Preparation of grain size-controlled tin oxide sols by hydrothermal treatment for thin film sensor application

Colloidal dispersions of crystalline SnO2 (sols) with a mean grain (crystallite) size controlled between 6 and 16 nm were prepared successfully from stannic acid gel by hydrothermal treatments under the condition of pH 10.5 and 200 degreesC or pH 12.2 and 250 degreesC. The growth of crystallites saturated in a few hours of hydrothermal treatment and the saturation values tended to increase with increasing SnO2 gel content, pH and temperature. The SnO2 grains remained monodispersed unless time of hydrothermal treatment was excessive. Thin films of SnO2 prepared on an alumina substrate from the sols by a spin-coating method responded sharply to H-2 gas. The magnitude of sensor response as well as its dependence on operating temperature were different significantly depending on the grain sizes of the starting sols. Among the sols with a mean grain size of 6, 8.5, and 10 nm, the last two gave large response to H-2, which reached a maximum at 400 or 350 degreesC, respectively. (C) 2004 Published by Elsevier B.V.