A chlorine-doped In2O3 nanoparticle-based unsymmetrical dimethylhydrazine gas sensor and its preparation method

Abstract

A unilateral dimethylhydrazine (UDMH) gas sensor based on chlorine-doped In2O3 nanoparticles and its preparation method belong to the technical field of semiconductor metal oxide gas sensors. The sensor comprises an Al2O3 ceramic tube substrate with two parallel, annular, and separate gold electrodes on its outer surface; a chlorine-doped In2O3 sensitive material coated on the outer surface of the Al2O3 ceramic tube and the gold electrodes; and a nickel-chromium heating coil placed within the Al2O3 ceramic tube. The present invention utilizes a simple hydrothermal method to dope non-metallic chlorine into the In2O3 material with the aid of an ionic solution, significantly improving the sensitivity of the In2O3-based sensor to UDMH (71.0 to 100 ppm) and accelerating the sensor's response speed to UDMH gas (2 seconds to 100 ppm). Furthermore, the sensor exhibits excellent selectivity, repeatability, and long-term stability, and has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor metal oxide gas sensors, and in particular relates to an unsymmetrical dimethylhydrazine gas sensor based on chlorine-doped In2O3 nanoparticles and a preparation method thereof. Background Art

[0002] Unsymmetrical dimethylhydrazine (UDMH) is a colorless, highly toxic, volatile compound that is liquid at room temperature. UDMH is also the primary fuel for missile, satellite, and spacecraft launch tests and launch vehicles. Due to its strong reducing properties, it is easily oxidized in air, producing a large number of toxic nitrogen-containing compounds. Therefore, it is necessary to detect and monitor UDMH leaks during storage and transportation.

[0003] Among the numerous types of gas sensors, resistive gas sensors using semiconductor metal oxide (MOS) as the sensitive material are among the most widely used due to their high sensitivity, high stability, good selectivity, fast response and recovery, simple fabrication, and low cost. Numerous methods exist to improve the gas-sensing properties of MOS, including increasing the material's specific surface area, creating heterojunctions, ion doping, and surface-modified catalysts. Ion doping includes both metal and non-metal doping, with non-metal doping, particularly halogen doping, creating defects on the material surface, increasing electron transfer efficiency, and thereby enhancing the sensing performance of semiconductor metal oxides.

[0004] In order to develop a high-performance UDMH gas sensor, the present invention uses a hydrothermal method to prepare Cl-doped In2O3 nanoparticles with the assistance of ionic solution. Gas-sensing performance tests confirm that the sensor prepared with this sensitive material has a high response to UDMH gas (71.0-100 ppm), a fast response time (2s), and good selectivity. Summary of the Invention

[0005] The present invention aims to provide an unsymmetrical dimethylhydrazine gas sensor based on chlorine-doped In2O3 nanoparticles and a preparation method thereof.

[0006] The present invention adopts a simple hydrothermal method, using 4.5 hydrated indium nitrate (In(NO3)3·4.5H2O), hexadecyl-3-methylimidazolium chloride ([C 16 Mim]Cl) dissolved in a mixture of methanol and aqueous ammonia serves as a precursor. After a hydrothermal reaction at high temperature, the sensitive material is obtained through washing, centrifugation, and calcination. The commercially available indirectly heated sensor employed in this invention features a simple manufacturing process, a compact size, and is amenable to industrial mass production. Therefore, it has significant application value and broad prospects for detecting UDMH gas in specific environments.

[0007] The present invention discloses a chlorine-doped In2O3 nanoparticle-based UDMH gas sensor comprising an Al2O3 ceramic tube substrate with two parallel, annular, and separate gold electrodes on its outer surface; a sensitive material coated on the outer surface of the Al2O3 ceramic tube and the gold electrodes; and a nickel-chromium heating coil placed within the Al2O3 ceramic tube. The sensitive material is based on chlorine-doped In2O3 nanoparticles (Cl-In2O3) and is prepared by the following steps:

[0008] (1) 0.6-0.9g In(NO3)3·4.5H2O and 0.05-0.08g [C 16 Mim]Cl was added to 20-40 mL of methanol and stirred continuously at room temperature for 10-20 minutes;

[0009] (2) adding 0.5-2 mL of a 4-5 mol / L aqueous ammonia solution to the solution obtained in step (1), and then stirring continuously at room temperature for 1-2 hours;

[0010] (3) The solution obtained in step (2) is transferred to a hydrothermal reactor, maintained at 160-200°C for 4-6 hours, taken out, naturally cooled to room temperature, and filtered. The obtained precipitate is washed by centrifugation with deionized water several times, and then dried at room temperature; the obtained powder is calcined in air at 500-700°C for 1-3 hours, and cooled to room temperature to obtain chlorine-doped In2O3 nanoparticles, which are recorded as Cl-In2O3;

[0011] The method for preparing the UDMH gas sensor based on chlorine-doped In2O3 nanoparticles (Cl-In2O3) of the present invention adopts a indirectly heated structure, and the steps are as follows:

[0012] (1) Cl-In2O3 and anhydrous ethanol are mixed in a mass ratio of 0.25 to 0.5:1 and ground to obtain a paste slurry; then a small amount of the slurry is evenly coated on the surface of an Al2O3 ceramic tube with two parallel, annular and separate gold electrodes on the outer surface with a brush, so that the Al2O3 ceramic tube and the gold electrodes are completely covered and a 20 to 30 μm thick sensitive material film is formed; the inner diameter of the Al2O3 ceramic tube is 0.6 to 0.8 mm, the outer diameter is 1.0 to 1.5 mm and the length is 4 to 5 mm; the width of a single annular gold electrode is 0.4 to 0.5 mm, and the distance between the two gold electrodes is 0.5 to 0.6 mm; a platinum wire is led out from the gold electrode, and its length is 4 to 6 mm;

[0013] (2) The coated Al2O3 ceramic tube is baked under an infrared lamp for 5 to 10 minutes. After the sensitive material is dried, a nickel-chromium heating coil with 20 to 30 turns is passed through the interior of the Al2O3 ceramic tube as a heating wire (the resistance value of the nickel-chromium heating coil is 25 to 35Ω). Finally, the Al2O3 ceramic tube is welded and packaged as a indirectly heated gas sensor to obtain a UDMH gas sensor based on chlorine-doped In2O3 nanoparticles.

[0014] The UDMH gas sensor based on chlorine-doped In2O3 nanoparticles prepared by the present invention has the following advantages:

[0015] 1. Cl-In2O3 nanoparticles were successfully prepared using a simple hydrothermal method with the assistance of ionic solutions. The synthesis method is simple and low-cost;

[0016] 2. By doping with a small amount of chlorine, the sensitivity of the In2O3-based sensor to UDMH was significantly improved (71.0-100 ppm). The sensor also has a fast response speed (2s-100 ppm) and good selectivity to UDMH gas, which has broad application prospects in detecting and monitoring UDMH leakage during transportation and storage.

[0017] 3. Using commercially available tube sensors, the device has simple process and small size, which is suitable for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 : XRD patterns of pure In2O3 and Cl-In2O3 sensitive materials;

[0019] Figure 2 (a) and Figure 2 (b) is pure In2O3, Figure 2 (c) and Figure 2 (d) SEM morphology of Cl-In2O3 sensitive material at different magnifications;

[0020] Figure 3 (a) Figure 3 (b) Figure 3 (c) Low-magnification TEM, high-magnification TEM and HRTEM images of Cl-In2O3 sensitive materials;

[0021] Figure 4 (a) is pure In2O3, Figure 4 (b) is the nitrogen adsorption-desorption isotherm curve of Cl-In2O3 sensitive material;

[0022] Figure 5 : is the sensitivity curve of the sensor to 100ppm UDMH gas at different operating temperatures in the comparative example and the embodiment;

[0023] Figure 6 : A bar graph showing the sensitivity of the sensor to 100 ppm of unsymmetrical dimethylhydrazine, hydrazine, methanol, ethanol, benzene, toluene, acetone, and formaldehyde in the embodiment;

[0024] Figure 7 (a) is a comparative example and Figure 7 (b) is the dynamic resistance curve of the sensor in the embodiment at 225°C in 100 ppm UDMH gas over time;

[0025] Figure 8 (a) is a comparative example and Figure 8 (c) is the dynamic response curve of the sensor at 225°C in 0.05-2 ppm UDMH gas over time in the embodiment (the inset is the dynamic resistance curve of the sensor at 225°C in 0.05 ppm UDMH gas over time in the comparative example and the embodiment); Figure 8 (b) is a comparative example and Figure 8 (d) is the dynamic response curve of the sensor in the embodiment at 225°C in 5-100 ppm UDMH gas over time;

[0026] Figure 9 : The sensitivity-UDMH concentration characteristic curve of the sensor to 0.05-100 ppm UDMH at 225° C. in the comparative example and the embodiment;

[0027] Figure 10 (a) is a comparative example and Figure 10 (c) is the linear fitting curve of the sensitivity of the sensor to 0.05-2 ppm UDMH at 225° C. in the embodiment; Figure 10 (b) is a comparative example and Figure 10 (d) is a linear curve of sensitivity to 2-100 ppm UDMH at 225° C. versus UDMH concentration of the embodiment;

[0028] Figure 11 : is the four-time repeatability curve of the sensor for 100 ppm UDMH at 225°C in the embodiment;

[0029] Figure 12 : The sensitivity-humidity characteristic curve of the sensor to 100 ppm UDMH at 225° C. and different humidity in the embodiment;

[0030] Figure 13 : is the long-term stability curve of the sensitivity of the sensor in the embodiment working at 225°C in 100ppm UDMH gas;

[0031] like Figure 1As shown, the XRD spectra of pure In2O3 and Cl-In2O3 are consistent with the In2O3 standard card 71-2194.

[0032] like Figure 2 As shown, the SEM images show that the morphology of pure In2O3 and Cl-In2O3 sensitive materials is nanoparticles; Cl doping does not significantly change the morphological characteristics of In2O3 sensitive materials.

[0033] like Figure 3 The TEM image of the Cl-In2O3 sensitive material shown shows that the morphology of the material is consistent with the SEM image, which is a nanoparticle with a size of tens of nanometers; the high-magnification TEM image shows a lattice spacing of 0.178nm and 0.256nm, which is consistent with the (440) and (400) crystal planes of In2O3.

[0034] like Figure 4 As shown in Figure 2, the N2 adsorption-desorption isotherms obtained by the Brunauer-Emmett-Teller (BET) and Barrett Joiner-Halenda (BJH) methods can characterize the specific surface area of ​​the material. In contrast, there is no significant difference in the specific surface area between pure In2O3 and the Cl-In2O3 sensitive material, but the pore volume of Cl-In2O3 is larger.

[0035] like Figure 5 As shown, the optimal operating temperature of the sensors in the embodiment and the comparative example is 225° C., and the sensitivities of the devices to 100 ppm UDMH at the optimal operating temperature are 71.0 and 18.2, respectively. Compared with the sensor in the comparative example, the sensitivity of the sensor in the embodiment is 3.9 times higher.

[0036] like Figure 6 As shown, the sensor in the embodiment has the highest response to UDMH, which is much higher than the response to hydrazine, methanol, ethanol, benzene, toluene, acetone and formaldehyde, indicating that the sensor in the embodiment has good selectivity to UDMH gas.

[0037] like Figure 7 As shown, the response time of the sensor in the comparative example to 100 ppm UDMH gas at an operating temperature of 225°C is 12 s, and the recovery time is 1048 s; the response time of the sensor in the embodiment to 100 ppm UDMH gas at an operating temperature of 225°C is 2 s, and the recovery time is 962 s, indicating that the sensor in the embodiment has a faster response and recovery characteristic to UDMH gas.

[0038] like Figure 8 As shown, the sensors in the comparative example and the embodiment exhibited excellent response and recovery characteristics to UDMH at different concentrations (0.05-100 ppm).

[0039] like Figure 9 As shown, compared with the comparative example, the sensor in the embodiment shows higher sensitivity to different concentrations of UDMH gas (0.05-100 ppm).

[0040] like Figure 10 As shown, the sensors in the comparative example and the embodiment have good sensitivity-concentration linear fitting relationships for both low concentration (0.05-2 ppm) and high concentration (2-100 ppm) of UDMH.

[0041] like Figure 11 As shown, the sensor in the embodiment exhibits consistent response recovery characteristics in four 100 ppm UDMH gas tests, indicating that the sensor in the embodiment has good repeatability for UDMH gas.

[0042] like Figure 12 As shown, with the increase of humidity, the sensitivity of the sensor in the embodiment to UDMH gas decreases. Under the humidity conditions of 18.3%, 33.5%, 55.8%, 75.5% and 95.4%, the sensitivity of the sensor in the embodiment to 100ppm UDMH gas is 72.8, 69.1, 50.0, 42.3 and 38.6 respectively.

[0043] like Figure 13 As shown, in the detection for 10 consecutive days, the sensor in the embodiment operating at a temperature of 225° C. has a small response fluctuation to 100 ppm UDMH gas and can maintain high sensitivity to UDMH gas for a long time.

[0044] Note: In this application, the sensitivity of the device (N-type semiconductor) in the test reducing gas is defined as the ratio of the resistance (R a / R g ), where R a Indicates the resistance between two gold electrodes in air (R a ), and R g Indicates the resistance value between the two gold electrodes in the gas to be measured (R g During the test, a static test system was used. The device was placed in a 1L gas cylinder, a certain amount of the VOC to be tested was injected, and the resistance change was observed and recorded. The corresponding sensitivity value was calculated. DETAILED DESCRIPTION

[0045] Comparative Example

[0046] The specific production process of the UDMH gas sensor using pure In2O3 sensitive material is as follows:

[0047] (1) Add 0.7636 g of In(NO3)3·4.5H2O to 30 mL of methanol and stir continuously at room temperature for 15 minutes;

[0048] (2) adding 1 mL of 4.7 mol / L ammonia solution to the solution obtained in step (1), and then stirring continuously at room temperature for 1.5 hours;

[0049] (3) The solution obtained in step (2) was transferred to a hydrothermal reactor, maintained at 180°C for 5 hours, removed, naturally cooled to room temperature, and filtered. The resulting precipitate was washed by centrifugation with deionized water several times and then dried at room temperature. The resulting powder was calcined in air at 600°C for 2 hours and cooled to room temperature to obtain In2O3 nanoparticles, which were recorded as pure In2O3. The product mass was about 50 mg.

[0050] (3) Take an appropriate amount of the material powder in step (3) and mix it with anhydrous ethanol in a mass ratio of 0.3:1, grind it to obtain a paste slurry, and then use a brush to dip a small amount of the slurry and evenly apply it on the surface of an Al2O3 ceramic tube with two parallel, annular and separate gold electrodes on the outer surface to completely cover it and form a 25 μm thick sensitive material film;

[0051] (4) The coated ceramic tube was baked under an infrared lamp for 8 minutes. After the sensitive material was dried, a nickel-chromium heating coil with 25 turns was passed through the interior of the Al2O3 ceramic tube as a heating wire. Finally, the above device was welded and packaged as a indirectly heated gas sensor to obtain a UDMH gas sensor based on pure In2O3 sensitive material.

[0052] The inner diameter of the Al2O3 ceramic tube is 0.7 mm, the outer diameter is 1.2 mm and the length is 4.5 mm; the width of a single annular gold electrode is 0.45 mm, and the distance between two gold electrodes is 0.55 mm; the length of the platinum wire extending from the gold electrode is 5 mm.

[0053] Example

[0054] The specific production process of the UDMH gas sensor using Cl-In2O3 sensitive material is as follows:

[0055] (1) 0.7636g In(NO3)3·4.5H2O and 0.0686g [C 16 Mim]Cl was added to 30 mL of methanol and stirred at room temperature for 15 minutes;

[0056] (2) adding 1 mL of 4.7 mol / L ammonia solution to the solution obtained in step (1), and then stirring continuously at room temperature for 1.5 hours;

[0057] (3) The solution obtained in step (2) was transferred to a hydrothermal reactor, maintained at 180°C for 5 hours, taken out, naturally cooled to room temperature, and filtered. The resulting precipitate was washed by centrifugation with deionized water several times and then dried at room temperature. The resulting powder was calcined in air at 600°C for 2 hours and cooled to room temperature to obtain chlorine-doped In2O3 nanoparticles, denoted as Cl-In2O3, with a product mass of about 50 mg.

[0058] (4) Take an appropriate amount of the material powder in step (3) and mix it with anhydrous ethanol in a mass ratio of 0.3:1, grind it to obtain a paste slurry, and then use a brush to dip a small amount of the slurry and evenly apply it on the surface of the Al2O3 ceramic tube with two parallel, annular and separate gold electrodes on the outer surface to completely cover it and form a 25 μm thick sensitive material film;

[0059] (5) The coated ceramic tube was baked under an infrared lamp for 8 minutes. After the sensitive material was dried, a nickel-chromium heating coil with 25 turns was passed through the interior of the Al2O3 ceramic tube as a heating wire. Finally, the above device was welded and packaged as a side-heated gas sensor to obtain a UDM gas sensor based on Cl-In2O3 sensitive material.

[0060] The inner diameter of the Al2O3 ceramic tube is 0.7 mm, the outer diameter is 1.2 mm and the length is 4.5 mm; the width of a single annular gold electrode is 0.45 mm, and the distance between two gold electrodes is 0.55 mm; the length of the platinum wire extending from the gold electrode is 5 mm.

Claims

1. A chlorine-doped In2O3-sensitive UDMH gas sensor, comprising an Al2O3 ceramic tube substrate with two parallel, annular, and discrete gold electrodes on its outer surface, a thin film of sensitive material coated on the outer surface of the Al2O3 ceramic tube and the gold electrodes, and a nickel-chromium heating coil placed within the Al2O3 ceramic tube; characterized by: The sensitive material is a chlorine-doped In2O3 nanoparticle sensitive material, and the material is prepared by the following steps: (1) 0.6-0.9g In(NO3)3·4.5H2O and 0.05-0.08g [C 16 Mim]Cl was added to 20-40 mL of methanol and stirred at room temperature for 10-20 minutes; [C 16 Mim]Cl is hexadecyl-3-methylimidazolium chloride; (2) adding 0.5-2 mL of a 4-5 mol / L aqueous ammonia solution to the solution obtained in step (1), and then stirring continuously at room temperature for 1-2 hours; (3) The solution obtained in step (2) is transferred to a hydrothermal reactor, maintained at 160-200°C for 4-6 hours, taken out, naturally cooled to room temperature, and filtered. The obtained precipitate is washed by centrifugation with deionized water several times, and then dried at room temperature; the obtained powder is calcined in air at 500-700°C for 1-3 hours, and cooled to room temperature to obtain chlorine-doped In2O3 nanoparticles, which are recorded as Cl-In2O3.

2. The unsymmetrical dimethylhydrazine gas sensor based on chlorine-doped In2O3 sensitive material according to claim 1, characterized in that: The thickness of the sensitive material film is 20 to 30 μm.

3. The UDMH gas sensor based on chlorine-doped In2O3 sensitive material according to claim 1, characterized in that: The inner diameter of the Al2O3 ceramic tube is 0.6-0.8 mm, the outer diameter is 1.0-1.5 mm and the length is 4-5 mm; the width of a single annular gold electrode is 0.4-0.5 mm, and the distance between two gold electrodes is 0.5-0.6 mm; a platinum wire is led out from the gold electrode, and its length is 4-6 mm.

4. A method for preparing a UDMH gas sensor based on a chlorine-doped In2O3 sensitive material according to any one of claims 1 to 3, comprising the following steps: (1) Cl-In2O3 and anhydrous ethanol are mixed in a mass ratio of 0.25 to 0.5:1 and ground to obtain a paste slurry. A small amount of the slurry is then evenly coated on the surface of an Al2O3 ceramic tube with two parallel, annular, and separate gold electrodes on its outer surface using a brush, so that the Al2O3 ceramic tube and the gold electrodes are completely covered and a sensitive material film is formed. (2) The coated Al2O3 ceramic tube is baked under an infrared lamp for 5 to 10 minutes. After the sensitive material is dried, a nickel-chromium heating coil with 20 to 30 turns is passed through the interior of the Al2O3 ceramic tube as a heating wire. Finally, the Al2O3 ceramic tube is welded and packaged as a indirectly heated gas sensor to obtain a UDMH gas sensor based on chlorine-doped In2O3 sensitive material.

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