Mechanism of scale formation

The mechanism of scale formation also determines whether a crack in the film surface layer can mend. If metal ions and electrons migrate outward, the oxide film propagates at the oxide atmosphere interface and the crack quickly closes. But when oxygen ions migrate inward, the oxide film propagates at the metal oxide interface and the crack cannot close. 

The mechanism of scale formation of each deposit is different. Calcium carbonate is the most common scale deposit. The solubility of CO2 decreases with increasing temperature and the equilibrium between CO2, COJ and HCO3 is upset. Bicarbonate ions break down (Temperature >70°C) causing liberation of CO2 and increase of C07 concentration. 

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