General kinetic equation one compound layer

The counterfluxes, jA and jB, of the A and B atoms across the bulk of the growing ApBq layer are assumed to be independent of each other as well. Indeed, in the ordered lattice of any chemical compound the atoms of each of its components can readily move on their own sublattice, thus not hindering the movement of the atoms of another component. 

Regrouping the terms of equation (1.21) gives an expression for the growth rate of the ApBq layer at interface 2 at the expense of diffusion of the A atoms and subsequent partial chemical reaction (1.2)  

Summation of the right-hand parts of equations (1.7) and (1.23) yields the general kinetic equation describing the rate of growth of the ApBq layer between initial substances A and B due to the simultaneous occurrence of partial chemical reactions (1.1) and (1.2)  

The only reason for the complicated look of equation (1.25) in comparison with equation (1.8) is that in general the values of the chemical constants k()m and k()A2 as well as those of the diffusional constants k]m and kU2 are not equal to each other. Even the proportionality of the diffusional 

Equation (1.27) produces a layer thickness-time dependence which at low values of x is close to the straight line 

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