Cold, anodized surfaces

[Paul.Jorden at eev.com]

Posted to CCD-world:
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Tim, & ccd-world,
 >
 > Does anyone have any experience of the gettering (or otherwise)
 > properties of cold, anodized surfaces within a dewar (that is,
 > _not_ the inner surface of the outer shell, but parts of a cold
 > table, etc.)...?
 >
As Dave has now said, the anodised surface will be very porous, and 
presumably a good getter.  Certainly (at RGO) we avoided it inside the 
dewar- as a warm surface- because it could outgas so much water vapour, 
 Presumably when cold, it will trap this.  I don't have any direct knowledge 
of what it does to other materials.
I still think I would avoid anodising in general, unless I wanted it to 
deliberately function as a sorb.  In this case, I would keep it separate 
from the detector vicininty- to allow independent temp. control, and 
minimise contamination.
Presumably a purpose-made sorb material has a higher efficiency.

If you want a vacuum refererence, have a look at:
     'Modern Vacuum Practice' Nigel Harris 1989 McGraw Hill
     ISBN 0-07-707099-2

By the way, I believe 'sorption' means the reversible process of trapping & 
releasing gases (eg zeolite, or other sorbs, used in cryostats). 
 'gettering' is chemi-sorption, which is a chemical trapping, and not 
reversible in general.

Cheers,
Paul
_______________________________________________________________
Dr Paul Jorden,  CCD Applications, EEV
Waterhouse Lane, Chelmsford, Essex, CM1 2QU, UK
Tel:      44 (0) 1245 -453458 (direct), -493493 (switchboard)
Fax:      44 (0) 1245 453224
see also:-     http://www.ccd.eev.com/

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