Zn-doped -Fe2O3 sensors for flammable gas detection: Effect of annealing on sensitivity and stability
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In this study, we investigated the effect of synthesis conditions and processing methods on the stability of gas sensors made of flame-synthesized Zn-doped -Fe2O3 particles. Nanocrystalline Zn-doped -Fe2O3 particles were synthesized by flame spray pyrolysis using either H2/Air or H2/O2 coflow diffusion flames. Transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller surface-area-measurement (BET) were employed to characterize the particles. Gas sensors were fabricated by applying the as-synthesized and annealed particles on interdigitated electrodes. High-temperature flame (H2/O2) generated nanometer-sized particles; lower temperature flame (H2/Air) generated micrometer-sized particles. The sensors made from as-synthesized particles showed a gas sensing sensitivity that was 20 times higher than the literature value. The sensors made of microparticles lost their sensing ability after three days of aging, but sensors made of nanoparticles did not show significant change after aging. XPS results showed significant Zn enrichment on the surface of as-synthesized particles. However, Zn concentration on the surface of particles decreased significantly after annealing. The results showed that sensors made of nanoparticles have higher gas sensing signal, and higher resistance towards aging than sensors made of microparticles. In addition, the annealing process is apparently related to the solid state diffusion of the Zn dopant. 2010 The Korean Society of Industrial and Engineering Chemistry.
