CCD-world: Aluminum finishes, and G-10

[Bruce Atwood]

The following was posted to CCD-world:

First, is this an LN2 cooled system?  If so see my paper in ICSOI Four. 
If you follow my recommendations on the use of zeolite and charcoal the
details of the materials you use are not very important.  I would avoid
both anodized aluminum and paper to limit the total amount of water in
the Dewar otherwise small G-10 parts are fine, bare machined aluminum
(some cleaning with detergent and/or solvent is worthwhile) is also
fine.  I use teflon wire and don't allow any electronic component in the
vacuum space.  
Many systems seem to include numerous near heroic measures (like nickel
plating the interior of an Aluminum Dewar) and forgo a few important
techniques.

We take a few * 10-5 Torr as the required pressure for vacuum insulation
that is limited by radiation from typical surfaces.  At 10-4 you will
see some heat input from conduction.


George Tylinski wrote:
> 
> The following was posted to CCD-world:
> 
> We are designing a CCD camera, intended to operate at about 10e-4 Torr.
> We're finalizing the material and finish specs, but, after looking in
> several books and the archive of this list, have some lingering questions:
> 
> 1) I have seen nothing on electroless Nickel plating of Aluminum parts.
> Would this not be a simple way to provide corrosion resistance (internal
> and external), low emissivity (internal to the dewar), and good electrical
> contact conductance (for ground straps)?
> 2) Is it generally considered OK for this vacuum range to leave the
> internal aluminum surfaces bare (i.e., self-passivated) even if they are
> not to be routinely chemically etched prior to assembly?
> 3) Are there any known problems with using [chemical conversion coating /
> chem film / iridite / alodine] on Aluminum in a vacuum? Is it my
> imagination or does it rub off too easily?
> 4) What is the difference between standard NEMA G-10 fiberglass and the
> G-10CR grade, and how important is it to use the CR grade at -100C?
> 5) How can the machined surfaces of fiberglass parts and circuit boards be
> sealed or fused or otherwise rendered dust-free?
> 6) Are there other discussion lists that might deal more exclusively with
> mechanical design of vacuum/cryogenic hardware?
> 
> Good/bad experience feedback on any of the above would be greatly
> appreciated.
> 
> Best Regards,
> George Tylinski
> 
> George Tylinski Mechanical Design & Analysis
> 503-515-3338 voice / 3339 fax
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-- 
Bruce Atwood
Director
Imaging Sciences Laboratory
Astronomy Department
The Ohio State University
174 W. 18th Ave.
Columbus, Ohio  43210-1106
(614) 292 6279 (V)
(614) 292 2928 (F)
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