[3dem] corrosion on cryo-holder & inside pumping station

[Mike Strauss]

Hi Tommi,

we have a similar situation in our Gatan pumping station.  It gets a lot of
use, and both holders we have attached are corroding quickly.  We don't let
it accumulate white or green crusts, but they oxidize very quickly and turn
an unhealthy shade of brown.  On top of this, we have a fair amount of oily
residue on the rod which needs to be cleaned off.  As far as I can tell,
this does not come from the microscope, but from the pumping station (our
negative stain holder does not have this problem, and it is often in the
microscope).

I think this issue has a number of causes.  The first is probably the water
the is condensing on the cold holder and causing corrosion, which you
address by warming it up in the station.  I'm not sure this will prevent
corrosion, but maybe it will help keep the vacuum clean in the pumping
station.

The second has to do with the design of the pumping station itself.  On
ours, there is no port to vent with nitrogen, and the vacuum is broken by
withdrawing the holder.  This introduces any manner of contamination in an
uncontrolled burst of gas.  Additionally, there is no possibility of
pre-pumping the holder tips with a roughing vacuum, which means the
molecular drag pump gets a shock every time the valves are opened.  I am
still tracking down the source of the oil, but I am guessing it comes from
the mdp somewhere.

After 1 1/2 years, our vacuum gauge failed, and upon opening it we
discovered it is absolutely filthy.  Clearly this needs to be serviced more
regularly.

please let me know if you find out anything more.

mike

On Wed, Sep 7, 2016 at 1:49 AM, Tommi White <tommibarhorst at gmail.com> wrote:

> Hello.
>
> We had some unfortunate issues with our Gatan 626 high tilt cryo-holder
> and Gatan Turbo pumping station.  We have spent  >$5K to clean everything
> from corrosion that built up both on the holder and inside the pumping
> station.  The corrosion looked like a whitish-blue crust on the tip of the
> cryo-holder, and according to the repairman, was all over the inside of the
> pumping station as well.  We eventually found the holder tip could be
> cleaned/removed using Wenol metal polish on a cotton swab.
>
> Prior to the corrosion issues, we would perform both warm-up/zeolite
> cycles on the pumping station, without removing the cryo-EM grid from the
> holder.  Once we started seeing corrosion, we would perform the warmup
> cycle in the loading station, remove the grid from the holder and perform
> zeolite cycle in the turbo-station.
>
> Negative effects included the shutter "grinding" during movement and/or
> the pumping station not pulling proper vacuums to maintain cryo-temperature
> during transfer with subsequent vacuum crashing.
>
> Has anyone else experienced this?  Does anyone know what may have caused
> this?  How do we prevent this from happening in the future?
>
> Thanks in advance,
>
> Tommi A. White, Ph.D.
>
> Assistant Professor of Biochemistry
>
> Associate Director, Electron Microscopy Core Facility
>
> University of Missouri
>
> W117 Veterinary Medicine Building
>
> 1600 East Rollins Street
>
> Columbia, MO 65211
>
> 573-882-8304
>
> WhiteTo at missouri.edu
>
> http://emc.missouri.edu
>
>
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>
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