Fe with 10-12%Al forms alpha solid solution. but Al does not dissolve any Fe Why ?
Is it because of lower valency atom can dissolve higher valency atom and not vice versa.Al, valency is 3 and Fe valency is 2. if we put Al in Fe then, avg valency is 5/2= 2.5 which is more than the valency of Fe and less than Al. please comment.
It has nothing to do with valence. There are examples where low valence metals dissolve in metals with high valence, but also reverse (for example, Ni-Cu and Cu-Ni solid solutions). Moreover, iron dissolves very well in liquid aluminum, only in solid solution does not iron remain (max 0.052% at 655°C). Why it is so is naturally caused by the atomic construction, but is much more complex than simple "vanlence rules".
Isn't it as simple as simple as the difference in atom radiuses? It seems logical that smaller radius atom would fit in a structure made up from larger radius atoms, but not the opposite. (Especially if the structure is closely packed like FCC)
Copper forms a solid solution in aluminum, but the atomic radius of copper is slightly greater than that of iron (128 picometers versus 126 picometers).
The phase diagram tells you that there is an intermetallic phase on the Al-rich side which is energetically more favourable than dissolving Co in Al.
Why this happens is not simply answered by valence counting or ionic radii, otherwise there would be no need for people to do density functional theory to determine these things...
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