Solid Electrolyte Oxygen Sensors

Abstract

The relevant developments in: science, engineering, and technology; and their confluence at different times resulting in the concept, feasibility, and the emergence of the solid electrolyte oxygen sensor, are traced from the last century to the present time when a number of commercial devices are marketed. General rules are set out for the choice of an electrolytic system for a solid electrolyte oxygen sensor. The major markets and applications for which the sensor is suitable are described and in particular the combustion efficiency market. The available commercial instruments are reviewed, and a number of desirable sensor features are identified. The theory of the oxygen solid electrolyte concentration cell is outlined and the major error contributing parameters reviewed. The design, development, optimisation, and fabrication of a miniature, rugged, accurate, versatile, and easy to manufacture sensor are detailed. The electrical conductivity of samples of solid electrolytes is examined by an especially developed A.C. measurement technique, and the influence of structural defects on the electrical conductivity is assessed as a potential means of solid electrolyte material quality control. The sensor's characteristics are evaluated in detail and errors due to sample gas composition are measured for a number of commonly encountered gases. The degrading effect of certain gases and reducing atmospheres on the sensor's electrodes is also investigated. The versatility of the design is demonstrated by using the sensor in different configurations: with a sealed-in reference, as an oxygen pump, and in a feedback mode. Examples of industrial commercial use of the sensor as: a flue gas oxygen analyser, and a wide-range instrument are described, showing its suitability for such applications.