A platinum-based alloy slurry for alumina co-firing and a heating electrode

Abstract

The present invention provides a platinum-based alloy slurry for alumina co-firing and a heating electrode. The platinum-based alloy slurry for alumina co-firing contains the following components in parts by weight: a) 65%-80% of a main conductive phase, wherein the main conductive phase is monodisperse spherical platinum-palladium alloy powder, and the particle size of the platinum-palladium alloy powder ranges from 200 to 300 nm; b) 1%-5% of an auxiliary conductive phase, wherein the auxiliary conductive phase is a metal organic compound; c) 0.5%-1% of a sintering aid, wherein the sintering aid is γ-Al2O3 powder or a mixed powder of γ-Al2O3 and α-Al2O3; and d) 15%-30% of an organic carrier.

Description

Technical Field

[0001] The present invention relates to the technical field of sensor heating electrodes, and in particular to a platinum-based alloy slurry for co-firing aluminum oxide and a heating electrode. Background Art

[0002] Platinum-based pastes offer unique advantages in sensor manufacturing and high-temperature co-fired (HTCC) electronic component applications. First, in terms of catalytic properties, platinum is a commonly used electrochemical catalytic phase, widely used in various gas detection and fuel cell applications, such as automotive exhaust NOx sensors. As a catalytic electrode material, it plays a decisive role in sensor response speed and sensitivity, making it one of the most critical factors in determining NOx sensor performance. Furthermore, platinum exhibits excellent high-temperature stability and corrosion resistance. On the one hand, platinum can withstand high-temperature sintering in air and still maintain high conductivity, giving it an unparalleled advantage in HTCC devices used in oxidizing atmospheres. Furthermore, platinum resists corrosion from various corrosive substances and maintains stable performance in harsh environments such as high temperature, high pressure, and high humidity. This provides a strong guarantee for the long-term stable operation of various sensors and extends their service life. Therefore, it is widely used as the material of choice for heating electrodes in NOx sensors. Regarding electrical properties, platinum in platinum-based pastes exhibits excellent conductivity and a stable temperature coefficient of resistance (TCR), ensuring accurate measurement and long-term stability of the current signal in the sensor.

[0003] However, conventional platinum-based slurries present numerous challenges when used in automotive sensor heating electrodes. During the sintering process, platinum particles easily penetrate the ceramic substrate, resulting in a loose conductive layer structure and reduced electrode density. This not only affects the electrode's conductivity but also shortens its service life, making it difficult to adapt to the long-term, high- and low-temperature fluctuations required by sensors. Furthermore, electrodes made with existing slurries have a high temperature coefficient of resistance (TCR), resulting in poor circuit control stability and difficulty in accurately controlling circuit parameters during temperature fluctuations. This leads to delayed sensor response and increased detection errors, limiting their application in high-precision exhaust gas component detection. Furthermore, the grain boundary effect creates high resistance at the interfaces between the conductive layer particles. When subjected to voltage surges, these interfaces become weak links in the entire circuit and are prone to damage. This results in insufficient voltage withstand capability for the electrode, making it unable to meet the complex operating conditions required by automotive power-on, such as the high voltage surges experienced during transients. Therefore, it is necessary to design a platinum-based alloy slurry and heating electrode for co-firing with alumina to address these issues. Summary of the Invention

[0004] The object of the present invention is to provide a platinum-based alloy slurry for alumina co-firing that can form a dense electrode layer, thereby achieving electrode requirements of low resistance, voltage shock resistance and long-term stability after sintering.

[0005] To achieve the above object, the present invention adopts the following technical solution: a platinum-based alloy slurry for alumina co-firing, which contains the following components in parts by weight:

[0006] a) 65%-80% of a main conductive phase, wherein the main conductive phase is a monodisperse spherical platinum-palladium alloy powder, and the particle size of the platinum-palladium alloy powder is in the range of 200-300 nm;

[0007] b) 1%-5% of an auxiliary conductive phase, wherein the auxiliary conductive phase is a metal organic compound;

[0008] c) 0.5%-1% sintering aid, wherein the sintering aid is γ-Al2O3 powder or a mixed powder of γ-Al2O3 and α-Al2O3;

[0009] d) 15%-30% organic carrier.

[0010] As a further improved technical solution of the present invention, the platinum-palladium alloy powder is prepared by the following method:

[0011] S1. Obtaining a platinum-palladium composite powder by a coprecipitation method: dissolving chloroplatinic acid and chloropalladic acid in a solvent to form a mixed solution, adding the mixed solution to an excess reducing agent solution at a temperature of 50-80° C., stirring until the reaction is complete, washing, and drying to obtain a platinum-palladium composite powder, wherein the platinum-palladium composite powder comprises platinum elemental powder and palladium elemental powder;

[0012] S2. Heat-treating the platinum-palladium composite powder under a protective atmosphere to obtain platinum-palladium alloy powder: the protective atmosphere is nitrogen or argon, the heat treatment temperature is 400-600° C., and the heat treatment time is 1-3 hours.

[0013] As a further improved technical solution of the present invention, in step S1, the particle size range of the platinum-palladium composite powder is 20-50 nm, and the molar ratio of palladium to platinum in the platinum-palladium composite powder is 1:3-1:5.

[0014] As a further improved technical solution of the present invention, in step S1, in the mixed solution, the molar concentration of chloroplatinic acid is 3-5 times the molar concentration of chloropalladic acid, the reducing agent is hydrazine hydrate, and the molar concentration of the reducing agent solution is 5-10 times the total molar concentration of chloroplatinic acid and chloropalladic acid.

[0015] As a further improved technical solution of the present invention, the particle size range of γ-Al2O3 is 3-20nm, and the specific surface area is 50-300 m2 / g.

[0016] As a further improvement to the present invention, the weight of α-Al2O3 added is 0-10% of the weight of γ-Al2O3, and the α-Al2O3 particle size ranges from 3-20nm. The combination of α-Al2O3 and γ-Al2O3 facilitates adjustment to match the shrinkage of the green ceramic film, improving co-firing compatibility and reliability.

[0017] As a further improved technical solution of the present invention, the organic carrier includes one or more of ethyl cellulose, acrylic resin, polycarbonate, epoxy resin, polyurethane resin, maleic anhydride resin, polystyrene, polyvinyl butyral or poly-α-methylstyrene resin, and a solvent.

[0018] As a further improved technical solution of the present invention, the solvent is one or more of diethylene glycol butyl ether, diethylene glycol butyl ether acetate, diethylene glycol ethyl ether acetate, terpineol, turpentine, butyl carbitol, and dibutyl phthalate.

[0019] As a further improved technical solution of the present invention, the metal element in the metal organic compound is palladium or iridium, and the metal organic compound can be decomposed into metal elements at a temperature of 300-500°C.

[0020] The present invention also aims to provide an alumina co-fired heating electrode with a dense electrode layer, low resistance, high pressure shock resistance and high stability.

[0021] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: an alumina co-fired heating electrode is prepared by sintering the platinum-based alloy slurry for alumina co-fired as described in any of the above items on a green porcelain tape, and the sintering temperature and time are set to: heating to 300°C and maintaining for 10-20 minutes, 300-500°C and maintaining for 20-30 minutes, 950-1050°C and maintaining for 20-30 minutes, and 1300-1500°C and maintaining for 1-2 hours; the green porcelain tape is an alumina green porcelain tape or a green porcelain tape with an alumina system slurry printed on the surface, and the alumina system slurry is a type of functional slurry with alumina as the main component.

[0022] It can be seen from the above technical solutions that the platinum-based alloy slurry for alumina co-firing of the present invention has at least the following effects:

[0023] (1) The platinum-based alloy slurry of the present invention is added with a metal organic compound that can be thermally decomposed and γ-Al2O3 that can change its crystal form during the sintering process, which improves the electrode density through precise synergy: in the early stage of slurry sintering, when the temperature reaches 300-500°C, the metal organic compound begins to decompose and produces metal element particles. These metal element particles are distributed between the platinum-palladium alloy particles. As the temperature continues to rise, the metal element and the platinum-palladium alloy are locally alloyed near the point contact of the particles, which reduces the barrier for the sintering growth of the platinum-palladium alloy particles themselves and initially promotes the densification of the electrode layer. Furthermore, when the temperature rises to 950°C, the high specific surface area γ-Al2O3 is transformed into low specific surface area α-Al2O3 at high temperature, and its volume shrinks. On the one hand, it adjusts the shrinkage rate of the slurry to match that of the alumina green ceramic film. On the other hand, its high specific surface area has a stronger fluxing effect on the metal particles, reducing the penetration of metal element particles into the ceramic substrate, which is beneficial to the interconnection and denseness of the platinum-palladium alloy particles and metal element particles in the xy plane direction. γ-Al2O3 cooperates with the alloying process initiated by the previous metal organic compound to further improve the overall density of the platinum heating electrode.

[0024] (2) The platinum-based alloy slurry of the present invention uses platinum-palladium alloy powder as the main conductive phase, which plays a role in reducing the electrode TCR throughout the entire process from slurry forming to final use, optimizing conductivity and stabilizing circuit control. By setting the ratio of platinum to palladium in the platinum-palladium alloy, the electrode TCR is significantly reduced from 3850ppm for pure platinum to approximately 1500ppm, effectively improving the stability of circuit control. During the operation of the sensor, even in the face of temperature changes, it can maintain stable resistance characteristics, extending the service life of the electrode and meeting the needs of electronic equipment such as automotive exhaust treatment sensors that require high circuit stability.

[0025] (3) The platinum-based alloy slurry of the present invention can enhance the circuit voltage resistance in stages: in the preparation process of the platinum-based alloy slurry, a uniform platinum-palladium alloy powder is formed by co-precipitating platinum-palladium composite powder in combination with an inert gas protection heat treatment process. On the one hand, it is beneficial to prevent the oxidation of metal palladium during the sintering process, and at the same time, the sintering interconnection between the platinum particles is dense, thereby improving the stability of circuit control and the life of the heating electrode; on the other hand, during the sintering process, the metal element produced by the decomposition of the metal organic compound is further locally alloyed with the platinum-palladium alloy, changing the conductive phase properties at the particle interface, so that the temperature coefficient of resistance TCR at the interface is lower than that of the platinum-palladium alloy. In the subsequent heating process of the electrode when it is energized, the resistance increase rate at the interface is lower than that of other parts, so that the local voltage increase rate at the particle interface is lower than the average value of the entire circuit. This feature effectively alleviates the shortcoming of the conductive layer particle interface in carrying voltage. From the slurry forming stage to the actual working process of the electrode, the ability of the entire circuit to withstand voltage shock is synergistically improved in stages, and it can adapt to complex working conditions such as high voltage shock at the moment of power on. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the SEM image of the electrode layer after sintering the slurry in Comparative Example 4.

[0027] Figure 2 This is the SEM image of the electrode layer after sintering the slurry in Example 2. DETAILED DESCRIPTION

[0028] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments. Example 1

[0029] Preparation of platinum-based alloy slurry A1 for alumina co-firing specifically includes the following steps:

[0030] S1. Prepare platinum-palladium composite powder by co-precipitation method: dissolve chloroplatinic acid and chloropalladic acid in a solvent to form a mixed solution, wherein the concentration of chloroplatinic acid is 0.08M and the concentration of chloropalladic acid is 0.02M; add the mixed solution to an excess of hydrazine hydrate solution within 15 minutes, and the concentration of the hydrazine hydrate solution is 1M. The temperature of the hydrazine hydrate solution is 75°C, and the mixture is kept warm and stirred until the reaction is complete. Wash the precipitate powder with deionized water 7-10 times and dry it to obtain platinum-palladium composite powder with a particle size range of 30-50nm (the widest distance of multiple powder particles is measured and counted using a scanning electron microscope to obtain the powder particle size distribution. The following particle size ranges are all obtained by this method). The platinum-palladium composite powder includes platinum element powder and palladium element powder, and the molar ratio of palladium to platinum is 1:4;

[0031] S2. Prepare platinum-palladium alloy powder by heat treatment: heat treat the platinum-palladium composite powder under a protective atmosphere: the protective atmosphere is argon, the heat treatment temperature is 450°C, and the heat treatment time is 2.5 hours to obtain monodisperse spherical platinum-palladium alloy powder with a particle size of 250-300nm; differential thermal-thermogravimetric analysis of the platinum-palladium alloy powder shows that no redox phenomenon occurs during the process from room temperature to 1500 degrees.

[0032] S3. Preparation of an organic vehicle: Accurately weigh 20 g of acrylic resin, 40 g of diethylene glycol butyl ether, and 40 g of diethylene glycol butyl ether acetate and add them to a container, place them in a constant temperature water bath at 80° C., stir at 500 rpm, and keep warm for 1 hour after they are completely dissolved to obtain an organic vehicle for later use;

[0033] S4. Platinum-palladium alloy powder, iridium acetylacetonate, γ-Al2O3 powder (particle size 3-20 nm, specific surface area 50-300 m2 / g (BET fast method)), and an organic carrier were mixed according to the weight proportions in Table 1, homogenized by a homogenizer, and then ground in a three-roll mill at a roller speed of 100 r / min and a pressure of 3 MPa for 5 rolls. Finally, the mixture was degassed under reduced pressure at a pressure of -80 kPa to obtain platinum-based alloy slurry A1 for alumina co-firing. Example 2

[0034] The preparation of platinum-based alloy slurry A2 for alumina co-firing specifically includes the following steps:

[0035] S1 is substantially the same as Example 1, except that the amounts of chloroplatinic acid and chloropalladic acid added are changed so that the molar ratio of palladium to platinum in the platinum-palladium composite powder is 1:3;

[0036] S2, consistent with Example 1;

[0037] S3. Preparation of an organic carrier: Accurately weigh 20 g of polycarbonate, 40 g of diethylene glycol butyl ether, and 40 g of diethylene glycol ethyl ether acetate and add them to a container, place them in a constant temperature water bath at 80°C, stir at 500 rpm, and keep warm for 1 hour after they are completely dissolved to obtain an organic carrier for later use;

[0038] S4. Mix platinum-palladium alloy powder, iridium acetylacetonate, γ-Al2O3 powder and organic carrier according to the weight proportions in Table 1, homogenize, roll-press and degas under reduced pressure in the same manner as in Example 1 to obtain platinum-based alloy slurry A2 for alumina co-firing. Example 3

[0039] Preparation of platinum-based alloy slurry A3 for alumina co-firing specifically includes the following steps:

[0040] S1 is substantially the same as Example 1, except that the amounts of chloroplatinic acid and chloropalladic acid added are changed so that the molar ratio of palladium to platinum in the platinum-palladium composite powder is 1:5;

[0041] S2, consistent with Example 1;

[0042] S3, consistent with Example 1;

[0043] S4. Mix platinum-palladium alloy powder, palladium acetylacetonate, γ-Al2O3 powder and organic carrier according to the weight proportions in Table 1, and perform homogenization, roller pressing and decompression degassing in the same manner as in Example 1 to obtain platinum-based alloy slurry A3 for alumina co-firing. Example 4

[0044] Preparation of platinum-based alloy slurry A4 for alumina co-firing specifically includes the following steps:

[0045] S1, consistent with Example 2;

[0046] S2, consistent with Example 1;

[0047] S3, consistent with Example 2;

[0048] S4. Mix platinum-palladium alloy powder, iridium acetylacetonate, γ-Al2O3 powder, α-Al2O3 powder and an organic carrier according to the weight proportions in Table 1, and homogenize, roll-press and degas under reduced pressure by the same method as in Example 1 to obtain platinum-based alloy slurry A4 for alumina co-firing. Example 5

[0049] Preparation of platinum-based alloy slurry A5 for alumina co-firing specifically includes the following steps:

[0050] S1, consistent with Example 2;

[0051] S2, consistent with Example 1;

[0052] S3, consistent with Example 2;

[0053] S4. Mix platinum-palladium alloy powder, palladium acetylacetonate, γ-Al2O3 powder, α-Al2O3 powder and an organic carrier according to the weight proportions in Table 1, and homogenize, roll-press and degas under reduced pressure by the same method as in Example 1 to obtain platinum-based alloy slurry A5 for alumina co-firing. Comparative Example 1

[0054] The platinum-based slurry B1 is prepared, specifically comprising the following steps:

[0055] S1. Directly purchase platinum powder and palladium powder and mix them, with the molar ratio of palladium to platinum being 1:3, and the particle size range of palladium and platinum being 30-50 nm;

[0056] S2. Preparation of organic carrier: same as in Example 2;

[0057] S3. Mix the platinum-palladium mixed powder, palladium acetylacetonate, γ-Al2O3 powder and organic carrier according to the weight proportions in Table 1, and homogenize, roll-press and degas under reduced pressure in the same manner as in Example 1 to obtain a platinum-based slurry B1. Comparative Example 2

[0058] The platinum-based slurry B2 is prepared, specifically comprising the following steps:

[0059] S1, consistent with Example 2;

[0060] S2, consistent with Example 1;

[0061] S3, consistent with Example 2;

[0062] S4. Mix platinum-palladium alloy powder, γ-Al2O3 powder and organic carrier according to the weight ratio in Table 1, homogenize, roll and degas under reduced pressure in the same manner as in Example 1 to obtain platinum-based slurry B2. Comparative Example 3

[0063] The platinum-based slurry B3 is prepared, specifically comprising the following steps:

[0064] S1, consistent with Example 2;

[0065] S2, consistent with Example 1;

[0066] S3, consistent with Example 2;

[0067] S4. Mix platinum-palladium alloy powder, iridium acetylacetonate, α-Al2O3 powder and organic carrier according to the weight proportions in Table 1, and homogenize, roll-press and degas under reduced pressure in the same manner as in Example 1 to obtain platinum-based slurry B3. Comparative Example 4

[0068] The platinum-based slurry B4 is prepared, specifically comprising the following steps:

[0069] S1, consistent with Example 2;

[0070] S2, consistent with Example 1;

[0071] S3, consistent with Example 2;

[0072] S4. Mix platinum-palladium alloy powder, α-Al2O3 powder and organic carrier according to the weight ratio in Table 1, homogenize, roll and degas under reduced pressure in the same manner as in Example 1 to obtain platinum-based slurry B4.

[0073] Table 1 Comparison of parameter settings of examples and comparative examples

[0074]

[0075] The performance tests were performed on the slurries of Examples 1 to 5 and Comparative Examples 1 to 4:

[0076] Preparation of heating electrodes: The slurries prepared in Examples 1 to 5 and Comparative Examples 1 to 4 were respectively printed on an alumina green tape substrate to form a pattern of lines with a length of 10 cm and a width of 0.1 cm, and then sintered at a gradient temperature: 300°C for 15 min, 400°C for 20 min, 1000°C for 30 min, and 1450°C for 2 h.

[0077] Evaluation of sintering density and matching degree with alumina substrate: For sintering density, the progress of scanning electron microscope (SEM) photographs of the electrode layer was observed, and a score of 1-10 was given according to the observed porosity and flatness results. Please refer to Table 2 for the evaluation results; for matching degree with alumina substrate, the present invention was evaluated by the maximum warpage after co-firing. Please refer to Table 2 for the evaluation results.

[0078] TCR (Temperature Coefficient of Resistance) Testing and Calculation: The resistance of electrodes printed with the pastes prepared in Examples 1-5 and Comparative Examples 1-4 was measured using an ohmmeter at 25°C and 125°C, and the TCR was recorded and calculated. The results are shown in Table 2.

[0079] Withstand voltage test: This test uses a multiple of input voltage / rated voltage to evaluate the maximum applied voltage the platinum heating circuit can withstand within 5 seconds under the same conditions. See Table 2 for the comparison results.

[0080] Table 2 Comparison of heating electrode performance parameters

[0081]

[0082] Example Analysis

[0083] In terms of density and matching degree with alumina substrate: As can be seen from Table 1 and Table 2, Examples 1-5 all added thermally decomposable metal organic compounds (iridium acetylacetonate or palladium acetylacetonate) and γ-Al2O3. In the early stage of sintering, the metal organic compound decomposes to produce metal element particles, which promotes the initial densification of the electrode layer; when the temperature rises to a high temperature, the γ-Al2O3 crystal phase transformation produces volume shrinkage, which is adjusted to match the shrinkage rate of the alumina green ceramic film. In addition, the high specific area has a fluxing effect on the metal particles, reducing the penetration of metal element particles into the ceramic substrate. In conjunction with the early alloying process, the sintering density of the embodiments reaches about 9.0 points, which is higher than the 8.0 points of the comparative example, thereby improving the overall density of the electrode. Please refer to Figure 2 As shown in the SEM image of the heating electrode made from slurry A2 in Example 2, no pores were observed, and the surface flatness was high and the density was the best. Figure 1 This is an SEM image of a heater electrode made from slurry B4 in Comparative Example 4. The electrode exhibits high porosity, a rough surface, and some discrete particles. Regarding compatibility with the alumina substrate, the maximum warpage of Examples 1-5 ranges from 0.11% to 0.15%, demonstrating that the slurry has good compatibility with the alumina substrate due to the combination of the alloyed primary and auxiliary conductive phases and the sintering aid.

[0084] In terms of TCR: Using platinum-palladium alloy powder as the primary conductive phase, the electrode TCR is effectively reduced by setting different platinum-palladium molar ratios. For example, the TCR of Examples 1-5 ranges from 1520-1723 ppm / °C, significantly lower than the 2210 ppm / °C of Comparative Example 1 and the 2285 ppm / °C of Comparative Example 2. In Example 2, a palladium-platinum molar ratio of 1:3 results in a higher degree of electron delocalization, a more regular lattice structure, and the lowest TCR. This optimizes conductivity throughout the entire process, from slurry formation to final use, stabilizes circuit control, and meets the needs of equipment with high circuit stability requirements.

[0085] In terms of voltage resistance, the input voltage / rated voltage ratio for Examples 1-5 ranged from 1.8 to 2.2, with Example 2 being the best. During the preparation process for Examples 1-5, a uniform platinum-palladium alloy powder was formed by co-precipitating platinum-palladium composite powder in conjunction with an inert gas heat treatment process. This prevented oxidation of the palladium metal and resulted in dense sintering and interconnection of the platinum particles. Simultaneously, the metal element produced by the decomposition of the metal organic compound partially alloyed with the platinum-palladium alloy, changing the conductive phase properties at the particle interface and reducing the TCR at the interface. When energized and heated, the resistance at the interface increased slowly, and the local voltage increase rate was lower than the circuit average, alleviating the voltage shortcoming at the interface of the conductive layer particles.

[0086] Comparative analysis

[0087] Comparative Example 1: Compared with Example 1, the molar ratio of platinum to palladium in the main conductive phase is the same, the auxiliary conductive phase and other components are the same, but Comparative Example 1 directly uses a mixture of platinum powder and palladium powder without alloying treatment, forming an inhomogeneous phase structure, which interferes with electron conduction. The room temperature resistance reaches 26.8Ω, the TCR is 2210ppm / ℃, and the sintering density and matching degree with the alumina substrate are both lower than those in Example 1; however, compared with pure platinum slurry, the TCR of Comparative Example 1 is significantly reduced.

[0088] Comparative Example 2: The proportion of the main conductive phase is the same as that of Example 2, but there is no auxiliary conductive phase, resulting in its performance in terms of resistance, TCR, sintering density and matching with the alumina substrate being inferior to that of Example 2, indicating that the auxiliary conductive phase plays an important role in optimizing electrode performance.

[0089] Comparative Example 3: Compared with Example 2, the sintering aid lacks γ-Al2O3. The resistance, TCR, and other properties of Comparative Example 3 are inferior to those of Example 2, indicating that γ-Al2O3 is superior to α-Al2O3 in improving electrode performance (such as density and compatibility with the alumina substrate).

[0090] Comparative Example 4: There is no auxiliary conductive phase and the sintering aid lacks γ-Al2O3. Its performance parameters such as resistance (34.1Ω), TCR (2151ppm / ℃), sintering density (7.5 points), matching degree with alumina substrate (0.28%) and voltage resistance are all poor, further illustrating the importance of the synergistic effect of multiple components in the present invention on improving electrode performance.

[0091] The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. The understanding of this specification should be based on those skilled in the art. Although this specification has described the present invention in detail with reference to the above embodiments, those skilled in the art should understand that those skilled in the art can still modify or make equivalent substitutions to the present invention, and all technical solutions and improvements thereof that do not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A platinum-based alloy slurry for alumina co-firing, characterized by: Contains the following components in parts by weight: a) 65%-80% of a main conductive phase, wherein the main conductive phase is a monodisperse spherical platinum-palladium alloy powder, and the particle size of the platinum-palladium alloy powder is in the range of 200-300 nm; b) 1%-5% of an auxiliary conductive phase, wherein the auxiliary conductive phase is a metal organic compound; c) 0.5%-1% sintering aid, wherein the sintering aid is γ-Al2O3 powder or a mixed powder of γ-Al2O3 and α-Al2O3; d) 15%-30% organic carrier.

2. The platinum-based alloy slurry for alumina co-firing according to claim 1, wherein: The platinum-palladium alloy powder is prepared by the following method: S1. Obtaining a platinum-palladium composite powder by a coprecipitation method: dissolving chloroplatinic acid and chloropalladic acid in a solvent to form a mixed solution, adding the mixed solution to an excess reducing agent solution at a temperature of 50-80° C., stirring until the reaction is complete, washing, and drying to obtain a platinum-palladium composite powder, wherein the platinum-palladium composite powder comprises platinum elemental powder and palladium elemental powder; S2. Heat-treating the platinum-palladium composite powder under a protective atmosphere to obtain platinum-palladium alloy powder: the protective atmosphere is nitrogen or argon, the heat treatment temperature is 400-600° C., and the heat treatment time is 1-3 hours.

3. The platinum-based alloy slurry for alumina co-firing according to claim 2, wherein: In step S1, the particle size of the platinum-palladium composite powder is in the range of 20-50 nm, and the molar ratio of palladium to platinum in the platinum-palladium composite powder is in the range of 1:3-1:

5.

4. The platinum-based alloy slurry for alumina co-firing according to claim 2, wherein: In step S1, in the mixed solution, the molar concentration of chloroplatinic acid is 3-5 times the molar concentration of chloropalladic acid, the reducing agent is hydrazine hydrate, and the molar concentration of the reducing agent solution is 5-10 times the total molar concentration of chloroplatinic acid and chloropalladic acid.

5. The platinum-based alloy slurry for alumina co-firing according to claim 1, wherein: The particle size of γ-Al2O3 ranges from 3-20 nm and the specific surface area is 50–300 m² / g.

6. The platinum-based alloy slurry for alumina co-firing according to claim 1, wherein: The added weight of α-Al2O3 is 0-10% of the added weight of γ-Al2O3, and the particle size range of α-Al2O3 is 3-20nm.

7. The platinum-based alloy slurry for alumina co-firing according to claim 1, wherein: The organic vehicle includes one or more of ethyl cellulose, acrylic resin, polycarbonate, epoxy resin, polyurethane resin, maleic anhydride resin, polystyrene, polyvinyl butyral or poly-α-methylstyrene resin, and a solvent.

8. The platinum-based alloy slurry for alumina co-firing according to claim 7, wherein: The solvent is one or more of diethylene glycol butyl ether, diethylene glycol butyl ether acetate, diethylene glycol ethyl ether acetate terpineol, turpentine, butyl carbitol, and dibutyl phthalate.

9. The platinum-based alloy slurry for alumina co-firing according to claim 1, wherein: The metal element in the metal organic compound is palladium or iridium, and the metal organic compound can be decomposed into a metal element at a temperature of 300-500°C.

10. An alumina co-fired heating electrode, characterized in that: The green porcelain tape is prepared by sintering the platinum-based alloy slurry for co-firing alumina according to any one of claims 1 to 9 on a green porcelain tape, and the sintering temperature and time are set to: heating to 300°C and maintaining for 10-20 minutes, 300-500°C and maintaining for 20-30 minutes, 950-1050°C and maintaining for 20-30 minutes, and 1300-1500°C and maintaining for 1-2 hours; the green porcelain tape is an alumina green porcelain tape or a green porcelain tape with an alumina system slurry printed on its surface.

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