I have seen phase separation as a phenomenon taking place.However I do not understand why this phenomenon occurs as a counter example to the natural laws of diffusion along the concentration gradient.During phase separation the richer side becomes richer with the atoms which it already has and becomes more and more deficient with the poorer atoms and vice-versa.Similar things will occur in the opposite case as well.Now please give me an insight to this phenomenon with close reference to factors like Chemical Potential etc.
If we look at the G-x curve of the alloy at a temperature where they phase separate, we can see that the free energy would be lower if they phase separate.
Also, for diffusion to occur, the driving force is chemical potential difference, which can be obtained from the G-x curve. In this case, the chemical potential would decrease if the same atom gets added to the side which is rich in that atom.
Phase separation and Coarsening are well known natural phenomena and important in physical chemistry and metallurgy. I would suggest you to go through the theories of spinodal decomposition which is also known as uphill diffusion (that is associated with negative diffusion constant). Ostwalds ripening is yet another example. Below I refer to some of the seminal works in these topics.
1. Cahn, John W., and John E. Hilliard. "Free energy of a nonuniform system. I. Interfacial free energy." The Journal of chemical physics 28.2 (1958): 258-267.
2. Langer, James S. "Theory of spinodal decomposition in alloys." Annals of Physics 65.1 (1971): 53-86.
3. Oono, Yoshitsugu, and Sanjay Puri. "Computationally efficient modeling of ordering of quenched phases." Physical review letters 58.8 (1987): 836.
And a video lecture
https://www.youtube.com/watch?v=pxv8Wruycc4&t=69s
Dear Rajorshi Koyal,
Why it happens?
Reason is simple there is a development of concentration gradient either by weight, area, mechanism by drivers, speed of concentration liquid, aged by diffusion couples inter diffusion zones, equilibrium composition of miscibility gap etc. But mechanism to understand needs strong analysis to how it happened in the zones.
A concentration gradient occurs when the concentration of particles is higher in one area than another. In passive transport, particles will diffuse down a concentration gradient, from areas of higher concentration to areas of lower concentration, until they are evenly spaced. The bigger the difference, the steeper the concentration gradient and the faster the molecules of a substance will diffuse.
In biological cells, it is seen that Polar Positioning of Phase-Separated Liquid Compartments in Cells Regulated by an RNA Competition Mechanism can drive a gradient of P granule assembly with similar spatial and temporal characteristics to P granule assembly in vivo.
IN metallurgy, the aging of the diffusion-couple caused the age hardening due to the precipitation of nanometric secondary element -rich precipitates in a primary rich matrix.
When gasoline becomes saturated, a layer of ethanol and water, known as phase separation, can form in the tank. Phase separation occurs when water enters a tank that contains an ethanol/ gasoline blended fuel.
If really wish to know the fact, one should study the phase separation dynamics in a density-matched liquid mixture in the presence of a weak linear concentration gradient, can understand the nucleation and decomposition occur simultaneously. Concentration width where interconnected domains can grow linearly with time, in different zone. Here mechanism could be understood.
Ashish
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