title: Protrusion and rising of a gel-based precipitation layer.
abstract: Two types of unstable growth of a precipitation layer in gel are discussed. A cation and an anion that are reactive diffuse from opposite ends of the gel to its center. A white turbid zone forms due to their reactions. When the concentration ratios for both the ions are far from stoichiometry, the turbid zone expands toward the lower-concentration side. However, when the ratio is nearly stoichiometric, unstable growth occurs. In a glass tube, a protrusion of the precipitation region from the turbid zone grows, which forms a long needle-like shape. When a free surface is present on the gel, the precipitation region protrudes from the gel surface to form a rising structure. Mapping the growing structure on a concentration diagram and using scanning electron microscopy to examine contained particles suggest that the reaction is restricted to a narrow region and the reaction product migrates through a path formed in the protrusive structure to form a bulk solid at the edge.
authors.affiliation: Department of Chemical Engineering & Materials Science, Doshisha University, 1-3 Tatara Miyakodani, Kyotanabe, Kyoto 610-0321, Japan.
authors.forename: Akihito
authors.initials: A
authors.lastname: Suzuki
authors.forename: Shouhei
authors.initials: S
authors.lastname: Yamaguchi
authors.forename: Takahiko
authors.initials: T
authors.lastname: Ban
authors.forename: Akihisa
authors.initials: A
authors.lastname: Shioi