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Subject:
From:
Graham Collins <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Fri, 12 Nov 2010 15:32:46 -0400
Content-Type:
text/plain
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It really has to be tough working in a technical industry with the name
Steve Smith, as a Red Green fan the first thing I thought of was duct
tape...  

Keep your stick on the ice,
 - Graham

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Landman
Sent: Friday, November 12, 2010 2:54 PM
To: [log in to unmask]
Subject: Re: [TN] UV radiation and conformal coating

Doug,

I sent your posting to an old college friend who is a physicist with a
great deal if working knowledge on chemical finishes as his company
makes paints and protective coatings for the marine environment.  He is
teamed with Bill Rollins at Raytheon Tucson on a grant from the MDA to
develop a whisker-tough conformal coating. 

He replied:

Bob,

Thanks for forwarding this to me.  I am not subscribed to the list, so
please post this for me.

All,

Varnish fails on wood of boats in one or a few years, due to the
ultraviolet of the sunlight eventually getting thru the varnish [even
with UV absorbers] and breaking down the cellulose of the wood below.
Cellulose has a lot of carbon-carbon and carbon-oxygen bonds.

Indeed; the loss of gloss of varnish is due to surface-oxidation by the
solar ultraviolet photons breaking the atomic bonds of the
material at the surface; those surface free radicals react almost
immediately with atmospheric oxygen, and are literally burned away.

A carbon-carbon bond has an energy of about 348 kilojoules per mole, and
will readily break with a barely-ultraviolet photon.

A carbon-oxygen bond has an energy of about 360 kilojoules per mole, and
a carbon-hydrogen bond about 413.  For more details, see
http://www.science.uwaterloo.ca/~cchieh/cact/c120/bondel.html .

Ultraviolet and even blue-visible photons have enough energy to break
these bonds.

Broken atomic bonds create free radicals, and some of these will bond
onto neighboring polymer chains, causing increased modulus, reduced
elongation, and in fact the polymer gets smaller. the reason flakes of
paint curl outwards when they fail is that the outer surface has more
tensile stress than the material below, due to free-radical damage at
the sunlight-exposed surface. So, you see, it's going on all the time
the sun shines.

Your conformal coating (made of carbon, hydrogen, oxygen and nitrogen
and perhaps other atoms) is doomed; it's only a matter of time.

Steve Smith
Www.smithandcompany.com



On Nov 11, 2010, at 8:20 AM, Douglas Pauls <[log in to unmask]>
wrote:

> Good morning all,
> 
> Does anyone know of any papers on the effects of UV light on conformal

> coating?  Not talking the cosmic radiation hard space kind.  I know it

> would be wavelength and intensity specific.  Got a question from one
of 
> our engineers and I, of course, gave the very intelligent answer of
"Beats 
> me".  But I have this wonderful resourse called Technet...............
> 
> Doug Pauls
> 
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