I would say that most materials can be crystallized and many of to high levels of crystallinity (grain boundaries or triple points may remain amorphous). Single crystals may be very difficult to produce and might require melting and controlled solidification. The most notable exception is probably polymers. While crystallization would result in a lower energy configuration for the polymer, this is often prevented (especially for polymers with complex structure and long chain lengths) because of the large configurational space of the polymer that is associated with bond rotation. The large configurational space allows the polymer chains to tangle, which physically constrains them and prevents them from reconfiguring into a crystal. The polymers that do crystallize are often only semicrystalline because of this.
If I understand you right, you don´t mean only a crystallization of an amorphous material by annealing. Maybe you mean a quasicrystal. It is not amorphous, but also not periodic. In the mean time, lots of quasicrystalline materials are prepared, for instance V-Ni-Si and Cr-Ni-Si alloys. But also natural quasicrystals exist.The alloy Al63Cu24Fe13 is quasicrystlline and was named icosahedrite.
Normally amorphous materials will be transformed into crystalline material by ageing. Complex materials take sometimes long time to be transformed meanwhile simple materials can ever be transformed in few hours. Precipitated materials while in contact with solution can dissolve and recrystallize into crystalline form (at least partially crystalline) in a slow process. This transformation in usually named as ageing.
Silas Derenzo: Can you name some of the materials for example ?
Hans-Ulrich Krebs: I meant only amorphous material, for example: Glass (silicate). Can glass (for example) can be crystallized ?
Yes, silicate glass can also be crystallized by annealing at higher temperatures.
But there are also a lot of other amorphous materials, like polymers (often) or metallic glasses (ZrCu, ZrFeB, ...). Look also for instance at William Johnsons articles for bulk amorphous metal glasses.
All amorphous materials can be crystallized (an amorphous structure is metastable), however getting an amorphous material to crystallize into a single crystal? That would be extremely difficult.
Some remarks:
1. Many biomaterials are amorphous by nature.
2. For all transformations it holds that the thermodynamics must be obeyed.
3. For many materials it holds that the amorphous state is metastable as compared to the crystalline state, then on principle the transformation 'amorphous --> crystalline ' is possible, but the kinetics determine whether or not this transformation proceeds.
4. Single crystals do not automatically represent the most stable form of crystalline matter.
5. In preparing single crystals, the kinetics play a key role.
Thanks :)
Hans-Ulrich Krebs, Lawrence Margulies, P. Van Mourik.
Margulies and van Mourik are absolutelly right! Just to answer your question, many precipitation products undergo this pathway: for example hydroxyapatite, a material obtained by precipitation takes some days to be trasformed partially into crystalline material.
The kinetics of transformation, as pointed out by van Mourik, determines the possibility of transformation and if ambient conditions are properlly adjusted this transformation can be enhanced or dellaied. Diamonds are crystalline carbon meanwile it is totally amorphous at stadndart conditions.
I would say that most materials can be crystallized and many of to high levels of crystallinity (grain boundaries or triple points may remain amorphous). Single crystals may be very difficult to produce and might require melting and controlled solidification. The most notable exception is probably polymers. While crystallization would result in a lower energy configuration for the polymer, this is often prevented (especially for polymers with complex structure and long chain lengths) because of the large configurational space of the polymer that is associated with bond rotation. The large configurational space allows the polymer chains to tangle, which physically constrains them and prevents them from reconfiguring into a crystal. The polymers that do crystallize are often only semicrystalline because of this.
Given the above discussion, the answer to the question 'Can any amorphous material etc?' is clearly: no!
Not all materials can be crystallized. Atactic polystyrene is an example of a polymer that does not crystallize, for example. This polymer exhibits a glass transition temperature, but no crystallization temperature or melting temperature.
That's only because the heating rate is too fast. If you heat it just below the melting temperature for long enough it will crystallize.
wait, did you actually say it has no melting temperature? Wow, hopefully that was a typo or I just wasted my time responding.
So you are saying it goes directly from a polymer form to a gas on heating? Ring up the guys in Sweden!
No, it is viscoelastic and exhibits a glass transition temperature. That is, it softens over a wide range of temperatures instead of having a melting temperature. Not all materials melt so this is not that strange. Some materials decompose or sublime into a gas.
Yes sublimation is possible, but it will still crystallize if kept under the sublimation temperature for long enough.
Dear Arumugakani
Which material you are talking about? please specify your question, otherwise the discussion has no bounds.
In order to have a crystalline structure, you need a repeating unit (unit cell), that allows to build the crystal according to symmetry operations. In atactic polymers, for example, you cannot define an unit cell, therefore you cannot have a crystal structure. It is not a technological issue, it is impossible by definition.
Andrea, I am not saying that a polymer can be crystalline. Of course that makes no sense. I am saying that a polymer will crystallize (a phase transformation) under the right conditions (T,P), since it would be a lower energy state. An amorphous structure is a meta-stable state thermodynamically. It is only the slow kinetics at ambient conditions that allow the structure to persist for an appreciable time scale. I hope that clears up the confusion.
Andrea, you are correct in that there is no crystal structure for an atactic polymer with a large side group. Polymers crystallize by chain folding. No amount of time at any temperature or extent of folding will allow the disordered side groups to somehow be ordered into a crystalline structure and so they can only be amorphous.
To circle back to the answer to the original question: No, not all amorphous materials can be made crystalline. This is not just my opinion. This information is readily available in polymer textbooks and there is plenty of good information on the internet. If this is not convincing to anyone, then we must agree to disagree.
I have to admit that doesn't make much sense to me. If you have a metastable structure and you give it enough energy (by temperature, pressure, E/M fields, etc...) to overcome the activation energy needed to form a nuclei, you will get a 1st order phase transformation (not chain folding) to a lower energy structure. It may be kinetically a very slow process, but it will occur, even at ambient conditions given enough time. It's a question of thermodynamics versus kinetics, which often leads to a lot of misunderstanding when thinking about what an equilibrium structure is.
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