Chemistry: electrical current producing apparatus – product – and – Fluid active material or two-fluid electrolyte combination... – Active material in molten state
Patent
1991-12-31
1993-12-14
Kalafut, Stephen
Chemistry: electrical current producing apparatus, product, and
Fluid active material or two-fluid electrolyte combination...
Active material in molten state
429174, 296232, 296234, 29730, 428653, H01M 208
Patent
active
052701352
DESCRIPTION:
BRIEF SUMMARY
This invention relates to bonds between metals and ceramic or vitreous materials and in particular to articles including a ceramic or vitreous member and a metal member bonded together to form a seal and to a method of securing a metal member to a ceramic or vitreous member to form a seal.
It is often necessary for a metal member to be bonded to a ceramic member to form a seal, a particular example being in the manufacture of sodium/sulphur cells used as secondary batteries.
Unlike conventional lead acid batteries in which a liquid electrolyte--dilute sulphuric acid--separates two solid electrodes, in a sodium/sulphur cell a solid electrolyte--generally beta alumina--separates two liquid electrodes, namely liquid sulphur and liquid sodium electrodes.
Such a sodium/sulphur cell is shown in FIG. 1 of the drawings which is a perspective view of the cell with part broken away. As shown the cell comprises a case 1 of, for example steel, in the form of a right circular cylinder and containing a solid electrolyte cup 2 of beta alumina, the cup 2 containing a sodium electrode 3, while a space between the case 1 and the cup 2 contains a sulphur electrode 4. For use, the cell is maintained at a temperature of between 300.degree. C. and 400.degree. C. such that the sodium and sulphur electrodes 3 and 4 are in liquid form.
The open end of the cup 2 is closed by an insulating disc 5 of alpha alumina, while the case 1 is closed by an annular sealing steel disc 6.
The case 1 serves as a terminal for the sulphur electrode 4, while the sodium electrode 3 contains an elongate metal current collector 8 which extends axially of the case 1 out through the disc 5 where it is connected to a centre terminal disc 7 mounted on the disc 5, the necessary connections being made by welding.
As sulphur is essentially non-conducting a means of making an electrical connection between the case 1 and the cup 2 has to be provided, and this is generally achieved by forming the sulphur electrode 4 as a carbon fibre mat impregnated with sulphur.
It will be appreciated that with such a cell the sodium and sulphur electrodes 3 and 4 can have their locations reversed.
With such a cell it is necessary for the alpha alumina disc 5 to seal the open end of the beta alumina cup 2 and this is generally effected by a glazing technique. It is also necessary for the disc 6 and the terminal disc 7 to be secured to the alpha alumina disc 5 to form seals, and since alpha alumina is both ionically and electronically insulating, diffusion bonding is generally used.
The types of diffusion bonding used fall into two broad classes, namely "low temperature" using temperatures 350.degree. C. and 650.degree. C., and "high temperature" using temperatures above 800.degree. C. However both of these methods have disadvantages. For example, both may require the use of a separate intermediate deformable sealing member between the metal and ceramic members to be bonded.
Because of the temperatures used in the different processes, low temperature bonding is carried out after the alpha alumina disc 5 is glazed to the beta alumina cup 2. The temperatures used in the low temperature bonding can induce failure of the glazing seal during subsequent manufacturing operations or during use of the cell. Furthermore the presence of a beta alumina cup further complicates the process of the diffusion bonding between the alpha alumina disc 5 and either one of the disc 6 or the terminal 7.
High temperature bonding requires the use of materials capable of withstanding the high temperatures used and the thermal stresses produced during the bonding operation. However high temperature bonding can be carried out prior to connection of the alpha alumina disc 5 to the beta alumina cup 2 and thus the stress level in this glazing connection can be kept to a minimum.
GB111760 (Philips) discloses the ultrasonic welding of ductile metals such as aluminium or copper to hard materials such as glass and other vitreous or ceramic substances. A foil of ductile metal, such as aluminium foil of thickness 0.
REFERENCES:
patent: 4530151 (1985-07-01), Kagawa et al.
patent: 4631685 (1986-12-01), Peter
patent: 4772293 (1988-09-01), Bugden et al.
patent: 4804131 (1989-02-01), de Meulenaer et al.
Perry, IBM Technical Disclosure Bulletin, vol. 21, #8, Jan. 1979, p. 3254, "Aluminum Spacer Bond Medium".
Tetsuji, Patent Abstracts of Japan, For Japanese 63/188483, Aug. 1988.
McLachlan Stuart
O'Neil-Bell Christopher
Chloride Silent Power Ltd.
Kalafut Stephen
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