CH4 sensing characteristics of K-, Ca-, Mg impregnated SnO2 sensors

Methane is very difficult to be detected by conventional thick film tin oxi de sensors because the gas has the strongest bond strength among hydrocarbo n gases. To develop highly sensitive methane gas sensors some alkaline cons tituents are added to SnO2 powder. The additives act as crystallite growth inhibitors upon heat treatment. SnO2 powder is impregnated with K, Ca and M g. The highest sensitivity was obtained for Ca-SnO2 sensor when it was heat -treated at 700 degreesC for 20 min. The sensitivity has been increased in the order of Mg-, pure, K-, and Ca-SnO2 sensors, corresponding to the rever se order of the crystallite sizes in those sensors. Additionally, Ca-SnO2 s ensors with Pt electrode located at upper and lower parts of the sensitive film exhibit 10% difference in sensitivity, indicating that CH4 can easily penetrate very small intraparticle voids. (C) 2001 Elsevier Science B.V. Al l rights reserved.