A porous ceramic for blocking ozone permeation in gas sensor packaging, its preparation method and application

Abstract

The present invention discloses a porous ceramic for preventing ozone permeation in gas sensor packaging, its preparation method and application. The preparation method includes: ball-milling calcined alumina, zinc oxide, iron oxide, chromium oxide, magnesium oxide, corn starch and water, adding methyl cellulose, polyethylene glycol, glycerol and polyvinyl alcohol, and obtaining a ceramic slurry after ball-milling; drying, grinding and sieving the ceramic slurry and then pressing to form a green ceramic body; sintering the green ceramic body in an air atmosphere to obtain a ceramic sheet; adding a polytetrafluoroethylene concentrated dispersion liquid to the cleaned ceramic sheet and sintering under inert gas protection to obtain the porous ceramic for preventing ozone permeation in gas sensor packaging. The ceramic of the present invention has excellent ozone barrier properties, and the gas permeation rates of other various gases are not affected. It is used for packaging semiconductor gas sensors, can ensure their stable operation, and has better hydrophobic and breathable properties, and can maintain its stable performance under high temperature and high humidity conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of sensors, and particularly relates to a porous ceramic for preventing ozone permeation in gas sensor packaging, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, the gas sensor technology at home and abroad has developed rapidly. Among them, small and micro gas sensors mainly based on MEMS have become the main development direction of gas sensors in the future due to their low energy consumption, small size, high sensitivity and other characteristics. Although the performance of gas sensors on the market is excellent at present, due to the limitations of the primary packaging materials, most gas sensors cannot take into account mechanical strength, thermal conductivity, long-term stability and other properties while ensuring hydrophobic and breathable properties, resulting in a significant reduction in the service life of the sensors.

[0003] At present, the main packaging material for gas sensors on the market is a waterproof and breathable membrane. Although the waterproof and breathable membrane has good waterproof and breathable properties, since it is a polymer thin film material, it is easy to age and break during long-term use in a complex working environment, resulting in a shortened service life. In addition, the waterproof and breathable membrane has poor light-shielding performance, high cost, and does not have gas selective filtration properties. These factors have led to its limitations as a gas sensor packaging material. During the waterproof process of the waterproof and breathable membrane product, the upper support layer is usually made of materials such as PET or steel sheet. During the processing and manufacturing process, there may be some sharp residues such as burrs on the surface of the support layer. When the waterproof and breathable membrane is impacted by external water or other media during use, it will deform. The burrs come into contact with the deformed part of the waterproof and breathable membrane, and it is easy to pierce the waterproof and breathable membrane under the condition of mutual extrusion, causing water to enter the electronic device and resulting in equipment damage. For this reason, there are also related patented products for protecting the waterproof and breathable membrane, such as a waterproof and breathable membrane assembly resistant to breakage (Chinese patent application document with publication number CN214654621U), but these products cannot substantially improve the performance of the waterproof and breathable membrane itself. On the contrary, they will increase the production cost and greatly reduce the scope of application.

[0004] In electronic packaging materials, ceramic packaging occupies a large proportion. The advantages of ceramic packaging are high mechanical strength, good electrical insulation, moisture resistance, heat shock resistance, high reliability, batch production, good light shielding property, long service life, etc. (Li Tingting, Peng Chaoqun, Wang Richu, Wang Xiaofeng, Liu Bing. Research progress of ceramic substrate materials for electronic packaging [J]. The Chinese Journal of Nonferrous Metals, 2010, 20(07): 1365-1374. DOI: 10.19476 / j.ysxb.1004.0609.2010.07.019). However, in order to obtain high mechanical strength and light shielding property, traditional packaging ceramics often have poor air permeability; when pursuing high air permeability, the hydrophobic property and mechanical strength are difficult to meet the requirements. These reasons have led to very few application examples of ceramics in the field of gas sensor packaging.

[0005] Therefore, in order to improve the service life of gas sensors and ensure their working stability and reliability, it is particularly important to develop a high-strength packaging material that is both hydrophobic and breathable and has selective permeability.

[0006] The Chinese patent application document with the publication number CN114085091A discloses a preparation method of an alumina filter layer, the obtained filter layer and its application in sensors. The preparation method includes the following steps: (1) Place alumina powder in a ball mill tank, add deionized water and polyethylene glycol, ball mill, and then add polyvinyl butyral resin and dioctyl phthalate and continue ball milling; (2) Take out the ball-milled slurry, remove the air bubbles in the slurry, sieve it, and then place it in a mold for drying; (3) Detach the dried block from the mold and then sinter it. The prepared filter layer has solid particles bonded to each other, grain growth, gradually reduced pores and grain boundaries, volume shrinkage, increased density, improved mechanical properties, making the filter layer surface dense, improving the pore structure, reducing the porosity, and greatly improving the gas selection performance of the filter layer, especially for volatile gases such as ethanol, but its ability to block oxidizing gases is poor. Summary of the Invention

[0007] The technical problem to be solved by the present invention is how to improve the performance of ceramics for sensor packaging in blocking oxidizing gases.

[0008] The present invention solves the above technical problems through the following technical means:

[0009] A preparation method of a porous ceramic for blocking ozone permeation in gas sensor packaging, including the following steps:

[0010] S1. Ball mill calcined alumina, zinc oxide, iron oxide, chromium oxide, magnesium oxide, corn starch and water in a ball milling device;

[0011] S2. Add methyl cellulose, polyethylene glycol, glycerol and polyvinyl alcohol to the ball milling device in S1, and obtain a ceramic slurry after ball milling;

[0012] S3. Dry, grind and screen the ceramic slurry in S2, and then press it to form a green ceramic body;

[0013] S4. Sinter the green ceramic body in an air atmosphere to obtain a ceramic sheet;

[0014] S5. Add a polytetrafluoroethylene concentrated dispersion liquid to the cleaned ceramic sheet, and then sinter it under the protection of an inert gas to obtain the porous ceramic for blocking ozone permeation used in the gas sensor package.

[0015] Preferably, in S1, the preparation method of the calcined alumina includes the following steps: Place the alumina in a muffle furnace, heat it to 1200 °C at a heating rate of 5 °C / min, then keep it at a constant temperature for 2 h, and obtain the calcined alumina after cooling.

[0016] Preferably, in S1, the weight ratio of the calcined alumina, zinc oxide, iron oxide, chromium oxide, magnesium oxide, and corn starch is 5-12:0.1-5:0.05-0.1:0.05-0.1:0.1-0.25:0.1-5; the mass-volume ratio of the calcined alumina to water is 5-12 g:20 mL.

[0017] Preferably, in S1, the rotation speed of the ball milling is 600 r / min and the time is 6 h; in S2, the rotation speed of the ball milling is 600 r / min and the time is 24 h.

[0018] Preferably, the mass ratio of the calcined alumina in S1 to the methyl cellulose in S2 is 5-12:0.1-0.3; in S2, the polyvinyl alcohol is a 10% polyvinyl alcohol solution, and the dosage ratio of the methyl cellulose, polyethylene glycol, glycerol, and 10% polyvinyl alcohol solution is 0.1-0.3 g:0.1-0.2 g:0.1-0.5 mL:1-2 mL.

[0019] Preferably, in S3, the pressure of the pressing is 20 MPa and the time is 1 min.

[0020] Preferably, in S4, place the green ceramic body in a muffle furnace, heat it to 500 °C at a heating rate of 1.5 °C / min in an air atmosphere and keep it at a constant temperature for 1 h, then heat it to 1400 °C at a heating rate of 3 °C / min and sinter it at a constant temperature for 6 h, and take it out after cooling with the furnace temperature to obtain the ceramic sheet.

[0021] Preferably, in S5, the polytetrafluoroethylene concentrated dispersion is added onto the cleaned ceramic sheet, and then heated to 400 °C at a heating rate of 4 °C / min under a nitrogen atmosphere and sintered at a constant temperature for 4 h to obtain the ozone-barrier porous ceramic for gas sensor packaging.

[0022] The present invention also provides an ozone-barrier porous ceramic for gas sensor packaging, which is prepared by using the preparation method of the ozone-barrier porous ceramic for gas sensor packaging described above.

[0023] The present invention also provides an anti-ozone gas sensor, which contains the ozone-barrier porous ceramic for gas sensor packaging described above.

[0024] The advantages of the present invention are as follows:

[0025] (1) Compared with the traditional waterproof and breathable film packaging, the porous ceramic packaging has good mechanical properties, longer durability and good light-shielding property, and can effectively protect the internal chips and materials of the sensor in a complex working environment;

[0026] (2) The porous ceramic packaging has low cost and is suitable for mass production;

[0027] (3) The porous ceramic packaging has selective permeability to some gases, and the formula can be changed according to actual needs to selectively filter out different gases, which can enhance the use stability of the sensor;

[0028] (4) The porous ceramic packaging is smaller in volume and higher in integration.

[0029] (5) Compared with the existing ceramic packaging materials, the porous ceramic packaging of the present invention has the characteristics of good air permeability and hydrophobicity. Compared with the gas sensor packaged by the traditional 3225 perforated cover plate, it can ensure the same sensor response under the same conditions.

[0030] (6) Compared with the existing ceramic packaging materials, due to the catalytic materials and pore sizes, the porous ceramic of the present invention can have selective permeability to some gases. For example, the anti-ozone performance of the porous ceramic can ensure the stability of the working resistance of the gas sensor in a complex environment (stable performance) and reduce the false alarm rate of the gas sensor.

[0031] (7) The ceramic of the present invention has the characteristics of antioxidant gas, and has excellent barrier characteristics to ozone gas, while the transmittance to other various gases is not affected. When used for packaging semiconductor gas sensors, it can ensure their stable operation and has better hydrophobic and breathable properties, and can pass the double 85 aging test and still maintain its stable performance under high temperature and high humidity conditions.

[0032] The present invention prepares a novel porous ceramic as a packaging material, ensuring that the sensor is waterproof, dustproof, breathable, with improved reliability, extended service life, and long-term stability in air; at the same time, ensuring that the mechanical strength of the gas sensor packaging material is improved, the light-shielding performance and heat-conducting performance are enhanced, and the production cost is reduced, effectively guaranteeing the safety and stability of the sensor chip; the porous ceramic packaging material has a certain gas selection and filtration property, expanding the application range of the gas sensor in special environments. Brief Description of the Drawings

[0033] Figure 1 Schematic diagram of the porous ceramic prepared in Example 1 of the present invention as a sensor packaging cover plate;

[0034] Figure 2 Variation of the ethanol response value of the sensor encapsulated with the porous ceramic prepared in Example 1 of the present invention and the 3225 traditional perforated cover plate;

[0035] Figure 3 Variation of the response values of the sensor encapsulated with the porous ceramic prepared in Example 1 of the present invention and the 3225 traditional perforated cover plate to R22, R454b, and ethanol gases;

[0036] Figure 4 Variation of the ozone response value of the sensor encapsulated with the porous ceramic prepared in Example 1 of the present invention and the 3225 traditional perforated cover plate;

[0037] Figure 5 Schematic diagram of the hydrophobic angle formed by water droplets on the ceramic surface;

[0038] Figure 6 Hydrophobic angle formed by water droplets on the ceramic surface prepared in Example 1;

[0039] Figure 7 Variation of the ozone response value of the sensor encapsulated with the porous ceramics prepared in Example 1 and Comparative Example 1 of the present invention;

[0040] Figure 8 Variation of the hydrogen response value of the sensor encapsulated with the porous ceramics prepared in Example 1 and Comparative Example 2 of the present invention.

[0041] Brief Description of the Drawings: 1 is the porous ceramic; 2 is the hydrophobic protection coating on the porous ceramic; 3 is the adhesive black glue; 4 is the base housing. Detailed Embodiments

[0042] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0043] The test materials, reagents, etc. used in the following embodiments can be obtained from commercial channels without special instructions.

[0044] For those not specifying specific technologies or conditions in the embodiments, they can all be carried out according to the technologies or conditions described in the literature in the field or according to the product specifications.

[0045] The polytetrafluoroethylene concentrated dispersion and polyvinyl alcohol in the following examples and comparative examples were purchased from Aladdin Chemical Reagent Co., Ltd.

[0046] Example 1

[0047] A preparation method of a porous ceramic for blocking ozone permeation in gas sensor packaging includes the following steps:

[0048] Step 1: Place alumina in a quartz glass dish, place it in a muffle furnace, heat it to 1200°C at a heating rate of 5°C / min, then keep it at a constant temperature for 2 h, take it out after cooling to room temperature and set it aside to obtain calcined alumina;

[0049] Step 2: Weigh 6 g of calcined alumina, 1 g of zinc oxide, 0.1 g of iron oxide, 0.1 g of chromium oxide, 0.25 g of magnesium oxide and 1 g of corn starch into a ball mill tank;

[0050] Step 3: Measure 20 mL of deionized water into the above ball mill tank;

[0051] Step 4: Seal the ball mill tank and place it in a ball mill, and ball mill for 6 h under the condition of a rotation speed of 600 r / min;

[0052] Step 5: Weigh 0.1 g of methyl cellulose and 0.2 g of polyethylene glycol (PEG 600) into the above ball mill tank;

[0053] Step 6: Measure 0.1 mL of glycerol and 2 mL of a 10% polyvinyl alcohol solution into the above ball mill tank, and continue to ball mill for 24 h under the condition of a rotation speed of 600 r / min;

[0054] Step 7: Take out the ball-milled ceramic slurry and place it in an oven at 70°C to dry to absolute dryness;

[0055] Step 8: Take out the dried ceramic slurry, grind it in a mortar and then pass it through a 100-mesh sieve to obtain ceramic powder for standby;

[0056] Step 9: Take the ceramic powder and put it into a mold, and press it in a hydraulic press for 1 minute under the pressure condition of 20 MPa to form a green ceramic body;

[0057] Step 10: Place the pressed green ceramic body in a muffle furnace, and heat it to 500 °C at a heating rate of 1.5 °C / min in an air atmosphere and keep it at a constant temperature for 1 h. The purpose is to remove the binder in the green ceramic body. Then continue to heat it to 1400 °C at a heating rate of 3 °C / min and keep it at a constant temperature for sintering for 6 h. Take it out after cooling with the furnace temperature to obtain a ceramic sheet;

[0058] Step 11: Take the prepared ceramic sheet and ultrasonically wash it in an ultrasonic washer with deionized water for 30 minutes, and repeat it 2 times;

[0059] Step 12: Take an appropriate amount of polytetrafluoroethylene concentrated dispersion liquid in a beaker, and immerse the ceramic sheet in it for 1 h;

[0060] Step 13: Place the impregnated ceramic sheet in a tube furnace, heat it to 400 °C at a heating rate of 4 °C / min in a nitrogen atmosphere and keep it at a constant temperature for sintering for 4 h. Take it out after cooling with the furnace temperature, and the hydrophobic modification is completed to obtain the porous ceramic for blocking ozone permeation used for gas sensor packaging.

[0061] Example 2

[0062] A preparation method of a porous ceramic for blocking ozone permeation used for gas sensor packaging, comprising the following steps:

[0063] Step 1: Put alumina in a quartz glass dish, place it in a muffle furnace and heat it to 1200 °C at a heating rate of 5 °C / min, then keep it at a constant temperature for 2 h, take it out after cooling to room temperature for standby, and obtain calcined alumina;

[0064] Step 2: Weigh 7 g of calcined alumina, 1 g of zinc oxide, 0.07 g of iron oxide, 0.05 g of chromium oxide, 0.17 g of magnesium oxide and 1.3 g of corn starch into a ball milling tank;

[0065] Step 3: Measure 20 mL of deionized water into the above ball milling tank;

[0066] Step 4: Seal the ball milling tank and place it in a ball mill, and ball mill it for 6 h under the condition of a rotation speed of 600 r / min;

[0067] Step 5: Weigh 0.3 g of methyl cellulose and 0.1 g of polyethylene glycol (PEG 600) into the above ball milling tank;

[0068] Step 6: Measure 0.5 mL of glycerol and 1 mL of a 10% polyvinyl alcohol solution and place them in the above ball mill jar. Continue ball milling for 24 h under the condition of a rotation speed of 600 r / min;

[0069] Step 7: Take out the ball milled ceramic slurry and place it in an oven at 70 °C to dry until completely dry;

[0070] Step 8: Take out the dried ceramic slurry, grind it in a mortar and then pass it through a 100-mesh sieve to obtain ceramic powder for standby;

[0071] Step 9: Take the ceramic powder and place it in a mold, and press it for 1 min under the condition of a pressure of 20 MPa in a hydraulic press to form a ceramic green body;

[0072] Step 10: Place the pressed ceramic green body in a muffle furnace, and raise the temperature to 500 °C at a heating rate of 1.5 °C / min in an air atmosphere and keep it at a constant temperature for 1 h. The purpose is to remove the adhesive in the ceramic green body. Subsequently, continue to raise the temperature to 1400 °C at a heating rate of 3 °C / min and keep it at a constant temperature for sintering for 6 h, and take it out after cooling with the furnace temperature to obtain a ceramic sheet;

[0073] Step 11: Take the prepared ceramic sheet and ultrasonically wash it with deionized water in an ultrasonic washing machine for 30 min, and repeat 3 times;

[0074] Step 12: Take an appropriate amount of polytetrafluoroethylene concentrated dispersion liquid in a beaker, and immerse the ceramic sheet in it for 1 h;

[0075] Step 13: Place the immersed ceramic sheet in a tubular furnace, and raise the temperature to 400 °C at a heating rate of 4 °C / min in a nitrogen atmosphere and keep it at a constant temperature for sintering for 4 h, and take it out after cooling with the furnace temperature. After the hydrophobic modification is completed, the porous ceramic for blocking ozone permeation used for gas sensor packaging is obtained.

[0076] Example 3

[0077] A preparation method of a porous ceramic for blocking ozone permeation used for gas sensor packaging, comprising the following steps:

[0078] Step 1: Place alumina in a quartz glass dish, place it in a muffle furnace, and raise the temperature to 1200 °C at a heating rate of 5 °C / min, and then keep it at a constant temperature for 2 h. After cooling to room temperature, take it out for standby to obtain calcined alumina;

[0079] Step 2: Weigh 10 g of calcined alumina, 1.5 g of zinc oxide, 0.05 g of iron oxide, 0.06 g of chromium oxide, 0.1 g of magnesium oxide and 2 g of corn starch and place them in a ball mill jar;

[0080] Step 3: Measure 20 mL of deionized water and place it in the above ball mill jar;

[0081] Step 4: Seal the ball milling jar and place it in a ball mill. Ball mill for 6 h under the condition of a rotation speed of 600 r / min;

[0082] Step 5: Weigh 0.15 g of methyl cellulose and 0.18 g of polyethylene glycol (PEG 600) into the above-mentioned ball milling jar;

[0083] Step 6: Measure 0.3 mL of glycerol and 1.5 mL of a 10% polyvinyl alcohol solution into the above-mentioned ball milling jar, and continue to ball mill for 24 h under the condition of a rotation speed of 600 r / min;

[0084] Step 7: Take out the ball milled ceramic slurry and place it in an oven at 70 °C to dry to absolute dryness;

[0085] Step 8: Take out the dried ceramic slurry, grind it in a mortar and pass it through a 100-mesh sieve to obtain ceramic powder for standby;

[0086] Step 9: Take the ceramic powder and place it in a mold, and press it in a hydraulic press for 1 min under the pressure condition of 20 MPa to form a ceramic green body;

[0087] Step 10: Place the pressed ceramic green body in a muffle furnace, and heat it to 500 °C at a heating rate of 1.5 °C / min in an air atmosphere and keep it at a constant temperature for 1 h. The purpose is to remove the adhesive in the ceramic green body. Subsequently, continue to heat it to 1400 °C at a heating rate of 3 °C / min and keep it at a constant temperature for sintering for 6 h. After cooling with the furnace temperature, take it out to obtain a ceramic sheet;

[0088] Step 11: Take the prepared ceramic sheet and ultrasonically wash it with deionized water in an ultrasonic washing machine for 30 min, and repeat it 2 times;

[0089] Step 12: Take an appropriate amount of polytetrafluoroethylene concentrated dispersion liquid in a beaker and apply it to the ceramic sheet with a brush;

[0090] Step 13: Place the coated ceramic sheet in a tube furnace, heat it to 400 °C at a heating rate of 4 °C / min in a nitrogen atmosphere and keep it at a constant temperature for sintering for 4 h. After cooling with the furnace temperature, take it out, and the hydrophobic modification is completed to obtain the porous ceramic for blocking ozone permeation used for gas sensor packaging.

[0091] The hydrophobicity of the porous ceramic is judged according to the hydrophobic angle θ of the water droplet dropped on the ceramic surface. As Figure 5 shown, when θ < 90°, it is partially wetted or wetted, hydrophilic; when θ > 90°, it is not wetted, hydrophobic; when θ > 150°, it is superhydrophobic; Drop water on the surface of the porous ceramic prepared in Example 1, and the hydrophobic angle is 132°, which has hydrophobicity. As Figure 6 shown.

[0092] The hydrophobicity of the porous ceramic encapsulated sensors prepared in Examples 1-3 was detected, and all of them met the hydrophobic standard. Specifically, the hydrophobic inspection standard for the porous ceramic encapsulated sensors is the double 85 test, that is, the ceramic encapsulated gas sensor is aged in a constant temperature and humidity chamber at a temperature of 85°C and a humidity of 85% for 10 days under the premise of normal power-on operation. If the sensitivity of the gas sensor remains unchanged before and after aging, it meets the hydrophobic standard.

[0093] Comparative Example 1

[0094] It is only different from Example 1 in that: in Step 2, zinc oxide is not contained, and the remaining steps are the same as those in Example 1.

[0095] One ceramic encapsulated gas sensor of Comparative Example 1 and one ceramic encapsulated gas sensor of Example 1 were taken respectively, and the two sensors were placed on the same test circuit board together. Subsequently, the circuit board was placed in a 20L gas sensor performance test chamber and aged for 30 minutes under the conditions of a heating voltage of 1.8V and a test voltage of 3.3V. Then, the ozone generator was turned on and placed in the gas sensor performance test chamber, and the change of Rs / R0 of the two encapsulated gas sensors was observed. The results are as Figure 7 shown. It can be seen from Figure 7 that when the addition amount of the raw material zinc oxide in the formula of Example 1 is 0 and the other conditions remain unchanged, the prepared ceramic is breathable but loses its ozone resistance (as shown by the ceramic encapsulation of Example 1 without zinc oxide in the figure), while the ceramic of Example 1 has stable ozone resistance.

[0096] Comparative Example 2

[0097] It is only different from Example 1 in that: in Step 2, corn starch is not contained, and the remaining steps are the same as those in Example 1.

[0098] One ceramic encapsulated gas sensor of Example 1 and one ceramic encapsulated gas sensor of Comparative Example 2 were taken respectively, and the two sensors were placed on the same test circuit board together. Subsequently, the circuit board was placed in a 20L gas sensor performance test chamber and aged for 30 minutes under the conditions of a heating voltage of 1.8V and a test voltage of 3.3V. Then, a certain amount of H2 was extracted using a syringe and injected into the gas sensor performance test chamber, and the change of Rs / R0 of the two encapsulated gas sensors was observed. The results are as Figure 8 shown. It can be seen from Figure 8 that according to the air permeability test results of Comparative Example 2 (as shown by the ceramic encapsulation of Example 1 without corn starch in the figure), in a hydrogen atmosphere with a gas concentration of 50 ppm, when the addition amount of the raw material corn starch in the formula of Example 1 is 0 and the other conditions remain unchanged, the prepared ceramic is not breathable, while the ceramic of Example 1 has good air permeability.

[0099] For gas sensors of the same model and the same production batch, porous ceramic encapsulation prepared in Example 1 and 3225 traditional perforated cover encapsulation were respectively used. The schematic diagram is as Figure 1 shown. The porous ceramic 1 with a hydrophobic protective coating 2 on its surface was encapsulated on the base shell 4 through adhesive black glue 3. The change of the response value under the same concentration of ethanol gas was detected. The specific test method is as follows: Take 2 gas sensors with ceramic encapsulation in Example 1 and 2 gas sensors with 3225 traditional perforated cover traditional encapsulation respectively. Place the 4 sensors together on the same test circuit board, and then place the circuit board in a 20L gas sensor performance test chamber. Under the conditions of a heating voltage of 1.8V and a test voltage of 3.3V, power on and age for 30 minutes. Then use a syringe to draw a certain amount of ethanol saturated vapor (ethanol gas concentration is about 80000 ppm) from an anhydrous ethanol bottle and inject it into the gas sensor performance test chamber, and observe the change of Rs / R0 of the two encapsulated gas sensors. The results are as Figure 2 shown. It can be seen from Figure 2 that the porous ceramic encapsulation has good air permeability, and the response degree of the gas sensor is more stable.

[0100] For gas sensors of the same model and the same production batch, porous ceramic encapsulation prepared in Example 1 and 3225 traditional perforated cover encapsulation were respectively used. According to the above test method, the change of the response value under the same concentration of gases such as R22, R454b, and ethanol was detected; among them, the gases of R22 and R454b used were 100% concentration refrigerant gases purchased; the results are as Figure 3 shown. Under the same test conditions, for the same type of gas sensor, 3225 traditional perforated cover and porous ceramic were respectively used for encapsulation, and then the response degrees of different concentrations of ethanol, R22, R454b and other gases were tested. The better the air permeability of the porous ceramic encapsulated sensor is, the closer the response degree is to that of the 3225 traditional perforated cover encapsulated sensor. It can be seen from Figure 3 that the hydrophobic modified porous ceramic still has good air permeability, maintains good permeability to a variety of gases, and the hydrophobic modification does not affect the air permeability of the ceramic.

[0101] For gas sensors of the same model and the same production batch, porous ceramic encapsulation prepared in Example 1 and 3225 traditional perforated cover encapsulation were respectively used. The change of the response value under the same concentration of ozone gas was detected. The ozone gas test method is as follows: The test environment and test voltage and other conditions are the same as those in Comparative Example 1 above. After the sensors in the gas sensor performance test chamber are powered on for 30 minutes, start the ozone generator in the chamber, and observe the change of Rs / R0 of the two encapsulated gas sensors. The results are as Figure 4 shown. It can be seen from Figure 4It can be seen that compared with the traditional 3225 perforated cover plate encapsulation, the hydrophobic modified porous ceramic has a certain barrier to ozone, which can effectively reduce the interference of ozone gas to the sensor.

[0102] Explanation: R0 is the resistance value of the sensor in air; Rs is the resistance value of the sensor under the target gas; the sensitivity S of the sensor to the gas = R0 / Rs, the larger the value, the higher the sensitivity of the sensor to the gas; Rs / R0 is the response value, the smaller the value, the higher the sensitivity of the sensor to the gas.

[0103] The ceramic sheet prepared by the method of the present invention has excellent mechanical properties, and also has good air permeability, water resistance and light shielding properties. It can block the penetration of oxidizing gases such as ozone, and at the same time allow various gases such as H2, R22, R454b, and ethanol to pass through.

[0104] During the test of the present invention, the encapsulated sensors are all gas sensors of the model HGS-1000 produced by Micro-Nano Sensing (Hefei) Technology Co., Ltd.

[0105] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of a porous ceramic for gas sensor packaging to block ozone permeation, characterized in that: It includes the following steps: S1. Ball-mill calcined alumina, zinc oxide, iron oxide, chromium oxide, magnesium oxide, corn starch and water in a ball-milling device; the weight ratio of the calcined alumina, zinc oxide, iron oxide, chromium oxide, magnesium oxide and corn starch is 5-12: 0.1-5：0.05-0.1：0.05-0.1：0.1-0.25：0.1-5； S2. Add methyl cellulose, polyethylene glycol, glycerol and polyvinyl alcohol to the ball-milling device in S1, and obtain a ceramic slurry after ball-milling; S3. Dry, grind and screen the ceramic slurry in S2, and then press it to form a green ceramic body; S4. Sinter the green ceramic body in an air atmosphere to obtain a ceramic sheet; S5. Add a polytetrafluoroethylene concentrated dispersion liquid to the cleaned ceramic sheet, and then sinter it under the protection of an inert gas to obtain the ozone-barrier porous ceramic for gas sensor packaging.

2. The preparation method of the porous ceramic for gas sensor packaging that blocks ozone permeation according to claim 1, wherein: In S1, the preparation method of the calcined alumina includes the following steps: Place the alumina in a muffle furnace and heat it to 1200°C at a heating rate of 5°C / min, then keep it at a constant temperature for 2 h, and obtain the calcined alumina after cooling.

3. The preparation method of the porous ceramic for gas sensor packaging that blocks ozone permeation, characterized in that: In S1, the mass-volume ratio of the calcined alumina to water is 5-12 g: 20 mL.

4. The preparation method of the porous ceramic for gas sensor packaging that blocks ozone permeation, characterized in that: In S1, the rotation speed of the ball-milling is 600 r / min and the time is 6 h; in S2, the rotation speed of the ball-milling is 600 r / min and the time is 24 h.

5. The preparation method of the porous ceramic for gas sensor packaging to block ozone permeation according to claim 1, characterized in that: The mass ratio of the calcined alumina in S1 to the methyl cellulose in S2 is 5-12: 0.1-0.3; in S2, the polyvinyl alcohol is a 10% polyvinyl alcohol solution, and the dosage ratio of the methyl cellulose, polyethylene glycol, glycerol and the 10% polyvinyl alcohol solution is 0.1-0.3 g: 0.1-0.2 g: 0.1-0.5 mL: 1-2 mL.

6. The preparation method of the porous ceramic for gas sensor packaging that blocks ozone permeation according to claim 1, characterized in that: In S3, the pressure of the pressing is 20 MPa and the time is 1 min.

7. The preparation method of the porous ceramic for gas sensor packaging that blocks ozone permeation according to claim 1, characterized in that: In S4, place the green ceramic body in a muffle furnace, heat it to 500°C at a heating rate of 1.5°C / min in an air atmosphere and keep it at a constant temperature for 1 h, then heat it to 1400°C at a heating rate of 3°C / min and sinter it at a constant temperature for 6 h, and take it out after cooling with the furnace temperature to obtain the ceramic sheet.

8. The preparation method of the porous ceramic for gas sensor packaging that blocks ozone permeation according to any one of claims 1-7, characterized in that: In S5, add the polytetrafluoroethylene concentrated dispersion liquid to the cleaned ceramic sheet, and then sinter it at a heating rate of 4°C / min to 400°C and keep it at a constant temperature for 4 h in a nitrogen atmosphere to obtain the ozone-barrier porous ceramic for gas sensor packaging.

9. A porous ceramic for gas sensor packaging that blocks ozone permeation, characterized in that: It is prepared by using the preparation method of the ozone-barrier porous ceramic for gas sensor packaging according to any one of claims 1-8.

10. An anti-ozone gas sensor, characterized in that: It contains the ozone-barrier porous ceramic for gas sensor packaging according to claim 9.

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