Particular attention has been paid to the "age" of the starting solution for a liquid phase synthesis of ceramic nanoparticles. That is, starting solutions were prepared and kept in a container for several days and then were used to make a precipitation. Metal oxalates (hydrate) were precipitated from ethanolic solutions of oxalic acid and metal nitrate (hydrate). Aging of the starting solutions resulted in a marked delay of the precipitation. Silica spheres were prepared from ethanolic solutions of tetraethylorthosilicate (TEOS) and ammonia water. Aging of the starting solutions enhanced the size and monodispersibility of the spheres. We infer that the delay in precipitation is due to microscopic homogenization in the solution structure among ethanol, water, and solute species. That is, even when the prepared starting solutions look clear, transparent, and homogeneous, they may involve less-dispersed aggregates of solute/solvent, which would enhance heterogeneous nucleation to reduce the delay.

Keywords: aging, oxalate precipitation in ethanolic solution, oxalic acid, silica sphere, Stober method