What is a subtance that when you put it in SLC, it will melt and then solidfy again?

Question

My friend asked me this and I know that there's gotta be a simple answer.

He said that there's no trick, no change in pressure, temp, etc.

Answer 1

Hi. I'll have to guess what SLC stands for. Any substance has to undergo a phase change to melt, usually by absorbing heat. This cools the medium from which the heat was drawn. A re-solidification usually gives off heat, in this case back into the medium. If the substance is a low melting point metal, such as Cerrolow, a eutectic alloy, the temperature difference does not have to be large, but your friend said NO temp change.... I'm thinking... Sorry, unless it is a really strange material like solid helium then I can't come up with any thing that does not violate conservation laws. (Please don't let the answer be "My heart" or some such! I worked pretty hard on this one.)