tribocatalytic processes are presented and discussed.