clearly_not_atara
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potassium tetraoxalate dihydrate
this thread is dedicated to everyone who ever complained about me not posting experimentals
I don't really have a living situation that allows me to build a lab (I don't even have my own room :p), but recently I figured I could attempt to
make some variations of Sorel cement:
http://en.wikipedia.org/wiki/Sorel_cement
Anyway, after some reading, I came up with the idea of replacing MgCl2 by KH(O2CCO2H)2*2H2O, potassium tetraoxalate dihydrate.
To 126 grams of oxalic acid dissolved in 750 mL of water at 50 C, a solution of 50 grams of potassium bicarbonate in 250 mL of water was slowly added,
with vigorous bubbling. A white precipitate formed immediately. The reaction mixture was allowed to cool for several hours and decanted.1
For want of proper drying equipment the rxn product was allowed to dry outside for three weeks, after which it was a dry polycrystalline cake easily
crushed into a free-flowing white powder.
Now the interesting question is -- how do I crush this into a very fine powder? I think I need to make some kind of makeshift ball mill.
1 - the remaining liquids were treated with crushed limestone before disposal
[Edited on 14-10-2018 by clearly_not_atara]
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fusso
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Quote: Originally posted by clearly_not_atara  | Now the interesting question is -- how do I crush this into a very fine powder? I think I need to make some kind of makeshift ball mill.
1 - the remaining liquids were treated with crushed limestone before disposal |
Why do you need
very fine powder? Why don't you just dump the waste oxalate down the drain? I don't think potassium oxalate is that harmful?
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clearly_not_atara
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I didn't want to have calcium oxalate precipitate in the drain pipes. And I didn't want the acidity to damage anything.
Cements are always finely ground in order to work properly. For a poorly soluble component like potassium tetraoxalate this is particularly important
as it might not fully react otherwise. I believe it was Nicodem who said:
"The single most important criterion for a successful synthesis is good mixing."
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Tsjerk
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Which reaction do you want to do with it?
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clearly_not_atara
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Cement formation! When partially hydrated finely ground MgO reacts with certain salts, it forms cementitious composites. These are used to make some
types of flooring and roofing as well as for repairing cement structures when a fix needs to be installed as quickly as possible (because the cement
sets quickly).
The effective co-salts include MgCl2, MgSO4, KH2PO4 and NH4H2PO4. Additionally, high-pressure concentrated aqueous carbon dioxide is also effective,
which is where the "smart money" is in magnesium cements these days. Unfortunately, magnesium-carbonate cements cannot be formed at ambient pressure,
as far as anyone can tell.
The MgCl2 and MgSO4 versions tend to be corroded by water, whereas the phosphate and carbonate cements are not. I wanted to see if a cement could be
formed with oxalate, and K tetraoxalate is ideal for a few reasons: K+ is the best counterion in the phosphate cements; low solubility means slower
setting which makes the product easier to work with (because Mg cements set ultra-fast anyway); low solubility also means less toxicity risk from
oxalate and ease of working with the powder vs. something hygroscopic and sticky.
I guess I'll get a few metal balls and a steel jar and maybe roll it down a hill or glue it to a skateboard/bicycle wheel, although I don't know where
to get grinding media. Or jars. Home Depot, probably, though.
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clearly_not_atara
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Update: while this was shelved (I moved, everything was in a closet for a while, then I was broke, etc), I was scooped by some Turks:
https://ui.adsabs.harvard.edu/abs/2019AGUFMGC31E1302E/abstra...
Which one of you told Erdogan?!
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