Two compound layers short conclusions

In the reaction controlled regime the layer of each of two chemical compounds ApBq and ArBs grows at the expense of two partial chemical reactions taking place at its interfaces with adjacent phases. 

Each of two growing compound layers is a product in the two and a reactant in one of the four partial chemical reactions taking place in the A-ApBq-ArBs-B system. 

In most reaction couples, the layer formed first should reach a certain minimal thickness before the second layer can occur. Both compound layers will then grow simultaneously until the full consumption of one of initial substances A or B. 

In any binary system, the sequence of formation of compound layers is governed by the rate of chemical transformations (partial chemical reactions) at phase interfaces. 

The layer thickness-time kinetic relationships are in general rather complicated, not merely parabolic. Depending on the values of the chemical and physical (diffusional) constants, their different portions can be described by linear, paralinear, asymptotic, parabolic and other laws. 

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