Synthesis of tin oxide (SnO2) by the oxallate route:: Effects of addition method and ageing

Aqueous solutions of tin (II) chloride dihydrate and oxalic acid dihydrate (both 0.04 M) were prepared and mixed by (1) dropwise addition and (2) instantaneous addition, with both involving addition of the latter to the former. Following filtering, washing, and drying, the precipitates were calcined and ground. The particle size and morphology of uncalcined and calcined tin oxalate were examined by electron microscopy and laser diffraction. The method of addition was important in that it influenced both the particle size and shape of tin oxalate. This resulted from the time effect of the ionic collision frequency and the proximity effect of the diffusion distance. As expected, ageing was important in that it caused grain growth and reduction of surface area of the tin oxalate. Although there appeared to be an effect of the method of addition on agglomeration of the tin oxide, this was a result of adsorption of atmospheric moisture, which depended on the relative humidity of the environment during grinding.