Nano-Amorphous Calcium Carbonate In Biomineralization

Recent results show that nano-amorphous calcium carbonate(ACC)plays important roles in calcium carbonate biomineralization.The assembly and phase transformation of ACC have great effects on the construction and orientation of crystals during the mineralization process.In this dissertation,we have studied the effects of inorganic and polyelectrolytes on the structure,synthesis,stability of ACC and the transformation mechanism from ACC to crystal phase.Furthermore,it is shown that ACC plays key roles in biomineralization.In addition,another improved strategy is provided for the biomimetic preparation of functional materials.Chapter 1:The research of biomineralization of calcium carbonate was reviewed and the background and contents of the dissertation was introduced.Chapter 2:The thermal behaviors of ACC and additive-ACC were detected by TGA/DSC.The phase transformation of ACC and additive-ACC was studied and characterized by IR and XRD in the presence of water.It was shown that water promoted and accelerated the transformation of ACC.Metastable vaterite or aragonite was obtained in the presence of low amount water and would transform to most stable calcite finally.But ACC could transform directly into calcite in the presence of high amount wate.In both the water-induced and the thermally-driven transformation of ACC,polyelectrolytes inhibited the crystallization process of ACC.It was proved that water and polyelectrolytes had important effects on the transformation of ACC.Chapter 3:The transformation of ACC was studied more in the presence of poly (4-sodium styrene sulfonate)(PSS)and a novel and simple method for the preparation of hollow calcium carbonate nanospheres under mild conditions was developed. Hollow vaterite nanospheres were achieved by low amount water-induced phase transformation of poly(4-sodium styrene sulfonate)-stabilized amorphous calcium carbonate(PSS-ACC)at room temperature.It was found that the sizes of resulted hollow structured nanospheres could be easily regulated by the content of PSS and the phase transformation could be greatly affected by the volume ratio of water to ethanol. A combination effect of PSS and water was emphasized in this formation process.It is important to control the amounts of PSS and water in the experiments so that a large scale of hollow vaterite nanospheres with different sizes can be achieved.Chapter 4:The effect of magnesium ion on the transformation of ACC was studied.ACC containing Mg ion had been synthesized by mixing sodium carbonate solution and calcium chloride solution in the presence of Mg ion at 4-6℃.It was shown that the magnesium content included in ACC directly affected the morphology and crystal phase of the products,which were also influenced by the water amount and transformation time.Aragonite could be obtained by Mg solution-induced transformation of the ACC.Chapter 5:Two kinds of ACC were synthesised in the absent of any additives. The preliminary results showed that they might have different fine structure.