Calcium oxalate crystallization in silica and sugar solutions-characterization of crystal phases and habits

The effects of silica (SiO2) and sugar on the crystallographic and morphological properties of calcium oxalate (CaOx) have been investigated using instrumental techniques including X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). Addition of SiO2 or sugar in a CaOx crystallization system promoted the formation of COT (calcium oxalate trihydrate) and COD (calcium oxalate dihydrate), respectively, and modified the crystal size and habit of COM (calcium oxalate monohydrate) crystals, the extent of which was dependent on the concentrations of SiO2 and sugar. A variety of mechanisms including electrostatic effects, geometrical matching and stereochemical compatibility between CaOx crystallites and polymeric SiO2/sucrose molecules have been proposed.