Why are solid solution alloys rare?

Answer 1

I'm not sure I understand your question. You see, by definition, all alloys are solid solutions, and there are plenty of alloys, like brass, steel, etc. Even the purest metal samples are actually alloys, as they always contain minor traces of other metals.

Solid-liquid solutions are also very common. The same goes for liquid-liquid solutions, gas-liquid and gas-gas.

What is very rare, however, is solid-gas solutions, with the best known example being a solution of hydrogen gas in palladium metal. Why this happens is, to my regret, mostly unknown. It might help to know that investigations have shown that hydrogen atoms basically distribute themselves randomly in the "gaps" in palladium's crystal molecular structure.

Answer 2

Solid solution alloys are rare because the size and shape of atoms must be similar for them to mix together in a solid solution. This limitation means that only a small number of elements can form solid solutions with each other. Additionally, factors such as differing crystal structures or electronegativity can further limit the formation of solid solution alloys.