Spinodal decomposition of binary alloys

When solid alloys have a positive heat of mixing, AHm, complete solid solution occurs above the temperature where TASm is more negative than the heat 

The kinetics of spinodal decomposition is complicated by the fact that the new phases which are formed must have different molar volumes from one another, and so tire interfacial energy plays a role in the rate of decomposition. Anotlrer important consideration is that the transformation must involve the appearance of concenuation gradients in the alloy, and drerefore the analysis above is incorrect if it is assumed that phase separation occurs to yield equilibrium phases of constant composition. An example of a binary alloy which shows this feature is the gold-nickel system, which begins to decompose below 810°C. 

These Huctuations lead to two more components to the Gibbs energy changes in the process. The hrst arises from the fact that the Huctuations represent a local gradient in composition, and hence there is a change in the number of 

If a fluctuation has a wavelength which is less dran this critical value, it will not be stable but will decay. 

E is Young s modulus and Vav is die average molar volume. Summing these terms the total Gibbs energy change accompanying the fluctuation, AG is 

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