Wednesday, January 12, 2011
Traditionally, Chilliwack has used salt to clear our roads as it is good to about -18˚C or 0˚F (and it rarely gets below -7˚C around here), but this year they've started using a different concoction, one that includes propylene glycol or other glycols to reduce the freezing point of water (other communities have used this type of thing for years, but we're finally getting around to it!).
As a note, most of our humectants can work as de-icers by reducing the freezing temperature of water, but I don't think you want to throw a ton of Hydrovance onto your windshield any time soon (mainly due to cost).
You can also use different types of salts to melt snow or weaken ice. Good old sodium chloride (NaCl, known as table salt or rock salt) will work because a brine solution (water mixed with salt) will lower the freezing point of water, but it can cause a lot of rust on our cars and corrosion in other metallic things. Calcium chloride (CaCl2) is being used a lot lately because it doesn't have the same effect on the environment (although it's not very evergreen tree friendly) and because it is good to really low temperatures (we're talking -52˚C or -82˚F as opposed to -18˚C for NaCl).
Unfortunately, no matter what de-icer you use, there are consequences for our environment. Urea can break down into ammonia, which can be toxic for animals. Salt can cause corrosion, and calcium chloride can upset our trees, and propylene glycol takes a long time to biodegrade and consumes oxygen as it breaks down.
See, even a snow day can be made more interesting with chemistry!