Iridium oxide sensors for acidity and basicity detection in industrial lubricants

The lubrication and automotive industries are seeking on-line sensors capable of determining the chemical condition and degree of degradation of industrial and automotive lubricants in order to signal the need for an oil change. Levels of acidity and basicity in non-aqueous media are parameters common to a wide variety of industrial fluids and closely related to rate of the lubricant oxidation breakdown. Therefore, development of chemcical devices capable of continuous monitoring of these parameters remains an important goal of industrial sensor research. Chronopotentiometric (CP) sensors based on solid-state reversible oxide films of iridium demonstrate a number of advantages for detection of acidity and basicity levels in non-aqueous industrial lubricants over other types of acidity sensors, such as glass electrode and ion-selective field effect transistors. Iridium, oxide sensors fabricated by different methods and having various geometric configurations (macro-scale versus microelectromechanical systems (MEMS)) were compared. The sensors demonstrated linear responses to changes in oil acidity and basicity that were in agreement with proposed electrochemical mechanisms. Studies of long term stability and durability of the metal oxide sensors in the oil solutions illustrated that improvement to the sensor fabrication process is needed. (C) 2003 Elsevier B.V. All rights reserved.