Is change of phase always reversible?

[trelek2]

If not please give me an example. I can't think of any... I also didn't come across any on the Internet...

 

[zero_delta]

The only example that comes to mind is that of a thermosetting polymer.

 

[Andy Resnick]

I can't tell what you mean, exactly- clearly, if water freezes and the ice is kept below 0 C, the phase change is irreversible. I wonder if you mean something more like a chemical reaction- when concrete sets for example, it will never revert back to it's dehydrated form... I don't know if it can be ground up and somehow processed back to the way it was.

Often 'irreversible' and 'equilibrium' must include the qualifier- 'how long do you want to wait'?

 

[Bob S]

In principle, yes, but carbon for example has 6 or more allotropes, including diamond, buckyballs, nanotunbes, etc. See
http://en.wikipedia.org/wiki/Allotropes_of_carbon
So melting or subliming some of these may not be reversible except in extreme conditions.
Bob S