Preparation and Gas Sensor Application of Ceramic Particles with Submicron-Size Spherical Macropores

Porous SnO2 and In2O3 powders (pr-SnO2 and pr-In2O3, respectively) were prepared by pyrolysis of atomized SnCl4 and In(NO3)(3) aqueous solutions containing polymethylmethacrylate (PMMA) microspheres (150 nm or 250 nm in diameter) as a template. Spherical macropores reflecting the morphology of the PMMA template could be formed in the pr-SnO2 and pr-In2O3 powders. H-2 response of the pr-SnO2 was low, but addition of Pt was effective for improving the H-2 response of the pr-SnO2. In addition, simultaneous loading of Pt and doping of Sb2O5 resulted in the largest H-2 response along with relatively low resistance in air. On the other hand, a pr-In-2-O-3 sensor showed much higher NO2 response than a conventional In2O3 sensor, which was fabricated with the nonporous powder prepared by hydrolysis of indium nitrate by an ammonia solution. These results show that introduction of macropores into ceramic powder used for sensor materials is very effective for improving their sensing properties.