[time-nuts] Fundamental limits on performance

Joseph M Gwinn gwinn at raytheon.com
Fri Sep 18 00:11:32 UTC 2009


Rick,

time-nuts-bounces at febo.com wrote on 09/17/2009 07:40:48 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 07:44 PM
> 
> Subject:
> 
> Re: [time-nuts] Fundamental limits on performance
> 
> Sent by:
> 
> time-nuts-bounces at febo.com
> 
> Yes, we use that process for assembling hermetic optics.  However, the
> glass package in the bulova photo looks like it has a conventional
> "tip off".  Why are you thinking that they use the optical
> sealing technique?

I didn't see the photo.  I was triggered by the comment that the high 
temperature needed to fusion seal a glass envelope would likely ruin the 
quartz piezo element.  Actually, the presence of a glass tip-off tube 
means only that they bake and evacuate the envelope after assembly and 
hermetic sealing, unless the tip-off tube is *very* large.

Joe Gwinn



> Rick
> 
> 
> Joseph M Gwinn wrote:
> > Rick,
> >
> >
> > 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 theinventor,
> > 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: <
http://psec.uchicago.edu/anodic_bonding/Field%20assisted%20Glass%20sealing.pdf
>
> >>.
> >
> > FIELD ASSISTED GLASS SEALING, GEORGE WALLIS, Electrocomponent Science 
and
> > Technology, 1975, Vol. 2, No. 1, pp. 45-53, printed in Great Britian.
> >
> >
> > Joe Gwinn




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