For an updated version, go here.
Last week the temperatures dipped far below freezing and someone asked me if there was a point at which ice-melt won’t work anymore. The answer is yes but don’t panic.
These substances work by disrupting the bonds between the ice molecules –making it harder for them join together and make a solid–but there is a limit to which they can depress a freezing point. The first study I could find on this topic was published in 1918 by Worth H. Rodebush. He measured the eutectic points of various salt solutions, essentially the lowest temperature they can reach before being solid. His figures match those found today so here is a partial list:
Salt, sodium chloride, NaCl -21 C or 1-6 F (works efficiently to melt ice at temperatures above 15 F). This is what Iowa uses primarily.
Calcium chloride -51 C or -60F ( for practical purposes it works above -20 F)
Potassium acetate -30C or -76F (safest for grass and concrete and most effective above -22 F)
Magnesium chloride -15 C or -5 F (best above 5 F)
The list above is for salts, inorganic compounds with ionic bonds.
Glycols such as propylene glycol are carbon-based compounds that can be used as deicers. These have a eutectic point of around -55 C which is -67 F. These are most often used on airplanes.
As you can see, these substances do have their limits but thankfully we rarely face these extreme temperatures–although we do on occasion reach -22 F in Iowa.
A temperature of -93 C or –136F has been recorded in Antartica by a satellite device with -128.6F (-89 C) being the coldest official temperature measured by a thermometer. So there’s a spot where de-icers wouldn’t be effective.
What’s the coldest a substance can get? Helium freezes at -458 F or -272 C. You’ll probably never see any of these temperatures so enjoy your de-icers in moderation, using caution below -22 F.
Why in moderation? De-icers can “aggravate” flaws in concrete and of course when wet, they make part the perfect combination to corrode your car–electrolyte, water, and air. They are the electrolyte. Besides eating up a lot of local and state road budgets, They also contribute quite a lot of sodium and chloride to the local waters.
Don’t forget, the lower temperature of deiced pavements can make pet paws get so cold that they can get frostbite, so protect your pets this winter and travel safely.