Phase Transformation Of Amorphous Calcium Carbonate

Biogenic calcium carbonate is one of the most widely distributed biominerals in nature, which the main component is inorganic phase of calcium carbonate and a small amount of organic phase is involved either. Recent study shows that amorphous calcium carbonate (ACC) plays as a precursor role, which has variability, plasticity, controllability and other properties. In this dissertation, we study the effect of both physical factor and chemical factors on the transformation of amorphous calcium carbonate. The main contents of this dissertation are as follows.Chapter 1:Biomineralizaiton of calcium carbonate was reviewed and the background of the dissertation is introduced.Chapter 2:In this chapter we use FTIR to measure the crystallization of ACC semi-quantitively from the methodological point.Chapter 3:In the chapter, amorphous calcium carbonate (ACC), a key model compound in biomimetic mineralization studies, is synthesized and dispersed into inert dispersants with different viscosities and the crystallization process is examined by using FT-IR spectroscopy and XRD. It is found that the inhibition of the transformation of ACC becomes more significant with increasing fluid viscosity. This phenomenon can be explained by the differences in ion diffusion in different media. Furthermore, the resulting crystals always have different morphologies and size distributions although they all have the calcite structure. This study implies that the importance of the fluid medium cannot be ignored in building a complete under-standing of biological control of biomimetic crystallizations.Chapter 4:The promotion of Mg2+for the formation of aragonite has been extensively studied in biomineralization. However, all the works mainly focuses on the polymorph switching. The details of the transformation of amorphous calcium carbonate into aragonite are seldom reported. In this chapter, we use powder X-ray diffraction, FTIR spectroscopy and scanning electron microscopy to monitor this process and found that in high ratio of Mg2+/Ca2+, there is a multiple step and contains a self-assembling process of nanoparticles. That the growth of aragonite is via the nanoparticles assemblying may have a great significance in understanding the mystery of aragonite formation, and have a potential significance in vivo experiment in biomineralization. Besides, the cooperation of PAA, PSS and Mg2+for the transformation of ACC is studied. The result shows that these additives can alter the crystallization of ACC and control the crystalline phase of the products.Chapter 5:Summary...