11/11/96
had to replace it. Anybody that has had to clean evaporated LaB6 off the
inside of their wehnelt can identify with my situation--it's doggone
hard on the fingers!!! Our service rep told me about a procedure that
uses HNO3 (nitic acid) but the instructions were unclear and seemed
incomplete. On top of that, he could not recall where his information
had come from. Is anybody familiar with this procedure or can you
possibly shed some light this subject? Thanks.
Bill
Bill Chissoe III
Electron Microscopist,University of Oklahoma
E-mail: wchiss@ou.edu Ph. (405)325-4391
Methods in Electron Microscopy, Portland Press, 1994 which relays a
recommendation by Peter Sewell of LAB-6 Inc. for removing LaB6 deposits from
Wehnelt cylinders by soaking for about a minute in a mixture of 1 part by
volume of conc HCl to 4 parts water followed by sequential rinses with water,
dilute ammonia, deionized water, and finally with reagent grade isopropyl
alcohol, and then drying with a jet of clean air. The section of the book
in which this comment appears discusses a number of other cleaning procedures
designed to reduce gas evolution in vacuum systems and to avoid
waste-disposal problems.
Along that line, I have recently discovered that a product called 'Soap
Scum Remover', manufactured by the Tilex company, is a VERY effective
cleaning agent. It contains a mixture of detergents and diethylene glycol
butyl ether that is really quite powerful. As I mentioned some time ago, it
will even remove diffusion pump oils (including silicone oils) from metal
surfaces. For cleaning most metal parts, all you need to do is scrub
thoroughly with SSR, rinse thoroughly with hot running water and then with
isopropyl alcohol, and blow dry with a jet blaster. (In addition, it is
great for taking gravy, spaghetti, grease, and similar spots off clothing,
and it is super for its intended purpose of cleaning soap scum off tubs and
shower curtains.)
Wil Bigelow
Wil_Bigelow@mse.engin.umich.edu
Use ammonia, not nitric acid! Just place the Wehnelt
in a beaker with some ammonia, leave it for an hour or over-night. Cover the
top and use a fumehood. Most of the deposit will just float off. Light
polishing with Wehnol or Pol is only sometimes required. This has to be
removed with solvents and another shorter period in ammonia followed by a
water rinse and drying. Very little "elbow grease" is required.
Do not use ammonia on copper or brass parts.
Do not use metal polish in pole piece bores.
Cheers
Jim Darley
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I would add two comments to what has already been said
about effective removal of deposits.
1) The less muscle required to remove deposits the better
because heavy pressure might bend the aperture.
2) Six micron diamond paste is very effective in removing
oxides; somewhat less effective on those purple crystal deposits.
A little "dab will do ya" applied gently with a Q-tip followed by
rinses with dilute HCl (1:5 w/H2O), mild alkaline to neutralize and/or
water, and usual solvent such as freon. This paste is available
through Valley Design Corporation (508-692-9549); no commercial
interest motivation. Obtained this procedure from friendly people
at Kimball Physics.
Don Gantz
Boston Univ Med School
gantz@med-biophd.bu.edu
wehnelts. There were several good suggestions, all of which sound
better than the method I have been using. Here is a brief summary:
nitric acid on a foam type swab, dilute(1:4) HCl- soak for a minute or
short sequential exposures, a commercial product called "Soap Scum
Remover", soaking in ammonia (1 hr. to overnight), and .25um diamond
paste in water-soluble base. I knew there had to be an easier way!!!
Fortunately, this is not something that needs to be done very often, but
I look forward to trying some of these suggestions in the future.
Bill Chissoe III
Electron Microscopist,University of Oklahoma
E-mail: wchiss@ou.edu Ph. (405)325-4391