Synthesis of Tin Oxide Powders by Homogeneous Precipitation. Structural and Morphological Characterization

Tin oxide (SnO2) powders were synthesized by two different routes by using the homogenous precipitation method. In both routes tin chloride (SnCl4 center dot 5H(2)O) was used as Sn precursor. First route consisted in preparing, separately, aqueous solutions of tin chloride and urea (CH4N2O) with identical molar concentration (0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, and 1.2). The starting solutions were obtained from a 1:2 mix of Sn and Urea solutions (volume proportion), and then simultaneously stirred and heated at 93 +/- 5 degrees C, until the solutions are completely precipitated (the precipitation started at 80 degrees C). In the second route the same tin chloride starting solution was used, but the precipitation was activated with ammonia (NH4OH) instead of urea. The ammonia was added drop by drop until the pH reached a value of 12. In this route, the molarity values were varied from 0.05M to 1.3M. The precipitates were filtered and dried in a normal atmosphere (air at room temperature) at 100 degrees C for 24 hr. For some trials the repeatability of the process was tested, in both routes. Finally, all synthesized powders were calcined in a normal atmosphere at 600 degrees C, 800 degrees C, and 1000 degrees C. Structural analysis, before and after calcination, of all synthesized powders was performed by X-Ray diffraction (XRD) to confirm the SnO2 phase. The morphological characteristics of the powders were analyzed by Scanning Electron Microscopy (SEM) technique. Effects of precipitation agent (urea and ammonia) and the calcination temperatures on structural and morphological properties of SnO2 powders are reported in this work.