Abstract
Triboelectrochemical reactions occur on solid–liquid interfaces in wide range of applications when an electric field strong enough and a frictional stress high enough are simultaneously imposed on the interfaces. A characteristic of triboelectrochemical reactions is that not only the thermal energy but also the electrical and mechanical energies can activate, assist, or mitigate the solid–liquid interface chemical reactions, the products of which affect electrical and tribological behavior of the interfaces inversely. In previous studies, we have found that the coupling of frictional and electric effects could physically change the migration, adsorption, and desorption behaviors of the polar molecules, ions, or charged particles included in aqueous or nonaqueous base lubricant toward or away from the interfaces and thus control the boundary lubrication. Recently, we have found that the friction coefficient and surface appearance of some kinds of metals could also be modulated to some extent even in pure water or pure base oils under external electric stimulations. We attribute these changes to the triboelectrochemical reactions occurred when a strong external electric field is imposed on. Based on the effective collision model of chemical reactions, a chemical potential equation, which includes both electrical and mechanical contributions, has been derived. The proposed chemical potential equation can be used to explain the observed triboelectrochemical phenomenon in experiments. Based on the model, a novel method for oxidation coloring of the selected areas in metal surfaces is proposed. Together with the physical adsorption and desorption model of lubricant additives, the triboelectrochemical reaction model can well explain the phenomena of potential-controlled boundary lubrication in different lubrication systems and also provides a theoretical basis for other solid–liquid interface processes under the effects of electromechanical coupling.
Highlights
Drilling wood to make fire is well known as the beginning event of mankind civilization
The results show that the noncontact area is within the potential window, while the contact area is in the regime of tribolelectrochemical reaction
Focused on the solid–liquid interfaces under the coupling of multi-physics, a chemical potential equation for modeling triboelectrochemical reactions has been proposed. It emphasizes the difference in electrochemical reactions between the friction contact area and noncontact area
Summary
Drilling wood to make fire is well known as the beginning event of mankind civilization. According to the above analysis, the collision model and transition state theory are accepted to discuss the influence of electricity on chemical reactions, as well as the pressure or shear force on the sliding process. Let us consider the electrochemical reaction in which Fe changes to Fe3+, the FIGURE 6 | Potential-controlled friction results of the Cu plate vs ZrO2 ball with pure H2O as lubricant, with the test range of surface potential ±0.6 V. According to the triboelectrochemistry model and the definition of boundary lubrication (Wen and Huang, 2017), the active control of friction in pure liquid is considered to be caused by changing the formation of the oxidation film in friction contact area. This method is expected to have broad applications in the fields of micro-nano machining, information records, surface finishing, and so on
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