A limiting current type oxygen sensor and preparation method thereof

Abstract

The present invention relates to a limiting current type oxygen sensor and a preparation method thereof, comprising the following steps: S1. Casting: using the first, second and third mixed powders to prepare casting slurries corresponding to the functional layer, transition layer and substrate layer respectively, casting and drying to obtain the functional layer cast sheet, transition layer cast sheet and substrate layer cast sheet for standby use; S2. Printing: printing the external electrode on the front of the top functional layer cast sheet, and printing the internal electrode on the back of the bottom functional layer cast sheet; punching the transition layer cast sheet located on the upper layer to form a reference channel; printing the heating electrode on the substrate layer cast sheet located in the middle of the substrate layer; S3. Stacking: stacking a plurality of functional layer cast sheets, transition layer cast sheets and substrate layer cast sheets from top to bottom, and hot isostatic pressing; S4. Sintering. The advantages of the present invention are that the transition effect of the transition layer is adjusted to successfully co-sinter the functional layer mainly composed of zirconium oxide and the substrate layer mainly composed of aluminum oxide, with low cracking rate and excellent comprehensive performance.

Description

Technical Field

[0001] The invention belongs to the field of vehicle oxygen sensors, and in particular relates to a limiting current type oxygen sensor and a preparation method thereof. Background Art

[0002] At present, automotive oxygen sensors are made in two ways. The former is made of multi-layer zirconia substrates, and the latter is made of multi-layer alumina substrates and single-layer zirconia substrates. The sensor functional layer and the substrate structural layer of the former are made of the same material, and the purpose of measuring the oxygen content in the atmosphere is achieved through the catalytic reduction reaction between the internal and external active electrodes. The advantage of this method is that the structural layer and the functional layer are made of the same material, the risk of cracking is small, and the substrate strength is high. The disadvantage is that the heater in the sensor integrated circuit is prone to leakage current after power is turned on, thereby affecting the sensor signal output and the insulation process control is difficult. The main component of the sensor functional layer of the latter is yttria-stabilized zirconia, and the main material of the structural layer is alumina. The advantage of this method is that since only the functional layer is made of zirconia material, there is no leakage risk at the heater end, which will not affect the sensor signal output, but the disadvantage is that the co-firing matching of alumina and zirconia materials is difficult, the risk of cracking during the firing process is high, and when alumina is the main substrate, the substrate strength is low. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a limiting current type oxygen sensor and a preparation method thereof, aiming to overcome the above-mentioned deficiencies existing in the prior art.

[0004] The technical solution of the present invention to solve the above technical problem is as follows: A method for preparing a limiting current type oxygen sensor, which comprises the following steps:

[0005] S1. Tape casting: Use the first mixed powder, the second mixed powder and the third mixed powder to prepare the tape casting slurry of the corresponding functional layer, the transition layer and the substrate layer respectively, and cast and dry the functional layer tape casting sheet, the transition layer tape casting sheet and the substrate layer tape casting sheet after vacuum degassing, and set aside; wherein the first mixed powder is composed of yttrium-stabilized zirconia and alumina, and the alumina content is 0.5-2%; the second mixed powder is composed of alumina, yttrium-stabilized zirconia and a sintering agent, the content of yttrium-stabilized zirconia is 50-70%, and the sintering agent is 5-15%; the third mixed powder is composed of alumina and a sintering agent, and the sintering agent content is 0.5-5%;

[0006] S2. Printing: Select the topmost functional layer cast sheet, print the external electrode on its front side, select the bottommost functional layer cast sheet, print the internal electrode on its back side; select several transition layer cast sheets on the upper layer, punch them to form reference channels; select the substrate layer cast sheet in the middle of the substrate layer, print the heating electrode on it;

[0007] S3. Lamination: stacking a plurality of functional layer cast sheets, a plurality of transition layer cast sheets and a plurality of substrate layer cast sheets from top to bottom, and then hot isostatic pressing to form a whole;

[0008] S4. Sintering: Cut the green body of the oxygen sensor into pieces and place them in a sintering furnace for sintering.

[0009] On the basis of the above technical solutions, the present invention can also make the following further specific selections or better selections.

[0010] Specifically, the casting slurry in S1 contains 30-50% of the mass of the corresponding mixed powder, 0.3-0.6% of the dispersant, 8-15% of the binder, 0.5-5% of the plasticizer and 0-1% of the defoamer.

[0011] Optimally, the solvent is a mixture of anhydrous ethanol and xylene in equal volume ratios, the dispersant is NOF AD-374M, AD-3172M or AD-508E, the binder is polyvinyl butyral, and the plasticizer is dibutyl phthalate.

[0012] Specifically, the sintering promoter in S1 is one or more of glass powder, yttrium oxide, lanthanum oxide, titanium oxide or magnesium oxide, preferably glass powder.

[0013] Specifically, the thickness of the functional layer cast sheet, the transition layer cast sheet and the substrate layer cast sheet are all in the range of 50-200 μm.

[0014] Optimally, a diffusion barrier layer is printed on the front side of the top functional layer cast sheet in S2, and the diffusion barrier layer covers the outer electrode; the content of yttrium-stabilized zirconia in the second powder in S1 is 60-65%.

[0015] Specifically, the diffusion barrier layer is formed by screen printing with diffusion ink, wherein the diffusion ink is a mixture of zirconium oxide, a pore former, an adhesive and a solvent in a weight ratio of 30:20:25:25.

[0016] Optimally, the transition layer cast sheet in S2 is printed and filled after punching using a filling slurry that can be completely decomposed at a high temperature above 1000°C.

[0017] Specifically, the hot isostatic pressing treatment conditions in S3 are to control the pressure at 25-45MPa, the temperature at 60-85°C, and the holding time at 5-20min; the sintering temperature in S4 is 1300-1500°C, and the holding time is 1-3h.

[0018] The present invention also provides a limiting current type oxygen sensor, which comprises a diffusion barrier layer, a functional layer, a transition layer and a substrate layer which are stacked in sequence from top to bottom, wherein an outer electrode is printed on the upper surface of the functional layer, and the diffusion barrier layer completely covers the outer electrode, and a reference channel which is concave in a groove is provided on the upper surface of the transition layer, and the reference channel extends outward to the side end surface of the transition layer and communicates with the outside, and an inner electrode is printed on the lower surface of the functional layer, and the inner electrode is located directly above the reference channel, and the inner electrode is located in the middle of the substrate layer. A heating electrode is provided, and the functional layer and the transition layer both contain yttrium-stabilized zirconia and aluminum oxide. The weight ratio of the yttrium-stabilized zirconia to aluminum oxide in the functional layer is between 49:1 and 199:1, and the weight ratio of the yttrium-stabilized zirconia to aluminum oxide in the transition layer is between 10:9 and 14:3 (corresponding to the preparation method in which "the second mixed powder consists of aluminum oxide, yttrium-stabilized zirconia and a sintering promoter, the content of yttrium-stabilized zirconia is 50-70%, and the content of the sintering promoter is 5-15%).

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] In the present invention, when preparing the limiting current type oxygen sensor, the raw materials used for the functional layer, the transition layer and the matrix layer are different. The first mixed powder corresponding to the functional layer is mainly composed of yttrium-stabilized zirconia, supplemented with only a small amount of aluminum oxide to adjust the shrinkage rate, while the matrix layer is just the opposite, mainly composed of aluminum oxide, and the most critical is the transition layer. The corresponding second mixed powder contains a lot of yttrium-stabilized zirconia and aluminum oxide, especially the difference in the amount of the two is greatly reduced compared with the corresponding difference in the first mixed powder, so that the shrinkage rate of the transition layer during sintering will not be too different from that of the functional layer and the matrix layer, thereby greatly reducing the probability of cracking during sintering.

[0021] The heater end (substrate layer) of the oxygen sensor provided by the present invention is mainly composed of aluminum oxide, which has high resistance, good insulation, no risk of leakage, and will not affect the sensor signal output. At the same time, due to the regulating transition effect of the transition layer, the co-firing matching of the substrate layer (mainly aluminum oxide) and the functional layer (mainly zirconium oxide) is good, and the risk of cracking during the firing process is small. In general, since zirconium oxide and aluminum oxide both have a considerable content in the oxygen sensor, after sintering and forming, the porcelain body density, bending strength and insulation resistance are moderate, and there are no obvious defects of low resistance of pure zirconium oxide type and low density and strength of ordinary aluminum oxide type, and the comprehensive performance is excellent. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A flow chart of a method for preparing a limiting current type oxygen sensor provided by the present invention;

[0023] Figure 2 A schematic cross-sectional view of a limiting current type oxygen sensor prepared by the present invention;

[0024] Figure 3 A schematic diagram of the structure of a limiting current type oxygen sensor prepared by the present invention;

[0025] Figure 4 This is the relationship between the pump current and the atmosphere lambda of the limiting current type oxygen sensor prepared in Example 1 of the present invention.

[0026] In the accompanying drawings, the components represented by the reference numerals are listed as follows:

[0027] 1. Diffusion barrier layer; 2. Functional layer; 3. Transition layer; 4. Matrix layer; 5. External electrode; 6. Internal electrode; 7. Reference channel; 8. Heating electrode. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0029] The present invention provides a limiting current type oxygen sensor, using Figure 1 The process flow shown in the figure is used for preparation and has the following characteristics: Figure 2 and 3 The structure shown in the figure comprises a diffusion barrier layer 1, a functional layer 2, a transition layer 3 and a base layer 4 which are stacked in sequence from top to bottom. An external electrode 5 is printed on the upper surface of the functional layer 2. The diffusion barrier layer 1 completely covers the external electrode 5. A reference channel 7 which is concave into a groove is provided on the upper surface of the transition layer 3. The reference channel 7 extends outward to the side end surface of the transition layer 3 and communicates with the outside. An internal electrode 6 is printed on the lower surface of the functional layer 2. The internal electrode 6 is located directly above the reference channel 7. A heating electrode is built into the middle of the base layer 4. 8. Both the functional layer 2 and the transition layer 3 contain yttrium-stabilized zirconia and alumina. The weight ratio of yttrium-stabilized zirconia to alumina in the functional layer 2 is between 49:1 and 199:1. The weight ratio of yttrium-stabilized zirconia to alumina in the transition layer 3 is between 10:9 and 14:3. When the weight ratio is 10:9, the transition layer is composed of 50% zirconia, 45% alumina and 5% sintering promoter. When the weight ratio is 14:3, the transition layer is composed of 70% zirconia, 15% alumina and 15% sintering promoter.

[0030] It should be noted that the total thickness of the limiting current type oxygen sensor provided by the present invention is about 1.5 mm, and the thicknesses of the functional layer 2, the transition layer 3 and the substrate layer 4 increase successively. The thickness of the functional layer 2 is about 200-320 μm, and the thickness of the diffusion barrier is set according to the actual situation and with reference to the usual practice (usually 50-220 μm). The functional layer 2, the transition layer 3 and the substrate layer 4 are respectively formed by correspondingly stacking several layers of the functional layer 2 cast sheet, the transition layer 3 cast sheet and the substrate layer 4 cast sheet (in other words, taking the substrate layer 4 as an example, it can be formed by stacking multiple layers of substrate cast sheets, and the thickness of each cast sheet is 50-200 μm, and the thickness of cast sheets of different layers can be the same or different). In addition, the contents known to those skilled in the art will not be repeated in the present invention, such as Figure 3 As shown, the outer electrode 5, the inner electrode 6 and the electric heating electrode are respectively connected to the external pins through the small holes opened on the corresponding cast sheets. For example, the depth of the reference channel 7 on the upper surface of the transition layer 3 is usually smaller than the thickness of the transition layer 3, and one end of the reference channel 7 is connected to the outside.

[0031] like Figure 1 As shown, the limiting current type oxygen sensor of the above structure is prepared by the methods described in the following embodiments. To avoid duplication, the methods used in the following embodiments and comparative examples are conventional methods in the art unless otherwise specified, and the pharmaceutical raw materials used are commercially available products unless otherwise specified.

[0032] In the following examples, each casting slurry contains 40% of the solvent, 0.5% of the dispersant, 12% of the binder, 2% of the plasticizer and 0.5% of the defoamer, accounting for the mass of the corresponding mixed powder. The solvent is a mixture of anhydrous ethanol and xylene in an equal volume ratio, the dispersant is a comb copolymer of NOF AD-374M, the binder is polyvinyl butyral, and the plasticizer is dibutyl phthalate. When it is necessary to print on the upper surface of the functional layer to form a diffusion barrier, it is carried out by screen printing. The main component of the diffusion barrier slurry (diffusion barrier printing ink) is zirconium oxide, and pores are formed by adding a pore-forming agent. The pore-forming agent is ultrafine carbon powder or magnesium aluminum spinel, the binder is one or more of ethyl cellulose and polyvinyl butyral resin, and the solvent is pine alcohol. After sintering at 1300℃-1500℃, the porosity of the diffusion barrier reaches 20%-60%, the pore diameter is 50nm-2um, and a sieve-like structure is formed; the specific gravity of the diffusion barrier printing ink is: 30 zirconium oxide: 20 ethyl cellulose or polyvinyl butyral resin: 25 ultrafine carbon powder or magnesium aluminum spinel: 25 solvent. When the depth of the reference channel is large (more than 180μm), the corresponding transition layer cast sheet needs to be printed and filled with a filling slurry that can be completely decomposed at a high temperature above 1000℃. The main component of the filling slurry is carbon powder, which is prepared with ethyl cellulose and an organic solvent (ethanol, etc.). Filling and punching with fillers is to avoid cracking caused by excessive height difference during sintering after stacking.

[0033] Example 1

[0034] A method for preparing a limiting current type oxygen sensor comprises the following steps:

[0035] S1. Tape casting: Use the first mixed powder, the second mixed powder and the third mixed powder to prepare the tape casting slurry of the corresponding functional layer, the transition layer and the substrate layer respectively, and cast and dry the functional layer tape casting sheet, the transition layer tape casting sheet and the substrate layer tape casting sheet after vacuum degassing, and set aside; wherein the first mixed powder is composed of yttrium-stabilized zirconia and alumina, and the alumina content is 1%; the second mixed powder is composed of alumina, yttrium-stabilized zirconia and glass powder, and the content of yttrium-stabilized zirconia is 60%, and the glass powder is 15%; the third mixed powder is composed of alumina and glass powder, and the glass powder content is 5%;

[0036] S2. Printing: Select the topmost functional layer cast sheet, print the external electrode on its front side, and after printing the external electrode, use diffusion barrier slurry to print on the front side to form a diffusion barrier layer, select the bottommost functional layer cast sheet, and print the internal electrode on its back side; select several transition layer cast sheets on the upper layer, punch holes in them to form reference channels, and print and seal the punched cast sheets with high-temperature easily decomposable fillers; select the substrate layer cast sheet located in the middle of the substrate layer, and print the heating electrode on it;

[0037] S3. Lamination: Several functional layer cast sheets, several transition layer cast sheets and multiple substrate layer cast sheets are stacked from top to bottom, and then hot isostatic pressing is performed to form a whole. The total thickness of the transition layer after lamination is about 450μm, and the thickness (also known as the depth) of the formed reference channel is about 150μm. One or two layers of punched transition layer cast sheets are stacked on top of the non-punched transition layer cast sheets; the thickness of the functional layer is about 290μm, and the thickness of the substrate layer is about 760μm; each cast sheet is in the form of a film with a thickness between 80-200μm; the conditions for hot isostatic pressing are to control the pressure at 25-45MPa, the temperature at 60-85℃, and the holding time at 5-20min;

[0038] S4. Sintering: Cut the oxygen sensor green body and place the green body in a silicon-molybdenum rod furnace for sintering. The sintering temperature is 1300-1500°C and the holding time is 1-3h.

[0039] Example 2

[0040] A method for preparing a limiting current type oxygen sensor comprises the following steps:

[0041] S1. Tape casting: Use the first mixed powder, the second mixed powder and the third mixed powder to prepare the tape casting slurry of the corresponding functional layer, the transition layer and the substrate layer respectively, and cast and dry the functional layer tape casting sheet, the transition layer tape casting sheet and the substrate layer tape casting sheet after vacuum degassing, and set aside; wherein the first mixed powder is composed of yttrium-stabilized zirconia and alumina, and the alumina content is 1.5%; the second mixed powder is composed of alumina, yttrium-stabilized zirconia and glass powder, and the content of yttrium-stabilized zirconia is 65%, and the glass powder is 10%; the third mixed powder is composed of alumina and glass powder, and the glass powder content is 2.5%;

[0042] S2. Printing: Select the topmost functional layer cast sheet, print the external electrode on its front side, and after printing the external electrode, use diffusion barrier slurry to print on the front side to form a diffusion barrier layer, select the bottommost functional layer cast sheet, and print the internal electrode on its back side; select several transition layer cast sheets on the upper layer, punch holes in them to form reference channels, and print and seal the punched cast sheets with high-temperature easily decomposable fillers; select the substrate layer cast sheet located in the middle of the substrate layer, and print the heating electrode on it;

[0043] S3. Lamination: Several functional layer cast sheets, several transition layer cast sheets and multiple substrate layer cast sheets are stacked from top to bottom, and then hot isostatic pressing is performed to form a whole. The total thickness of the transition layer after lamination is about 400μm, and the thickness (also known as the depth) of the reference channel formed is about 180μm. Two layers of punched transition layer cast sheets are stacked on top of a layer of unpunched transition layer cast sheet; the thickness of the functional layer is about 260μm, and the thickness of the substrate layer is about 740μm; each cast sheet is in the form of a film with a thickness between 80-200μm; the conditions for hot isostatic pressing are to control the pressure at 25-45MPa, the temperature at 60-85℃, and the holding time at 5-20min;

[0044] S4. Sintering: Cut the oxygen sensor green body and place the green body in a silicon-molybdenum rod furnace for sintering. The sintering temperature is 1300-1500°C and the holding time is 1-3h.

[0045] Example 3

[0046] A method for preparing a limiting current type oxygen sensor comprises the following steps:

[0047] S1. Tape casting: Use the first mixed powder, the second mixed powder and the third mixed powder to prepare the tape casting slurry of the corresponding functional layer, the transition layer and the substrate layer respectively, and cast and dry the functional layer tape casting sheet, the transition layer tape casting sheet and the substrate layer tape casting sheet after vacuum degassing, and set aside; wherein the first mixed powder is composed of yttrium-stabilized zirconia and alumina, and the alumina content is 2%; the second mixed powder is composed of alumina, yttrium-stabilized zirconia and glass powder, and the content of yttrium-stabilized zirconia is 70%, and the glass powder is 10%; the third mixed powder is composed of alumina and yttrium oxide, and the yttrium oxide content is 1%;

[0048] S2. Printing: Select the topmost functional layer cast sheet, print the external electrode on its front side, and after printing the external electrode, use diffusion barrier slurry to print on the front side to form a diffusion barrier layer, select the bottommost functional layer cast sheet, and print the internal electrode on its back side; select several transition layer cast sheets on the upper layer, punch holes in them to form reference channels, and print and seal the punched cast sheets with high-temperature easily decomposable fillers; select the substrate layer cast sheet located in the middle of the substrate layer, and print the heating electrode on it;

[0049] S3. Lamination: Several functional layer cast sheets, several transition layer cast sheets and multiple substrate layer cast sheets are stacked from top to bottom, and then hot isostatic pressing is performed to form a whole. After lamination, the total thickness of the transition layer is about 420μm, and the thickness (also known as the depth) of the formed reference channel is about 220μm. One or two layers of punched transition layer cast sheets are stacked on top of the non-punched transition layer cast sheets; the thickness of the functional layer is about 300μm, and the thickness of the substrate layer is about 780μm; each cast sheet is in the form of a film with a thickness between 80-200μm; the conditions for hot isostatic pressing are to control the pressure at 25-45MPa, the temperature at 60-85℃, and the holding time at 5-20min;

[0050] S4. Sintering: Cut the oxygen sensor green body and place the green body in a silicon-molybdenum rod furnace for sintering. The sintering temperature is 1300-1500°C and the holding time is 1-3h.

[0051] Example 4

[0052] A method for preparing a limiting current type oxygen sensor comprises the following steps:

[0053] S1. Tape casting: Use the first mixed powder, the second mixed powder and the third mixed powder to prepare the tape casting slurry of the corresponding functional layer, the transition layer and the substrate layer respectively, and cast and dry the functional layer tape casting sheet, the transition layer tape casting sheet and the substrate layer tape casting sheet after vacuum degassing, and set aside; wherein the first mixed powder is composed of yttrium-stabilized zirconia and alumina, and the alumina content is 1%; the second mixed powder is composed of alumina, yttrium-stabilized zirconia and glass powder, and the yttrium-stabilized zirconia content is 50%, and the glass powder is 15%; the third mixed powder is composed of alumina and titanium oxide, and the titanium oxide content is 0.5%;

[0054] S2. Printing: Select the topmost functional layer cast sheet, print the external electrode on its front side, and after printing the external electrode, use the diffusion barrier slurry to print on the front side to form a diffusion barrier layer, select the bottommost functional layer cast sheet, and print the internal electrode on its back side; select several transition layer cast sheets on the upper layer, punch them to form reference channels, and in this embodiment, do not print high-temperature easily decomposable fillers; select the substrate layer cast sheet located in the middle of the substrate layer, and print the heating electrode on it;

[0055] S3. Lamination: Several functional layer cast sheets, several transition layer cast sheets and multiple substrate layer cast sheets are stacked from top to bottom, and then hot isostatic pressing is performed to form a whole. The total thickness of the transition layer after lamination is about 460μm, and the thickness (also known as the depth) of the reference channel formed is about 100μm. One or two layers of punched transition layer cast sheets are stacked on top of the non-punched transition layer cast sheets; the thickness of the functional layer is about 320μm, and the thickness of the substrate layer is about 680μm; each cast sheet is in the form of a film with a thickness between 80-200μm; the conditions for hot isostatic pressing are to control the pressure at 25-45MPa, the temperature at 60-85℃, and the holding time at 5-20min;

[0056] S4. Sintering: Cut the oxygen sensor green body and place the green body in a silicon-molybdenum rod furnace for sintering. The sintering temperature is 1300-1500°C and the holding time is 1-3h.

[0057] Comparative Example 1

[0058] Compared with Example 1, the difference is that the first mixed powder in this comparative example does not contain aluminum oxide; the content of yttrium-stabilized zirconium oxide in the second mixed powder is 75%, and the rest remains unchanged.

[0059] Comparative Example 2

[0060] Compared with Example 1, the difference is that in this comparative example, the content of aluminum oxide in the first mixed powder is 5%; the content of yttrium-stabilized zirconium oxide in the second mixed powder is 40%, and the rest remain unchanged.

[0061] According to the method described in the above embodiments and comparative examples, limiting current type oxygen sensors were prepared. After multiple batches of preparation, the cracking conditions of the oxygen sensors prepared in each embodiment and comparative example were counted and the cracking rate (ratio of the number of cracks to the total number) was calculated. The total number of oxygen sensors obtained in each embodiment and comparative example was the same, as shown in the following table:

[0062] Group Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Cracking rate ＜0.1％ ＜0.2％ ＜0.4％ ＜0.5％ ≧1.4％ ≧1.1％

[0063] The present invention also tests the physical properties of various embodiments, comparative examples and typical commercially available oxygen sensor products (average values ​​are taken from multiple samples tested multiple times), and the results are shown in the following table:

[0064]

[0065]

[0066] The oxygen sensor products made in each embodiment were tested, and the relationship curves between the pump current and the atmosphere lambda reflecting the output characteristics were basically the same as Figure 4 As shown, it can be seen that its output characteristics are good and meet the use requirements.

[0067] From the above cracking rate data and product physical property data, it can be seen that when preparing the oxygen sensor according to the preparation method provided by the present invention, the functional layer, the transition layer and the substrate layer are respectively made of powders containing zirconium oxide and aluminum oxide in different proportions to form a casting slurry and cast into a casting sheet, which is then stacked and sintered. By controlling the appropriate ratio of zirconium oxide and aluminum oxide in the transition layer, it can be ensured that the cracking rate is greatly reduced during sintering, and a limiting current type oxygen sensor product co-sintered with zirconium oxide and aluminum oxide is obtained. Its bending strength is close to the excellent strength of pure zirconium oxide products, and the insulation resistance is greatly improved, and the comprehensive performance is excellent.

[0068] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a limiting current type oxygen sensor, characterized in that: The steps include: S1. Tape casting: Use the first mixed powder, the second mixed powder and the third mixed powder to prepare the tape casting slurry of the corresponding functional layer, the transition layer and the substrate layer respectively, and vacuum degassing and drying to obtain the functional layer tape casting sheet, the transition layer tape casting sheet and the substrate layer tape casting sheet for standby use; wherein the first mixed powder is composed of yttrium-stabilized zirconia and alumina, and the alumina content is 0.5-2%; the second mixed powder is composed of alumina, yttrium-stabilized zirconia and a sintering agent, and the content of yttrium-stabilized zirconia is 50-70%, and the sintering agent is 5-15%; the third mixed powder is composed of alumina and a sintering agent, and the sintering agent content is 0.5-5%; S2. Printing: Select the topmost functional layer cast sheet, print the external electrode on its front side, select the bottommost functional layer cast sheet, print the internal electrode on its back side; select several transition layer cast sheets on the upper layer, punch them to form reference channels; select the substrate layer cast sheet in the middle of the substrate layer, print the heating electrode on it; S3. Lamination: stacking a plurality of functional layer cast sheets, a plurality of transition layer cast sheets and a plurality of substrate layer cast sheets from top to bottom, and then hot isostatic pressing to form a whole; S4. Sintering: Cutting the green oxygen sensor into pieces and sintering them in a sintering furnace to obtain; After punching, the transition layer cast sheet in S2 is filled and printed with a filling slurry that can be completely decomposed at a high temperature above 1000°C.

2. The method for preparing a limiting current type oxygen sensor according to claim 1, characterized in that: The casting slurry in S1 contains 30-50% of the mass of the corresponding mixed powders as solvent, 0.3-0.6% of the dispersant, 8-15% of the binder, 0.5-5% of the plasticizer and 0-1% of the defoamer.

3. The method for preparing a limiting current type oxygen sensor according to claim 2, characterized in that: The solvent is a mixed liquid of anhydrous ethanol and xylene in equal volume ratios, the dispersant is NOF AD-374M, AD-3172M or AD-508E, the adhesive is polyvinyl butyral, and the plasticizer is dibutyl phthalate.

4. The method for preparing a limiting current type oxygen sensor according to claim 2, characterized in that: The sintering promoter in S1 is one or more of glass powder, yttrium oxide, lanthanum oxide, titanium oxide or magnesium oxide.

5. The method for preparing a limiting current type oxygen sensor according to claim 2, characterized in that: The thickness of the functional layer cast sheet, the transition layer cast sheet and the substrate layer cast sheet are all in the range of 50-200 μm.

6. The method for preparing a limiting current type oxygen sensor according to claim 1, characterized in that: A diffusion barrier layer is also printed on the front side of the top functional layer cast sheet in S2, and the diffusion barrier layer covers the outer electrode; the content of yttrium-stabilized zirconia in the second powder in S1 is 60-65%.

7. The method for preparing a limiting current type oxygen sensor according to claim 6, characterized in that: The diffusion barrier layer is formed by screen printing with diffusion ink, wherein the diffusion ink is formed by mixing zirconium oxide, a pore former, an adhesive and a solvent in a weight ratio of 30:20:25:

25.

8. The method for preparing a limiting current type oxygen sensor according to claim 1, characterized in that: The hot isostatic pressing treatment conditions in S3 are to control the pressure at 25-45MPa, the temperature at 60-85°C, and the holding time at 5-20min; the sintering temperature in S4 is 1300-1500°C, and the holding time is 1-3h.

9. A limiting current type oxygen sensor, characterized in that: It is prepared by the method according to any one of claims 1 to 8.

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