Abstract
Clarification of the sensing mechanism ofα-Fe2O3 and γ-Fe2O3 gas sensors was attempted. The information on the surface states of iron oxides at working temperature (400° C forα-Fe2O3 and 250° C forγ-Fe2O3) was obtainedin situ by applying thein situ CEMS. Theα-Fe2O3 gas sensor, prepared by the precipitation of Fe(OH)3 from a solution of iron (III) sulphate and tin (IV) chloride, was composed of fine particles (−15 nm) and was superior in sensitivity to otherα-Fe2O3. The gas sensitivity was found to depend on the amounts of remaining sulphate ion, the microstructure and a small amount of iron (II) species generated through the reduction ofα-Fe2O3. The sensing mechanism ofγ-Fe2O3 gas sensor was confirmed to be due to the reduction ofγ-Fe2O3 to the low resistive Fe3-x O4 by combustible gas and to depend on the crystal structure.
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