[time-nuts] Distribution amp - Use a video amp unit ?

[Chuck Harris]

Pure quartz glass, which is silicon dioxide, softens (bends) at 1665C, and
melts at something around 2000C.

Softening and melting are not the same thing.  At the softening point glass can
be bent without breaking, at the melting point (which is quite wide) it flows
like a liquid.  It has to get above the flow point to be able to adhere to the
Dumet seals on the wire.

Soda lime glass melts at about 1500C, as I said, but it bends at about 900C.

The highly leaded glasses that they used to use to make glass diodes melt at
about 700C, and the highly "zinced" glasses that they currently use melt at
about 560C.

I have made metal-glass vacuum seals, and they are done at the liquid point
of the glass.  At that point, the glass flows and sticks to itself, and just
about everything.  It is the same temperature used to weld two pieces of like
glass to each other.  At the bending point, however, glass won't stick to
other glass.

-Chuck Harris


ALAN MELIA wrote:
> I dont think so, pure quartz melts at, I think, 1440C but glasses (like
> lead-glass) melt at much lower temperatures 500 to 600C. Remember the chemical
> glass-blowing skill of the technicians.
>
> The glass mix has to be formulated to match the expansion rate of the lead seals.
> A iron alloy with a small expansion coeff. whose name I dont recall was used for
> the leads. Glasses soften well below melting temperature (I remember "sucked in"
> 807 and 6146 tubes that had dissipated a few watts to many) Then the softened
> glass is "rolled" onto the lead. If you look carefully at some glass wire-ended
> diodes you will see a slight waist where this happened. The seal and adhesion is a
> thin metal/oxide/glass interface. Soldering temps rarely cause trouble but bending
> the lead wire close to the glass should be avoided. I used an oxy-hydrogen flame
> micro-welder for making connections for high temp life tests, so the wires got
> quite hot, but not close to the metal-glass seal. I only had peripheral knowledge
> of glass technology but most of the technology was developed in the lamp and valve
> (tube ) industries. I guess there are great references in the web now :-))
>
> Alan G3NYK