From the Microscopy List Server:

Dear Listers,
A question about SEM column cleaning.
How should I clean the condenser pole pieces? For other components like wehnelt cap, anode, etc., I use abravise paste for metals and acetone to wash it, but I'm not sure if this is treatement might be too strong for pole pieces. Thanks.
Davide

Dear All,
I service technician from Zeiss told me NEVER to sonicate pure iron pole pieces, so I never did this.
From another technician I learned this:
1- depending how dirty the surface is: cotton swaps and diamond polish with 0,25 micron grain size; no polish like Wenol or normal household metal ploish please...
2- brake cleaner
3- soap and water
4- aceton or ethanol some times
5- drying at 60 degrees C
It works well with all the inliner / aperture surfaces in my LaB6 SEM... In my older Cambridge times, when I had to clean pure iron pole pieces a lot, I used this also.
Stefan

Hi
The main consideration when cleaning pole pieces is "Will I remove any metal?" Any technique that removes metal, no matter how careful you are, will eventually spoil the pole piece by changing its shape.

I feel pole pieces that have individual poles could be washed in a solvent in an ultra sonic cleaner. I fail to understand how vibration will alter the pole piece shape if cleaned individually? However pole pieces where the two poles are fixed together (often soldered) should never be placed in an ultrasonic cleaner; the vibration may crack the solder interface!

I had client who used a dental drill with a polishing head to clean the mouth of the cathode (cathode aperture) for 15 years. They manufacturers service technician noticed that he could not correct for condenser astigmatism, even after twice cleaning the condenser system. I became involved when they asked for my advice and I suggested the technician take a good look at the cathode? Sure enough the aperture was an ellipse!

I was also brought in on an objective lens astigmatism problem where once again the manufacturer's technician had tried everything he could think of. The lens was water cooled with water that was too cold and condensation had attacked the body of the lens producing permanent astigmatism, too great to compensate. A warning to all that the water flow is for the situation when the lens is on (100kV typically 5 amps of current being passed), but what happens when the electronics are switched off overnight, should you switch off?

I still marvel at the wondrous ways people use to clean cathodes. It is a very simple task that should take about 15 minutes, the time consuming element is often the filament alignment.

Ammonia solution (HH4OH) at a concentration in excess of 25% will clean a cathode in an ultrasonic cleaner in about 10 minutes in most cases; ammonia being a solvent for tungsten. Wash away the solution and rinse for 30 seconds in alcohol, dry as rapidly as possible and check with a hand lens.
Steve