Water-resistant protective layer of nitrogen-oxygen sensor, nitrogen-oxygen sensor and preparation method of nitrogen-oxygen sensor

Abstract

The invention relates to the technical field of nitrogen-oxygen sensors, and discloses a nitrogen-oxygen sensor water-resistant protective layer, a nitrogen-oxygen sensor and a preparation method of the nitrogen-oxygen sensor, the nitrogen-oxygen sensor comprises a nitrogen-oxygen sensor chip, and the outer part of the tail end of the nitrogen-oxygen sensor chip is coated with the water-resistant protective layer; the water-resistant protective layer comprises the following components in parts by mass: 100 parts of protective layer powder, 1-6 parts of a pore forming agent, 10-20 parts of a binder, 0.5-5 parts of a dispersing agent, 0.5-5 parts of a defoaming agent and 10-20 parts of a solvent; the protective layer powder comprises 40-60 parts of spinel powder, 20-40 parts of aluminum oxide powder and 20-40 parts of calcium carbonate powder. According to the water-resistant protective layer, spinel, aluminum oxide and calcium carbonate are used as main raw materials, a flower-shaped microstructure can be formed after sintering, meanwhile, a porous structure is prepared in combination with a pore forming agent, and the hydrophobic performance and the heat preservation performance of the nitrogen-oxygen sensor are greatly improved when the tail end of the nitrogen-oxygen sensor is coated with the water-resistant protective layer; the influence of thermal shock on the nitrogen-oxygen sensor is reduced, and the service life of the nitrogen-oxygen sensor is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of nitrogen oxygen sensors, and in particular to a water-resistant protective layer of a nitrogen oxygen sensor, a nitrogen oxygen sensor and a preparation method thereof. Background Art

[0002] The nitrogen oxide sensor is an electronic component based on oxygen ion conduction of functional ceramics. It utilizes multi-layer high-temperature co-fired ceramic technology to sinter a porous metal ceramic composed of precious metals such as Pt, Au, Rh and ZrO2 on a YSZ (yttrium stabilized zirconia) substrate, analyzes and collects micro-electric signals, and thus identifies NOx characteristic signals.

[0003] Usually, the measured gas contains water vapor. The water droplets produced by the condensation of water vapor will adhere to the surface of the nitrogen oxide sensor heated to a high temperature. Therefore, the thermal shock caused by the water droplets attached to the surface of the nitrogen oxide sensor element will act on the sensor element, causing cracks on the surface of the sensor element, and then causing the sensor element to crack.

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

[0005] The problem with the prior art is that the thermal shock caused by water droplets attached to the surface of the nitrogen oxide sensor element will act on the sensor element, causing cracks on the surface of the sensor element. In order to solve the above problem, the present invention provides a water-resistant protective layer for a nitrogen oxide sensor, a nitrogen oxide sensor and a preparation method thereof. By coating a protective layer on the end of the nitrogen oxide sensor, a large number of flower-like structures formed by stacking sheet structures exist in its microscopic morphology, which greatly improves the hydrophobicity of the protective layer. At the same time, since the prepared protective layer has a porous structure, it can also greatly improve the thermal insulation performance of the nitrogen oxide sensor, reduce the influence of water vapor in the measured gas on the thermal shock of the sensor, and extend the service life of the nitrogen oxide sensor.

[0006] The present invention is achieved through the following technical solutions: In a first aspect, the present invention provides a water-resistant protective layer for a nitrogen oxygen sensor, comprising the following components by mass fraction: 100 parts of protective layer powder, 1 to 6 parts of a pore-forming agent, 10 to 20 parts of a binder, 0.5 to 5 parts of a dispersant, 0.5 to 5 parts of a defoaming agent, and 10 to 20 parts of a solvent; The protective layer powder includes 40-60 parts of spinel powder, 20-40 parts of aluminum oxide powder, and 20-40 parts of calcium carbonate powder.

[0007] The water-resistant protective layer of the present invention uses spinel, alumina and calcium carbonate as main raw materials, and can form a flower-like structure microstructure after sintering. At the same time, it is combined with a pore-forming agent to form a porous structure. When coated on the end of the nitrogen oxygen sensor, the hydrophobicity and thermal insulation performance of the nitrogen oxygen sensor are greatly improved, the influence of thermal shock on the nitrogen oxygen sensor is reduced, and the service life of the nitrogen oxygen sensor is extended.

[0008] In a specific embodiment, the spinel powder has a particle size of 20-40 μm, and the alumina powder has a particle size of 0.05-1 μm.

[0009] In a specific embodiment, the pore-forming agent is one or more of carbon black powder, polymethyl methacrylate, and polyethylene, with a particle size of 0.5 to 50 μm; the binder is one or more of alumina sol, silica sol, and titanium dioxide sol; and the dispersant is one or more of triethylhexyl phosphate and sodium tripolyphosphate.

[0010] In a specific embodiment, the defoaming agent is one or more of polydimethylsiloxane and ethylene oxide; the solvent is one or a mixture of deionized water, ethanol, and glycerol.

[0011] In a second aspect, the present invention provides a method for preparing a water-resistant protective layer of a nitrogen oxygen sensor, the steps of which are as follows: After the spinel powder, alumina powder and calcium carbonate powder are uniformly mixed, a pore former, a binder, a dispersant, a defoamer and a solvent are added and mixed in a ball mill to obtain a protective layer slurry.

[0012] In a specific embodiment, the viscosity of the protective layer slurry is 500-10000 mPa·s.

[0013] In a third aspect, the present invention provides a nitrogen oxygen sensor, comprising a nitrogen oxygen sensor chip, wherein the outer end of the nitrogen oxygen sensor chip is coated with the nitrogen oxygen sensor water-resistant protective layer or the nitrogen oxygen sensor water-resistant protective layer slurry prepared by the preparation method.

[0014] In a specific embodiment, the coating thickness of the water-resistant protective layer is 100-500 μm.

[0015] In a fourth aspect, the present invention provides a method for preparing a nitrogen oxygen sensor, comprising the following steps: 1) vertically placing the nitrogen oxygen sensor chip into the protective layer slurry, so that the end of the nitrogen oxygen sensor chip is immersed in the protective layer slurry and is completely covered by the slurry; 2) After being immersed for a certain period of time, the nitrogen oxygen sensor chip is pulled upward to complete the immersion, and then dried, and finally the nitrogen oxygen sensor chip is baked to obtain the nitrogen oxygen sensor.

[0016] In a specific embodiment, in step 2), the pulling speed is 0.1~5mm / s, and the drying temperature is 50~200°C; the calcination temperature of the coated nitrogen oxygen sensor chip is 900~1300°C, and the sintering time is 0.5~5 h.

[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. A water-resistant protective layer for a nitrogen oxide sensor, a nitrogen oxide sensor and a preparation method thereof provided in an embodiment of the present invention uses spinel, alumina and calcium carbonate as main raw materials, can form a flower-like microstructure after sintering, and is combined with a pore-forming agent to form a porous structure, has good hydrophobicity and thermal insulation performance, and is coated on the end of the nitrogen oxide sensor, which can reduce the impact of thermal shock on the nitrogen oxide sensor and extend the service life of the nitrogen oxide sensor; 2. The embodiments of the present invention provide a water-resistant protective layer for a nitrogen oxide sensor, a nitrogen oxide sensor and a method for preparing the same. By coating a protective layer on the end of the nitrogen oxide sensor, a large number of flower-like structures with a proportion greater than 30% formed by stacking sheet structures exist in its microscopic morphology, which greatly improves the hydrophobicity of the protective layer. At the same time, since the prepared protective layer has a porous structure, the thermal insulation performance of the nitrogen oxide sensor can also be greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 This is a SEM image of the flower-like structure of the water-resistant protective layer at the end of the nitrogen oxygen sensor provided by the present invention; Figure 2 The regional EDS surface scanning element distribution of the water-resistant protective layer at the end of the nitrogen and oxygen sensor provided in Example 1 of the present invention; Figure 3 This is an enlarged SEM image of the flower-like structure of the water-resistant protective layer at the end of the nitrogen oxygen sensor provided in Example 1 of the present invention; Figure 4 A SEM image of a flower-like structure of the water-resistant protective layer at the end of the nitrogen oxygen sensor provided in Example 1 of the present invention at a lower magnification; Figure 5 A SEM image of a lower magnification of the flower-like structure of the water-resistant protective layer at the end of the nitrogen oxygen sensor provided in Example 1 of the present invention; Figure 6 This is a SEM image of the water-resistant protective layer at the end of the nitrogen oxygen sensor provided in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0020] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary 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.

[0021] 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 obscuring the present invention, well-known materials or methods are not specifically described.

[0022] 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" appearing 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 suitable combination and / or subcombination. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0023] In the description of the present invention, the directions or positional relationships indicated by terms such as “front”, “rear”, “left”, “right”, “up”, “down”, “vertical”, “horizontal”, “high”, “low”, “inside” and “outside” are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limiting the scope of protection of the present invention.

[0024] Usually, the measured gas contains water vapor. The water droplets produced by the condensation of water vapor will adhere to the surface of the nitrogen oxide sensor heated to a high temperature. Therefore, the thermal shock caused by the water droplets attached to the surface of the nitrogen oxide sensor element will act on the sensor element, causing cracks on the surface of the sensor element, and then causing the sensor element to crack.

[0025] In order to solve the above technical problems: In a first aspect, the present invention provides a water-resistant protective layer for a nitrogen oxygen sensor, comprising the following components by mass fraction: 100 parts of protective layer powder, 1 to 6 parts of a pore-forming agent, 10 to 20 parts of a binder, 0.5 to 5 parts of a dispersant, 0.5 to 5 parts of a defoaming agent, and 10 to 20 parts of a solvent; The protective layer powder includes 40-60 parts of spinel powder, 20-40 parts of aluminum oxide powder, and 20-40 parts of calcium carbonate powder.

[0026] The water-resistant protective layer of the present invention uses spinel, aluminum oxide and calcium carbonate as main raw materials, and can form a flower-like microstructure after sintering, such as Figure 1 As shown; at the same time, a porous structure is formed by combining with a pore-forming agent, and coating it on the end of the nitrogen oxide sensor greatly improves the hydrophobicity and thermal insulation performance of the nitrogen oxide sensor, reduces the impact of thermal shock on the nitrogen oxide sensor, and extends the service life of the nitrogen oxide sensor.

[0027] In a specific embodiment, the spinel powder has a particle size of 20-40 μm, and the alumina powder has a particle size of 0.05-1 μm.

[0028] In a specific embodiment, the pore-forming agent is one or more of carbon black powder, polymethyl methacrylate, and polyethylene, with a particle size of 0.5~50μm; the binder is one or more of alumina sol, silica sol, and titanium dioxide sol; the dispersant is one or more of a polycarboxylic acid dispersant and a phosphate dispersant.

[0029] In a specific embodiment, the defoaming agent is one or more of an organosilicon defoaming agent and a polyether defoaming agent; the solvent is one or a mixture of deionized water, ethanol, and glycerol.

[0030] In a second aspect, the present invention provides a method for preparing a water-resistant protective layer of a nitrogen oxygen sensor, the steps of which are as follows: After the spinel powder, alumina powder and calcium carbonate powder are uniformly mixed, a pore former, a binder, a dispersant, a defoamer and a solvent are added and mixed in a ball mill to obtain a protective layer slurry.

[0031] In a specific embodiment, the viscosity of the protective layer slurry is 500-10000 mPa·s.

[0032] In a third aspect, the present invention provides a nitrogen oxygen sensor, comprising a nitrogen oxygen sensor chip, wherein the outer end of the nitrogen oxygen sensor chip is coated with the nitrogen oxygen sensor water-resistant protective layer or the nitrogen oxygen sensor water-resistant protective layer slurry prepared by the preparation method.

[0033] In a specific embodiment, the coating thickness of the water-resistant protective layer is 100-500 μm.

[0034] In a fourth aspect, the present invention provides a method for preparing a nitrogen oxygen sensor, comprising the following steps: 1) vertically placing the nitrogen oxygen sensor chip into the protective layer slurry, so that the end of the nitrogen oxygen sensor chip is immersed in the protective layer slurry and is completely covered by the slurry; 2) After being immersed for a certain period of time, the nitrogen oxygen sensor chip is pulled upward to complete the immersion, and then dried, and finally the nitrogen oxygen sensor chip is baked to obtain the nitrogen oxygen sensor.

[0035] In a specific embodiment, in step 2), the pulling speed is 0.1~5mm / s, and the drying temperature is 50~200°C; the calcination temperature of the coated nitrogen oxygen sensor chip is 900~1300°C, and the sintering time is 0.5~5 h.

[0036] The present invention coats a protective layer at the end of the nitrogen oxygen sensor, and a large number of flower-like structures with a proportion greater than 30% formed by stacking of sheet-like structures exist in the microscopic morphology. Figure 1 As shown, the hydrophobicity of the protective layer is greatly improved. At the same time, since the prepared protective layer has a porous structure, the thermal insulation performance of the nitrogen oxide sensor can also be greatly improved. Figure 2 for Figure 1 The EDS surface scanning element distribution of the water-resistant protective layer is shown in Table 1. Table 1 shows the content of each element. It can be seen that its element composition is consistent with the raw material selection.

[0037] Table 1 element wt% at% O 49.16 67.63 Mg 0.76 0.68 Al 14.67 11.97 Si 1.15 0.90 Ca 34.27 18.82 Total 100 100

[0038] Example 1 An embodiment of the present invention provides a method for preparing a nitrogen oxygen sensor, comprising the following steps: (1) Weigh 5 g of spinel powder with a particle size of 30 μm, 2.5 g of alumina powder with a particle size of 0.3 μm, and 4.46 g of calcium carbonate powder, and add them into a ball mill; (2) Weigh 0.6 g of polymethyl methacrylate with a particle size of 3 μm, 2 g of silica sol, 0.5 g of triethylhexyl phosphate, 0.5 g of polydimethylsiloxane, and 0.93 g of glycerol, and add them to a ball mill; (3) Weigh 20 g of zirconium oxide beads and add them to the ball mill; (4) Setting the rotation speed of the planetary ball mill to 500 r / min and the ball milling time to 40 min, thereby obtaining a slurry for forming a water-resistant protective layer of a nitrogen oxide sensor; (5) Dip-coating the slurry onto the designated area at the end of the nitrogen oxide sensor chip by dipping and pulling, wherein the pulling speed is 0.2 mm / s; (6) Place the dip-coated nitrogen oxygen sensor chip into a drying oven, set the oven temperature to 70°C, and dry for 1 hour; (7) Place the dried nitrogen oxygen sensor chip into a muffle furnace, set the muffle furnace sintering temperature to 1100°C, and the sintering time to 3 h.

[0039] Through the above steps, a water-resistant protective layer of the nitrogen oxide sensor is obtained, and the thickness is 350 μm. The obtained water-resistant protective layer of the nitrogen oxide sensor is characterized accordingly, such as Figure 3 As shown in the figure, the surface of the water-resistant protective layer presents a porous structure combined with a local flower-like structure. Figure 4 and Figure 5 It can be seen that the flower-like structure accounts for approximately 50% of the entire surface.

[0040] Example 2 An embodiment of the present invention provides a method for preparing a nitrogen oxygen sensor, comprising the following steps: (1) Weigh 5 g of spinel powder with a particle size of 30 μm, 3.223 g of alumina powder with a particle size of 0.3 μm, and 3.737 g of calcium carbonate powder, and add them into a ball mill; (2) Weigh 0.6 g of polymethyl methacrylate with a particle size of 3 μm, 2 g of silica sol, 0.5 g of sodium tripolyphosphate, 0.5 g of ethylene oxide, and 0.93 g of glycerol respectively, and add them into a ball mill; (3) Weigh 20 g of zirconium oxide beads and add them to the ball mill; (4) Setting the rotation speed of the planetary ball mill to 500 r / min and the ball milling time to 40 min, thereby obtaining a slurry for forming a water-resistant protective layer of a nitrogen oxide sensor; (5) Dip-coating the slurry onto the designated area at the end of the nitrogen oxide sensor chip by dipping and pulling, wherein the pulling speed is 0.2 mm / s; (6) Place the dip-coated nitrogen oxygen sensor chip into a drying oven, set the oven temperature to 70°C, and dry for 1 hour; (7) Place the dried nitrogen oxygen sensor chip into a muffle furnace, set the muffle furnace sintering temperature to 1100°C, and the sintering time to 3 h.

[0041] Through the above steps, a water-resistant protective layer of the nitrogen oxide sensor is obtained, with a thickness of 350 μm.

[0042] Example 3 An embodiment of the present invention provides a method for preparing a nitrogen oxygen sensor, comprising the following steps: (1) Weigh 5 g of spinel powder with a particle size of 30 μm, 3.947 g of alumina powder with a particle size of 0.3 μm, and 3.013 g of calcium carbonate powder, and add them into a ball mill; (2) Weigh 0.6 g of polymethyl methacrylate with a particle size of 3 μm, 2 g of silica sol, 0.5 g of triethylhexyl phosphate, 0.5 g of polydimethylsiloxane, and 0.93 g of glycerol, and add them to a ball mill; (3) Weigh 20 g of zirconium oxide beads and add them to the ball mill; (4) Setting the rotation speed of the planetary ball mill to 500 r / min and the ball milling time to 40 min, thereby obtaining a slurry for forming a water-resistant protective layer of a nitrogen oxide sensor; (5) Dip-coating the slurry onto the designated area at the end of the nitrogen oxide sensor chip by dipping and pulling, wherein the pulling speed is 0.2 mm / s; (6) Place the dip-coated nitrogen oxygen sensor chip into a drying oven, set the oven temperature to 70°C, and dry for 1 hour; (7) Place the dried nitrogen oxygen sensor chip into a muffle furnace, set the muffle furnace sintering temperature to 1100°C, and the sintering time to 3 h.

[0043] Example 4 An embodiment of the present invention provides a method for preparing a nitrogen oxygen sensor, comprising the following steps: (1) Weigh 5 g of spinel powder with a particle size of 30 μm, 2.5 g of alumina powder with a particle size of 0.3 μm, and 4.46 g of calcium carbonate powder, and add them into a ball mill; (2) Weigh 0.12 g of polymethyl methacrylate with a particle size of 3 μm, 2 g of silica sol, 0.5 g of sodium tripolyphosphate, 0.5 g of ethylene oxide, and 0.93 g of glycerol respectively, and add them into a ball mill; (3) Weigh 20 g of zirconium oxide beads and add them to the ball mill; (4) Setting the rotation speed of the planetary ball mill to 500 r / min and the ball milling time to 40 min, thereby obtaining a slurry for forming a water-resistant protective layer of a nitrogen oxide sensor; (5) Dip-coating the slurry onto the designated area at the end of the nitrogen oxide sensor chip by dipping and pulling, wherein the pulling speed is 0.2 mm / s; (6) Place the dip-coated nitrogen oxygen sensor chip into a drying oven, set the oven temperature to 70°C, and dry for 1 hour; (7) Place the dried nitrogen oxygen sensor chip into a muffle furnace, set the muffle furnace sintering temperature to 1100°C, and the sintering time to 3 h.

[0044] Example 5 An embodiment of the present invention provides a method for preparing a nitrogen oxygen sensor, comprising the following steps: (1) Weigh 5 g of spinel powder with a particle size of 30 μm, 2.5 g of alumina powder with a particle size of 0.3 μm, and 4.46 g of calcium carbonate powder, and add them into a ball mill; (2) Weigh 0.36 g of polymethyl methacrylate with a particle size of 3 μm, 2 g of silica sol, 0.5 g of triethylhexyl phosphate, 0.5 g of polydimethylsiloxane, and 0.93 g of glycerol, and add them to a ball mill; (3) Weigh 20 g of zirconium oxide beads and add them to the ball mill; (4) Setting the rotation speed of the planetary ball mill to 500 r / min and the ball milling time to 40 min, thereby obtaining a slurry for forming a water-resistant protective layer of a nitrogen oxide sensor; (5) Dip-coating the slurry onto the designated area at the end of the nitrogen oxide sensor chip by dipping and pulling, wherein the pulling speed is 0.2 mm / s; (6) Place the dip-coated nitrogen oxygen sensor chip into a drying oven, set the oven temperature to 70°C, and dry for 1 hour; (7) Place the dried nitrogen oxygen sensor chip into a muffle furnace, set the muffle furnace sintering temperature to 1100°C, and the sintering time to 3 h.

[0045] Comparative Example 1 (1) Weigh 10 g of spinel powder with a particle size of 30 μm and add it to a ball mill; (2) Weigh 0.6 g of polymethyl methacrylate with a particle size of 3 μm, 2 g of silica sol, 0.5 g of triethylhexyl phosphate, 0.5 g of polydimethylsiloxane, and 0.93 g of glycerol, and add them to a ball mill; (3) Weigh 20 g of zirconium oxide beads and add them to the ball mill; (4) Setting the rotation speed of the planetary ball mill to 500 r / min and the ball milling time to 40 min, thereby obtaining a slurry for forming a water-resistant protective layer of a nitrogen oxide sensor; (5) Dip-coating the slurry onto the designated area at the end of the nitrogen oxide sensor chip by dipping and pulling, wherein the pulling speed is 0.2 mm / s; (6) Place the dip-coated nitrogen oxygen sensor chip into a drying oven, set the oven temperature to 70°C, and dry for 1 hour; (7) Place the dried nitrogen oxygen sensor chip into a muffle furnace, set the muffle furnace sintering temperature to 1100°C, and the sintering time to 3 h.

[0046] The prepared water-resistant protective layer of the nitrogen and oxygen sensor was characterized accordingly, such as Figure 6 As shown, it can be seen that there is only a pore-like structure but no flower-like structure on the surface.

[0047] Comparative Example 2 (1) Weigh 5 g of spinel powder with a particle size of 10 μm, 2.5 g of alumina powder with a particle size of 2 μm, and 4.46 g of calcium carbonate powder, and add them into a ball mill; (2) Weigh 0.6 g of polymethyl methacrylate with a particle size of 3 μm, 2 g of silica sol, 0.5 g of triethylhexyl phosphate, 0.5 g of polydimethylsiloxane, and 0.93 g of glycerol, and add them to a ball mill; (3) Weigh 20 g of zirconium oxide beads and add them to the ball mill; (4) Setting the rotation speed of the planetary ball mill to 500 r / min and the ball milling time to 40 min, thereby obtaining a slurry for forming a water-resistant protective layer of a nitrogen oxide sensor; (5) Dip-coating the slurry onto the designated area at the end of the nitrogen oxide sensor chip by dipping and pulling, wherein the pulling speed is 0.2 mm / s; (6) Place the dip-coated nitrogen oxygen sensor chip into a drying oven, set the oven temperature to 70°C, and dry for 1 hour; (7) Place the dried nitrogen oxygen sensor chip into a muffle furnace, set the muffle furnace sintering temperature to 1100°C, and the sintering time to 3 h.

[0048] Comparative Example 3 An embodiment of the present invention provides a method for preparing a nitrogen oxygen sensor, comprising the following steps: (1) Weigh 5 g of spinel powder with a particle size of 30 μm, 2.5 g of alumina powder with a particle size of 0.3 μm, and 4.46 g of calcium carbonate powder, and add them into a ball mill; (2) Weigh 0.84 g of polymethyl methacrylate with a particle size of 3 μm, 2 g of silica sol, 0.5 g of triethylhexyl phosphate, 0.5 g of polydimethylsiloxane, and 0.93 g of glycerol, and add them to a ball mill; (3) Weigh 20 g of zirconium oxide beads and add them to the ball mill; (4) Setting the rotation speed of the planetary ball mill to 500 r / min and the ball milling time to 40 min, thereby obtaining a slurry for forming a water-resistant protective layer of a nitrogen oxide sensor; (5) Dip-coating the slurry onto the designated area at the end of the nitrogen oxide sensor chip by dipping and pulling, wherein the pulling speed is 0.2 mm / s; (6) Place the dip-coated nitrogen oxygen sensor chip into a drying oven, set the oven temperature to 70°C, and dry for 1 hour; (7) Place the dried nitrogen oxygen sensor chip into a muffle furnace, set the muffle furnace sintering temperature to 1100°C, and the sintering time to 3 h.

[0049] Comparative Example 4 An embodiment of the present invention provides a method for preparing a nitrogen oxygen sensor, comprising the following steps: (1) Weigh 5 g of spinel powder with a particle size of 30 μm, 2.5 g of alumina powder with a particle size of 0.3 μm, and 4.46 g of calcium carbonate powder, and add them into a ball mill; (2) Weigh 1.08 g of polymethyl methacrylate with a particle size of 3 μm, 2 g of silica sol, 0.5 g of triethylhexyl phosphate, 0.5 g of polydimethylsiloxane, and 0.93 g of glycerol, and add them to a ball mill; (3) Weigh 20 g of zirconium oxide beads and add them to the ball mill; (4) Setting the rotation speed of the planetary ball mill to 500 r / min and the ball milling time to 40 min, thereby obtaining a slurry for forming a water-resistant protective layer of a nitrogen oxide sensor; (5) Dip-coating the slurry onto the designated area at the end of the nitrogen oxide sensor chip by dipping and pulling, wherein the pulling speed is 0.2 mm / s; (6) Place the dip-coated nitrogen oxygen sensor chip into a drying oven, set the oven temperature to 70°C, and dry for 1 hour; (7) Place the dried nitrogen oxygen sensor chip into a muffle furnace, set the muffle furnace sintering temperature to 1100°C, and the sintering time to 3 h.

[0050] Comparative Example 5 This comparative example is a nitrogen oxygen sensor without adding a water-resistant protective layer.

[0051] Test Case For the water-resistant protective layers of the nitrogen oxide sensors obtained in Examples 1 to 5 and Comparative Examples 1 to 5, limiting current influence experiments were respectively carried out.

[0052] First, the heating part of the nitrogen oxide sensor before obtaining the water-resistant protective layer is energized to heat the sensor to 840°C. On this basis, a main pump voltage of 1000mV is applied in the atmospheric atmosphere to obtain the main pump current. The same test is performed on the nitrogen oxide sensor after obtaining the water-resistant protective layer, and the influence of the limiting current is judged based on the change in the main pump current before and after applying the water-resistant protective layer.

[0053] For the water-resistant protective layer of the nitrogen oxygen sensor obtained in the embodiment and the comparative example, the proportion of the flower-like structure was calculated based on the cross-sectional SEM image.

[0054] The water-resistant protective layers of the nitrogen oxygen sensors obtained in the examples and comparative examples were visually checked for cracks and peeling (peeling).

[0055] Water immersion resistance tests were performed on the water-resistant protective layers of the nitrogen oxygen sensors obtained in the embodiment and the comparative example.

[0056] Specifically, first, the heating part of the nitrogen oxide sensor is energized to heat the sensor to 840°C. On this basis, in the atmospheric atmosphere, each pump unit of the sensor is operated normally and the main pump current Ip0 reaches a stable state.

[0057] Then, in this state, a predetermined amount of water is dripped onto the sensor heating part to check whether the pump current change exceeds the threshold before and after the water drop is added. If the pump current change does not exceed the threshold, water drops are continued to be dripped and the pump current confirmation is repeated. The dripping amount at which the pump current Ip0 changes beyond the threshold is defined as the limit water immersion amount, and the thermal shock resistance of the protective layer is determined by this.

[0058] Table 2 shows the evaluation results of the flower-like structure ratio of the water-resistant protective layer of the nitrogen oxygen sensor in the embodiments and comparative examples, cracks and peeling of the protective layer, limiting current influence, and limiting water immersion amount.

[0059] Table 2 Sample No. Flower-like structure ratio Cracking and peeling Limiting current effect Water resistance Example 1 50% none ◎ ◎ Example 2 46% none ◎ ◎ Example 3 41% none ○ ○ Example 4 56% none ○ ○ Example 5 44% none ○ ○ Comparative Example 1 0 have × × Comparative Example 2 0 none × × Comparative Example 3 37% have × × Comparative Example 4 31% have × × Comparative Example 5 0 - - × It should be noted that in the column "Limiting current influence" in Table 1, samples judged to have a limiting current drop of 10% or less are marked with "◎". Samples judged to have a limiting current drop of 10% or more and less than 30% are marked with "○". Samples judged to have a limiting current drop of 30% or more are marked with "×".

[0060] In the "Water Intrusion Resistance" column of Table 1, samples with a water intrusion limit of 30 μl or more are marked with "◎". Samples with a water intrusion limit of 15 μl or more and less than 30 μl are marked with "○". Samples with a water intrusion limit of less than 15 μl are marked with "×".

[0061] It can be seen from Comparative Example 1 that the flower-like structure of the present application cannot be obtained by using only spinel raw materials, and the performance of the obtained coating is poor.

[0062] It can be seen from Comparative Example 2 that when the particle size of spinel is too small and the particle size of alumina is too large, the flower-like structure of the present application cannot be formed. Although the combination of the three components improves the problem of coating cracking, its water resistance is still very poor.

[0063] It can be seen from Comparative Examples 3 and 4 that as the content of the pore-forming agent increases, the limiting current and water resistance of the water-resistant protective layer are greatly affected.

[0064] The specific implementation methods described above further illustrate the objectives, 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.

Claims

1. A water-resistant protective layer for a nitrogen and oxygen sensor, characterized in that: The composition comprises the following components by mass fraction: 100 parts of protective layer powder, 1-6 parts of pore former, 10-20 parts of binder, 0.5-5 parts of dispersant, 0.5-5 parts of defoamer and 10-20 parts of solvent; The protective layer powder includes 40-60 parts of spinel powder, 20-40 parts of aluminum oxide powder, and 20-40 parts of calcium carbonate powder.

2. The water-resistant protective layer for a nitrogen oxygen sensor according to claim 1, characterized in that: The particle size of the spinel powder is 20-40 μm, and the particle size of the alumina powder is 0.05-1 μm.

3. The water-resistant protective layer for a nitrogen oxygen sensor according to claim 1, characterized in that: The pore-forming agent is one or more of carbon black powder, polymethyl methacrylate, and polyethylene; the binder is one or more of alumina sol, silica sol, and titanium dioxide sol; and the dispersant is one or more of triethylhexyl phosphate and sodium tripolyphosphate.

4. The water-resistant protective layer for a nitrogen oxygen sensor according to claim 1, characterized in that: The defoaming agent is one or more of polydimethylsiloxane and ethylene oxide; the solvent is one or a mixture of deionized water, ethanol and glycerol.

5. The method for preparing the water-resistant protective layer of the nitrogen oxygen sensor according to any one of claims 1 to 4, characterized in that: Here are the steps: After the spinel powder, alumina powder and calcium carbonate powder are uniformly mixed, a pore former, a binder, a dispersant, a defoamer and a solvent are added and mixed in a ball mill to obtain a protective layer slurry.

6. The method for preparing a water-resistant protective layer for a nitrogen oxygen sensor according to claim 5, characterized in that: The viscosity of the protective layer slurry is 500-10000 mPa·s.

7. A nitrogen oxygen sensor, characterized in that: It comprises a nitrogen oxygen sensor chip, the end of which is coated externally with the nitrogen oxygen sensor water-resistant protective layer according to any one of claims 1 to 4 or the nitrogen oxygen sensor water-resistant protective layer slurry prepared by the preparation method according to claim 5 or 6.

8. A nitrogen oxygen sensor according to claim 7, characterized in that: The coating thickness of the water-resistant protective layer is 100~500μm.

9. The method for preparing a nitrogen oxygen sensor according to claim 7 or 8, characterized in that: The steps include: 1) vertically placing the nitrogen oxygen sensor chip into the protective layer slurry according to claim 5, so that the end of the nitrogen oxygen sensor chip is immersed in the protective layer slurry and is completely covered by the slurry; 2) After being immersed for a certain period of time, the nitrogen oxygen sensor chip is pulled upward to complete the immersion, and then dried, and finally the nitrogen oxygen sensor chip is baked to obtain the nitrogen oxygen sensor.

10. The method for preparing a nitrogen oxygen sensor according to claim 9, characterized in that: In step 2), the pulling speed is 0.1~5mm / s, and the drying temperature is 50~200°C; the sintering temperature of the coated nitrogen oxygen sensor chip is 900~1300°C, and the sintering time is 0.5~5 h.

Images