Fyndium
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Registered: 12-7-2020
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Rate of crystallization
Do you have any specific routine when crystallizing stuff? Do you put it in cold space or fridge, let it just cool at room temp, or insulate the
container somewhat to slow down the cooling rate to grow much larger crystals?
I dug through this topic a little when I faced the fact that fast crystallization, or worst case crashing will cause a lot of impurities, inclusions
and other non-wanted gunk so I thought would it be good idea to put the flask in an insulated box to cool it slowly? Now that it's getting cold
outdoors, a styrofoam box would slowly go all the way down to 0, instead of room temp.
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teodor
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Registered: 28-6-2019
Location: Heerenveen
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It depends on the salt properties and impurities. Iron will precipitate with copper even being in very small amounts, so crystallisation doesn't help
for the separation of these two.
Problem with small crystals (rapid crystallisation) that they have very big absorption properties, some salts like BaSO4, even PbCl2 very hard to get
pure from solution which contains other ions.
One method of getting PbCl2 is layering, I did a post about that.
I try to get average size of crystals if possible.
And if I need exclude some impurity I try to do it as much as possible by chemical way before the crystallisation.
Also consider that many of salts should be crystallised from acidic solution and they hold the traces of acid.
In SM library, for example in Henderson & Fernelius there are a lot of good excercies to make crystallisation of different types of salts.
[Edited on 26-10-2020 by teodor]
[Edited on 26-10-2020 by teodor]
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