[M-IS14] Interface- and nano-phenomena on crystal growth and dissolution

[MIS14-03] Visualization of pH distribution during calcium carbonate formation in gel media

Shinji Matsumoto², *Jun Kawano¹, Kousei Miki², Takashi Toyofuku³, Yukiko Nagai³, Takaya Nagai¹ (1.Faculty of Science, Hokkaido University, 2.Graduate School of Science, Hokkaido University, 3.JAMSTEC)

Keywords:pH, visualization, calcium carbonate polymorph

Recent progress in experimental and computational techniques has revealed that the growth mechanisms of minerals in aqueous solutions are more complicated than we had imagined. To understand these mechanisms, analyzing the local conditions of the crystal growth environment is important. Recently, we succeeded in visualizing the distribution of pH around a calcium carbonate crystal dissolving in an aqueous solution using a fluorescent probe. In the present study, this technique was applied to observe the change of pH distribution during calcium carbonate formation in gel media.
Here we performed the synthesis of calcium carbonate on the counter-diffusion method with agar gel by using CaCl₂ and NaHCO₃ solutions and observed the formation process under a laser confocal microscope. pH distribution during the process was visualized by using HPTS (8-hydroxypyrene-1,3,6-trisulfonic acid) as a fluorescent probe. As a result, rhombohedral and otoconia-like calcite and dumbbell-shaped aragonite were formed. Observation of pH distribution shows these deferent polymorphs formed in environments with different trends in pH change. Furthermore, the local pH environments in which they form could be different. These results could provide new insights into the knowledge of the formation of calcium carbonate polymorphs.