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Author: Subject: Drying, grinding and sieving of powders?
Fyndium
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[*] posted on 21-9-2020 at 06:25
Drying, grinding and sieving of powders?


When drying precipitates, is it necessary and or how do you usually break the lumps? Do you agitate the mass during drying to facilitate faster evaporation or just let it dry completely and then sieve it to container? What is the best method of grinding powders when generally speaking of organic compounds?
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Maurice VD 37
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[*] posted on 21-9-2020 at 11:39


You also may use a mortar and grind the lumps with a pistil
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macckone
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[*] posted on 21-9-2020 at 11:50


There are a lot of questions there.
1) sometimes lumps are a big deal and other times they aren't, it depends on what it is and what you are using it for.
2) sometimes I agitate and sometimes I don't, it depends.
3) it depends. Mortar and pestle are fine for some things, other things I just use a scoop to break it up, still others I use a grinder or ball mill.
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Frankenshtein
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[*] posted on 21-9-2020 at 13:15


Agitation should be good unless it causes precipitate to fall through the glass frit filter, I guess that wont happen if you're using a paper filter. I've heard the bottom dries up and blocks the higher layers from being able to dry. You could watch nilered's video on youtube of basic copper carbonate to see an example. If you're letting the thing dry on a drying pan, the more surface area and thin it is, the better. Breaking up chunks would be required in this case.
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Fyndium
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[*] posted on 21-9-2020 at 13:46


Some stuff like MgSO4 and CaCl2 cause rock hard crust formation, which is not impermeable but definitely slows things down. It is absolute PITA to break it down, unless you spread it few mm thin on an oven pan, which makes life much easier. These are a lot easier since they don't decompose in any humane temps, but many organic compounds are totally another matter. They don't seem to crust as easily, but they do form clumps, which slow down drying and I usually agitate them and break the clumps in the drying vessel with spatula or paint scraper to maximize the surface area for evaporation. This is somewhat arduous though since the stuff needs to be removed from the oven often.

Apparenty removing all lumps is not necessary, especially during synthesis steps, but at least the stuff I'm gonna store any longer, I want to be dry and homogenous, so I usually sieve them.

Btw I haven't noticed any stuff leaching through the glass frit upon agitation. I always agitate the stuff in the filter when I wash it with something.
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