[DTU student #12]

Some crystals will undergo amorphization prior to melting, for example MOF and ZIF crystals. I have analyzed this by combination of DSC and X-RD, and they do become amorphous before they melt. But how can they melt if they are amorphous?

As I understand, melting as a first order phase transition, should be "reserved" for crystalline materials?
And amorphous materials should have a glass transition. So when the crystal become amorphous, and loses all bragg peaks in X-RD, how can it melt afterwards?

In amorphization, is some of the crystal regions maintained somehow, even though it does not have any bragg peaks?

[Enthalpy]

I'd say (please take with mistrust):

In solids, even amorphous, the chemical and intermolecular bonds stay among the same pairs of atom, while in liquids, the bond from an atom jumps more easily from one partner to an other?

Then, a liquid is different from both an amorphous and a crystalline solid.

[Intanjir]

Do you have a phase diagram for such a material?

Is it possible that there are two very different crystal forms and that the lower temperature form becomes disordered as temperature increases but that the material is initially unable to reorganize into the new stable form in a reasonable time frame? Then as temperature increases the new form would crystallize and then eventually 'melt' once the amorphous state was the truly thermodynamically stable form.

[DTU student #12]

I am afraid I do not have a phase diagram for the material. I cannot find much information about it, so I suspect it is quite "new" it that regard.

There are an exotherm peak prior to melting in the DSC curve, which I am quite sure is due to a recrystallization. However, the product is heated and cooled by 10K/min, and the melt-quenched sample is entirely amorphous in the X-RD, so I am not sure whether the heating/cooling rate is low enough for nucleation and crystal growth to occur.