RU2379670C1 - Electrochemical element and method of its manufacturing - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: invention is related to measurement equipment and may be used to manufacture detectors of oxygen concentration measurement in various gases and in wide area of pressures of oxygen partial pressure - from 5 kPa to 100 kPa. Electrochemical element consists of jointly annealed layers and comprises oxygen pump, measurement cell with solid electrolytes from stabilised zirconium dioxide with applied porous platinum electrodes, layer of platinum heater, which is arranged between insulating layers, layer that prevents diffusion of oxygen ions between solid electrolytes of measurement cell and oxygen pump, besides solid electrolytes of oxygen pump and measurement cell are arranged from zirconium dioxide, which is stabilised with yttrium and scandium oxides in cubic crystalline phase in the form of layers with thickness of 10-50 mcm, and layer that prevents diffusion of oxygen ions between solid electrolytes of measurement cell and oxygen pump is made of zirconium dioxide stabilised with magnesium oxide in monoclinic crystalline phase with thickness of 350-600 mcm.

EFFECT: improved accuracy of measurement due to reduction of ionisation and losses of current through solid electrolytes of measurement cell, oxygen pump, increased resistance of electrochemical element to temperature cyclic drops in process of heating up to 700-1000°C and cooling.

4 cl, 2 dwg

Description

The invention relates to measuring technique and can be used for the manufacture of sensors for measuring oxygen concentration in various gases (air, nitrogen, combustible gases, automobile exhaust gases) and in a wide range of oxygen partial pressure pressures (from 5 to 100 kPa).

For the electrochemical cell used to measure oxygen concentration, a design is known (US Patent No. 4610741 dated 09.09.1986 according to class C03B 29/00), which consists of co-sintered layers: a measuring cell with a solid zirconia electrolyte and porous platinum electrodes , an oxygen pump with a solid zirconia electrolyte and porous platinum electrodes, a platinum heating element located between the insulating layers of an alumina-based material. Current is supplied to the electrodes of the oxygen pump, and oxygen is pumped from the external atmosphere and pumped into the cavity located between the layers of solid electrolytes. The oxygen concentration in this design is proportional to the time during which a certain amount of oxygen is pumped and pumped from the cavity, proportional to the current supplied to the electrodes of the oxygen pump.

An electrochemical cell of this kind has a problem in measuring accuracy due to leakage of oxygen ions through the solid electrolytes of the measuring cell and pump.

In the technical solution (US patent No. 7163609 dated January 16, 2007 according to class G01N 27/407) this problem is solved by introducing 10-200 μm thick gaskets into the electrochemical cell, in which there is a cavity for pumping and pumping oxygen. This layer is made of a material based on alumina with zirconia. For compatibility during heating and cooling of layers in an electrochemical cell of this type, aluminum oxide is added to zirconia, which increases the thermomechanical properties of the cell, but the conductive ones are reduced. The US patent (No. 6676817 B2 dated January 13, 2004, class G01N 27/407) also uses a solid zirconia-based electrolyte with the addition of alumina.

The closest technical solution to the claimed is (US patent No. 5169513 from 8/12/1992, class G01N 27/407). In this solution, porous, fully stabilized zirconium dioxide (SDC) in the cubic crystalline phase is used as the solid electrolyte of the oxygen pump in order to increase the heat resistance while maintaining the conductive properties, and the solid electrolyte of the measuring cell is made of material based on partially stabilized zirconium dioxide (CSDC) in the tetragonal phase and the layer preventing the leakage of oxygen ions between solid electrolytes is made of porous SDC. This design has a drawback, which is that as a solid electrolyte of the measuring cell, ChSDC is used in the tetragonal crystalline phase. It is known that materials based on PSF tetragonal crystalline phase have improved mechanical properties, but lower ionic conductivity than SDS. With prolonged temperature application, the degradation of properties in ChSDC is observed due to the reverse polymorphic tetragonal-monoclinic transformation, which occurs with a change in volume.

The objective of the present invention is to improve the measurement accuracy by reducing ionization and current loss through solid electrolytes of the measuring cell, oxygen pump, increasing the resistance of the electrochemical cell to temperature cyclic changes when heated to 700-1000 ° C and cooling.

In the present invention, the objective is achieved in that the solid electrolytes of the measuring cell and the oxygen pump are composed of zirconia in a cubic crystalline phase with high conductivity, low resistivity of less than 5 Ohm · cm and are used in the form of very thin layers of 10-50 μm. This increases the heat resistance and strength of the sintered electrochemical cell. The cavity for pumping and pumping oxygen is located in a ceramic layer based on zirconia stabilized with magnesium oxide in a monoclinic crystalline phase 350-600 μm thick with high resistivities of more than 100 Ohm · cm. This layer plays the role of a gasket preventing the leakage of oxygen ions between the solid electrolytes of the electrochemical cell. In addition, this layer in this design of the electrochemical cell is a carrier for all other thin layers: layers of solid electrolytes of a measuring cell 10–50 µm thick and an oxygen pump 10–50 µm thick, platinum porous electrodes 10–20 µm, and a heating element 10–10 µm thick. 20 microns, located between the insulating layers of aluminum oxide with a thickness of 20-30 microns. The design of the electrochemical cell in this technical solution has another advantage over the prototype. The layer is a carrier layer and is made of zirconia in a monoclinic phase, stabilized with magnesium oxide, which has increased heat resistance under temperature conditions of operation of an electrochemical cell with an integrated platinum heater. The electrochemical cell of the present invention withstands heating to 700-1000 ° C in a few seconds when the heater is turned on, and it suddenly cools when the heater is turned off.

The closest technical solution to the claimed method is a method of manufacturing an electrochemical cell of a patent (US No. 5169513 dated 8/12/1992, according to class G01N 27/407). The method described in the patent includes the following operations: the manufacture of the main supporting layers in the form of ceramic films from partially stabilized zirconia in the tetragonal crystalline phase and which are solid electrolytes of the measuring cell and oxygen pump, applying a layer of fully stabilized zirconia acting as a diffusion-regulating layer oxygen ions, applying layers of platinum porous electrodes, applying a layer of a heating element located between the isolates layers, packaging, pre-firing, sintering. The use of solid electrolytes of zirconium dioxide in the tetragonal phase as the supporting layers is a drawback of this technical solution. It is known that zirconia in the tetragonal phase at temperature (700-1000 ° C) for a long time is subjected to degradation of strength properties due to the tetragonal-monoclinic transition occurring with a change in volume.

A method of manufacturing an electrochemical element of the present technical solution includes the following operations: production of a layer as a carrier layer that prevents diffusion of oxygen ions between the solid electrolytes of the measuring cell and the oxygen pump and consisting of zirconia stabilized with magnesium oxide in a monoclinic crystalline phase. Layers of solid electrolytes of the measuring cell and the oxygen pump, consisting of zirconia stabilized with yttrium and scandium oxides, are deposited on this layer; sintering of the packed layers is carried out in one stage at 1350-1550 ° C between two plates of zirconia stabilized with 7-8 mol%. % yttrium oxide having an open porosity in the range of 15-20%. Sintering of electrochemical elements in one stage is carried out through the use of plates of zirconia of a certain composition and porosity. This makes the method more technological. Sintering between other plates (different composition, different porosity) causes adhesion of electrochemical elements during sintering, which causes their curvature.

The design of the inventive electrochemical cell is shown in figure 1, 2,

where 1 is the external porous platinum electrode of the oxygen pump;

2 - a layer of solid electrolyte of an oxygen pump;

3 - internal porous platinum electrode of the oxygen pump;

4 - an insulating layer;

5 - platinum heater;

6 - an insulating layer;

7 - a layer that prevents the diffusion of oxygen ions between the solid electrolytes of the measuring cell and the oxygen pump;

8 - external porous platinum electrode of the measuring cell;

9 - layer of solid electrolyte of the measuring cell;

10 - internal porous platinum electrode of the measuring cell;

11 - an internal cavity for pumping and pumping oxygen out of the air;

12 - oxygen pump;

13 - measuring cell

A method of manufacturing an electrochemical cell is carried out by the following method.

Zirconia powder stabilized with 8-9 mol.% Magnesium oxide with a specific surface of 7-8 m ² / g and a pycnometric density of at least 5.89 g / m ^{3 is} mixed with 60 wt.% Polyvinyl butyral, 32 wt.% Trichlorethylene, 5 wt.% demethylphthalate, 2 wt.% syntamide. A ceramic film 350-600 microns thick is cast onto a mylar film, dried at 130 ° C. Billet size 70 · 5 mm is cut from the film. A cavity with a diameter of 0.6 mm is cut out in these blanks. The following layers are successively applied to blanks by screen printing from a paste consisting of a powder of the appropriate composition and a solution of polyvinyl butyral in terpineol with a ratio of 1:10:

- an insulating layer of aluminum oxide with a thickness of 20-30 microns;

- a layer of a heating platinum element with a thickness of 10-20 microns;

- an insulating layer of aluminum oxide with a thickness of 20-30 microns;

- platinum porous electrodes 10-20 μm,

- layers of solid electrolytes from zirconia stabilized with 3-4 mol.% yttrium oxide and 6-7 mol.% scandium oxide with a thickness of 10-50 microns.

Sintering of electrochemical cells is carried out in an air atmosphere at 1350-1500 ° C in one stage between zirconia plates with an open porosity of 35-40%.

Electrochemical cells were tested as part of an automotive sensor in the exhaust gas at 350 ° C and 850 ° C. The experimental data are presented in the table. The time to exit to the mode of electrochemical cells (example No. 1) made by the design and method of the present invention is less than in comparative examples No. 2-6. The results of thermal cycling for 500 hours show the advantages of electrochemical cells manufactured according to the present technical solution than in comparative examples. The values of the resistivity of solid electrolytes from zirconia of the composition of the measuring cell and oxygen pump ZrO ₂ + 3-4 mol.% Y ₂ O ₃ + 6-7 mol.% Sc ₂ O ₃ in the cubic crystalline phase and was 4-5 Ohms · Cm, and the resistivity of the composition ZrO ₂ + 3-4 mol.% Y ₂ O ₃ in the tetragonal phase is 8-10 Ohm · cm.

No. The thickness of solid electrolytes, microns The chemical and phase composition of the material of solid electrolytes, mol.% Sintering temperature, ° С Time to exit to mode, c Thermal cycling results 1000 - air 500 h one 10-50 ZrO ₂ + 3-4 mol.% Y ₂ O ₃ + 6-7 mol.% Sc ₂ O ₃
cubic phase 1350 6-7 No cracks 2 300-400 ZrO ₂ + 3-4 mol.% Y ₂ O ₃ + 6-7 mol.% Sc ₂ O ₃ cubic phase 1600 10-12 No cracks 3 300-400 ZrO ₂ + 3-4 mol.% Y ₂ O ₃
tetragonal phase 1600 10-15 cracks four 10-50 ZrO ₂ + 3-4 mol.% Y ₂ O ₃
tetragonal phase 1500 10-11 cracks

Claims (4)

1. An electrochemical cell consisting of co-fired layers and containing an oxygen pump, a measuring cell with solid electrolytes from stabilized zirconia coated with porous platinum electrodes, a platinum heater layer located between the insulating layers, a layer that prevents the diffusion of oxygen ions between the solid electrolytes of the measuring cell and an oxygen pump, characterized in that the solid electrolytes of the oxygen pump and the measuring cell are made of dioxide zirconia stabilized with yttrium and scandium oxides in the cubic crystalline phase in the form of layers with a thickness of 10-50 μm, and the layer that prevents the diffusion of oxygen ions between the solid electrolytes of the measuring cell and the oxygen pump is made of zirconia stabilized with magnesium oxide in a monoclinic crystalline phase with a thickness of 350 -600 microns. 2. The electrochemical cell according to claim 1, characterized in that the content of stabilizing oxides for solid electrolytes of the measuring cell and the oxygen pump is 3-4 mol.% Yttrium oxide and 6-7 mol.% Scandium oxide. 3. The electrochemical cell according to claim 1, characterized in that the content of the stabilizing magnesium oxide layer, preventing the diffusion of oxygen ions between the solid electrolytes of the measuring cell and the oxygen pump, is 8-9 mol.%. 4. A method of manufacturing an electrochemical cell, including the manufacture of the main load-bearing layers in the form of ceramic films of stabilized zirconia, applying platinum porous electrodes, applying a layer of a heating element located between the insulating layers, packaging, pre-firing, sintering, characterized in that as a carrier layer use a layer that prevents the diffusion of oxygen ions between the solid electrolytes of the measuring cell and the oxygen pump and consisting of wild zirconium oxide stabilized with magnesium oxide in the monoclinic crystalline phase, layers of solid electrolytes of the measuring cell and an oxygen pump, consisting of zirconia stabilized with yttrium and scandium oxides, are applied to this layer, sintering of the packed layers is carried out in one stage at 1350-1550 ° C between two plates of zirconia stabilized with 7-8 mol.% yttrium oxide having an open porosity in the range of 15-20%.

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