laminated glass tubes

Subject:	laminated glass tubes
Date:	Fri, 18 Dec 2009 15:08:59 +0100

Hi!

I make display glass tubes with high pressure content (up to 200 bar).
To protect the tubes from damage and to protect the spectators from
shrapnel in case of an explosion I try to make a protective cover.

Previously I used polycarbonate tube which is strong enough, but is easy
to scratch and may turn brittle eventually. So I'm looking for something
that will last 100+ years. I try to make laminated glass tubes. Filling
the 1-3mm gap between concentric glass tubes with polyester produced
bubbles as the polyester shrunk when it set.

Can you recommend other materials to fill the gap? They should ...

last very long (100+ years)
excellent optical clarity
The temperature range might be -40 °C (cold weather) to 70 °C (inside a
car in full sun).

Preferably they should be...

tough
low viscosity so I can get them in the gap
index of refraction and thermal expansion similar to borosilicate glass
- 1,52 and 5 * 10^−6
not too expensive

Currently I'm thinking of ...

1) hydrocarbon gel such as in gel candles. It might be fluid enough so
it will not detach from the glass surfaces when its volume grows and
shrinks with varying temperature. But I'm afraid the hydrocarbons might
evaporate.

2) crystal clear polyurethane resin.

3) crystal clear silicone or modified silicone/silane (MS-polymer)

4) Other crystal clear sealants

Actually just a simple (viscous) liquid (glycerol) might do the job, if
it could be sealed in the gap reliably.

Thanks, Bernhard