4.5. HOW IS ACC FORMED?

Figure 4.7: Representation of the molecular structure of amorphous Calcium carbonte (ACC).

Classical Nucleation Theory:	Non-Classical Theory:	Alternative Route (liquido-liquido separation)¹ :
Classical Nucleation Theory: nucleation is a stochastic process where thermodynamic fluctuations induce cluster formations (atomic groupings) which are highly unstable in relation to dissolution – the atoms conglomerate and separate, and the clusters fall apart with the same ease as they form. Eventually the clusters can increase in size and free energy, until a certain limit (of instability, or difficulty in keeping itself thermodynamically stable) is passed, after energy gains by forming groups overcomes the inherent onus of interface creation, and growth continues spontaneously.	Nonclassical nucleation theory: recent observations of long lasting nanometric atomic clusters present before nucleation brought a new predominating vision of the formation of CaCO₃ where the nucleation pathway is “nonclassical”, involving stable prenucleation groups (or metastable) in relation to both dissolution and growth. In this model, large quantities of CaCO3 are formed primarily by aggregation of these clusters.	Alternate Routes (liquid-liquid separation): the persistence of a liquid phase of CaCO₃ stabilized by polymers under environmental conditions, in a immiscible supersaturated phase form, regulated by factors such as pH. This model wasn’t witnessed through direct experimentation, only through virtual environment simulations (mathematical modeling); but, it is quite befitting the observed phenomenon in intra and extracellular nucleation zones. From this bi phase solution (supersaturated vesicles of hydrated CaCO₃ in the middle of another liquid phase) the clusters organize themselves in the formation of an amorphous solid phase, precipitated in specific regions on the surface.

Classical Nucleation Theory:

Non-Classical Theory:

Alternative Route (liquido-liquido separation)¹ :

Classical Nucleation Theory: nucleation is a stochastic process where thermodynamic fluctuations induce cluster formations (atomic groupings) which are highly unstable in relation to dissolution – the atoms conglomerate and separate, and the clusters fall apart with the same ease as they form. Eventually the clusters can increase in size and free energy, until a certain limit (of instability, or difficulty in keeping itself thermodynamically stable) is passed, after energy gains by forming groups overcomes the inherent onus of interface creation, and growth continues spontaneously.

Nonclassical nucleation theory: recent observations of long lasting nanometric atomic clusters present before nucleation brought a new predominating vision of the formation of CaCO₃ where the nucleation pathway is “nonclassical”, involving stable prenucleation groups (or metastable) in relation to both dissolution and growth. In this model, large quantities of CaCO3 are formed primarily by aggregation of these clusters.

Alternate Routes (liquid-liquid separation): the persistence of a liquid phase of CaCO₃ stabilized by polymers under environmental conditions, in a immiscible supersaturated phase form, regulated by factors such as pH. This model wasn’t witnessed through direct experimentation, only through virtual environment simulations (mathematical modeling); but, it is quite befitting the observed phenomenon in intra and extracellular nucleation zones. From this bi phase solution (supersaturated vesicles of hydrated CaCO₃ in the middle of another liquid phase) the clusters organize themselves in the formation of an amorphous solid phase, precipitated in specific regions on the surface.