課題番号 ：S-19-CT-0123
利用形態 ：共同研究
利用課題名（日本語） ：炭酸ストロンチウムのフラクタル結晶成長
Program Title (English) ：Fractal Crystal Growth of Strontium Carbonate
利用者名（日本語） ：カトヤ　ドレルップ1 、カートハウス　オラフ2
Username (English) ：Katja Drerup1, Olaf Karthaus2
所属名（日本語） ：1ドイツ・シュトゥットガルト大学、2公立千歳科学技術大学
Affiliation (English) ：1Universität Stuttgart, Germany, 2Chitose Institute of Science and Technology, Japan

1. Summary
Using a biomimetic method, strontium carbonate can be cocrystallized with silicate on different surfaces. Surfaces such as glass, polymer films and various pollen were used in this research. The goal was to analyze the crystal growth and crystal morphology depending on various parameters.
There is an equilibrium reaction of Sr2+ with SiO32- and carbon dioxide in an aqueous solution. The concentration of carbon dioxide can be controlled by adding dimethylcarbonate, which hydrolyses to methanol and CO2 and hence infleunces the crystal growth rate
After a certain period of time the samples were analyzed with a scanning electron microscope (SEM, JEOL JSM-7800F). While on the polymer films and some pollen species nearly no crystals could be observed, crystals on glass and on uneven pollen surfaces could be found. The shapes of the crystals varied from surface to surface and depended on the carbon dioxide concentration and the duration of the growth.
2. Experimental
Water, SrCl2, Na2SiO3 and dimethylcarbonate were mixed in a petri dish. Polymer films, either with or without embedded pollen grains were prepared by spin coating (Mikasa HD7) of a polymer solution on micro cover glass, which was then gently floated upside down on the solution. After 30 minutes to 3 days the glass cover was rinsed, dried and analyzed by SEM/EDS.

3. Results and Discussion

Fig. 1: SEM images of pollen with crystals on its surface.
Figure 1 shows crystals on two different kind of pollen. It was shown that an uneven pollen surface benefits the formation of crystals. The shape of the crystals cannot be predicted, but certain pollen seem to show tendencies to e.g. bulky, trumpet-like, pointed or brain-like crystals. The crystal shape within a sample on one pollen species is the same. A long growth period with a steadily low CO2 concentration resulted in many branched crystals, while a short time period with high concentration showed few bulky crystals. SEM images and EDX analysis show that the crystals contain strontium carbonate and silicon dioxide (Fig. 2).

Fig. 2: SEM images of pollen with crystal (left) and with elemental analysis of Si and Sr density (right).
4. Literature
[1] S. Kobayashi et al, E-J.Surf.Sci.Nanotechnol. 2017, 15, 65. [2] V. Fischer, O. Karthaus, Phys. Chem. Chem. Phys. 2015, 17, 6695.
5. Publication: none