Okada Shuhei, Kurahashi Naoya, Tanida Yukihiro
Marketing Headquarters, Yokogawa Electric Corporation, Musashino City, Tokyo, Japan.
Department of Fundamental Technology, Kyoto Prefectural Technology Center for Small and Medium Enterprises, Kyoto City, Kyoto, Japan.
PLoS One. 2025 May 12;20(5):e0323421. doi: 10.1371/journal.pone.0323421. eCollection 2025.
Vaterite is a crystalline polymorph of anhydrous calcium carbonate (CaCO3), which exhibits relatively low stability compared to other two polymorphs, calcite and aragonite. Vaterite particles have properties such as large specific surface area, high porosity, and high solubility; hence, research has been made in wide range of applications from material additive to drug delivery. X-ray diffractometry (XRD) is capable of identifying polymorphs of calcium carbonate. However, depending on the base material and the installed state, it may not always be suitable for non-destructive observation. This study reveals that vaterite-to-calcite crystal phase transition degree can be quantified by the absorption spectrum in terahertz range. The vaterite concentration and the terahertz absorption peak intensity near 3.3 THz showed linearity with correlation coefficient of R2 = 0.934 in our experiment. The findings allow us to quantitatively evaluate vaterite-to-calcite crystal phase transition in non-destructive and non-invasive way.
球霰石是无水碳酸钙（CaCO₃）的一种晶体多晶型物，与其他两种多晶型物方解石和文石相比，其稳定性相对较低。球霰石颗粒具有比表面积大、孔隙率高和溶解度高等特性；因此，人们对其在从材料添加剂到药物递送等广泛应用领域进行了研究。X射线衍射法（XRD）能够识别碳酸钙的多晶型物。然而，根据基材和安装状态的不同，它可能并不总是适用于无损观测。本研究表明，球霰石到方解石的晶相转变程度可以通过太赫兹范围内的吸收光谱进行量化。在我们的实验中，球霰石浓度与3.3太赫兹附近的太赫兹吸收峰强度呈线性关系，相关系数R² = 0.934。这些发现使我们能够以无损和非侵入的方式定量评估球霰石到方解石的晶相转变。
