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 (SnCl₄·5H₂O) 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°C, until the solutions are completely precipitated (the precipitation started at 80°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°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 600⁰C, 800⁰C, and 1000⁰C. 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.