Electrodeposition of nanocrystalline SnO2 coatings with two-layer microstructure

Nanocrystalline and two-layered SnO2 coatings were obtained by electrodeposition at 85 degreesC in nitric acid solution. The coating was composed of an upper porous layer and an underlying dense layer, about 400 nm and 12 mum, respectively in thickness for the coating deposited at -0.6 V vs. Ag/AgCl for 10 min. The porous structure of the upper layer possessed a large surface area of 34.3 m(2)/g, while the underlying high-density layer promoted the adhesion between the substrate and the porous layer. Both the upper and the underlying layers were constructed by nanocrystalline grains, and the sizes of the grains were 5 and 10 nm, respectively. The present study also showed that a very small amount of metallic Sn co-existed in the coating with a concentration of less than 3 mol%. Results from X-ray diffraction, deposition weight gains, X-ray photoelectron spectrum, scanning electron microscopy and transmission electron microscopy were described and correlated with the deposition reactions and characteristics of the coatings. In summary, although as a low-temperature process, the electrodeposition is of great potential to prepare nanocrystalline coatings with a high porosity and a good adhesion simultaneously. (C) 2004 Elsevier B.V. All rights reserved.