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

Methane is very difficult to be detected by conventional thick film tin oxide sensors because the gas has the strongest bond strength among hydrocarbon gases. To develop highly sensitive methane gas sensors some alkaline constituents are added to SnO2 powder. The additives act as crystallite growth inhibitors upon heat treatment. SnO2 powder is impregnated with K, Ca and Mg. The highest sensitivity was obtained for Ca-SnO2 sensor when it was heat-treated at 700°C for 20 min. The sensitivity has been increased in the order of Mg-, pure, K-, and Ca-SnO2 sensors, corresponding to the reverse order of the crystallite sizes in those sensors. Additionally, Ca-SnO2 sensors 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.