JP4101078B2 - Sulfur compound gas detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sulfur compound gas detection element.
[0002]
[Prior art]
A semiconductor gas detection element that detects the presence or absence of gas by connecting an electrode to a metal oxide semiconductor (tin oxide) whose resistance value changes due to gas adsorption and desorption has been conventionally detected. It is used as a container.
[0003]
On the other hand, recently, development of a gas sensor for performing auto ventilation (automatic ventilation) in a residence such as a toilet or a kitchen has been demanded. That is, the main malodorous components such as toilets and kitchens contain hydrogen sulfide and mercaptans, and these gas concentrations range from several ppb to several hundred ppb to maintain a comfortable living environment. A gas sensing element that can be detected is needed. However, the lower limit concentration detectable by the conventional metal oxide semiconductor gas sensing element was higher than several hundred ppb.
[0004]
Therefore, in Patent Documents 1 and 2, after applying an alkoxide solution of tin to an insulating substrate, the alkoxide solution is thermally decomposed to form a tin oxide film, and another metal (usually an oxide of oxide) is formed on the tin oxide film. Have been proposed to increase gas detection sensitivity.
[0005]
However, in the method described above, the gas sensitivity is relatively good, but the recovery response when the atmosphere is switched from hydrogen sulfide to air is not preferable. On the other hand, if the sensor temperature is increased to 400 ° C., the recovery responsiveness is improved, but this time the gas sensitivity is drastically lowered. Heat cleaning for heating the sensor to improve recovery response is also known, but in this case, continuous measurement cannot be performed and another circuit for heat cleaning is required.
[0006]
In order to solve the above problems, a gas detection element has been developed in which the main component of the metal oxide semiconductor to which sulfur-based gas is adsorbed and desorbed is tungsten oxide and the additive added to the metal oxide is at least one selected from precious metals. (See Patent Document 3).
[0007]
In other words, the sensitivity to sulfur-based gases such as hydrogen sulfide and mercaptans is greatly improved by changing the metal oxide that is the main component of the gas detection element from conventional tin oxide to highly acidic tungsten oxide. Therefore, it is considered that problems such as a decrease in gas sensitivity are alleviated and a gas detection element capable of detecting a sulfur-based gas in a range of several ppb to several hundred ppb is obtained.
[0008]
[Patent Document 1]
JP-A-63-313048 [Patent Document 2]
JP-A-63-313049 [Patent Document 3]
Japanese Patent Laid-Open No. 06-18467
[Problems to be solved by the invention]
However, according to the above-described sulfur compound gas detection element, the sensitivity output is improved and a significant output can be obtained even for a sulfur-based gas in the range of several ppb to several hundred ppb, but selectivity with other miscellaneous gases. However, it was not sufficient for practical use, and there was still room for improvement.
[0010]
Therefore, in view of the above circumstances, the object of the present invention is to improve the sulfur compound gas sensitivity of a sulfur compound gas detection element having a sensitive layer mainly composed of a tungsten oxide semiconductor, and to reduce sulfur in the range of several ppb to several hundred ppb. An object of the present invention is to provide a gas detection element capable of detecting a system gas and improving gas selectivity to withstand practical use.
[0011]
[Means for Solving the Problems]
In order to achieve this object, the characteristic configuration of the sulfur compound gas detection element of the present invention is:
A sensitive layer mainly composed of a tungsten oxide semiconductor to which a lead component and a copper component are added is provided, and the ratio of the added amount of the copper component to the added amount of the lead component is (Pb: Cu) = (4: 1) In that point,
Relative amount said tungsten oxide of the lead component, Ri 0.2mol% ~4mol% der,
The amount of the copper component added is preferably 0.05 mol% to 1 mol% with respect to the tungsten oxide .
[0012]
The component ratio of lead to tungsten is determined by the molar ratio of each metal atom and is expressed as mol%.
[0013]
[Function and effect]
That is, according to the sulfur compound gas detection element of the present invention, in addition to improving the sensitivity to sulfur compound gas by tungsten oxide, selective sensitivity to sulfur compounds can be improved by lead . In addition to improving the sulfur compounds sensitivity by pre Kinamari, when containing copper, the increased sensitivity of synergistically increased, further, is also shortened gas detection response time. Furthermore, when the ratio of the addition amount of the copper (Cu) component to the addition amount of the lead (Pb) component is about (Pb: Cu) = (4: 1), the gas having high sensitivity and selectivity to the sulfur compound gas. A sensing element is obtained. Thus, a high-performance sulfur compound gas detecting element that can withstand practical use can be provided. In the case of the present invention, the sensitivity as the resistance change rate as the resistance ratio when the gas detection element detects the detection target gas containing the gas to be detected with respect to the resistance when the gas detection element detects air. Appears.
[0014]
As the addition amount of the lead component, if the addition amount is too small, the catalytic effect is not sufficiently exhibited.
Since the long-term stability as a whole sensitive layer and the quality stability in production tend to decrease as the amount added increases, it is preferably 4 mol% or less.
[0015]
Also, the addition amount of the copper component, since the addition amount becomes the catalyst effect is less likely to appear the less, preferably greater than or equal to 0.05 mol%, in accordance with increasing the addition amount tends to output value itself decreases observed Therefore, it has been experimentally confirmed that it is desirable to make it 1 mol% or less.
[0016]
In general, the lead component in the present invention is impregnated with a solution of a lead compound in a sensitive layer mainly composed of tungsten oxide, and then baked and supported in the form of an oxide. The compound may be supported in the form of the above compound, or may be supported in the form having the same activity as that of the oxide. These leads supported in the form of various lead compounds are called lead components.
[0017]
In addition, the sulfur compound referred to in the present invention refers to a compound group containing sulfur and having similar gas detection characteristics for various gas detection elements, such as hydrogen sulfide, methyl mercaptan, butyl mercaptan, and dimethyl sulfide. To do.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
As shown in FIG. 1, the sulfur compound gas detection element 1 of the present invention is provided with a comb-shaped electrode 1a on the surface of an alumina substrate, and a metal oxide semiconductor paste mainly composed of tungsten oxide is applied on the comb-shaped electrode 1a. The sensitive layer 1b is provided by baking at 600 ° C. for 2 hours. A platinum thin film heater 1c is provided on the back surface of the alumina substrate and is used to maintain the operating temperature of the gas detection element.
Further, the sensitive layer 1b is impregnated with an aqueous solution of a lead component such as lead nitrate and then baked at 550 ° C. for 0.5 hour to carry the lead component. The amount of lead nitrate impregnated can be adjusted by dropping a predetermined amount of a lead nitrate aqueous solution into the sensitive layer in small amounts using a capillary to impregnate the lead layer. Similarly, the copper component can also be supported on the sensitive layer by impregnating and baking an aqueous solution of a copper component such as copper nitrate.
Here, using a 2 mol% lead nitrate and copper nitrate aqueous solution, the lead impregnation amount of 0.2 mol% to 4 mol% with respect to tungsten oxide, and the ratio of the copper content to the lead content is (Pb: The catalyst support layer was formed so that the copper content was Cu) = (4: 1) to (1: 4).
In addition, it is thought that the said lead component and copper component are carry | supported by the said sensitive layer by the form of an oxide by baking.
[0019]
As shown in FIG. 2, the gas detection device is configured to incorporate the above-described sulfur compound gas detection element 1 in the gas detection circuit 2 and obtain a gas detection output. The gas detection output obtained from the sulfur compound gas detection element is input to the control unit 3 to determine whether or not the sulfur compound concentration has reached a level requiring an alarm. Here, when it is determined that an alarm is required, the control unit 3 outputs an alarm signal to the alarm unit 4, and the alarm unit 4 sounds an alarm buzzer, an alarm sound, and the like.
[0020]
【Example】
Embodiments of the present invention will be described below with reference to the drawings.
(1) Lead component support As the above-described sulfur compound gas detection element 1, a gas detection characteristic for various gas components is obtained by using a sensitive layer 1b mainly composed of tungsten oxide and supporting 0.7 mol% of a lead component. As a result, it was as shown in FIG. Further, when the gas detection characteristics of a gas detection element that does not carry lead and has a sensitive layer made of only tungsten oxide were examined in the same manner, it was as shown in FIG. The gas detection characteristic is a ratio (Rair / Rg) of the resistance value (Rg) in the detection target gas including the detection gas of the gas detection element and the resistance value (Rair) in clean air not including the detection gas. The resistance change rate (sensitivity) obtained as follows is determined as the dependency of the gas to be detected.
[0021]
As shown in FIG. 3 (b), the gas detection element that does not support lead and has a sensitive layer mainly composed of tungsten oxide includes, for example, toluene (C ₆ H ₅ CH ₃ ), ethylbenzene (C ₆ H ₅ C _2). H _5), trimethylbenzene _{(C 6 H 3 (CH 3} ) 3) aromatic volatile organic compounds such as (VOC) gas or the like, for the various gas components, at concentrations of a few hundred ppb order (1 ppm or less) Even in such a case, it can be seen that it exhibits high sensitivity, but its gas detection characteristics show similar tendencies for various gas components, making it difficult to selectively detect specific gases. You can see that In particular, for sulfur compounds, the resistance change rate does not change much as compared with other gas components, so that it is difficult to obtain sufficient sensitivity.
[0022]
On the other hand, the sulfur compound gas detection element of the present invention in which a lead component is supported is particularly about several hundred ppb (1 ppm) with respect to hydrogen sulfide, which is an example of a sulfur compound, as shown in FIG. It can be seen that even with the following concentrations, high sensitivity is exhibited and high selectivity is exhibited.
[0023]
Next, when the sulfur compound concentration is 100 ppb, the dependence of the resistance change rate of the gas detection element on the amount of the lead component supported is examined, and the result is as shown in FIG. From FIG. 4, it can be read that the sulfur compound gas detection elements obtained by variously changing the loading amount of the lead component show a high rate of change in resistance. In particular, referring to FIG. When a high value of 6 or more is shown, it can be seen that the detection sensitivity of the low concentration sulfur compound gas is set higher than that of the high concentration aromatic VOC gas component. Even if it is changed, a resistance change rate of 6 or more is realized in a wide range. Therefore, it turns out that it can utilize effectively as a sulfur compound gas detection element.
In addition, if the amount of lead component added is too small, the catalytic effect will not be sufficiently exerted, and as the amount of lead component added increases, the long-term stability of the sensitive layer as a whole and the quality stability in production are likely to deteriorate. From 0.2 to 4 mol% is preferable, and it is considered that a high rate of change in resistance is particularly exhibited at a supported amount of 0.4 to 3 mol%.
[0024]
(2) Copper component loading Gas sensing elements (Pb: Cu) = (4: 1) to (4: 1) in which the loading amount of the lead component in the previous embodiment is fixed to 0.7 mol% and the loading amount of the copper component is variously changed. 1: 4) was prepared, and the sensitivity characteristics of each gas detection element to sulfur compound (hydrogen sulfide) gas were examined, and the result was as shown in FIG.
As shown in FIG. 5, the gas detection element mainly composed of tungsten oxide supporting lead increases the rate of change in resistance by supporting the copper component, and further increases the resistance by increasing the amount of supported copper. It turns out that the rate of change tends to a downward trend.
Therefore, it is preferable that the copper component is added in an amount equivalent to (Pb: Cu) = (4: 1) equivalent to the lead component supported on the sensitive layer. Based on the relationship of FIG. 4 described above, it was found that a supported amount of 0.05 mol% to 1 mol% is particularly preferable for the tungsten oxide sensitive layer.
Further, such a gas detection element may not have a sufficient output response time, and further improvement is desired from such another aspect. It has been confirmed that the response speed is also improved.
Further, when the gas detection characteristics of the above-described gas detection element (Pb: Cu) = (4: 1) (Pb & Cu) were examined, it was as shown in FIG. FIG. 6 shows that the resistance change rate with respect to the sulfur compound (here, hydrogen sulfide (H ₂ S)) is greatly improved by supporting the copper component as compared with the case where only the lead component is supported (Pb). On the contrary, the resistance change rate with respect to the aromatic VOC component (trimethylbenzene is illustrated here) is greatly reduced. Therefore, it turns out that the selectivity with respect to the sulfur compound gas in detection object gas is improved greatly.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional perspective view of a sulfur compound gas detection element. FIG. 2 is a schematic view of a gas detection device. FIG. 3 is a graph showing gas detection characteristics of the sulfur compound gas detection element of the present invention. FIG. 5 is a graph showing the dependency of the sulfur component gas detection element on the amount of lead component added. FIG. 5 is a graph showing the copper component addition amount dependency of the sulfur compound gas detection element of the present invention. Graph showing gas detection characteristics
DESCRIPTION OF SYMBOLS 1 Sulfur compound gas detection element 1a Comb electrode 1b Sensing layer 2 Gas detection circuit 3 Control part 4 Alarm part

Claims (2)

A sulfur compound gas sensing element including a sensitive layer mainly composed of a tungsten oxide semiconductor to which a lead component and a copper component are added ,
The sulfur compound gas detection element whose ratio of the addition amount of the said copper component with respect to the addition amount of the said lead component is (Pb: Cu) = (4: 1) . Relative amount said tungsten oxide of the lead component, Ri 0.2mol% ~4mol% der,
The sulfur compound gas detection element according to claim 1, wherein an addition amount of the copper component is 0.05 mol% to 1 mol% with respect to the tungsten oxide .

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