Abstract: The kaolin-based porous substrates were prepared by press molding-sintering method， and the surface morphology and porestructure of kaolin-based porous substrates prepared at different sintering temperatures were investigated. In₂O₃ micromaterials were synthesized on the surface of kaolin-based porous substrates by thermal evaporation method. The morphology and structure of kaolin-based porous substrates and In₂O₃3 micromaterials were investigated by XRD， SEM， FTIR and Archimedes drainage method. The results indicate that the optimal kaolin-based porous substrate at the sintering temperature of 1 200 ℃ shows the pore size of approximately 45 μm， the apparent porosity of 32.71%， the bulk density of 1.48 g/cm3， and the flexural strength of 15.08 MPa. In₂O₃ products prepared on the substrate has a comb structure with good crystallinity.The diameter and length of comb finger are in the range of 1~10 μm and 20~80 μm， respectively， and the length of comb handle is about 1 mm. Gas sensing results show that the In₂O₃ microcoms has good selectivity， reversibility and repeatability for NO₂ gas. Its sensitivity to NO2 concentration of 0.001% gas increases first and then decreases with the increase of operating temperature， and response time and recovery time reduced with increasing operating temperature. The maximum of the sensitivity of 44.4 was obtained at an optimum operating temperature of 200 ℃. The response time and recovery time are 21 s and 106 s， respectively. There is a linear correlation that the sensitivity of the In₂O₃ microcombsincreases with increasing NO₂ gas concentration. The response time is shortened as the NO₂ concentration increases， and the recovery time increases as the NO₂ concentration increases.

Key words: Kaolin-based porous substrate, In₂O₃micromaterials, NO₂, Gas sensing properties