Sciencemadness Discussion Board

Crystals from vapor?

Exouxas - 18-4-2017 at 01:27

Hey!

I've tried growing some salt crystals at home, and tiny crystals are growing on the side of my glass.


Here's an explanation of how I've grown the crystals:

Heated water and saturated it with salt.

Cleaned a plain cylindrical drinking glass with alcohol.

Poured the saturated water into the glass.

Covered glass with a clean piece of cloth so that it filters dust but lets air through.


At this point I've let it sit for about a month and the water is down to about 1/3 of what it started with.

But one strange thing that I noticed was that tiny crystals (a lot of them) grew on one side of the glass, above the water level that it started out with. And the cloth has hardened.

Does this mean that the saturated water vaporized and remained saturated, then the salt crystallized when the vapor condensed?

DrP - 18-4-2017 at 02:39

The growing on one side of the glass can be explained by assuming that that is where the first crystals were seeded and they continued to add to the existing crystals rather than starting new sites for growth. TIP: Next time add an already formed crystal to the solution... as the water evaporates, the salt molecules should add to the already formed crystal and it should grow, rather than starting 100s of new ones from whatever seed sites it can find on the side of the glass.

The cloth hardening? Maybe some of the salt molecules got carried up to the cloth, somehow transported during the water evaporation - idk.

Amos - 18-4-2017 at 06:01

How hard is the cloth exactly? Clothes left to dry in the sun or air are definitely much stiffer than those you wash in a machine in my experience.

But no, in the case of nearly all inorganic salts, an almost undetectable amount of the solute goes airborne when water evaporates from a solution.

Sulaiman - 18-4-2017 at 06:23

pure speculation ;

given that there are some crystals on the side,
saturated salt solution will be drawn up the walls by capillary/wicking/surface tension effect
higher liquid will be in less saturated air
(also minutely warmer and/or cooler than the bulk of the liquid at different times of day / temperatures)
so more crystals will develop, raising the local level, increasing evaporation rate, increasing crystal deposition rate ......
thin narrow stalagmites would grow up the wall (crystalmites ?)
once this effect reaches the cloth
saturated liquid will continuously 'wick' up the crystals and across the cloth
evaporation from the cloth causing crystals - stiffening the cloth

?

P.S. a tiny speck of a non-reactive dye, (I don't know which dye, maybe food colour?)
applied to the crystalmites may give clues ?

[Edited on 18-4-2017 by Sulaiman]

Exouxas - 18-4-2017 at 23:26

I forgot to take pictures when I came home, but the cloth is stiffer than "dry" and I see some salt on it. It makes somewhat the same sound as wood when knocking on it type of hard.

I'm not sure if this has anything to do with it but the cloth covered more of one side of glass than the other and that's the same side that the salt grew.

There hasn't been any direct sunlight there and there are no nearby heat sources.

Sulaiman, where do you want me to apply the food colour? On the middle of the crystal growth or into the saturated water?


Thanks for all the responses.

Sulaiman - 19-4-2017 at 01:27

on the wall, about 1/2-way between the top of the liquid level and the top of the container, where there are crystals
just the tiniest ammount that is visible

if my 'crystalmites' / 'wicking' speculation is true,
then dye should travel upwards
if vapour is condensing on the walls then the dye should travel downwards
I guess :)

Exouxas - 19-4-2017 at 11:04

Hey, felt the water level has gone a bit too far down to put food colouring to check, but I'll try to do everything the same way again.

And in addition to that I'll have a separate glass with a seed crystal. Should I suspend the seed crystal or is it fine if I put it at the bottom of the glass?

Anyways, here are some pics of the current glass: https://imgur.com/a/Kdz1w

Σldritch - 21-4-2017 at 14:26

Almost all my salt solutions evaporated in repurposed glass jars does this, even more than shown here. I had one jar of ammonium chloride form small coral like structures at the top of the jar almost a centimeter in hight.

Maybe the surface of these jars are slightly porous unlike borosilicate glass beakers which do not seem to form much of these climbing salt crystals. I doubt this phenomenon stems from residual solution from swirling the jars because it has climbed almost a decimeter from the hight the solution was swirled to.

alking - 23-4-2017 at 09:56

Quote: Originally posted by Sulaiman  
pure speculation ;

given that there are some crystals on the side,
saturated salt solution will be drawn up the walls by capillary/wicking/surface tension effect
higher liquid will be in less saturated air
(also minutely warmer and/or cooler than the bulk of the liquid at different times of day / temperatures)
so more crystals will develop, raising the local level, increasing evaporation rate, increasing crystal deposition rate ......
thin narrow stalagmites would grow up the wall (crystalmites ?)
once this effect reaches the cloth
saturated liquid will continuously 'wick' up the crystals and across the cloth
evaporation from the cloth causing crystals - stiffening the cloth

?

P.S. a tiny speck of a non-reactive dye, (I don't know which dye, maybe food colour?)
applied to the crystalmites may give clues ?

[Edited on 18-4-2017 by Sulaiman]


This is what I was thinking, capillary action pulling the solution up which then either evaporate or drops in temperature and you get crystallization. As more crystals grow the further it carries up the glass until it reaches the cloth.

MrHomeScientist - 24-4-2017 at 07:49

It is a capillary/wicking action. Crystals can form at the surface of the solution against the side of the glass. As the solution level drops, these crystals wick some solution up onto them, where they form more crystals at the new water level and a little higher up above the original crystals. This forms the "crystalmites" you see. I've had this process go so far that crystals grew up the side, over the rim, down the outside, and across the table a good 6 inches. Pretty cool actually. Shows what happens when you forget about things!

I'm almost positive the phenomenon is called "creep," but I can't find any reference to that now.