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Frit Sealing
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Ceramic Rod & Tube

Aluminum Nitride Substrates



Frit Sealing MACOR® Machinable Glass Ceramic

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.

See also: Materials > MACOR®

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