Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!haven!umd5!cgs
From: cgs@umd5.umd.edu (Chris Sylvain)
Newsgroups: sci.electronics
Subject: Re: Repairing Intermittent Circuit Boards
Message-ID: <4495@umd5.umd.edu>
Date: 3 Feb 89 18:35:43 GMT
References: <2910@hound.UUCP> <1677@kodak.UUCP>
Reply-To: cgs@umd5.umd.edu (Chris Sylvain)
Organization: University of Maryland, College Park
Lines: 35

In article <1677@kodak.UUCP> ornitz@kodak.UUCP (barry ornitz) writes:
] In article <2910@hound.UUCP> wa2sff@hound.UUCP (J.WILKES) writes:
]] [...]
]] Does anyone have any ideas or know of non-freon based "freeze"?
] 
] The component "freeze" sprays are generally dichlorodifluoromethane, often
] called Freon-12 or Refrigerant-12; they are one member of a family of fluoro-
] carbons usually known as Freon.  Unfortunately the same chemical inertness
] that makes it safe for electronic applications (non-flammable, low toxicity)
] also makes it linger in the atmosphere for years before reacting to harmless
] products.  During this time, it can interact with the UV-ozone reactions in
] the upper atmosphere.
] 
] [...]

As I learned from an atmospheric chemist (and from a short research paper
I wrote), the reason R-12 (or CCl2F2) lasts so long in the atmosphere is that
there is no chemical "handle" in the lower atmosphere that can break up
the molecule. There are two notable refrigerants with nearly the same
refrigerant effect as R-12, and very similar chemical non-reactivity:
R-22 (CHClF2) and R-134A. R-134A is expensive (I don't have the paper in
front of me, and I don't recall the formula for R-134A). R-22 has been
produced for many, many years.

The difference is that R-22 is a hydrochlorofluorocarbon. The hydrogen atom
gives nature a handle on the molecule, so its lifetime in the lower atmosphere
is greatly reduced.

..then there's the less saturated (carbon bonds) cousin of a CFC that was/is?
used as a propellant in whipped cream containers that is as toxic as phosgene..
-- 
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.. and shun the frumious Bandersnatch! ..
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