Pore-filling platinum paste for nitrogen-oxygen sensor and preparation method of pore-filling platinum paste

Abstract

The invention discloses pore-filling platinum paste for a nitrogen-oxygen sensor and a preparation method of the pore-filling platinum paste, and relates to the field of electronic paste preparation, the preparation method comprises the following steps: S1, carrying out non-contact stirring and mixing on a carrier and a dispersing agent at 20-25 DEG C; s2, adding a thixotropic agent, and stirring and mixing in a non-contact manner; s3, adding a sintering aid, and stirring and mixing in a non-contact manner; s4, adding aluminum oxide, and stirring and mixing in a non-contact manner; s5, adding platinum powder and a solvent in batches, and stirring and mixing in a non-contact manner to obtain mixed slurry; s6, the mixed slurry is subjected to gradient grinding through a three-roller mill, and the pore-filling platinum slurry is obtained. According to the platinum paste prepared by the invention, the process stability of the whole process of filling, drying and sintering is realized, the continuity and insulating property of a conductive path are also remarkably improved, a material foundation is laid for long-term reliable operation of a nitrogen-oxygen sensor, meanwhile, the PET mask cost in a hole-filling conductive method is saved, and the platinum paste has obvious technical economy advantages.

Description

Technical Field

[0001] This invention relates to the field of electronic paste preparation technology, and in particular to a pore-filling platinum paste for nitrogen and oxygen sensors and its preparation method. Background Technology

[0002] Nitrogen oxide (NOx) sensors, as core devices for monitoring the concentration of NOx in gases, are widely used in fields such as automotive exhaust emission control, industrial waste gas treatment, and ambient air quality monitoring. Their performance directly affects the ability to meet pollutant emission limits and the effectiveness of environmental regulations. With increasingly stringent global environmental protection requirements, NOx sensors are evolving towards higher precision, higher stability, and longer lifespan. The fabrication technology of their core component, the ceramic chip, has become crucial for improving sensor performance. Ceramic chips are typically manufactured from multiple layers of ceramic films through processes such as printing, stacking, and sintering. The conductivity of the interlayers between the films is fundamental to signal transmission and electrochemical performance. Therefore, how to construct a stable and reliable conductive path within the multilayer ceramic structure has become a core technical challenge in the manufacturing process of NOx sensors.

[0003] In existing technologies, there are three main methods for achieving conductivity in the separator layer of ceramic chips:

[0004] 1. Through-hole conductive method: Platinum paste is printed and air is drawn from the bottom layer to form a conductive layer on the hole wall. This method is simple to operate, but in order to avoid cracking of the hole structure during isostatic pressing, the pressure parameters must be strictly controlled, which may result in insufficient density of the conductive layer, affecting the insulation performance and structural stability during long-term use.

[0005] 2. The through-hole conductive method involves punching holes in a PET mask and a green film tape together, filling the holes with slurry using a steel plate scraping method, and then compacting it under isostatic pressing before circuit printing. Although this method can ensure conductivity and insulation, the use of PET mask and special steel plate significantly increases material costs and process complexity.

[0006] 3. Side-coating conductive method: The electrodes are placed on the side of the ceramic chip and conductive connection from the inside to the surface is achieved by side coating paste. Because the electrodes are exposed on the side, this method cannot form effective insulation and isolation, and is easily affected by external environmental interference, resulting in sensor signal drift and shortened lifespan.

[0007] The green film of the nitrogen-oxygen sensor has a thickness of 0.2 to 0.5 mm and a pore diameter of 0.3 to 1 mm. Currently, many platinum pastes on the market cannot meet the pore-filling requirements of nitrogen-oxygen sensors. They generally have problems such as poor viscosity compatibility and insufficient solid content, which makes them prone to cracking after filling and drying, further affecting the continuity and reliability of the conductive path.

[0008] Therefore, it is necessary to improve upon the shortcomings of existing technologies in order to solve the above problems. Summary of the Invention

[0009] This invention overcomes the shortcomings of the prior art and provides a platinum paste for filling holes in nitrogen and oxygen sensors and its preparation method. The platinum paste prepared by this invention not only achieves process stability throughout the filling, drying and sintering process, but also significantly improves the continuity of its conductive path and insulation performance, laying a material foundation for the long-term reliable operation of nitrogen and oxygen sensors. At the same time, it eliminates the cost of PET mask in the hole-filling conductive method, and has obvious technical and economic advantages.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a platinum paste for filling holes in a nitrogen-oxygen sensor, comprising the following components in parts by mass:

[0011]

[0012] In a preferred embodiment of the present invention, the carrier is selected from at least one of PII Company's VS31H, VS31L, or VS31XL; wherein the viscosity of VS31H is 2500 kcps, the viscosity of VS31L is 130 kcps, and the viscosity of VS31XL is 50 kcps.

[0013] In a preferred embodiment of the present invention, the solvent is selected from PII TS31.

[0014] In a preferred embodiment of the present invention, the dispersant is selected from PII DS007 and comprises 65 wt% modified polymer and 35 wt% ethylene glycol.

[0015] In a preferred embodiment of the present invention, the thixotropic agent is selected from PII Company TX003, which contains 50 wt% terpineol and 50 wt% acrylate copolymer.

[0016] In a preferred embodiment of the present invention, the sintering aid is selected from PII Company Z3-1, which contains 50 wt% naphtha and 50 wt% zirconium oxide dispersion.

[0017] In a preferred embodiment of the present invention, the alumina is selected from PII Company's A16SG alumina powder with a purity of 100%.

[0018] This invention provides a method for preparing a pore-filling platinum paste for a nitrogen and oxygen sensor, comprising the following steps:

[0019] S1. Mix the carrier and dispersant by non-contact stirring at 20-25°C;

[0020] S2. Add a thixotropic agent to the product of S2 and mix it by non-contact stirring.

[0021] S3. Add sintering aid to the product of S3 and mix it by non-contact stirring.

[0022] S4. Add alumina to the product of S4 and mix using non-contact stirring.

[0023] S5. Add platinum powder and solvent to the product of S5 in portions, with each addition of platinum powder ≤100g. Mix using non-contact stirring, and cool to room temperature between each mixing step to obtain a mixed slurry.

[0024] S6. The mixed slurry is subjected to gradient grinding through a three-roll mill. The gap between the front rolls is gradually reduced from 140μm to 5μm, and the gap between the rear rolls is gradually reduced from 70-100μm to 10μm. The roll speed is 160rpm, and the pore-filling platinum slurry is obtained.

[0025] In a preferred embodiment of the present invention, in steps S1, S2, S3 and S4, the non-contact stirring is: revolution at 1900-2100 rpm, rotation at 900-1100 rpm, and stirring time of 1-2 min; in step S5, the non-contact stirring is: revolution at 1900-2100 rpm, rotation at 900-1100 rpm, and stirring time of ≤30 s per cycle.

[0026] In a preferred embodiment of the present invention, in step S6, the gaps between the front rollers in the gradient grinding process are sequentially 140μm, 120μm, 100μm, 80μm, 60μm, 40μm, 20μm, 10μm and 5μm, and the gaps between the rear rollers are sequentially 70-100μm, 60-90μm, 50μm, 40μm, 30μm, 20μm, 10μm, 10μm and 10μm; the gaps between the front and rear rollers in each stage are ground once, and the gaps between the front and rear rollers in the final stage are ground 3-5 times.

[0027] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0028] (1) This invention provides a platinum paste for filling micropores in a nitrogen-oxygen sensor and its preparation method. It uses ultra-high solid content platinum powder and a specific composite carrier to construct a dense conductive network framework at the molecular level. At the same time, the long-chain polymer and short-chain molecules in the carrier form a gradient entanglement structure, which causes the viscosity of the paste to decrease instantaneously under shear force when filling micropores, so as to achieve smooth injection of deep holes with a diameter of 0.3-1mm. Under static conditions, the polymer chains quickly recover entanglement and form a three-dimensional network structure in synergy with the acrylate cross-linked polymer in the thixotropic agent, locking the platinum powder particles and avoiding uneven filling caused by sedimentation. This solves the defects of existing low-viscosity pastes that are not filled properly and high-viscosity pastes that are difficult to inject.

[0029] (2) In this invention, the zirconium oxide dispersed phase in the sintering aid produces a local pinning effect between the oxygen vacancies on its surface and the platinum lattice, which inhibits the high-temperature diffusion rate of platinum atoms and buffers the thermal expansion mismatch between platinum and the ceramic matrix. This eliminates the cracks in the pores caused by shrinkage stress concentration during drying and sintering from the root. At the same time, the alumina powder forms Al-O-Si covalent bond bridging at the interface between the slurry and the film, which enhances the interfacial bonding force and avoids peeling during isostatic pressing. Combined with the ultrafine dispersion system formed by stepwise non-contact stirring and gradient three-roll milling, it ensures that the internal stress is released uniformly during the slurry drying process, which can eliminate the cracking phenomenon caused by component agglomeration or stress concentration in traditional processes. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a photograph of the test piece after the platinum paste for filling the pores in Example 1 of the present invention has been dried.

[0032] Figure 2 This is a photograph of the test piece after the platinum paste used for filling holes in Comparative Example 1 of this invention has been dried. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0035] It should be noted that the raw materials, equipment and reagents used in this invention can all be purchased from the market or obtained through existing preparation methods.

[0036] A platinum paste for filling holes in a nitrogen-oxygen sensor comprises the following components in parts by weight:

[0037]

[0038] In some specific embodiments, the carrier is selected from at least one of VS31H, VS31L, or VS31XL from PII (Polymer Innvations, Inc.); wherein H represents a high molecular chain, VS31H has a viscosity of 2500 kcps, L represents a low molecular chain, VS31L has a viscosity of 130 kcps, and XL represents an ultra-low molecular chain, VS31XL has a viscosity of 50 kcps.

[0039] In some specific implementations, the solvent is selected from PII TS31.

[0040] In some specific embodiments, the dispersant is selected from PII DS007, which contains 65 wt% of the modified polymer and 35 wt% of ethylene glycol.

[0041] In some specific embodiments, the thixotropic agent is selected from PII TX003, which contains 50 wt% terpineol and 50 wt% acrylate copolymer.

[0042] It should be noted that TX003 is a cross-linked polymeric paste-like thixotropic agent formed by copolymerization of acrylic acid esters. It has strong thickening ability and good anti-settling properties, which can effectively improve the low shear viscosity of the slurry and improve its thixotropy, allowing the slurry to better present a paste-like form and be easier to fill in the pores.

[0043] In some specific embodiments, the sintering aid is selected from PII Company Z3-1, which contains 50 wt% naphtha and 50 wt% zirconium oxide dispersion.

[0044] It should be noted that Z3-1 is a liquid additive that improves the sintering characteristics of metal slurries and mitigates the shrinkage between conductive slurries and ceramic powders. It is a highly dispersed fine zirconia liquid in aliphatic hydrocarbons and is a very effective sintering control additive that can effectively control the local growth of platinum particles, making the slurry more uniform.

[0045] In some specific embodiments, the alumina is selected from PII Company's A16SG alumina powder, with a purity of 100%.

[0046] It should be noted that the addition of alumina is used to enhance the adhesion between the platinum paste and the cast film, and the amount of alumina added is related to the resistance of the platinum paste after firing.

[0047] This invention provides a method for preparing a pore-filling platinum paste for a nitrogen and oxygen sensor, comprising the following steps:

[0048] S1. Mix the carrier and dispersant by non-contact stirring at 20-25°C;

[0049] S2. Add a thixotropic agent to the product of S2 and mix it by non-contact stirring.

[0050] S3. Add sintering aid to the product of S3 and mix it by non-contact stirring.

[0051] S4. Add alumina to the product of S4 and mix using non-contact stirring.

[0052] S5. Add platinum powder and solvent to the product of S5 in portions, with each addition of platinum powder ≤100g. Mix using non-contact stirring, and cool to room temperature between each mixing step to obtain a mixed slurry.

[0053] S6. The mixed slurry is subjected to gradient grinding through a three-roll mill. The gap between the front rolls is gradually reduced from 140μm to 5μm, and the gap between the rear rolls is gradually reduced from 70-100μm to 10μm. The roll speed is 160rpm, and the pore-filling platinum slurry is obtained.

[0054] In some specific implementations, in steps S1, S2, S3 and S4, the non-contact stirring is: revolution at 1900-2100 rpm, rotation at 900-1100 rpm, and stirring time of 1-2 min; in step S5, the non-contact stirring is: revolution at 1900-2100 rpm, rotation at 900-1100 rpm, and stirring time of ≤30 s per cycle.

[0055] It should be noted that the stirring time for a single stirring session should not exceed 30 seconds. Platinum powder will release a large amount of heat at high speed, causing the slurry volume to expand and spray out of the slurry box. Therefore, the second stirring session should only be started after the heat from the first stirring session has fully cooled down.

[0056] In some specific embodiments, in step S6, the gaps between the front rollers in the gradient grinding process are sequentially 140μm, 120μm, 100μm, 80μm, 60μm, 40μm, 20μm, 10μm and 5μm, and the gaps between the rear rollers are sequentially 70-100μm, 60-90μm, 50μm, 40μm, 30μm, 20μm, 10μm, 10μm and 10μm; the gaps between the front and rear rollers in each stage are ground once, and the gaps between the front and rear rollers in the final stage are ground 3-5 times.

[0057] To further simplify and make the present invention achieve its objectives and effects, the present invention will be further illustrated in conjunction with the following specific embodiments and comparative examples, but the present invention is not limited to the scope of the embodiments described herein.

[0058] The raw materials and proportions of the pore-filling platinum pastes used in Examples 1-7 are different, as shown in Table 1, with the raw materials measured in parts by mass.

[0059] Table 1: Raw materials and proportions for the preparation of pore-filling platinum pastes in Examples 1-7

[0060]

[0061]

[0062] Example 1

[0063] A method for preparing a pore-filling platinum paste for a nitrogen-oxygen sensor includes the following steps:

[0064] S1. Mix VS31H, VS31L and DS007 at 25℃ with non-contact stirring for 1 minute at a revolution speed of 2000 rpm and a rotation speed of 1000 rpm.

[0065] S2. Add TX003 to the product of S2 and mix it by non-contact stirring at 2000 rpm revolution and 1000 rpm rotation for 1 minute.

[0066] S3. Add Z3-1 to the product of S3 and mix by non-contact stirring at 2000 rpm revolution and 1000 rpm rotation for 1 minute.

[0067] S4. Add A16SG to the product of S4 and mix by non-contact stirring at 2000 rpm revolution and 1000 rpm rotation for 1 minute.

[0068] S5. Add platinum powder and TS31 to the product of S5 in portions. The amount of platinum powder added at one time is 100g. Mix at a revolution speed of 2000rpm and a rotation speed of 1000rpm for 30s in a non-contact stirring manner. Cool to room temperature between two consecutive stirring sessions to obtain a mixed slurry.

[0069] S6. The mixed slurry is subjected to gradient grinding through a three-roll mill. The gap between the front rolls is gradually reduced from 140μm to 120μm, 100μm, 80μm, 60μm, 40μm, 20μm, 10μm and 5μm, and the gap between the rear rolls is gradually reduced from 80μm to 70μm, 50μm, 40μm, 30μm, 20μm, 10μm, 10μm and 10μm. The gap between the front and rear rolls at each stage is ground once, and the gap between the front and rear rolls at the last stage is ground four times. The roll speed is 160rpm to obtain the pore-filling platinum slurry.

[0070] To verify the success of the pore-filling platinum slurry in Example 1, a drying cracking rate test was conducted. The specific test steps were as follows:

[0071] 1. A 250μm thick nitrogen and oxygen sensor green film strip was used as the substrate. Through holes with a diameter of 0.3mm were uniformly prepared on the film strip using a precision punching machine. The hole spacing was set to 5mm. Each test piece was 5cm×5cm in size and contained 100 through holes distributed in a 10×10 array. Five parallel test pieces were prepared for each group of experiments to reduce errors.

[0072] 2. Place the pore-filling platinum slurry from Example 1 in a constant temperature environment of 25°C, and use a 200-mesh stainless steel scraper to scrape and fill along the pore array direction at a 45° angle and a speed of 50 mm / s to ensure that the slurry completely covers the through holes and flows naturally into the holes. After scraping and filling, use a lint-free cloth to gently wipe the surface of the membrane tape of excess slurry.

[0073] 3. Place the filled test piece into a forced-air drying oven, set the drying temperature to 120℃, the drying time to 30min, the heating rate to 5℃ / min, and maintain the air flow rate inside the oven at 0.5m / s during the drying process;

[0074] 4. After drying, remove the test pieces and allow them to cool naturally to room temperature. Observe each of the 100 through holes on each test piece and record the number of through holes with cracked walls, cracked edges, and through cracks. Calculate the average cracking rate of each group of test pieces according to the formula: cracking rate = (total number of cracked through holes / total number of through holes) × 100%.

[0075] The test piece after drying of the platinum paste used to fill the pores in Example 1 is shown below. Figure 1 As shown, its cracking rate is only 1.9%, ensuring uniform release of internal stress during the slurry drying process and eliminating cracking caused by component agglomeration or stress concentration in traditional processes.

[0076] Example 2

[0077] This embodiment is basically the same as Embodiment 1, except that the raw materials are different, as shown in Table 1.

[0078] Example 3

[0079] This embodiment is basically the same as Embodiment 1, except that the raw material ratio is different, as shown in Table 1.

[0080] Example 4

[0081] This embodiment is basically the same as Embodiment 1, except that the raw material ratio is different, as shown in Table 1.

[0082] Example 5

[0083] This embodiment is basically the same as embodiment 1, except that the raw materials and their proportions are different, as shown in Table 1.

[0084] Example 6

[0085] This embodiment is basically the same as embodiment 1, except that the raw materials and their proportions are different, as shown in Table 1.

[0086] Example 7

[0087] This embodiment is basically the same as embodiment 1, except that the raw materials and their proportions are different, as shown in Table 1.

[0088] Comparative Example 1

[0089] This comparative example is basically the same as Example 1, except that: step S6 is as follows: the mixed slurry is ground by a three-roll mill with a front roll gap of 140 μm and a rear roll gap of 80 μm. The front and rear roll gaps are ground 4 times with a roll speed of 160 rpm to obtain a pore-filling platinum slurry.

[0090] Comparative Example 2

[0091] This comparative example is basically the same as Example 1, except that: Step S6 is specifically as follows: the mixed slurry is subjected to gradient grinding through a three-roll mill, the gap between the front rolls is gradually reduced from 140μm to 80μm and 5μm, and the gap between the rear rolls is reduced from 80μm to 40μm and 10μm. The gap between the front and rear rolls at each stage is ground once, and the gap between the front and rear rolls at the last stage is ground four times. The roll speed is 160rpm, and a pore-filling platinum slurry is obtained.

[0092] Performance testing: The pore-filling platinum slurries obtained in Examples 2-7 and Comparative Examples 1-2 were subjected to drying cracking rate tests using the same performance testing methods as the pore-filling platinum slurry obtained in Example 1. The results are shown in Table 2.

[0093] Table 2: Performance test results of platinum slurry for filling pores obtained in Examples 2-7 and Comparative Examples 1-2

[0094]

[0095]

[0096] As shown in Table 2:

[0097] A comparison of Examples 1 and Examples 2-7 reveals that: Example 2, which replaced VS31L with VS31XL, resulted in a decrease in the overall viscosity of the carrier system. Its short-chain molecules could not form effective entanglement with the long chains of VS31H, weakening the polymer chain orientation reconstruction ability under shear force. It was difficult to restore the three-dimensional network structure in a static state, and the platinum powder particles were prone to sedimentation. The density of the slurry in the pores was uneven after filling. During the drying process, the low-viscosity slurry accumulated at the edge of the pore opening due to its excessive leveling properties. When the water evaporated, the surface tension gradient increased, causing the pore wall to crack. The cracking rate rose to 13.2%, which directly affected the structural integrity of the sensor ceramic chip and led to a decrease in the continuity of the conductive path.

[0098] Example 3: Increasing the amount of VS31L and decreasing the amount of VS31H disrupts the gradient viscosity balance of the carrier. Excessive short-chain molecules occupy the entanglement sites between long chains, weakening the synergistic effect between the thixotropic agent TX003 and the carrier. The shear thinning effect of the slurry is too strong during filling, making it difficult for the slurry in the pores to maintain its shape. After drying, through-cracks appear due to uneven distribution of internal stress, with a cracking rate as high as 31.7%. This will lead to poor conductive contact between the layers of the sensor film, signal transmission delay, and insulation failure during long-term use.

[0099] In Examples 4-7, the carrier dosage deviated from the appropriate dosage. In Example 4, the reduced proportion of polymer chains led to insufficient support of the carrier skeleton. In Example 5, the excessively high proportion of ultra-low molecular weight chains led to uncontrolled viscosity of the carrier system. In Example 6, the lack of polymer chain skeleton support resulted in excessively high initial viscosity of the slurry. Under shear force, the untangling was insufficient, resulting in poor slurry fluidity during filling and the formation of voids in the micropores. During drying, internal stress accumulated, the pinning effect of zirconium oxide was insufficient to buffer the stress, and after the carrier entanglement gradient was destroyed, the slurry lost its static recovery and particle locking ability. The agglomeration of platinum powder and uneven dispersion of alumina together led to an increase in the cracking rate.

[0100] A comparison between Example 1 and Comparative Example 1 reveals that: Comparative Example 1 did not employ gradient grinding, but only used a fixed gap of 140μm / 80μm ​​for grinding. Consequently, the platinum powder agglomerates in the slurry were not sufficiently broken up. Large agglomerates (>5μm) formed rigid contact points within the pores, leading to rapid evaporation of moisture between the agglomerates during drying, resulting in micro-explosions. Figure 2 As shown, this leads to radial cracks appearing on the pore wall, with the cracking rate rising to 33.1%. This causes the resistance value of the sensor's conductive path to fluctuate more widely, raising the detection limit and failing to meet the requirements for monitoring low concentrations of nitrogen oxides.

[0101] A comparison between Example 1 and Comparative Example 2 reveals that in Comparative Example 2, skipping some intermediate gaps during gradient grinding results in a wide particle size distribution in the slurry. Coarse and fine particles form an "arch bridge effect" within the pores. During drying, fine particles shrink preferentially, while coarse particles hinder stress release, leading to the appearance of annular cracks within the pores. The cracking rate rises to 19.4%, which will cause the sensor to experience increased crack propagation due to the difference in thermal expansion coefficients under high-temperature operating conditions, ultimately resulting in the loss of conductivity.

[0102] The above description is based on the preferred embodiments of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered exemplary and non-limiting in all respects. The scope of the invention is defined by the appended claims rather than the foregoing description, and all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0103] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A platinum paste for filling holes in a nitrogen-oxygen sensor, characterized in that, The components include the following parts by mass:

2. The platinum paste for filling holes in a nitrogen-oxygen sensor according to claim 1, characterized in that: The carrier is selected from at least one of PII Company's VS31H, VS31L, or VS31XL; wherein the viscosity of VS31H is 2500 kcps, the viscosity of VS31L is 130 kcps, and the viscosity of VS31XL is 50 kcps.

3. The platinum paste for filling holes in a nitrogen-oxygen sensor according to claim 1, characterized in that: The solvent is selected from PII TS31.

4. The platinum paste for filling holes in a nitrogen-oxygen sensor according to claim 1, characterized in that: The dispersant is selected from PII DS007, which contains 65 wt% modified polymer and 35 wt% ethylene glycol.

5. The platinum paste for filling holes in a nitrogen-oxygen sensor according to claim 1, characterized in that: The thixotropic agent is selected from PII's TX003, which contains 50 wt% terpineol and 50 wt% acrylate copolymer.

6. The platinum paste for filling holes in a nitrogen-oxygen sensor according to claim 1, characterized in that: The sintering aid is selected from PII Company Z3-1, which contains 50 wt% naphtha and 50 wt% zirconium oxide dispersion.

7. The platinum paste for filling holes in a nitrogen-oxygen sensor according to claim 1, characterized in that: The alumina is selected from PII Company's A16SG alumina powder, with a purity of 100%.

8. A method for preparing a pore-filling platinum paste for a nitrogen-oxygen sensor based on any one of claims 1-7, characterized in that, Includes the following steps: S1. Mix the carrier and dispersant by non-contact stirring at 20-25°C; S2. Add a thixotropic agent to the product of S2 and mix it by non-contact stirring. S3. Add sintering aid to the product of S3 and mix it by non-contact stirring. S4. Add alumina to the product of S4 and mix using non-contact stirring. S5. Add platinum powder and solvent to the product of S5 in portions, with each addition of platinum powder ≤100g. Mix using non-contact stirring, and cool to room temperature between each mixing step to obtain a mixed slurry. S6. The mixed slurry is subjected to gradient grinding through a three-roll mill. The gap between the front rolls is gradually reduced from 140μm to 5μm, and the gap between the rear rolls is gradually reduced from 70-100μm to 10μm. The roll speed is 160rpm, and the pore-filling platinum slurry is obtained.

9. The method for preparing a pore-filling platinum paste for a nitrogen-oxygen sensor according to claim 8, characterized in that: In steps S1, S2, S3, and S4, the non-contact stirring is: revolution at 1900-2100 rpm, rotation at 900-1100 rpm, and stirring time of 1-2 minutes; in step S5, the non-contact stirring is: revolution at 1900-2100 rpm, rotation at 900-1100 rpm, and stirring time of ≤30 seconds per cycle.

10. A method for preparing a pore-filling platinum paste for a nitrogen-oxygen sensor according to claim 8, characterized in that... In step S6, the gaps between the front rollers in the gradient grinding process are sequentially 140μm, 120μm, 100μm, 80μm, 60μm, 40μm, 20μm, 10μm and 5μm, and the gaps between the rear rollers are sequentially 70-100μm, 60-90μm, 50μm, 40μm, 30μm, 20μm, 10μm, 10μm and 10μm; the gaps between the front and rear rollers in each stage are ground once, and the gaps between the front and rear rollers in the final stage are ground 3-5 times.

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