Naked Science Forum

Non Life Sciences => Chemistry => Topic started by: Martin Fennell on 23/12/2012 11:32:00

Title: Why is ice sometimes very hard to scrape off?
Post by: Martin Fennell on 23/12/2012 11:32:00

Martin Fennell  asked the Naked Scientists:
   
Hi,

As usual - love the show. (http://www.thenakedscientists.com/HTML/podcasts/)

My question is - given the recent cold weather in the UK I am having to scrape ice off the car windows each morning. Sometimes the ice almost falls off, sometimes it seems welded to the window, even when the car thermometer says the temperature is the same. Why is this, and, more importantly, how can I predict the ice conditions so I could have an extra 5 minutes in bed?

Thanks

Martin

What do you think?

Title: Re: Why is ice sometimes very hard to scrape off?
Post by: CliffordK on 24/12/2012 08:27:08

I'm not sure what the conditions you are encountering are.

In the past I've noticed that trying to remove freezing rain from a windshield can be like chipping concrete. 

However, you likely would have noticed the freezing rain.  But, along the same path, perhaps some nights the humidity is higher causing a greater buildup of frost.

Often idling the vehicle with the heater on for a few minutes can help with scraping the ice.  Beware of cars that lock their doors automatically when you've left the keys in the ignition, the car idling, and you're outside in the cold busy scraping the windows!!!

Title: Re: Why is ice sometimes very hard to scrape off?
Post by: lightarrow on 24/12/2012 11:27:06

Hi Martin. I know that situation too. When I have the possibility, I leave the car with the windshield opposing a building, just a few metres apart: the building's heat is enough to avoid the effect, if the temperature outside doesn't go down too much.
Anyway, inside of my car I always keep a small bottle with a mechanical spray, like some perfum's bottles, with ethanol inside: some spotted sprays on the ice (and around the wipers), wait some seconds, and then I can action the wipers. But the wipers' gum is a bit damaged by the alcohol, they say (I have used it just a few times and haven't noticed any difference).

The fact sometimes the ice is very hard probably depends on how much the crystals are braided each other, forming probably a sort of composite material (like fiberglass or carbon fiber) and on the condition in which the first water crystallized on the windshield (temperature included, of course, but not only this).