Re: EPR cavity refurbishing?
G. Pearson (gpearson@blue.weeg.uiowa.edu)
Tue, 9 Apr 1996 18:54:11 -0500
> From: ben.bangerter@yale.edu (B. W. Bangerter)
> To: ammrl@bloch.cchem.berkeley.edu
>
> I have an old Varian e-109 EPR spectrometer, and the rectangular x-band
> cavity is in bad need of refurbishing - cleanup and silver plating in
> particular. ...
Ben,
A machinist should be able to clean up the surfaces (or do it yourself),
and could fix mechanical stuff if that were to be needed. Any decent plating
company should be able to handle the plating job.
FWIW, when I was in grad school, we designed our own cavities and had a
machinist fabricate them -- usually, out of brass. (In fact, all the ESR and
ENDOR spectrometers in the group were completely home brew, except for the
electromagnets.)
We sent our cavities out to a plating company, with instructions to plate
silver on them, followed by a "rhodium flash" on top. As I recall, we
specified the thickness of the silver coating so that it was at least a couple
of skin depths thick, and the rhodium was a fraction of a skin depth thick. I
vaguelly recall "a few microinches" for the rhodium, but don't quote me on
that.
The purpose of the super-thin rhodium covering over the silver is to inhibit
corrosion; it's thin so that it does not significantly degrade the Q.
Without the rhodium, the surface of the silver corrodes and the Q goes to pot
in a hurry. Why rhodium? Because it worked, and because rhodium is a
standard thing for platers to put on silver jewelry. Gold does not work. If
you put a gold flash over silver, the gold will diffuse into the silver, and
you'll quickly be back to square one with a surface which corrodes easily.
Hope this helps. -- Gerry
---------------------------------------------------------------
Gerald A. Pearson INTERNET: gerald-pearson@uiowa.edu
Chem. Dept., Univ. of Iowa OFFICE: 319-335-1336
Iowa City, IA 52242-1219, USA LABS: -1332, -0073 FAX -1270
---------------------------------------------------------------