Sealing compositions for bonding ceramics to metals

Abstract

Abstract 1,173,386. Ceramic seals. WESTINGHOUSE ELECTRIC CORP. 26 April, 1967 [30 June, 1966], No. 19145/67. Heading B3V. [Also in Division C1] A method of sealing ceramic or refractory metal members to ceramic members comprises applying a sealing composition to the members, securing the sealing areas together, and heating the assembly to secure a bond, the composition of the sealing material after the sealing operation being, by weight per cent: and 0.5-10% of at least one of: SiO 2 BaO, ZrO 2 , SrO, TiO 2 , BeO, ThO 2 , Y 2 O 3 . Also included may be 0À5-3À5% by weight of Nd 2 O 3 , Ta 2 O 5 , W0 3 , Nb 2 O 5 , V 2 O 5 . A chart is included listing examples. The method may be applied to sealing Ta, Nb or ceramic, e.g. alumina, discs 12; 14 or caps on the ends of high-temperature metal vapour lamps 10 of alumina. Alumina rings 24, 26 are sealed to the discs 12, 14. One method preparing the sealing composition includes mixing 1 mole of CaCO 2 with ¢ a mole of alumina in powder form and adding the selected other constituents. Amyl acetate and cellulose acetate are included to obtain the desired viscosity and adhesion, and the composition is applied by brushing or spraying, after sand-blasting and cleaning the metal. The seals are air-dried before the assembly is located in a molybdenum clamping fixture, Fig. 2, having a tantalum R.F. susceptor 40. Alternatively, the sealing composition may be formed into compacted preforms. The fixture is placed on a rod. 48 within the R.F. coil of a vacuum furnace and subjected to a heating schedule, Fig. 3 (not shown). Another method of preparing the sealing composition to avoid a degassing period in the furnace includes melting the composition in a gas crucible furnace, pouring the molton mixture into water, ball-milling the mixture in distilled water to a fine powder, adding amyl acetate and cellulose acetate and subjecting the mixture to ultrasonic vibrations. A different firing schedule, Fig. 4 (not shown), may then be used. After evacuation of the tube 10 and insertion of the discharge sustaining filling, the tantalum tube 18 is closed and welded at 22. The expansion ratio of the tube 10, end plates and the sealing material match each other.

Inventors

• 👤 Richard B Grekila
• 👤 Shih-Ming Ho
• 👤 William J Knochel
• 👤 Francis C M Lin

Bibliographic Details