CN113390930B - SnO based on double pulse driving 2 CO gas sensor of Pd sensitive material and preparation method thereof - Google Patents
SnO based on double pulse driving 2 CO gas sensor of Pd sensitive material and preparation method thereof Download PDFInfo
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
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- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/14—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of an electrically-heated body in dependence upon change of temperature
Abstract
SnO based on double pulse driving 2 A CO gas sensor of Pd sensitive material and a preparation method thereof belong to the technical field of gas sensors. The heating type bypass heating structure is a bypass heating type structure which is formed by a ceramic tube substrate with two gold electrodes on the outer surface, and nano linear SnO coated on the outer surface of the ceramic tube and the gold electrodes 2 Pd sensitive material, nickel-chromium heating coil in the ceramic tube, double pulse driven DC current source, resistance measuring meter and upper computer. The invention pre-adsorbs O by using the high-temperature pre-heating sensitive material ‑ 、O 2‑ The rest stage accelerates the permeation of gas molecules to the surface of the sensitive material, and the high response and extremely low detection lower limit of CO gas are obtained. The developed CO gas sensor with high performance has response improved by about 33 times compared with the traditional driving mode, and the lower detection limit is reduced by 400 times to 5ppb. In addition, the sensor also has good stability and good application prospect in the aspect of environmental monitoring of low-concentration CO gas.
Description
Technical Field
The invention belongs to the technical field of gas sensors, and particularly relates to a double-pulse-drive-based SnO (metal oxide semiconductor) 2 -a CO gas sensor of Pd-sensitive material and a method for its preparation.
Background
With the rapid development of industrialization, the use of a large amount of energy sources, such as toxic and harmful gases caused by combustion of coal, natural gas, petroleum and the like, has become a serious problem threatening human health and safety. CO is a pollutant with strong toxicity to blood and nervous system, and CO in air enters human blood through respiratory system and combines with hemoglobin in blood, myoglobin in muscle and respiratory enzyme containing ferrous iron to form reversible combination. The combination of carbon monoxide and hemoglobin not only reduces the oxygen carrying capacity of blood cells, but also inhibits and delays the analysis and release of oxyhemoglobin, so that the body tissues are necrotized due to hypoxia, and the serious people can endanger the lives of people. The U.S. department of health gate uses carbon hemoglobin not exceeding 2% as the basis for establishing the CO limit standard in air. Considering the safety of the elderly, children and patients with cardiovascular diseases, the Chinese environmental health department prescribes: the daily average concentration of CO in air must not exceed 1 mg/cubic meter (0.8 ppm); the maximum allowable concentration for one measurement is 3 mg/cubic meter (2.4 ppm). It follows that it is necessary to develop a CO gas sensor that is inexpensive, practical, and has a high sensitivity and a low detection limit.
Based on such a demand, various nationists have been devoted to develop a CO gas sensor having high performance and applied to environmental monitoring, industrial production safety, and the like. The sensor based on the oxide semiconductor sensitive material has the advantages of high sensitivity, quick response recovery, good selectivity, high reliability and the like, and is very suitable for real-time, continuous and on-line monitoring. SnO (SnO) 2 In recent years, researchers have received a lot of attention to meet these characteristics. The sensitive material SnO used in the invention 2 Pd is a typical n-type semiconductor, which upon contact with gaseous CO, has a reduced resistance, i.e. converts the change in gaseous environment into a detectable electrical signal. In addition to tailoring the composition and nanostructure of the sensing material, strategies to improve the sensor drive scheme also help to improve sensing performance. Because of SnO 2 The surface of the material is usually adsorbed with a large amount of O at a high temperature of 350-400 DEG C 2- Ions. Under low temperature conditions, the gas is more easily adsorbed on the surface of the metal oxide. Therefore, a double-pulse driving heating mode sensor is designed, so that the surface of the material can adsorb a large amount of O under the condition of high-temperature preheating 2- Ions adsorb a large amount of gas at low temperature, undergo a severe reaction at an operating temperature, and detect the gas response. Thereby having larger than the traditional constant current driving modeIs provided. Therefore, snO with high performance based on double pulse driving heating mode is developed 2 The Pd sensitive material CO sensor has very important significance in various fields such as environmental monitoring and the like.
Disclosure of Invention
The invention aims to provide a double-pulse-driven SnO 2 -a CO gas sensor of Pd-sensitive material and a method for its preparation.
The invention relates to a double-pulse-driven SnO-based device 2 The CO gas sensor of Pd sensitive material is a double pulse driven heating by-pass structure, which consists of a ceramic tube substrate with two parallel, annular and separated gold electrodes on the outer surface, nano linear SnO coated on the outer surface of the ceramic tube and the gold electrodes 2 The Pd sensitive material, a nickel-chromium heating coil arranged in the ceramic tube, a double pulse driving direct current source, a resistance measuring meter and an upper computer, wherein two gold electrodes and the nickel-chromium heating coil of the ceramic tube are welded on a side heating type hexagonal tube seat through a platinum wire; when the sensor works, programming is performed through software, and a direct current source driven by double pulses is controlled by an upper computer to provide double pulse current for the nickel-chromium heating coil, so that the nickel-chromium heating coil sequentially works in a preheating stage, a resting stage and a working stage, wherein the temperature of the preheating stage is 350-400 ℃, the temperature of the resting stage is 10-30 ℃, the temperature of the working stage is 40-60 ℃, and the time of the preheating stage, the resting stage and the working stage is 5-20 s respectively; measuring direct current resistances Ra and Rg between two gold electrodes at the tail end of a working stage of the sensor in the air and CO gas atmosphere with different concentrations respectively by a resistance measuring meter, transmitting resistance signals to an upper computer, calculating to obtain the sensitivity S=Ra/Rg of the sensor under different concentrations of CO (as shown in figure 2), and further establishing a relation curve of the concentration of CO and the sensitivity (as shown in figure 7); and then measuring the direct current resistance Rg between two gold electrodes in the atmosphere with unknown concentration CO at the tail end of the working stage through a resistance measuring meter, wherein the Ra value is only related to the temperature and is irrelevant to the concentration of CO, the sensitivity S value of the sensor under the concentration is obtained through S=Ra/Rg calculation, and the concentration of CO is obtained through 'the relation curve of the concentration of CO and the sensitivity'.
The manufacturing method and the working mode of the double pulse driving in the invention are as follows:
the double pulse driving mode is that Microsoft Visual Studio development environment is written into application software by using C++ and is loaded in the upper computer, and data real-time receiving and transmitting are carried out and controlled through the serial port of the upper computer and the serial ports of the double pulse driving direct current source and the resistance measuring meter. The cycle of the double pulse current is divided into three phases, namely a preheating phase, a resting phase and a working phase, wherein the nickel-chromium heating coil is preheated at a high temperature in the preheating phase, the preheating temperature is 350-400 ℃, the nickel-chromium heating coil is stopped to be heated in the resting phase, the resting temperature is room temperature (10-30 ℃), the nickel-chromium heating coil is heated in the working phase, the response of the sensor is measured, and the working temperature is 40-60 ℃ (shown in figure 4). SnO in the high temperature preheating stage 2 The surface of Pd sensitive material adsorbs a large amount of O 2- Ions, snO in rest stage 2 The surface of Pd sensitive material adsorbs a large number of CO gas molecules and a large number of O 2- Ions and a large amount of CO gas molecules react violently in the working stage, thereby greatly improving SnO 2 -response of Pd-sensitive material to CO gas. At the end of the working phase, i.e. at the end of one double pulse period, the resistance of the direct current resistor between the gold electrodes (Ra in air, rg in CO atmosphere) is measured to calculate the response value of the sensor, response value s=ra/Rg. The double pulse driving mode is different from the traditional driving mode in that the traditional constant current heating is changed into double pulse current heating, and other detection methods are unchanged.
The nano linear SnO of the invention 2 The Pd sensitive material is prepared by the following steps:
(1) Firstly, 0.4 to 0.5g Sncl 2 ·2H 2 O is dissolved in a mixed solvent of 10mL of Dimethylformamide (DMF) and 95% absolute ethanol by mass fraction (the volume ratio of the dimethylformamide to the absolute ethanol is 1:1), stirred for 15-30 min, and then 0.015-0.03 g of PdCl is added 2 Stirring with 0.5-1.5 g polyvinylpyrrolidone (PVP) for 5-6 h;
(2) Carrying out electrostatic spinning on the precursor liquid obtained in the step (1), wherein the electrostatic spinning adopts a 19G needle head, the voltage is 10-20 KV, the speed of the precursor liquid flowing out of the needle head is controlled to be 0.02-0.04 ml/min by an injection pump, the distance between the needle head and a collecting roller is 15-20 cm, the rotating speed of the roller is 500-1000 revolutions/min, tinfoil paper is stuck on the roller, the roller rotates and collects for 2-3 h, and an electrospun product is obtained on the tinfoil paper;
(3) Calcining the obtained product at 400-600 ℃ for 1.5-3.0 h after spinning to prepare nano linear SnO 2 -Pd-sensitive material;
the invention relates to a double-pulse-driven SnO-based device 2 The preparation method of the CO gas sensor of the Pd sensitive material comprises the following steps:
(1) Taking nano linear SnO 2 The mass ratio of Pd sensitive material to absolute ethyl alcohol with the mass fraction of 95 percent is 0.25-0.5: 1 uniformly mixing to form a slurry, dipping the slurry by a brush, uniformly coating the surface with Al with two parallel, annular and mutually separated gold electrodes 2 O 3 The outer surface of the ceramic tube is completely covered with the gold electrode, and the thickness of the sensitive material is 15-30 mu m; al (Al) 2 O 3 The inner diameter of the 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 gold electrode is 0.4-0.5 mm, and the interval between two gold electrodes is 0.5-0.6 mm; the length of the platinum wire lead led out from the gold electrode is 4-6 mm;
(2) Al to be coated with sensitive material 2 O 3 Sintering the ceramic tube at 400-450 ℃ for 1.5-3.0 h, and then passing a nickel-chromium heating coil (with 50-60 turns) with a resistance value of 30-40 omega through Al 2 O 3 The inside of the ceramic tube is provided with double pulse current for the nickel-chromium heating coil by a double pulse driving direct current source under the control of an upper computer, so that the nickel-chromium heating coil works in a preheating stage, a resting stage and a working stage respectively, the temperature of the preheating stage is 350-400 ℃, the temperature of the resting stage is 10-30 ℃, the temperature of the working stage is 40-60 ℃, and the time of the preheating stage, the resting stage and the working stage is 5-20 s respectively; welding two gold electrodes and a nickel-chromium heating coil of a ceramic tube on a side heating type hexagonal tube seat through a platinum wire;
(3) Finally aging the sensor in an air environment at 200-400 ℃ for 2-3 days to obtain the double-pulse-driven SnO 2 -CO gas sensor of Pd sensitive material.
Working principle:
SnO 2 pd is a typical n-type semiconductor, which upon contact with gaseous CO, has a reduced resistance, i.e. converts the change in gaseous environment into a detectable electrical signal. When SnO 2 The oxygen molecules in the air when the Pd-based CO gas sensor is placed in the air and heated to a certain temperature (300-400 ℃) will be taken from SnO 2 The surface takes electrons and takes O 2- 、O - In the form of (a) O 2- 、O - Will be adsorbed to SnO 2 Surface, snO 2 Will increase in baseline resistance and O 2- The resulting rise in baseline resistance is more dramatic. Due to SnO at different temperatures 2 The oxygen adsorption on the surface is different (300-350 ℃ C. To adsorb O) - Mainly, the catalyst is used for adsorbing O at 350-400 DEG C 2- Mainly). From the formulas (1) and (2), O 2- Ion to CO molecular reaction is compared with O - More electrons are released by reaction with CO molecules, resulting in a greater response of the sensor. Therefore, the preheating temperature is set to be 350-400 ℃ on the one hand, so that a large amount of O can be adsorbed on the surface of the material in advance 2- Ions, the baseline resistance of the material in the working stage is greatly improved; on the other hand, the extent of reaction with CO gas during the working phase may be exacerbated. Due to O 2- The ions are not substantially extracted from SnO at low temperatures (10-30 ℃) for about 20 seconds 2 The surface of the semiconductor is dissociated, and CO gas molecules are more easily adsorbed on SnO at low temperature than at high temperature 2 The semiconductor surface is provided with a low-temperature rest time for adsorbing a large amount of CO gas molecules, the rest temperature is set to be 10-30 ℃, and the rest time is set to be 5-20 seconds, so that the adsorption quantity of the CO gas molecules can be ensured, and O can be maintained 2- The number of ions is substantially unchanged. Because of SnO 2 The optimum operating temperature of Pd for CO gas is about 50deg.C (as shown in FIG. 6), so the operating temperature is set to 40-60deg.C. When SnO 2 When the Pd sensitive material contacts CO gas in the working stage, the CO gas molecules pre-adsorbed on the material surface will react with pre-adsorbed oxygen anions (O 2- 、O - ) Violent reactions (see formulas 1, 2) that result in electron re-release to SnO 2 Pd-composite nanofiber conduction band, thereby reducing material resistance. The following further describes the change of the material resistance in three phases of double pulse driving in air and CO gas:
when the double pulse drive sensor is placed in an air tank:
high temperature preheating time to make SnO 2 The surface of the material is pre-adsorbed with a large amount of O 2- But the baseline resistance is very low due to too high a temperature electron excitation; the electrons on the surface of the material are sharply reduced due to the sharp reduction of the temperature in the rest time, and a great amount of O which is pre-adsorbed in the preheating time 2- Without dissociation, the baseline resistance of the material can be sharply increased by 100-500 times; in the working phase, since the working temperature (40-60 ℃) is not high, the baseline resistance in the working phase further rises (as shown by the rising curve in the upper part of fig. 5), and finally the resistance at the end of the working phase in air is taken as Ra.
When the double pulse drive sensor is placed in a CO gas bottle:
the high temperature preheating time also leads to SnO 2 The surface of the material is pre-adsorbed with a large amount of O 2- The resistance is very low due to too high a temperature for electron excitation; during rest time due to rapid decrease in temperature, but increased adsorption of CO gas causes pre-adsorbed O of the material 2- The reaction with CO gas is started, so that the resistance of the material only slightly increases by about 2-5 times (CO gas concentration is 10-100 ppm), and the material is far less increased in an air bottle; in the working phase, the working temperature (40-60 ℃) is set, the oxygen ions are expected to react further on the surface of the material, the resistance of the material is reduced again (as shown by the lower reduced curve in fig. 5), and finally the resistance at the tail end of the working phase in CO gas is Rg.
Double pulse driving mode to make SnO 2 The baseline resistance of the material in the air is greatly increased, so that SnO 2 The resistance of the material in CO gas is slightly reduced, so that the response of the sensor is greatly improved. The resistance at the end of the measurement time in air was taken as Ra, the resistance at the end of the measurement time in CO gas was taken as Rg, and s=ra/Rg was defined as the response of the sensor (as shown in fig. 5). The change of the resistivity is converted into an electric signal by the sensor to be received by the measuring end, thereby achievingThe purpose of detecting CO.
CO+O (adsorption) - →CO 2 +e - (equation 1)
CO+O (adsorption) 2- →CO 2 +2e - (equation 2)
The invention has the advantages that:
(1) The invention prepares SnO by using electrostatic spinning technology 2 The Pd sensing material nanowire has uniform size distribution, and provides an effective sensitive material for developing a high-performance CO sensor.
(2) SnO used in the present invention 2 The Pd sensitive material has high sensitivity to CO, and the nanowire structure is beneficial to gas diffusion, so that rapid adsorption and desorption can be realized.
(3) The response to CO using the pulse drive method is improved by a factor of 33 over the conventional measurement method.
(4) The lower limit of detection of CO by adopting a pulse driving mode is reduced by 400 times to reach 5ppb compared with the traditional measuring mode, and trace detection of CO gas is facilitated.
(5) The developed sensor has good stability and strong reliability.
(6) SnO made by the invention 2 The Pd-based CO gas sensor has the advantages of simple manufacturing process, simple and convenient steps of the preparation method and low cost, and is suitable for industrial mass production.
Drawings
Fig. 1: snO of the present invention 2 -schematic structural diagram of Pd-based CO sensor.
Fig. 2: pulse-driven SnO of the present invention 2 -Pd-based CO sensor system diagram.
Fig. 3: snO of the present invention 2 SEM pictures (a) and (b) of Pd nanowires, corresponding to all examples, all with one SnO 2 Pd-sensitive material.
Fig. 4: the invention relates to a function relation of a preheating temperature, a resting temperature and a working temperature, preheating time, resting time and working time of pulse driving.
Fig. 5: the response (sensitivity) S of the inventive double pulse drive mode defines a schematic.
Fig. 6: snO of the present invention 2 Pd sensitive material sensitivity to 100ppm CO gas and baseline resistance in air as a function of temperature (25-400 ℃ C.) in a constant temperature drive mode (type II).
Fig. 7: snO of the present invention 2 -sensitivity as a function of CO gas concentration for three drive modes, type-0, type-1, type-2, of Pd-based CO sensor in 0.005-100 ppm CO atmosphere. pulse-0 is in constant temperature driving mode and the temperature is SnO 2 -the optimal working temperature of the Pd-sensitive material at constant temperature for CO gas is 50 ℃; the pulse-1 type is a double pulse driving mode with preheating temperature of 370 ℃, resting temperature of 20 ℃, working temperature of 150 ℃, preheating time, resting time and working time of 10 seconds respectively; the pulse-2 type is a double pulse driving mode with a preheating temperature of 370 ℃, a resting temperature of 20 ℃, a working temperature of 50 ℃, and a preheating time, a resting time and a working time of 10 seconds respectively.
Fig. 8: the preheating temperature is 370 ℃, the rest time is 20 ℃, the working temperature is 50 ℃, and the preheating time, the rest time and the working time are respectively 10 seconds under the driving mode (pulse-2 type) of the invention SnO 2 -concentration gradient profile of resistance change of Pd-based CO sensor in CO gas of different concentrations in CO atmosphere of 5-30000 ppb.
Fig. 9: the preheating temperature is 370 ℃, the rest time is 20 ℃, the working temperature is 50 ℃, and the preheating time, the rest time and the working time are respectively 10 seconds under the driving mode (pulse-2 type) of the invention SnO 2 Long-term stability curve of Pd-based CO sensor.
As shown in fig. 1, the names of the components are: al (Al) 2 O 3 Insulating ceramic tube 1, platinum wire (four) 2, annular gold electrode (two) 3, nickel-chromium heating coil 4, snO 2 Pd sensitive material 5.
As shown in fig. 2, a computer with a display is used as an upper computer to control the double pulse to drive the direct current source and the resistance measuring meter to heat the sensor and receive the resistance information of the sensor in real time.
As shown in FIG. 3 (a), snO 2 Pd nanowires are relatively uniform and continuous in size, each nanowire having a diameter of 50 to 100nm. Fig. 3 (b) shows a nano-scale filiform structure, and it can be seen that the surface of the nanowire presents small particles, is rough, increases the surface area, and is easy for the inhalation of gas molecules.
As shown in FIG. 4, the maximum preheating temperature of pulse driving is 350-400 ℃; stopping heating to room temperature (10-30 ℃) during rest time; the working temperature is lower and is 40-60 ℃. The preheating time, the resting time and the working time are respectively 5-20 s.
As shown in fig. 5, the definition of the response (sensitivity) S of the double pulse driving mode of the present invention is schematically shown. Only the resistance value at the end of the resistance change curve in the working phase was taken, the value at the upper rising end of the curve (in air) was Ra, and the value at the lower falling end of the curve (in gas) was Rg, s=ra/Rg.
As shown in FIG. 6, in SnO 2 In a constant temperature driving mode (type-0) of the Pd sensitive material, the sensitivity to 100ppm CO gas appears as two peaks with the change of temperature (25-400 ℃) and the sensitivity is smaller at the maximum of 4.6,150 ℃ when one peak is 50 ℃, and is 3.2. The triangular point curve is SnO 2 -a curve of baseline resistance in air of Pd-sensitive material with temperature (25-400 ℃).
As shown in fig. 7, the sensor sensitivity is a function of CO concentration (0.005-100 ppm) for the three drive modes. The lower limit of detection of CO gas in pulse-0 constant temperature driving mode at the optimal working temperature of 50 ℃ is only 2ppm, and the response (sensitivity) of the constant temperature driving mode to 100ppm CO gas is 4.6; the preheating temperature of pulse-1 type is 370 ℃, the resting temperature is 20 ℃, the working temperature is 150 ℃, the detection lower limit of a double pulse driving mode of preheating time, resting time and working time of 10 seconds is 100ppb, and the response (sensitivity) to 100ppm CO gas is 27.5; the pulse-2 type is a driving mode with a preheating temperature of 370 ℃, a rest time of 20 ℃, a working temperature of 50 ℃ and a preheating time, a rest time and a working time of 10 seconds respectively. It is noted that the lower limit of the concentration of CO that can be detected by the pulse-2 type drive mode sensor is 5ppb, the corresponding sensitivity is 1.142, and the response (sensitivity) to 100ppm of CO gas is 149.5.
As shown in FIG. 8, the preheating temperature is 370 ℃, the rest time is 20 ℃, and the working temperature isSnO in a driving mode (pulse-2 type) with a preheating time, a resting time and a working time of 10 seconds at 50 DEG C 2 Change curve of sensitivity of Pd-based CO sensor under CO (5-30000 ppb) atmosphere of different concentrations. In order to facilitate the observation of the graph, only the resistance change curve during the working time is listed, so that the resistance curve is discontinuous, as shown by a dotted curve, and the resistances at the end of the measuring time are connected by a dotted line, so that a concentration gradient curve in a traditional mode is formed. As can be seen from the graph, the resistance in the CO gas at a low concentration (5 to 100 ppb) (non-hatched area dotted curve in the graph) tended to increase, and as the gas concentration gradually increased, the resistance in the CO gas increased first and then decreased (1000 ppb), and the resistance in the CO gas at a high concentration (30000 ppb) tended to decrease slowly. It can be seen from the figure that the sensor resistance decreases significantly when the ambient composition of the sensor changes from air to CO (unshaded areas in the figure). And as the concentration of the detection gas CO increases, the more obvious the resistance change of the sensor is, i.e., as the CO concentration increases, the sensitivity increases.
As shown in FIG. 9, snO 2 Long-term stability of Pd-based CO sensors. The sensitivity of the sensor to 100ppm CO was tested in a two week period at a preheat temperature of 370 ℃, a rest time of 20 ℃, an operating temperature of 50 ℃, and a drive mode (pulse-2 type) with a preheat time, a rest time, and an operating time of 10 seconds each. The fluctuation range of the sensitivity is 130-150 in two weeks, and basically remains in a stable range. It follows that the sensor exhibits good stability.
Detailed Description
Comparative example 1:
with SnO not driven by double pulses 2 Pd nano wires are used as sensitive materials to manufacture a pulse-0 type CO sensor, and the specific manufacturing process comprises the following steps:
1. 0.4513g Sncl 2 ·2H 2 O was dissolved in a mixed solvent of 10mL of Dimethylformamide (DMF) and 95% by mass of absolute ethanol (the volume ratio of dimethylformamide to absolute ethanol: 1:1), stirred for 20 minutes, and then 0.019g of PdCl was added 2 Re-stirring with 1g polyvinylpyrrolidone (PVP)Stirring for 6h;
2. filling the solution into a 10mL syringe, carrying out electrostatic spinning, and using a 19G needle with voltage of 16KV and distance between the needle and a collecting device of 16cm, wherein the rotating speed of the device is 700 revolutions per minute;
3. calcining the obtained product in a muffle furnace at 500 ℃ for 2 hours after spinning;
4. proper amount of nano linear SnO is taken 2 Pd sensitive material, 0.35 mass ratio with ethanol: 1mg was uniformly mixed to form a slurry. The Al with two parallel, annular and separated gold electrodes is coated on the surface by dipping the slurry with a brush 2 O 3 The outer surface of the ceramic tube is completely covered with the gold electrode; the thickness of the nanomaterial on the outer surface of the ceramic tube is 25 μm. (Al) 2 O 3 The inner diameter of the ceramic tube is 0.7mm, the outer diameter is 1.2mm, and the length is 4.5mm; the width of a single gold electrode is 0.45mm, and the interval between two gold electrodes is 0.55mm; a platinum wire lead led out from the gold electrode has a length of 5 mm);
5. sintering the coated ceramic tube at 430 ℃ for 2h, and then passing a nickel-chromium heating coil with a resistance value of 35 omega through Al 2 O 3 And a constant current drive is provided inside the ceramic tube through a direct current source, and finally the ceramic tube is welded on the universal side heating type hexagonal tube seat through a platinum wire.
6. Finally aging the sensor in 300 ℃ air environment for 2.5 days, thereby obtaining the constant-current driven tubular SnO 2 Pd sensitive material pulse-0 type CO gas sensor.
7. The sensor tested the sensitivity of the sensor to 100ppm CO over a constant temperature drive range of 25-400 ℃. (as shown in FIG. 6)
Example 1
With SnO 2 Pd nano wires are used as sensitive materials, and a pulse-1 type tubular CO gas sensor with preheating temperature of 370 ℃, resting temperature of 20 ℃, working temperature of 150 ℃, preheating time, resting time and working time of 10s respectively is manufactured by a double pulse driving heating mode, and the specific manufacturing process is as follows:
1. 0.4513g Sncl 2 ·2H 2 O was dissolved in 10mL Dimethylformamide (DMF) with a mass fraction of 95% freeThe mixed solvent of the ethanol and the water (the volume ratio of the dimethylformamide to the absolute ethanol is 1:1) is stirred for 20min, and then 0.019g of PdCl is added 2 Stirring with 1g polyvinylpyrrolidone (PVP) for a further 6h;
2. filling the solution into a 10mL syringe, carrying out electrostatic spinning, and using a 19G needle with voltage of 16KV and distance between the needle and a collecting device of 16cm, wherein the rotating speed of the device is 700 revolutions per minute;
3. calcining the obtained product in a muffle furnace at 500 ℃ for 2 hours after spinning;
4. proper amount of nano linear SnO is taken 2 Pd sensitive material, 0.35 mass ratio with ethanol: 1mg was uniformly mixed to form a slurry. The Al with two parallel, annular and separated gold electrodes is coated on the surface by dipping the slurry with a brush 2 O 3 The outer surface of the ceramic tube is completely covered with the gold electrode; the thickness of the nanomaterial on the outer surface of the ceramic tube is 25 μm. (Al) 2 O 3 The inner diameter of the ceramic tube is 0.7mm, the outer diameter is 1.2mm, and the length is 4.5mm; the width of a single gold electrode is 0.45mm, and the interval between two gold electrodes is 0.55mm; a platinum wire lead led out from the gold electrode has a length of 5 mm);
5. sintering the coated ceramic tube at 430 ℃ for 2h, and then passing a nickel-chromium heating coil with a resistance value of 35 omega through Al 2 O 3 The ceramic tube is internally provided with a preheating temperature, a resting temperature and a working temperature by driving a direct current source through double pulses, wherein the preheating temperature is 370 ℃, the resting temperature is 20 ℃, the working temperature is 150 ℃, and the preheating time, the resting time and the working time are respectively 10s. Finally, the ceramic tube is welded on the universal side heating type hexagonal tube seat through a platinum wire.
6. The development environment of Microsoft Visual Studio2012 and the serial port and pulse driving software program of the upper computer are written in C++, and the serial port and pulse driving software program is installed in the upper computer and connected with the system (figure 2).
7. Finally aging the sensor in 300 ℃ air environment for 2.5 days, thereby obtaining the tubular SnO with double pulse driving heating mode 2 -Pd sensitive material CO gas sensor.
8. The sensor was tested for sensitivity to 100ppm co in pulse-1 drive mode with a preheat temperature of 370 ℃, a rest temperature of 20 ℃, an operating temperature of 150 ℃, and a preheat time, a rest time, and an operating time of 10 seconds each.
Example 2
With SnO 2 Pd nano wires are used as sensitive materials, and a pulse-2 type tubular CO gas sensor with preheating temperature of 370 ℃, resting temperature of 20 ℃, working temperature of 50 ℃, preheating time, resting time and working time of 10s respectively is manufactured, wherein the specific manufacturing process comprises the following steps:
1. 0.4513g Sncl 2 2H2O was dissolved in a mixed solvent of 10mL of Dimethylformamide (DMF) and 95% by mass of absolute ethanol (the volume ratio of dimethylformamide to absolute ethanol was 1:1), stirred for 20 minutes, and then 0.019g of PdCl was added 2 Stirring with 1g polyvinylpyrrolidone (PVP) for a further 6h;
2. filling the solution into a 10mL syringe, carrying out electrostatic spinning, and using a 19G needle with voltage of 16KV and distance between the needle and a collecting device of 16cm, wherein the rotating speed of the device is 700 revolutions per minute;
3. calcining the obtained product in a muffle furnace at 500 ℃ for 2 hours after spinning;
4. proper amount of nano linear SnO is taken 2 Pd sensitive material and ethanol in a mass ratio of 0.35mg:1mg was uniformly mixed to form a slurry. The Al with two parallel, annular and separated gold electrodes is coated on the surface by dipping the slurry with a brush 2 O 3 The outer surface of the ceramic tube is made to cover the gold electrode completely, and the thickness of the nanometer material on the outer surface of the ceramic tube is 25 mu m. (Al) 2 O 3 The inner diameter of the ceramic tube is 0.7mm, the outer diameter is 1.2mm, and the length is 4.5mm; the width of a single gold electrode is 0.45mm, and the interval between two gold electrodes is 0.55mm; a platinum wire lead led out from the gold electrode has a length of 5 mm);
5. sintering the coated ceramic tube at 430 ℃ for 2h, and then passing a nickel-chromium heating coil with a resistance value of 35 omega through Al 2 O 3 The ceramic tube is internally provided with a preheating temperature and a working temperature by driving a direct current source through double pulses, the preheating temperature is 350 ℃, the working temperature is 50 ℃, and the preheating time, the rest time and the working time are respectively 10s. Finally, the ceramic tube is welded on the universal side heating type hexagonal tube seat through a platinum wire.
6. The Microsoft Visual Studio2012 development environment and C++ programming upper computer serial port and pulse driving software program are installed in the upper computer and connected with the system (shown in figure 2).
7. Finally aging the sensor in 300 ℃ air environment for 2.5 days, thereby obtaining the tubular SnO with double pulse driving heating mode 2 -Pd sensitive material CO gas sensor.
8. The sensor was tested for sensitivity to 100ppm CO in pulse-2 drive mode with a preheat temperature of 370 ℃, a rest temperature of 20 ℃, an operating temperature of 50 ℃, and a preheat time, a rest time, and an operating time of 10 seconds each.
Table 1: nano linear SnO2-Pd CO gas sensor based on three driving modes of pulse-0, pulse-0 and relationship data of sensitivity and driving type in 100ppm CO atmosphere
| Sensor type | Sensitivity (Ra/Rg) |
| pulse-0 | 4.6 |
| pulse-1 | 27.5 |
| pulse-2 | 145.5 |
The invention is not a matter of the known technology.
The above embodiments are provided to illustrate the technical concept and features of the present invention and are intended to enable those skilled in the art to understand the content of the present invention and implement the same, and are not intended to limit the scope of the present invention. All equivalent changes or modifications made in accordance with the spirit of the present invention should be construed to be included in the scope of the present invention.
Claims (4)
1. SnO based on double pulse driving 2 -CO gas sensor of Pd-sensitive material, characterized in that: the surface of the ceramic tube substrate is provided with two parallel, annular and separated gold electrodes, and the nano linear SnO coated on the outer surface of the ceramic tube and the gold electrodes 2 -Pd sensitive material, nickel-chromium heating coil placed in the ceramic tube, double pulse driving dc current source, resistance measuring meter and upper machine composition; welding two gold electrodes and a nickel-chromium heating coil of a ceramic tube on a side heating type hexagonal tube seat through a platinum wire; wherein, the nano linear SnO 2 The Pd sensitive material is prepared by the following steps:
(1) 0.4 to 0.5g Sncl 2 ·2H 2 O is dissolved in 10mL of mixed solvent of dimethylformamide and absolute ethyl alcohol with the mass fraction of 95%, and the volume ratio of the dimethylformamide to the absolute ethyl alcohol is 1:1, stirring for 15-30 min, and then adding 0.015~0.03 g PdCl 2 Stirring with 0.5-1.5 g polyvinylpyrrolidone for 5-6 h;
(2) Carrying out electrostatic spinning on the solution obtained in the step (1), wherein a 19G needle is adopted in the electrostatic spinning, the voltage is 10-20 KV, the flowing speed of the precursor liquid from the needle is controlled to be 0.02-0.04 ml/min by an injection pump, the distance between the needle and a collecting roller is 15-20 cm, the rotating speed of the roller is 500-1000 revolutions/min, tin foil paper is stuck on the roller, the roller rotates and collects for 2-3 hours, and an electrospun product is obtained on the tin foil paper;
(3) Calcining the obtained product at 400-600 ℃ for 1.5-3.0 h after spinning is finished to obtain nano linear SnO 2 Pd-sensitive material.
2. A double pulse drive-based SnO as claimed in claim 1 2 -CO gas sensor of Pd-sensitive material, characterized in that: al (Al) 2 O 3 Ceramic tubeThe inner diameter of the steel wire is 0.6-0.8 mm, the outer diameter of the steel wire is 1.0-1.5 mm, and the length of the steel wire is 4-5 mm; the width of each gold electrode is 0.4-0.5 mm, and the distance between the two gold electrodes is 0.5-0.6 mm; and a platinum wire is led out from the gold electrode, and the length of the platinum wire is 4-6 mm.
3. A double pulse drive-based SnO as claimed in claim 1 2 -CO gas sensor of Pd-sensitive material, characterized in that: the upper computer controls the double pulse driving direct current source to provide double pulse current for the nickel-chromium heating coil, so that the nickel-chromium heating coil sequentially works in a preheating stage, a resting stage and a working stage, the temperature of the preheating stage is 350-400 ℃, the temperature of the resting stage is 10-30 ℃, the temperature of the working stage is 40-60 ℃, and the time of the preheating stage, the resting stage and the working stage is 5-20 s respectively; measuring direct current resistances Ra and Rg between two gold electrodes at the tail end of a working stage of the sensor in the air and CO gas atmosphere with different concentrations respectively by a resistance measuring meter, transmitting resistance signals to an upper computer, calculating to obtain the sensitivity S=Ra/Rg of the sensor under different concentrations of CO, and further establishing a 'relation curve of CO concentration and sensitivity'; and then measuring the direct current resistance Rg between two gold electrodes in the atmosphere with unknown concentration CO at the tail end of the working stage through a resistance measuring meter, calculating to obtain the sensitivity S value of the sensor under the concentration through S=Ra/Rg, and calculating to obtain the concentration of CO through a relation curve of the concentration of CO and the sensitivity.
4. A double pulse drive-based SnO according to any one of claims 1 to 3 2 The preparation method of the CO gas sensor of the Pd sensitive material comprises the following steps:
(1) Taking nano linear SnO 2 The mass ratio of the Pd sensitive material to the absolute ethyl alcohol with the mass fraction of 95% is 0.25-0.5: 1 uniformly mixing to form a slurry, dipping the slurry by a brush, uniformly coating the surface with Al with two parallel, annular and separated gold electrodes 2 O 3 The outer surface of the ceramic tube is completely covered with the gold electrode, and the thickness of the sensitive material is 15-30 mu m;
(2) Al to be coated with sensitive material 2 O 3 And sintering the ceramic tube at 400-450 ℃ to obtain the ceramic tube 1.5-3.0 h, and then passing a nickel-chromium heating coil with the resistance value of 30-40 omega through Al 2 O 3 Welding two gold electrodes and a nickel-chromium heating coil of the ceramic tube on a side heating type hexagonal tube seat through a platinum wire inside the ceramic tube;
(3) Finally aging the sensor in an air environment at 200-400 ℃ for 2-3 days to obtain the double-pulse-driven SnO 2 -CO gas sensor of Pd sensitive material.
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