Abstract
Tubular agglomerates of calcium carbonate crystals (the CC-tubes) were formed from 1 M calcium chloride and 1 M sodium carbonate, and the formation mechanism was investigated. A cylindrical jacketed glass vessel was used as a crystallizer. The newly designed crystallizer was composed of two compartments that were divided by a cation-exchange membrane. The crystallizer was vertically placed and the two solutions were separately placed in each compartment. The CC-tubes were formed in vertical against the surface of the cation-exchange membrane in the upper sodium carbonate solution side. The growth of the CC-tubes was observed through a plane window of the top of the crystallizer by a digital microscope in order to study the growth mechanism of the tubes. In the early stage of crystallization, small cubic crystals appeared on the membrane. Although most parts of the membrane surface were covered with crystals, some small spots on the membrane surface were not covered with crystals. The CC-tubes grew from the uncovered parts. We concluded that the uncovered spots are important for the generation of the CC-tubes. A possible mechanism of the growth of the CC-tubes was proposed.
