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

[Bowman, Valorie D]

Dear Mike, Tommi, All,


Although the turbo pumps are touted as "oil free" that's only relatively true when compared to the old fashioned rotary vaned pumps.  The turbo pumps all have a oil cassette in them to keep the turbo lubricated.  That's the source of your oil (see red below).


It is very dangerous to your turbo pump to vent by withdrawing the holder, even if you have closed the butterfly valves to (in theory) isolate the ports from the turbo. "An uncontrolled burst of gas" can cause your turbo to wobble & hit the sides and cause a gouge in the metal fins or shaft.  Someone did that to mine!  It was too bad to get rebuilt-- I had to replace it. ($$$)    I rewrote the procedure to include SHUTTING DOWN THE PUMP before removing the holders.  We vent by opening one of the other unused ports to go to atmosphere rather than yanking on the O ring.




Valorie Bowman

vdb at purdue.edu
494-5643
EM Facility Laboratory Manager/
Senior Research Electron Microscopist
Purdue Cryo EM Facility
Purdue University
________________________________
From: 3dem <3dem-bounces at ncmir.ucsd.edu> on behalf of Mike Strauss <mikestrauss13 at crystal.harvard.edu>
Sent: Tuesday, September 13, 2016 7:06 AM
To: Tommi White
Cc: 3dem at ncmir.ucsd.edu
Subject: Re: [3dem] corrosion on cryo-holder & inside pumping station

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<mailto: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<tel:573-882-8304>
WhiteTo at missouri.edu<mailto:WhiteTo at missouri.edu>
http://emc.missouri.edu


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