CCD-world: Chem film in dewars

[Willie Koorts]

The following was posted to CCD-world:


On Wed, 29 Sep 1999, Brian McLeod wrote:

> Does anyone have any experience (positive or negative) with
> chemical film coatings on aluminum in CCD dewars.
> I've heard claims that it is better than 
> bare aluminum in a vacuum and improves the outgassing 
> properties.  But I thought I would appeal to the CCD folk
> for comments.


Hi Brian

My only experience with vacuum coatings was with the previous generation
of Infrared Lab dewars with the conical top, where they used such a
coating - since this top section was a casting, the possibility of
traps/leaks existed.  After machining part of the dewar, we found a lot of
metal swarf collected and got stuck to this coating (which had a sticky
finish, even when dry).  I asked IRlabs for advice which told me to clean
it off with acetone and re-spray the coating - which comes in an aerosol
can, but I since lost the exact details.  We cleaned it off but never
bothered re-applying it and was quite happy with the hold time of the
system (>24 hours).  

Since we never had an opportunity to run a hold time test beforehand we
were unable to tell if it made any difference.  What put me off this
particular coating was the fact that it stays sticky and seem to collect
all sort of nasties!  Being soluble in acetone made it impossible to clean
with our cleaning regime at the time, which included acetone.

Willie

                       Mr. W.P. Koorts ( wpk at saao.ac.za )    
                     South African Astronomical Observatory 
                   PO Box 9   Observatory  7935  South Africa
                 Tel.(27) (21) 447 0025  Fax.(27) (21) 447 3639
               World   Wide   Web  ( Work ) http://www.saao.ac.za
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