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when does melting occurs?


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I have learnt a module about phase transformation. It states that melting occurs at the melting point because the liquid can always wet its solid,mathematically, it is [math]\gamma_{SV}>\gamma_{SL}+\gamma_{LV}[/math].

 

I am wondering does it mean that melting can occurs a bit lower than the melting temperature because the interfacial energy also perform as a kind of driving force.

 

In addition, can anyone think a way that make melting starts from inside the solid not the surface?

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Under many conditions there will be some vapor and liquid present below the melting point, but AFAIK it's at the surface. But the melting point is the melting point — it accounts for whatever is happening the interface (it's at a specified pressure)

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The energy distribution of molecules accounts for the fact that some melting occurs below the melting point; it's just in equilibrium with freezing at the same temperature. If you had pressure differences throughout the solid, couldn't you start melting from the inside?

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I think melting from the inside could occur if you uniformly heated the object just up to before its melting point at a certain pressure. Then once uniformly heated, begin to cool the object on the suface. Then instananeously decrease the pressure on the object. The molecules inside which are hotter on the inside will move more freely on the outside and you might be able to get some internal melting if you don't decrease the pressure too much or cool it off too little.

 

I think...:doh:

 

Otherwise the only way I can imagine internal melting is if the object was made of two material, the material in the center having a much lower melting point than the 2nd.

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