High-sensitivity decomposed gas sensor of air switch cabinet

Abstract

The invention relates to the field of gas detection, and discloses a high-sensitivity decomposition gas sensor for an air switch cabinet, which takes a Co3O4 / Cr2O3 / YSZ ternary composite material as a sensitive electrode, and is prepared by the following method: step (1): ball-milling yttrium oxide stabilized zirconia powder, tabletting and then firing a solid electrolyte; (2) coating two fine Pt welding wires on the surface of the YSZ solid electrolyte, and calcining the YSZ solid electrolyte to prepare a sensor substrate; and (3) weighing Co3O4, Cr2O3 and YSZ powder, adding absolute ethyl alcohol and zirconium oxide balls for wet ball milling, naturally drying after ball milling, mixing with an organic carrier, performing silk-screen printing, coating on a sensor substrate, and calcining to form a sensitive electrode layer. The sensor adopts the ternary composite material as the sensitive electrode, the performance of each component is retained, the detected NO is as low as 10 * 10 <-6 >, and the reproducibility is good.

Description

Technical Field

[0001] The invention relates to the field of gas detection, and in particular to a high-sensitivity decomposition gas sensor for an air switch cabinet. Background Art

[0002] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0003] The filling gas in the air switch cabinet is usually sulfur hexafluoride (SF6) or nitrogen (N2), which are stable under normal working conditions. However, when a partial discharge or local overheating fault occurs, a series of chemical reactions will be triggered. Nitrogen may react with oxygen under discharge conditions to produce nitrogen oxides, such as nitric oxide (NO) and nitrogen dioxide (NO2), which can further react to produce ozone (O3). The accumulation of gases generated by these reactions, especially nitrogen oxides and ozone, can cause damage to both the equipment and the environment. They can corrode metal parts inside the equipment, reduce insulation performance, and even pose a threat to human health, so it is necessary to detect faults in a timely manner.

[0004] Electrochemical sensors are popular in the field of gas detection because of their high selectivity. They can accurately identify target gases in complex gas environments. However, their operating temperatures are generally high and their service life is relatively short. Optical gas sensors are a new type of sensor that detects target gases by optical methods. There are two main types: absorption spectrum and fluorescence. Optical gas sensors have the characteristics of high sensitivity, high precision, and long life, but their high cost and difficulty in use restrict their development. Sensors based on solid electrolytes are suitable for reliable measurement of nitrogen oxides in the above environments due to their excellent high-temperature stability and selectivity. Solid electrolyte sensors usually rely on specific sensitive materials to detect target gases, but these materials are still not stable enough in the overheated environment generated by air switch cabinets, affecting the performance and reliability of the sensor; and most solid electrolyte sensors currently use one sensitive material with a single sensitive characteristic. The sensitivity, reproducibility, stability and selectivity of the sensor are mainly related to the performance of the sensitive electrode material.

[0005] For the detection of nitrogen oxides, currently available methods include La 0.6 Ca 0.4 Mn 0.8 Ni 0.2 O 3-δMartin et al. prepared a YSZ-based impedance NOx sensor composite electrode using YSZ / Cr2O3 and obtained excellent sensor performance. The sensitive electrode of this material has a particle size of about 200 nanometers and is covered on the electrolyte surface in a loose and porous state, which is conducive to gas diffusion and mass transfer. The sensor exhibits good response-recovery characteristics and has little effect on O2 concentration, while having good reproducibility, stability and selectivity. NO x The detection range is 8×10 -6 -50×10 -6 , in the range of O2 concentration from 2% to 18.9%, the sensor is sensitive to NO x The response value is linearly correlated with the NOx concentration. However, this material may still have problems such as high cost and complex preparation process, and it is urgent to develop more reliable composite material sensitive electrodes. Summary of the invention

[0006] The purpose of the present invention is to provide a highly sensitive decomposition gas sensor for an air switch cabinet in view of the defects of the current prior art, using a Co3O4 / Cr2O3 / YSZ ternary composite material as a sensitive electrode.

[0007] The technical solution of the present invention is as follows:

[0008] On one hand, the present invention provides a sensitive electrode for an air switch cabinet, wherein the sensitive electrode is made of a Co3O4 / Cr2O3 / YSZ ternary composite material.

[0009] Another aspect of the present invention provides a method for preparing a sensitive electrode of an air switch cabinet, comprising the following steps:

[0010] Step (1): Co3O4, Cr2O3 and YSZ powders were weighed according to a weight ratio of Co3O4:Cr2O3:YSZ of 5:15:80, and anhydrous ethanol and zirconia balls were added for wet ball milling;

[0011] Step (2): After ball milling, the mixture is dried naturally; the powder mixed in step (1) is uniformly mixed with an organic carrier at a mass ratio of 3:7, and coated on a sensor substrate by screen printing; after calcination at 1000° C., a sensitive electrode layer is formed on the sensor substrate.

[0012] Preferably, the organic carrier in step (2) comprises 94%wt terpineol and 6%wt ethyl cellulose.

[0013] Another aspect of the present invention provides a method for preparing a highly sensitive decomposition gas sensor for an air switch cabinet, comprising the sensitive electrode as described above.

[0014] Another aspect of the present invention provides a method for preparing a highly sensitive decomposition gas sensor for an air switch cabinet as described above, which specifically comprises the following steps:

[0015] Step (1): Preparation of solid electrolyte: Add 1.5wt% PVB to yttria-stabilized zirconia (YSZ) powder, weigh accurately and place in a Teflon ball grinding jar. After continuous ball milling for 24 hours, dry the slurry at room temperature. Then weigh 0.8g of dry powder with an electronic balance and put it into a mold. Use a manual tablet press to press it into a circular sheet with a diameter of 13mm at 5MPa. Finally, the sheet is molded by a 300MPa cold isostatic press. Place the pressed sheet in a muffle furnace and sinter at 1500-1700℃ for 5-7h to obtain a dense YSZ solid electrolyte substrate.

[0016] Step (2): Preparation of sensor substrate: Two thin Pt welding wires are coated on the surface of the YSZ solid electrolyte, and the ends of the Pt welding wires are fixed by the bonding effect of the Pt solder paste. The solid electrolyte coated with platinum slurry is then calcined at 700°C-900°C for 0.5h-1.5h to produce the sensor substrate. When a self-heating sensor is prepared, the YSZ solid electrolyte described in step (2) is a 51×4×1mm strip YSZ (3mol% Y2O3), and the back side of the thin Pt welding wires arranged opposite to each other is printed with a heating circuit.

[0017] Step (3): Preparation of sensitive electrode: Co3O4, Cr2O3 and YSZ powders were weighed according to the weight ratio of Co3O4:Cr2O3:YSZ of 5:15:80, and anhydrous ethanol and zirconium oxide balls were added for wet ball milling; after ball milling, they were naturally dried. The mixed powder was evenly mixed with the organic carrier in a mass ratio of 3:7 and coated on the close electrolyte side by screen printing. After calcination at 1000°C, a sensitive electrode layer was formed on the sensor substrate.

[0018] According to a preferred embodiment, the organic carrier comprises 94%wt terpineol and 6%wt ethyl cellulose.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. A highly sensitive decomposition gas sensor for air switch cabinets. Existing solid electrolyte nitrogen oxide sensors use a single sensitive electrode material, which limits the detection range and has poor sensor performance at high temperatures. This sensor uses Co3O4 / Cr2O3 / YSZ ternary composite material as a sensitive electrode, which exhibits good response recovery characteristics for NO and can detect NO as low as 10×10 -6The NO gas has excellent repeatability. Compared with semiconductor sensors, ceramic sensors and other solid electrolyte nitrogen oxide sensors, it is more suitable for gas monitoring in air switch cabinets.

[0021] 2. A highly sensitive decomposition gas sensor for air switch cabinets can not only retain the performance of each component, but also adjust the sensitive characteristics by changing the proportion of its components, so as to better meet the needs of specific gas detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is the sensor response recovery characteristic diagram;

[0023] Figure 2 This is the sensor repeatability test data diagram;

[0024] Figure 3 This is the SEM image of the sensor used in this application. DETAILED DESCRIPTION

[0025] It should be noted that the test methods in the following examples are conventional methods unless otherwise specified. The test materials used in the following examples are all commercially available. The quantitative tests in the following examples were repeated three times, and the results were averaged.

[0026] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0027] Example 1 A method for preparing a highly sensitive decomposition gas sensor for an air switch cabinet

[0028] The present invention introduces an impedance-type NOx sensor using a Co3O4 / Cr2O3 / YSZ ternary composite material as a sensitive electrode. x Self-heating sensor.

[0029] Step (1) Preparation of solid electrolyte: 1.5wt% PVB (binder) is added to yttria-stabilized zirconia (YSZ) powder (3mol% Y2O3, Suzhou Youzinc Nanomaterials Co., Ltd., 99%, 50nm), accurately weighed and placed in a Teflon ball grinding jar. Add an appropriate amount of anhydrous ethanol and zirconium oxide pellets to the ball grinding jar, seal it tightly, and place it on an automatic ball mill. After continuous ball milling for 24 hours, the slurry is dried at room temperature. Then 0.8g of dry powder is weighed with an electronic balance and placed in a mold. Use a manual tablet press to press it into a circular sheet with a diameter of 13mm at 5MPa. Finally, the sheet is molded by a 300MPa cold isostatic press. The pressed sheet is placed in a muffle furnace and calcined at 1600℃ for 6h to obtain a dense YSZ solid electrolyte substrate.

[0030] Step (2) Preparation of sensor substrate: Two thin Pt welding wires are coated on the surface of the YSZ solid electrolyte, and the ends of the Pt welding wires are fixed by the bonding effect of the Pt solder paste. The solid electrolyte coated with platinum slurry is then calcined at 800°C for 1 hour to produce the sensor substrate. The sensor substrate of the self-heating sensor in this embodiment is a 51×4×1 mm strip YSZ (3 mol% Y2O3) with two platinum wires printed on the surface and a heating circuit printed on the back.

[0031] Step (3) Preparation of sensitive electrode: 5 g of nano-Co3O4 (Shanghai Aladdin Biochemical Technology Co., Ltd., 99.5%), 15 g of nano-Cr2O3 (Shanghai Aladdin Biochemical Technology Co., Ltd., 98%) and 80 g of YSZ powder were weighed according to the weight ratio of Co3O4:Cr2O3:YSZ = 5:15:80, and anhydrous ethanol and zirconium oxide balls were added for wet ball milling. After the ball mill is completed, it is naturally dried. The mixed powder is evenly mixed with an organic carrier (94%wt pine oil + 6%wt ethyl cellulose) at a mass ratio of 3:7, and coated on both sides of the sensor substrate by screen printing. After calcination at 1000°C, a sensitive electrode layer with a certain thickness is formed on a dense electrolyte substrate.

[0032] That is, the impedance-type NO with Co3O4 / Cr2O3 / YSZ ternary composite material as sensitive electrode was obtained. x Self-heating sensor. SEM images of the surface and cross section of the self-heating sensor are shown in Figure 2. Figure 3 As shown. Figure 3 a It can be seen that the Co3O4 / Cr2O3 / YSZ composite sensitive electrode is composed of irregular particles with a particle size between 100-200nm. Figure 3 b is a SEM image of the cross section of the sensor. The dense part at the bottom of the image is the YSZ solid electrolyte, and the loose and porous part at the top is the sensitive electrode.

[0033] Step (4) Performance test:

[0034] Response recovery characteristics: The time required for the sensor signal to rise from zero to a certain percentage of the ventilation balance point is called the response time, and the time taken for the sensor ventilation balance state to recover to 10% signal is called the recovery time. The response time is obtained by continuously passing NO standard gas and then taking out the sensor to obtain the recovery time. The results are as follows: Figure 1 As shown, the sensor exhibits good response recovery characteristics to NO.

[0035] Repeatability: Four sets of sensors were connected in parallel for sensitivity performance testing. The test results are as follows: Figure 2 The four groups of sensors have the same response law and can detect NO as low as 10×10 -6.The response value of the four sets of sensors is 1500×10 -6 NO is 9.8, 9.4, 8.9 and 9.1 respectively, and the m-axis difference rate is 9%. It can be seen that the self-heating sensor has excellent reproducibility.

[0036] The above-mentioned embodiments only express the specific implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the protection scope of the present application. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the technical solution concept of the present application, and these all belong to the protection scope of the present application.

Claims

1. A sensitive electrode for an air switch cabinet, characterized in that: The sensitive electrode adopts Co3O4 / Cr2O3 / YSZ ternary composite material.

2. A method for preparing a sensitive electrode of an air switch cabinet, characterized in that: The steps include: Step (1): Co3O4, Cr2O3 and YSZ powders were weighed according to a weight ratio of Co3O4:Cr2O3:YSZ of 5:15:80, and anhydrous ethanol and zirconia balls were added for wet ball milling; Step (2): After ball milling, the mixture is dried naturally; the powder mixed in step (1) is uniformly mixed with an organic carrier at a mass ratio of 3:7, and coated on a sensor substrate by screen printing; after calcination at 1000° C., a sensitive electrode layer is formed on the sensor substrate.

3. The method for preparing a sensitive electrode of an air switch cabinet according to claim 2, characterized in that: The organic carrier in step (2) comprises 94%wt terpineol and 6%wt ethyl cellulose.

4. A highly sensitive decomposition gas sensor for an air switch cabinet, characterized in that: It comprises a sensitive electrode for an air switch cabinet as claimed in claim 1.

5. The method for preparing a highly sensitive decomposition gas sensor for an air switch cabinet as claimed in claim 4, characterized in that: The steps include: Step (1): Preparation of solid electrolyte: ball milling YSZ powder, drying it; pressing it into a round sheet; then molding the sheet; sintering the pressed sheet at 1500°C-1700°C for 5h-7h to obtain a dense YSZ solid electrolyte substrate; Step (2): Preparation of sensor substrate: coating two thin Pt welding wires on the surface of YSZ solid electrolyte; calcining the solid electrolyte at 700°C-900°C for 0.5h-1.5h to produce the sensor substrate; Step (3): Preparation of sensitive electrode: Prepare a sensitive electrode layer on the sensor substrate of step (2) according to the method for preparing a sensitive electrode for an air switch cabinet according to claim 2 or 3.

6. The method for preparing a highly sensitive decomposition gas sensor for an air switch cabinet according to claim 5, characterized in that: When a self-heating sensor is prepared, the YSZ solid electrolyte described in step (2) is a 51×4×1 mm strip YSZ, and a heating circuit is printed on the back side of the thin Pt welding wire arranged opposite to it.

7. The method for preparing a highly sensitive decomposition gas sensor for an air switch cabinet according to claim 5, characterized in that: The step (1) of pressing the sheet into a circular sheet is pressing the sheet into a circular sheet with a diameter of 13 mm at 5 MPa.

8. The method for preparing a highly sensitive decomposition gas sensor for an air switch cabinet according to claim 5, characterized in that: The molding in step (1) is to mold the sheet by a cold isostatic press at 300 MPa.

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