Dry ice is frozen
carbon dioxide. A block of dry ice has a surface temperature of -109.3
degrees F (-78.5 degrees C). Dry ice also has the very nice feature of
sublimation
-- as it melts it turns directly into carbon dioxide gas rather than a
liquid. The super-cold temperature and the sublimation feature make dry
ice great for refrigeration. For example, if you want to send something
frozen across the country, you can pack it in dry ice. It will be frozen
when it reaches its destination and there will be no messy liquid left
over like you would have with normal ice.
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Dry
Ice Safety
If you
ever have a chance to handle dry ice, you want to be sure to wear heavy
gloves. The super-cold surface temperature can easily damage your skin
if you touch it directly. For the same reason you never want to taste or
swallow dry ice either.
Another
important concern with dry ice is ventilation. You want to make sure the
area is well-ventilated. Carbon dioxide is heavier than air and it can
concentrate in low areas or in enclosed spaces (like a car or a room where
dry ice is sublimating). Normal air is 78% Nitrogen, 21% Oxygen and only
0.035% Carbon Dioxide. If the concentration of carbon dioxide in the air
rises above 5%, carbon dioxide can become toxic. Be sure to ventilate any
area that contains dry ice, and do not transport it in a closed vehicle. |
To make dry ice, you start
with a high-pressure container full of liquid carbon dioxide. When you
release the liquid carbon dioxide from the tank, the expansion of the liquid
and the high-speed evaporation of carbon dioxide gas cools the remainder
of the liquid down to the freezing point, where it turns directly into
a solid. If you have ever seen a carbon dioxide fire extinguisher in action
you have seen this carbon dioxide snow form in the nozzle. You compress
the carbon dioxide snow to create a block of dry ice. |
