JPS5958349A - Gas detecting element - Google Patents

Abstract

PURPOSE:To provide high sensitivity for gaseous methane as well by using a compsn. contg. 0.1-50mol% tin, zirconium and titanium in total of additives respectively in terms of stannic oxide, zirconium oxide and titanium oxide as a gas sensitive element. CONSTITUTION:At least one among tin (Sn), zirconium (Zr) and titanium (Ti) are added as an additive to magnesium ferrite (MgFe2O4) contg. 0.005-10wt% sulfate ions. The compsn. contg. 0.1-50mol% said elements in total of additives respectively in terms of stannic oxide (SnO2), zirconium oxide (ZrO2) and titanium oxide (TiO2) is used as a gas sensitive element. Then the high sensitivity for gaseous methane is obtd. even at a relatively low operating temp. of 400 deg.C without adding any noble metal catalyst at all.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Use 71J The present invention relates to a gas detection element using a composite metal oxide semiconductor used to detect combustible gases.

Conventional configuration and its problems iEL year-■ "i2! < PI gas detection element I'・
Various researches have been conducted regarding 1. ', 11, 1, this is getting worse, 3rd grade construction, mainly in general households,
In the intestines, etc. - LIJ) Accidents caused by sexual gases ＼・Accidents due to poisoning caused by Okinaichi Nonos have been occurring frequently, and is it a big problem? This is strongly caused by the L-party problem and the fact that it is C2).

! 11 Hz; 7 CasQ, ] 1, explosion, lowering limit (L
In recent years - Therefore, gas detection elements using metal oxides such as stannic oxide (SnO2) and non-ma type ferric oxide (γ-P'e203) have been put into practical use, and have been applied to gas leak detection, cooling, etc. ing. And, no matter what kind of situation occurs, the presence of J-pan gas can be detected as soon as possible until the LEL is reached, and an attack can be prevented.''

By the way, even one bottle of liquefied natural gas (LNG), whose main component is methane gas, is now available for general household use, and it is gradually becoming popular. Therefore, the demand for gas detection elements that can detect methane gas, which is the main component of LNG, with high sensitivity has become extremely large.

Of course, gas detection elements sensitive to methane gas have already been developed, but most of them are catalyzed by gases such as Problems with toxicity - Problems include low sensitivity to methane gas and large changes in rj'l' and '+ over time.

For example, since methane gas itself is a very stable gas, there is peace of mind that a detection element with sufficient sensitivity and high activity is highly active. In order to achieve this, various measures have been taken, such as adding a transmetallic catalyst to the susceptor carrier once a month, or operating the susceptor at a considerably high temperature, for example, 460''C or higher. However, the current situation is that the properties are still insufficient for practical use.

OBJECT OF THE INVENTION The present invention has been made in view of the above circumstances, and is based on the use of precious metals. 400 without adding any -1
The goal is to realize a gas detection element with high sensitivity to methane even at relatively low operating temperatures.

Structure of the Invention The present invention is directed to the use of red sea bream, Noumunoeshii l-(MgFe204
) in a gas sensing element using a gas sensitive body and l-
This was discovered while conducting research on the effects of various anions contained in this gas on the gas sensitivity characteristics as well as the effects of additives. In other words, the gas sensing element of the present invention “N is 0.
Additives to MgFe204 containing 6% of 005-10: at least one of Sn, Zr and T1 are added to SnO2, ZrO2 and Ti, respectively.
Exchanging O2 and adding C 'l'/71VC: 0.1~ in amount
A material containing 60 mol% was used as the Gasm Y core, and the gas feeling was L1°. , (1st part of the body) L(gFe20+ K S
By adding n, Zr or 1°1,
The gas sensitivity characteristics and its reliability have been dramatically improved, and the actual fTJ is sufficiently large even for the aforementioned methane gas.
? : This was achieved by discovering that it was possible to achieve a certain degree.

DESCRIPTION OF EMBODIMENTS The present invention will now be described in detail. First, in Example 1, we will discuss the case where the amount of acid ions contained in MgFe2O4 is kept constant, and the amount of additives Sn, Zr, or T1 and their combinations are changed. do.

[Example 1] A commercially available reagent for magnesium oxide (MgO) was used at 20.9, and a commercially available reagent for ferric oxide (Fe20+) was used at 80.9. Zozo J
zzono 1. Balance f'I'y, L was used for groove mixing in a stainless steel pot for 5 hours. This mixture was dried, ground and then heated to 1300°C at 211°C. '
41i! l Heat treatment: T! T! did. Grind it again and
As an additive to add sulfuric acid/f-on 6- to this,
Ferric sulfate (Fe 2 (so 4 ) 3-, IF12
0) Add the reagent to 25. ! 7 was added and mixed for 2 hours on a raikai rock. These mixtures were equally divided into several parts, and commercially available stannic oxide (sno2), zirconium oxide (Zr02) and titanium oxide (TiO2) samples were added to each part.
Audience 7, added singly or in combination is 7. Then, each powder is further milled using the L miller-C311.
,'j was dry-mixed for a period of time. And for each of these
Add Fupain Gu and make grains of ioo~200μ in size.
The particles were carefully sized. Next, these powders were pressure-molded into a target shape and molded in air at 600 PaC for 1 hour. Next, on the surface of this sintered body, a pair of comb-shaped electrodes were formed by vaporizing Au (7, on the back side, 1v rl' platinum,
A sensing element was created by pasting the heating element IC with an inorganic adhesive and using it as a heater. , apply current to this heating element: l[uji-i-
The operating temperature IW of the element was controlled by adjusting the electric current b11゛ and the value of the element. 1l11
I felt sad.

1 in the air. -The resistance value (Ra) of dry air is: '+1. It was measured in a measuring container with a volume of sog, and the value (Ilg) was measured in a measuring container with a volume of sog.
5. Inject methane (CH4) and hydrogen (H2) of 8% or more at a rate of 10 ppm for 7 seconds. When the concentration reached 0.2% by volume, I''1.
It's blasphemy 11. By choosing the gas concentration to be measured as 0.2%, the detection ffl'!, which is practically required as a gas detection element, can be achieved. : I'x is the lower explosive limit concentration (L
This is because the LEL of each of the above gases is approximately 2% by volume to 5% by volume.

The presence of sulfate ions (304-) still contained in the gas sensitive material was confirmed by infrared absorption spectrum, and the contained t
iii, identified from T G - D T A Ill I line and fluorescent X-ray analysis. As a result, the amount of sulfate ions contained in these sintered sensitive bodies was 14 to 0.18 tonne %.

FIGS. 1 to 3 show the dependence of gas sensitivity characteristics when additives are added independently.

M3 response! One case is (1) Gas feeling IBI (Ra71g
) −(IO resistance aging rate ΔR(sensor 400 ”
(Evaluation was made using the initial jυ (change rate for 11 units) of the resistance value when held at a temperature of 1, for 2000 hours. Table 1 also shows the gas sensitivity ( Ra71g) and resistance change rate over time (ΔR) are shown.R is indicated in parentheses in the table.

As is clear from Figures 1 to 3 and Table 1,
Sn, Zr f) or T1 in China or yarn [1
By adding them together, the gas sensitivity characteristics (gas sensitivity: 1 Fta/Rg) are greatly improved. What should be noted is the change in resistance value over time, and by adding this one additive, the rate of change is reduced to 1J. It can be seen that the gas sensitivity 'l'!+' (jl-) and the reliability can be dramatically improved.

In the present invention, the total amount of additives 4;'' is limited to 0.1 to 50 mol%. - No effect on improving gas sensitivity characteristics and reliability can be seen; on the other hand, if it exceeds 60 mol%, the resistance (and the resistance itself increases).
This is also because the characteristics lack stability. In the table, those marked with a half mark and 1 to 1 correspond to these, and are listed as comparative examples in Table 1.

Table 1 Cedar end rice Comparative example By the way, in general, the power of the metal oxide in the amorphous state of the sensor is more sensitive to physicochemical phenomena such as adsorption phenomena for combustible gases than those that are crystallized. Life 1. However, using a commercially available sample that is nearly completely crystallized, MgFe is easily formed.
2C) + also contains monosulfate iono, j-W, and E',
By adding Sn, Zr or 1゛1 -J- to
<Si, 1~Kamokone 2 is meridian 11, Y p is stable 2, so as a result, the gas sensitivity is very large and the business confidence! It can be seen that PI'1 can be realized. −.

The following is a description of the case where the actual M1 (iL in Example 1) is a sintered body, the amount of sulfate ions 1η contained is constant, and the combination of additives is different. .

As shown below, in Example 2, the sensitive body is a sintered film, and contrary to Example 1, the additives are added at a constant rate.
If you change 1)- of the sulfate ion, then +71
In Example 2, it was confirmed that the present invention is effective even when the sensitive material is a sintered film; Describe whether the amount of σ) has an effect on the gas-sensitive characteristics.

[Example 2] I l %c, MgF prepared by the same method as Example 1
e 2041009VC1 Also commercially available oxidation II II
15 (5nO2), Zircola oxide J, (ZrO2)
and -f-tane oxide (TiO2) reagents were taken in the proportions shown in Table 2, and each was thoroughly mixed on a shallow rock for 2 u+J. Next, each mixed powder was divided into 8"('i), and this was divided into 6"1"
Was revived by Yue Takumi for 11 weeks (t + fi 7 Bin Xiao Wan 21 Tai (F
e2 (S04) 5-r) 120) Pour the solution, and then pour each powder on a rocky shore for 1t1.
' Mixed for 7 minutes. In this way, as a representative example, a monolayer of oxide composition has 3 monolayers (trial half, 1.A-C) = sulfate ion, and 8 types of bacteria for each oxide composition. , a total of 24,001:α samples were obtained.

(Margin JP 0o59-58.' (49(4) Table 2 Several mixed powders thus obtained were heat treated in air at a temperature of 400"G for 2:1?tl. Next, this powder was sized to a size of 50 to 100 microns, and l-reethanolamine was added to form a paste.Meanwhile, as a substrate for a gas detection element, an alumina sheet of 5 layers, 1 m each, and 0.5 mm thick was prepared. Prepare the entire board, print gold paste in a comb shape at intervals of 0.5 mm on this surface 7, and bake it to form a pair of (i'i
Form a II-type electrode. So, on the back side of the alumina substrate, a commercially available ruthenium oxide glaze resistor was printed between the gold electrodes and baked to serve as a heater.

Next, apply the above-mentioned paste to the surface of the board with approximately 65μ of F2.
After printing on the paper and drying naturally at room temperature)
Gradually heat to a temperature of 400℃, and at this temperature 1
Holds time. At this stage, the paste evaporated and applied to the sintered film of each oxide composition containing sulfate ions.

The J19 d of this gas sensitive material was approximately 60μ. In this way, gas sensing element-J' was obtained.

In addition, to identify the sulfuric acid contained in the gas-sensitive membrane, since a portion of each of the above pastes is printed on an alumina substrate, the size of the paste I is: 1 - 1 - in the same manner as above, rather than d. 4
00 'C temperature 11 fever 12, ko:, l+, 7.
-) T G-D1゛A and fluorescent X-ray analysis/υ]. Confirmation of the presence of sulfate ions in Example 1
The gas sensitivity of each sensing element was determined by analyzing the infrared absorption spectrum.
41 Measured in the same manner as in Example 1. Figures 1 to 6 of the 41st column show the relationship between the sample A-CO gas sensitivity (Ra/Fig) with different oxide compositions and the sulfuric acid ions contained therein. ', Table 3 shows the sutra [1, 'I
As a representative characteristic 4+ll, test 1i:4A-C containing 2 to 571 sulfate ions at 11% was planned in the same manner as in Example 1/1j1 resistance value 1-j7 Indicates the necessity rate. In addition, in Example 2: 1.
・Itishiri, the test subject Kasutoji-C has been using methane for a month.

As is clear from FIGS. 4 to 6, the sensitive body is a sintered film -=-C"b, which is almost the same as /C obtained in Example 1!
1〒Gender is a:t. As is clear from Table 3 and 1, ↓) (The rate of change in the head over time is also always small, as in Example 1 and 17.

1) Go to CC1''r' diagram/See Figure 6d: As you can see, the amount of sulfate ions is 01Q05ra-rl amount%.
'! f-f rl:jSn, Zr or &:I:
The effect of the present invention can be expected without the effect of addition of Tj, 7'i
:stomach. On the other hand, if it exceeds 10.0% by weight, the properties will be unstable ('l'), or the gas-rich element J' of the present invention will be impractical in terms of strong winds. Nine (
1.(i acid ion) O1○05~10.0 weight-1
%/2- &: J knee, 1: Depends on the reasons stated above.

Table 3 By the way, in Examples 1 and 2, commercially available oxide samples were used as 1 and 10'1. iura iJ: +2
(i'J et al. departure j Emperor 3'1 and production 2 [law is not limited).

Although methane, hydrogen, or propane were used as the gases to be tested in this embodiment, the effects of the present invention are by no means limited to these gases.

It goes without saying that it is also effective against flammable gases such as Eczema, insulin, and alcohol.

As explained above, the gas sensing element of the present invention r.
Sn, Zro, and Ruiba T1 are added as additives to MgFe2O4, which is known as sulfate ion. This makes me feel like gas! '1 was hit in a flying manner, and in this case, the metal catalyst was removed.
．． Clear skies detection is said to be T11/(-400' for methane gas), which is relatively low.
-(= 4) l Always achieves high sensitivity.
The main component: methane gas) is in response to the social needs of increasing demand for 1T-C, and its effects are on the order of 4-C. Ma/
This is another effect of the present invention.
By energizing the TM, the change in resistance over time can be significantly reduced.In other words, this brings tremendous wealth to improving the reliability of the element, which is the most important element of any sensing element. be.

[Brief explanation of the drawing]

Figures 1 to 3 show the relationship between the amount of additives and the sensitivity (Ra/Rg) to methane and water resistance over time (ΔR) in one embodiment of the present invention. Figures 4 to 6 show the effects of sulfate ion 3 in other embodiments of the present invention and 7+'i L!!L (R /Rg) is shown in the figure for three representative sol acid yl dicompositions. Name No. 4 Amount of sulfuric acid ion (V amount Z) Figure 5 θoo7 o, ol

Claims (2)

[Claims] (1) Sulfate ion is 0. Addition of tin (Sn), di/l/2V, =
1) , /, (Zr) O”: Bichikun (Ti) less +! 2'l, hi, nitsuga, respectively SnO2, Z
A gas sensing element characterized in that a total of 11 additives calculated by Jet to rO2 and 1°102 are used as a gas sensitive material. (2) A sintered body in which the gas sensitive body is formed by pressure molding and firing, and is a sintered film obtained by printing and firing paste. (1), the gas sensing element described in TI'1.