Reducing gas-sensing properties of ferrite compounds MFe₂O₄ (M = Cu, Zn, Cd and Mg)

Four kinds of ferrites, MFe₂O₄ (M = Cu, Zn, Cd and Mg), having high specific surface area (40-80 m²/g) were prepared by a coprecipitation method and tested for sensing properties to reducing gases of CO, H₂, LPG, C₂H₅OH and C₂H₂. The gas sensitivity depended considerably on the kinds of ferrites and the gases to be detected. All of the ferrites were more sensitive to C₂H₂, C₂H₅OH or LPG than to H₂ or CO. Among the ferrites, the gas sensitivity tended to decrease in the order MgFe₂O₄ to approximately CdFe₂O₄>CuFe₂O₄>ZnFe₂O₄, which was in fact coincident with the increasing (or decreasing) order in specific surface area (or grain size). It was revealed that MgFe₂O₄ and CdFe₂O₄ were the most sensitive and selective to LPG and C₂H₂, respectively, among the ferrites tested.