THE BEHAVIOR OF TIN DIOXIDE SENSORS IN EXHAUST ENVIRONMENTS AT LOW AND INTERMEDIATE TEMPERATURES

Tin dioxide has been employed for at least 20 years in solid-state gas sensors and their general purpose usage in the ambient atmosphere is contrasted with that of some other metal oxides conventionally employe d in the exhaust environment. Electron transfer mechanisms are thought to be predominant in the former, whilst the effect of oxygen vacancie s is more often invoked as an explanation of behaviour in the latter. This difference has arisen largely as a result of the respective appli cation temperatures. Some tin dioxide-based sensors are tested in an e xhaust stream alongside two conventional oxides (niobia and titania), in order to determine their suitability for indicating air : fuel rati o (AFR) at the temperatures at which tin dioxide sensors are commonly operated.