Preparation of nanostructured tin oxide using a sol-gel process based on tin tetrachloride and ethylene glycol

A sol-gel process starting with tin tetrachloride and ethylene glycol as precursors, has been successfully used to prepare nanostructured tin oxide powders. The molecular structure evolution during the process has been identified using infrared spectroscopy and the underlying reaction mechanisms of the sol-gel process are proposed. Results suggest that the -OHCH2CH2OH- prevent Cl- ions from access to tin ions due to steric effect and hence increase the stability of the sol solution. Ethylene glycol functions not only as a complexion agent to form a polymer network but also as a spacer to modulate the distance between metal ions, preventing metal oxide particles from aggregation during earlier stages of organics removal. Further, conversion of xerogel to tin oxide are studied using thermogravimetric analysis, X-ray diffraction, and electron microscopy. It is found that cassiterite begins to form at a temperature as low as 250 degrees C when organics start to burn off. However, nanocrystalline tin oxide powders are formed only after the chemically bonded hydroxyl groups are completely removed at about 600 degrees C. (C) 1999 Kluwer Academic Publishers.