Tribochemistry, tribocatalysis, and the negative-ion-radical action mechanism

Abstract

Terms such as tribochemistry, catalysis, and tribocatalysis are often used to account for various tribological findings, especially those relating to boundary lubrication. The major goal of this article is to present/discuss tribochemistry and tribocatalysis mostly in terms of the negativeion-radical action mechanism (NIRAM). This article also briefly overviews most recent books and book chapters and discusses selected physical and chemical phenomena in the boundary friction contact concerning tribochemistry and tribocatalysis.A catalyst provides a new and easier pathway for reactant molecules to be converted into product molecules. What exactly does the term tribocatalysis mean? Is there any relationship between tribochemistry and tribocatalysis? This article attempts to answer these questions and will demonstrate the importance of the NIRAM approach and the concept of NIRAM-hard and soft acids and bases in tribochemistry, catalysis, and tribocatalysis. It is demonstrated that in both tribochemical reactions and some heterogeneous catalytic reactions, intermediate reactive species are formed by the same mechanism mostly governed by the NIRAM approach. Emphasis is on the role of thermal electrons (thermionic emission) on catalysis and both thermal electrons and exo-electrons on tribocatalysis. Some examples of tribocatalytic reactions are also introduced. The relationship between adhesive wear, especially severe-mild wear transition, is discussed from the point of view of tribochemical reactions between environmental gases and a worn surface.

Squeezing out hydrated protons: low-frictional-energy triboelectric insulator charging on a microscopic scale

“…84 and 94). 108,109 Tribochemical reactions have been explained to be induced by "triboemission" of low-energy electrons (1 to 4 eV), which are emitted by chemical bond scission. 20 Triboemitted charge carriers of both polarities have been detected in experiments for different insulating materials, and the quantity of emitted charge carriers has been found to increase for higher loads (∼1 N) and surface damage.…”

“…116 Simulations have also indicated that adsorbed water may enhance the heterolytic mechanical breaking of chemical bonds, 117 and it has been suggested that adsorbed water molecules may be decomposed tribochemically into hydrogen radicals and a hydroxyl anions by emitted triboelectrons. 109 A quantification of these mechanisms would be important for differentiating between water-based versus water-enhanced charging mechanisms.…”

General Approach to Mechanochemistry and Its Relation to Tribochemistry

“…The same is due to heterogeneous catalysis (HetCat) and tribocatalysis [11]. Principles and applications of HetCat are compiled in [12].…”

“…Figure 8 illustrates the NIRAM reaction cycle. Most recent review [11] is on the NIRAM approach and shows its interrelationship with tribocatalysis. The application of the NIRAM approach explains the role of exoelectrons in some relevant tribochemical reactions detailed in [29].…”

“…The NIRAM concept is based on the hypothesis that low energy electrons (1 to 4 eV), emitted from rubbing surfaces, can be the key factor in some tribochemical reactions [11,29,40,51].The concept of the MARs generation process in polymers is based on the polymer mechanical degradation via two types C -C bond cleavage: (i) homogeneous and (ii) heterogeneous. Generation process of polymer mechano-anions is combined with the polymer triboelectricity phenomenon caused by mechanical scission of the polymer main chain on a friction surface.…”