Hydration protective layer model

Popular models of hydration of clinker minerals can be divided into the delayed nucleation model and the protective layer model. 

The mechanisms that have already been described for pure cement compounds form abasis for a study ofthe hydration mechanism of portland cement. The conduction calorimetric curves of C3S and portland cement are similar except portland cement may yield a third peak for the formation of monosulfate hydrate (Fig. 1). The detailed influence of C3A and C4AF on the hydration of C3S and CjS in cement is yetto be worked out. The delayed nucleation models and the protective layer models, taking into account the possible interactions, have been reviewed. 1 1 Although the initial process is not clear for C3S (in cements), it appears that C3A hydration products form through solution and topochemical processes. 

Corrosion and Passivity. The inhibition of dissolution is important m the corrosion of metals and building materials. Passivity is imparted to many metals by overlying oxides, the so-called passive films the inhibition of the resolution of these passive layers protects the underlying material. Figure 13 eves a schematic model of the hydrated passive film on iron. 

---