Interfacial charging performances of electrode coated silicon nitride in aqueous solution based on zeta potential investigation

The lubrication condition of friction pairs in water or aqueous solutions is crucial to the performance and lifespan of key mechanical components in engineering applications. In our previous research, a promising in-situ self-sensing method was proposed based on liquid-solid triboelectric signals generated from the rotation-induced streaming current. However, the comprehension of the interfacial charging mechanism and the enhancement of the signal outputs from the viewpoint of zeta potential are deficient. Besides, the influence of a convergent channel on zeta potential needs further investigation, which fits most engineering conditions for seals or bearings due to the hydrostatic or hydrodynamic effect. Herein, electrode coated silicon nitride (Si₃N₄) composites are prepared by laser machining and magnetron sputtering. The interfacial charging mechanism is proposed based on the comprehensive investigation of electrode area ratio, surface roughness, and liquid ion concentration on zeta potential. The zeta potential originates from the combined efforts of the dissolution of metallic electrodes and the hydration effect of Si₃N₄. The interfacial charging mechanism can be interpreted by the ion absorption of ceramic substrate and the conduction behaviors of electrode layers. Moreover, samples with convergent profiles along the fluid flow exhibit a higher absolute value of zeta potential than divergent ones, and a negative relationship between zeta potential and convergent slope is observed. Finally, design criteria for self-sensing friction pairs are proposed for enhancement of interfacial charging performances: optimal electrode area ratio of 40%, surface roughness of 0.1–0.2 μm, aqueous solution with a moderate number of hydrated ions. Working conditions with a large variation of film gap are more advisable in terms of discernibility and sensitivity. This work builds a bridge between the interface charging mechanism and the self-sensing application of liquid-solid triboelectric behaviors based on streaming current input.