Bonding slurry for sensor and preparation method thereof

Abstract

The invention discloses bonding slurry for a sensor and a preparation method of the bonding slurry, and relates to the field of electronic inorganic slurry and preparation methods of the electronic inorganic slurry, the bonding slurry comprises pretreatment powder and an organic carrier, the pretreatment powder comprises zirconium oxide and an inorganic additive, and the inorganic additive comprises alpha aluminum oxide, alpha aluminum oxide and alpha aluminum oxide. The organic carrier comprises a solvent and a binder. The thermal expansion coefficient of the slurry is changed by adding the alpha aluminum oxide into the pretreated powder, and the bonding slurry is set to be the mixture of the pretreated powder and the organic carrier, so that the thermal expansion coefficient of the bonding slurry is adjusted, and the thermal expansion coefficient of the bonding slurry is better matched with the thermal expansion coefficient of other parts such as a casting substrate; the purposes of reducing thermal stress generated by temperature change and reducing the risk of cracking and layering of the sensor are achieved.

Description

Technical Field

[0001] The present invention relates to the field of electronic inorganic slurry and a preparation method thereof, and in particular to a bonding slurry for a sensor and a preparation method thereof. Background Art

[0002] Nitrogen oxide sensors are core components of automotive exhaust emission control systems. Based on the ionic conductivity of ceramic materials, they detect the potential difference generated by different concentrations of nitrogen oxides and provide accurate feedback to the engine control system, thereby achieving effective control of exhaust emissions. Current nitrogen oxide sensors still have shortcomings in manufacturing and use. For example, when the heater pattern area is large, the bonding area between ceramic sheets is relatively small, resulting in insufficient bonding strength. In actual use, the sensor must withstand complex temperature changes, mechanical vibration, and chemical corrosion, which makes the ceramic sheets extremely prone to cracking and delamination, ultimately leading to sensor failure and the inability of the automotive exhaust emission control system to operate normally. For another example, in a multi-layer nitrogen oxide sensor, differences in the thickness of the insulating layer will cause uneven stress distribution during the stacking process, which may lead to stacking failure. In the subsequent sintering process, the stress differences are further amplified, causing the sensor to crack, seriously reducing the yield rate and service life.

[0003] To address these issues, an appropriate amount of bonding slurry is typically applied between ceramic sheets to enhance the bonding strength. Therefore, the development of bonding slurry has become a key breakthrough. However, zirconium oxide, a key component of the bonding slurry, has a significant impact on the stability of the sensor under temperature fluctuations due to its thermal expansion coefficient, making the risk of sensor cracking and delamination still prevalent.

[0004] In view of this, this application is hereby filed. Summary of the Invention

[0005] The purpose of the present invention is to provide a bonding slurry for sensors and a preparation method thereof. By adding α-alumina to the pretreated powder to change the thermal expansion coefficient of the slurry, and setting the bonding slurry as a mixture of the pretreated powder and an organic carrier, the problem that when zirconium oxide is used as an important component of the bonding layer slurry in the prior art, the risk of cracking and delamination of the sensor in a temperature-changing environment is still prevalent.

[0006] The embodiment of the present invention is achieved through the following technical solution: The embodiment of the present invention provides a bonding slurry for a sensor, including a pretreated powder and an organic carrier, the pretreated powder includes zirconium oxide and an inorganic additive, the inorganic additive includes α-alumina, and the organic carrier includes a solvent and a binder.

[0007] Specifically, α-Al2O3 is a stable phase of aluminum oxide, which has high hardness, high density (3.98g / cm 3), low thermal expansion coefficient (about 7.85×10 -6 / ℃) and good dimensional stability, and almost no shrinkage changes will occur under the influence of temperature. In the embodiments of the present invention, by adding inorganic additives, the thermal expansion coefficient of the slurry is adjusted to better match the thermal expansion coefficients of other components such as the cast substrate, which can effectively reduce the thermal stress caused by temperature changes.

[0008] Optionally, the zirconium oxide is yttrium-stabilized zirconia (8YSZ), the mass percentage of the yttrium-stabilized zirconia (8YSZ) in the slurry is 64-75%, the mass percentage of the inorganic additive in the slurry is 1-5%, and the rest is an organic carrier.

[0009] Specifically, the hardness of zirconia is close to that of diamond, and it has excellent wear resistance. At the same time, its thermal expansion coefficient is low, about 10×10 -6 / K, which makes it have better dimensional stability in high temperature environment, and can further reduce the volume change caused by phase change, thereby improving the dimensional stability and mechanical properties of the material, inhibiting the crack expansion of zirconia, and thus improving the fracture toughness of the material. At the same time, yttrium oxide can reduce the sintering temperature of zirconia, promote densification, and reduce grain growth during the sintering process, thereby improving the uniformity and strength of the material.

[0010] Optionally, the organic vehicle further comprises a dispersant, a defoaming agent, a thixotropic agent and a leveling agent.

[0011] Specifically, the primary function of a dispersant is to prevent powder particles (such as zirconium oxide and yttrium oxide) from agglomerating in a slurry. Powder particles in liquids often aggregate together due to van der Waals forces and electrostatic attraction, forming large clusters. Dispersants adsorb onto the particle surface, forming a charge or steric barrier that prevents contact between particles.

[0012] During the preparation and processing of slurry, stirring and mixing operations can easily introduce air and form bubbles. Defoamers reduce the surface tension of bubbles, causing them to burst, thereby reducing the generation of foam.

[0013] The thixotropic agent can make the slurry have a higher viscosity when it is still, and the viscosity decreases rapidly under the action of shear force. In the embodiment of the present invention, it can reduce deformation and defects in the molding process, improve the precision and quality of the product, and prevent the slurry from stratification or precipitation during storage and transportation.

[0014] Leveling agents reduce the surface tension of the slurry surface, promote the formation of a uniform surface during the molding process, reduce the unevenness of the surface tension, and prevent defects such as orange peel and ripples on the coating or molding surface.

[0015] Optionally, the binder accounts for 5-15% of the slurry mass, the solvent accounts for 5-15% of the slurry mass, the dispersant accounts for 0.5-2% of the slurry mass, the defoamer accounts for 0.5-2% of the slurry mass, the leveling agent accounts for 0.5-2% of the slurry mass, and the thixotropic agent accounts for 0.1-1% of the slurry mass.

[0016] Optionally, the binder includes at least one of polyacrylic acid resin, ethyl cellulose, polyvinyl butyral, and dibutyl phthalate; The solvent includes at least one of terpineol, turpentine, butyl carbitol, and acetate.

[0017] Optionally, the dispersant includes at least one of polycarboxylic acids, phosphates, alkyls, and silane coupling agents; illustratively, it may be at least one of CTAB, KD9, SDS, PVP, and triethanolamine; The defoaming agent includes at least one of silicone and polyether; for example, it can be at least one of GPE, BYK, and dimethyl silicone oil; The leveling agent includes at least one of silicone, acrylate, and polysiloxane; The thixotropic agent includes at least one of hydrogenated castor oil, modified urea solution, and polyamide wax.

[0018] Optionally, the particle size of the pretreated powder is less than or equal to 2.5 μm, and the concentration range of D50 is 0.4 μm to 1.2 μm.

[0019] In order to better solve the above problems, an embodiment of the present invention further provides a method for preparing a bonding slurry for a sensor, comprising the following steps: Powder pretreatment involves mixing zirconia, α-alumina, and / or γ-alumina, followed by sintering, ball milling, and sieving to produce a pretreated powder. Preferably, yttrium-stabilized zirconia (8YSZ) is used for the zirconia. 8YSZ can lower the sintering temperature, promote densification, reduce grain growth during sintering, refine grains, and improve material uniformity and strength. It should be noted that γ-alumina transforms to α-Al2O3 at temperatures between 1050 and 1200°C.

[0020] The pretreated powder and the organic carrier are sequentially mixed, stirred, rolled, and degassed to obtain a bonding slurry; The viscosity of the bonding slurry is 50,000-75,000 mPa•s.

[0021] In an embodiment of the present invention, gamma-alumina, an inorganic additive, is added to yttrium-stabilized zirconia (8YSZ). During a pretreatment process, the gamma-alumina is converted into alpha-alumina. The treated YSZ powder and the alpha-alumina formed by the inorganic additive form a more compact microstructure, allowing the alpha-alumina to adjust the thermal expansion coefficient of the yttrium-stabilized zirconia (8YSZ). α-alumina has a stable phase structure and a relatively stable effect on the thermal expansion coefficient of yttrium-stabilized zirconia (8YSZ). The regularly shaped α-alumina is more evenly distributed within the 8YSZ matrix, forming a tighter interface. This allows the α-alumina to more effectively influence the thermal expansion behavior of the 8YSZ, thereby adjusting the sintering shrinkage matching between the bonding layer and the tape-cast sheet.

[0022] Optionally, the sintering temperature is 1100-1250° C., and the sintering time is 1.5-2.5 hours.

[0023] Optionally, the ball milling speed is 2200-2500 rpm / min, and the ball milling time is 20-50 h; The mixing and stirring is carried out using a centrifugal mixer with a stirring speed of 2000-2800 rpm / min and a stirring time of 10-30 min.

[0024] Compared with the prior art, the embodiments of the present invention have the following advantages and beneficial effects: 1. In an embodiment of the present invention, α-alumina is added to the pretreated powder to change the thermal expansion coefficient of the slurry, and the bonding slurry is set to be a mixture of the pretreated powder and an organic carrier, so as to adjust the thermal expansion coefficient of the bonding slurry to better match the thermal expansion coefficient of other components such as the cast substrate, thereby reducing the thermal stress caused by temperature changes and reducing the risk of cracking and delamination of the sensor. The α-alumina can be directly added or converted into α-alumina by adding γ-alumina and sintering.

[0025] 2. In this embodiment of the present invention, the inorganic additive gamma-alumina is added to yttrium-stabilized zirconia (8YSZ). During the pretreatment process, the gamma-alumina is converted into alpha-alumina. The treated 8YSZ powder and the alpha-alumina formed by the inorganic additive form a more compact microstructure, which adjusts the thermal expansion coefficient of zirconia. The stable phase structure of alpha-alumina makes its effect on the thermal expansion coefficient of yttrium-stabilized zirconia (8YSZ) relatively stable. The regularly shaped alpha-alumina is more evenly distributed in the yttrium-stabilized zirconia (8YSZ) matrix, forming a closer interface. This allows the alpha-alumina to more effectively influence the thermal expansion behavior of 8YSZ, thereby adjusting the sintering shrinkage matching between the bonding layer and the cast sheet.

[0026] 3. The present invention pre-treats zirconium oxide powder by calcining and ball milling, thereby improving the drawbacks of the original powder's wide particle distribution and irregular particle shape. Calcination enhances the compaction of the original agglomerated particles and irregular particles, while ball milling breaks up the agglomeration of the powder, narrowing the powder distribution area and reducing the particles. This allows for a more uniform dispersion of the powder in the organic carrier, improving the sintering activity of the zirconium oxide, reducing porosity, and thus increasing the mechanical strength of the slurry. Yttrium oxide can also lower the sintering temperature of the zirconium oxide, promoting densification, while reducing grain growth during the sintering process and improving the uniformity and strength of the material.

[0027] 4. This embodiment of the present invention adjusts the ratio of zirconia powder, selecting yttrium-stabilized zirconia (8YSZ) as the preferred raw material, and adjusts the types and ratios of inorganic additives to achieve a smaller particle size and higher sintering activity after pretreatment. The ultrafine powder obtained through pretreatment in this embodiment of the present invention enables more uniform dispersion of the slurry. By optimizing the type and ratio of the organic carrier, a uniform and stable slurry with low viscosity and high solids content can be obtained, effectively solving the delamination and cracking problem that occurs in nitrogen oxide sensors after layered sintering. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 This is a diagram of the bonding slurry prepared in Example 1; Figure 2 This is a sintering morphology of the bonding slurry prepared in Example 1 in sensor application; Figure 3 This is a cracking diagram of the bonding slurry prepared in Comparative Example 1 in sensor application. DETAILED DESCRIPTION

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0031] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are intended to fall within the scope of protection of the present invention.

[0032] It should be noted that similar numbers and letters represent similar items in the following figures, so once an item is defined in one figure, it does not need to be further defined or explained in subsequent figures.

[0033] In the description of the present invention, it should be noted that the terms "first", "second", "third", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0034] Example In the prior art, an appropriate amount of bonding slurry is often applied between ceramic sheets to enhance the bonding strength between the ceramic sheets. However, zirconium oxide, as an important component of the bonding layer slurry, has a thermal expansion coefficient that has a huge impact on the stability of the sensor in a temperature-changing environment. The embodiment of the present invention takes the improvement of the bonding layer slurry as a breakthrough. By adding inorganic additives, the thermal expansion coefficient of the bonding slurry is adjusted to better match the thermal expansion coefficient of other components such as the cast substrate, which can effectively reduce the thermal stress caused by temperature changes and reduce the risk of sensor cracking and delamination. At the same time, by controlling the particle size distribution of zirconium oxide, the physical properties of the bonding layer slurry can be further optimized, its bonding strength and stability can be enhanced, and the problem of insufficient bonding force caused by the large printing area of ​​the heating electrode and the small bonding area can be compensated. Improving the solid content of zirconium oxide improves the stress distribution of the slurry in the multilayer structure, alleviates the stress concentration caused by the difference in the thickness of the insulating layer, and reduces the failure of the laminate and cracking after sintering.

[0035] Specifically, an embodiment of the present invention provides a method for preparing a bonding slurry for a sensor, wherein the bonding slurry includes a pretreated powder and an organic carrier, and the specific preparation method includes the following steps: Step 1: Powder pretreatment: Weigh the powder raw materials by mass percentage, wherein the mass percentage of yttrium-stabilized zirconia (8YSZ) in the slurry is 64-75%, and the mass percentage of inorganic additives in the slurry is 1-5%. The powders are evenly mixed and placed in a sintering furnace for sintering, and then ball milled using a planetary ball mill. The treated ultrafine powder is sieved; Among them, the inorganic additive is one of γ alumina, α alumina or a mixture of the two, which functions to form a tighter interface with the substrate and match the stability of the thermal expansion coefficient change of the substrate. Preferably, γ alumina is alumina, and D50 is concentrated in 0.1μm~1μm; the sintering temperature is 1100~1250℃, and the sintering time is 1.5~2.5h. During the ball milling process, the ball mill speed is set to 2200~2500rpm / min, and the ball milling time is 20~50h. The obtained uniformly dispersed ultrafine powder is preferably calcined at 1200℃ and the ball milling time is 40h; the particle size of the zirconium oxide powder in the ultrafine powder is 0.3μm~2.5μm, and the D50 is preferably concentrated in 0.4μm~1.2μm.

[0036] Step 2: Preparation of organic vehicle: Weigh the binder, dispersant, defoamer, thixotropic agent, leveling agent and solvent by weight, add them to the polytetrafluoroethylene slurry tank, and mix them evenly. The binder accounts for 5-15% of the total weight of the slurry, the dispersant accounts for 0.5-2% of the total weight of the slurry, the defoamer accounts for 0.5-2% of the total weight of the slurry, the thixotropic agent accounts for 0.1-1% of the total weight of the slurry, the leveling agent accounts for 0.5-2% of the total weight of the slurry, and the solvent accounts for 5-15% of the total weight of the slurry; The binder includes at least one of polyacrylic acid resin, ethyl cellulose, polyvinyl butyral, and dibutyl phthalate; specifically, it may be at least one of CTAB, KD9, SDS, PVP, and triethanolamine; The solvent includes at least one of terpineol, turpentine, butyl carbitol, and acetate; The dispersant includes at least one of polycarboxylic acids, phosphates, alkyls, and silane coupling agents; specifically, it may be at least one of KD9, SDS, PVP, and triethanolamine; The defoaming agent includes at least one of silicone and polyether; specifically, it can be at least one of GPE, BYK, and dimethyl silicone oil; The leveling agent includes at least one of silicone, acrylate and polysiloxane; The thixotropic agent includes at least one of hydrogenated castor oil, modified urea solution, and polyamide wax.

[0037] Step 3: Preparation of slurry: Place the prepared pretreated powder and organic carrier into a polytetrafluoroethylene slurry tank, add zirconium balls into the slurry tank and stir at a stirring speed of 2000-2800 rpm / min for 10-30 min; Step 4: Slurry rolling: The mixed and stirred slurry is rolled using a three-roll mill to mix it evenly and obtain a uniformly dispersed adhesive slurry with a viscosity of 50,000 to 75,000 mPa∙s. The slurry is vacuum degassed and stored.

[0038] Example 1: The embodiment of the present invention provides a method for preparing a bonding slurry for a sensor, wherein the bonding slurry includes a pretreated powder and an organic carrier. The specific preparation method includes the following steps: Step 1: Powder pretreatment: Weigh the powder raw materials by mass percentage, where the mass percentage of yttrium-stabilized zirconia powder (8YSZ) in the slurry is 64%, and the mass percentage of inorganic additives in the slurry is 1%. Mix the powders evenly and place them in a sintering furnace for sintering. Then, use a planetary ball mill to mill them and sieve them to obtain the treated ultrafine powder. Among them, the inorganic additive is α-alumina, and D50 is concentrated in 0.1μm~1μm, which serves to form a tighter interface with the substrate and match the stability of the thermal expansion coefficient change of the substrate; the sintering temperature is 1100℃, and the sintering time is 2h. During the ball milling process, the ball mill speed is set to 2200rpm / min, and the ball milling time is 20h. The obtained uniformly dispersed ultrafine powder has a particle size of yttrium-stabilized zirconia powder (8YSZ) of 0.65μm, and D50 is concentrated in 0.4μm~1.2μm.

[0039] Step 2: Preparation of organic carrier: Weigh the binder, dispersant, defoamer, thixotropic agent, leveling agent and solvent according to the mass ratio, add them to the polytetrafluoroethylene slurry tank, and mix them evenly. Among them, the binder polyvinyl butyral accounts for 14.9% of the total weight of the slurry, the dispersant KD9 accounts for 1% of the total weight of the slurry, the defoamer dimethyl silicone oil accounts for 2% of the total weight of the slurry, the thixotropic agent BYK accounts for 0.1% of the total weight of the slurry, the leveling agent polysiloxane accounts for 2% of the total weight of the slurry, and the solvents turpentine and butyl carbitol account for 11% and 4% of the total weight of the slurry respectively; Step 3: Preparation of slurry: Place the prepared pretreated powder and organic carrier into a polytetrafluoroethylene slurry tank, add zirconium balls into the slurry tank and stir at a stirring speed of 2000 rpm / min for 30 min; Step 4: Slurry rolling: The mixed slurry is rolled using a three-roll mill to mix it evenly and obtain a uniformly dispersed adhesive slurry with a viscosity of 58000mPa·s (such as Figure 1 The slurry is vacuum degassed and then stored.

[0040] Example 2: The embodiment of the present invention provides a method for preparing a bonding slurry for a sensor, wherein the bonding slurry includes a pretreated powder and an organic carrier. The specific preparation method includes the following steps: Step 1: Powder pretreatment: Weigh the powder raw materials by mass percentage, where the zirconia powder (8YSZ) accounts for 73% of the mass percentage of the slurry and the inorganic additives account for 2% of the mass percentage of the slurry. Mix the powders evenly and place them in a sintering furnace for sintering. Then, use a planetary ball mill to ball mill and sieve to obtain the treated ultrafine powder. Among them, the inorganic additive is γ-alumina, and D50 is concentrated in 0.1μm~1μm, which serves to form a tighter interface with the substrate and match the stability of the thermal expansion coefficient change of the substrate; the sintering temperature is 1100℃, and the sintering time is 2h. During the ball milling process, the ball mill speed is set to 2200rpm / min, and the ball milling time is 40h. The obtained uniformly dispersed ultrafine powder has a particle size of yttrium-stabilized zirconia powder (8YSZ) of 0.52μm, and D50 is concentrated in 0.4μm~1.2μm.

[0041] Step 2: Preparation of organic carrier: Weigh the binder, dispersant, defoamer, thixotropic agent, leveling agent and solvent by mass, add them to a polytetrafluoroethylene slurry tank, and mix them. The binder dibutyl phthalate accounts for 15% of the total weight of the slurry, the dispersant CTAB accounts for 0.5% of the total weight of the slurry, the defoamer GPE accounts for 0.5% of the total weight of the slurry, the thixotropic agent hydrogenated castor oil accounts for 0.5% of the total weight of the slurry, the leveling agent acrylate accounts for 0.5% of the total weight of the slurry, and the solvent turpentine accounts for 8% of the total weight of the slurry.

[0042] Step 3: Preparation of slurry: Place the prepared pretreated powder and organic carrier into a polytetrafluoroethylene slurry tank, add zirconium balls into the slurry tank and stir at a stirring speed of 2800 rpm / min for 10 min; Step 4: Rolling of the slurry: The mixed and stirred slurry is rolled using a three-roll mill to mix it evenly and obtain a uniformly dispersed bonding slurry with a viscosity of 63450 mPa·s. The slurry is vacuum degassed and then stored.

[0043] Example 3: This embodiment of the present invention provides a method for preparing a bonding slurry for a sensor. The difference from Example 1 is that the mass percentage of zirconium oxide powder (8YSZ) in the slurry is 63%, the inorganic additive is γ-alumina, and the mass percentage of the inorganic additive in the slurry is 2%. The sintering temperature is 1150°C, the ball milling time is 20h, the particle size of the yttrium-stabilized zirconia powder (8YSZ) in the ultrafine powder is 0.88μm, and the viscosity of the bonding slurry is 69080mPa•s. The other steps remain unchanged.

[0044] Example 4: The embodiment of the present invention provides a method for preparing a bonding slurry for a sensor, wherein the bonding slurry includes a pretreated powder and an organic carrier. The specific preparation method includes the following steps: Step 1: Powder pretreatment: Weigh the powder raw materials by mass percentage, wherein the mass percentage of zirconium oxide in the slurry is 67%, and the mass percentage of inorganic additives in the slurry is 3%. The powders are evenly mixed and placed in a sintering furnace for sintering, and then ball milled using a planetary ball mill and sieved to obtain the treated ultrafine powder; Among them, the inorganic additive is γ-alumina, and D50 is concentrated in 0.1μm~1μm, which serves to form a tighter interface bonding with the substrate and match the stability of the thermal expansion coefficient change of the substrate; the sintering temperature is 1150℃, and the sintering time is 2h. During the ball milling process, the ball mill speed is set to 2200rpm / min, and the ball milling time is 40h. The obtained uniformly dispersed ultrafine powder has a particle size of zirconia powder of 0.6μm, and D50 is concentrated in 0.4μm~1.2μm.

[0045] Step 2: Preparation of organic vehicle: Weigh the binder, dispersant, defoamer, thixotropic agent, leveling agent and solvent according to their mass proportions, add them to a polytetrafluoroethylene slurry tank, and mix them evenly. The binder dibutyl phthalate accounts for 10% of the total weight of the slurry, the dispersant CTAB accounts for 2% of the total weight of the slurry, the defoamer GPE accounts for 2% of the total weight of the slurry, the thixotropic agent hydrogenated castor oil accounts for 1% of the total weight of the slurry, the leveling agent acrylate accounts for 2% of the total weight of the slurry, and the solvent turpentine accounts for 13% of the total weight of the slurry; Step 3: Preparation of slurry: Place the prepared pretreated powder and organic carrier into a polytetrafluoroethylene slurry tank, add zirconium balls into the slurry tank and stir at a stirring speed of 2000 rpm / min for 30 min; Step 4: Slurry rolling: The mixed and stirred slurry is rolled using a three-roll mill to mix it evenly and obtain a uniformly dispersed bonding slurry with a viscosity of 56100 mPa·s. The slurry is vacuum degassed and then stored.

[0046] Example 5: The embodiment of the present invention provides a method for preparing a bonding slurry for a sensor. The difference from Example 2 is that the mass percentage of zirconium oxide powder (8YSZ) in the slurry is 70%, the inorganic additive is γ-alumina, and the mass percentage of the inorganic additive in the slurry is 5%. The proportions of the components of the organic solvent change in corresponding proportions as the pretreatment powder changes. The sintering temperature is 1200°C, the ball milling time is 20h, the particle size of the yttrium-stabilized zirconia powder (8YSZ) in the ultrafine powder is 0.95μm, and the viscosity of the bonding slurry is 72390mPa•s. The other steps remain unchanged.

[0047] Example 6: The embodiment of the present invention provides a method for preparing a bonding slurry for a sensor. The difference from Example 2 is that the mass percentage of zirconium oxide powder (8YSZ) in the slurry is 77%, the inorganic additive is γ-alumina, and the mass percentage of the inorganic additive in the slurry is 3%. The proportions of the components of the organic solvent change in corresponding proportions as the pretreatment of the powder changes. The sintering temperature is 1200°C, the ball milling time is 30h, the particle size of the yttrium-stabilized zirconia powder (8YSZ) in the ultrafine powder is 0.61μm, and the viscosity of the bonding slurry is 71400mPa•s. The other steps remain unchanged.

[0048] Example 7: The embodiment of the present invention provides a method for preparing a bonding slurry for a sensor. The difference from Example 2 is that the mass percentage of zirconium oxide powder (8YSZ) in the slurry is 61%, the inorganic additive is γ-alumina, and the mass percentage of the inorganic additive in the slurry is 4%. The proportions of each component of the organic solvent change in corresponding proportions as the pretreatment powder changes. The sintering temperature is 1200°C, the ball milling time is 40h, the particle size of the yttrium-stabilized zirconia powder (8YSZ) in the ultrafine powder is 0.5μm, and the viscosity of the bonding slurry is 50380mPa•s. The other steps remain unchanged.

[0049] Example 8: The embodiment of the present invention provides a method for preparing a bonding slurry for a sensor. The difference from Example 2 is that the mass percentage of zirconium oxide powder (8YSZ) in the slurry is 79%, the inorganic additive is γ-alumina, and the mass percentage of the inorganic additive in the slurry is 1%. The proportions of the components of the organic solvent change in corresponding proportions as the pretreatment powder changes. The sintering temperature is 1200°C, the ball milling time is 50h, the particle size of the yttrium-stabilized zirconia powder (8YSZ) in the ultrafine powder is 0.32μm, and the viscosity of the bonding slurry is 62090mPa•s. The other steps remain unchanged.

[0050] Example 9: The embodiment of the present invention provides a method for preparing a bonding slurry for a sensor. The difference from Example 2 is that the mass percentage of zirconium oxide powder (8YSZ) in the slurry is 75%, the inorganic additive is γ-alumina, and the mass percentage of the inorganic additive in the slurry is 5%. The proportions of each component of the organic solvent change in corresponding proportions with the changes in the pretreated powder. The sintering temperature is 1250°C, the ball milling time is 30h, the particle size of the yttrium-stabilized zirconia powder (8YSZ) in the ultrafine powder is 0.87μm, and the viscosity of the bonding slurry is 74600mPa•s. The other steps remain unchanged.

[0051] Example 10: The embodiment of the present invention provides a method for preparing a bonding slurry for a sensor. The difference from Example 2 is that the mass percentage of zirconium oxide powder (8YSZ) in the slurry is 72%, the inorganic additive is γ-alumina, and the mass percentage of the inorganic additive in the slurry is 3%. The proportions of the components of the organic solvent change in corresponding proportions as the pretreatment of the powder changes. The sintering temperature is 1250°C, the ball milling time is 40h, the particle size of the yttrium-stabilized zirconia powder (8YSZ) in the ultrafine powder is 0.57μm, and the viscosity of the bonding slurry is 64000mPa•s. The other steps remain unchanged.

[0052] Example 11: The embodiment of the present invention provides a method for preparing a bonding slurry for a sensor. The difference from Example 2 is that the mass percentage of zirconium oxide powder (8YSZ) in the slurry is 62%, the inorganic additive is γ-alumina, and the mass percentage of the inorganic additive in the slurry is 3%. The proportions of each component of the organic solvent change in corresponding proportions as the pretreatment powder changes. The sintering temperature is 1250°C, the ball milling time is 50h, the particle size of the yttrium-stabilized zirconia powder (8YSZ) in the ultrafine powder is 0.41μm, and the viscosity of the bonding slurry is 52400mPa•s. The other steps remain unchanged.

[0053] Comparative Example 1: A method for preparing a bonding slurry is provided. The difference from Example 2 is that the mass percentage of zirconium oxide powder (8YSZ) in the slurry is 83%, the inorganic additive is γ-alumina, and the mass percentage of the inorganic additive in the slurry is 2%. The proportions of each component of the organic solvent change in corresponding proportions as the pretreated powder changes. The powder is not sintered during pretreatment, the particle size of the yttrium-stabilized zirconia powder (8YSZ) in the powder is 1.35 μm, and the viscosity of the bonding slurry is 95,800 Pa•s. The other steps remain unchanged.

[0054] Comparative Example 2: A method for preparing a bonding slurry is provided. The difference from Example 2 is that the mass percentage of zirconia powder (8YSZ) in the slurry is 58%, the inorganic additive is γ-alumina, and the mass percentage of the inorganic additive in the slurry is 7%. The proportions of each component of the organic solvent change in corresponding proportions with the changes in the pretreated powder. The sintering temperature is 1100°C, the ball milling time is 20h, the particle size of the yttrium-stabilized zirconia powder (8YSZ) in the ultrafine powder is 0.68μm, and the viscosity of the bonding slurry is 67800mPa•s. The other steps remain unchanged.

[0055] Comparative Example 3: A method for preparing a bonding slurry is provided. The difference from Example 2 is that the mass percentage of zirconia powder (8YSZ) in the slurry is 65%, the inorganic additive is γ-alumina, and the mass percentage of the inorganic additive in the slurry is 5%. The proportions of each component of the organic solvent change in corresponding proportions with the changes in the pretreated powder. The sintering temperature is 1300°C, the ball milling time is 20h, the particle size of the yttrium-stabilized zirconia powder (8YSZ) in the ultrafine powder is 0.89μm, and the viscosity of the bonding slurry is 107900mPa•s. The other steps remain unchanged.

[0056] Comparative Example 4: A method for preparing a bonding slurry is provided. The difference from Example 2 is that the mass percentage of zirconia powder (8YSZ) in the slurry is 81%, the inorganic additive is γ-alumina, and the mass percentage of the inorganic additive in the slurry is 4%. The proportions of each component of the organic solvent change in corresponding proportions with the changes in the pretreated powder. The sintering temperature is 1200°C, the ball milling time is 40h, the particle size of the yttrium-stabilized zirconia powder (8YSZ) in the ultrafine powder is 0.5μm, and the viscosity of the bonding slurry is 110800mPa•s. The other steps remain unchanged.

[0057] Comparative Example 5: A method for preparing a bonding slurry is provided. The difference from Example 2 is that the mass percentage of zirconia powder (8YSZ) in the slurry is 75%, no inorganic additives are added, and no pretreatment is performed. The particle size of the yttrium-stabilized zirconia powder (8YSZ) in the ultrafine powder is 1.29 μm, and the viscosity of the bonding slurry is 87,000 mPa•s. The other steps remain unchanged.

[0058] It should be noted that the viscosity test of the bonding paste refers to the national standard GB / T17473.5-2008 "Test method for viscosity determination of precious metal pastes for microelectronics technology".

[0059] The adhesive pastes prepared in Examples 1 to 11 and Comparative Examples 1 to 5 were respectively printed on a cast sheet using a 300-mesh nylon mesh or a stainless steel mesh by screen printing. The printed cast sheet was allowed to stand for 8 minutes and then baked in an oven at 85° C. for 30 minutes to obtain a laminated sensor. Figure 3 This is a cracking diagram of the bonding slurry prepared in Comparative Example 1 in sensor application. Figure 2 This is the sintering morphology of the bonding paste prepared in Example 1 in sensor application. Figure 2 and Figure 3 By comparison, it can be seen that applying the bonding slurry prepared in the embodiment of the present invention to the sensor can effectively solve the delamination and cracking problem of the nitrogen and oxygen sensor after stacking and sintering.

[0060] The bonding slurries prepared in Examples 1 to 11 and Comparative Examples 1 to 5 were tested for leveling, film forming properties, and adhesion. The test results are shown in Table 1 below.

[0061] The leveling test method is: under constant temperature and humidity conditions, use a scraper or applicator to apply the slurry to a transparent substrate (such as PET film), and observe the surface at an angle under a light source to see if it is even and whether there are defects such as orange peel or ripples. The following criteria are used for judgment: A: Completely leveled, smooth surface, without any defects (such as orange peel, brush marks, pits); B: Slight orange peel or ripples, visible only at certain angles; C: Obvious orange peel or ripples, but does not affect functionality; D: Severe orange peel, brush marks or local unevenness affecting the appearance.

[0062] Film-forming property test method: For the nitrogen and oxygen sensor bonding layer slurry obtained in the example, the film-forming property was visually confirmed. The slurry was evenly coated on the cast substrate and allowed to stand for 5-10 minutes. The slurry was then placed under a microscope and the number of bubbles per unit area was counted. The judgment level was as follows: A: The number of bubbles per unit area is less than 5; B: The number of bubbles per unit area is greater than 5 and less than 20; C: The number of bubbles per unit area is greater than 20 and less than 50; D: The number of bubbles per unit area is greater than 50.

[0063] The test method for adhesion refers to the national standard GB / T9286-1998 "Scratch test for paint and varnish films".

[0064] Table 1

[0065] Referencing Table 1, Examples 1-3 demonstrate that using zirconia as the primary powder material, pre-treating the zirconia powder with inorganic additives, and then mixing it with an organic vehicle facilitates the preparation of a bonding layer slurry with excellent leveling, adhesion, and film-forming properties. This slurry, in particular, enhances the bond strength between YSZ cast sheets and provides excellent sintering compatibility with other materials in oxygen and nitrogen sensors. Due to the high bond strength and shrinkage-matching properties of the bonding layer prepared using this slurry, its application in oxygen and nitrogen sensors can improve their airtightness and mechanical properties.

[0066] Comparison of Examples 1-11 with Comparative Example 3 shows that within the pretreatment temperature range of 1100-1250°C, all Examples exhibit excellent leveling (A) and film-forming properties (A), with most achieving adhesion leveling of Grade 1 (optimal). However, increasing the temperature to 1300°C for Comparative Example 3 resulted in excessive grain coarsening, decreased leveling (B) and film-forming properties (B), and poorer adhesion (Grade 4) compared to the Examples. Therefore, the calcination temperature should be between 1100°C and 1250°C.

[0067] From the comparison of Examples 1 to 3 with Comparative Example 1, it can be seen that when the powder is not pretreated, the leveling and film-forming properties of the slurry are reduced, and the adhesion of the slurry on the substrate is poor and the bonding force is not strong, resulting in cracking of the chip ( Figure 3 ), alumina is added to YSZ and pre-calcined. This promotes chemical bonding between the two phases through a high-temperature solid-phase reaction, optimizing thermal expansion coefficient matching and reducing interfacial stress during thermal cycling. This also strengthens interphase adhesion, inhibits abnormal YSZ grain growth, and enhances densification and sintering stability. Calcination also improves high-temperature phase stability, reduces the risk of monoclinic phase transitions, and enhances the material's mechanical strength and thermal shock resistance. In contrast, simple mixing without calcination can lead to thermal expansion coefficient mismatch, interfacial defects, and uneven performance, resulting in weak bonding after printing.

[0068] Comparison of Example 5 and Example 8 with Example 4 shows that increasing the ultrafine zirconium oxide powder content to 85% reduces the slurry's leveling and film-forming properties, and its adhesion deteriorates. Increasing the solids content also reduces the slurry's fluidity, making it difficult to apply during screen printing.

[0069] By comparing Examples 1 to 11 and Comparative Example 2, it can be seen that when the content of γ-alumina is 1% to 5%, the slurry is well bonded to the substrate, and has excellent leveling and film-forming properties. Excessive inorganic additive γ-alumina may cause a mismatch in the thermal expansion coefficient with the substrate, interface degradation, and the like, which may prevent better bonding with the YSZ substrate.

[0070] A comparison of Examples 1, 3, and 7 shows that both α-alumina and / or γ-alumina can adjust the thermal expansion coefficient of the bonding slurry to better match that of other components, such as the tape-cast substrate. This effectively reduces thermal stress caused by temperature changes and lowers the risk of sensor cracking and delamination. γ-alumina is preferred.

[0071] By comparing Example 5 and Comparative Example 5, it is found that the original YSZ grains are larger than 1 μm, and the leveling and film-forming properties of the slurry are reduced. Analysis shows that the particle size of the original powder grains is relatively dispersed, and the large particle size makes it impossible to obtain a slurry with high solid content and low viscosity, which is not conducive to screen printing.

[0072] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, improvements, and the like made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention. It should be noted that the structures or components illustrated in the accompanying drawings are not necessarily drawn to scale, and that descriptions of known components, processing techniques, and processes are omitted to avoid unnecessarily limiting the present invention.

Claims

1. A bonding slurry for a sensor, characterized in that: The invention comprises a pre-treated powder and an organic carrier. The pre-treated powder comprises zirconium oxide and an inorganic additive. The inorganic additive comprises alpha alumina. The organic carrier comprises a solvent and a binder.

2. The bonding slurry for a sensor according to claim 1, characterized in that: The zirconium oxide is yttrium-stabilized zirconia, and the mass percentage of the yttrium-stabilized zirconia in the slurry is 64-75%. The mass percentage of the inorganic additive in the slurry is 1-5%, and the rest is organic carrier.

3. The bonding slurry for a sensor according to claim 2, characterized in that: The organic carrier further comprises a dispersant, a defoaming agent, a thixotropic agent and a leveling agent.

4. The bonding slurry for a sensor according to claim 3, characterized in that: The binder accounts for 5-15% of the slurry mass, the solvent accounts for 5-15% of the slurry mass, the dispersant accounts for 0.5-2% of the slurry mass, the defoamer accounts for 0.5-2% of the slurry mass, the leveling agent accounts for 0.5-2% of the slurry mass, and the thixotropic agent accounts for 0.1-1% of the slurry mass.

5. The bonding slurry for a sensor according to claim 1, characterized in that: The binder includes at least one of polyacrylic acid resin, ethyl cellulose, polyvinyl butyral, and dibutyl phthalate; The solvent includes at least one of terpineol, turpentine, butyl carbitol, and acetate.

6. The bonding slurry for a sensor according to claim 3, characterized in that: The dispersant includes at least one of polycarboxylic acids, phosphates, alkyls, and silane coupling agents; The defoaming agent includes at least one of silicone and polyether; The leveling agent includes silicone; The thixotropic agent includes at least one of hydrogenated castor oil, modified urea solution, and polyamide wax.

7. The bonding slurry for a sensor according to claim 1, characterized in that: The particle size of the pretreated powder is less than or equal to 2.5 μm, and the concentration range of D50 is 0.4 μm to 1.2 μm.

8. A method for preparing a bonding slurry for a sensor according to any one of claims 1 to 7, characterized in that: The following steps are involved: Powder pretreatment, including mixing zirconium oxide, alpha alumina and / or gamma alumina and then sequentially sintering, ball milling, and sieving to obtain pretreated powder; The pretreated powder and the organic carrier are sequentially mixed, stirred, rolled, and degassed to obtain a bonding slurry; The viscosity of the bonding slurry is 50,000-75,000 mPa•s.

9. The method for preparing a bonding slurry for a sensor according to claim 8, characterized in that: The sintering temperature is 1100-1250° C., and the sintering time is 1.5-2.5 hours.

10. The method for preparing a bonding slurry for a sensor according to claim 8, characterized in that: The ball milling speed is 2200-2500 rpm / min, and the ball milling time is 20-50 h; The mixing and stirring is carried out using a centrifugal mixer with a stirring speed of 2000-2800 rpm / min and a stirring time of 10-30 min.

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