Gas-sensitive slurry as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of gas sensors, and discloses gas-sensitive slurry as well as a preparation method and application thereof. The gas-sensitive slurry is prepared from the following raw materials: a metal oxide gas-sensitive material, platinum powder, silica sol, an organic carrier, carboxymethyl cellulose, low-temperature molten glass powder, sodium dodecyl sulfate and an antioxidant. According to the gas-sensitive slurry prepared by the invention, the proper metal oxide gas-sensitive material, the organic carrier and other admixtures are selected, so that the film forming thickness is uniform, the adhesion is good, the hygroscopicity is low and the oxidation resistance is strong after the gas-sensitive slurry is coated on an MEMS chip, and the prepared MEMS gas sensor is good in repeatability, stable in long-term work and excellent in reliability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas sensor, in particular to a gas sensitive slurry and its preparation method and application. BACKGROUND

[0002] Formaldehyde is widely used because of its simple production process and abundant raw material supply. It is needed in the synthesis of surfactants, plastics, rubber, leather, building materials, and disinfection and preservation processes. At the same time, formaldehyde is harmful to human health. After inhaling high concentration formaldehyde, it can cause serious irritation of the respiratory tract and headache. Regularly inhaling small amounts of formaldehyde may cause chronic poisoning and even cancer. Therefore, it is increasingly important to develop a gas sensor with high sensitivity, short response time, low working temperature and good selectivity for formaldehyde.

[0003] The existing formaldehyde gas sensor has good sensitivity and fast response speed in a short time after purchase, but after being idle for a period of time, the response speed will obviously decay, the repeatability is poor, and the resistance baseline is easy to drift. The main reason is that the gas sensitive slurry coated on the sensor deteriorates due to oxidation and aging after immersion, resulting in poor reliability of the gas sensitive material. Therefore, it is of great significance to develop a gas sensitive slurry with good repeatability, long-term working stability, and less response speed decay for formaldehyde detection in daily life. SUMMARY

[0004] In order to solve the above technical problems, a gas sensitive slurry with good repeatability, long-term working stability, and good slurry film-forming property, excellent reliability and anti-aging performance is developed. The present application provides a gas sensitive slurry and its preparation method and application.

[0005] In the first aspect, the present application provides a gas sensitive slurry, which comprises the following raw materials by weight: metal oxide gas sensitive material 160-250 parts, platinum powder 6-15 parts, silica sol 15-28 parts, organic carrier 80-150 parts, carboxymethyl cellulose 5-15 parts, low-temperature melting glass powder 6-13 parts, sodium dodecyl sulfonate 2-5 parts and antioxidant 1.5-2.5 parts.

[0006] By adopting the above technical scheme, the low-temperature melting glass powder is added to the gas sensitive slurry, so that the gas sensitive slurry can be sintered at a lower temperature, improving the density and sealing property of the gas sensitive coating, enhancing the adhesion between the gas sensitive slurry coating and the base, and also improving the corrosion resistance and high-temperature oxidation resistance of the gas sensitive slurry. The platinum powder can play a sensitizing role, making the gas sensitive material respond faster to formaldehyde gas. The addition of silica sol in the gas sensitive slurry can make the silicon dioxide particles doped in the metal oxide gas sensitive material, so that the water molecules are preferentially adsorbed by the silicon dioxide particles, thereby reducing the adsorption of water molecules on the O 2-On the adsorption sites, the amount of adsorbed oxygen is reduced and the adsorbed species is changed, which leads to the adsorption of too many water molecules on the material surface, causing poisoning, significantly reducing the resistance and sensor response, thereby improving the long-term working stability of the gas-sensitive paste.

[0007] Further, the organic carrier includes epoxy resin, cyanate ester resin and terpineol in a weight ratio of 3-5:2:14-20.

[0008] By adopting the above technical solution, the epoxy resin and the cyanate ester resin copolymerize under heating conditions to form macromolecules with a highly cross-linked grid structure, which has a low moisture absorption characteristic, and can effectively avoid the problem of damage of the gas-sensitive paste due to water absorption during use and storage; secondly, the cross-linked copolymerized organic carrier can improve the flexibility of the sintered gas-sensitive layer and can prevent the occurrence of cracks in the gas-sensitive layer during sintering.

[0009] Further, the metal oxide gas-sensitive material is selected from one of a zinc metatitanate nanofiber gas-sensitive material, a zinc metatitanate nanomicrosphere gas-sensitive material and a zinc metatitanate nanosheet gas-sensitive material.

[0010] Further, the preparation method of the zinc metatitanate nanosheet includes the following steps: 1) mixing zinc nitrate hexahydrate, tin tetrachloride pentahydrate, tetrabutyl titanate, urea and polyvinylpyrrolidone, adding deionized water, stirring, and preparing a solution; 2) moving the solution prepared in step 1 into a polytetrafluoroethylene hydrothermal reaction kettle, reacting at 150-180℃ for 12h, filtering the residue, washing and drying to prepare a powder; 3) mixing citric acid and the powder prepared in step 2, adding to tetrahydrofuran, stirring, adding nickel sulfamate, ultrasonic dispersion, distilling to remove tetrahydrofuran, and drying at room temperature to prepare an intermediate material; 4) calcining the intermediate material prepared in step 3 at 550℃ for 2h to prepare a zinc metatitanate nanosheet gas-sensitive material.

[0011] Further, the raw materials of the zinc metatitanate nanosheet include zinc nitrate hexahydrate, tin tetrachloride pentahydrate, tetrabutyl titanate and nickel sulfamate in a weight ratio of 13-15:16-18:0.2-0.5:0.6-0.8.

[0012] By adopting the above technical solution, the zinc metatitanate is reacted with citric acid to obtain a complex, nickel sulfamate is added for sufficient dispersion, the solvent is distilled off, and calcination is performed to prepare a zinc metatitanate nanosheet gas-sensitive material doped with nickel nanoparticles, and the dispersibility of the nickel nanoparticles is good, which can well improve the agglomeration of the nickel nanoparticles in the zinc metatitanate nanosheet.

[0013] After doping titanium, the zinc metatungstate nanosheet gas-sensitive material has a wider band gap, smaller resistivity and higher catalytic activity; after doping nickel, the zinc metatungstate nanosheet can form more pore structures, improve the specific surface area, facilitate the adsorption and desorption of gas, improve the catalytic activity of the sensor surface, and further improve the sensitivity of the sensor.

[0014] In a second aspect, the application provides a preparation method of a gas-sensitive slurry, comprising the following preparation steps: S1, mixing a metal oxide gas-sensitive material, an organic carrier, carboxymethyl cellulose, sodium dodecyl sulfonate and an antioxidant, and then performing ball milling to obtain a gas-sensitive slurry base A; S2, mixing a part of the gas-sensitive slurry base A prepared in step S2 with silica sol and platinum powder, and then performing ball milling to obtain a gas-sensitive material slurry B, and mixing the remaining part of the gas-sensitive slurry base A with low-temperature melting glass powder, and then performing ball milling to obtain a gas-sensitive material slurry C; S3, respectively heating the gas-sensitive material slurry B and the gas-sensitive material slurry C to 150-180 DEG C, stirring and reacting for 15-30 min to perform heat treatment, and the heat-treated gas-sensitive material slurry B and the heat-treated gas-sensitive material slurry C together constitute a gas-sensitive slurry.

[0015] Further, in step S2, the weight ratio of the amount of the gas-sensitive slurry base A used for preparing the gas-sensitive material slurry B to the amount of the gas-sensitive slurry base A used for preparing the gas-sensitive material slurry C is 1-2:3-5.

[0016] In a third aspect, the application provides an application of the above-mentioned gas-sensitive slurry on a MEMS gas sensor.

[0017] Further, the preparation method of the MEMS gas sensor comprises the following steps: T1, using a screen printing device to transfer the gas-sensitive material slurry C in claim 6 to the interdigital electrodes of a MEMS micro-heater substrate, and then solidifying to obtain a gas-sensitive film C; T2, using an inkjet printing device to transfer the gas-sensitive material slurry B in claim 6 to the interdigital electrodes of the MEMS micro-heater substrate after T1, and then solidifying to obtain a gas-sensitive film B; T3, sequentially performing annealing, cutting, gold ball welding and ceramic packaging on the interdigital electrodes of the MEMS micro-heater substrate after step T2 to obtain a MEMS gas sensor.

[0018] Further, the thickness of the gas-sensitive film C is 5-30 um, and the thickness of the gas-sensitive film B is 3-15 um.

[0019] In summary, the application has at least one of the following beneficial technical effects: The gas sensitive slurry prepared in the application has uniform film thickness, good adhesion, low hygroscopicity and strong oxidation resistance after being coated on the MEMS chip by selecting appropriate metal oxide gas sensitive materials, organic carriers and other additives, so that the prepared MEMS gas sensor has good repeatability, long-term working stability and excellent reliability. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 SEM image of the gas sensitive slurry prepared in Example 2; Figure 2 Gas sensitive response sensitivity test diagram of the MEMS gas sensor prepared in Application Example 2 at different temperatures to 100ppm formaldehyde gas; Figure 3 Long-term stability test diagram of the MEMS gas sensor in Application Example 2, Application Example 8 and Application Comparative Example 1; Figure 4 Response speed comparison diagram of the MEMS gas sensor prepared in Application Example 2, Application Example 6, Application Example 7, Application Example 8 and Application Comparative Example 1 after a certain working time. DETAILED DESCRIPTION

[0021] The application will be further described in detail below in combination with examples.

[0022] The application designs a gas sensitive slurry, which comprises the following raw materials in parts by weight: metal oxide gas sensitive material 160-250 parts, platinum powder 6-15 parts, silica sol 15-28 parts, organic carrier 80-150 parts, carboxymethyl cellulose 5-15 parts, low-temperature melting glass powder 6-13 parts, sodium dodecyl sulfonate 2-5 parts and antioxidant 1.5-2.5 parts.

[0023] The gas sensitive slurry of the application is prepared by the following method, comprising the following steps: S1, mixing the metal oxide gas sensitive material, the organic carrier, the carboxymethyl cellulose, the sodium dodecyl sulfonate and the antioxidant, and then ball milling to obtain a gas sensitive slurry base A; S2, mixing a part of the gas sensitive slurry base A prepared in step S2 with the silica sol and the platinum powder, and then ball milling to obtain a gas sensitive material slurry B, and mixing the remaining part of the gas sensitive slurry base A with the low-temperature melting glass powder, and then ball milling to obtain a gas sensitive material slurry C; S3, respectively heating the gas sensitive material slurry B and the gas sensitive material slurry C to 150-180℃, and stirring for 15-30min for heat treatment, and the heat treated gas sensitive material slurry B and the heat treated gas sensitive material slurry C together constitute the gas sensitive slurry.

[0024] The gas sensitive slurry of the application can be applied on the MEMS gas sensor.

[0025] The technical problem solved by the present application is that the existing formaldehyde gas sensor has good sensitivity and fast response speed in a short time after purchase, but after being idle for a period of time, the response speed is significantly attenuated, the repeatability is poor, and the resistance baseline is prone to drift, etc. The main reason is that the gas sensitive paste coated on the sensor is deteriorated due to oxidation and aging after immersion, resulting in poor reliability of the gas sensitive material. The gas sensitive paste in the present application selects appropriate metal oxide gas sensitive material, organic carrier and other doping materials, so that the film thickness is uniform, the adhesion is good, the hygroscopicity is low, and the oxidation resistance is strong after being coated on the MEMS chip, so that the prepared MEMS gas sensor has good repeatability, long-term working stability and excellent reliability.

[0026] Examples 1-5 Examples 1-5 are gas sensitive pastes with different weight proportions, and the specific proportions are shown in Table 1 (unit: weight parts) Table 1 The organic carrier in Examples 1-5 is epoxy resin, cyanate ester resin and terpineol with a weight ratio of 4:2:15.

[0027] The antioxidant in Examples 1-5 is antioxidant 1010.

[0028] The metal oxide gas sensitive material in Examples 1-5 is zinc metatitanate nanosheet gas sensitive material, and the specific preparation method includes the following steps: 1) Mix zinc nitrate hexahydrate, tin tetrachloride pentahydrate, tetrabutyl titanate, urea and polyvinylpyrrolidone, add deionized water, stir, and prepare a solution; 2) Move the solution prepared in step 1 into a polytetrafluoroethylene hydrothermal reactor, react at 160℃ for 12h, filter the residue, wash and dry to obtain a powder; 3) Mix citric acid and the powder prepared in step 2, add to tetrahydrofuran, stir, add nickel sulfamate, ultrasonic dispersion for 30min, distill tetrahydrofuran, and dry at room temperature to obtain an intermediate material; 4) Calcine the intermediate material prepared in step 3 at 550℃ for 2h to obtain zinc metatitanate nanosheet gas sensitive material.

[0029] The weight ratio of zinc nitrate hexahydrate, tin tetrachloride pentahydrate, tetrabutyl titanate and nickel sulfamate is 14:16:0.4:0.8.

[0030] The preparation method of the gas sensitive paste in Examples 1-5 includes the following steps: S1, mixing the metal oxide gas sensitive material, the organic carrier, the carboxymethyl cellulose, the sodium dodecyl sulfonate and the antioxidant, and then ball milling at 200 rpm for 30 min to obtain a gas sensitive slurry base A; S2, mixing a part of the gas sensitive slurry base A prepared in step S2 with the silica sol and the platinum powder, and then ball milling at 500 rpm for 30 min to obtain a gas sensitive material slurry B, and mixing the remaining part of the gas sensitive slurry base A with the low-temperature melting glass powder, and then ball milling at 500 rpm for 30 min to obtain a gas sensitive material slurry C; S3, respectively heating the gas sensitive material slurry B and the gas sensitive material slurry C to 180℃ for heat treatment, and stirring for 30 min, and the gas sensitive material slurry B and the gas sensitive material slurry C after heat treatment together constitute a gas sensitive slurry.

[0031] The weight ratio of the amount of the gas sensitive slurry base A used for preparing the gas sensitive material slurry B to the amount of the gas sensitive slurry base A used for preparing the gas sensitive material slurry C is 1:4.

[0032] Examples 6-7 Example 6 is based on Example 2, and the difference is that the organic carrier in Example 6 includes epoxy resin, cyanate ester resin and pine oil alcohol with a weight ratio of 3:2:20.

[0033] Example 7 is based on Example 2, and the difference is that the organic carrier in Example 7 includes epoxy resin, cyanate ester resin and pine oil alcohol with a weight ratio of 5:2:14.

[0034] Example 8 Example 8 is based on Example 2, and the difference is that the zinc metatitanate nanosheet gas sensitive material in Example 8 is prepared by the following steps: 1) mixing zinc nitrate hexahydrate, tin tetrachloride pentahydrate, tetrabutyl titanate, urea and polyvinylpyrrolidone, and then adding deionized water and stirring to obtain a solution; 2) moving the solution prepared in step 1 into a polytetrafluoroethylene hydrothermal reaction kettle, and then reacting at 160℃ for 12h, and then filtering to obtain a filter residue, and then washing and drying to obtain a powder; 3) calcining the powder prepared in step 2 at 550℃ for 2h to obtain a zinc metatitanate nanosheet gas sensitive material.

[0035] Comparative Example 1 Comparative Example 1 is based on Example 2, and the difference is that no low-temperature melting glass powder is added to the organic carrier in Comparative Example 1.

[0036] Application Examples 1-8 and Comparative Example 1 The gas sensitive paste prepared in Example 1-8 and Comparative Example 1 is used to prepare a MEMS gas sensor, which corresponds to Application Examples 1-8 and Comparative Example 1, respectively. The preparation method of the MEMS gas sensor prepared in Application Examples 1-8 and Comparative Example 1 comprises the following steps: T1, using a screen printing device, the gas sensitive material paste C in claim 6 is transferred to the interdigital electrode of the MEMS micro-heater substrate, and baked at 80℃ for 60min for curing, to prepare a gas sensitive film C; T2, using an inkjet printing device, the gas sensitive material paste B in claim 6 is transferred to the interdigital electrode of the MEMS micro-heater substrate treated by T1, and baked at 80℃ for 60min for curing, to prepare a gas sensitive film B; T3, the interdigital electrode of the MEMS micro-heater substrate treated by step T2 is sequentially subjected to annealing, cutting, gold ball welding and ceramic packaging, to prepare a MEMS gas sensor.

[0037] The annealing temperature is 500℃, and the annealing time is 4h; the thickness of the cured gas sensitive film C is 25um, and the thickness of the cured gas sensitive film B is 12um.

[0038] Performance detection 1. The gas sensitive response sensitivity of the MEMS gas sensor prepared in Application Example 2 to 100ppm formaldehyde gas at different temperatures is measured, and the determination results are shown in Table 1. Figure 2 .

[0039] To Figure 2 The analysis of the data shows that the MEMS gas sensor prepared in Application Example 2 exhibits the best response value at 220℃, i.e., the optimal working temperature of the MEMS gas sensor prepared in the present application is about 220℃.

[0040] 2. The gas sensitive response sensitivity of the MEMS gas sensors prepared in Application Examples 1-8 to 0.2ppm, 2ppm and 50ppm formaldehyde gas at room temperature is measured, and the determination results are shown in Table 2.

[0041] Table 2 The analysis of the data in Table 3 shows that the sensitivity response values of Application Examples 1-5 to different concentrations of formaldehyde gas are significantly better than those of Application Examples 6-8, and therefore, the MEMS gas sensor prepared in the present application has high sensitivity to formaldehyde gas, good selectivity, and simple manufacturing process, and the manufacturing conditions are easy to meet.

[0042] 3. The long-term working stability of the MEMS gas sensor prepared in Application Example 2, Application Example 8 and Application Comparative Example 1 was determined, and the sensitivity response values at room temperature to 2 ppm of formaldehyde gas at 15, 30, 60, 90, 120, 150 and 180 days were determined and plotted into a line graph, and the test results are shown in Figure 2 .

[0043] Through analysis of Figure 2 , it can be seen that the MEMS gas sensor prepared in Application Example 2 and Application Example 8 has a significantly smaller decrease in the sensitivity response value to 2 ppm of formaldehyde gas at room temperature over time than the MEMS gas sensor prepared in Application Comparative Example 1; the MEMS gas sensor prepared in Application Example 2 has a smaller decrease in the sensitivity response value to 2 ppm of formaldehyde gas at room temperature over time than the MEMS gas sensor prepared in Application Example 8; therefore, the zinc metatungstate nanosheet gas-sensitive material doped with nickel nanoparticles has better long-term stability, and the addition of low-temperature melting glass powder in the gas-sensitive slurry enables the gas-sensitive slurry to be sintered at a lower temperature, improves the compactness and sealing property of the gas-sensitive coating, and also improves the long-term stability of the MEMS gas sensor prepared from the gas-sensitive slurry.

[0044] 4. The response speed of the MEMS gas sensor prepared in Application Example 2, Application Examples 6-8 and Application Comparative Example 1 after long-term working was determined, and the test results are shown in Figure 4 .

[0045] According to Figure 4 , the MEMS sensor of the present application has a significantly lower decay in the response speed after long-term working.

[0046] The above are preferred embodiments of the present application, and are not intended to limit the protection scope of the present application, therefore: any equivalent changes made according to the structure, shape, principle of the present application should be covered within the protection scope of the present application.

Claims

1. A gas sensitive paste, characterized in that, The raw materials include the following components by weight: 160-250 parts of metal oxide gas sensitive material, 6-15 parts of platinum powder, 15-28 parts of silica sol, 80-150 parts of organic carrier, 5-15 parts of carboxymethyl cellulose, 6-13 parts of low-melting glass powder, 2-5 parts of sodium dodecyl sulfonate and 1.5-2.5 parts of antioxidant.

2. The gas sensitive paste according to claim 1, characterized in that, The organic carrier comprises epoxy resin, cyanate ester resin and terpineol in a weight ratio of 3-5:2:14-20.

3. The gas sensitive paste according to claim 1, characterized in that, The metal oxide gas sensitive material is selected from one of zinc metatitanate nanofiber gas sensitive material, zinc metatitanate nanomicrosphere gas sensitive material and zinc metatitanate nanosheet gas sensitive material.

4. The gas sensitive paste according to claim 3, characterized in that The preparation method of the zinc metatitanate nanosheet comprises the following steps: 1) mixing zinc nitrate hexahydrate, tin tetrachloride pentahydrate, tetrabutyl titanate and urea with polyvinylpyrrolidone, adding deionized water, stirring to prepare a solution; 2) moving the solution prepared in step 1 into a polytetrafluoroethylene hydrothermal reactor, reacting at 150-180℃ for 12h, filtering the residue, washing and drying to prepare a powder; 3) mixing citric acid and the powder prepared in step 2, adding into tetrahydrofuran, stirring, adding nickel sulfamate, ultrasonic dispersion, distilling tetrahydrofuran, drying at room temperature to prepare an intermediate material; 4) calcining the intermediate material prepared in step 3 at 550℃ for 2h to prepare the zinc metatitanate nanosheet gas sensitive material.

5. The gas sensitive paste according to claim 4, characterized in that The raw materials of the zinc metatitanate nanosheet include zinc nitrate hexahydrate, tin tetrachloride pentahydrate, tetrabutyl titanate and nickel sulfamate in a weight ratio of 13-15:16-18:0.2-0.5:0.6-0.

8.

6. A preparation method of the gas sensitive paste according to any one of claims 1-5, comprising the following steps: S1, mixing the metal oxide gas sensitive material, the organic carrier, the carboxymethyl cellulose, the sodium dodecyl sulfonate and the antioxidant, and then ball milling to obtain a gas sensitive paste base A; S2, mixing a part of the gas sensitive paste base A prepared in step S2 with the silica sol and the platinum powder, and then ball milling to prepare a gas sensitive material paste B, and mixing the remaining part of the gas sensitive paste base A with the low-melting glass powder, and then ball milling to prepare a gas sensitive material paste C; S3, respectively heating the gas sensitive material paste B and the gas sensitive material paste C to 150-180℃, stirring and reacting for 15-30min for heat treatment, and the heat treated gas sensitive material paste B and the heat treated gas sensitive material paste C together constitute the gas sensitive paste.

7. The method of claim 6, wherein the gas sensitive paste is prepared by mixing the conductive material, the dielectric material, and the gas sensitive material. In step S2, the amount of the gas sensitive paste base A used for preparing the gas sensitive material paste B and the amount of the gas sensitive paste base A used for preparing the gas sensitive material paste C have a weight ratio of 1-2:3-5.

8. Application of the gas sensitive paste according to any one of claims 1-5 to a MEMS gas sensor.

9. Use of the gas-sensitive paste according to claim 8 on a MEMS gas sensor, characterized in that, The preparation method of the MEMS gas sensor comprises the following steps: T1, using a screen printing device to transfer the gas sensitive material paste C in claim 6 to the interdigital electrodes of a MEMS micro-heater substrate, and curing to prepare a gas sensitive film C; T2, using an inkjet printing device to transfer the gas sensitive material paste B in claim 6 to the interdigital electrode of the MEMS micro-heater substrate treated by T1, and solidify to obtain a gas sensitive film B; T3, after annealing, cutting, gold ball welding and ceramic packaging of the interdigital electrode of the MEMS micro-heater substrate treated by T2, a MEMS gas sensor is obtained.

10. Use of the gas sensitive paste according to claim 8 on a MEMS gas sensor, characterized in that, The thickness of the gas sensitive film C is 5-30 um, and the thickness of the gas sensitive film B is 3-15 um.

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