Criterion of First Phase Choice at Reaction-Diffusion Processes

Criterion of First Phase Choice at Reaction-Diffusion Processes 

Formation and phase-growth processes observed in the diffusion zone at interdiffusion in a binary metal system often turn out to be different from the ideal case. 

Let us consider a solid-state reaction between two almost mutually insoluble materials A and B, at which we get two or more intermediate phases to form and grow. If for some reason, at a certain stage of a process, the layer of only one intermediate phase i starts growing with an average concentration (molar fraction) of the B component Cb = Ci, the growth rate of the thickness AX is defined as the product of the average interdiffusion coefficient D in this phase and the homogeneity interval width of the phase, Acii 

Here Xi is characteristic length, connected with the finite reaction rate at interfaces, and 

the difference between chemical potentials is determined by a simple approximate equation which is nominally similar to a finite-difference form of the second derivative in the concentration space  

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