MadSci Network: Other |
Are these shapes growing upwards out of each ice cube? If so, then
you are seeing "ice spires" or "ice spikes". These occur when water
freezes from the bottom up, and they occur because water
expands as it freezes. Most other liquids contract upon
freezing, and they create conical depressions rather than
conical "spires". You may have seen these sorts of conical
depressions if you've ever made candles or watched liquid wax
solidify.
During normal freezing, water at 0C degrees is less
dense than slightly warmer water, and for this reason the layer of
ice will start growing at the top of a body of water. In a
freezer, the ice cubes normally freeze first at the top. The
layer of ice is flat and no "ice spires" are formed.
Sometimes ice will freeze without developing a solid layer
on top, and when it does, "ice spires" can appear. In a freezer,
this typically occurs after a power failure when all the
ice cubes have melted. When power is restored, the freon coils
cool the bottom of the tray of ice cubes, and solid ice first
develops at the bottom of the tray. As the tray cools, ice grows
upwards, and ice also appears on the walls of the tray and
grows inwards. The remaining body of water becomes smaller.
Here is the critical part: because water expands as it freezes,
the growing layer of ice leaves less and less room for the
remaining water in the center of the cube. This water is
slowly pushed upwards. The upper lip of the ice will follow
the water as it rises, resulting in a slowly growing "spire"
which has a liquid center. Here's a crude diagram:
____ __--| |--__ ___-- | | --___ SLOWLY FREEZING | | | | ICE CUBE WITH | | | | LIQUID WATER IN | |____| | THE MIDDLE | | | | |________________________|Just before the liquid center freezes solid, it rises fairly fast, so the end result is a sharp "tooth" made of solid ice.
| / \ _/ \_ __-- --__ ___-- --___ | | FREEZING IS COMPLETE, | | A CONICAL "CUSP" OR | | "SPIKE" IS FORMED. | | | | |________________________|Why are your spikes tilted, or curved? I don't know. Maybe your freezer has a fan, and the moving air pushes on the droplet of water at the top of the growing spike, causing it to continually move sideways as the ice grows taller.
I found one website which has photos:
http://www.yk.psu.edu/~kx t7/IceSpikes.html
You can demonstrate this effect yourself. Place a large
metal object such as a frying pan in your freezer. Let it
become frosty cold. Then drip some small drops of water
onto the chilled metal and watch what happens. The water
will freeze from the bottom up, and each droplet of ice
will develop a tiny "cusp" at the top. It will be very
small, but the sharp point is easily felt by a fingertip.
I've never tried it, but I suspect that it's possible
to make true "sprires" by using a chilled metal block
with a deep hollow on top. Fill the hollow with water,
and the cold metal would cause
the water to freeze inwards and push the remaining liquid
upwards into a tall spire.
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