球状バテライトから針状アラゴナイトの生成

抄録

　This study conducts basic research on formation of needle-like aragonite from spherical calcite. This study investigates formation of needle-like aragonite from spherical calcite. The single spherical vaterite phase was synthesized by adjusting the initial pH to 2.5 in the CaCl₂–Na₂CO₃–H₂O reaction system. Spherical vaterite was suspended in pure water at 60–92℃. At a suspension concentration of 2.5 mass% and a reaction time of 2 hours, vaterite dissolved and precipitated to form aragonite and calcite at temperatures above 77℃. The formation rate of aragonite was more than 85%. The long length of the formed needle-like aragonite was 35 μm and the aspect ratio was 30. The short length of aragonite increased with increasing temperature. The critical amount of vaterite to aragonite was determined by varying the suspension concentration and time. The critical amount increased with increasing temperature, reaching 3.6 g・100 cm^－3 at 90℃. The short length of the aragonite formed became longer as the suspension concentration increased.