JPS6126022B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of manufacturing a membrane structure oxygen sensor element. Examples of conventional membrane-structured oxygen sensor elements include those shown in FIGS. 1 and 2. 1st
The figure is a schematic cross-sectional view of an oxygen sensor element manufactured by a conventional manufacturing method, and FIGS. 2a to 2e are manufacturing process diagrams thereof. To explain according to the diagram, the heating element 5 is embedded in the diaphragm layer 1 cut into an appropriate size from an alumina green sheet, or the heating element 5 is placed on one side of one of the two green sheets. A reference electrode 2 (see Fig. 2b) and an oxygen ion conductive solid electrolyte are placed on the surface of the diaphragm layer 1 (see Fig. 2a), which is formed by printing 5 and pasting the other green sheet on this surface (see Fig. 2a). 3 (see Figure 2c),
The oxygen sensor element was manufactured by sequentially stacking the measurement electrodes 4 (see FIG. 2d) in an unfired state and then firing them simultaneously. Alternatively, the oxygen sensor element was manufactured by firing each layer. In such a conventional manufacturing process, when laminating the reference electrode 2, screen printing is performed by making a paste of powder such as platinum (Pt) or its alloy, or a metal-metal compound such as a Ni-NiO mixture. I was doing it. Furthermore, when laminating the oxygen ion conductive solid electrolyte 3, a mixed powder of ZrO ₂ --CcO or the like is made into a paste and screen printing is performed. Furthermore, in order to laminate the measurement electrodes 4, a paste of powder of platinum (Pt) or its alloy was used and screen printing was performed. Alternatively, the measurement electrode 4 has been provided only by physical vapor deposition (PVD). Finally, a protective layer 7 (see FIG. 2e) was applied. However, in the conventional manufacturing method of such a membrane-structured oxygen sensor element, firing is performed simultaneously after lamination, or firing is performed for each lamination, which requires firing at a high temperature. Since the manufacturing method was to obtain the electrode by firing it,
The crystal grains of the oxygen partial pressure detection part, especially the measurement electrode 4 that is in direct contact with the gas to be measured, grow, and the contact area with the gas to be measured decreases, making it difficult to reach the equilibrium oxygen partial pressure for generating an electromotive force. There was a problem that the response was slow. In addition, in the case of membrane-structured oxygen sensor elements, the fired electrodes are often provided by screen printing and are relatively rough, so the contact area with the gas to be measured is small compared to the electrode area.
In addition, the so-called three-phase interface where the gas to be measured, solid electrolyte, and measurement electrode come into contact is also small compared to the electrode area, so catalytic reactions and electrode reactions are not promoted and it is difficult to reach the equilibrium oxygen partial pressure for generating electromotive force. There was a problem that the reaction speed of the oxygen sensor element was slow. On the other hand, in an oxygen sensor element in which the measuring electrode 4 is provided only by a physical vapor deposition method,
Although a satisfactory result was obtained regarding the reaction rate, there was a problem in that the adhesion strength of the measuring electrode 4 was weak, so that the measuring electrode 4 peeled off during the durability, resulting in poor durability. Furthermore, some tubular oxygen sensor elements have a cermet measuring electrode and then a second measuring electrode is provided over a wider area than this electrode by physical vapor deposition.
As mentioned above, there was a problem in that it was easy to peel off during durability. The present invention was made by focusing on such conventional problems, and preferably uses a deposition method such as sputtering, ion plating, or vacuum evaporation only on a fired measurement electrode using cermet. The adhesion strength between the fired measurement electrode and the solid electrolyte is improved by providing an electrode and preventing the solid electrolyte and the first measurement electrode from directly contacting each other except for through-holes in the fired measurement electrode, and further By filling the fired measuring electrode and its internal through holes with the first measuring electrode formed by the vapor deposition method, the surface area of the measuring electrode and the three-phase interface are increased, thereby significantly promoting the catalytic reaction of the measuring electrode and the electrode reaction. The aim is to solve the above problems. Hereinafter, the present invention will be explained in more detail based on the drawings. FIG. 3 is a schematic cross-sectional view of a membrane-structured oxygen sensor element 10 manufactured using the method of an embodiment of the present invention, and FIG. 4 is an illustration of the oxygen sensor element 10 shown in FIG. 3.
This is an explanatory diagram showing the manufacturing process of the diaphragm layer 11, which can maintain the strength as a substrate, is formed from two diaphragm layer materials 11a and 11b, and both diaphragm layer materials 11
The heating element 15 and the tips of the three lead wires 20, 21, 22 are inserted between a and 11b, and the heating element is inserted through the three through holes 17, 18, 19 formed in the upper diaphragm layer material 11a. 15 and lead wire 20,
A diaphragm layer 11 (see FIG. 4a) is prepared with the connecting portions 21 and 22 exposed. Here, it is convenient to use alumina green sheets as the diaphragm layer materials 11a and 11b, and other materials such as mullite, spinel, forsterite, and steatite can also be used. Further, it is preferable to embed a resistor made of an electronic conductor such as a platinum wire in the heating element 15, or to use a paste made of a resistor made of a platinum wire or the like and printed thereon. Further, the heating element 15 is electrically connected to lead wires 20 and 22 via through holes 17 and 19. As the lead wires 20, 21, and 22, it is preferable to use a material having corrosion resistance and electronic conductivity, such as platinum wire. Next, a reference electrode 1 is placed on the diaphragm layer 11 (see FIG. 4a).
2, for example, by screen printing (Fig. 4b)
reference). The reference electrode 12 may be made of a material that generates a reference oxygen partial pressure, such as a metal such as Ni-NiO.
Mixtures of metal oxides can be used, or porous platinum or its alloys (Ru, Pd, Rh, Os, Ir−
It is convenient to use an electronically conductive material such as Pt (Pt, etc.). When laminating the layers, these materials can be made into a paste and can be easily applied by, for example, screen printing. After drying this, when layering the oxygen ion conductive solid electrolyte 13, for example,
A solid electrolyte paste made of mixed powders such as ZrO ₂ -Y ₂ O ₃ and ZrO ₂ -CaO is laminated by screen printing (see Fig. 4c). This solid electrolyte includes CaO, Y ₂ O ₃ , SuO, MgO, ThO ₂ ,
ZrO ₂ stabilized with WO ₃ , Ta ₂ O ₅ etc., or
Bi ₂ O ₃ stabilized with Nb 2 O ₅ , SrO, WO ₃ , Ta ₂ O ₅ , Y ₂ O ₃ , etc., and _{Y 2 O 3} stabilized with ThO ₂ , CaO, etc. can be used. can. Then,
After drying the solid electrolyte 13, when laminating the measurement electrode 14, for example, a paste of cermet containing appropriate amounts of platinum or its alloy powder and oxide powder is screen printed (see Fig. 4). (see d). The material for the measurement electrode 14 is not only platinum but also after firing: (1) porous, (2) good catalytic performance, (3) electronic conductivity, and (4) corrosion resistance. Any material may be used as long as it has properties such as, for example, platinum-based alloys such as Pt-Rh alloy (Ru, Pd, Rh, Os, Ir-
Pt etc.) are suitable. Further, the above-mentioned oxide may be any oxide as long as it can ensure the bonding strength between the measurement electrode 14 and the solid electrolyte 13, for example,
Fe ₂ O ₃ , NiO, Cr ₂ O ₃ , CuO, ZrO ₂ , MgO,
Various single oxides such as CaO, Y ₂ O ₃ , Al ₂ O ₃ , TiO ₂ or mixtures thereof are suitable. Among them, especially when considering the effect of mutual diffusion due to firing, the same material as the solid electrolyte 13, for example,
It has been found that the use of ZrO ₂ -CaO, ZrO ₂ -Y ₂ O ₃ , ZrO ₂ -MgO, etc. can ensure sufficient bonding strength between the measurement electrode 14 and the solid electrolyte 13. After drying, the unfired stacked layers are simultaneously fired at 1500° C. for 2 hours in the air. Alternatively, the reference electrode 12, the oxygen ion conductive solid electrolyte 13, and the measurement electrode 14 can be stacked and fired under various conditions each time they are dried. The elements obtained by simultaneous firing or firing each layer as described above are ultrasonically cleaned in an organic solvent and dried. Subsequently, after applying masking that opens only above the measurement electrode 14, a second measurement electrode 16 (see FIG. 4e) is formed on the measurement electrode 14 by vapor deposition.
will be established. In this case, the vapor deposition method for providing the first measurement electrode 16 includes sputtering, ion plating, vacuum vapor deposition, etc., and each of these will be described later. After that, a protective layer 17 (see FIG. 4 f) is provided on the entire surface of the element, and the measurement electrode 1
4 and 16 are made contactable with the gas to be measured via the protective layer 17. This protective layer 17 includes alumina,
It is coated using mullite, calcium zirconate, etc., for example, by thermal spraying. In the oxygen sensor element manufactured by this method, the reference oxygen partial pressure when the reference oxygen partial pressure generating substance is provided, or the reference oxygen partial pressure controlled by passing a direct current between the electrodes 12 and 14, and the measurement By measuring the output voltage generated according to the difference between the oxygen partial pressure in the gas to be measured and the corresponding measured oxygen partial pressure at the electrode 14, the partial pressure of oxygen in the gas to be measured can be detected over a long period of time. can. For example, by detecting the oxygen concentration in the exhaust gas of an automobile engine, it becomes possible to control the air-fuel ratio of the engine, and also to control the combustion of other combustion equipment or the atmosphere in the furnace. Hereinafter, a specific example in which the first measurement electrode 16 is provided by a vapor deposition method will be described in more detail. When sputtering is used as the vapor deposition method for providing the above-mentioned measurement electrode 16, first, the device with the fired measurement electrode 14 provided on the outermost surface is prepared through the steps shown in FIGS. 4a to 4d, as shown in FIG. As shown in FIG. 3, only the portion of the fired measuring electrode 14 that contacts the solid electrolyte 13 (or smaller in size) is attached to a mask with a pattern of holes and set in a sputtering device. At this time, the solid electrolyte 13 and the first measurement electrode 16 are made not to come into direct contact with each other except for the through hole portion in the fired measurement electrode 14.
In this sputtering, the vacuum is evacuated to a level higher than 10 ^-5 Torr, and then 1×10 ^-3 to 5×
Ar gas is introduced in the range of 10 ^-2 Torr. The reason for once evacuation to high vacuum is to reduce the influence of impurities, especially residual gas. In addition, the pressure of Ar gas during sputtering is 1×10 ^-3 to 5×
The reason for setting 10 ^-2 Torr is that if the vacuum is too high, glow discharge will be difficult to occur, and if the vacuum is too low, the film will be contaminated by residual gas and introduced gas, and the spatter atoms will be scattered, slowing down the deposition rate. . Therefore, depending ^on the adhesion, ^purity , productivity, etc. of the sputtering film formed, a
is optimal. Thereafter, sputtering is performed with a power of about 0.15 to 0.3 KW to attach the first measurement electrode 16 (see FIG. 4e). At this time, it is preferable to use platinum or an alloy containing platinum such as platinum-rhodium as the target material in consideration of electron conductivity and catalytic activity. Further, it is preferable that the thickness of the first measurement electrode 16 formed by this sputtering is 0.5 μm or less. On the other hand, when using ion plating as the vapor deposition method for providing the above-mentioned first measurement electrode 16, first, the element with the fired measurement electrode 14 provided on the outermost surface is formed through the steps shown in FIGS. 4a to 4d. As shown in FIG. 4e, the fired measurement electrode 14 is attached to a mask having a pattern of holes only in the portion that contacts the solid electrolyte 13, and then set in an ion plating apparatus. At this time, the solid electrolyte 13 and the first measurement electrode 16 are
Direct contact is avoided except for through-hole portions in the fired measurement electrode 14. Therefore, in ion plating, the vacuum is evacuated to a level higher than 10 ^-5 Torr, and then O ₂ gas or O ₂ -Ar mixed gas is introduced at a pressure in the range of 1 x 10 ^-3 to 5 x 10 ^-2 Torr. The reason for once evacuation to a high vacuum is to prevent the influence of impurities, especially residual gas. Moreover, the reason why O ₂ or O ₂ -Ar mixed gas is used as the introduced gas is because these gases are used to perform ion plating in the firing area in contact with the first measurement electrode 16 provided by the ion plating method. The measurement electrode 14 and the surface of the oxygen ion conductive solid electrolyte 13 that communicates only through the through-hole portion of the fired measurement electrode 14 are cleaned and activated by the ion bombardment of O ^2- ions generated from these gases. state and that O ₂ is present at the first measurement electrode 16
This is because the introduced gas pressure is 1×10 ^-3 to 5×
The reason for setting 10 ^-2 Torr is that if the vacuum is too high, glow discharge will be difficult to occur, and if the vacuum is too low, the inside of the device will be oxidized and contaminated because O ₂ is introduced, and the introduced gas will not enter the inside of the measurement electrode 16. This is because the evaporated and ionized electrode material is scattered, reducing productivity. In this manner, after introducing the gas, an electric field is applied to cause a discharge, and power is applied to the vapor deposited material to form the measurement electrode 16 (see FIG. 4e). At this time, it is desirable to use platinum or an alloy containing platinum such as platinum-rhodium as the vapor deposition material in consideration of electronic conductivity, catalytic activity, and corrosion resistance. Further, it is preferable that the thickness of the first measuring electrode 16 formed by this ion plating is 0.5 μm or less. On the other hand, when vacuum evaporation is used as the evaporation method for providing the above-mentioned first measurement electrode 16, the element having the fired measurement electrode 14 provided on the outermost surface is similarly prepared through the steps shown in FIGS. 4a to 4d. As shown in FIG. 4e, the fired measurement electrode 14 is attached to a mask having a pattern with holes only in the portion that contacts the solid electrolyte 13, and then set in a vacuum evaporation apparatus. At this time, the solid electrolyte 13 and the first measurement electrode 16 are made not to come into direct contact with each other except for the through-hole portion in the fired measurement electrode 14. Therefore, in vacuum evaporation,
Evacuate to a higher vacuum than the 10 ^-5 Torr stand, then 1×
O ₂ gas or O ₂ in the range of 10 ^-3 to 5×10 ^-2 Torr
-Introduce Ar mixed gas. The reason for once evacuation to a high vacuum is to reduce the influence of impurities, especially residual gas, on discharge. In addition, the reason why O ₂ or O ₂ -Ar mixed gas is used as the introduced gas is that when sputter etching is performed using these gases, communication is made only through the fired measurement electrode 14 in contact with the evaporation electrode and its through hole. This is because the surface of the oxygen ion conductive solid electrolyte 13 becomes active, and the introduced gas pressure is 1 × 10 ^-3 ~ 5
The reason why the pressure is set at ×10 ^-2 Torr is that if the vacuum is too high, glow discharge will be difficult to occur, and if the vacuum is too low, the efficiency of sputter etching will decrease due to scattering of residual gas and introduced gas molecules. in this way,
After the gas is introduced, an electric field is applied to cause glow discharge, and the surface layer of the solid electrolyte 13 is sputter-etched through the fired measurement electrode 14 or its through-hole.
After sputter etching, evacuate to a high vacuum of 10 ^-5 Torr or higher again. The reason for evacuation to a high vacuum at this time is to exhaust contaminants ejected by sputter etching and to prevent these impurities from being drawn into the vapor deposition electrode. Thereafter, power is applied to the vapor deposited material to form the measurement electrode 16 (see FIG. 4e). At this time, platinum or an alloy containing platinum such as platinum-rhodium is preferably used as the deposition material in consideration of electron conductivity and catalytic activity. Further, at this time, it is preferable that the thickness of the measurement electrode formed by vacuum evaporation is 0.5 μm or less. In this state, the solid electrolyte 13 is in direct contact with the first measurement electrode 16 only through the through hole in the fired measurement electrode 14. As described above, in the method of the present invention, the first measurement electrode 16 is further provided on the measurement electrode 14, which is preferably fired using a cermet material, by a vapor deposition method such as sputtering, ion plating, or vacuum evaporation. The reason for this is explained below. First, rather than the conventional oxygen sensor element having only the fired measurement electrode 14, sputtering,
The reason why the oxygen sensor element 10 according to the method of the present invention in which the second measurement electrode 16 is further provided by ion plating, vacuum evaporation, etc. is superior is as follows. That is, when simultaneously firing the diaphragm layer 11, the reference electrode 12, the solid electrolyte 13, and the measurement electrode 14, the diaphragm layer 11 made of alumina or the like as a structural base is
In order to obtain the strength of the solid electrolyte 13 and the oxygen ion conductive solid electrolyte 13, approximately
It is necessary to fire at 1500°C to ensure sufficient sintering. At this time, in the measurement electrode 14 made of Pt or its alloy, as shown in FIG. 5a, Pt or its alloy aggregates and crystal grains grow. Furthermore, the measurement electrode 14 obtained by firing each laminated layer based on other manufacturing methods also yields the same results as in the case of simultaneous firing described above. Furthermore, if the measuring electrode 14 is provided by screen printing, the paste grains will be much coarser than those produced by the vapor deposition method, and will tend to look like the one shown in FIG. 5a because it needs to be fired at a high temperature. Here, in FIG. 5a, the grains of the fired measurement electrode 14 are coarse, and the electrode surface area in contact with the gas to be measured is small.
It is a schematic enlarged view of a state in which the surface of the oxygen ion conductive solid electrolyte 13 is visible from the through-hole portion of the fired measuring electrode 14 due to its relatively porous nature. In such a state as shown in FIG. 5a, the gas to be measured - the measurement electrode -
The so-called three-phase interface in contact with the solid electrolyte is small compared to the electrode area, and the electrode surface area in contact with the gas to be measured is reduced, resulting in a decrease in the catalytic performance of the measurement electrode 14, and the electrode reaction is not promoted, resulting in a decrease in the response of the oxygen sensor element. The speed will be slower. This fired measurement electrode 1
Further, a third measurement electrode 16 is formed on top of 4 by a vapor deposition method.
5b, the vapor deposited layer fills the upper surface of the fired measurement electrode 14 and its through-hole, and the solid electrolyte 13 only flows through the through-hole of the fired measurement electrode 14. It comes into direct contact with the first measurement electrode 16, and as a result, the surface area of the electrode in contact with the gas to be measured increases significantly, and the number of three-phase interfaces increases significantly, promoting the catalytic reaction and the electrode reaction, thereby improving the oxygen sensor element. response becomes faster. Here, when focusing only on the response speed of the oxygen sensor element, the measurement electrode 1 is
Since the response speed is improved by providing the oxygen ion conductive solid electrolyte 13 in the manufacturing process of the oxygen sensor element shown in FIG. It is also conceivable to provide the measurement electrode 14 directly on the solid electrolyte 13 by a vapor deposition method similar to the method of the invention. Also, the 6th
As shown in Figures a and b, in the manufacturing process of the oxygen sensor element, after providing the oxygen ion conductive solid electrolyte 13, a pattern is formed by hollowing out a part (in Figure 6 a, one rectangular part, in Figure 6 b It is also conceivable to provide the measurement electrode 14 in a rectangular shape (4 places are hollowed out), and then provide the measurement electrode 16 thereon by a vapor deposition method similar to the method of the present invention. However, as mentioned above, the response speed of the oxygen sensor element manufactured in this way is certainly faster than that of the oxygen sensor element made only of the fired measuring electrode 14, that is, up to the process shown in FIG. Sexuality becomes extremely bad. In addition, when the protective layer 17 is provided by plasma spraying or the like, the oxygen sensor element, which is only the measurement electrode 14 by vapor deposition, or the sixth
As shown in Figures a and b, a part of the fired measuring electrode 14 is hollowed out so that the first measuring electrode 16 formed by vapor deposition is in direct contact with the solid electrolyte 13 at a place other than the through hole of the fired measuring electrode 14. In the case of a sensor element, during use, peeling may occur from the measurement electrode portion provided by the vapor deposition method, and the protective layer 17 may also peel off, which is undesirable. Furthermore, when considering the durability of the oxygen sensor element, when providing the first measurement electrode 16 only on the fired measurement electrode 14 by vapor deposition, the oxygen sensor A considerable difference occurs in the durability of the elements, as will be described later. That is, the fired measurement electrode 1
As the material for the solid electrolyte 13, a cermet which is a mixture of a metal and an oxide is used. In particular, platinum or an alloy containing platinum and an oxide containing the same component system as the solid electrolyte 13 (for example, ZrO ₂ -CaO, ZrO ₂ - Y ₂ O ₃ ,
When a cermet which is a mixture of ZrO ₂ --MgO, etc.) is used, it has excellent catalytic performance, electronic conductivity, corrosion resistance, and adhesion strength to the solid electrolyte 13. On the other hand, if a material other than cermet, such as platinum or an alloy containing platinum, is used as the fired measurement electrode 14, it can have excellent catalytic performance, electronic conductivity, and corrosion resistance.
The adhesion strength to the solid electrolyte 13 is not very sufficient, and there is a risk that separation may occur between the solid electrolyte 13 and the fired measuring electrode 14 that does not use cermet during use or during durability. Therefore, it is desirable to use cermet as the material for the firing measuring electrode 14. On the other hand, in some tubular oxygen sensor elements, the oxygen ion-conducting solid electrolyte and the measurement electrode provided by vapor deposition are in direct contact with each other in areas other than the through-hole portion of the fired measurement electrode (for example, , Japanese Unexamined Patent Publication No. 1983-90294, Utility Model Application No. 54-57081
Similar to the case shown in Fig. 6, the bonding strength between the measurement electrode provided by the vapor deposition method and the oxygen ion conductive solid electrolyte is insufficient, so the measurement electrode tends to peel off during durability. have. Next, the results of evaluation tests conducted on oxygen sensor elements having various configurations will be described.
The oxygen sensor elements subjected to the evaluation test were as follows a to h.
There are 8 types. Therefore, the manufacturing method of the oxygen ion conductive solid electrolyte 13 of the oxygen sensor elements a to h shown in the following table will be explained. First, Figures 3 and 4 a
As shown in FIG.
11b, a platinum paste prepared by kneading platinum and lacquer at a weight ratio of 7:3 is printed in the shape shown by the dotted line in FIG. 4a, and dried to form the unfired heating element 1.
form 5. Next, as shown in Figure 4a, 3
Main platinum lead wire (0.2mmφ×7mm) 20,2
1 and 22 are arranged on the alumina green sheet 11b, and the other alumina green sheet (5× 9×0.7
(t) mm) 11a are laminated under pressure to form a diaphragm layer 11 in an unfired state. In addition, as the heating element 15, an electronically conductive resistor such as a platinum wire may be embedded, or powder of such an electronically conductive material may be printed in the form of a paste similar to the platinum paste described above. Further, as the lead wires 20, 21, and 22, a material other than platinum wire that is corrosion resistant and has electron conductivity may be used. Next, the diaphragm layer 11
(See FIG. 4a) When providing the reference electrode 12 thereon, the platinum paste is printed in the shape shown in FIG. 4b and dried. Reference electrode 1
The thickness of No. 2 was 15 to 20 μm after firing. When providing the oxygen ion conductive solid electrolyte 13 on this, a solid electrolyte paste prepared by kneading 5 mol% Y ₂ O ₃ -95 mol% ZrO ₂ powder and lacquer at a weight ratio of 7:3 is printed, After drying, an oxygen ion conductive solid electrolyte 13 in an unfired state was formed (see FIG. 4c). At this time, the thickness of the solid electrolyte 13 after firing was set to 20 to 40 μm. This solid electrolyte includes CaO, Y ₂ O ₃ , SrO, MgO,
ZrO ₂ stabilized with ThO ₂ , WO ₃ , Ta ₂ O ₅ etc., or Bi ₂ O ₃ stabilized with Nb ₂ O ₅ , SrO, WO ₃ , Ta ₂ O ₅ , Y ₂ O ₃ etc., and even Y ₂ O ₃ stabilized with ThO ₂ , CaO, etc. can be used. The stacked layers up to the solid electrolyte 13 in this manner are used for manufacturing each of the following oxygen sensor elements a to h. (a) Cermet firing measurement electrode only (comparison product); When using cermet, which is a mixture of metal and ceramic, as the electrode material, the mixing ratio of ceramic and metal should be 3% ≦volume of ceramic layer/total of cermet layer. Product×
It is desirable to set the range to 100≦30%. Specifically, 95 wt _% Pt-5 wt% (5 mol% _Y2O3-95
Mol% ZrO ₂ ) (by volume 11 vol% Pt−89 vol%
(5 mol % Y ₂ O ₃ - 95 mol % ZrO ₂ )) Using a cermet paste prepared by kneading powder and lacquer at a weight ratio of 7:3, print lamination was performed on the solid electrolyte 13. A measurement electrode 14 is provided. At this time, the thickness of the measuring electrode 14 after firing is 10 to 15 μm.
Make it so. Furthermore, the same ceramic material as the solid electrolyte 13 is used as the cermet material. Furthermore, the measurement electrode 14
After laminating, dry and heat in air at 1500℃ for 2
Simultaneously fired under certain time conditions. Alternatively, the reference electrode 12, solid electrolyte 13, and measurement electrode 14 may be stacked and fired each time they are dried. After this, Figure 4 f
As shown in FIG. 2, a porous protective layer 17 was provided by depositing spinel powder over the entire oxygen sensor element by plasma spraying. The thickness of the protective layer 17 at this time is 60
It was made to be ~8μ. (b) Only the fired measurement electrode that is not made of cermet (comparative product); one in which the solid electrolyte 13 is laminated (the fourth
On top of figure c), add platinum and lattice at a weight ratio of 7:3.
Using platinum paste kneaded at a ratio of
Measurement electrodes 14 were stacked in an unfired state in the shape shown in FIG. As the measurement electrode material in this case, other than platinum, a material having a catalytic action and electron conductivity can be used. The thickness of the measuring electrode 14 at this time is set to 10 to 15 μm after firing. Note that the subsequent firing and protective layer 1
7. The adhesion was the same as in a above. (c) A first measurement electrode (product of the present invention) only on the fired cermet measurement electrode; The cermet measurement electrode 14 laminated and fired in a above is used. The fired element is ultrasonically cleaned in an organic solvent, dried, and then masked using a mask having an opening 10% smaller than the area of the measurement electrode 14. Next, a first measurement electrode 16 is provided by vacuum depositing platinum.
At this time, the film thickness of the first measuring electrode 16 is set to 0.4 to 0.5 μm. After this, in the same manner as a, the protective layer 1
7 will be provided. (d) A second measuring electrode (comparative product) centered around the fired cermet measuring electrode; using the same cermet paste as in (a) above, the cermet paste was spread on the solid electrolyte 13 in the pattern shown in Figure 6a and b. After printing the measuring electrode 14 of
As in the case described above, the first measurement electrode 16 was provided by vacuum evaporation using a mask with a pattern 10% smaller than the external dimensions of the fired measurement electrode 14. In addition, in the same way as in (c) above, the first measurement electrode 14 is laminated using cermet paste on the solid electrolyte 13 and then fired, and then a mask with a pattern larger than the area of the measurement electrode 14 is used. An oxygen sensor element was also produced in which a first measuring electrode 16 was provided by vacuum evaporation so that the solid electrolyte 13 and the second measuring electrode 16 were in direct contact with each other on the outer side of the fired measuring electrode 14. (e) The first measuring electrode (product of the present invention) is placed only on the fired measuring electrode; using the same platinum paste as used in (b) above, the second measuring electrode 14 is placed on the solid electrolyte 13 shown in FIG. are laminated and fired, and then, as shown in (c) above, the first measurement electrode 16 is provided by vacuum deposition using a mask with a pattern 10% smaller in area than the fired measurement electrode 14. (f) Measuring electrode deposited on a solid electrolyte (comparative product); A measuring electrode 4 made of platinum was provided on the solid electrolyte 3 shown in FIG. 1 only by vacuum deposition. (g) The vapor deposition measurement electrode is in contact with the solid electrolyte (comparative product); This oxygen sensor element is of a tubular type, and
The measurement electrode provided by physical vapor deposition is in direct contact with the solid electrolyte. (h) A second measuring electrode (product of the present invention) only on the fired cermet measuring electrode; It was manufactured in exactly the same way except that ion sputtering was used instead of vacuum deposition in (c) above. Next, when the eight types of oxygen sensor elements shown in (a) to (h) above are used to measure the amount of oxygen in the exhaust gas of an automobile engine and control the air-fuel ratio of the engine, 10 in driving test
The results of examining the mode emission values and the results of durability tests in predetermined running modes are shown in FIG. 7 and the table, respectively. In FIG. 7, it has been confirmed that the faster the response speed of the oxygen sensor element is, the closer the above value is to the origin (0 for NOx, CO, and HC). As can be seen from FIG. 7, the oxygen sensor elements (c, d, e,
f, g, h) have better 10-mode emission values, and in particular, the 10-mode emission values of the membrane structure type oxygen sensor elements (c, d, e, f, h) are closer to the origin. It can be seen that the response speed is excellent. From this, it can be seen that when the measurement electrode is provided by vapor deposition, the electrode surface area is greatly increased, and the electrode reaction and catalytic reaction are promoted by increasing the electrode surface area at the three-phase interface described above, thereby increasing the response speed of the oxygen sensor element. This was confirmed. On the other hand, the table shows the durability test results of the eight types of oxygen sensor elements shown in (a) to (h) above in constant running mode, and the atmospheric temperature (exhaust gas temperature) to which the oxygen sensor elements are exposed in this durability test is 450~850
℃, and the atmosphere changes periodically between 0.3% and 5% CO. Furthermore, the results shown in the table are a compilation of visual observation results every 50 hours during the durability test.

[Table] As is clear from the above table, among the membrane structure type oxygen sensor elements (a, c, d, h) using cermet as the material of the fired measurement electrode, the oxygen sensor elements (a, c, h) can guarantee a durability of 250 hours or more, but the oxygen sensor element d, in which the solid electrolyte and the second measurement electrode provided by vapor deposition are in direct contact with each other at a place other than the through-hole in the fired measurement electrode, has a longer durability than the above. It can be seen that the durability is also inferior. In addition, the highly durable oxygen sensor element a
As shown in FIG. 7, the response speed is not very good. On the other hand, membrane structure type oxygen sensor elements (b, e) that do not use cermet as the material of the fired measurement electrode
Although the durability is about the same as that of about 200 hours, the response speed of the oxygen sensor element e, in which the first measurement electrode is provided by vapor deposition, is considerably superior. On the other hand, the oxygen sensor element f in which measurement electrodes are provided only by vapor deposition has considerably poor durability. Furthermore, in the membrane structure type oxygen sensor element d and the tubular type oxygen sensor element g, which are provided with a fired measurement electrode made of cermet,
Due to the strong adhesion strength of the fired cermet measurement electrode,
Although it is thought that the durability is good, in reality, since the measurement electrode provided by the above-mentioned vapor deposition method and the solid electrolyte are in direct contact, the measurement electrode may peel off from the contact area, and the protective layer may peel off. Peeling occurs,
During the durability test, it was confirmed that the peeling spread to the part of the fired measurement electrode. As mentioned above, when considering an oxygen sensor element that can increase response speed and improve durability, it is preferable to print it using a cermet material.
It is preferable to further provide a first measurement electrode 16 on the fired measurement electrode 14 by a vapor deposition method in such a manner that it does not come into direct contact with the solid electrolyte 13 except for the through-hole portion of the fired measurement electrode 14. In this case, the reason why it is desirable that the first measurement electrode 16 provided by vapor deposition is only one layer and its thickness is 0.5 μm or less is as follows. That is, since the printed and fired measuring electrode 14 is fired at a relatively high temperature, the particles of the printed and fired measuring electrode 14 aggregate, and the particles of the printed and fired measuring electrode 14 are larger than the particles of the first measuring electrode 16 provided by the vapor deposition method. It is quite rough and has a rough surface. Such an appropriate surface roughness can be achieved by the vapor deposition method.
When providing a layer, it acts like a nucleus for the growth of the deposited film. For this reason, when providing the first measurement electrode 16, there is no need to divide it into two layers and form something corresponding to the core in the first layer, and the fired measurement electrode 14 with an appropriate surface roughness is not required. Even if only the first measurement electrode 16 is provided on top, the adhesion form is quite good and the adhesion strength is also very strong. Therefore, it is not necessary to perform vapor deposition in two or more layers, such as preliminary vapor deposition, heat treatment, and vapor deposition again. Furthermore, the film thickness of the first measurement electrode 16 provided by the vapor deposition method is as follows:
The reason why it is desirable to set the thickness to 0.5μ or less is that if it is too thick, the first measurement electrode 16 formed by vapor deposition with small particles will cover the fired measurement electrode 14 with a rough surface, and conversely, the number of three-phase interfaces and the electrode This is because the surface area decreases and catalytic reactions and electrode reactions are no longer promoted. Therefore, if the first measurement electrode 16 is too thick, no improvement in response speed can be expected. In this case, if the film thickness of the first measurement electrode 16 is made as small as possible within a range that does not impede the response speed and durability, the amount of platinum or platinum-containing alloy used as the electrode material can be reduced. Moreover, the manufacturing time can be shortened. As explained above, according to this invention,
A fired measurement electrode formed on a solid electrolyte, preferably made of a cermet material, is further coated with sputtering, ion plating, vacuum, etc. in a manner that does not directly contact the solid electrolyte at any part other than the through-holes in the fired electrode. A first measurement electrode is provided by a vapor deposition method such as vapor deposition, and at this time, the first measurement electrode
Even if it is just a layer, it is sufficiently excellent, and the membrane layer is desirably 0.5 μ or less, so that the gas to be measured - oxygen ion conductive solid electrolyte -
Since we were able to increase the three-phase interface where the three measurement electrodes come into contact and also increase the electrode surface area in contact with the gas to be measured, it is possible to improve the electrode reaction and catalytic reaction of the measurement electrode, and the oxygen The response speed of the sensor element can be considerably increased. Because the response speed of the oxygen sensor element becomes faster,
For example, when used as an oxygen sensor element to detect the oxygen concentration in the exhaust gas of an automobile engine, the emission values in 10 mode, 11 mode, etc. will be considerably improved, and the controllability of the above engine can be considerably improved. . In addition, since the response speed at low temperatures is fast, engine startability can be improved. By utilizing the roughness of the surface of the fired measuring electrode by printing and firing to provide the second measuring electrode by vapor deposition, the adhesion force of the first measuring electrode can be considerably increased, and the adhesion form is also good. Therefore, the first measurement electrode may have a one-layer structure, and steps such as preliminary vapor deposition and heat treatment that are necessary when using two or more layers can be omitted. Further, since the first measurement electrode is sufficiently good even when its film thickness is 0.5 μm or less, it is possible to improve productivity and reduce cost. When cermet is used as the material for the fired measurement electrode, it is possible to ensure even more sufficient adhesion strength between the fired measurement electrode and the solid electrolyte, and the second measurement electrode can be provided only on top of it by vapor deposition. Therefore, in addition to improving the response speed of the oxygen sensor element described above, it is possible to further improve the durability. It brings about excellent effects such as

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional explanatory diagram of a membrane structure oxygen sensor element manufactured by a conventional manufacturing method, FIGS. 2 a to e are explanatory diagrams showing the manufacturing process of the oxygen sensor element of FIG.
The figure is a schematic cross-sectional explanatory diagram showing an example of a membrane-structured oxygen sensor element based on the method of the present invention.
Figures 5a and 5b are explanatory diagrams showing the manufacturing process of the oxygen sensor element shown in Figure 5. Figures 5a and 5b are enlarged sectional explanatory diagrams showing the state after firing the measuring electrode and the state after forming the first measuring electrode on the measuring electrode, respectively. , Figure 6 a, b
7 is an explanatory diagram showing a comparative state in the process of manufacturing an oxygen sensor element according to the method of the present invention, and FIG. 7 is a graph showing measurement results of 10-mode emission values of various oxygen sensor elements. 11... Diaphragm layer, 12... Reference electrode, 13...
Oxygen ion conductive solid electrolyte, 14... baking measurement electrode, 16... th measurement electrode.

Claims (1)

[Claims] 1. In manufacturing a membrane-structured oxygen sensor element, which is formed by laminating a diaphragm layer, a reference electrode, an oxygen ion conductive solid electrolyte, and a measuring electrode, and in which the measuring electrode can come into contact with a gas to be measured. , a film characterized in that, after laminating and firing the measuring electrode on the solid electrolyte, masking is applied to open only above the measuring electrode, and then a second measuring electrode is provided on the measuring electrode by a vapor deposition method. A method for manufacturing a structural oxygen sensor element. 2. A method for manufacturing a membrane-structured oxygen sensor element according to claim 1, wherein the measurement electrode is laminated using a cermet made of a mixture of platinum or an alloy containing platinum and an oxide having the same composition as the solid electrolyte. . 3. The method for manufacturing a membrane-structured oxygen sensor element according to any one of claims 1 to 2, in which the vapor deposition method uses platinum or an alloy containing platinum as the material. 4 The film thickness of the first measurement electrode was reduced to 0.5μ by vapor deposition.
A method for manufacturing a membrane structure oxygen sensor element according to any one of claims 1 to 3 provided below.