CN117405741A - Gas sensor element and preparation method thereof - Google Patents

Abstract

The application discloses a gas sensor element comprising a ceramic sensitive chip, an alumina substrate and a TSP coating; printing the aluminum oxide substrate on the upper and lower surfaces of the ceramic sensitive chip, and printing the aluminum oxide substrate on the left and right side surfaces after the ceramic sensitive chip is cut; a single-layer TSP coating is arranged outside the alumina substrate layer. The application adopts the silk-screen basal layer and then impregnates the single-layer coating, so that the problem of lower bonding strength between the coating and the matrix existing in the impregnation process can be solved; and the single-layer structure slurry has the same components and the same shrinkage of the inner side and the outer side, avoids the risk of sensor precision reduction caused by interlayer cracking and outer layer peeling of a two-layer or three-layer structure due to the difference of material thermal expansion rate, and finally has good water resistance and air permeability, the drip test can reach more than 20 mu L, meets the use requirement, and is suitable for mass production.

Description

Gas sensor element and preparation method thereof

Technical Field

The application relates to a gas sensor element and a preparation method thereof, and belongs to the technical field of gas sensors.

Background

When the gas sensor is used, the temperature in the exhaust pipe is lower than the dew point of water within a period of time just after the engine is started, water vapor generated by fuel combustion can be condensed into water drops in the exhaust pipe, and the water drops are attached to the surface of the ceramic sensitive chip to cause thermal stress to cause cracking of the ceramic sensitive chip. Therefore, a TSP coating (Thermal Shock Protection Layer, TSP thermal shock protection) can be provided at the entire detection position of the chip operation to suppress cracking of the chip due to thermal shock caused by local temperature reduction caused by water immersion; and simultaneously, toxic substances such as Mg and the like can be prevented from invading the inside of the chip. However, if the TSP coating is unreasonably arranged, the chip temperature rise is affected to be slow, and the heat activation time is prolonged; in addition, there is a thermal expansion difference between the TSP coating and the chip, and the TSP coating is easy to flake off from the chip due to vibration generated in the environment during high-temperature use, and also has to ensure good bonding strength with the chip substrate.

At present, the structure of the TSP coating is mainly two layers or more than two layers, and the manufacturing process is mainly two types: plasma spraying and dipping.

As in the case of CN 113597552A and CN 113614523A, each of the three layers is a three-layer structure, the first layer is provided with only two main surfaces, the second and third layers are plasma sprayed, and in the case of CN 113597552a, peeling of the coating is suppressed by mainly providing the first layer with two main surfaces longer than the second and third layers. However, it was found through practical experiments that the first layer was provided only on 2 principal surfaces as an adhesion layer for connecting the substrate and the TSP coating layer, and the bonding strength was insufficient. Because the contact area of the coating with 2 side surfaces and the front end surface is far smaller than that with 2 main surfaces, the coating at the side surfaces and the front end is easier to peel off from the matrix at first, and finally the whole coating is dropped in a lump, so that the product is invalid.

In the patent CN 113614523a, the ratio of the porosity to the thickness of the inner layer and the outer layer is changed to ensure rapid temperature rise and maintain the overall strength of the coating so as to inhibit water penetration. In practice, plasma spraying is to spray a jet nozzle with a high speed to form a TSP coating by spraying a flame stream of 12000-16000 ℃ to melt the material at a high temperature to a semi-molten or molten state onto the substrate surface. In experiments, the porosity of the ceramic material in a molten state is generally lower than about 3-10%, the ceramic material is difficult to be improved to more than 15%, the temperature rising speed of a chip is seriously influenced after plasma spraying, and the starting time is prolonged by more than one time; the inner layer porosity mentioned in the patent is difficult to control to 50-70%, and the measure of pore-forming by adding pore-forming material into the hot coating is also difficult to realize, and the pore-forming agent is vaporized before reaching the matrix at high temperature of over ten thousand ℃; the deposition rate of the powder on the chip is low when spraying, and only a few microns or more than ten microns can be sprayed at each time, so that the powder utilization rate is low and the waste is large; after each spraying, the spraying is carried out after waiting for cooling, and the spraying is repeated for a plurality of times to reach the thickness of 800-1000 mu m expected in the patent; in experiments, the hidden microcracks are easily generated in the zirconia matrix by adopting roughening treatment such as sand blasting and the like before spraying and rapid cooling and rapid heating in the spraying process. The plasma spraying process equipment is expensive, the process is complex, and the strength of the matrix is easy to be secondarily damaged. Gradually replaced by a dipping method with simple process and low cost.

As another example, patent documents CN112739665A and CN 112752738A propose to impregnate a two-layer structure by an impregnation process, and to improve the water resistance by defining the porosity and the particle size ratio of the inner and outer sides of the coating layer. The inner side has a porosity of 30-85% (preferably 60-70%) and is larger than the outer side, a large number of projections having a size of 1.0 μm or less and composed of ceramic fine particles having a particle size of 10nm to 1.0 μm or less are formed around a large number of ceramic fine particles having a particle size of 5.0 μm to 40 μm on the outer side in a dispersed manner, and the ceramic fine particles are connected directly or via the ceramic fine particles to form a coating structure having a porosity of 5-50%, and the weight ratio of coarse particles to fine particles is 3-35. Experiments on examples show that the higher the porosity of the inner side, the more pores the smaller the contact area with the substrate, the poorer the bonding strength, and the coating is liable to peel off from the substrate in large scale. And the outside ceramic coarse grain size particle diameter is large, the addition amount is more, ceramic particles are few, the sintering densification is difficult, or the sintering temperature is higher, the particles are difficult to completely wrap and connect coarse grains, if 50 nanometer-sized particles in the embodiment are adopted for impregnation, then the particles are easy to crack during drying and solidification, and the lotus effect with high water repellency is difficult to form. In addition, the coating is of a two-layer structure, the inner layer and the outer layer are respectively made of different materials and have different porosities, the shrinkage of the two different slurries is asynchronous in the drying process and the sintering process, the layers and the layers are easily cracked or the outer layers are easily cracked, and the cracking and the peeling of the outer layers occur in the use process of long-term temperature rise and temperature reduction of the gas sensor, so that the risk of the reduction of the test precision of the sensor is caused.

Disclosure of Invention

In order to solve the problems, the application provides a gas sensor element and a preparation method thereof, wherein a single-layer coating is adopted after a basal layer is silk-screened, so that the problem that the bonding strength between the coating and a matrix is lower in the common dipping process can be solved; and the single-layer structure slurry has the same components and the same shrinkage of the inner side and the outer side, avoids the risk of sensor precision reduction caused by interlayer cracking and outer layer peeling of a two-layer or three-layer structure due to the difference of material thermal expansion rate, and finally has good water resistance and air permeability, the drip test can reach more than 20 mu L, meets the use requirement, and is suitable for mass production.

According to one aspect of the present application, there is provided a gas sensor element comprising a ceramic sensitive chip, an alumina substrate and a TSP coating;

the alumina substrate is printed on the upper surface and the lower surface of the ceramic sensitive chip, and the alumina substrate is printed on the left side surface and the right side surface of the cut ceramic sensitive chip; a single-layer TSP coating is arranged outside the alumina substrate layer; the thickness of the alumina substrate layer is 20-40 mu m, and the porosity is 30-50%.

Specifically, the alumina slurry is prepared by mixing alumina powder with an organic carrier, ball milling and three rollers, wherein the solid content is controlled to be 50-60%, and the ink slurry suitable for screen printing is prepared, and the organic carrier is ethyl cellulose solution.

Optionally, the roughness of the alumina substrate layer is 10-20 μm.

Optionally, the TSP coating has a thickness of 800-1000 μm, a porosity of 24-45% and an average pore size of 0.5-5.0 μm.

Alternatively, the TSP coating is obtained after sintering from a composite slurry comprising ceramic coarse powder and ceramic fine powder.

Optionally, the grain size of the ceramic coarse powder is 2-10 μm, the grain size of the ceramic fine powder is 0.02-0.8 μm, and the weight ratio of the ceramic coarse powder to the ceramic fine powder is (1-4): 1.

optionally, the composite slurry further comprises a high temperature binder, an organic binder, a pore-forming agent, a dispersant, and a solvent.

Specifically, the composite slurry comprises, by weight, 20-40 parts of ceramic coarse powder, 10-30 parts of ceramic fine powder, 2-8 parts of high-temperature binder, 1-6 parts of organic binder, 6-20 parts of pore-forming agent, 0.5-3 parts of dispersing agent and 30-50 parts of solvent.

Optionally, the ceramic coarse powder is one or more of alumina, magnesia-alumina spinel, mullite and the like;

the ceramic fine powder is one or more of zirconia, alumina, titania, silica, magnesia and the like.

Optionally, the high-temperature binder is one or more of silicon oxide, aluminum oxide, bismuth oxide and zinc oxide, the organic binder is one or more of acrylic acid and polyvinyl alcohol, the pore-forming agent is one or more of carbon powder, starch and organic resin balls, the dispersing agent is one of ammonium polycarboxylate and ammonium polyacrylate, and the solvent is one or more of water, ethanol and isopropanol; the viscosity of the composite slurry is 500-3000 mPa.s.

According to still another aspect of the present application, there is provided a method for manufacturing a gas sensor element as described above, characterized by comprising the steps of:

(1) Firstly, printing alumina slurry on the upper and lower surfaces of a ceramic sensitive chip, then printing the alumina slurry on the left and right side surfaces of the cut ceramic sensitive chip, and carrying out high-temperature sintering with the ceramic sensitive chip at 1350-1500 ℃ for 2-6 hours to form the ceramic sensitive chip attached with the alumina substrate;

(2) The tail end of the ceramic sensitive chip is clamped by a tool and rotated, the detection part at the front end of the ceramic sensitive chip is vertically immersed into the composite slurry, the ceramic sensitive chip is immediately lifted up after reaching the preset coating length position (11-13 mm), the superfluous composite slurry is thrown away, the coating is dried and solidified, and the impregnation is repeated once after the first impregnation is completed;

(3) After the impregnation of the TSP coating is finished, the sintering cooling is carried out for 1 to 3 hours at the temperature of 1000 to 1200 ℃ to obtain the high-temperature-resistant ceramic material.

Optionally, the total thickness of the first dip coating layer in the step (2) is 400-500 μm, and the final total thickness is controlled to be 800-1000 μm after repeating the step.

Benefits that can be produced by the present application include, but are not limited to:

1. the gas sensor element provided by the application can improve the surface roughness of a substrate to 10-20 mu m by adjusting slurry, can realize mutual osmosis occlusion between the substrate and the TSP coating in all directions, has good bonding strength between an alumina substrate and a ceramic matrix and between the alumina substrate and the TSP coating, is not easy to crack and peel off, and has good waterproof and air permeability.

2. According to the gas sensor element, the porosity of the alumina substrate and the porosity of the TSP coating are controlled, so that on one hand, the sensing performance of the element can be improved, and the adsorption and detection of gas molecules are facilitated; on the other hand, the pore structure of the TSP coating forms a tiny channel in the coating, so that the air permeability is ensured, the waterproof performance is improved, and the element can still work normally in a wet environment.

3. According to the gas sensor element, the ceramic coarse powder and the fine powder are adopted and the proportion is limited, so that the coarse powder plays a role in a framework in a coating, the thermal shock resistance is good, the fine powder plays a role in bonding in the coating, good adhesion is guaranteed, meanwhile, the phenomenon that the coating is easily peeled off from a ceramic matrix in the long-term vibration use process can be avoided under the proportion, if the coarse powder is more, the fine powder is less or the fine powder is larger in size, the bonding performance of bonding the coarse powder with each other cannot be fully exerted, the coating structure is too loose and waterproof, the coating structure is poor, if the fine powder is too much, the serous membrane is easy to shrink and crack after dipping and drying, other surface defects such as foaming, pinholes, volcanic pits and the like can also appear, and the product percent of pass is greatly reduced due to poor control of the production process.

4. According to the gas sensor element, the high-temperature binder is added and the addition amount is limited, the sintering temperature can be reduced by generating the liquid phase during melting, ceramic solid particles are mutually bonded to form a whole, the internal strength of the coating is higher, the adhesion with a substrate is further improved, and the bonding strength and the waterproof performance of the coating are finally improved.

5. According to the preparation method of the gas sensor element, the alumina substrate is presintered and the composite slurry is subjected to multiple dipping processes, so that uniformity of thickness of the surface and thickness of the side surface of the coating can be realized, scraping or grinding of tools or sand paper for each layer of coating is not needed, the height difference of the film thickness can be controlled within 0.05mm, and microcracks generated by inconsistent shrinkage of the coating in a drying process and a firing process due to uneven thickness are prevented; and a smooth boundary layer is formed on the surface of the coating after each impregnation, drying and curing process is carried out, the boundary layer between layers is slightly denser than the porous layer inside, and the heat insulation and the water resistance of the coating can be further improved.

Drawings

The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the application and do not constitute an undue limitation to the application. In the drawings:

FIG. 1 is a photograph of the appearance of an alumina substrate layer of example 1 of the present application;

FIG. 2 is a SEM crystalline phase photograph of an alumina substrate layer of example 1 of the present application;

FIG. 3 is an SEM crystalline phase photograph of a TSP coating of example 1 of the present application;

FIG. 4 is a cross-sectional SEM photograph of the combination of the TSP coating and alumina substrate of example 1 of the present application (platinum electrode between the ceramic chip and alumina substrate);

FIG. 5 is a schematic cross-sectional view of a gas sensor element of the present application in the width direction;

fig. 6 is a schematic cross-sectional structure of a gas sensor element of the present application along the length direction.

Reference numerals: tsp coating; 2. an alumina-based substrate; 3. ceramic sensitive chips.

Detailed Description

The present application is described in detail below with reference to examples, but the present application is not limited to these examples.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The reagents or materials used in the present invention may be purchased in conventional manners, and unless otherwise indicated, they may be used in conventional manners in the art or according to the product specifications. In addition, any methods and materials similar or equivalent to those described herein can be used in the methods of the present invention. The preferred methods and materials described in this patent are illustrative only.

In addition, the total thickness of the first dip coating layer in step (2) of the present application is 400-500 μm, and the total thickness of the upper and lower surfaces is referred to as the sum of the thicknesses of the two layers d1+d2 in fig. 5 and 6, and since fig. 5 and 6 are both diagrams of the final product, the condition after the first dip is not exhibited, d1+d2 after the first dip is 400-500 μm, and the final total thickness after repeating once is controlled to 800-1000 μm, that is, d1+d2 in fig. 5 and 6 of the present application is 800-1000 μm.

D3 and d4 in fig. 5 and 6 are both 10-20 μm, and for better embodying the relationship of the layers in the figures, the dimensional scale in the figures of the present application is not true, but is only referred to as a reference.

Example 1

The gas sensor element comprises a ceramic sensitive chip 3, an alumina substrate 2 and a TSP coating 1; the alumina substrate 2 is printed on the upper surface and the lower surface of the ceramic sensitive chip 3, and the alumina substrate 2 is printed on the left side surface and the right side surface after the ceramic sensitive chip 3 is cut; the TSP coating 1 is disposed outside the alumina substrate 2.

The thickness of the alumina substrate layer 2 is 30 mu m, and the porosity is 40%; the roughness of the alumina substrate layer 2 was 14 μm. The TSP coating 1 had a thickness of 950 μm, a porosity of 35% and an average pore size of 2. Mu.m. The TSP coating 1 is obtained by sintering composite slurry, and the composite slurry comprises, by weight, 30 parts of ceramic coarse powder, 15 parts of ceramic fine powder, 5 parts of high-temperature binder, 4 parts of organic binder, 10 parts of pore-forming agent, 1 part of dispersing agent and 35 parts of solvent.

The grain size of the ceramic coarse powder is 5 mu m, the grain size of the ceramic fine powder is 0.3 mu m, and the weight ratio of the ceramic coarse powder to the ceramic fine powder is 2:1. the ceramic coarse powder is alumina, and the ceramic fine powder is zirconia. The high-temperature binder is silicon oxide, the organic binder is acrylic acid, the pore-forming agent is organic resin spheres, the dispersing agent is ammonium polycarboxylate, and the solvent is ethanol; the viscosity of the composite slurry was 2000 mPas.

The preparation method comprises the following steps:

(1) Firstly, printing alumina slurry on the upper surface and the lower surface of a ceramic sensitive chip 3, printing the alumina slurry on the left side surface and the right side surface after the ceramic sensitive chip 3 is cut, and carrying out high-temperature sintering with the ceramic sensitive chip 3 at 1400 ℃ for 2.5 hours to form the ceramic sensitive chip 3 attached with the alumina substrate 2;

(2) The tail end of the ceramic sensitive chip 3 is clamped by a tool, the tail end of the ceramic sensitive chip 3 rotates, the detection part at the front end of the ceramic sensitive chip 3 is vertically immersed into the composite slurry, the ceramic sensitive chip is immediately lifted up after reaching the preset coating length position (12 mm), the superfluous composite slurry is thrown away, the coating is dried and solidified, and the impregnation is repeated once after the first impregnation is completed;

(3) After the impregnation of the TSP coating 1 is completed, the temperature is kept at 1100 ℃ for 2 hours, and the product is obtained after sintering and cooling.

Wherein, the total thickness of the first dip coating layer in the step (2) is 450 mu m, and the final total thickness is controlled to be 950 mu m after repeating the steps once.

Example 2

The gas sensor element comprises a ceramic sensitive chip 3, an alumina substrate 2 and a TSP coating 1; the aluminum oxide substrate 2 is printed on the upper surface and the lower surface of the ceramic sensitive chip 3, and the aluminum oxide substrate 2 is printed on the left side surface and the right side surface of the cut ceramic sensitive chip 3; the TSP coating 1 is disposed outside the alumina substrate 2.

The alumina substrate layer 2 has a thickness of 40 μm and a porosity of 50%; the roughness of the alumina substrate layer 2 was 20 μm. The TSP coating 1 had a thickness of 800 μm, a porosity of 24% and an average pore size of 1. Mu.m. The TSP coating 1 is obtained by sintering composite slurry, and the composite slurry comprises, by weight, 20 parts of ceramic coarse powder, 20 parts of ceramic fine powder, 3 parts of high-temperature binder, 6 parts of organic binder, 8 parts of pore-forming agent, 3 parts of dispersing agent and 40 parts of solvent.

The grain diameter of the ceramic coarse powder is 3 mu m, the grain diameter of the ceramic fine powder is 0.1 mu m, and the weight ratio of the ceramic coarse powder to the ceramic fine powder is 1:1. the ceramic coarse powder is alumina, and the ceramic fine powder is alumina. The high-temperature binder is silicon oxide, the organic binder is acrylic acid, the pore-forming agent is carbon powder, the dispersing agent is ammonium polycarboxylate, and the solvent is ethanol; the viscosity of the composite slurry was 1000 mPas.

The preparation method comprises the following steps:

(1) Firstly, printing alumina slurry on the upper surface and the lower surface of a ceramic sensitive chip 3, cutting the ceramic sensitive chip 3, then printing the alumina slurry on the left side surface and the right side surface, and carrying out high-temperature sintering with the ceramic sensitive chip 3 at 1350 ℃ for 5 hours to form the ceramic sensitive chip 3 attached with the alumina substrate 2;

(2) The tail end of the ceramic sensitive chip 3 is clamped by a tool, the tail end of the ceramic sensitive chip 3 rotates and is vertically immersed into the composite slurry, the ceramic sensitive chip 3 is immediately lifted up after reaching a preset coating length position (11 mm), superfluous composite slurry is thrown away, the coating is dried and solidified, and the impregnation is repeated once after the first impregnation is completed;

(3) After the impregnation of the TSP coating 1 is completed, the temperature is kept at 1000 ℃ for 3 hours, and the product is obtained after sintering and cooling.

Wherein, the total thickness of the first dip coating layer in the step (2) is 400 mu m, and the final total thickness is controlled to be 800 mu m after repeating the step.

Example 3

The gas sensor element comprises a ceramic sensitive chip 3, an alumina substrate 2 and a TSP coating 1; the alumina substrate 2 is printed on the upper surface and the lower surface of the ceramic sensitive chip 3, and the alumina substrate 2 is printed on the left side surface and the right side surface after the ceramic sensitive chip 3 is cut; the TSP coating 1 is disposed outside the alumina substrate 2.

The thickness of the alumina substrate layer 2 is 20 mu m, and the porosity is 30%; the roughness of the alumina substrate layer 2 was 10 μm. The TSP coating 1 had a thickness of 1000 μm, a porosity of 45% and an average pore size of 5.0. Mu.m. The TSP coating 1 is obtained by sintering composite slurry, and the composite slurry comprises 40 parts of ceramic coarse powder, 8 parts of ceramic fine powder, 7 parts of high-temperature binder, 2 parts of organic binder, 12 parts of pore-forming agent, 1 part of dispersing agent and 30 parts of solvent in parts by weight.

The grain diameter of the ceramic coarse powder is 10 mu m, the grain diameter of the ceramic fine powder is 0.7 mu m, and the weight ratio of the ceramic coarse powder to the ceramic fine powder is 5:1. the coarse ceramic powder is magnesia-alumina spinel, and the fine ceramic powder is titanium oxide. The high-temperature binder is alumina, the organic binder is polyvinyl alcohol, the pore-forming agent is organic resin spheres, the dispersing agent is ammonium polycarboxylate, and the solvent is water; the viscosity of the composite slurry was 3000 mPas.

The preparation method comprises the following steps:

(1) Firstly, printing alumina slurry on the upper surface and the lower surface of a ceramic sensitive chip 3, printing the alumina slurry on the left side surface and the right side surface after the ceramic sensitive chip 3 is cut, and carrying out high-temperature sintering with the ceramic sensitive chip 3 at 1500 ℃ for 1.5 hours to form the ceramic sensitive chip 3 attached with the alumina substrate 2;

(2) The tail end of the ceramic sensitive chip 3 is clamped by a tool, the tail end of the ceramic sensitive chip 3 rotates, the detection part at the front end of the ceramic sensitive chip 3 is vertically immersed into the composite slurry, the ceramic sensitive chip is immediately lifted up after reaching a preset coating length position (13 mm), superfluous composite slurry is thrown away, the coating is dried and solidified, and the impregnation is repeated once after the first impregnation is completed;

(3) After the impregnation of the TSP coating 1 is completed, the TSP coating is obtained after heat preservation for 1h at 1200 ℃ and sintering and cooling.

Wherein, the total thickness of the first dip coating layer in the step (2) is 500 mu m, and the final total thickness is controlled to be 1000 mu m after repeating the step.

Example 4

Example 4 differs from example 1 in that: the weight ratio of ceramic coarse powder to ceramic fine powder in example 4 was 3:1.

example 5

Example 5 differs from example 1 in that: the weight ratio of ceramic coarse powder to ceramic fine powder in example 5 was 1:2.

comparative example 1

Comparative example 1 differs from example 1 in that: the alumina base layer of comparative example 1 was provided on only the upper and lower main surfaces.

Comparative example 2

Comparative example 2 differs from example 1 in that: the alumina substrate of comparative example 2 was provided on only the upper and lower main surfaces, and had a two-layer structure, with an inner layer having a high porosity of 60% and an outer layer having a low porosity of 20%.

Comparative example 3

Comparative example 3 differs from example 1 in that: comparative example 3 simulates the example in experimental publication CN112739665 a. Adjusting the ratio of coarse powder and fine powder, and coarse particles (the average particle size of alumina is 6 μm) of the inner slurry: microparticle (titanium dioxide average particle diameter of 0.25 μm) =1: 1, a step of; outer layer slurry coarse particles (spinel average particle size 20 μm): fine particles (average particle diameter of magnesium oxide is 0.05 μm) =20: 1.

comparative example 4

Comparative example 4 differs from example 1 in that: the alumina substrate was provided on only the upper and lower main surfaces, and in comparative example 4, a plasma spraying process was used, a dipping process was not used, only ceramic coarse powder was used, the porosity was 15%, and the coating thickness was 700. Mu.m.

Comparative example 5

Comparative example 5 differs from example 1 in that: the amount of the high-temperature adhesive added in comparative example 5 was 10 parts.

Experimental example

1. Test method

(1) The immersion resistance test method comprises the following steps: the water repellency of the TSP coating was evaluated on a drip test apparatus. Test conditions: the ceramic sensitive chip was heated to 780℃and was aligned with the front (pump electrode face) and side 4.5mm positions of the chip by dPette electronic pipettor (specification 0.5-10. Mu.L), and water was dropped 0.5. Mu.L each time for 10 seconds, and the total amount of water dropped when IP0 was suddenly increased was read as a criterion for judging whether cracking occurred in the ceramic chip when the pump current IP0 was suddenly increased. (when the ceramic sensitive chip cracks due to thermal shock caused by water droplets when they are in the TSP protective coating, oxygen flows into the inner first main chamber through the cracked portion, and the value of the pump current Ip0 becomes large.)

Drop volume = 0.5 μl, drip mode: probe pipetting, time interval > 10s, ceramic core temperature=780 ℃, finally reading total water tolerance (μl) occurring when IP0 increases rapidly.

(2) The high-temperature vibration test method comprises the following steps: the binding strength of the TSP coating was evaluated. The sensor with TSP coating was placed on a high temperature vibrating device consisting of a vibrator connected to a propane gas burner. Exposing the sensor to temperature and vibration curves, frequency: a.50. 100. 250Hz is set at a frequency of 150, acceleration: 30 g..40 g..50G., vibration scan period: 30 minutes/scan period; gas temperature: at 850 ℃ (combustion gas λ set to 1.05); test time: 150h; vibration direction: up and down vibration (sensor direction is not fixed). After vibration is completed, an industrial CT machine is used for scanning whether each part of the TSP coating is dropped or cracked.

(3) The air permeability evaluation method comprises the following steps: the gas permeability of the coating was evaluated by testing whether the IP0 current was reduced and the start-up time was extended before and after the ceramic sensitive chip was immersed in the TSP coating. The ceramic sensitive chip was heated from room temperature to 780 ℃ at the operating temperature, and the IP0 pump current between the first pump oxygen electrode and the external electrode in air was measured to see if the ceramic sensitive chip affected the air intake and pump oxygen capabilities after the TSP coating was added. Start time: and testing the time from the start of power-on (the start of dew point arrival) to the output of a stable signal during normal operation of the sensor by the sensor control unit, and judging whether the rapid heating capacity of the ceramic sensitive chip is affected after the TSP coating is added.

(4) The thermal shock resistance testing method comprises the following steps: the ceramic sensitive chip with the TSP coating is placed in a box furnace, heated to 200 ℃ from room temperature, kept for 0.5h, taken out and quickly immersed in cold water (25+/-5 ℃) and the coating is dried under the condition of no peeling, and the experiment is repeated after drying, and the temperature is increased by 50 ℃ each time compared with the last temperature until the TSP coating on the sample peels off. At the end of the experiment, the highest temperature at spalling was recorded to evaluate the thermal shock resistance of the coating.

2. Evaluation criteria

Regarding the water resistance, the maximum water drop amount was 20. Mu.L or more as a result of the test, the water resistance of the coating was judged to be excellent, the maximum water drop amount was between 10 and 20. Mu.L, the water resistance of the coating was judged to be good, and the maximum water drop amount was 10. Mu.L or less, the water resistance of the coating was judged to be poor.

Regarding air permeability, the IP current of the test result is reduced within 200 mu A, the starting time is within 45 seconds, which shows that the air permeability of the coating is good, and the ceramic sensitive chip temperature rising performance and the oxygen pumping capability are not affected; the IP current is reduced by 200-500 mu A, the starting time is within 45-55 seconds, which shows that the air permeability of the coating is better; the IP current drops above 500 muA and the start time is above 55 seconds, indicating poor air permeability of the coating.

With respect to the bonding strength, the coating was free from cracking and peeling at various portions after the high-temperature vibration test, indicating good bonding. The major, side, front or outer layers of the coating had different degrees of spalling or cracking, indicating poor bond strength.

Regarding the thermal shock resistance, the highest temperature of the coating layer is above 550 ℃ when the coating layer is peeled off rapidly and rapidly, and the coating layer is judged to have good thermal shock resistance; the highest temperature is within 400-550 ℃ when peeling, and the coating is judged to have better thermal shock resistance; the highest temperature at peeling was 400 ℃ or lower, and it was judged that the coating was inferior in thermal shock resistance.

The results of the above tests are shown in Table 1.

Table 1 results of Performance test of each sample

As can be seen from the above experimental results, examples 5 and comparative examples 2, 4, 5 were inferior in breathability, except that each of the performance test results of examples 1, 2 and 4 prepared by the methods and materials defined in the present application was excellent; the bond strength of example 3 and comparative examples 1-3 was poor. Example 3 and comparative examples 1 and 3 were generally waterproof and highly dispersible.

In this specification, each embodiment is described in a progressive manner, and identical and similar parts of each embodiment are all referred to each other, and each embodiment mainly describes differences from other embodiments. In particular, for system embodiments, since they are substantially similar to method embodiments, the description is relatively simple, as relevant to see a section of the description of method embodiments.

The foregoing is merely exemplary of the present application and is not intended to limit the present application. Various modifications and changes may be made to the present application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc. which are within the spirit and principles of the present application are intended to be included within the scope of the claims of the present application.

Claims (10)

1. A gas sensor element comprising a ceramic sensitive chip, an alumina substrate, and a TSP coating;

the alumina substrate layers are arranged on the upper surface and the lower surface of the ceramic sensitive chip, and after the ceramic sensitive chip is cut, the alumina substrate layers are arranged on the left side surface and the right side surface; a single-layer TSP coating is arranged outside the alumina substrate layer;

the thickness of the alumina substrate layer is 20-40 mu m, and the porosity is 30-50%.

2. The gas sensor element according to claim 1, wherein the roughness of the alumina substrate layer is 10-20 μm.

3. The gas sensor element according to claim 1, wherein the TSP coating has a thickness of 800-1000 μm, a porosity of 24-45% and an average pore size of 0.5-5.0 μm.

4. A gas sensor element according to claim 3, wherein the TSP coating is obtained after sintering from a composite slurry comprising ceramic coarse powder and ceramic fine powder.

5. The gas sensor element according to claim 4, wherein the ceramic coarse powder has a particle diameter of 2 to 10 μm and the ceramic fine powder has a particle diameter of 0.02 to 0.8 μm, and the weight ratio of the ceramic coarse powder to the ceramic fine powder is (1-4): 1.

6. the gas sensor element of claim 4, wherein the ceramic coarse powder is one or more of alumina, magnesia-alumina spinel, and mullite;

the ceramic fine powder is one or more of zirconia, alumina, titania and magnesia.

7. The gas sensor element of claim 4, wherein the composite slurry further comprises a high temperature binder, an organic binder, a pore former, a dispersant, and a solvent.

8. The gas sensor element of claim 7, wherein the high temperature binder is one or more of silica, alumina, bismuth oxide, and zinc oxide, the organic binder is one of acrylic acid and polyvinyl alcohol, the pore-forming agent is one or more of carbon powder, starch, and organic resin spheres, the dispersant is one of ammonium polycarboxylate and ammonium polyacrylate, and the solvent is one or more of water, ethanol, and isopropanol.

9. A method of manufacturing a gas sensor element according to any one of claims 1-8, comprising the steps of:

(1) Firstly, printing alumina slurry on the upper and lower surfaces of a ceramic sensitive chip, printing the alumina slurry on the left and right side surfaces of the cut ceramic chip, and sintering the ceramic sensitive chip and the alumina slurry at high temperature at 1350-1500 ℃ to form the ceramic sensitive chip attached with an alumina substrate;

(2) The tail end of the ceramic sensitive chip is clamped by the fixture and rotated, the detection part at the front end of the ceramic sensitive chip is vertically immersed into the composite slurry, the ceramic sensitive chip is immediately lifted up after reaching the preset coating length position, the superfluous composite slurry is thrown away, and the coating is dried and solidified, and the impregnation is repeated once after the first impregnation is completed;

(3) After the impregnation of the TSP coating is finished, the sintering cooling is carried out for 1 to 3 hours at the temperature of 1000 to 1200 ℃ to obtain the high-temperature-resistant ceramic material.

10. The gas sensor element according to claim 9, wherein the total thickness of the dip coating layer of the step (2) is 400-500 μm for the first time, and the final total thickness is controlled to be 800-1000 μm after repeating the above steps.