What's the Answer?

I received this email from a subscriber and am sorry to say could not find an answer. After several emails ANN finally found the explanation. I found it very interesting and pass it along.

EMAIL FROM ANN:

I have been searching all over the web, to no avail.
Lately I have found maybe 2 or 5% of my ice cubes have a long sliver of ice sticking up from them. I have no idea what is causing this.
Not doing anything different or new that I can think of.
Anyone having any information, please email me directly.
Thanks ANN

ANN'S RESEARCH AND ANSWER: Re: What would cause curved stalactites in my icecubes in the freezer?
Date: Thu Aug 24 17:52:08 2000
Posted By: William Beaty, Electrical Engineer / Physics explainer / K-6 science textbook content provider Area of science: Other ID: 962404441.Ot

Message:

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.

Just before the liquid center freezes solid, it rises fairly fast, so the end result is a sharp "tooth" made of solid ice.

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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