In situ infrared attenuated total reflectance spectroelectrochemical study of lubricant degradation

An attenuated total reflectance (ATR) infrared (IR) cell was designed using a boron-doped silicon wafer as the optically transparent electrode to simultaneously perform ATR-IR spectroscopic and electrochemical impedance measurements. The degradation of industrial lubricants was investigated by monitoring the near-surface concentration of hydrocarbons, detergents and anti-wear additives and the formation of degradation products, while polarizing the cell using electrochemical impedance spectroscopy (EIS). The detergent and the anti-wear agent concentration on and near the silicon surface, based on the IR spectra, and the sum of bulk solution and charge transfer resistance, based on the impedance spectra, were all at a maximum for 30 h drain oil, and then decreased for later drain oils. These results agree with other independent measurements, such as oil viscosity, total acid number (TAN), and total base number (TBN) to indicate that the lubricant is significantly degraded after 30 h in the engine test. These data demonstrate the potential use of the ATR silicon-based electrochemical cell as a monitoring device for lubricant degradation, and as an effective analytical tool capable of studying interfacial kinetics, surface interactions of the additives, and performance of silicon-based spectroelectrochemical devices.