# US 4,398,980 A · Method for fabricating a seal between a ceramic and a metal alloy

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- Number: US 4,398,980 A
- Document ID: US4398980A
- Status: Granted
- Kind: A
- Application number: 06/286,422
- Filed: 1981-07-24
- Granted: 1983-08-16
- Earliest claimed: 1981-07-24
- Inventors: Paul V. Kelsey, Jr.; William T. Siegel
- Web page: https://patentgrep.com/patent/US4398980A

## CPC

- C04B 37/021: {in a direct manner, e.g. direct copper bonding [DCB]}
- B23K 35/38: Selection of media, e.g. special atmospheres for surrounding the working area
- G01N 27/07: Construction of measuring vessels; Electrodes therefor
- C04B 2235/656: characterised by specific heating conditions during heat treatment
- C04B 2235/6567: Treatment time
- C04B 2235/6582: Hydrogen containing atmosphere
- C04B 2237/32: Ceramic
- C04B 2237/34: Oxidic
- C04B 2237/341: Silica or silicates
- C04B 2237/403: Refractory metals
- C04B 2237/405: Iron metal group, e.g. Co or Ni
- C04B 2237/525: by heating
- C04B 2237/54: Oxidising the surface before joining
- Y10S 228/903: Metal to nonmetal
- C04B: LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE {(roofing granules E04D7/005)}; CERAMICS (devitrified glass-ceramics C03C10/00); REFRACTORIES; TREATMENT OF NATURAL STONE
- B23K: SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS

## Abstract

A method of fabricating a seal between a ceramic and an alloy comprising the steps of prefiring the alloy in an atmosphere with a very low partial pressure of oxygen, firing the assembled alloy and ceramic in air, and gradually cooling the fired assembly to avoid the formation of thermal stress in the ceramic. The method forms a bond between the alloy and the ceramic capable of withstanding the environment of a pressurized water reactor and suitable for use in an electrical conductivity sensitive liquid level transducer.

## Claims

### Claim 1

A method of fabricating a seal between a ceramic and a metal alloy comprising:
prefiring the alloy in a reducing atmosphere with an oxygen partial pressure less than or equal to 10.sup.-10 Pa,
cooling the alloy in said reducing atmosphere,
placing the ceramic in contact with the alloy,
firing the ceramic and alloy in air, and
cooling the ceramic and alloy to a temperature below a firing temperature but above ambient temperature, holding at said temperature for a set period of time, then cooling to ambient temperature whereby a seal is formed therebetween.

### Claim 2 (depends on 1)

The method of claim 1 wherein the prefiring of the alloy is done in an atmosphere with an oxygen partial pressure of less than 10.sup.-14 Pa.

### Claim 3 (depends on 1)

The method of claim 1 wherein the prfiring of the alloy is of a duration of 1 to 4 hours.

### Claim 4 (depends on 3)

The method of claim 3 wherein the prefiring of the alloy is carried out at a temperature between 950.degree.-1150.degree. C.

### Claim 5 (depends on 1)

The method of claim 1 wherein the firing of the ceramic and alloy in air is of a duration of 5 to 30 minutes.

### Claim 6 (depends on 5)

The method of claim 5 wherein the firing of the ceramic and alloy is carried out at a temperature between 950.degree.-1150.degree. C.

### Claim 7 (depends on 6)

The method of claim 6 wherein the firing of the ceramic and alloy is carried out so that the temperature of the ceramic and alloy rises from ambient temperature to about 1050.degree. C. in less than 2 minutes.

### Claim 8 (depends on 1)

The method of claim 1 wherein the fired ceramic and alloy are cooled from firing temperature to about 800.degree. C. and are held at about 800.degree. C. for about three minutes before cooling to ambient temperature.