Evolution Equations for Order Parameters

3 EVOLUTION EQUATIONS FOR CONSERVED AND NON-CONSERVED ORDER PARAMETERS 

The Cahn-Hilliard equation applies to conserved order-parameter kinetics. For the binary A-B alloy treated in Section 18.1, the quantity in Eq. 18.22 is the change in homogeneous and gradient energy due to a change of the local concentration cB and is related to flux by 

Therefore, the accumulation gives a kinetic equation for the concentration cB(f, t) in an A-B alloy  

The first term on the right-hand side in Eq. 18.25 is diffusive. The second term accounts for interfacial-energy penalties from concentration gradients. 

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