DE3026801A1 - DEVICE FOR DETERMINING THE OXYGEN CONCENTRATION AND METHOD FOR THE PRODUCTION THEREOF - Google Patents

Description

DESCRIPTION

The invention relates to a device or probe or

an element for the detection or for the determination or for the measurement of Oxygen concentration using a solid that conducts oxygen ions Electrolytes and a method for their production and in particular a device for determining the oxygen concentration, which is determined by layer-by-layer Application of the solid electrolyte and formed by electrodes on a substrate and a process for their manufacture.

A variety of devices have been used to determine the Oxygen concentration suggested, including one that can be achieved by layering a reference electrode, a solid electrolyte and a measuring electrode a plate-shaped substrate, and a device made by Application of a solid electrolyte to a plate-shaped substrate, application a reference electrode and a measuring electrode on the solid electrolyte and Covering the reference electrode with a dense material has been formed. In these cases, the plate-shaped substrate generally consists of aluminum oxide, while the solid electrolyte consists of zirconia, that with calcium oxide, yttria or magnesia has been stabilized.

That used to form the solid electrolyte discussed above Zirconium oxide changes reversibly at a temperature of around 900 to 12000C from a monoclinic shape to a tetragonal shape (square shape) around, with a volume change of 7 - 9%.

As a result, if the solid on the alumina substrate applied solid electrolyte of zirconia to the above-mentioned temperature heated or cooled from the above-mentioned temperature that constitutes it Zirconia is subject to a change in volume, causing breakage of the solid electrolyte can lead, so that the solid electrolyte formed from zirconium oxide is only a small one Has heat resistance. To solve this problem, it has already been suggested to mix the zirconia with an additive or stabilizer by reaction with the zirconium oxide a thermally stable, solid solution with the cubic shape of the Zirconia to form, thereby contributing to the volume change of the solid electrolyte change in temperature is reduced. Such additives are, as mentioned earlier was calcium oxide, yttrium oxide or magnesium oxide.

Much research has been carried out into the choice of additives and the amount of additive to be added, on the basis of which it was proposed to use a reduced amount of the additive in order to achieve that about 30% of the zirconia remains in the monoclinic form, including 2 to 6% by weight calcium oxide can be used as an additive.

However, even if you have the device for determining the oxygen concentration provided with the solid electrolyte prepared in this way and this device for determining the oxygen concentration in the exhaust gases of an automobile internal combustion engine examined, cracks form in the solid electrolyte and the solid electrolyte already dissolves at a relatively early point in the examination period from the plate-shaped substrate. During this examination are repeated thermal Shocks carried out at which the temperature for a period of about 2 minutes increased from room temperature to about 8000C and then during one Time of about 2 minutes is lowered back to room temperature.

This destruction and detachment of the solid electrolyte appears to be one To be a consequence of the significantly different thermal expansion coefficients of the alumina used to form the plate-shaped substrate (about 7.8 x 10-6 / OC in sintered state) and the solid -6 electrolyte (about 9.54 x 10 / OC for ZrO2 containing 10% by weight of CaO and about 9.00 x 10 / OC- for 20% by weight of Y203 -containing ZrO2).

The object of the present invention is now to provide a device or to specify a probe for determining the oxygen concentration, which is not suffers from the disadvantages of conventional oxygen probes and those also with repeated thermal shocks do not cause cracks or detachment of the solid electrolyte of the alumina substrate shows.

This object is now achieved by the device according to the main claim.

The subject of the invention is therefore the device for determination the oxygen concentration according to claim 1 and the process for its preparation according to claim 3.

The subclaims relate to particularly preferred embodiments the device according to the invention or

the method of their manufacture.

The device according to the invention for determining the oxygen concentration consists of a layer of a solid electrolyte that conducts oxygen ions, supported by an alumina substrate. The layer from the solid Electrolyte consists of zirconium oxide and contains one of the oxides yttrium oxide and Erbium oxide in an amount of 4.0 to 7.0 mol% based on zirconium oxide.

The solid electrolyte layer is used to manufacture the device preferably formed by the in the form of a paste on the substrate printed solid electrolyte burns at a temperature of 1350 to 15500C.

In the device according to the invention show the layer from the solid Electrolytes and the substrate have very similar coefficients of thermal expansion. As a result the device according to the invention tends to determine the oxygen concentration not to form cracks in and detach the solid electrolyte from the substrate so that good adhesion is maintained even when the device is or probe is subjected to repeated strong thermal shocks, as described in the exhaust gases of an internal combustion engine can be found.

The device according to the invention for determining the oxygen concentration and the process for their preparation will now be described in greater detail with reference to FIG the accompanying drawings explained. In the drawings: FIG. 1 shows a schematic Top view of a preferred embodiment of the device according to the invention for determining the oxygen concentration and FIG. 2 is a schematic sectional view the device shown in FIG. 1 for determining the oxygen concentration.

According to the invention, in a device for determining the oxygen concentration, in which a solid electrolyte that conducts oxygen ions and electrodes in layers are arranged on a plate-shaped substrate, the solid electrolyte made of zirconium oxide and contains yttria or erbium oxide as a stabilizer in an amount from 4.0 to 7.0 mol%, based on zirconium oxide, is also used in the production the inventive device for determining the oxygen concentration of the solid electrolyte fired at a temperature of 1350-1550.

As shown in Figs. 1 and 2, the erfindungsgertfäß comprises Device for determining the oxygen concentration or the oxygen probe a plate-shaped substrate 1, one applied to the plate-shaped substrate 1 Comparison electrode 2, an oxygen ion arranged on the comparison electrode 2 conductive solid electrolyte 3 and one applied to the solid electrolyte 3 Measuring electrode 4. However, the teaching according to the invention is also applicable to other embodiments of devices for determining the oxygen concentration applicable in the Wise built up that the solid electrolyte directly onto the plate-shaped substrate applied and then the comparison electrode and the measuring electrode on the solid electrolyte are arranged, after which the reference electrode with a dense Material is covered.

The experiments described below were used a plate-shaped substrate 1 made of alumina and a solid electrolyte made of zirconium oxide (zirconium dioxide), which contains yttrium oxide (Y203) as a stabilizer, carried out. among the exempters there were 4 kinds of powdery ones firm Made by mixing zirconia with yttria under electrolytes Change in mole percentage of yttria with respect to zirconia, such as it is given in Table I below. These powdered electrolytes were with an organic binder (a mixture of.

Ethyl cellulose and terpineol) mixed around four types of pasty To form electrolytes. Then the four pasty electrolytes by screen printing on the surfaces of the corresponding plate-shaped substrates Printed in aluminum oxide. Then those with the pasty solid Electrolytes printed plate-like substrates using those in the following Table I specified conditions fired to form a layer or coating a solid electrolyte with a thickness of 10 to 20 µm on the surface of the Form plate-shaped substrate and produce four samples in this way.

Then the coefficient of thermal expansion was a part of the The solid electrolyte layer of each sample was measured and the resulting Measured values are also listed in Table I. Furthermore, part of a Each sample is subjected to a thermal shock test to determine the adhesion between the plate-shaped substrate and the solid electrolyte to evaluate which test the temperature is repeatedly increased and decreased in the range of 3000C to 8000C became. The results obtained here are also summarized in Table I.

TABLE I. Stabilizer Burning Conditions Particle Heat Evaluation Overall content (temperature ° C) size expansion during competition (Mol%) (x time (h) (µm) coefficient of thermal shock (1 / ° C) test 2.0 1400 x 2 less abnormal bad bad than 10 expansion 4.0 1400 x 2 less 8.20 x 10-6 excellent excellent as 10 net records 7.0 1400 x 2 less 7.65 x 10-6 excellent excellent as 10 net records 10.0 1400 x 2 less 9.00 x 10-6 bad bad than 10 It can be seen from Table I above that when the stabilizer content is 4.0 or 7.0 mol%, based on the solid electrolyte, the coefficients of thermal expansion of the solid electrolytes are 8.20 × 10 6 / 0C and 7.65 ×, respectively 106 / 0C. These coefficients of thermal expansion are similar to that of aluminum oxide (7.8 x 10 / "C). In the thermal shock test, increasing and decreasing the temperature in the range of 3000C to 8000C was repeated two thousand times, the samples having their stabilizer content 2.0 mol% and 10, respectively , 0 mol% were cracked and showed peeling of the solid electrolyte from the plate-shaped substrate, in contrast to the samples whose stabilizer contents were 4.0 mol% and 7.0 mol%, respectively, no cracks and no peeling of the solid electrolyte can be detected from the plate-shaped substrate.

Thus, if the solid electrolyte is made of zirconia, the yttria in an amount of 4.0 to 7.0 mol%, based on zirconium oxide, as a stabilizer contains, is firmly bonded to the substrate made of aluminum oxide, so result very similar thermal expansion coefficients of the solid electrolyte and the substrate, so that the device obtained for determining the oxygen concentration a has excellent resistance to thermal shock. It has shown, that according to the invention the formation of cracks in the solid electrolyte and the detachment of the solid electrolyte from the plate-shaped substrate is more effective Way to prevent if one can reduce the coefficient of thermal expansion of the solid electrolyte is set to be 0.9 to 1.1 times the coefficient of thermal expansion of the plate-shaped substrate on which the solid electrolyte is applied in the form of a solid layer. It has continued to be beneficial proven to select the particle size of the powdery solid electrolyte in such a way that that they are 5.0 microns or less, and more preferably about 0.7 microns or less on average amounts to. Furthermore, the above-mentioned investigations were carried out using Repeatedly erbium oxide instead of yttrium oxide as a stabilizer. In this case it has been shown that one has very similar coefficients of thermal expansion of solid Can receive electrolytes on the one hand and plate-shaped substrate on the other hand, when adding erbium oxide in an amount ranging from 4.0 to 7.0 mol% to the solid Electrolyte clogs.

Further research was carried out to determine the influence of the To investigate the firing temperature while the amount of stabilizer added is kept constant. In the investigations, this was used as a powdery solid electrolyte Zirconia mixed with 5.0 mole% yttria as a stabilizer and it was through Mix a pasty with the organic binder described above solid electrolyte produced. The pasty solid electrolyte was screen printed printed on the surface of the plate-shaped substrate formed from aluminum oxide, in order to produce an unfired layer of the solid electrolyte of the desired thickness form.

In this way, seven plate-shaped substrates with the pasty solid electrolyte produced.

The obtained plate-shaped substrates were then for two Hours at the temperatures given in Table II below with formation of seven samples burned. The coefficient of thermal expansion was then determined solid electrolyte of each sample measured.

Furthermore, each sample was subjected to a thermal shock test, at which increases and decreases the temperature two thousand times in the range of 3000C to 8000C became. The results obtained are also shown in Table II.

TABLE II Stabilizer Burning Part Particle Heat Evaluation content temperature size expansion coefficient in the total (Mol%) (° C) (µm) effizinet thermal shock rating (1 / ° C) test 5.0 1300 less than 6.90 x 10-6 good bad 10 5.0 1350 less than 7.20 x 10-6 excellent excellent 10 net net 5.0 1400 less than 7.32 x 10-6 excellent excellent 10 net net 5.0 1500 less than 7.42 x 10-6 excellent excellent 10 net net 5.0 1550 less than 7.20 x 10-6 excellent excellent 10 net net 5.0 1600 less than 6.88 x 10-6 good bad 10 5.0 1650 less than abnormal bad bad 10 expansion From Table II above it can be seen that with a stabilizer content of 5.0 mol% based on the solid electrolyte, the coefficient of thermal expansion of the solid electrolyte is similar to that of the plate-shaped alumina substrate in those samples which were fired at temperatures in the range of 1350 to 1550C have been. It could also be observed that these samples showed no cracks and that the solid electrolytes did not peel off from the plate-shaped substrate. In contrast, no satisfactory results are obtained in the thermal shock test with those samples in the preparation of which the firing process was carried out at a temperature which was outside the above-specified firing temperature range.

From the results given in Table II it is still to realize that the particle size of the solid material used to make the layer Electrolytes used powdered solid electrolytes preferably 5.0 cm and averages 0.7 pm or less.

The same studies were carried out using erbium oxide instead of yttrium oxide carried out as a stabilizer, the firing temperature varies and the addition amount of the stabilizer to the solid electrolyte is constant was held. These results showed the same results as those determined with yttrium oxide, which also shows in this case that the firing temperature is preferably kept in the range from 1350 to 1550C.

Furthermore, an X-ray diffraction study was carried out on the samples, those using the stabilizer in an amount ranging from 4.0 to 7.0 Mol%, based on the solid electrolyte, by firing at a temperature in Range from 1350 to 15500C. It was found that 40 up to 70 percent by volume of the solid electrolyte from that present in cubic form Material consists, whereby it is achieved that the coefficient of thermal expansion of the solid electrolyte is similar to that of the plate-shaped substrate, that is, the thermal coefficient of the solid electrolyte 0.9 to 1.1 times the coefficient of thermal expansion of the plate-shaped substrate.

According to the invention, the coefficient of thermal expansion of the solid Electrolytes of a device or probe for determining the oxygen concentration adjusted to be 0.9 to 1.1 times the coefficient of thermal expansion of the plate-shaped substrate, wherein a plate-shaped substrate is made Aluminum oxide and a solid electrolyte of zirconium oxide, which is one of the oxides Yttrium oxide and erbium oxide in an amount of 4.0 to 7.0 mol% based on zirconium oxide contains as a stabilizer, and the solid electrolyte at a firing temperature burns in the range from 1350 to 15500C. This can effectively promote the formation of cracks in the solid electrolyte and the peeling of the solid electrolyte from the plate-shaped substrate can be prevented even if the device or the probe for determining the oxygen concentration in the exhaust gases of a Internal combustion engine used where the device or probe repeated strengthen exposed to thermal shocks.

The device according to the invention thus shows for determining the oxygen concentration good adhesion between the plate-shaped substrate for very long periods of time and the solid electrolyte.

SUMMARY A device or a probe for determination the oxygen concentration with a substrate (1) made of aluminum oxide and one with solid electrolytes that conduct oxygen ions in contact with the substrate (3) which solid electrolyte consists of zirconia and one of the oxides is yttria and erbium oxide in an amount of 4.0 to 7.0 mol%, based on zirconium oxide, and a process for their production are described. With the one constructed in this way The device or probe will prevent the formation of cracks in the solid electrolyte and prevents the solid electrolyte from becoming detached from the substrate.

Claims (8)

Device for determining oxygen concentration and method for their manufacture priority: July 16, 1979, Japan, No. 54-89244 CLAIMS Device for determining the oxygen concentration characterized by a Substrate (1) made of aluminum oxide, an oxygen ion in contact with the substrate conductive layer (3) made of a solid electrolyte, what fixed Electrolyte consists of zirconium oxide and one of the oxides yttrium oxide and erbium oxide in an amount of 4.0 to 7.0 mol% based on zirconium oxide; and with electrodes (2,4) in contact with the solid electrolyte. 2. Apparatus according to claim 1, d a d u r c h g e k e n n z ei c h n e t that the layer (3) of the solid electrolyte has a thickness in the range of 10 to 20; im having. 3. Method of making a device for determining the Oxygen concentration with a substrate (1), one with the substrate in contact standing solid electrolyte (3) which conducts oxygen ions and with the solid Electrolyte in contact electrodes (2,4), d u r c h e k e n n z e i n e t to form the substrate from alumina; the solid electrolyte of zirconium oxide, which is one of the oxides yttrium oxide and erbium oxide in an amount contains from 4.0 to 7.0 mol% based on zirconium oxide; and the fixed ones Electrolyte burns at a temperature of 1350 to 15500C. 4. The method according to claim 3, d a d u r c h g e k e n n z e i c h n e t that one can have an unfired layer of a solid electrolyte on the substrate before the solid electrolyte is burned. 5. The method according to claim 4, d a d u r c h g e k e n n z e i c h n e t that powdered zirconium oxide is used to form the unfired layer mixed with one of the oxides yttrium oxide and erbium oxide; an organic binder with the mixture of the powdery zirconium oxide and one of the oxides yttrium oxide and erbium oxide mixed to form a paste of the solid electrolyte; and applying the solid electrolyte paste to the surface of the substrate. 6. The method according to claim 5, d a d u r c h g e k e n n z e i c h n e t that one can powdery zirconium oxide with a particle size of less used as 5.0 jim. 7. The method according to claim 6, d a d u r c h g e k e n n z e i c h n e t that one is powdered zirconia with an average particle size of 0.7 pm begins. 8. The method according to claim 5, d a d u r c h g e k e n n z e i c h n e t that the organic binder is a mixture of ethyl cellulose and Terpineol used.