I just found a mix of NaCl/KCl (50/50) that I allowed to evaporate for about 6+ months and it formed a thin crystal wall the entire way up a 1qt mason
jar, down the outside and a circle about 1-2" diameter around the jar. To start it was a pretty saturated solution but the jar was at most 1/2 full
when allowed to "start".
I've found this to happen with NaCl/KNO3 mix, ammonium sulfate and a number of other salts - possibly even NaOH.
I'm wondering if this action has a name and why it occurs. I was trying to make crystals. I've found that this happens at all temps, and more time
seems to allow for it to spread further.
I've always wondered about salt bridges and what they are/how they work & how to make one. Is this similar but without a support structure?Sulaiman - 25-5-2017 at 00:12
Until we find the proper name for this effect,
I have taken the liberty of naming the structure a 'crystalmite'
(crystal stalagmite)
[Edited on 25-5-2017 by Sulaiman]Melgar - 25-5-2017 at 12:03
It's a bit simpler than that. At the edge of the solution, it will tend to evaporate faster, because there is less liquid around, and because the
solution level is going down. As the liquid evaporates, crystals form, and if they are small crystals, there will be gaps between them, through which
the solution will move through by capillary action. This will pull the solution further and further from the edge of the liquid, until there are no
more crystals to move through, and it reaches the edge where it's exposed to air and evaporates, thus creating more crystals. This is driven by
evaporation as well as the energy loss when crystals form.
Trees use a similar principle to get nutrients out of the ground and to their leaves. Fungi use it as well. The earth as we know it couldn't exist
without evaporation-driven solute transportation. (Evaporation-driven solute transportation sounds like a good name for this effect, no?)MrHomeScientist - 25-5-2017 at 12:17
I was quite sure it is called "creep" but now can't find any references to that name being used.
Yes, that is the correct term. I found it used in my quantitative analysis textbook in reference to barium sulfate's tendency to creep as it dries
from an aqueous solution.annaandherdad - 31-3-2018 at 17:46
I've heard it called "evaporative creep".
I was involved in a project to separate the salts in seawater by fractional crystallization. I just did it because it would be fun and the kids were
interested. One of the references I looked at said that evaporative creep could be avoided by using polyethylene containers instead of glass. I
never tried it, so I can't confirm.
However, in my own work with glass I did find that a dust-free environment prevents evaporative creep, at least for several days, at least for
crystallizing (mostly) sodium chloride out of sea water.
I also found that activated charcoal is very effective in removing the organic matter from seawater.
