JPS60100755A - Gas sensor - Google Patents

Abstract

PURPOSE:To prevent the deterioration in sensitivity with gaseous alcohol with age with a gas sensor by mixing a heat insulating material such as silica and alumina added with a small amt. of V2O5 with SnO2. CONSTITUTION:A heater 12 is inserted into an insulating alumina pipe 4 attached with a pair of electrodes 6 and 8 to heat a gas sensor 2 and the change in the resistance value of a gas sensitive SnO2 film 10 is taken out. The film 10 is formed by adding a small amt. of V2O5 to a heat insulating material such as silica colloid or the like which does not spoil the sensitivity of said film in spite of reaction with SnO2 and mixing the same with SnO2. The deterioration in the sensitivity of the sensor 2 with H2 and gaseous alcohol such as ethanol is thus prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a gas sensor that utilizes changes in the resistance value of SnO2.

Many attempts have been made to improve the characteristics of SnO2 gas sensors using additives. Despite these efforts, one issue that remains unresolved is the aging of H2 and ethanol.

That is, when a gas sensor is used for a long period of time, its sensitivity to H2 and ethanol gradually increases. According to experiments conducted by the present inventor, it was found that the change over time to H2 and ethanol becomes more significant as the temperature at which the gas sensor is used increases.

The inventor discovered that when a small amount of V2O5 is added to 5no2, H
We have found that 1)) prevents the change over time to 2 and ethanol. Next, it was found that the same effect was produced even when silica colloid or alumina carrying a small amount of V2O5 was mixed with 5n02.

Why does V2O5 added to things other than Sn 02 become 5n0?
It is not clear whether it suppresses the change over time of 2. However, this invention begins with this discovery. In this invention, H2
Prevents changes over time to alcohol gases such as ethanol and ethanol.

Each example will be described below.

The structure of the gas sensor is shown in FIG. This gas sensor (
2) is a pair of electrodes F6 in an alumina insulating tube (4).
1. (Install 81, S, o2 gas sensitive crotch (1υ
) is designed to extract the change in resistance value. Then, insert the heater O9 into the insulating tube (4), and insert the gas sensor (
2) Heat. There are many known examples of gas sensor structures, and various structures other than those shown here can be used.

This gas-sensitive film (lO) consists of SnO2 and a small amount of V2O.
As the heat-resistant insulating material, for example, a-At203 or r-At203, which is an aggregate of SnO2, or 5no.
Any material that does not react with 5no2 and impair its sensitivity, such as silica colloid, which is the sintering agent of No. 2, may be used.

Using α-At203 with 1 μm of V205 added, α
-Mixing weight ratio of At2o3 and SnO2 to 1:2.1
The test was conducted in three stages: 1.2.5:1, and all samples were able to suppress the change over time to H2 and ethanol to the same extent. Also 12 wins 97 in s; o2 conversion
When using hydrosyl silicate with the addition of V2O5,
A test was conducted with the amount of hydrosyl silicate added in terms of 5i02 equivalent to 5n02100r divided into two types: 2r and 6F(7), and sufficient effects were obtained in both cases. In this way, the amount of heat-resistant insulating material added can be changed freely, and in practice, the amount added is determined based on the I" property of each heat-resistant insulating material, such as aggregate and sintering agent. That's fine.

The addition 1j of V2O5 per gram of heat-resistant insulating material is broadly 50 μf to 50 TI9, then preferably 50
μm to 20mf, most preferably 801)7 to 3■
shall be. The effect of adding V2O5 is as follows: heat resistance 1 yarn 1 material 1
Even with the addition of 100 μ2 per 1 ml, it becomes significantly thicker (it becomes larger as the amount of i addition increases, and 7 Jl of 2 additions per t my)
becomes saturated. By the way, if the amount of V2O5 added is increased unnecessarily or unnecessarily, the sensitivity to various gases will decrease, the resistance of the gas sensor (2) will increase, and the power
21 will be lost. The upper limit of V2O5'IIA force 11 varies depending on the type of heat-resistant insulating material,
-Cannot be established by law. The upper limit of the addition amount is the lowest when α-AA203 is used, and in this case, it is preferably 20 m7 or less per α-AA2031 f. However, in the example using γ-AA203, 50 per 17
Even with the addition of Ki, the adverse effects were small.

Test examples of the gas sensor (2) will be described below along with manufacturing examples.

5002100 Prepare one carrying pdo of fpo, sy. PdO is used to improve sensitivity and response to gases, and may be replaced with other additives such as Pt+ALI, or may be omitted.

200 mesh pass extension - At203 is impregnated with an aqueous solution of metal vanadium dissolved in nitric acid, and after drying, 650
Heated in air for 30 minutes to 0.1-10η/t
α-At203 carrying V2O5 of At20a is obtained. Note that by heating to 650° C., the vanadium compound is thermally decomposed, and most of it becomes V2O5. Although it is thought that vanadium exists in a trace amount such as V2O4 in addition to V2O5, the added amount is shown assuming that all of the added vanadium has been converted to V2O5. Since it is difficult to support a high concentration of V2O5 with the impregnation method, the same α-A
50~/f on t203! Add At203nov205 powder and heat to 650°C for 80 minutes in air to obtain a high concentration of V2.
A-A7203 was obtained by carrying O5. Addition of V2O5 (Z-At203, α-At203: 5
The weight ratio of n02 is 1:2.1:1.2.5:L, 5n
02, dispersed in water and applied to the insulating tube (4),
The gas-sensitive membrane (1
0). Then 5 m7/l At2o3 and 50~/? γ-Az2o3 (specific surface area 80n?, #) on which V2O5 of A7203 was supported by an impregnation method was obtained. The weight ratio of γ-At 203 and γ-At 3102 is set to 1=1 to form a gas sensitive film t101. The addition of V2O5 and the manufacturing process of the gas-sensitive film are the same as in the case of α-At203.

Additionally, 25 cc of water and 3 cc of hydrochloric acid Q were added to 75 cc of VV Rickettsia, and the mixture was stirred for 30 minutes to obtain silicic acid hydrochloride. A reaction solution of metal vanadium and nitric acid was added to this hydrosilicic acid, and 5i021j' and 9
A vanadium compound of 7η (in terms of V2O5) is supported. The insulating tube (4) provided with a coating film of 5no2 was immersed in hydrosilicic acid supporting a vanadium compound, and
C. for 10 minutes in air to effect decomposition of the hydrosil into a gel and thermal decomposition to V2O5. Here, 5i02
The weight ratios of 5n02 and 5n02 are set to 2:100 and 6:100.

Using 5 of each of these gas sensors (2), at 25°C.
Measurement is performed under an atmosphere of -65% RH.

The concentration of each gas is set to 2000 pp, and the heating temperature of the gas sensor 12) is set to 400°C. However, even if the heating temperature of the gas sensor 12) is exceeded, the results will not change. Figure 2 shows α-A with 11/1 myV2O5 added.
Gas sensor (2
) shows the temporal characteristics of Figure 3 shows α- without V2O5 addition.
It shows the aging characteristics of the same product except that At2 o3 was added.

Looking at the characteristics at the start of energization, the sensitivity to various gases and the resistance value (R8) do not change. However, with no V2O5 added, the sensitivity to R2 and ethanol increases over time. On the other hand, when V2O5 was added, no change over time was observed.

The table shows the results when changing the amount and type of heat-resistant insulating material. Note that the relative sensitivity to various gases is almost the same, so only the sensitivity to isobutane is shown.

1 1 α-At203 50 1J 2 1 α-At203100 1.28 1 α-A
lzOa 250 1.24 0” 1-AltxOs
100 5.85 5 1.05 6 50 1.0 7 0 Qin 5402 6 5.7 8 7 Ml, 05 9 7 5 units) 2 2 1.1 Qin mark is conventional example UL a edge 1 y per y) V2O5m, 121 5
Amount added per 100f of HO2 1.31 After 120 days of energization, f[air conductivity and initial! Ratio to air conductivity, (41 Ratio of resistance value in air to resistance value in isobutane.

1・1 4B 11.8 1.1 72 1.7 1.1 62 52 4.7 52 20 1.0 47 21 1.0 45 25 4.8 59 1.2 1.0 57 1.5 1. 05 67 0.9 It can be seen that the effect of suppressing changes over time due to V2O5 can be obtained regardless of the type or amount of the heat-resistant insulating material.

Next, SnO2 and α-At203 were mixed in a weight/weight ratio of 1:1.
The effect of the amount of V2O5 added was investigated using as an example a mixture of V2O5 and V2O5. FIG. 4 shows the effect of suppressing changes over time, where the horizontal axis shows the amount of V2O5 per α-At20317, and the vertical axis shows the ratio of the electrical conductivity after 120 days of energization to the initial electrical conductivity. The addition of 01■/fA7203 significantly suppresses the change over time, and this effect is saturated when 17yAt2o3 or more is added.

When V2O5 is added in an amount greater than 1 to /lAt203, the sensitivity to various gases decreases and the resistance value of the gas sensor (2) increases. The results are shown in FIG.

Although the sensitivity to isobutane and cH4 is illustrated, the sensitivity to other gases also showed similar behavior. V2O5 amount 10■
/ f At, 20:l, the sensitivity decreases slightly 15
When it is set to 0~/r At203, it decreases significantly. However, the upper limit of the amount of V2O5 varies depending on the heat-resistant insulating material, and in the case of γ-At203, even when 50 ri/y of Az203 was added, the decrease in sensitivity was small. (Sample 6 in the table).

Note that the effect of suppressing changes over time was effective only for the gas sensor (2) using 5n02, and was not effective for the sensors using In2O3 or Zllo. Also, V2O5 is 5b20
3, Nb2O5, and Ta205, the effect was lost.

As explained above, according to the present invention, it is possible to prevent the gas sensor from changing over time into alcohol/recurse such as H2 or ethanol.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway view of the gas sensor of the embodiment, FIG. 2 is a characteristic diagram of the gas sensor of the embodiment, and FIG. 3 is a characteristic diagram of a conventional gas sensor. FIG. 4 and FIG. 5 are characteristic diagrams of the gas sensor of the example. Patent applicant Figaro Giken Co., Ltd. Figure 1 Figure 2 -6-air -0-C0 00 Time (day) Figure 3 @-a! r -0-C0 Time (day) Fig. 4 0 0.1 1 10 100 100V203 (@A1203)

Claims (1)

[Claims] II) A gas sensor comprising 5n02 mixed with a heat-resistant insulating substance, characterized in that V2O5 is added to the heat-resistant insulating substance.