KR20020037185A - Gas sensor having good sensitivity and selectivity and process for the preparation thereof - Google Patents

Abstract

PURPOSE: A gas sensor and method for manufacturing the same is provided to achieve a high sensitivity and selectivity of sensor with respect to carbon monoxide(CO) and hydrogen gas. CONSTITUTION: A gas sensor comprises a gas sensor layer made of a reducing gas sensing material, and an anode and a cathode arranged at both sides of the gas sensor layer. The gas sensor layer contains a material composed of xCuO minus(1 minus x)SnO2(wherein x is larger than 0 and smaller than 0.1). The gas sensor layer contains ZnO component, and XCuO minus yZnO minus(1 minus x minus y)SnO2(wherein x is larger than 0 and smaller than 0.1, y is larger than 0 and smaller than 0.99, and x plus y is larger than 0 and smaller than 1). Thus, a gas sensor having a superior sensitivity and selectivity with respect to a carbon monoxide at a low temperature and a hydrogen gas at a high temperature, is obtained.

Description

Gas sensor with excellent sensitivity and selectivity and its manufacturing method {GAS SENSOR HAVING GOOD SENSITIVITY AND SELECTIVITY AND PROCESS FOR THE PREPARATION THEREOF}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor gas sensor for sensing a reducing gas and a method for manufacturing the same, particularly from a SnO ₂ sensing material added with CuO and optionally ZnO, each having selective sensing ability for both carbon monoxide and hydrogen gas. It relates to a manufactured gas sensor and a method of manufacturing the same.

Carbon monoxide (CO) gas is a colorless, odorless and toxic gas that is likely to leak through incomplete combustion processes in industry and homes. Currently commercially available CO gas sensor is a semiconductor gas sensor using SnO ₂ as a sensing material. The semiconductor gas sensor has the advantage that the device is simple and the production cost and the maintenance cost are relatively low. As described above, the semiconductor gas sensor using SnO ₂ detects most of the reducing gas. There is a disadvantage of malfunction due to other gases or moisture.

In addition, the detection material of the commercially available CO gas sensor has improved characteristics by adding noble metal additives such as Pt and Pd while using SnO ₂ as a parent material having excellent sensitivity and operating at a relatively low temperature (Kousuke Ihokura and Joseph). Watson, "The Stannic Oxide Gas Sensor, principles and applications", CRC Press, 1994, pp 11-23). However, due to the use of precious metals, there is a problem that the manufacturing cost of the sensor is high.

Thus, there is an urgent need for inexpensive sensors with good sensitivity and selectivity for CO gas.

Hydrogen gas, on the other hand, is a colorless, odorless, lightest gas that is highly flammable and is used as a fuel of high efficiency. In addition, hydrogen gas is the next generation energy source, and its utility value is very high, so the use of hydrogen gas will increase further. However, the outflow of highly explosive hydrogen gas directly causes large fires, so there is an urgent need to develop a sensor that can detect this.

Accordingly, an object of the present invention is to develop a new sensor material having a selective sensitivity to CO and H ₂ gas in order to solve the problem of the lack of selective sensitivity of the sensing material of the conventional semiconductor gas sensor.

1A and 1B are graphs of sensitivity of carbon monoxide (200 ppm) and hydrogen gas (200 ppm) of a gas sensor using pure SnO ₂ and CuO—SnO ₂ according to the present invention as sensing materials, respectively, according to temperature change;

2A and 2B are graphs comparing sensitivity of carbon monoxide (200ppm) and hydrogen gas (200ppm), which vary according to the amount of CuO added to the gas sensor according to the present invention, at 160 ° C. and 280 ° C., respectively.

3A and 3B are graphs comparing sensitivity of carbon monoxide (200ppm) and hydrogen gas (200ppm), which vary according to the heat treatment temperature of the gas sensor according to the present invention, at 160 ° C. and 280 ° C., respectively.

4 is a graph measuring a current value changed at 160 ° C. according to concentrations of carbon monoxide and hydrogen gas of a gas sensor according to the present invention;

5a and b are graphs comparing sensitivity of carbon monoxide (200ppm) and hydrogen gas (200ppm), which vary according to the amount of ZnO addition of the gas sensor according to the present invention, at 200 ° C. and 350 ° C., respectively.

In order to achieve the above object, in the present invention, in the reducing gas sensor comprising a gas sensitive layer formed from a reducing gas sensing material and the anode and cathode on both sides thereof, the gas sensitive layer is xCuO- (1-x) SnO ₂ Provided is a gas sensor, characterized in that it comprises a material of composition (where 0 <x <0.1).

In the present invention, in the gas sensor of the present invention, the gas-sensitive layer further contains ZnO, wherein xCuO-yZnO- (1-xy) SnO ₂ (where 0 <x <0.1, 0 <y <0.99.0). <x + y <1) may comprise a material of composition.

In addition, in the present invention, the production of a gas sensor according to the present invention comprising mixing CuO powder and any ZnO powder and SnO ₂ powder, followed by drying and heat treatment to form a sintered body, and forming electrodes on both sides of the sintered body. Provide a method.

In addition, in the present invention, after mixing the ZnO powder and SnO ₂ powder to form a sintered body by drying and heat treatment, the sintered body is impregnated with CuO solution and then heat-treated to form a sintered body, and then the electrodes on both sides of the sintered body It provides a method of manufacturing a gas sensor, comprising forming a.

Hereinafter, the present invention will be described in more detail.

The present invention provides a sensitivity and selectivity for a CO gas and a hydrogen gas of a sensor by using CuO added to a SnO ₂ material in a gas sensitive layer in a gas sensitive layer sensitive sensor such as carbon monoxide (CO) gas or hydrogen gas. Characterized in that improved. The gas sensitive layer according to the invention exhibits sensitivity at temperatures in the range of 100 to 300 ° C., but in particular exhibits the highest CO gas sensing selectivity at temperatures of about 160 ° C., and maximum hydrogen gas sensing selectivity at temperatures of about 280 ° C. Indicates. Considering that the maximum CO gas detection temperature of pure SnO ₂ is 340 ° C., when CuO is incorporated into SnO ₂ according to the present invention, CO and hydrogen gas can be detected at a significantly lower temperature.

The SnO ₂ material in which CuO is mixed is wet mixed with powder of each material in a small amount of solvent using a method such as a ball mill according to a conventional method, and then dried at about 100 ° C., It can be obtained by heat treatment at a temperature in the range of about 700 to 900 ℃.

In the gas sensitive layer material of the gas sensor according to the present invention, the amount of CuO added is preferably 10 mol% or less, preferably 1 mol% or less, based on SnO ₂ , in order to obtain appropriate sensitivity.

The gas sensitive layer material of the gas sensor according to the present invention may further comprise a ZnO component. By mixing ZnO with CuO-added SnO ₂ , the reaction temperature for hydrogen gas is induced at a high temperature and the temperature for carbon monoxide is kept at a low temperature, thereby selecting selectivity for carbon monoxide gas at low temperatures and hydrogen gas at high temperatures. Can increase the selectivity. At this time, the amount of ZnO component used is 99 mol% or less, preferably 1 to 40 mol%, based on SnO ₂ .

According to the present invention, the ZnO-containing CuO-SnO ₂ gas sensitive layer material is dried and heat-treated after wet mixing ZnO powder and CuO powder with SnO ₂ powder in a predetermined molar ratio by a conventional powder mixing method as described above. Alternatively, ZnO powder and SnO ₂ powder may be obtained by forming a sintered body heat-treated by powder mixing first, then immersing it in a CuO solution, followed by drying and heat treatment.

In the gas sensitive layer according to the present invention formed as described above, a gas sensor may be manufactured using ordinary Pt, Au, or the like as an electrode, and the method of applying the electrode may include painting, screen printing, or sputtering ( sputtering).

The gas sensor according to the present invention may be manufactured in a conventional shape, for example, in the form of a disc, a thick film, a thin film, and the like, and the production may be performed in a conventional method, for example, press molding. (press molding), screen printing, sputtering, or the like.

In this application, the sensitivity of the gas sensor is increased by measuring the current (I _AIR ) passing through the sensing material under a voltage applied in the air and then injecting the gas (CO or H ₂ ) to be detected at a constant concentration. (I _CO or I _H2 ) is measured and defined as the ratio. That is, the sensitivity to carbon monoxide S _CO = I _CO / I _AIR and the sensitivity to hydrogen gas are defined as S _H2 = I _H2 / I _AIR . Herein, selectivity is defined as the ratio of sensitivity to carbon monoxide and sensitivity to hydrogen, selectivity to carbon monoxide is defined as S _CO / S _H2 , and selectivity to hydrogen is defined as S _H2 / S _CO .

Hereinafter, the present invention will be described in detail through examples.

Example 1

SnO ₂ commercial powder and CuO commercial powder were placed in ethanol and mixed uniformly for 12 hours by a wet ball mill to obtain a mixed slurry containing 1, 2, 5 and 10 mol% CuO. The mixed slurry was dried at 100 ° C., molded using a mold, hydrostatically molded at a pressure of 2 ton / cm ² , and then heat treated again at 800 ° C. to form a coin-shaped gas-sensing CuO · SnO ₂ sintered body. To complete.

In order to measure the gas-sensing characteristics of the obtained gas-sensing material, platinum electrodes were applied to both sides of the coin-shaped sensing material and heat-treated again at 600 ° C. for 30 minutes. The gas detectability of the material was measured.

Separately, a gas sensor was fabricated as described above using SnO ₂ material without CuO mixing, and the gas sensing performance was measured. The result was obtained from a gas sensor obtained using a sensitive material containing 1 mol% of CuO. And are shown in FIGS. 1A and 1B, respectively. The sensitivity of the sensor is determined by measuring air resistance by injecting air having a relative humidity of 23% at room temperature for at least 1 hour and measuring a resistance changed after injecting a gas diluted with 200 ppm of CO or H _2. to be.

From Fig. 1, the sensitivity of pure SnO ₂ material shows the maximum value at around 350 ° C., and the sensitivity to hydrogen is higher than that of carbon monoxide at the entire measurement temperature, but when 1 mol% CuO is added, the maximum sensitivity is lowered. It can be seen that it has a higher sensitivity to carbon monoxide at low temperatures and to hydrogen at high temperatures.

When using the CuO-containing gas sensitive material according to the present invention, the results of comparing the sensitivity for carbon monoxide and hydrogen gas at 160 ℃ and 280 ℃ when the addition amount of CuO up to 10 mol% is compared to Figures 2a and 2b The selectivity for carbon monoxide at 160 ° C. and the selectivity for hydrogen at 280 ° C. were calculated according to the amount of added CuO, and are shown in Table 1 together with the sensitivity results.

CuO addition amount (mol%) 160 ℃ 280 ℃ CO sensitivity H ₂ sensitivity CO selectivity CO sensitivity H ₂ sensitivity H ₂ selectivity 0 2.0 4.7 0.4 4.4 8.3 1.9 One 7.2 4.2 1.7 2.4 3.5 1.5 2 5.4 2.8 1.9 2.3 3.6 1.6 5 4.8 2.6 1.8 2.6 5.0 1.9 10 5.3 2.9 1.8 2.6 5.2 2.0

It can be seen from FIG. 2 and Table 1 that the sensitivity to carbon monoxide is higher at 160 ° C. and higher at 280 ° C. for hydrogen.

Example 2

The same procedure as in Example 1 was carried out except that 1 mol% CuO and 3 mol% ZnO powder were mixed in the SnO ₂ commercial powder and heat treatment was performed at 700 to 900 ° C., and the sensitivity of the obtained sensor was measured. .

3a and b are graphs comparing the sensitivity of carbon monoxide (200ppm) and hydrogen gas (200ppm) according to the heat treatment temperature of the sensitive layer of the gas sensor manufactured above at 160 ℃ and 280 ℃. As shown in FIG. 3, when a material obtained by simultaneously adding CuO and ZnO to SnO ₂ according to the present invention was used in a sensitive layer, much better than the result of Example 1 in which only CuO was added to SnO ₂ , 160. Selectivity to carbon monoxide at &lt; RTI ID = 0.0 &gt; C &lt; / RTI &gt; In particular, when the heat treatment at a low temperature of 700 ℃, the sensitivity is excellent, especially the sensitivity to carbon monoxide appears 7 times higher than hydrogen. The sensitivity of carbon monoxide and hydrogen at 160 ° C. and 280 ° C. of the sensor was calculated and shown in Table 2 together with the sensitivity results.

Heat treatment temperature 160 ℃ 280 ℃ CO sensitivity H ₂ sensitivity CO selectivity CO sensitivity H ₂ sensitivity H ₂ selectivity 700 ℃ 12.0 1.7 7.1 4.3 13.8 3.2 750 ℃ 12.1 2.0 6.1 3.7 16.4 4.4 850 ℃ 5.0 1.7 2.9 4.0 12.6 3.2 900 ℃ 3.1 1.5 2.1 3.4 10.4 2.0

The change in the measured current value is shown in FIG. 4 by increasing the concentrations of carbon monoxide and hydrogen up to 1000 ppm at 160 ° C for heat treatment at 700 ° C. From Fig. 4, even if the concentration of hydrogen gas is increased to 1000 ppm, the current change is very small, whereas the current change by the carbon monoxide gas is very large, thereby preventing the malfunction by the hydrogen gas when detecting the carbon monoxide gas.

Example 3

SnO ₂ commercial powder and ZnO commercial powder were mixed in the same manner as in Example 2 to prepare a molded article having a composition of (1-x) SnO ₂ -xZnO (x = 0.03, 0.1, 0.3, 0.4, 0.6, 0.8, and 0.99). After that, heat treatment was performed at 800 ° C. to form a coin gas sensitive material.

The sintered bodies and the separate SnO ₂ sintered bodies were immersed in a 1 wt% CuO solution prepared in advance for 1 hour, and then heat-treated again at 750 ° C. The CuO solution was prepared by dissolving Cu (NO ₃ ) .3H ₂ O metal salt in distilled water by the Pechini method and then adding ammonia water (NH ₄ OH) to precipitate the copper hydroxide (Cu (OH) ₂ ) precipitate. The precipitate was added to ethylene glycol, heated to 80 ° C., and citric acid was dissolved therein to prepare a transparent liquid phase. The amount of added CuO is about 0.05 mol% based on SnO ₂ , given the amount and concentration of CuO solution filled in the pores.

The sensor was fabricated in the same manner as in Example 1 using the sensitive layer material, and the sensitivity of carbon monoxide (200 ppm) and hydrogen gas (200 ppm) of the manufactured sensor was performed in the same manner as in Example 1. It is shown in 5, and the selectivity for carbon monoxide and hydrogen gas is calculated and shown in Table 3 with the sensitivity results.

Furtherance 200 ℃ 350 ℃ CO sensitivity H ₂ sensitivity CO selectivity CO sensitivity H ₂ sensitivity H ₂ selectivity SnO ₂ (Cu) 4.2 3.0 1.4 2.2 4.3 2.0 97SnO ₂ -3ZnO (Cu) 13.9 2.5 5.5 2.3 9.4 4.1 90SnO ₂ -10ZnO (Cu) 11.2 2.5 4.6 3.8 12.4 3.3 70SnO ₂ -30ZnO (Cu) 8.5 3.4 2.5 3.4 10.4 3.1 60SnO ₂ -40ZnO (Cu) 7.4 2.8 2.6 4.0 11.3 2.8 40SnO ₂ -60ZnO (Cu) 5.6 2.6 2.2 4.8 9.7 2.0 20SnO ₂ -80ZnO (Cu) 4.2 2.1 2.0 4.7 9.8 2.1 1SnO ₂ -99ZnO (Cu) 2.7 1.7 1.6 2.8 5.4 1.9

As can be seen from FIG. 5 and Table 3, as in Example 2, when ZnO is added together with SnO ₂ rather than CuO alone, the sensitivity to carbon monoxide is higher at 200 ° C than at hydrogen, and at 350 ° C. The sensitivity to hydrogen is higher, especially when 3 mol% of ZnO is added.

According to the present invention, when a SnO ₂ material containing CuO and an optional ZnO is used as a main material in a gas sensitive layer, a gas sensor having excellent detection selectivity with respect to CO and hydrogen gas can be obtained.

Claims (5)

A gas sensor comprising a gas sensitive layer formed from a reducing gas sensing material and an anode and a cathode on both sides thereof, wherein the gas sensitive layer has a composition of xCuO- (1-x) SnO ₂ (where 0 <x <0.1). A gas sensor, characterized in that it comprises a material. The method of claim 1, The gas sensitive layer further comprises a ZnO component to form a material of composition xCuO-yZnO- (1-xy) SnO ₂ (where 0 <x <0.1, 0 <y <0.99, 0 <x + y <1). Gas sensor, characterized in that it comprises. After mixing CuO powder and SnO ₂ powder, drying and heat-treating to form a sintered body of xCuO- (1-x) SnO ₂ (where 0 <x <0.1) composition, and forming electrodes on both sides of the sintered body A method of manufacturing a gas sensor according to claim 1 comprising. CuO powder, ZnO powder and SnO ₂ powder are mixed, dried and heat treated to give xCuO-yZnO- (1-xy) SnO ₂ , where 0 <x <0.1, 0 <y <0.99, 0 <x + y <1 The manufacturing method of the gas sensor of Claim 2 including forming the sintered compact of composition, and forming electrodes in the both sides of this sintered compact. ZnO powder and SnO ₂ powder are mixed, dried and heat treated to form a sintered body having a composition of yZnO- (1-y) SnO ₂ (where 0 <y <0.99), and the sintered body is impregnated with CuO solution and then heat treated. After forming a sintered body of xCuO-yZnO- (1-xy) SnO ₂ (where 0 <x <0.1, 0 <y <0.99, 0 <x + y <1), electrodes are formed on both sides of the sintered body. A method of manufacturing a gas sensor according to claim 2 comprising forming.