[time-nuts] Fundamental limits on performance

Joseph M Gwinn gwinn at raytheon.com
Thu Sep 17 23:06:25 UTC 2009


time-nuts-bounces at febo.com wrote on 09/17/2009 01:10:32 PM:

> From:
> "Rick Karlquist" <richard at karlquist.com>
> To:
> "Discussion of precise time and frequency measurement" <time-
> nuts at febo.com>
> Date:
> 09/17/2009 01:20 PM
> Subject:
> Re: [time-nuts] Fundamental limits on performance
> Sent by:
> time-nuts-bounces at febo.com
> Lux, Jim (337C) wrote:
> >> impurities.  The JHU crystals are apparently in some type of glass
> >> enclosure which can take the high temperatures, and the 
> paper seemed to
> The processing temperature is limited by the phase change of the
> quartz.  Above a certain temperature, it is permananently changed
> to another form that is useless for oscillators.  Is there any
> evidence that these crystals are actually baked out at a higher
> temperature than cold weld copper packaged ones?  The link to
> JHU was broken.

There is a glass sealing approach that does not involve melting the glass. 
  I forget the name of the process (ionophoresis?), but one prepares the 
surfaces to be sealed by grinding and polishing them to be optical flats 
(or nearly so).  The pieces are held in contact, flat to flat, and the 
assembly is heated.  When glass is above about 100 C, it becomes an 
electrical conductor.  A current is then passed from one piece to the 
other through the contacted flats.  This causes ionic migration and 
welding, yielding a hermetic seal with no messy epoxies or the like.  I 
read the patent on this, but no longer recall the name of the inventor, 
but it was a big deal in the sealing of gas laser tubes.

Found it.  The founding patent is US 3,397,278.

Here is a paper on the process: <

Technology, 1975, Vol. 2, No. 1, pp. 45-53, printed in Great Britian.

Joe Gwinn

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