Zirconium oxide-based gas sensor electrode wire slurry and preparation method thereof

Abstract

The invention discloses zirconium oxide-based gas sensor electrode wire slurry and a preparation method thereof, and relates to the technical field of electrode wire slurry, the zirconium oxide-based gas sensor electrode wire slurry comprises the following components by weight: 60-90 wt% of platinum powder, 0.1-2 wt% of alumina powder, 2-20 wt% of YSZ powder, and the balance of an organic carrier. According to the electrode wire slurry, the YSZ powder is added into the electrode wire slurry, so that more compact contact can be formed between a wire and a ceramic substrate, and gaps and defects at an interface are reduced, so that a sensor has excellent performances of accurate and stable signal transmission and short starting time.

Description

Technical Field

[0001] The invention relates to the technical field of electrode wire slurry, and in particular to a zirconium oxide-based gas sensor electrode wire slurry and a preparation method thereof. Background Art

[0002] In traditional gas detection technology, there is a core element of a gas sensor for motor vehicle exhaust analysis. For example, the patent document with publication number CN111024796B discloses a gas sensor, which uses a matrix structure constructed of a multi-layer oxygen ion conductor solid electrolyte, and integrates a multi-stage gas processing chamber inside. The technical features are specifically manifested as follows: the three-stage processing chamber is sequentially arranged in the stacked electrolyte matrix, and the inner wall of each chamber is respectively configured with a main pump unit, an auxiliary pump unit and a detection unit (hereinafter collectively referred to as an inner electrode), and the wires connected to each inner electrode are encapsulated between the upper and lower electrolyte layers. The main pump unit reduces the oxygen concentration of the measured gas to the ppm level that does not affect NOx detection through the action of an electrochemical oxygen pump, and the auxiliary pump chamber reduces the oxygen concentration of the measured gas to the ppb level, while achieving complete conversion of NOx compounds to NO molecules. The detection electrode containing Pt / Rh catalytic alloy promotes the dissociation of NO into N2 and O2, and the external electrode is connected through a wire to form an oxygen pump circuit, outputs the limiting current generated by the dissociated oxygen, and establishes a linear correspondence between the current signal and the NOx concentration to achieve accurate detection.

[0003] When the heating system of the component is activated, the system needs to go through a specific response cycle to achieve the calibrated detection accuracy. This period of time is called the start-up time (i.e., light-off time). This stage mainly involves: clearing the interfering oxygen components remaining in the non-target gas in the detection chamber. Specifically, this time parameter is defined as the time required from power-on to the time when the background oxygen concentration in the detection chamber drops to the detection threshold, and its duration is negatively correlated with the system preheating performance.

[0004] After the sensor chip is manufactured, it is necessary to test the chip to determine whether the sensor startup time is within the required range (<90s). However, during the test, it was found that there were chips whose startup time was far beyond the usage range. This phenomenon can be easily attributed to the insufficient oxygen pumping capacity of the inner electrode. Even by improving the oxygen pumping activity of the inner electrode, the startup time cannot be effectively reduced. Moreover, by accelerating the temperature rise rate, intervening in pump control in advance and other electronic control measures, the startup speed cannot be significantly accelerated. Summary of the invention

[0005] After careful research by the inventor, it was found that the above measures still cannot effectively solve the main reason for the extended startup time of the gas sensor: the electrode wire slurry in the gas sensor is generally composed of platinum (Pt) and insulating material alumina. During the sintering process, due to the volatilization of organic components and the difference between the thermal expansion coefficients of platinum and alumina and the ceramic matrix, gaps are generated between the electrode wire part inside the ceramic chip and the ceramic matrix. These gaps are equivalent to additional internal cavities, which causes the sensor element to spend more time to pump out the remaining oxygen in the gaps when starting. Moreover, since the gaps extend a certain length in the ceramic matrix, it is particularly difficult to extract the oxygen in the gaps. Therefore, it manifests as an abnormal increase in the startup time.

[0006] Based on the problem that after sintering, a cavity is formed between the electrode wire and the electrolyte layer due to the mismatch in sintering shrinkage between the materials, the current sensor electrode wire and the upper and lower ceramic substrates are sintered. The present invention provides a zirconium oxide-based gas sensor electrode wire slurry and a preparation method thereof, so that the bonding force between the electrode wire and the substrate formed after co-firing is strong and the electrode performance is stable, thereby making the startup time of the nitrogen oxygen sensor fast.

[0007] The present invention is achieved through the following technical solutions: In a first aspect, the present invention provides a zirconium oxide-based gas sensor electrode wire slurry, which comprises the following components by weight percentage: 60wt%~90wt% of platinum powder, 0.1wt%~2wt% of alumina powder, 2wt%~20wt% of YSZ powder, and the balance is an organic carrier.

[0008] The present invention adds YSZ powder to the electrode wire slurry. On the one hand, the YSZ powder has good oxygen ion conductivity at high temperature, is highly sensitive to changes in oxygen content in the sensor tail gas, and can partially replace the amount of precious metals, thereby reducing costs. On the other hand, the added YSZ powder has excellent thermal shock resistance and a large thermal expansion coefficient, which adjusts the shrinkage matching consistency between the electrode slurry and the substrate, avoiding the problems of fracture, microcracks, cavities, etc. caused by inconsistent shrinkage between the electrode wire and the substrate and the wire in an environment with rapid temperature changes. In addition, the amount of YSZ powder added in the present invention is controlled, which can not only meet the requirement of no gaps after sintering, thereby reducing the startup time of the nitrogen oxygen sensor, but also prevent the resistance of the wire from being too large, thereby affecting the VP0 value of the pump electrode, thereby obtaining a ceramic chip with excellent performance.

[0009] The electrode wire prepared by the electrode wire slurry of the present invention is of high quality, which helps to ensure the stability of the operation of the nitrogen oxide sensor. Through its good conductivity and stability, the interference and loss in the signal transmission process can be reduced. The electrode wire slurry of the present invention has a high and dense bonding strength with the ceramic substrate, which can effectively avoid the formation of cavities around the wire, thereby shortening the startup time of the nitrogen oxide sensor and effectively controlling exhaust emissions.

[0010] The inner electrode requires abundant pores to produce enough three-phase interfaces for electrode reaction, and the inner electrode wire portion preferably has a dense structure with extremely low porosity. Therefore, the screen-printed pattern is preferably a scheme in which the inner electrode and the wire portion are printed separately, and different electrode slurries are used for the inner electrode and the inner electrode wire portion. The electrode wire slurry in the present application is suitable for sensor elements composed of oxygen ion conductive solid electrolytes, especially for wire portions connected to electrodes distributed inside the chamber.

[0011] The particle size of the platinum powder is 300nm~700nm, and the particle size of the aluminum oxide powder is 0.05μm~1μm.

[0012] Among them, in order to match the shrinkage of the substrate and improve the adhesion, YSZ powder (yttrium stabilized zirconia powder) with the same molar ratio as the ceramic substrate is preferred, and 5YSZ or 8YSZ is more preferred.

[0013] Furthermore, the organic carrier includes an organic binder and a surfactant, and the weight ratio of the organic binder to the surfactant is (70-85): (15-30). Preferably, the weight ratio of the organic binder to the surfactant is (70-85): (20-25).

[0014] Furthermore, the organic binder comprises an organic resin and an organic solvent, and the weight ratio of the organic resin to the organic solvent is (15-30): (70-85). Preferably, the weight ratio of the organic resin to the organic solvent is (20-25): (70-85). Furthermore, the organic resin includes any one or more of ethyl cellulose, polyvinyl butyral, methacrylic acid, acrylic resin, epoxy resin, and nitrocellulose.

[0015] Furthermore, the organic solvent includes any one or more of turpentine terephthalate, butyl carbitol, tributyl citrate, dibutyl phthalate, and propionate.

[0016] Furthermore, the surfactant includes any one or more of a dispersant, a defoamer, a leveling agent, and a thixotropic agent.

[0017] The dispersant includes any one or more combinations of PVP, CTAB, SDS, triethanolamine, and KD9.

[0018] The leveling agent includes any one or more combinations of polysiloxanes, acrylates, and phosphate-modified acrylic acid.

[0019] The thixotropic agent includes any one or more combinations of hydrogenated castor oil, palmitic acid, furoic acid, polyamide wax and polyurethane.

[0020] The defoaming agent includes a polyether defoaming agent, specifically including any one or more combinations of GP, GPE, BYK, and dimethyl silicone oil.

[0021] In a second aspect, the present application provides a method for preparing a zirconium oxide-based gas sensor electrode wire slurry, comprising the following steps: Preparation of organic binder: adding organic resin into organic solvent according to weight percentage, stirring until completely dissolved, to obtain organic binder; Preparing an organic vehicle: adding a surfactant to an organic binder, and continuing to stir to uniformly mix the organic binder and the surfactant to obtain an organic vehicle; Dispersing electrode wire slurry: according to weight percentage, platinum powder, alumina powder and YSZ powder are fully mixed, and then the prepared organic system is added to the mixed powder in proportion, and the mixture is fully stirred and dispersed evenly, and then the electrode wire slurry is obtained after grinding and dispersion, vacuum stirring and centrifugal degassing.

[0022] Furthermore, a ceramic three-roller grinder is used for grinding and dispersing, wherein the ceramic rollers of the ceramic three-roller grinder are made of zirconium oxide.

[0023] Furthermore, the vacuum stirring centrifugal degassing process is: firstly put the ground and dispersed slurry into a polytetrafluoroethylene cup and stir it thoroughly, then put it into a non-contact planetary stirring vacuum degassing machine, and carry out the three steps of low-speed dispersion stirring, high-speed dispersion stirring and vacuum degassing in sequence.

[0024] Furthermore, when preparing the organic carrier and the organic system, the stirring temperature is controlled at 60°C to 80°C.

[0025] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) The present invention adds YSZ powder to the electrode wire slurry, and after co-firing, a tighter bond is formed between the wire and the substrate, which reduces cavities or defects at the bonding point, thereby improving the start-up time of the sensor without affecting other properties of the ceramic chip.

[0026] (2) The present invention adds YSZ powder to the electrode wire slurry. Since YSZ powder has good oxygen ion conductivity at high temperature and is highly sensitive to changes in oxygen content in the sensor exhaust gas, it can partially replace the amount of precious metals, thereby reducing the production cost of the electrode wire slurry.

[0027] (3) The present invention adds YSZ powder to the electrode wire slurry. Due to its excellent thermal shock resistance and large thermal expansion coefficient, the shrinkage matching consistency between the electrode slurry and the substrate is adjusted, thereby avoiding the problems of fracture, microcracks, cavities, etc. caused by inconsistent shrinkage between the electrode wire and the substrate and the wire in an environment with rapid temperature changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solution in the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 This is a SEM morphology image of the electrode wire slurry prepared in Example 1 of the present invention after sintering; Figure 2 This is a SEM morphology image of the electrode wire slurry prepared in Example 3 of the present invention after sintering; Figure 3 This is a SEM morphology image of the electrode wire slurry prepared in Comparative Example 1 after sintering; Figure 4 This is a simplified schematic diagram of the oxygen pump electrode; Figure 5 It is a schematic diagram of the silk-screen pattern of the pump electrode and the electrode wire; Figure 6 Schematic diagram of the silk-screen pattern of the common electrode.

[0030] Reference numerals: 1-common electrode, 2-main pump oxygen electrode, 3-first layer electrolyte substrate, 4-auxiliary pump electrode, 5-electrode wire, 6-second layer electrolyte substrate, 7-common electrode pin, 8-main pump electrode pin, 9-auxiliary pump electrode pin. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. The illustrative embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0032] In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it is apparent to one of ordinary skill in the art that these specific details need not be employed to practice the present invention. In other embodiments, in order to avoid confusing the present invention, well-known materials or methods are not specifically described.

[0033] Throughout the specification, references to "one embodiment," "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in conjunction with the embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "one embodiment," "an embodiment," "an example," or "an example" that appear in various places throughout the specification do not necessarily all refer to the same embodiment or example. In addition, particular features, structures, or characteristics may be combined in one or more embodiments or examples in any appropriate combination and / or sub-combination. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. In addition, those skilled in the art will be able to combine and combine different embodiments or examples described in this specification and features of different embodiments or examples, without contradicting each other.

[0034] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0035] Example 1

[0036] This embodiment provides a method for preparing a zirconium oxide-based gas sensor electrode wire slurry, which is carried out according to the following steps: S1. Preparation of an organic binder: Weigh the raw materials according to the mass percentage composition: 15.95 g ethyl cellulose, 31.91 g turpentine alcohol, 25.53 g butyl carbitol and 6.38 g dibutyl phthalate, add ethyl cellulose into an organic solvent at 60° C., stir until completely dissolved, and obtain an organic binder.

[0037] S2. Preparation of organic carrier: Add 16.18 g of dispersant KD9 and 4.05 g of defoamer BYK to the organic binder prepared in S1 and pour into a dissolving tank. Continue to mix the organic binder and surfactant evenly at 60° C. to obtain an organic carrier.

[0038] S3. Electrode slurry dispersion: according to the formula ratio, weigh 24.61g of platinum powder, 1.57g of 5YSZ powder and 0.52g of alumina powder and mix them evenly. Take 3.3g of organic carrier and put it into a polytetrafluoroethylene cup. Then pour the mixed powder into the cup. Then put it into a non-contact planetary stirring vacuum degassing machine. After stirring and dispersing thoroughly at low speed and high speed, the mixed slurry is further ground and dispersed in a ceramic three-roll grinder. Finally, the slurry is subjected to vacuum stirring and centrifugal degassing.

[0039] Example 2

[0040] This embodiment provides a method for preparing a zirconium oxide-based gas sensor electrode wire slurry, which is carried out according to the following steps: S1. Preparation of an organic binder: Weigh the raw materials according to the mass percentage composition: 15.60 g ethyl cellulose, 31.20 g turpentine alcohol, 24.96 g butyl carbitol and 6.24 g dibutyl phthalate, add ethyl cellulose into an organic solvent at 60° C., stir until completely dissolved, and obtain an organic binder.

[0041] S2. Preparation of organic carrier: Add 14.67 g of dispersant KD9 and 7.33 g of defoamer BYK to the organic binder prepared in S1 and pour into a dissolving tank. Continue to mix the organic binder and surfactant at 60° C. to obtain an organic carrier.

[0042] S3. Electrode slurry dispersion: according to the formula ratio, weigh 23.29g of platinum powder, 2.59g of 5YSZ powder and 0.52g of alumina powder and mix them evenly; take 3.6g of organic carrier and put it into a polytetrafluoroethylene cup, then pour the mixed powder into the cup, and then put it into a non-contact planetary stirring vacuum degassing machine, stir and disperse it thoroughly by low-speed dispersion stirring and high-speed dispersion stirring, and then further grind and disperse the mixed slurry in a ceramic three-roll grinder, and finally subject the slurry to vacuum stirring and centrifugal degassing.

[0043] Example 3

[0044] This embodiment provides a method for preparing a zirconium oxide-based gas sensor electrode wire slurry, which is carried out according to the following steps: S1. Preparation of an organic binder: Weigh the raw materials according to the mass percentage composition: 15.60 g ethyl cellulose, 31.20 g turpentine alcohol, 24.96 g butyl carbitol and 6.24 g dibutyl phthalate, add ethyl cellulose into an organic solvent at 60° C., stir until completely dissolved, and obtain an organic binder.

[0045] S2. Preparation of organic carrier: Add 14.67 g of dispersant KD9 and 7.33 g of defoamer BYK to the organic binder prepared in S1, pour into a dissolving tank, continue to mix the organic binder and surfactant at 60° C. to obtain an organic carrier.

[0046] S3. Electrode slurry dispersion: according to the formula ratio, weigh 22.52 g of platinum powder, 3.36 g of 5YSZ powder and 0.52 g of alumina powder and mix them evenly. Take 3.6 g of organic carrier and put it into a polytetrafluoroethylene cup. Then pour the mixed powder into the cup. Then put it into a non-contact planetary stirring vacuum degassing machine. After fully stirring and dispersing evenly according to low-speed dispersion stirring and high-speed dispersion stirring, the mixed slurry is further ground and dispersed in a ceramic three-roll grinder. Finally, the slurry is vacuum stirred and centrifuged for degassing.

[0047] Example 4

[0048] This embodiment provides a method for preparing a zirconium oxide-based gas sensor electrode wire slurry, which is carried out according to the following steps: S1. Preparation of an organic binder: Weigh the raw materials according to the mass percentage composition: 15.98 g ethyl cellulose, 31.97 g turpentine alcohol, 25.58 g butyl carbitol and 6.39 g dibutyl phthalate, add ethyl cellulose into an organic solvent at 60° C., stir until completely dissolved, and obtain an organic binder.

[0049] S2. Preparation of organic carrier: Add 13.38 g of dispersant KD9 and 6.69 g of defoamer BYK to the organic binder prepared in S1 and pour into a dissolving tank. Continue to mix the organic binder and surfactant evenly at 60° C. to obtain an organic carrier.

[0050] S3. Electrode slurry dispersion: according to the formula ratio, weigh 21.24 g of platinum powder, 4.35 g of 5YSZ powder and 0.51 g of alumina powder and mix them evenly. Take 3.9 g of organic carrier and put it into a polytetrafluoroethylene cup. Then pour the mixed powder into the cup. Then put it into a non-contact planetary stirring vacuum degassing machine. After stirring and dispersing thoroughly at low speed and high speed, the mixed slurry is further ground and dispersed in a ceramic three-roll grinder. Finally, the slurry is subjected to vacuum stirring and centrifugal degassing.

[0051] Example 5

[0052] This embodiment provides a method for preparing a zirconium oxide-based gas sensor electrode wire slurry, which is carried out according to the following steps: S1. Preparation of an organic binder: Weigh the raw materials according to the mass percentage composition: 15.09 g ethyl cellulose, 30.17 g turpentine alcohol, 24.14 g butyl carbitol and 6.03 g dibutyl phthalate, add ethyl cellulose into an organic solvent at 60° C., stir until completely dissolved, and obtain an organic binder.

[0053] S2. Preparation of organic carrier: Add 18.43 g of dispersant KD9 and 6.14 g of defoamer BYK to the organic binder prepared in S1 and pour into a dissolving tank. Continue to mix the organic binder and surfactant evenly at 60° C. to obtain an organic carrier.

[0054] S3. Electrode slurry dispersion: according to the formula ratio, weigh 20.24 g of platinum powder, 5.06 g of 5YSZ powder and 0.51 g of alumina powder and mix them evenly. Take 4.2 g of organic carrier and put it into a polytetrafluoroethylene cup. Then pour the mixed powder into the cup. Then put it into a non-contact planetary stirring vacuum degassing machine. After stirring and dispersing thoroughly at low speed and high speed, the mixed slurry is further ground and dispersed in a ceramic three-roll grinder. Finally, the slurry is subjected to vacuum stirring and centrifugal degassing.

[0055] Example 6

[0056] This embodiment provides a method for preparing a zirconium oxide-based gas sensor electrode wire slurry, which is carried out according to the following steps: S1. Preparation of an organic binder: Weigh the raw materials according to the mass percentage composition: 15.95 g ethyl cellulose, 31.91 g turpentine alcohol, 25.53 g butyl carbitol and 6.38 g dibutyl phthalate, add ethyl cellulose into an organic solvent at 60° C., stir until completely dissolved, and obtain an organic binder.

[0057] S2. Preparation of organic carrier: Add 16.18 g of dispersant KD9 and 4.05 g of defoamer BYK to the organic binder prepared in S1 and pour into a dissolving tank. Continue to mix the organic binder and surfactant evenly at 60° C. to obtain an organic carrier.

[0058] S3. Electrode slurry dispersion: according to the formula ratio, weigh 25.58 g of platinum powder, 0.60 g of 5YSZ powder and 0.52 g of alumina powder and mix them evenly. Take 4.2 g of organic carrier and put it into a polytetrafluoroethylene cup. Then pour the mixed powder into the cup. Then put it into a non-contact planetary stirring vacuum degassing machine. After fully stirring and dispersing evenly according to low-speed dispersion stirring and high-speed dispersion stirring, the mixed slurry is further ground and dispersed in a ceramic three-roll grinder. Finally, the slurry is vacuum stirred and centrifuged for degassing.

[0059] Example 7

[0060] This embodiment provides a method for preparing a zirconium oxide-based gas sensor electrode wire slurry, which is carried out according to the following steps: S1. Preparation of an organic binder: Weigh the raw materials according to the mass percentage composition: 16.03 g ethyl cellulose, 32.07 g turpentine alcohol, 25.65 g butyl carbitol and 6.41 g dibutyl phthalate, add ethyl cellulose into an organic solvent at 60° C., stir until completely dissolved, and obtain an organic binder.

[0061] S2. Preparation of organic carrier: Add 17.00 g of dispersant KD9 and 2.83 g of defoamer BYK to the organic binder prepared in S1 and pour into a dissolving tank. Continue to mix the organic binder and surfactant evenly at 60° C. to obtain an organic carrier.

[0062] S3. Electrode slurry dispersion: according to the formula ratio, weigh 19.00 g of platinum powder, 6.00 g of 5YSZ powder and 0.50 g of alumina powder and mix them evenly. Take 4.5 g of the organic carrier and put it into a polytetrafluoroethylene cup. Then pour the mixed powder into the cup. Then put it into a non-contact planetary stirring vacuum degassing machine. After fully stirring and dispersing evenly by low-speed dispersion stirring and high-speed dispersion stirring, the mixed slurry is further ground and dispersed in a ceramic three-roll grinder. Finally, the slurry is vacuum stirred and centrifuged for degassing.

[0063] Comparative Example 1 This comparative example provides a method for preparing an electrode wire slurry. Unlike Example 1, no YSZ powder is added in this comparative example, and the method is carried out according to the following steps: This embodiment provides a method for preparing a zirconium oxide-based gas sensor electrode wire slurry, which is carried out according to the following steps: S1. Preparation of an organic binder: Weigh the raw materials according to the mass percentage composition: 15.95 g ethyl cellulose, 31.91 g turpentine alcohol, 25.53 g butyl carbitol and 6.38 g dibutyl phthalate, add ethyl cellulose into an organic solvent at 60° C., stir until completely dissolved, and obtain an organic binder.

[0064] S2. Preparation of organic carrier: Add 16.18 g of dispersant KD9 and 4.05 g of defoamer BYK to the organic binder prepared in S1 and pour into a dissolving tank. Continue to mix the organic binder and surfactant evenly at 60° C. to obtain an organic carrier.

[0065] S3. Electrode slurry dispersion: according to the formula ratio, weigh 26.176g of platinum powder and 0.524g of alumina powder and mix them evenly. Take 3.3g of organic carrier and put it into a polytetrafluoroethylene cup. Then pour the mixed powder into the cup. Then put it into a non-contact planetary stirring vacuum degassing machine. After stirring and dispersing thoroughly at low speed and high speed, the mixed slurry is further ground and dispersed in a ceramic three-roll grinder. Finally, the slurry is vacuum stirred and centrifuged for degassing.

[0066] Comparative Example 2 This comparative example provides a method for preparing an electrode wire slurry. The difference from Example 1 is that in S3, the ratio of YSZ powder to platinum powder added in this comparative example is 1:99, that is, 25.91g of platinum powder, 0.26g of 5YSZ powder and 0.52g of alumina powder are added by weight, and the other processes are the same as Example 1.

[0067] Comparative Example 3 This comparative example provides a method for preparing an electrode wire slurry. Different from Example 1, in S3, the ratio of YSZ powder to platinum powder added in this comparative example is 25:75, that is, 18.97 g of platinum powder, 6.32 g5YSZ powder and 0.51 g of alumina powder are added by weight, and the other processes are the same as Example 5.

[0068] The electrode wire slurries prepared in Examples 1 to 7 and Comparative Examples 1 to 3 were subjected to the following tests.

[0069] 1. The prepared conductor paste is printed on the ceramic substrate in a certain shape by screen printing. The gap is filled with the connection paste, and then it is isostatically laminated with another ceramic substrate. The laminated ceramic substrate is cut into long strips and then placed in a high-temperature sintering furnace for sintering. After cooling out of the furnace, the cross section of the fired long strip substrate is observed using a scanning electron microscope.

[0070] According to the cross-sectional morphology of the conductor slurry and the ceramic substrate, the combination of the conductor slurry and the ceramic substrate is judged according to the following standards: A: The wire is completely integrated with the substrate; B: There is a crack between the wire and the substrate but it is not completely peeled off; C: The wire is directly peeled off from the substrate.

[0071] 2. Prepare the sensor according to the method known in the industry, and print each wire paste on the substrate by screen printing according to the wire shape designed for the sensor. After the printing and drying of various patterns of the sensor are completed, the layers of ceramic substrates are pressed together to form a laminate, and a multi-layer laminate sensor element is obtained. The laminate is fired at a specified firing temperature to obtain a sensor chip.

[0072] Start-up time test method: Install the sensor in the detection equipment and introduce clean air into the installation cavity of the detection equipment: After the clean air stabilizes to 1m / s, power on the sensor and preheat it for 15s. After the preheating is completed, send a "dew point signal" to the sensor, and the sensor starts to heat up rapidly until it reaches the normal operating temperature (about 800 ℃).

[0073] Startup test time determination: Startup time: Under air, the sensor is electrically heated to the normal operating temperature, and when NOx outputs an accurate measurement value (dew point to status bit switching time) NOx <10ppm, it is the sensor startup time; judge according to the following standards: A: The chip startup time is less than 65s; B: The chip startup time is greater than 65s but less than 90s; C: The chip startup time is greater than 90s.

[0074] VP0 is the adjustable pump voltage applied between the sensor common electrode and the main pump electrode. It is the initial working voltage value corresponding to the sensor pump electrode. Under the action of the pump voltage VP0, oxygen is pumped in or out according to the oxygen concentration in the exhaust gas, and the oxygen concentration in the first gas chamber is finally controlled at a low but relatively fixed level. The setting of the VP0 value has a great influence on the stability, linearity, measurement accuracy, response speed and service life of the nitrogen oxygen sensor.

[0075] The ceramic chip structure of the present invention is a ceramic chip structure formed by stacking multiple layers of electrolyte substrates as is well known in the industry. Figure 4 This is a simplified schematic diagram of the ceramic chip pump electrode of this invention, which includes a common electrode 1, a main pump oxygen electrode 2, and a first layer electrolyte substrate 3. Figure 5 It is a schematic diagram of the silk-screen pattern of the pump electrode and the electrode wire in this invention, which includes an auxiliary pump electrode 4, an electrode wire 5, and a second layer of electrolyte substrate 6. Figure 6It is a schematic diagram of the silk-screen pattern of the common electrode in this invention, which includes a common electrode pin 7, a main pump electrode pin 8, and an auxiliary pump electrode pin 9.

[0076] The structure of the nitrogen oxide sensor chip is a common nitrogen oxide sensor chip structure in the industry. The current control method known in the industry is used to test the joint pump performance of the ceramic chip. The test equipment: 8-channel nitrogen oxide chip test fixture, test conditions: atmosphere: air, V1=425mV, V2=450mV, IP1=7μA, T=840℃. When the path meets the above conditions, the electrical performance test is started to obtain the VP0 measurement value.

[0077] The test results are shown in Table 1.

[0078] Table 1

[0079] like Figure 1 , which is a SEM morphology of the electrode wire slurry prepared in Example 1 after sintering; Figure 2 This is a SEM morphology image of the electrode wire slurry prepared in Example 3 after sintering; Figure 3 This is the SEM morphology of the electrode wire slurry prepared in Comparative Example 1 after sintering.

[0080] From the above test results, it can be seen that the paste prepared by the wire paste formula defined in the embodiment of the present invention has achieved good results after sintering and bonding with the substrate. That is, it shows that the addition of YSZ powder increases the shrinkage rate of the electrode paste, so that it keeps the same shrinkage as the upper and lower electrolyte substrates of the wire during the sintering process, which can effectively solve the problem of forming a cavity between the electrode wire and the electrolyte layer due to the mismatch of sintering shrinkage between materials, thereby making the signal transmission of the sensor accurate and stable.

[0081] In addition, the above test results show that the electrode wire prepared by the wire slurry of the present invention has achieved good results in the start-up time of the sensor, and the start-up time is less than 65s, which shows that the addition of YSZ powder can effectively solve the problem of long sensor start-up time.

[0082] In the wire slurry formula, if the YSZ powder content is too high, the resistance value of the wire will be too large, thereby affecting the current and potential distribution in the circuit, and then affecting the chemical reaction balance on the surface of the pump electrode, so that the actual potential difference on the pump electrode is reduced. In order to maintain the normal operation of the pump electrode, the control circuit will increase the VP0 value at this time to ensure that there is enough current passing through the pump electrode. When the YSZ content is too low, due to the difference in shrinkage between the wire and the electrolyte substrate, a cavity is formed, and the gas concentration in the chamber becomes higher. It is necessary to increase the VP0 value to ensure that the chamber concentration reaches the set concentration. If VP0 is too large, it will have a greater impact on the pump electrode measurement value, linearity, response speed, and life of the circuit components. It can be seen from the test data of Comparative Example 3 that after the amount of YSZ powder exceeds the range specified in this application, although the start-up time and the slurry are better combined with the substrate, its VP0 is too large. If VP0 is too large, the linearity of the pump electrode deteriorates, the life is shortened, and the response speed will also slow down.

[0083] In summary, the present invention has verified through the above experiments that in the formula of the electrode guide slurry, only by limiting the YSZ powder within the dosage range of the present invention can the bonding force between the electrode wire formed by the electrode wire slurry after co-firing and the substrate be strong and the electrode performance be stable, thereby enabling the sensor to have excellent performance of accurate and stable signal transmission and fast startup time.

[0084] Finally, it should be noted that the specific implementation methods described above further describe the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention. For those skilled in the art, it is obvious that the present application is not limited to the details of the above exemplary embodiments, and the present application can be implemented in other specific forms without departing from the spirit or basic features of the present application. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present application is limited by the attached claims rather than the above description, and it is intended to include all changes that fall within the meaning and scope of the equivalent elements of the claims in the present application.

Claims

1. A zirconium oxide-based gas sensor electrode wire slurry, characterized in that: The invention comprises the following components by weight percentage: 60wt% to 90wt% of platinum powder, 0.1wt% to 2wt% of alumina powder, 2wt% to 20wt% of YSZ powder, and the balance is an organic carrier.

2. The zirconium oxide-based gas sensor electrode wire slurry according to claim 1, characterized in that: The organic carrier includes an organic binder and a surfactant, and the weight ratio of the organic binder to the surfactant is (70-85): (15-30).

3. The zirconium oxide-based gas sensor electrode wire slurry according to claim 2, characterized in that: The organic binder includes an organic resin and an organic solvent, and the weight ratio of the organic resin to the organic solvent is (15-30): (70-85).

4. The zirconium oxide-based gas sensor electrode wire slurry according to claim 3, characterized in that: The organic resin includes any one or more of ethyl cellulose, polyvinyl butyral, methacrylic acid, acrylic resin, epoxy resin, and nitrocellulose.

5. The zirconium oxide-based gas sensor electrode wire slurry according to claim 3, characterized in that: The organic solvent includes any one or more of turpentine alcohol, butyl carbitol, tributyl citrate, dibutyl phthalate, and propionate.

6. The zirconium oxide-based gas sensor electrode wire slurry according to claim 2, characterized in that: The surfactant includes any one or more of a dispersant, a defoamer, a leveling agent, and a thixotropic agent.

7. A method for preparing a zirconium oxide-based gas sensor electrode wire slurry, characterized in that: The following steps are involved: Preparation of organic binder: adding organic resin into organic solvent according to weight percentage, stirring until completely dissolved, to obtain organic binder; Preparing an organic vehicle: adding a surfactant to an organic binder, and continuing to stir to uniformly mix the organic binder and the surfactant to obtain an organic vehicle; Dispersing electrode wire slurry: according to weight percentage, platinum powder, alumina powder and YSZ powder are fully mixed, and then the prepared organic system is added to the mixed powder in proportion, and the mixture is fully stirred and dispersed evenly, and then the electrode wire slurry is obtained after grinding and dispersion, vacuum stirring and centrifugal degassing.

8. The method for preparing a zirconium oxide-based gas sensor electrode wire slurry according to claim 7, characterized in that: A ceramic three-roller mill is used for grinding and dispersing, wherein the ceramic rollers of the ceramic three-roller mill are made of zirconium oxide.

9. The method for preparing a zirconium oxide-based gas sensor electrode wire slurry according to claim 7, characterized in that: The vacuum stirring centrifugal degassing process is as follows: firstly, the ground and dispersed slurry is placed in a polytetrafluoroethylene cup and fully stirred, and then placed in a non-contact planetary stirring vacuum degassing integrated machine, and the process is carried out in three steps: low-speed dispersing stirring, high-speed dispersing stirring, and vacuum degassing.

10. The method for preparing a zirconium oxide-based gas sensor electrode wire slurry according to claim 7, characterized in that: When preparing the organic carrier and the organic system, the stirring temperature is controlled at 60°C~80°C.

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