Supervariate ceramics: phase diagrams of biomineral systems and tunning of their crystallization process

Abstract

Ceramics are a vital component of life to form the skeletons, teeth, shells, coccolith, etc. The most common biogenic ceramics are calcium carbonate for invertebrates and calcium phosphates for vertebrates. In contrast to the difficulty for modern technology to produce ceramics (due to their high hardness and melting points), how life effortlessly builds up stunning ceramic structures under mild aqueous conditions remains a big puzzle. Our recent research indicates that biomineralization might be accomplished through the multi-ionic amorphous gelatinous material produced from common salt precursor solutions (the supervariate strategy) which offers high stability and convenience in material storage, transportation, molding, fusion, and mending. Here this study reports the phase diagrams of a few key supervariate systems synthesized by mixing solutions of the Ca, Mg, carbonate, and phosphate (PO₄^3-, HPO₄^2-, or H₂PO₄^-) ions, the most abundant and essential ionic species for biogenic ceramics. It is revealed that the precipitation, gelation, and crystallization behaviors and hydration levels of the supervariate biomineral gels can be fine-tuned by simply controlling the ion compositions.

This study investigated the impact of NaCl addition on calcium carbonate crystallization, which has significant implications for various industrial processes, such as desalination and carbon capture. The experimental results indicated that the presence of NaCl had a significant effect on the size, morphology, and polymorph selection of calcium carbonate crystals. The NaCl concentration was found to affect the crystal morphology, with higher NaCl concentrations leading to smaller and more spherical crystals. Additionally, the presence of NaCl induced a shift in the preferred polymorph selection of calcium carbonate from calcite to aragonite. These findings provide valuable insights into the mechanisms underlying calcium carbonate crystallization in the presence of NaCl and can inform the design of more efficient and effective industrial processes

Chapter 1 gives an introduction to the research background of the properties, synthesis methodologies and applications of supervariate biominerals and amorphous calcium carbonate (ACC), respectively.

Chapter 2 interprets the mechanism and properties of phase diagram of supervariate biomineralization system.

Chapter 3 gives the characterization and result discussion of NaCl in tunning the crystallization process of calcium carbonate (CaCO₃).

Chapter 4 gives the characterization and result discussion of fusion and crystallization behavior of calcium carbonate (CaCO₃).

Chapter 5 gives the conclusions and future prospects of the thesis, which clarifies the highlights and outcomes of research works.

Date of Award	28 Oct 2025
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Yangyang LI (Supervisor) & Jian LU (Co-supervisor)