Structure and dehydration of hydrous tin dioxide xerogel

Hydrous tin dioxide xerogel with the composition SnO2 • 1.75H 2O is built of tin-oxygen-hydroxide fragments. Water molecules (no more than 1 mol) in the grain structure are kept by hydrogen bonds. Xerogel is dehydrated in the range 50-890°C in two stages. Below 123°C, molecular water is removed and the polycondensation of ≡Sn-O(H)-Sn≡ bridge groups occurs. There also takes place the transition of some water molecules from the molecular to hydroxide form as follows: ≡Sn-O-Sn≡ + H 2O → 2≡Sn-O-H. All processes occur within individual grains. Above 123°C, water removal is due to the polycondensation of tin-oxygen groups. As a result, grains are coarsen. After 200°C, their structure is determined as cassiterite coated by tin oxyhydrate. © 2007 Pleiades Publishing, Inc.