Re: Beryllium Oxide

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Mddeming@xxxxxxx 

Hi Dave, All,
For what may be of interest only to those who remember their high 
school chemistry, BeO2 doesn't exist. Since Be is a metal of valence 
+2 the oxide is BeO, not BeO2.

Matt D.

In a message dated 12/31/06 8:07:54 P.M. Eastern Standard Time, 
tesla@xxxxxxxxxx writes:
Original poster: David Speck <dave@xxxxxxxxxxxxxxxx>

I would concur with the vacuum feedthrough identification for the insulators.
I have several like these, and when properly identified, they usually
go for big bucks on eBay ($150+ each).  The advantage of using Be02
is that the high thermal conductivity helps minimize thermal expansion effects.

If you want to keep a high vacuum intact, having your insulators move
when they get hot is likely to cause leaks.  In many semiconductor
processing apps, the vacuum chambers can have big temperature
differentials between the inside and outside, and the situation is
complicated further if you are running heavy currents for vapor
deposition filaments through the centers of the insulators.  The
better the heat conduction through the insulator, the less thermal
expansion you are likely to have to deal with.
I would expect that they are pretty much pure BeO2, except for a
little binder.  They are pretty much inert when intact.   It was the
best material available around the time of WWII, before modern
plastics like Teflon and Delrin came into common use.
Interesting correlation -- the best best thermal conductors are
usually the best electrical conductors.  Exceptions exist -- Al2O3 is
used in the typical white computer heatsink grease.  Chemically
inert, decent heat conductor, but good insulator.  Diamond is also a
good heat conductor, though a good insulator.
HTH,
Dave