Abstract
Calcium carbonate was crystallized by using a specially designed device for crystallization that is a jacketed cylindrical glass tube placed in the lateral and divided into two compartments by a cation-exchange membrane. Solutions of calcium chloride and sodium carbonate were separately placed in each compartment. Calcium ions penetrated into the opposite compartment through the cation-exchange membrane, and there reacted with carbonate ions. Calcium carbonate crystals grew on the surface of cation-exchange membrane and formed cylindrical tubes self-assembled in vertical against the membrane surface. Inner and outer diameter of the cylindrical tube formed at 50°C was about 15 and 30 µm respectively, and the length was 200-400 µm. Most of the calcium carbonate tubes were composed of micro-crystals of the calcite. Micro-crystals of the vaterite also formed cylindrical tubes in particular in the early stage of crystallization.
