Re: Beryllium Oxide

["Tesla list" <tesla@xxxxxxxxxx>]

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

Tesla list wrote:
> Original poster: Bert Hickman <bert.hickman@xxxxxxxxxx>
>
> Hi Godfrey,
>
> These sound very much like vacuum feedthrough insulators.