A method for preparing a gas sensor for detecting H2S gas at low temperature

Abstract

This invention discloses a method for preparing a gas sensor for detecting H2S gas at low temperatures. The specific process is as follows: crystalline zinc acetate, glycine, sodium sulfate, and sodium hydroxide are used as reaction materials to prepare flaky ZnO nanopowders via a hydrothermal method. This powder is then subjected to in-situ sulfurization treatment using a sodium sulfide solution to produce ZnS / ZnO nanopowders. After precipitation, washing, and drying, a sintering aid is added, mixed, and ground to form a slurry. The slurry is evenly coated onto an alumina ceramic tube with gold electrodes at both ends. The sintering temperature is controlled to produce an indirectly heated ZnS / ZnO gas sensor. Compared to existing technologies, this invention has the advantages of a simple preparation process, rational design, low energy consumption, and high sensitivity.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a method for preparing a gas sensor for detecting H2S gas at low temperature. Background Art

[0002] The deteriorating ecological environment has created an urgent need for efficient, real-time gas monitoring. The development of gas sensors with superior performance is a crucial issue for the socio-economic development of humanity. While gas sensors have been widely used to detect various toxic, harmful, explosive, and volatile substances, their application areas are expanding with the advancement of science and technology. This is especially true during oil and gas field development, where hydrogen sulfide gas may be present in drilling sites or oil and gas production areas. To prevent hydrogen sulfide poisoning accidents, when drilling in hydrogen sulfide-containing oil and gas fields, in addition to installing wind vanes on the derrick, on the side of the drilling platform, in the mud circulation system, and in safety zones, a certain number of hydrogen sulfide detectors and alarms should also be installed within the well site.

[0003] However, the operating temperature of the MQ136 semiconductor metal oxide gas sensor currently sold on the market is 350°C, which is higher than the ignition point of hydrogen sulfide gas of 296°C. Therefore, there is a great safety hazard during use. Therefore, the preparation of hydrogen sulfide gas sensors with excellent performance at low temperatures has become an indispensable condition for the development of today's society. However, the traditional single ZnO gas-sensitive material has poor response to hydrogen sulfide gas at low temperatures and is easily corroded by hydrogen sulfide gas. Therefore, a method for preparing a gas sensor for low-temperature detection of H2S gas is urgently needed to solve the above problems. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the above technical problems and provide a method for preparing a gas sensor for detecting H2S gas at low temperature with simple preparation process, reasonable design, low energy consumption and high sensitivity.

[0005] To solve the above technical problems, the present invention provides a technical solution: a method for preparing a gas sensor for detecting H2S gas at low temperature, the specific process is as follows: using crystalline zinc acetate, glycine, sodium sulfate and sodium hydroxide as reaction raw materials, preparing flaky ZnO nanopowder by a hydrothermal method, using sodium sulfide solution for in-situ sulfurization treatment to obtain ZnS / ZnO nanopowder, after precipitation, water washing and drying, adding a sintering aid, mixing and grinding to prepare a slurry, and evenly applying the slurry to an alumina ceramic tube with gold electrodes at both ends. The sintering temperature is controlled to obtain a indirectly heated ZnS / ZnO gas sensor.

[0006] As an improvement, the molar ratio of the crystalline zinc acetate, glycine, sodium sulfate and sodium hydroxide is 1:2-3:1-1.5:4-5, the crystalline zinc acetate is dissolved in an ethanol solution, and glycine and sodium sulfate are dissolved in an aqueous solution, and the mixture is stirred for 1 to 2 hours, and then sodium hydroxide is slowly added dropwise, and rapid stirring is continued for 30 minutes.

[0007] As an improvement, the hydrothermal reaction temperature is 160-200° C., the hydrothermal reaction time is 6-12 hours, and the precipitate is centrifugally washed three times with deionized water to obtain ZnO flaky nanopowder.

[0008] As an improvement, the concentration of the sodium sulfide aqueous solution is 0.3 mol / L, the sulfidation temperature is 60-70°C, the sulfidation time is 5-8 minutes, the obtained sulfide is centrifugally washed three times with deionized water to remove impurity ions in the precipitate, and then the precipitate is dried in a blast drying oven at 80-90°C for 1-2 hours to obtain ZnS / ZnO nanopowder.

[0009] As an improvement, the sintering aid is low-temperature glass powder, glacial acetic acid ethanol solution and methyl cellulose.

[0010] As an improvement, the mass ratio of the gas-sensitive slurry is ZnO / ZnS nanopowder: low-temperature glass powder: glacial acetic acid: methyl cellulose is 75-80:5-7:14-18:1-5, poured into a mortar and fully ground for 30-50 minutes to make it evenly ground, and an appropriate amount of ethanol is dripped into the mortar to adjust the slurry viscosity and blend it into a gas-sensitive slurry.

[0011] As an improvement, the alumina ceramic tube with gold electrodes at both ends is ultrasonically cleaned with ethanol for 20 seconds and then dried for later use.

[0012] As an improvement, a Ni-Cr heating wire is inserted into the ceramic tube of the indirectly heated gas sensor and welded to the fixed pin of the heating wire electrode, and the platinum wire lead of the gold electrode of the gas sensor is welded to the fixed pin of the electrode. The gas-sensitive slurry is evenly applied to the dried ceramic tube with a brush, and dried in a blast drying oven at 100-110°C for 6-8 hours. After drying, it is sintered in an argon-protected sintering furnace at a sintering temperature of 400-600°C and a holding time of 1-2 hours. The tube is aged for 3-5 days at a working voltage of 3V to obtain an indirectly heated ZnS / ZnO low-temperature H2S gas sensor.

[0013] After adopting the above method, the present invention has the following advantages:

[0014] 1. ZnS / ZnO nanopowders are directly prepared by hydrothermal method combined with in-situ sulfurization technology. The crystal size of ZnS / ZnO nanopowders is controllable, operability is strong, and reproducibility is good, which is suitable for large-scale and industrial production;

[0015] 2. It realizes low-temperature hydrogen sulfide gas detection and leakage alarm, which is highly safe to use and improves the explosion-proof level of the alarm. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The XRD diagram of the ZnS / ZnO nanopowder obtained in the preparation method of the gas sensor for detecting H2S gas at low temperature of the present invention.

[0017] Figure 2 This is a SEM image of the ZnS / ZnO nanopowder obtained in Example 1 of the method for preparing a gas sensor for detecting H2S gas at low temperature of the present invention.

[0018] Figure 3 This is a response recovery curve of the ZnS / ZnO gas sensor obtained in Example 2 of the method for preparing a gas sensor for detecting H2S gas at low temperature of the present invention to 10 ppm hydrogen sulfide gas.

[0019] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or technical descriptions. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work. DETAILED DESCRIPTION

[0020] The study found that the addition of glycine and sodium sulfate changed the rod-shaped growth mechanism of traditional ZnO crystals growing along the C-axis direction, and grew into a lamellar structure through hydrolysis and complexation reaction, so that the subsequent in-situ sulfurization reaction can be completed in a short time, forming a heterojunction semiconductor-type ZnS / ZnO composite nanopowder with surface modified ZnS. A small amount of low-temperature glass powder was added during the preparation of the slurry to improve the mechanical strength of the gas-sensitive coating and avoid shedding due to mechanical vibration during transportation, installation or use. However, the addition of glass powder will cause the initial resistance of the component to increase. When the mass ratio of glass powder added is controlled within the range of 5-7%, the obtained gas-sensitive component was not found to fall off when it fell from a 1-meter-high table. Therefore, the impact of mechanical vibration on the component during use or installation is relatively small. The gas sensor obtained by this inventive method has a sensitivity of more than 10 to 10ppm hydrogen sulfide gas at an operating temperature of 100-200°C, and a response time of less than 20s. Under the same test conditions, when testing 100ppm ethanol, formaldehyde, ammonia, and methane gases, the responsiveness of the gas sensor is very low. Therefore, the gas sensor has high selectivity for hydrogen sulfide gas.

[0021] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific embodiments with reference to the accompanying drawings.

[0022] Example 1:

[0023] Commercially available analytically pure crystalline zinc acetate, glycine, sodium sulfate and sodium hydroxide were used, and the molar ratio of crystalline zinc acetate, glycine, sodium sulfate and sodium hydroxide was 1:1.5:1:4. Crystalline zinc acetate was first dissolved in ethanol solution, and glycine and sodium sulfate were dissolved in aqueous solution. The mixture was stirred for 1 hour, and then sodium hydroxide was slowly added dropwise and continued to be stirred rapidly for 30 minutes. The solution was transferred to a hydrothermal reactor, and the hydrothermal reaction temperature was controlled at 180°C and kept warm for 9 hours. The precipitate was then centrifuged and washed 3 times with deionized water to obtain ZnO flaky nanoparticles. The obtained powder was sulfided with a 0.3 mol / L sodium sulfide aqueous solution at a sulfiding temperature of 60°C for 5 minutes, and the obtained sulfide was centrifugally washed 3 times with deionized water to remove impurity ions in the precipitate. The precipitate was then dried in a blast drying oven at 85°C for 2 hours to obtain ZnO / ZnS nanopowder. The ingredients were prepared according to the ratio of ZnS / ZnO nanopowder: low-temperature glass powder: glacial acetic acid: methyl cellulose = 75:5:17:3, poured into an agate mortar and fully ground for at least 30 minutes; an appropriate amount of Ethanol is used to adjust the viscosity of the slurry and blend it into a gas-sensitive slurry. The alumina ceramic tube with gold electrodes at both ends is ultrasonically cleaned with ethanol for 20 seconds and then dried for use. The gas-sensitive slurry is evenly applied to the dried ceramic tube with a brush and dried in a blast drying oven at 100°C for 6 hours. After drying, it is sintered in an argon-protected sintering furnace at a sintering temperature of 600°C and a holding time of 2 hours. After cooling in the furnace, a indirectly heated gas-sensitive element is obtained. The Ni-Cr heating wire is inserted into the ceramic tube of the indirectly heated gas-sensitive element and welded to the heating wire electrode. Fixed pin; weld the platinum wire lead of the gold electrode of the gas-sensitive element to the fixed pin of the electrode, and age it at a working voltage of 3V for 3 days to obtain a indirectly heated ZnS / ZnO low-temperature detection H2S gas sensor. Tested by the Weisheng gas-sensitive material tester WS-30B, the obtained indirectly heated ZnS / ZnO gas sensor has the ability to detect hydrogen sulfide gas at low temperatures. At an operating temperature of 100°C, the sensitivity to 10ppm hydrogen sulfide gas can reach 70, the response time is 20s, and the selectivity to hydrogen sulfide gas is very high.

[0024] Example 2:

[0025] On the basis of Example 1, the hydrothermal reaction temperature was changed to 160°C, and the other preparation processes remained unchanged. The obtained indirectly heated ZnS / ZnO gas sensor had low-temperature detection capability for hydrogen sulfide gas. At an operating temperature of 100°C, the sensitivity to 10 ppm hydrogen sulfide gas could reach 60, the response time was less than 20s, and the selectivity for hydrogen sulfide gas was very high.

[0026] Example 3:

[0027] On the basis of Example 1, the hydrothermal reaction temperature was changed to 200°C, and the other preparation processes remained unchanged. The obtained indirectly heated ZnS / ZnO gas sensor had low-temperature detection capability for hydrogen sulfide gas. At an operating temperature of 100°C, the sensitivity to 10 ppm hydrogen sulfide gas could reach 65, the response time was less than 20s, and the selectivity for hydrogen sulfide gas was very high.

[0028] Example 4:

[0029] On the basis of Example 1, the hydrothermal holding time was changed to 6 hours, and the other preparation processes remained unchanged. The obtained indirectly heated ZnS / ZnO gas sensor had low-temperature detection capability for hydrogen sulfide gas. At an operating temperature of 100°C, the sensitivity to 10 ppm hydrogen sulfide gas could reach 84, the response time was less than 20s, and the selectivity for hydrogen sulfide gas was very high.

[0030] Example 5:

[0031] On the basis of Example 1, the hydrothermal holding time was changed to 12 hours, and the other preparation processes remained unchanged. The obtained indirectly heated ZnS / ZnO gas sensor had low-temperature detection capability for hydrogen sulfide gas. At an operating temperature of 100°C, the sensitivity to 10 ppm hydrogen sulfide gas was only 24, the response time was less than 20s, and the selectivity for hydrogen sulfide gas was very high.

[0032] Example 6:

[0033] On the basis of Example 1, the sulfurization time was changed to 10 minutes, and the other preparation processes remained unchanged. The obtained indirectly heated ZnS / ZnO gas sensor had low-temperature detection capability for hydrogen sulfide gas. At an operating temperature of 100°C, the sensitivity to 10 ppm hydrogen sulfide gas was only 12, the response time was less than 20s, and the selectivity for hydrogen sulfide gas was very high.

[0034] Example 7:

[0035] On the basis of Example 1, the molar ratio of crystalline zinc acetate, glycine, sodium sulfate and sodium hydroxide was changed to 1:3:1.5:5, and the other preparation processes remained unchanged. The obtained indirectly heated ZnS / ZnO gas sensor had low-temperature detection capability for hydrogen sulfide gas. At an operating temperature of 100°C, the sensitivity to 10 ppm hydrogen sulfide gas could reach 45, the response time was less than 20s, and the selectivity for hydrogen sulfide gas was very high.

[0036] Example 8:

[0037] On the basis of Example 1, the mass ratio of ZnS / ZnO nanopowder: low-temperature glass powder: glacial acetic acid: methyl cellulose was changed to 75:7:16:2, and the other preparation processes remained unchanged. The obtained indirectly heated ZnS / ZnO gas sensor had low-temperature detection capability for hydrogen sulfide gas. At an operating temperature of 100°C, the sensitivity to 10 ppm hydrogen sulfide gas could reach 30, the response time was less than 20s, and the selectivity for hydrogen sulfide gas was very high.

[0038] The above description of the present invention and its embodiments is non-limiting. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. In short, if a person skilled in the art is inspired by the above and, without departing from the purpose of the present invention, designs structures and embodiments similar to the technical solution without inventiveness, they shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing a gas sensor for detecting H2S gas at low temperature, characterized in that: The specific process is as follows: Using crystalline zinc acetate, glycine, sodium sulfate, and sodium hydroxide as reaction raw materials, flaky ZnO nanopowders are prepared by a hydrothermal method. In-situ sulfurization treatment is performed using a sodium sulfide solution to obtain ZnS / ZnO nanopowders. After precipitation, washing, and drying, a sintering aid is added, mixed, and ground to prepare a slurry. The slurry is evenly coated onto an alumina ceramic tube with gold electrodes at both ends. The sintering temperature is controlled to obtain an indirectly heated ZnS / ZnO gas sensor. The molar ratio of the crystalline zinc acetate, glycine, sodium sulfate and sodium hydroxide is 1:2-3:1-1.5:4-5. The crystalline zinc acetate is dissolved in an ethanol solution, and glycine and sodium sulfate are dissolved in an aqueous solution. The mixture is stirred for 1 to 2 hours, and then sodium hydroxide is slowly added dropwise, and the mixture is continuously stirred rapidly for 30 minutes.

2. The method for preparing a gas sensor for detecting H2S gas at low temperature according to claim 1, characterized in that: The hydrothermal reaction temperature is 160-200° C., the hydrothermal reaction time is 6-12 hours, and the precipitate is centrifugally washed three times with deionized water to obtain ZnO flaky nanopowder.

3. The method for preparing a gas sensor for detecting H2S gas at low temperature according to claim 1, characterized in that: The concentration of the sodium sulfide aqueous solution is 0.3 mol / L, the sulfidation temperature is 60-70° C., and the sulfidation time is 5-8 minutes. The obtained sulfide is centrifugally washed three times with deionized water to remove impurity ions in the precipitate, and then the precipitate is dried in a blast drying oven at 80-90° C. for 1-2 hours to obtain ZnS / ZnO nanopowder.

4. The method for preparing a gas sensor for detecting H2S gas at low temperature according to claim 1, characterized in that: The sintering aids are low-temperature glass powder, glacial acetic acid ethanol solution and methyl cellulose.

5. The method for preparing a gas sensor for detecting H2S gas at low temperature according to claim 1, characterized in that: The gas-sensitive slurry is prepared in a mass ratio of ZnO / ZnS nanopowder: low-temperature glass powder: glacial acetic acid: methyl cellulose of 75-80:5-7:14-18:1-5. The mixture is poured into a mortar and fully ground for 30-50 minutes to make it evenly ground. An appropriate amount of ethanol is dripped into the mortar to adjust the slurry viscosity and blend it into a gas-sensitive slurry.

6. The method for preparing a gas sensor for detecting H2S gas at low temperature according to claim 1, characterized in that: The alumina ceramic tube with gold electrodes at both ends is ultrasonically cleaned with ethanol for 20 seconds and then dried for later use.

7. The method for preparing a gas sensor for detecting H2S gas at low temperature according to claim 1, characterized in that: A Ni-Cr heating wire is inserted into a ceramic tube of a indirectly heated gas-sensitive element and welded to the fixed pin of the heating wire electrode. A platinum wire lead of a gold electrode of the gas-sensitive element is welded to the fixed pin of the electrode. A gas-sensitive slurry is evenly applied to the dried ceramic tube with a brush, and the tube is dried in a blast drying oven at 100-110°C for 6-8 hours. After drying, the tube is sintered in an argon-protected sintering furnace at a sintering temperature of 400-600°C and a holding time of 1-2 hours. The tube is aged at a working voltage of 3V for 3-5 days to obtain an indirectly heated ZnS / ZnO low-temperature H2S gas sensor.

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