mad science with snowflakes

[eub]

There are many ways to grow snowflakes (see the Designer's Page), but my favorite starts with something called a vapor diffusion chamber. This is essentially nothing more than an insulated box that is kept cold on the bottom (say -40C) and hot on the top (say +40C).

Electric fields can affect the growth of ice crystals in several interesting ways, and can be used to grow long thin needles of crystalline ice (see the Designer's Page). The electric effects come about because electric fields influence the way water molecules diffuse through the air in the vicinity of the ice surface. If we charge up a growing crystal, then electrostatics dictates that strong electric fields will be set up around the crystal. The fields and field gradients will be particularly strong near any sharp points on the crystal. Since water molecules have an intrinsic electric polarizability, the electric fields tend to polarize the water molecules. If the field also has a strong gradient, then the polarized molecules are attracted in the direction of stronger fields.

The first improvement came from my realization that the best electric needles grow only when certain chemical vapors are added to the diffusion chamber. Silicone caulk vapor seems to work best, although acetic acid does almost as well, and even gasoline vapors do pretty well.

Growth of Electrodynamically Levitated Crystals
A novel approach to producing artificial snow crystals is to levitate the growing crystals in an electrodynamic trap (a Paul-type ion trap).

Comments

[eub.livejournal.com]

And hey! It's those ice prongs that form sticking out of my ice cubes!
http://www.its.caltech.edu/~atomic/snowcrystals/icespikes/icespikes.htm

Cool

[brokengoose.livejournal.com]

I always assumed that, like stalagmites, those ice spikes were the result of dripping from above.

Re: Cool

[hattifattener]

You can make shorter versions by taking a spoonful of clear water and pressing the bottom of the spoon into a block of dry ice — you get a smooth sort of horn shape with an "ice nipple" on top. It's fun to watch it form. (Thanks to the local weird sciences salon for this demo. A bizarre mix of science and … uh … stuff.)

Re: Cool

[jinian.livejournal.com]

Jinx. :)

Re: Cool

[eub.livejournal.com]

LJ needs seconds on the comment timestamp.

Re: Cool

[eub.livejournal.com]

This is interesting. I would have expected it to be important to have cooling from above, freezing most of the top layer.

Re: Cool

[eub.livejournal.com]

Mine always seem to grow diagonally. I wonder why that is.

[jinian.livejournal.com]

It's pretty easy to make small ice spikes by holding a metal spoon full of water to a piece of dry ice, which is maybe not what the folks at that link would expect. It only works for small ones because the spoon inevitably jitters some as the carbon dioxide flees its warmth.