GB956365A - Glass-to-metal seals - Google Patents

Abstract

In a glass to metal seal of the kind in which the metal member surrounds the glass member and is of massive construction, equality of the expansion coefficients of the two members is brought about to obviate tensile fracturing of the glass, by using a metal member comprising a metal capable of being strengthened by a dispersed-phase-hardening process, the metal being so strengthened prior to, or during, the process of making the seal, or by heating the seal subsequent to its formation. The expression "dispersed-phase-hardening process" includes any process in which a metal is strengthened or hardened by having a phase of particles other than the main phase dispersed therein, and therefore includes precipitation hardening. Examples of suitable glass-metal pairs are: (a) A glass comprising 45% SiO2, 30.4% PbO, 19.8% alkali metal oxide, and 4.8% CaF2, can be sealed at 800 DEG C. to a metal comprising silver alloyed with 0.05% to 0.25% by weight of aluminium or with 0.5% to 0.3% of magnesium and 0.1% to 0.3% of nickel. With 0.2% aluminium or 0.2% magnesium and 0.2% nickel, the silver may be strengthened by internal oxidation prior to sealing to the glass, by heating the metal in air at 600 DEG C. to 800 DEG C. Four hours heating being sufficient for metal 0.04 inch thick. (b) A glass comprising 45% SiO2, 20% alkali metal oxide, 19% alkaline earth metal oxide, 11% ZnO and 5% CaF2 is sealed at 950 DEG C. to a metal comprising copper alloyed with 0.5% of chromium. The seal is then rapidly transferred to an oven at 450 DEG C. to 500 DEG C. and cooled therein for two hours before cooling to room temperature. (c) A glass comprising 48% of SiO2, 17% alkali metal oxide, 19% alkaline earth metal oxide, 11% ZnO and 5% CaF2 is sealed to the metal of Example (b) at 900 DEG C. for fifteen minutes. The seal is then kept at 450 DEG C. for four hours and then cooled at 5 DEG C. per minute. A compression seal of this type can be raised to 250 DEG C. for soldering processes. (d) Copper alloyed with 0.25% of zirconium can be used in Examples (b) and (c) instead of copper and chromium.ALSO:In a glass to metal seal, the metal is capable of being strengthened by a dispersed-phase-hardening process and is so strengthened prior to, or during, the process of making the seal, or by heating the seal subsequent to its formation. The expression "dispersed-phase-hardening process" includes any process in which a metal is strengthened or hardened by having a phase of particles other than the main phase dispersed therein and therefore includes precipitation hardening. Examples of such metals are: (a) Silved alloyed with 0.05-0.25% by weight of aluminium or with 0.05-0.3% of magnesium and 0.1-0.3% of nickel. With 0.2% of aluminium or 0.2% magnesium and 0.2% nickel, the silver may be strengthened by internal oxidation prior to sealing the glass, by heating the metal in air at 600-800 DEG C., four hours heating being sufficient for metal 0.04 inch thick ; (b) Copper alloyed with 0.5% of chromium which is sealed to glass at 950 DEG C. The seal is then rapidly transferred to an oven at 450-500 DEG C. and cooled therein for two hours before cooling to room temperature ; (c) Copper alloyed with 0.25% of zirconium which can be treated as in Example (b).