| 1. |
Capable
of producing hermetic seals on Macor, forsterite and metals such as
Sylvania #4, Dumet, 52% nickel alloys, chrome-iron stainless steel,
platinum and Sealmet. |
| 2. |
Surface
finish should be 200 (US mesh) grit. Where feedthroughs will be
installed, holes should be drilled 76 to127 microns (.003" to .005")
oversize. |
| 3. |
Ensure
that the sealing surfaces are absolutely clean. (see Cleaning.) |
| 4. |
Glass
frit can be applied by dipping, spraying, painting, screen printing or
extrusion. |
| 5. |
Frit
should be mixed between 5:1 and 15:1 frit to vehicle depending upon
application method. Make only as much slurry as needed to produce a
seal. The slurries have a short shelf life. |
| 6. |
Vehicle
can be obtained commercially from suppliers such as Ferro and
Drakenfeld. |
| 7. |
You
can produce your own vehicle using amyl acetate or denatured alcohol
with about 1.2% nitrocellulose or equivalent added as an organic binder. |
| 8. |
After
applying the frit, it must be thoroughly dried. Oven drying is
recommended but heat lamps can also be used. Keep drying temperature
below 350°C (660°F). Suggested drying cycle is heat at
200°C (360°F) per hour to 200°C
(390°F), hold for 15
minutes and then cool at the same rate. |
| 9. |
To
fuse the frit to the Macor to improve handling, heat at 150° to
200°C (270° to 360°F) per hour to the softening
point of
the frit. Hold for 5 to 10 minutes and cool at the same rate. |
| 10. |
Sealing
cycles will depend upon seal geometry and sizes. A starting point for
experimentation is a heating rate of 150° to 300°C
(depending
upon size) to the sealing temperature and then holding at temperature
for the time specified by the frit supplier. |
| 11. |
Maintain
an oxidizing environment in the furnace at all times. |
| 12. |
Adhere
to all health and safety recommendations from the frit supplier. |
| 13. |
Seals
may be of either vitreous or devitrified glass. The devitrified seals
are generally mechanically stronger and many can be machined however,
they cannot be reworked if the seal leaks. A vitreous seal can be
reworked if it leaks or is misaligned. |
