JPS6170447A - Gas detecting element - Google Patents

Abstract

PURPOSE:To obviate the change in the sensitivity of a gas detecting element of a metallic oxide semiconductor, etc. with time by aging the gas detecting element in an atmosphere of sulfide. CONSTITUTION:The metallic oxide semiconductor such as SnO2 or Fe2O3 or the catalyst element deposited with Pd, Pt, etc. on a carrier such as Al2O3 is used as the gas detecting element. Such gas detecting element is poisoned by the sulfide SO2, (CH3)2S, etc. and the sensitivity thereof decreases in an initial period but the sensitivity does not change with time thereafter. The gas detecting element is thereupon aged and poisoned in the atmosphere of the sulfide such as SO2 and (CH3)2S. The resulted gas detecting element is subjected to the initial change with time where the change is significant to decrease the subsequent change with time and therefore the element is capable of detecting LPG and city gas, etc. with good accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a human detection element, and a gas detection element mainly using a metal oxide semiconductor or supporting a combustion catalyst.

[Background technology 1 Generally, this type of gas detection element includes 51102, F
Semiconductor devices using metal oxide semiconductors such as e, O, ZnO, etc., and A I 20 h, S i 02 etc. (')
Catalytic combustion elements having a combustion catalyst supported on a carrier such as Pd or PL are available. Semiconductor elements detect gas by utilizing the property that the conductivity of the element changes when combustible gas is adsorbed on the gas detection surface of the element, and catalytic combustion elements detect lIf flammability. Gas is detected by utilizing the fact that when gas comes into contact with the element and burns, the temperature of the element changes and the conductivity of the element changes. The detection target of these gas detection elements is mainly LPG (main components are propane and methane).
and city gas (main components are hydrogen, methane, and carbon oxides), or as mentioned above, the presence of flammable gas is detected by adsorption or combustion of flammable gas, so it is a detection target. It is sensitive to volatile gases such as combustible gases and organic solvents other than combustible gases, and may cause false alarms when the above-mentioned element is used in a gas leak alarm. In particular, when cooking in a kitchen, large amounts of alcohol and smoke are temporarily generated from meat, fish, vegetables, seasonings, cooking oil, etc., and these gases can sometimes cause false alarms. In addition, in places such as underground cafeterias, where the amount of cooking and cooking time is higher than in a typical home, and where ventilation is poor, false alarms may occur during cooking, and the sensitivity of the detection element may deteriorate over time. As a result, false alarms are more likely to occur, or warnings may not be output when they should be sent. For example, in semiconductor devices, gas is detected by adsorption of gas molecules, so if the device is in contact with gas molecules for a long time, the gas molecules will be adsorbed, and the sensitivity will gradually increase, making false alarms more likely. On the other hand, in a catalytic combustion element, its function as a catalyst deteriorates over time due to surface contamination, and its sensitivity mainly to methane decreases, so that an alarm may not be output in the event of a gas leak.

Although various studies have been conducted on the causes of such changes over time in the sensing element, the causes have not been clarified until now. Therefore, in the past, in order to select the gas to be detected and avoid sensitivity to unnecessary gases, the gas detection surface of the sensing element was covered with a selective filter, which allowed only the gas to be detected to pass through the sensing element. There is one that comes into contact with the gas detection surface of the sensor. These selective filters are adsorption filters that adsorb unnecessary gases,
Combustion-type filters that burn unnecessary gases using catalysts are known, and adsorption-type filters include zeolite,
Diatomaceous earth, activated alumina, activated carbon, etc. are used, and as combustion type filters, platinum, paranoyum,
There are supported combustion catalysts such as Ronoame.

However, since the cause of the change in sensitivity of gas detection elements over time had not been clarified until 2007, it was necessary to use these selective filters to remove temporarily generated alcohol and smoke from the VA. Although it can be set, it cannot be set to remove components that cause changes in sensitivity over time, making it impossible to avoid changes over time.

[Objective of the Invention 1] The present invention has been made in view of the above-mentioned points, and its main object is to provide a gas sensing element that prevents changes in sensitivity over time.

[Disclosure of the Invention 1 The present invention discloses a gas sensing element that has been subjected to aeoning in a sulfide atmosphere until there is no change in sensitivity due to sulfide, thereby allowing the element to change over time in advance, thereby reducing the change over time during subsequent use. be done.

First, it is necessary to understand the causes of changes over time, which were previously unknown.
In addition to analyzing the major components, we also conducted experiments to determine whether each gas causes changes in the sensing element over time. As a result, it was found that the primary cause of change over time was SO2, and the secondary causes were (CH,) and S.

Next, the sensing element was left in an atmosphere containing a mixture of these sulfides (SO2+(CH,)2S) (hereinafter vL@
(referred to as Ehnong), it was found that although there was a slight change over time in the initial period, there was almost no change over time in the sensing element after a short period of poison aging.

Examples in which poison aging was performed under various conditions based on the above experiments will be described in detail below. In the following examples, a city gas semiconductor element manufactured by Matsushita Electronic Components Co., Ltd. was used as a gas detection element. The following measurement method was used to determine whether there was a change in sensitivity over time.

(Measurement method) After measuring the sensitivity of the gas detection element to methane and hydrogen in purified air at a DP of 13°C, the gas detection element was housed in a lath chamber and energized to detect SO2 and (CH
,) 1 a day so that both 2S and 2S have a concentration of lpp...
Gas was poured into the glass chamber/bar at a rate of 1.5 times, and this was repeated every day.One week later, the sensitivity to methane and hydrogen was measured again in purified air at a D'P of 13°C. In this way, sensitivity measurements were carried out every week, and this continued for three weeks.

(Example 1) Electricity was applied for 4 days in a normal air atmosphere, and then S
120. An atmosphere was formed in which O, (CH,), and S each had a concentration of 10 ppm. Poison aging was performed for 3 days in a glass chamber.

When the sensitivity change over time of this gas detection element was measured using the above-mentioned measurement method-2, as shown in FIG. 1, the result was that there was almost no change over time. Here, the open line shows resistance III to air, the broken line shows resistance to ivy, and the one-dot chain line shows resistance to hydrogen gas. Lord, 1
Regarding the measurement, the three points are 500 ppm and 100 ppm, respectively, from the top.
+o, 4500 ppI11 is shown. Similar notations are used in the figures below.

(Example 2) Electricity was applied for 4 days in a normal air atmosphere, and then S
Poisoning was carried out for 3 days in a 12α gas chamber in which an atmosphere was formed in which O2 and (c Hx ) 2 S were both at a concentration of 51) pm.

Also in this example, as shown in FIG. 2, almost no change in sensitivity over time was observed.

(Example 3) S02 and (C)I,)2S and 10 ppm of
Poisoning aging was carried out for one day in an atmosphere of rA degree.

In this example, as shown in FIG.
There was almost no change in sensitivity.

(Comparative Example 1) For comparison with the example, electricity was applied for 4 days in a normal air atmosphere, and then the concentration of only SO was 10 ppm.
Poisoning was carried out for 3 days in an atmosphere of

As a result of the measurement, as shown in the tA4 diagram, a slight change in sensitivity over time was observed. This is (C1-1,>28
This is thought to be due to the fact that no poisoning treatment was carried out.

(Comparative Example 2) Furthermore, as Comparative Example 2, measurements were performed without any poisoning aging, and as shown in Figure 5, it was observed that the thickness (change in sensitivity was observed) Ta.

As is clear from the above results, 2% bodies (So, (C
The detection element subjected to poisoning aging for both H, )2S) shows almost no change in sensitivity over time, and it was concluded that this can prevent changes in sensitivity over time.

[Effect of the Invention 1] As described above, the present invention performs aging in a sulfide atmosphere until the sensitivity change due to sulfide disappears, thereby ending the slow initial change over time. This has the advantage that subsequent changes over time can be prevented, and as a result, a gas detection element with stable sensitivity over time can be obtained. Therefore, this human detection element (
Gas detectors that are heavily used do not generate false alarms and can be used stably for a long period of time.

[Brief explanation of the drawing]

1 to 3 are operation explanatory diagrams showing the measurement results of Examples 1 to 3 of the present invention, respectively. FIG. 4 is an operation explanatory diagram showing the measurement results of Comparative Example 1. FIG. 5 is an operation explanatory diagram showing the measurement results of Comparative Example 1. FIG. 2 is an operation explanatory diagram showing measurement results of No. 2; Agent Patent Attorney Ishi 1) Long 7111 Figure 1r2rIJ J+Terama (Japanese)
B (Japanese) Figure 3 Figure s4 *NI (B) M CB) Figure 5 Procedural amendment (voluntary) December 27, 1981 Patent Application No. 1 '72104 2, Invention Name of Gas Detection Element 3, Relationship with the person making the amendment Patent applicant Location 1048 Oaza Kadoma, Kadoma City, Osaka Name Name (583) Matsushita Electric Works Co., Ltd. Representative Iku Kobayashi 4, Agent

Claims (1)

[Claims] (1) A gas detection element characterized in that it is aged in a sulfide atmosphere until sensitivity changes due to sulfides disappear.