Method of processing "BPS" glass ceramic and seals made therewit

Details Method of processing "BPS" glass ceramic and seals made therewit Method of processing "BPS" glass ceramic and seals made therewit

1996-09-03

1998-10-13

Mosley, Terressa

Stock material or miscellaneous articles

Composite

Of quartz or glass

428 344, 428 357, 428 369, B32B 1706

Patent

active

058209891

ABSTRACT:
A glass ceramic composition, a glass ceramic-to-metal seal, and more specifically a hermetic glass ceramic-to-metal seal prepared by subjecting a glass composition comprising, by weight percent, SiO.sub.2 (65-80%), LiO.sub.2 (8-16%), Al.sub.2 O.sub.3 (2-8%), K.sub.2 O (1-8%), P.sub.2 O.sub.5 (1-5%), B.sub.2 O.sub.3 (0.5-7%), and ZnO (0-5%) to the following processing steps: 1) heating the glass composition in a belt furnace to a temperature sufficient to melt the glass and crystallize lithium phosphate, 2) holding at a temperature and for a time sufficient to create cristobalite nuclei, 3) cooling at a controlled rate and to a temperature to cause crystallization of lithium silicates and growth of cristobalite, and 4) still further cooling in stages to ambient temperature. This process produces a glass ceramic whose high coefficient of thermal expansion (up to 200.times.10.sup.-7 in/in/.degree.C.) permits the fabrication of glass ceramic-to-metal seals, and particularly hermetic glass ceramic seals to nickel-based and stainless steel alloys and copper.

REFERENCES:
patent: 2392314 (1946-01-01), Dalton
patent: 3220815 (1965-11-01), McMillan et al.
patent: 3564587 (1971-02-01), Ellis
patent: 4414282 (1983-11-01), McCollister et al.
patent: 4536203 (1985-08-01), Kramer
patent: 4921738 (1990-05-01), Cassidy

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