In article , Tim Williams says...

And so on and so forth; the eutectic layers interact through contact,
diffusion, and mutual solubility on melting to once again form an homogenous
liquid.

This is the realm of solid-solution chemistry. It's really very,
very complicated. There are folks who make entire careers out of
understanding things exactly like this.

The details of how this stuff works is of considerable technological
interest. There are books just full of nothing but phase diagrams
for different alloy compositions.

The original question I think was looking for a very basic
intuitive answer. I didn't reply because I thought he did
not want to hear about phase diagrams, etc.

Also because it was a 'why' question and I'm not very good
at those - better at "how" questions.

Jim


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