抄録
The crystal shape of calcium hydroxide (Ca (OH) 2) is characterized by hexagonal plate-like crystal in the same way as that of kaolinite clay. The calcium hydroxide could be expected as new raw material instead of the clay for inorganic filler in paper, plastics and rubber. In the present work, attempts were made to investigate the effect of synthetic conditions of the CaCl2-Na OH reaction on crystal forms such as size, shape and homogeneity of Ca (OH) 2 crystal, the most suitable synthetic conditions for artificial control of the crystal forms were clarified.
The homogeneity of crystals was mainly influenced by the rate of dropping NaOH solution into CaCl2 solution, and the rapid dropping of 200 ml/sec found to be effective. The crystal size and shape were easily controlled by the concentration and the temperature of reactant solutions. At the temperature 20°C, the concentration above 0.5 N gave fine crystals below 1 μm and the concentration below 0.25 N gave truncated crystals of hexagonal pillar of about 3×6 μm. At the temperature above 50°C, the crystal consisted of hexagonal pillar with the developed (001), (010) and (100) faces but the crystal size changed to fine particle as the result of decrease in solubility of Ca (OH) 2 at high temperature.
The controls of thickness and width of Ca (OH) 2 crystal were made easily by dropping NaOH solution into CaCl2 solution containing methanol. That is, the thickness of the hexagonal pillar-like crystal was controlled without changing plane width of the crystal as the result of friction of (001) face in layer structure by adding methanol and then the width of the plate-like crystal was controlled by changing the synthetic concentration and temperature. It made possible to synthesize homogeneous crystal with thin hexagonal plate.
