Powder metallurgy processes – Powder metallurgy processes with heating or sintering – Metal and nonmetal in final product
Patent
1993-05-25
1994-12-20
Walsh, Donald N.
Powder metallurgy processes
Powder metallurgy processes with heating or sintering
Metal and nonmetal in final product
419 5, 419 19, 419 20, 419 45, 204424, 204425, 204426, 204421, B22F 704
Patent
active
053743903
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a process in for producing a layer system for gas sensors. German Offenlegungsschrift, or Laid Open Patent Application 29 04 069 discloses layer systems for gas sensors, in particular for lambda probes or polarographic probes, in which an interlayer of fully stabilised zirconium dioxide is formed on a partially stabilised solid electrolyte body before applying metallic or cermet electrodes. This layer sequence makes it possible to exploit the good mechanical strength and high thermal-shock resistance of partially stabilised solid electrolyte material, while at the same time, however, avoiding the disadvantages of these solid electrolyte materials in sensor manufacture. Irreversible transformation of metastable tetragonal ZrO.sub.2 into monoclinic ZrO.sub.2 produces microstructure damage, initially at the surface of the ceramic and then in the interior of the ceramic as well as a result of crack propagation. Monoclinic zirconium dioxide has, however, also the further disadvantage that it virtually does not conduct O.sup.-2 ions. The irreversible phase transformation tetragonal to monoclinic zirconium dioxide at the boundary surface between solid electrolyte body and electrodes therefore results in a further disadvantage, namely in a reduction of the electrolyte/electrode/test gas three-phase boundary and, consequently, in an impairment of the electrode function.
The phase transformation of the tetragonal ZrO.sub.2, which initially starts at the surface, is substantially suppressed, according to German Offenlegungsschrift, or Laid Open Patent Application 29 04 069, by applying an interlayer of fully stabilised ZrO.sub.2 between solid electrolyte body and electrode.
Furthermore, German Offenlegungsschrift, or Laid Open Patent Application 28 52 638 discloses the improvement of the load carrying capacity of gas sensors by using ceramic materials having different sintering activity for the layer system composed of solid electrolyte and cermet electrodes, in which connection the ceramic material for the supporting structure of the cermet electrode should be less sintering-active than the ceramic material of the solid electrolyte.
SUMMARY OF THE INVENTION
The process according to the present invention is characterized by (a) providing a cermet electrode material comprising an ion-conducting ceramic material and an electron conducting material interdispersed with each other; (b) adding an excess amount of a stabilizing substance to the electrode material; (c) applying at least one layer of the electrode material of (b) to an ion-conducting solid ceramic electrolyte optionally containing a stabilizing substance of lower concentration than necessary for full stabilization; and (d) forming a fully stabilized transition region in at least the surface boundary zone of said electrolyte and electrode. The process of the present invention produces gas sensors which comprise an ion-conducting solid electrolyte and an electrode which are essentially ceramic material which forms a supporting structure and from an electroconducting material. It is characterized in that stabilizer oxides and/or compounds which form stabilizer oxides on exposure to high temperature, are added to the electrode material in proportions above those necessary for the full stabilization of the electrode ceramic. The stabilizer oxides at least partially penetrate the surface of the partially stabilized solid electrolyte on applying the cermet electrode and/or during the sintering process and produce fully stabilized transition regions at that point which have increased ion conductivity. This process provides an improved method of producing gas sensors having good mechanical properties and high load carrying capacity of the electrodes. By adding stabilizer oxides to the electrode material in proportions above those necessary for the full stabilisation of the electrode ceramic, a more efficient manufacturing process is provided for the layer system and dispenses with the application of a fully stab
REFERENCES:
patent: 3776831 (1973-12-01), Roy et al.
patent: 3989614 (1976-11-01), Tien
patent: 4152234 (1979-05-01), Pollner
patent: 4170530 (1979-10-01), Watanabe et al.
patent: 4265724 (1981-05-01), Haecker et al.
patent: 4276142 (1981-06-01), Topp et al.
patent: 4283441 (1981-08-01), Haecker et al.
patent: 4296148 (1981-10-01), Friese
patent: 4299627 (1981-11-01), Shinohara et al.
patent: 4347113 (1982-08-01), Fischer et al.
patent: 4354912 (1982-10-01), Friese
patent: 4409135 (1983-10-01), Akimune et al.
patent: 4847172 (1989-07-01), Maskalick et al.
patent: 5032248 (1991-07-01), Kanamaru et al.
Greaves John N.
Robert & Bosch GmbH
Walsh Donald N.
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