A porous ceramic with gas selective permeability, its preparation method and application

Abstract

The present invention discloses a porous ceramic with gas selective permeability, its preparation method and application. The preparation method of the ceramic includes the following steps: S1. Calcined alumina, zinc oxide, manganese oxide, magnesium oxide, polyethylene glycol, corn starch and water are ball-milled in a ball-milling device; S2. Methyl cellulose and glycerol are added to the ball-milling device in S1, and a ceramic slurry is obtained after ball-milling; S3. The ceramic slurry in S2 is dried, ground, sieved and then pressed to form a green ceramic body; S4. The green ceramic body is sintered in an air atmosphere to obtain a ceramic sheet; the sintering temperature is 1500-1600 °C; S5. Hydrogen-containing silicone oil and ethyl acetate solution are mixed to prepare a hydrophobic agent solution, and the ceramic sheet is immersed in the hydrophobic agent solution to obtain a porous ceramic with gas selective permeability. The ceramic prepared by the present invention has excellent mechanical properties, and also has good air permeability, waterproof performance, ozone resistance and ethanol resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of encapsulation materials, and particularly relates to a porous ceramic with gas selective permeability, a preparation method thereof, and an application thereof. Background Art

[0002] With the improvement of the market's requirements for the performance of gas sensors, the anti-interference ability of the sensors becomes particularly important. During the operation of gas sensors, they are often affected by some interfering gases, resulting in the sensors being unable to accurately identify and respond to target gases. Currently, composite filter layers are commonly used in the market to filter out these interfering gases. For example, for the gas sensor of FIGARO model TGS2610-E00, this sensor is equipped with a filter cover that can eliminate the influence of interfering gases such as alcohol and has a sensitive characteristic with extremely high selectivity for methane gas. However, these composite filter layers are relatively large in volume, complex in process, and high in cost, and are not suitable for being applied to small and micro gas sensors mainly based on MEMS.

[0003] 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, and long service life, etc. [Li Tingting, Peng Chaoqun, Wang Richu, Wang Xiaofeng, Liu Bing. Research progress of electronic packaging ceramic substrate materials [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 relatively poor air permeability; when high air permeability is pursued, 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.

[0004] Therefore, in order to improve the anti-interference ability 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 gas selective permeability.

[0005] 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 a sensor. The preparation method includes the following steps: (1) placing alumina powder in a ball mill tank, adding deionized water and polyethylene glycol, ball milling, and then adding polyvinyl butyral resin and dioctyl phthalate and continuing to ball mill; (2) taking out the ball-milled slurry, removing the air bubbles in the slurry, sieving, and then placing it in a mold for drying; (3) detaching the dried block from the mold and then sintering. The prepared filter layer has solid particles bonded to each other, grain growth, gradually reduced pores and grain boundaries, volume shrinkage, increased density, and improved mechanical properties, making the surface of the filter layer dense, improving the pore structure, reducing the porosity, and greatly improving the gas selectivity of the filter layer, especially for volatile gases such as ethanol. However, its gas selectivity is still not good enough.

[0006] The existing sensors disclose an ethanol-resistant filter encapsulation layer, but its process is complex, the cost is high, it is not suitable for use in small-volume MEMS gas sensors, and it cannot effectively filter out dust, impurities, and ozone gas in the air, which easily causes interference of these pollutants to the sensitive elements of the sensor. At the same time, the humidity resistance is insufficient, reducing the accuracy and stability of the sensor. Summary of the Invention

[0007] The technical problem to be solved by the present invention is how to obtain a ceramic material that selectively transmits hydrogen and simultaneously blocks the transmission of ozone and ethanol.

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

[0009] A preparation method of a porous ceramic with gas selective permeability, including the following steps:

[0010] S1. Ball milling calcined alumina, zinc oxide, manganese oxide, magnesium oxide, polyethylene glycol, corn starch, and water in a ball milling device;

[0011] S2. Adding methyl cellulose and glycerol to the ball milling device in S1, and ball milling to obtain a ceramic slurry;

[0012] S3. Drying, grinding, and sieving the ceramic slurry in S2, and then pressing to form a green ceramic body;

[0013] S4. Sintering the green ceramic body in an air atmosphere to obtain a ceramic sheet; wherein, the sintering temperature is 1500 - 1600 °C;

[0014] S5. Mixing hydrogen-containing silicone oil with an ethyl acetate solution to prepare a water repellent solution, and then immersing the ceramic sheet in the water repellent solution to obtain the porous ceramic with gas selective permeability.

[0015] Preferably, in S1, the method for preparing the calcined alumina comprises the following steps: placing alumina in a muffle furnace, heating it at a heating rate of 5 °C / min to 1200 °C, then maintaining the temperature for 2 h, and obtaining the calcined alumina after cooling.

[0016] Preferably, in S1, the mass ratio of the calcined alumina, zinc oxide, manganese oxide, magnesium oxide, polyethylene glycol, and corn starch is 5-12:1-2:1-12:0.2-0.5:0.2-0.5:1-2; the mass-to-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 24 h; in S2, the rotation speed of the ball milling is 600 r / min and the time is 6 h; in S3, during the pressing process, the pressure is 20 MPa and the time is 1 min.

[0018] Preferably, the dosage ratio of the calcined alumina, methyl cellulose, and glycerol is 5-12 g:0.1-0.5 g:0.1-0.5 ml.

[0019] Preferably, in S4, the green ceramic body is placed in a muffle furnace, heated in an air atmosphere at a heating rate of 1-2 °C / min to 500 °C and maintained at this temperature for 1 h, then continuously heated at a heating rate of 1-2 °C / min to 1500-1600 °C and sintered at a constant temperature for 1-3 h, and then cooled to room temperature at a cooling rate of 1-2 °C / min and taken out to obtain a ceramic sheet.

[0020] Preferably, in S5, the mass fraction of hydrogen silicone oil in the hydrophobic agent solution is 10-20 wt%; the impregnation time is 2 h.

[0021] The present invention also provides a porous ceramic with gas selective permeability, which is prepared by using the preparation method of the porous ceramic with gas selective permeability.

[0022] The present invention also provides an application of the porous ceramic with gas selective permeability in a gas sensor.

[0023] The present invention also provides an ethanol- and ozone-resistant gas sensor containing the porous ceramic with gas selective permeability.

[0024] Preferably, the ethanol- and ozone-resistant gas sensor is an ethanol- and ozone-resistant hydrogen MEMS sensor.

[0025] The advantages of the present invention are as follows:

[0026] (1) The preparation method of the present invention specifically selects calcined alumina, zinc oxide, manganese oxide, magnesium oxide, polyethylene glycol, corn starch, methyl cellulose and glycerol as raw materials. The obtained ceramic sheet has excellent gas selective permeability. Then, the ceramic sheet is impregnated and hydrophobically modified in a hydrophobic agent solution prepared from hydrogen-containing silicone oil and ethyl acetate, and silicon-based hydrophobic groups are incorporated into the porous ceramic to endow it with hydrophobic properties.

[0027] (2) Using the porous breathable ceramic of the present invention as the encapsulation material of the sensor ensures that the sensor is waterproof, dustproof, breathable, has improved reliability, extended service life and is stable in the air for a long time. At the same time, it can block ethanol and ozone and has gas selective permeability.

[0028] (3) The mechanical strength of the ceramic prepared by the present invention used as the gas sensor encapsulation material is improved, the light shielding performance and heat conduction performance are enhanced, and the production cost is reduced, which can effectively ensure the safety and stability of the sensor chip.

[0029] (4) The porous ceramic prepared by the present invention has a certain gas selective filtration property, can effectively filter out interfering gases such as ozone and ethanol, can achieve high-selectivity response to different gases, and expands the application range of gas sensors in special environments.

[0030] (5) The porous ceramic prepared by the present invention has the characteristics of high specific surface area and controllable pore size distribution, and can improve the sensitivity of gas sensing elements.

[0031] (6) The porous ceramic material prepared by the present invention has high chemical stability and heat resistance, and can ensure the long-term stable performance of the sensor when used for sensor encapsulation.

[0032] (7) The porous ceramic prepared by the present invention can filter out dust and impurities in the air, and at the same time has better gas selectivity. Among them, the selective permeability to H2 is the best, and almost all other gases can be filtered out, thereby reducing the influence of external interference on the sensor and improving the anti-interference performance of the sensor. This ceramic can be used as a cover plate encapsulation to make an H2 sensor. Description of the Drawings

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

[0034] Figure 2 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 ethanol and H2 gases;

[0035] Figure 3 Variation of the 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 to ozone gas;

[0036] Figure 4 The variation of the response value of the sensor encapsulated with the porous ceramics prepared in Example 1 and Comparative Example 1 of the present invention to ethanol gas;

[0037] Figure 5 The variation of the response value of the sensor encapsulated with the porous ceramics prepared in Example 1 and Comparative Example 2 of the present invention to ethanol gas;

[0038] Figure 6 The variation of the response value of the sensor encapsulated with the porous ceramics prepared in Comparative Example 3 of the present invention and the 3225 traditional perforated cover plate to ethanol;

[0039] Figure 7 The variation of the response value of the sensor encapsulated with the porous ceramics prepared in Example 1 of the present invention and the 3225 traditional perforated cover plate to hydrogen gas.

[0040] 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 shell. Detailed implementation manners

[0041] 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 protection scope of the present invention.

[0042] The test materials and reagents used in the following embodiments can be obtained from commercial channels without special instructions.

[0043] 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 this field or according to the product specifications.

[0044] Example 1

[0045] A preparation method of a porous ceramic with gas selective permeability includes the following steps:

[0046] Step 1: Place alumina in a quartz glass dish, put 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 obtain calcined alumina;

[0047] Step 2: Weigh 12 g of calcined alumina, 1.5 g of zinc oxide, 12 g of manganese oxide, 0.2 g of magnesium oxide, 0.3 g of polyethylene glycol (600) and 1 g of corn starch into a ball mill tank;

[0048] Step 3: Measure 20 mL of deionized water into the above ball mill jar;

[0049] Step 4: Seal the ball mill jar and place it in a ball mill. Ball mill for 24 h under the condition of a rotation speed of 600 r / min;

[0050] Step 5: Weigh 0.1 g of methyl cellulose and 0.5 mL of glycerol into the above ball mill jar;

[0051] Step 6: Set the rotation speed of the ball mill to 600 r / min and continue to ball mill for 6 h;

[0052] Step 7: Take out the ball-milled ceramic slurry and place it in an oven at 70 °C and dry it to absolute dryness;

[0053] 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;

[0054] Step 9: Take the ceramic powder and place it in a mold. Press it in a hydraulic press at a pressure of 20 MPa for 1 min to form a green ceramic body;

[0055] Step 10: Place the pressed green ceramic body in a muffle furnace. Under an air atmosphere, raise the temperature to 500 °C at a heating rate of 2 °C / min and keep it at a constant temperature for 1 h to remove the binder in the green ceramic body. Then continue to raise the temperature to 1500 °C at a heating rate of 2 °C / min and keep it at a constant temperature for 1 h. Then cool it to room temperature at a cooling rate of 1.5 °C / min and take it out to obtain a ceramic sheet;

[0056] Step 11: Take the prepared ceramic sheet and ultrasonically wash it with deionized water in an ultrasonic washer for 30 min, and repeat 2 times;

[0057] Step 12: Pour hydrogen-containing silicone oil into an ethyl acetate solution to prepare a solution with a concentration of 10 wt%. Then place the ceramic sheet in the solution and soak it for 2 h. Take it out and place it in an oven at 100 °C and dry it for 5 min, and then place it in an oven at 150 °C and dry it for 3 min to obtain the porous ceramic with gas selective permeability.

[0058] Example 2

[0059] A preparation method of a porous ceramic with gas selective permeability, comprising the following steps:

[0060] Step 1: Place alumina in a quartz glass dish and place it in a muffle furnace. Raise the temperature to 1200 °C at a heating rate of 5 °C / min, then keep it at a constant temperature for 2 h, cool it to room temperature and take it out to obtain calcined alumina;

[0061] Step 2: Weigh 5 g of calcined alumina, 2 g of zinc oxide, 2 g of manganese oxide, 0.5 g of magnesium oxide, 0.5 g of polyethylene glycol (600) and 2 g of corn starch into a ball milling tank;

[0062] Step 3: Measure 20 mL of deionized water into the above-mentioned ball milling tank;

[0063] Step 4: Seal the ball milling tank and place it in a ball mill, and ball mill for 24 h under the condition of a rotation speed of 600 r / min;

[0064] Step 5: Weigh 0.4 g of methyl cellulose and 0.1 mL of glycerol into the above-mentioned ball milling tank;

[0065] Step 6: Set the rotation speed of the ball mill to 600 r / min and continue to ball mill for 6 h;

[0066] Step 7: Take out the ball-milled ceramic slurry and place it in an oven at 70 °C to dry to absolute dryness;

[0067] 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;

[0068] Step 9: Take the ceramic powder and put it into a mold, and press it in a hydraulic press for 1 min at a pressure of 20 MPa to form a ceramic green body;

[0069] Step 10: Place the pressed ceramic green body in a muffle furnace, and heat it to 500 °C at a heating rate of 1 °C / min in an air atmosphere and keep it at a constant temperature for 1 h to remove the binder in the ceramic green body. Subsequently, continue to heat it to 1600 °C at a heating rate of 1.5 °C / min and keep it at a constant temperature for 3 h, and then cool it to room temperature at a cooling rate of 2 °C / min and take it out to obtain a ceramic sheet;

[0070] 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 3 times;

[0071] Step 12: Pour hydrogen-containing silicone oil into an ethyl acetate solution to prepare a solution with a concentration of 20 wt%, then place the ceramic sheet in the solution and impregnate it for 2 h, take it out and place it in an oven at 100 °C for 5 min, and then place it in an oven at 150 °C for 3 min to obtain the porous ceramic with gas selective permeability.

[0072] Example 3

[0073] A preparation method of a porous ceramic with gas selective permeability, comprising the following steps:

[0074] Step 1: Place alumina in a quartz glass dish and put 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. After cooling to room temperature, take it out to obtain calcined alumina;

[0075] Step 2: Weigh 10 g of calcined alumina, 1 g of zinc oxide, 2 g of manganese oxide, 0.4 g of magnesium oxide, 0.2 g of polyethylene glycol (600), and 1.5 g of corn starch into a ball milling jar;

[0076] Step 3: Measure 20 mL of deionized water into the above ball milling jar;

[0077] Step 4: Seal the ball milling jar and place it in a ball mill. Ball mill for 24 h under the condition of a rotational speed of 600 r / min;

[0078] Step 5: Weigh 0.5 g of methyl cellulose and 0.3 mL of glycerol into the above ball milling jar;

[0079] Step 6: Set the rotational speed of the ball mill to 600 r / min and continue to ball mill for 6 h;

[0080] Step 7: Take out the ball milled ceramic slurry and place it in an oven at 70 °C to dry it to absolute dryness;

[0081] 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;

[0082] Step 9: Take the ceramic powder into a mold and press it in a hydraulic press for 1 min at a pressure of 20 MPa to form a green ceramic body;

[0083] Step 10: Place the pressed green ceramic body in a muffle furnace. In an air atmosphere, heat it to 500 °C at a heating rate of 1.5 °C / min and keep it at a constant temperature for 1 h to remove the binder in the green ceramic body. Then continue to heat it to 1550 °C at a heating rate of 1 °C / min, keep it at a constant temperature for 2 h, and then cool it to room temperature at a cooling rate of 1 °C / min and take it out to obtain a ceramic sheet;

[0084] Step 11: Take the prepared ceramic sheet and ultrasonically wash it with deionized water in an ultrasonic washing machine for 30 min, repeat 3 times;

[0085] Step 12: Pour hydrogen - containing silicone oil into an ethyl acetate solution to prepare a solution with a concentration of 15 wt%. Then immerse the ceramic sheet in the solution for 2 h, take it out, place it in an oven at 100 °C for 5 min, and then place it in an oven at 150 °C for 3 min to obtain the porous ceramic with gas selective permeability.

[0086] Comparative Example 1

[0087] It is only different from Example 1 in that: in Step 2, 12 g of calcined alumina, 1.5 g of zinc oxide, 0.2 g of magnesium oxide, 0.3 g of polyethylene glycol (600), and 1 g of corn starch are weighed and placed in a ball milling tank.

[0088] One porous ceramic encapsulated gas sensor of Example 1 and one porous ceramic encapsulated gas sensor of Comparative Example 1 are taken respectively. The two sensors are placed together on the same test circuit board, and then the circuit board is placed in a 20 L gas sensor performance test chamber. Under the conditions of a heating voltage of 1.8 V and a test voltage of 3.3 V, it is energized and aged for 30 minutes. Then, a certain amount of ethanol gas is extracted with a syringe and injected into the gas sensor performance test chamber, and the change of Rs / R0 of the two encapsulated gas sensors is observed. The results are as Figure 4 shown. It can be seen from Figure 4 that in an atmosphere with an ethanol gas concentration of 100 ppm, after removing manganese oxide from the formulation of Example 1, the sensor encapsulated with ceramics loses the characteristic of resisting ethanol gas, while the sensor encapsulated with ceramics in Example 1 has stable ethanol resistance performance.

[0089] Comparative Example 2

[0090] It is only different from Example 1 in that: in Step 10, the temperature is raised to 1400 °C and sintered at a constant temperature.

[0091] The performance of the ceramics of Comparative Example 2 is tested according to the method in Comparative Example 1. The results are as Figure 5 shown. It can be seen from Figure 5 that in an atmosphere with an ethanol gas concentration of 100 ppm, the sensor encapsulated with the ceramics of Comparative Example 2 loses the characteristic of resisting ethanol gas (i.e., the ceramics encapsulated and sintered at 1400 °C in Example 1 shown in the figure), while the ceramics in Example 1 are sintered at 1500 °C, and the sensor encapsulated with them has stable ethanol resistance performance.

[0092] Comparative Example 3

[0093] A preparation method of porous ceramics includes the following steps:

[0094] Step 1: Place 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, and obtain calcined alumina;

[0095] 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 and place them in a ball milling tank;

[0096] Step 3: Measure 20 mL of deionized water into the above ball milling tank;

[0097] Step 4: Seal the ball milling jar and place it in the ball mill. Ball mill for 6 h under the condition of a rotation speed of 600 r / min.

[0098] Step 5: Weigh 0.1 g of methyl cellulose and 0.2 g of polyethylene glycol (PEG 600) into the above-mentioned ball milling jar.

[0099] Step 6: Measure 0.1 mL of glycerol and 2 mL of a 10% polyvinyl alcohol solution into the above-mentioned ball milling jar. Continue to ball mill for 24 h under the condition of a rotation speed of 600 r / min.

[0100] Step 7: Take out the ball milled ceramic slurry and place it in an oven at 70 °C to dry to absolute dryness.

[0101] 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.

[0102] Step 9: Take the ceramic powder into 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.

[0103] Step 10: Place the pressed ceramic green 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. 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. Take it out after cooling with the furnace temperature to obtain a ceramic sheet.

[0104] Step 11: Take the prepared ceramic sheet into an ultrasonic washing machine and wash it ultrasonically with deionized water for 30 min, and repeat it 2 times.

[0105] Step 12: Take an appropriate amount of polytetrafluoroethylene concentrated dispersion liquid into a beaker and immerse the ceramic sheet in it for 1 h.

[0106] Step 13: Place the immersed ceramic sheet in a tubular 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.

[0107] For gas sensors of the same model and the same production batch, the porous ceramics prepared in Example 1 and the 3225 traditional perforated cover plate packaging were respectively used for packaging. The schematic diagram is as Figure 1As shown, the porous ceramic 1 with a hydrophobic protective coating 2 on its surface is encapsulated on the base housing 4 by adhesive black glue 3, and the change of Rs / R0 (response value) under the same concentration of ethanol gas and H2 gas is detected. The specific test method is as follows: Take 2 ceramic-encapsulated gas sensors of Example 1 or Comparative Example 3 and 2 traditional 3225 perforated cover plate-encapsulated gas sensors respectively. Place the 4 sensors 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 extract a certain amount of ethanol saturated vapor (ethanol gas concentration is about 80,000 ppm) from an anhydrous ethanol bottle and H2 gas and inject them into the gas sensor performance test chamber, and observe the change of Rs / R0 of the three types of encapsulated gas sensors. The results are as Figure 2 and Figure 6 shown. As can be seen from Figure 2 , for the two sensors (i.e., those shown as Ceramic Encapsulation-1 and Ceramic Encapsulation-2) encapsulated with the ceramic prepared in Example 1, when ethanol gas is introduced, the Rs / R0 numerical curve has no fluctuation and the value remains at 1, indicating that ethanol gas has no interference on it. In contrast, for the 2 traditional 3225-encapsulated sensors, when ethanol gas is introduced, the Rs / R0 numerical curve fluctuates significantly and decreases. Subsequently, when H2 gas (concentration is 50 ppm) is introduced, the Rs / R0 numerical curves of the two different types of encapsulated sensors both fluctuate, which excludes the possibility that the ceramic encapsulation is airtight and causes the sensor to have no response to ethanol gas. Thus, it can be known that compared with the traditional 3225 encapsulation, the porous ceramic encapsulation prepared in Example 1 has a good barrier effect on ethanol gas, has good air permeability to H2 gas, and has obvious selective permeability. As can be seen from Figure 6 , the porous ceramic-encapsulated sensor prepared in Comparative Example 3 has good ethanol air permeability, and the response degree of the gas sensor is more stable.

[0108] For gas sensors of the same model and the same production batch, the porous ceramic encapsulation of Example 1 and the traditional 3225 perforated cover plate encapsulation are respectively adopted, and the change of the response value under the same concentration of ozone gas is detected. The specific detection method is as follows: The test environment, test voltage and other conditions are the same as 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 types of encapsulated gas sensors. The results are as Figure 3 shown, where Ceramic Encapsulation-1 and Ceramic Encapsulation-2 represent the sensors encapsulated with the ceramic of Example 1. As can be seen from Figure 3 , compared with the traditional 3225 perforated cover plate encapsulation, the porous ceramic encapsulation has a good barrier effect on ozone gas and can effectively reduce the interference of ozone gas on the sensor.

[0109] Description: R0 is the resistance value of the sensor in the air; Rs is the resistance value of the sensor in the target gas; the sensitivity S of the sensor to the gas is S = R0 / Rs. The larger the value, the higher the sensitivity of the sensor to the gas; Rs / R0 is the response value, and the smaller the value, the higher the sensitivity of the sensor to the gas.

[0110] Take 1 porous ceramic encapsulated gas sensor of Example 1 and 1 3225 traditional perforated cover plate encapsulated gas sensor respectively, place the two 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 H2 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 7 shown. From Figure 7 the air permeability test results, it can be seen that in an H2 atmosphere with a gas concentration of 50 ppm, the response speed, recovery speed, and response degree of the ceramic encapsulated sensor of Example 1 to H2 are similar to those of the 3225 traditional encapsulation, and its air permeability performance is excellent.

[0111] The ceramic sheet prepared by the method of the present invention has excellent mechanical properties, and also has good air permeability and waterproof properties. The sensor encapsulated with it has anti-ozone and anti-ethanol properties, and can selectively permeate hydrogen.

[0112] The sensors used in the above tests are HGS-1001 type semiconductor sensors produced by Micro-Nano Sensing (Hefei) Technology Co., Ltd. The performance of this ceramic is the same for all sensors, without contingency and specific adaptability.

[0113] 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 method for preparing a porous ceramic with gas selective permeability, characterized in that: It includes the following steps: S1. Ball-mill calcined alumina, zinc oxide, manganese oxide, magnesium oxide, polyethylene glycol, corn starch and water in a ball-milling device; the mass ratio of calcined alumina, zinc oxide, manganese oxide, magnesium oxide, polyethylene glycol, corn starch is 5 - 12:1 - 2:1 - 12:0.2 - 0.5:0.2 - 0.5:1 - 2; S2. Add methyl cellulose and glycerol 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; wherein, the sintering temperature is 1500 - 1600 °C; S5. Mix hydrogen-containing silicone oil with ethyl acetate solution to prepare a hydrophobic agent solution, and then immerse the ceramic sheet in the hydrophobic agent solution to obtain the porous ceramic with gas selective permeability.

2. The preparation method of the porous ceramic with gas selective permeability according to claim 1, characterized in that: In S1, the preparation method of the calcined alumina includes the following steps: Place 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.

3. The preparation method of the porous ceramic with gas selective permeability according to claim 1, 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 with gas selective permeability according to claim 1, characterized in that: In S1, the rotation speed of the ball-milling is 600 r / min and the time is 24 h; in S2, the rotation speed of the ball-milling is 600 r / min and the time is 6 h; in S3, during the pressing process, the pressure is 20 MPa and the time is 1 min.

5. The preparation method of the porous ceramic with gas selective permeability according to claim 1, characterized in that: The dosage ratio of the calcined alumina, methyl cellulose, glycerol is 5 - 12 g:0.1 - 0.5 g:0.1 - 0.5 mL.

6. The preparation method of the porous ceramic with gas selective permeability 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 - 2 °C / min in an air atmosphere and keep it at a constant temperature for 1 h, then continue to heat it to 1500 - 1600 °C at a heating rate of 1 - 2 °C / min and keep it at a constant temperature for sintering for 1 - 3 h, and then cool it to room temperature at a cooling rate of 1 - 2 °C / min and take it out to obtain the ceramic sheet.

7. The preparation method of the porous ceramic with gas selective permeability according to any one of claims 1-6, characterized in that: In S5, the mass fraction of hydrogen-containing silicone oil in the hydrophobic agent solution is 10 - 20 wt%; the impregnation time is 2 h.

8. A porous ceramic with gas selective permeability, characterized in that: It is prepared by using the preparation method of the porous ceramic with gas selective permeability according to any one of claims 1 - 7.

9. An application of the porous ceramic with gas selective permeability according to claim 8 in a gas sensor.

10. An ethanol and ozone resistant gas sensor, characterized in that: It contains the porous ceramic with gas selective permeability according to claim 8.

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