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Author: Subject: Most hydrophilic: MgO, CaCl2, Cu(NO3)2, Ca(NO3)2, CuSO4, NH4NO3 - Very interesting Results!!
RogueRose
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[*] posted on 7-9-2017 at 12:31
Most hydrophilic: MgO, CaCl2, Cu(NO3)2, Ca(NO3)2, CuSO4, NH4NO3 - Very interesting Results!!


Well, I didn't really think there would be any question about which of these would absorb atmospheric water faster but the results are astounding, IMO.

Just to make sure we are all on the same page with what hydrate level and purity I'm talking about, here is the list of the products:

MgO - Side walk deicer
CaCl2 - Side walk deicer (says 77& but that means that about 20-23% is water - so it's a hydrate already)
Ca(NO3)2 - fertilizer - hydrated
NH4NO3 - Fairly pure powder - probably close to 98-99+%
Cu(NO3)2 - very pure 99+% - very blue crystals (looks basically like the sulfate)
CuSO4.5H2O - 99+% pure - pentahydrate

After a year of sitting exposed to the elements in the same setting, the MgO is a solid brick and is dripping a MgO solution while the CaCl2 is somewhat caked together on the top of the container while the bottom 80% is still the same as it was before.

The Cal Nit has changed slightly by caking at the top 5-8% while the rest remain the same.

I've seen no change at all in the CuSO4, Cu(NO3)2 of NH4NO3. I was very surprised at these as I expected some absorption of liquid and maybe there has been but not enough to pool any liquid in the container.

The MgO has almost doubled in weight while the CaCl2 is only about 10% heavier. I would never have thought this and I'm trying to figure out how the MgO is absorbing so much water and if it is forming a hydrate then a solution?? I havent' been able to find a MgO hydrate so this is a little confusing.

Anyone have any idea as to why I'm getting this result and how the MgO is absorbing so much?

I'd like to try this with anhydrous CaCl2 and CuSO4 and then do a weight test to see which absorbs more.

Also, when people talk about the strength of a dessicant, are they talking about "how much they can absorb" as in quantity, or how strong the pull is such as being able to pull the last 2-3% of moisture out of the air where other dessicants can't do it.
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DraconicAcid
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[*] posted on 7-9-2017 at 12:51


Your MgO isn't forming a hydrate- it's forming a hydroxide first. MgO + H2O --> Mg(OH)2 Magnesium oxide and hydrixide aren't very soluble, so I'm surprised that it's forming a solution.



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feacetech
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[*] posted on 7-9-2017 at 19:54


https://en.wikipedia.org/wiki/Critical_relative_humidity

is a helpful parameter

however contaiminats can quickly change this usually for the worse

Calcined magnasite MgO and Burnt lime CaO are a bitch if you get the dust on the back of your sweaty neck

as above forms a hydroxide and genrates heat when water is added

aformention hot hydroxide + skin = ouch

[Edited on 8-9-2017 by feacetech]
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Magpie
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[*] posted on 8-9-2017 at 06:59


When I worked we had a LUWA vertical dryer with a rotor that wiped the inside surface and the powder fell to a vapor locked outlet for disposal. The steam jacket was kept at about 365 deg F. Mg(NO3)2 would not dry. So we pre-treated the feed with NaOH to convert it to insoluble Mg(OH)2 which would dry to a powder.

[Edited on 8-9-2017 by Magpie]

[Edited on 8-9-2017 by Magpie]




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AJKOER
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[*] posted on 9-9-2017 at 10:51


The MgO may do more than just form Mg(OH)2. If sunlight is a factor in exposure to the elements, note that MgO is also photoactive, but not to the extent of say TiO2.

In the presence of impurities, more chemistry could be occurring, adding to the mass of the MgO!

[Edited on 9-9-2017 by AJKOER]
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clearly_not_atara
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[*] posted on 9-9-2017 at 11:09


MgO also absorbs CO2 from the air over time. This adds more weight than water. Copper nitrate is volatile when anhydrous isn't it? IIRC it can only be prepared in a hydrogen-free protocol (Cu + N2O5 or similar)

[Edited on 9-9-2017 by clearly_not_atara]
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kmno4
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[*] posted on 9-9-2017 at 11:46


Quote: Originally posted by RogueRose  

MgO - Side walk deicer

:D
Funny (or sad) thing, how many "chemists" here uncritically discuss this MgO....

Besides, this is one of the most stupid topics in this year.




Klaszczę w dłonie, by było mnie więcej....
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