>         I am looking for an adhesive with the following properties:
>
>         1. Capable of bonding kovar to sapphire.
>         2. Hermetic seal.=20
>         3. Thermal coefficient of expansion (TCE) of approximately 5.66
> x 10^-6 in/in /=B0C=20
>             (0 to 100 =B0C range).   =20
>         4. Translucent.
>         5. Fast curing, with no outgassing.
>
>         I need to bond two sapphire windows to each side of a 2.5" kovar
> wheel.=20
>         The kovar wheel has two gas filled chambers. One chamber is
> filled with carbon monoxide and the other with
> nitrogen.
>
>         Since sapphire and kovar have similar thermal expansion
> coefficients (between 3.24 - 5.66 x 10^-6 in/in/=B0C),=20
>  it would be ideal if the adhesive also had a low thermal
> coefficient of expansion.
>
>         The completed wheel assembly will be rotated at  1800 rpm under
> very little vibration.=20
>
>         Below is a drawing of what I would like to build. Thank you in
> advance for your consideration.
> =20
>         Ron Hom
>         Advanced Pollution Instrumentation, Inc.

The only suggestion I can up with dosen't involve adhesives.  Many
years ago I bonded sapphire to kovar using a glass frit, and then
firing it.  I made a slurry of powdered glass (can't remember the grade
number) and acetone, placed the sapphire lens on the kovar base, and
introduced the slurry around the  seam using a fine artists brush.
Capillary action pulled the frit between the kovar and lens.  This
was followed by firing the entire assembly in a high temperature
oven.

Tom Hybiske
General Atronics Corp.

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