Spikecicles (reprise)

Recently, I have been noticing small vertical spikes in some of the cubes in my ice trays. For those who haven’t seen this before, small (2-30mm) spikes are forming in the center of the cubes. They often tilt in random directions. There is no evident condensation above the cubes.

I wondered about what could be causing them, so naturally I started my research in the SDMB archives. The phenomenon, which I will refer to as “spikecicles,” has been covered in Ice cube stalagmites? (Nov 1999), Ice Stalagmites (Jun 2000), Spikecicles? (Oct 2000), and ice (Feb 2001). There may be others that my search terms didn’t uncover. As tomndeb once stated, the Jun 2000 thread provided some of the better possible explanations.

There is also some discussion of this at Ice cube phenomenon, which has pictures of spikecicles and several reasonable (and some silly) hypotheses. It is also on the web at Freezer Phenomenon #3, MadSci Network, and doubtless many other places.

Some of the ideas proposed on SDMB to explain this phenomenon are given below:

SandWriter: “One wild theory is that it is some sort of reverse sublimation during the defrost cycle of the freezer. Another wild ass guess is that the purified water is compressed in the middle, then breaks through the ice and instantly freezes due to a drop in pressure”

JoeyBlades: “Alternatively, if the defrost cycle is just slightly warmer, the condensation might fall and the small water droplets would refreeze fairly instantly forming stalagmite like structures. These might tend to be mostly vertical, but defrost cycles and air currents from blowers might make them tend to lean once they reach a certain height. Come to think of it, a leaning structure, under the right conditions might take on the shape of the wedges depicted. One way to check out this theory would be to look for smooth bumps directly above the ice trays. This would be indicative of condensation droplets freezing and thawing.”

DJScherr: “As water freezes it expands, as it expands it should start to form a kind of ‘bubble’ on top due to survace tension. (like when you pour water over the top of a glass it domes.”

Cornflakes: “…the ice cubes are freezing inwards from the outside of the tray. Since water expands as it transitions into a solid (aka: ice), the stuff has to go somwhere, namely out the unfrozen area in the middle at the top.”

ZenBeam: “The ice cubes as they are freezing are kept at 32 degrees F, warmer than the rest of the freezer. Air currents are caused by the higher temperature of the ice, which draws air across horizontally across the ice surface toward a point in the middle, causing a small amount of sublimation from the surface. At the middle of the cube, the air currents come together, and deposit the water molecules there. The tilting is caused by pre-existing air currents flowing in the direction of the tilt.”

Personally, I tend to favor the theory that as the water freezes from the outside in, it causes pressure in the center as the water expands. But clearly, although it has been pondered many times by people much more intelligent that me, there seems to be no universally agreed-upon explanation to what causes spikecicles. Could this indeed be a mystery that only The World’s Smartest Human Being can solve? C’mon, Cecil, only you can authoritatively put this one to rest once and for all!

These are all speculations, so why would there be any agreement?

Here are two experiments which MIGHT show what’s going on.

Recently on a hobby forum (on JL Naudin’s, I think), someone noticed that their fridge was making Ice Spikes reliably and repeatedly. Being a fringe physicist, the guy assumed that the large coils of wire stored on top of the fridge were the cause. But removing the coils didn’t stop the spikes. He tried various things, and eventually found that any blockage of the freezer fan would eliminate the spikes.

Apparently the spikes need cold wind blowing.

I’ve performed inadvertant experiments. When first plugging in a warm freezer full of warm ice-cube trays, ice spikes form. But if I put a warm ice cube tray into a cold freezer, I just get ice cubes.

This suggests to me that the bottom of the freezer must be colder than the air. Because the bottom of the freezer is full of cooling coils, it will freeze first when the power is first turned on.

One result would be that the bottom of the ice cube tray will freeze first (and the sides too, if it’s metal.) Ice normally freezes from the top down: the coldest water rises to the top, the top skins over, then the skin thickens. If this occurs, I bet it stops any ice-spikes from growing. But if the bottom of the tray is in contact with the cooling coils, and if the air is still slightly warm, then the ice cubes will grow from the bottom up, leaving a pool of open water in the center of each cube.

One last concept: wax shrinks when it hardens, and if you’ve ever tried making a big wide candle, you’ve seen the result: a cone-shaped hole in the center. The wax freezes from the outside in, shrinking as it goes, so the pool of molten wax moves down and down as freezing progresses, which creates a “trombone mouth” cavity on top of the candle.

Since ice expands as it freezes, maybe the ice-spikes are just the reverse of the hole in the top of the jar full of hardening wax?

If you drip a drop of water onto a chilled metal plate, it ALWAYS forms a tiny sharp peak at the top. Try it.