JP3191420B2 - Gas sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention relates in particular to hydrogen sulfide (H
₂ S), it relates to a gas sensor for detecting the sulfur-based gas mercaptan.

[0002]

2. Description of the Related Art Conventionally, a semiconductor gas sensor in which an electrode is connected to a metal oxide semiconductor (SnO ₂ ) whose resistance value changes due to adsorption and desorption of a gas and the presence or absence of a gas is detected by measuring the resistance value has been known. It is used as a gas leak alarm.

On the other hand, recently, there has been a demand for the development of a gas sensor for performing automatic ventilation (automatic ventilation) in a house such as a toilet or a kitchen. That is,
The main odor components in toilets and kitchens are H ₂ S,
Ammonia, amines and mercaptans, these gases must have a concentration of several ppb to maintain a comfortable living environment.
A sensor that can detect in the range of several ppm is required. However, the concentration detectable by a conventional metal oxide semiconductor gas sensor is several hundred ppm or more.

Therefore, Japanese Patent Application Laid-Open Nos. 63-313048 and 63-313049 disclose that an alkoxide solution of Sn is applied to an insulating substrate, and then the alkoxide solution is thermally decomposed to form SnO _2. Proposals have been made to increase the gas detection sensitivity by adding another metal (usually in the form of an oxide) to the _two films.

[0005]

However, in the above-described method, the atmosphere is H ₂ S although the gas sensitivity is relatively good.
Recovery responsiveness when switching from air to air is poor. On the other hand, if the sensor temperature is increased to 400 ° C., the recovery responsiveness is improved, but the gas sensitivity sharply decreases this time. Heat cleaning in which a sensor is heated to enhance recovery responsiveness is also known. However, in this case, continuous measurement cannot be performed, and another problem is that a separate circuit for heat cleaning is required. .

[0006]

The present invention to solve the above problems BRIEF SUMMARY OF THE INVENTION may, WO ₃ powder mainly of a metal oxide semiconductor for adsorbing and desorbing hydrogen sulfide or mercaptan containing gas and WO _3, a metal oxide Au by impregnation or colloid adsorption
After adding 0.2-0.8 wt%, baking
The resulting porous sintered body was used as a gas sensor .

[0007]

[Effect] The metal oxide which is the main component of the gas sensor is
By changing from SnO ₂ to strongly acidic WO ₃ , 10 ppb ~
1 ppm hydrogen sulfide or mercaptan gas concentration
That gas detection is possible, sensitivity of the gas sensor was above greatly <br/> direction.

[0008]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Here, FIG. 1 is a perspective view showing an example of the gas sensor according to the present invention, and FIG. 2 is a partially enlarged sectional view of the gas sensor. FIG. 3 is a perspective view showing another example of the gas sensor according to the present invention.

In the gas sensor 1 shown in FIGS. 1 and 2, a pair of comb-shaped Au electrodes 3, 3 are formed on an alumina substrate 2 by firing, and a metal oxide semiconductor layer 4 connected to the Au electrodes 3, 3 is also fired. The heater 5 is formed on the surface of the alumina substrate 2, and a heater 5 is embedded in the alumina substrate 2. This metal oxide semiconductor layer 4 is obtained by adding Au to WO ₃ .
Note that the electrode may be directly buried in the metal oxide semiconductor layer having a certain thickness without forming the metal oxide semiconductor layer in a thin film on a substrate such as alumina.

The method for producing the metal oxide semiconductor layer 4 will be described below. First, ammonium paratungstate
_{{(NH 4) 10W 12 O} 41 · 5H 2 O} it was used as a starting material, which 600 ° C. in air. Pyrolyze for 5 hours to obtain a powder sample of WO3. Next, Au is added to the powder sample, and the powder obtained by baking in air at 600 ° C. for 5 hours is kneaded with a vehicle, molded, and then fired to form the metal oxide semiconductor layer 4. For the addition of Au , an impregnation method or a colloid adsorption method is used.

In a gas sensor 11 shown in FIG. 3, a pair of Pt wires 13 are wound around a cylindrical alumina tube 12, and this Pt wire 1
A metal oxide semiconductor layer 14 made of a porous sintered body obtained by adding Au to WO ₃ so as to enclose the layers 3 and 13 is formed.

Among the above additives, Au showed good results in both response and gas sensitivity. Therefore,
The following experiment was performed on the element to which Au was added. FIG.
An element formed by adding 0.5% by weight of Au on WO3 (hereinafter, referred to as WO ₃ -0.5Au elements) in H2S concentration 1ppm atmosphere was investigated the relationship between the device temperature and the gas sensitivity The result. Here, the gas sensitivity was represented by the ratio S = Ra / Rs between the resistance value Ra in the air and the resistance value Rs in the test gas (air containing hydrogen sulfide or mercaptan).

FIG. 5 shows the relationship between the amount of Au added to WO ₃ and the gas sensitivity. The temperature was measured at 300 ° C. in a 1 ppm H ₂ S atmosphere. From the figure, A
It was found that the addition amount of u was around 0.5% by weight the most appropriate amount, and the gas sensitivity was increased.

FIG. 6 shows a WO ₃ element without additives and W ₃
For an O ₃ -0.5Au element, at an element temperature of 300 ° C., H
_This is a study of the relationship between 2S concentration (ppb) and gas sensitivity. Located linear relationship between the logarithmic value of the gas sensitivity of the logarithmic value and the element of H2S concentration from the figure, according to the present invention WO ₃ -0.
It was found that the 5Au element can detect a thin H ₂ S concentration of about 1/50 with the same sensitivity as the WO ₃ element alone.

FIG. 7 shows the relationship between the gas sensitivity and the methyl mercaptan concentration (ppb) at a device temperature of 300 ° C. for a WO ₃ -0.5Au device according to the present invention.
As apparent from the figure, the logarithmic value of the gas sensitivity of the logarithmic value and the element of methyl mercaptan concentration is in the same linear relationship as in the H ₂ S, it exhibited a high gas sensitivity unchanged almost the H ₂ S.

FIG. 8 is a response curve of the WO ₃ -0.5Au device according to the present invention with respect to the H ₂ S concentration of 0.1 ppm, and the vertical axis represents a logarithmic value of a change rate (R / R0) of the device resistance. is there. As shown in this figure, this element is an excellent device that can detect odor in only about 1 minute after the generation of odor, and can completely recover in about 4 minutes without using heat cleaning. I found it.

[0017]

According to the present invention as described EFFECT above, trowel selects the WO ₃ as a metal oxide consisting mainly constituting the metal oxide semiconductor gas sensor, this was added Au, 10
ppb to 1 ppm hydrogen sulfide or mercaptan-based gas concentration
Enables gas detection in degrees, it is possible to greatly increase the sensitivity of the gas sensor may be a gas sensor further excellent in both response speed and the recovery speed.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a gas sensor according to the present invention.

FIG. 2 is a partially enlarged cross-sectional view of the gas sensor.

FIG. 3 is a perspective view showing another example of the gas sensor.

FIG. 4 is a graph showing a relationship between element temperature and gas sensitivity to H ₂ S of the gas sensor.

FIG. 5 is a graph showing the relationship between the amount of Au added to H ₂ S and the gas sensitivity of the gas sensor.

FIG. 6 is a graph showing a relationship between H ₂ S concentration and gas sensitivity of the gas sensor.

FIG. 7 is a graph showing a relationship between methyl mercaptan concentration and gas sensitivity of the gas sensor.

FIG. 8 is a graph showing a response curve of the gas sensor to H ₂ S.

[Explanation of symbols]

1, 11: gas sensor, 2, 12: alumina substrate, 3,
Reference numeral 13 denotes an electrode, 4, 14 denotes a metal oxide semiconductor layer, and 5 denotes a heater.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Norio Miura 3-17-5 301, Hirao, Chuo-ku, Fukuoka City, Fukuoka Prefecture (56) References Journal of Vacuum Science & Technology logistics A, 8 (4) 1990, p. 3634 −3638 (58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 27/12

Claims (2)

(57) [Claims] 1. A gas sensor utilizing a change in resistance value due to adsorption and desorption of a gas to a metal oxide semiconductor in which an additive is added to a main metal oxide, wherein the gas is a hydrogen sulfide or mercaptan-based gas sensor. The main metal oxide is WO ₃ , the additive is Au, and the WO ₃ powder is impregnated or
After adding Au by the colloid adsorption method, baking
A gas sensor characterized by being a porous sintered body obtained . 2. The gas sensor according to claim 1, wherein
And adding 0.2 to 0.8 wt% of Au.
Ruga scan sensor.