Experimental demonstration for the morphological evolution of crystals grown in gel media

The morphological evolution of the inorganic crystals (Ba(NO ₃)₂, NH₄Cl, H₃BO₃, and K₂Cr₂O₇) was demonstrated in various kinds of organic gel media (agar, gelatin, pectin, and poly (vinyl alcohol)). As the gel density increased, the morphology grown in the gel matrix remarkably changed from polyhedral single crystals exhibiting specifc habits into dendritic forms consisting of irregularly branched polycrystalline aggregates regardless of the sorts of inorganic compounds and gelling agents. The evolution from polyhedrons into dendrites via skeletal forms is ascribed to an increase in the influence of diffusion of the solutes on the crystal growth. Since gel media generally suppress the mobility of ions, densification of the media decreased the apparent diffusion rate of the solutes and finally promoted the formation of diffusion-limited morphologies including skeletal, dendritic, and branched forms. Peculiar curved and helical branches were observed in dendrites with crystals having a triclinic system (H₃BO₃ and K ₂Cr₂O₇) because the connections of subunits were deviated in the polycrystalline aggregates.