Water Soluble Deicers
Date: Winter 2009-2010
Why are airplane de-icers soluble in water?
The short answer to your question is that any deicer has to be soluble in
water to work. In a way, your question is rather like asking if it
is possible to
make coffee, if the coffee did not dissolve in water!
When a deicer such as ethylene glycol is sprayed on ice, the ice begins to
"dissolve" into the deicer. As more and more ice dissolves in the deicer, the
volume of the deicer-water mixture become larger, thus there is more and
more liquid water and deicer mixture, and the dissolving of the remaining ice
goes progressively faster. It is important to understand that the
of water (from melted ice) and deicer, cannot freeze any more because the
deicer dissolved or mixed with the water lowers the freezing point of the
mixture (just as adding antifreeze to the water in a car's cooling system,
lowers its freezing point, and keeps the mixture from freezing).
If deicer did not dissolve in water, none of the above would work. The deicer
would just sit there and not interact with either ice or water. Any
somehow was still liquid, would be just pure water (since the deicer would
not mix with it), and would instantly freeze.
In order to "de-ice" the de-icer must be soluble in water. Otherwise it
could not affect the equilibrium temperature of the solid water ice and the
liquid water. To a first approximation, it is the number of particles (ions
and/or non-ionic particles) that dissolves in the water that changes the
efficiency of the de-icer. This is why de-icers tend to be mixtures of ionic
compounds -- for example, Ca(Cl)2 + urea
CO(NH2)2. The former produces three ions per mol; the latter produces only
one particle per mol, but is very water soluble. This is a bit
over-simplified because corrosion, and other factors must also be taken into
Aircraft deicers work on the same principle as the salt we put on
our roads or walkways during winter or the antifreeze we put in car
radiators. They salt used on roads is usually NaCl, CaCl2, or MgCl2.
They work by slowly dissolving into the snow and ice and the
combination of the heat of solution and freezing point depression
helps melt the snow and keep it from refreezing. The antifreeze in
cars is usually ethylene glycol and it works by lowering the
freezing point of water so that it will remain liquid at lower
temperatures. Aircraft deicers are usually formulations that include
ethylene glycol or propylene glycol. Chloride salts are not allowed
because they can speed up the corrosion of metals. In order for the
deicer to work, it must dissolve into any water that is formed or
present and lower the temperature of freezing for that solution -
preventing it from forming ice once it has become a liquid solution.
So, in answer to your question, the deicer must first dissolve into
water before it can act to lower the freezing point and prevent ice
Look up "colligative properties" and "freezing point depression" in
this site if you want to know more about the principles behind the
lowering of the freezing point.
Greg (Roberto Gregorius)
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Update: June 2012