Electrochemical sensors for on-line monitoring of aging effects and water-surfactant interactions in industrial lubricants

Multifrequency electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and chronopotentiometry (CP) were employed as a basis for on-line electrochemical sensors for diversified composition analysis of fully formulated industrial lubricants. These electrochemical techniques appeared as powerful yet inexpensive tools specifically capable of on-line detection and monitoring of major contaminants of typical industrial lubricants, such as water, as well as oxidative degradation. MEMS technology was employed for design and fabrication of these electrochemical sensors.;Laboratory and on-line experimental data for oil-water interaction kinetics based on EIS and CV was compared to computational analysis. On-line data was used to characterize water interactions (micellization, evaporation and electrolysis) with fresh and drain diesel oils. A computational analysis model was developed from literature describing oil-water interactions to support the experimental data and establish the kinetics of these interactions. The model illustrates changes in the oil-water system over time and increases understanding of the experimental data. CP sensors based on solid-state reversible oxide films of Ir and Pd demonstrated capabilities for monitoring lubricant oxidation and degradation. Experimental results showed linear responses to changes in oil acidity and were in agreement with suggested electrochemical mechanisms. Future work should be focused at improving long term stability of sensors in oil solutions.