Normally the crystalline phase of a matter has a higher density compared to its liquid state (and therefore the solid phase sinks in its liquid).
Ice may be an exception (as its density is lower than that of water), but what about ceramic materials en metallic glass types? Do their amorphous phases always have a lower density compared to the crystalline phases?
And what is the difference in density between a crystal and the amorphous phase?
It's a rather interesting question. I am not pretty sure, but you could try to take a look at porous materials, e.g. zeolites or MOFs.
From minerals substances SiO2 has one of the largest volume growth in the transformation of crystalline in amorphous. Density of beta-quartz is 2.65 g/cm3 and of quartz glass 2.2 g/cm3.
With calcium carbonates, the formation of a crystalline phase from an amorphous state is normally guided by a dehydration step. Ikaite (CaCO3*6H2O, stable at low T) is more hydrated than its predecessor (presumably~CaCO3*1H2O), therefore the density decreases slightly upon crystallization. It must be said though that this is most likely a dissolution-reprecipitation mechanism, and therefore both compounds have little in common.
Dear Eric,
I'm sorry that I will not go into any particular examples. It seems crystalline state is the most efficient way (on certain structural level) to fill the space. It usually can be described in terms of "long-range order" or "close packing"... That's why the density of crystalline phase will be maximal. Disordered or "short-range" ordered amorphous state can't reach it because it isn't "packed" in optimal way (like the clothes in my closet :)).
Concerning real materials, hypothetically, there is a case when the "density of amorphous state" may be higher. It is when you have an impurity which is "heavier" (I mean with greater Z number) than your amorphous matrix. But just hypothetically.
Thanks for your question!
Andrei
Dear Erik Carton,
I have got the impression that your question lacks clear and sharp distinction of the cases to be envisaged.
1. The case of a compound of given composition that can be present as a crystal and in an amorphous state at the same temperature
2. The case of a glass as an undercooled liquid (e.g. window plane glasses) does not have its counterpart in a crystalline form.
3. Many polymers are semi-crystalline, so the comparison between crystalline and amorphous in these polymers depends on the respective volume fractions.
4. At the melting temperature of e.g. a pure metal, solid and liquid are in equilibrium. Solidification only proceeds at a certain undercooling as compared to the equilibrium melting/solidification temperature. So, it seems to me very difficult to expect that at the equilibrium temperature solid would sink in the liquid of the same composition.
5.I think that the free volume should be taken into account when considering the relative density.
6. I note that only one example of an amorphous compound having a higher relative density as compared to its crystalline counterpart is sufficient for a negative answer to your question.
According to the theory is that the amorphous alloys have lower density than the alloys of the same chemical composition but in a crystalline state. I made a lot of research and I often have a problem with that because all the studies show that the amorphous alloys which I investigated have a higher density than their crystalline counterparts.
Andreia. Krasilin gave a very good and reasonable answer.
Well, unfortunately the answer to this question is not simple :).
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