CCD-world: Removing anodisation

[Tim Abbott]

The following was posted to CCD-world:


Dear CCD-world,

	As some of you may know we are facing some significant issues
of outgassing from anodised surfaces inside a dewar.  We have
apparently got rid of some pump oil contamination (by repeated and
tedious baking and pumping of the dewar and contents) but still 
have problems with water vapour.  We have asked around about 
removing the anodisation and have recently learned that soaking
in NaOH will remove the colour pigment and (some of) the oxide.
The resulting surface is dull in appearance implying that it
is still porous.  Scraping with a knife renders the surface 
glossy and ball-blasting it makes it look like any other ball-blasted 
surface (at least, to the naked eye).  Some 25um of surface material
is removed in the process.  A photograph and summary is available at:

http://www.astro.ku.dk/~ijaf/NOTCam/deanodize.html

Unfortunately, we cannot ball-blast all surfaces, such as between
the teeth of the cog shown in the photograph.

My question is this:  does anyone know if the NaOH-treated surface
will have any malignant effects on the vacuum or otherwise, and does
anyone have any words of caution about trying this with large surface
areas of anodised aluminium within a cryogenic dewar?  For example, does
the ball-blasting merely cap-over the porous holes, and then cause
more problems later with outgassing from the resulting traps?

Best regards,

	Tim Abbott

-- 
Tim Abbott                                                    tabbott at not.iac.es
Support Astronomer                               http://www.not.iac.es/~tabbott/
                           Nordic Optical Telescope
       Apartado 474 E-38700, Santa Cruz de La Palma, Canary Islands, Spain
- -- CCD-world -- --
CCD-world is fully moderated. Send posts to CCD-world at astro.ku.dk
Standard replies will go to the list; address personal replies manually.
For more information, please go to:  http://www.not.iac.es/CCD-world/