From: "Andreas Derwahl" 
To: "'Ray Desmarais'" , "Atm-US
\(E-mail\)" 
Reply-To: "Andreas Derwahl" 


>  I Have spent a great deal of time on this and have not found
> any answers.
> That certanly does not mean that there is not the magic stuff
> for bonding.
> I have found that most adhesives just can't meet the
> challange for the long
> haul.
> so far only fusing seems to work
> I tried to open this thread a long time ago with no responses.
> maybe together this problem can be solved.
> one of the problems is that these experiments need to be
> carried out for years,
> not weeks or months.You still need to sag a faceplate for a
> mirror to get a
> flat back.
> Kirkham and ritchey played with this a long time ago.
> A chemist might be the most helpful here
> I just tried everything I could think of or could find in the
> way of adhesives.
> grinding and polishing the surfaces seems to help
> press on
>
> RAY
> Ray Desmarais


I've found some information that might be useful here:

http://lmis2.epfl.ch/publications/ASDS2000.pdf

While it is not exactly what we're looking for it has some hints on the
preparation of the surfaces as well as on gluing techniques. They use as I
assumed a strong acid with an oxidant - sulfuric acid with hydrogenperoxide
- to clean and protonate the glass surface. Surface preparation is very
important for this quest as seems to be pressure.

To reduce the thermal stress and increase the strenght of the bond it seems
a good strategy to make the glue layer as thin as possible. In order to
achieve that, matching the surfaces to be bonded as good as possible is
desirable and also to apply pressure while gluing. In the paper they bond
the primed glass surfaces just by pressing without any glue at elevated
temperature (100 - 200 deg C) and high pressure (up to 50 Mpa). Their
second method uses epoxy glue at 90 deg C and 1 Mpa pressure. This does not
seem feasable (20 tonnes on a 10" mirror), but maybe one can get away
with lower pressure?

Also important seems to be the joint design. Because in a ribbed mirror
there's no sufficient heat bridges between front and back plate, the joint
desing should be able to mediate the stress of the two plates of different
size. I might be wrong here, but to me that implies avoiding radial
arrangement of the ribs and prefering concentric. Also the thickness of the
ribs might be important. Thinner might be better?

In the paper they also give reference to other methods of gluing glass, one
is using HF (very nasty stuff to handle, definitely not!!! recommended for
the amateur), another is using the waterglass solution I was refering to
earlier. I'll try to get my hands on that one.

Andreas

--- BBBS/NT v4.00 MP