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How to dehydrate a solid crystal?

  1. Aug 16, 2011 #1
    How to dehydrate a solid crystal???

    I have a solid crystal with structural channels in it which are filled with water molecules. The size of each channel is 2.5 to 5 angstrom and a water molecule is 2.7 angstrom on its longest side. What is the best way to dehydrate it???
    I have tried heating it and its been a good process but not good enough to fully dehydrate it...

    Thanks in advance :)
     
  2. jcsd
  3. Aug 17, 2011 #2

    Borek

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    Re: How to dehydrate a solid crystal???

    Drying over molecular sieves? Concentrated sulfuric acid or P2O5?

    Compare http://www.mercury-ltd.co.il/admin/userfiles/image/Information/Drying%20Agents.pdf [Broken].
     
    Last edited by a moderator: May 5, 2017
  4. Aug 17, 2011 #3
    Re: How to dehydrate a solid crystal???

    A very very informative pdf Thanks a lot :)

    Just one question; some of these channels have a diameter less than the 2.7 angstrom and these drying agents wont be able to enter such channels... The water in these channels are probably trapped during crystallization. How to get these molecules in touch with the drying agents?!

    Immersing the crytal in Sulfuric acid or P2O5 and heating it to few hundred degrees can help? perhaps because of expansion of channels and increased kinetic motion of the molecules???

    Thanks again
     
    Last edited by a moderator: May 5, 2017
  5. Aug 17, 2011 #4

    Borek

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    Re: How to dehydrate a solid crystal???

    No no, you don't immerse the crystal. You keep it in a closed container above the drying agent. The idea is that water leaves the crystal and gets absorbed by the drying agent, as both processes are in equilibrium, you end with most of the water trapped where it is thermodynamically more stable (in the drying agent, if it is properly selected).

    Immersion is for drying solvents (liquids), but then it is a matter of putting drying agent into liquid. I haven't heard about drying done the other way (that is, putting dried substance into liquid that is a drying substance).

    No idea what to do if the water is trapped in such a way it can't leave the crystal. At the same time, I don't think crystal is so rigid water molecules can't diffuse to the surface, it just needs time. Elevated temperature will for sure speed up the process.
     
  6. Aug 19, 2011 #5
    Re: How to dehydrate a solid crystal???

    I see!!! Thanks for the info :)

    Just one last question; is it safe to place sulfuric acid in a sealed crucible and heat it to 300Celcius (can I go even higher like 850C?)???

    I have an electric furnace and can sustain the temp accurately for long durations, but I'm not sure if the preasure build up may cause any damage or not?
     
    Last edited: Aug 19, 2011
  7. Aug 19, 2011 #6

    Borek

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    Re: How to dehydrate a solid crystal???

    Actually the temperature things is tricky. For sure elevated temperature will help water leave the crystal, but I am not sure it will speed up the dehydration process, as it will also affect equilibrium at the other end (increasing water vapor pressure). Could be some initial increase in temperature followed by the cold period will be best, but I am just guessing.

    Compare http://en.wikipedia.org/wiki/Desiccator
     
  8. Aug 19, 2011 #7
    Re: How to dehydrate a solid crystal???

    You are right... I guess I have to keep cookin & lookin lol

    I was thinking... This is a silicate crystal so its soluble in H2SO4 & HF acids... Can I somehow "enlarge" those channels without much damage to the xtal itself???!

    What kind of setup can you think of which may enlarge the structural channels, by dissolving its walls in acid but keeping the main bulk of the xtal safe???

    Many thanks in advance Borek :)
     
  9. Aug 20, 2011 #8

    Borek

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    Re: How to dehydrate a solid crystal???

    I doubt you will be able to modify the crystal this way, I am afraid modification will mean destruction of the structure.
     
  10. Aug 20, 2011 #9
    Re: How to dehydrate a solid crystal???

    What about immersing the xtal in HF for a very short interval??? because the structural channels are sorrounded by SiO3...

    Here is how the structure looks like: http://youtu.be/-kS4zWyYLJk
     
  11. Aug 21, 2011 #10

    Borek

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    Re: How to dehydrate a solid crystal???

    It won't work, you will etch the surface, but not channels. Just like water needs time to get out, HF won't be able to get in.
     
  12. Aug 21, 2011 #11
    Re: How to dehydrate a solid crystal???

    What if I use an electric stiring device and stir the acid around the crystal with a very high speed???

    I mean; can stirring with high speed limit the reaction between the surface and the acid in order to provide enough time for HF (which is less than 2 angstrom, Right?) to enter channels???

    Thanks again :)
     
    Last edited: Aug 21, 2011
  13. Aug 22, 2011 #12

    Borek

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    Re: How to dehydrate a solid crystal???

    Won't work.
     
  14. Aug 23, 2011 #13

    chemisttree

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    Last edited by a moderator: Apr 26, 2017
  15. Aug 25, 2011 #14
    Re: How to dehydrate a solid crystal???

    Interesting paper... Thanks Chemisttree :)

    Actually I have tried heating at 700C for 12 hours, but can't get all the type 2 water molecules (the ones prependicular to the direction of channel) out!

    Type 1 molecules can be dehydrated by heating but not the type 2s :(

    Thats why I was hoping to find a chemical process by acids etc which might increase the diameter of the channel just a little bit to accelerate the process. HF sounds good because its only 2 angstrom in size, & beryl is solluble in HF but as Borek suggested there are problems... Do you know any chemical process which might cause a partial destruction of channels but not the rest of the xtal?

    Btw the crystals are worthless and I have a bunch of them so please tell me whatever comes to your mind :)

    Thanks again :)
     
    Last edited by a moderator: Apr 26, 2017
  16. Aug 25, 2011 #15

    chemisttree

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    Re: How to dehydrate a solid crystal???

    The only idea I have, and I haven't researched it, is to try and find a wavelength of radiation that the Al-O-Si-H2O absorbs and hit the crystal with that frequency while trying to dehydrate. Get that bond length oscillating and I'm thinking that the water will more loosely held and easier to remove. Right now you're doing that with heat but there might be a special frequency that excites just that bond. Don't know what the EM absorption spectrum is for your beryl might be. Library time!
     
  17. Aug 27, 2011 #16
    Re: How to dehydrate a solid crystal???

    That's an interesting idea chemistree :)

    But still considering beryl in trade & markets makes me think people are using certain chemicals to dehydrate natural beryl without disclosing. I found this bixbite (Red color Beryl) on eBay which was for sale & parts of the surface look like chemically etched!

    There's no reason to immerse a "polished" beryl in some chemical of this sort unless they want to cause partial destruction of the channel in order to "dye" the channels. If you look at the other pictures of this same stone, the color is neither even nor "zoned"...

    What do you think?

    This the bixbite I am talking about:

    http://i.ebayimg.com/00/$(KGrHqIOKnUE4Ky8qwPGBODH9ZVz!w~~0_3.JPG
     
    Last edited: Aug 27, 2011
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