JPH10246714A - Gas sensor material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a gas sensor of high detection sensitivity by adding a specific amount of one of Gd, Y, La, Nd, Ca, Mg and Ba to a gas-sensing material of SnO2 or a mixture of SnO2 and Al2 O3 . SOLUTION: Gold electrodes 2A, 2B and 4A', 4B' are set at a rear face of a square alumina substrate 1. A heater 3 of ruthenium oxide is formed between the gold electrodes 2A and 2B. Gold electrodes 4A, 4B are set at a front face and connected to the gold electrodes 4A', 4B' via through holes. A gas- sensing material of SnO2 or a mixture of SnO2 and Al2 O3 is applied and baked between the gold electrodes 4A and 4B. Any one of Gd, Y, La, Nd, Ca, Mg and Ba is added by approximately 0.2-50atm.% to the gas-sensing material. Since detection sensitivity to volatile organic compounds and formaldehyde is improved as a result of the addition, a gas sensor of high sensitivity to volatile organic compounds, formaldehyde of low concentration is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a volatile organic compound called so-called VOC or formaldehyde (HCH).
The present invention relates to a gas sensor material for detecting O).

[0002]

2. Description of the Related Art Conventionally, SnO has been used to detect indoor air pollution caused by tobacco and exhaust gas from combustion equipment.
₂ and other semiconductor gas sensors using semiconductor materials.

[0003]

By the way, in recent years, with the increase in airtightness of houses, contamination of indoor air by VOC and formaldehyde generated from building materials has become a problem, and consideration has been given to comfort and health. And at least 1pp
There is a demand for a system that detects VOC and formaldehyde even at a low concentration of less than m and automatically ventilates indoor air. However, in a conventional semiconductor gas sensor using SnO ₂ or the like, VO of 1 ppm or less is
There is a problem that it is difficult to detect C and formaldehyde.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a gas sensor material having high detection sensitivity for VOC and formaldehyde.

[0005]

According to the first aspect of the present invention,
To achieve the purpose, VOC and formaldehyde
Gas sensor used for gas sensor to be detected gas
The material is SnO _TwoOr SnO_TwoAnd Al_TwoO_ThreeBlend of
Gd, Y, L as additives to gas-sensitive materials consisting of compounds
a, Nd, Ca, Mg, Ba is approximately 0.2%
Characterized by adding approximately 50 atomic percent
And the conventional SnO_TwoOr SnO_TwoAnd Al_TwoO_Three
Volatile organic compounds compared to gas-sensitive materials consisting of
The detection sensitivity of substances and formaldehyde is improved.
Gas sensitive to high concentrations of VOC and formaldehyde
Sensor can be realized.

According to a second aspect of the present invention, there is provided a gas sensor material used for a gas sensor using VOC and formaldehyde as a detection target gas, comprising SnO ₂ or SnO ₂ and Al _2.
Gd, as an additive to a gas-sensitive material comprising a mixture of O ₃
It is characterized in that at least two of Y, La, Nd, Ca, Mg, and Ba are added in a total amount of about 0.2 to about 50 atomic percent, and the conventional SnO ₂ or SnO ₂ and Al ₂ Since the detection sensitivity of volatile organic compounds and formaldehyde is improved as compared with a gas-sensitive material composed of a mixture of O ₃ , a gas sensor that is highly sensitive to low concentrations of VOC and formaldehyde can be realized,
In addition, the change with time of the resistance value can be reduced as compared with the first aspect of the invention.

According to a third aspect of the present invention, there is provided a gas sensor material used for a gas sensor using VOC and formaldehyde as a detection target gas, comprising SnO ₂ or SnO ₂ and Al _2.
Y and L are added as additives to a gas-sensitive material consisting of a mixture of O _3.
a to a total of about 0.2 to about 50 atomic percent, and is more volatile than a conventional gas-sensitive material composed of SnO ₂ or a mixture of SnO ₂ and Al ₂ O _3. Since the detection sensitivity of reactive organic compounds and formaldehyde is improved, it is possible to realize a gas sensor that is highly sensitive to low concentrations of VOC and formaldehyde,
Moreover, the change with time of the resistance value can be reduced as compared with the first aspect of the invention.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration of a gas sensor using the present embodiment. In the present embodiment, the thickness is 0.3 mm.
And a square alumina substrate (Al ₂
As shown in FIG. 1B, gold electrodes 2A, 2B and 4A ', 4B' for heaters are provided on the back surface of an O ₃ substrate 1 and a heater 3 made of ruthenium oxide is formed between the gold electrodes 2A, 2B. doing. Further, the back surface of the gold electrode 4A via the through-hole on the surface ', 4B' and connected gold electrodes 4A, 4B are provided as shown in FIG. 1 (a), the gold electrodes 4A, to span between 4B SnO ₂ Alternatively, a gas-sensitive material composed of SnO ₂ and Al ₂ O ₃ (alumina) is applied and fired.

The adjustment of SnO ₂ will now be described. First, an aqueous solution of SnCl ₄ (tin chloride) is hydrolyzed with NH ₃ to obtain a stannate sol, and the obtained stannate sol is air-dried and then dried in air. For example, at 500 to 850 ° C, 1
Baking for an hour to obtain SnO ₂ . P for this SnO ₂
impregnated with an aqueous solution of d (palladium), for example, 500
Pd is thermally decomposed in air at 1 ° C. for 1 hour. The role of Pd here is to improve the response (speed) of the device to VOC and formaldehyde, and need not be added.

Also, instead of Pd, Pt (platinum), Rh
Noble metals such as (rhodium) and Au (gold) and transition metals such as W (tungsten) and Mo (molybdenum) can also be used. Thus to mixing equal amounts of Pd or for example 1000 mesh alumina SnO ₂ or the metal of the metal was allowed to carry an alternative to it as an aggregate to SnO ₂ not to carry, as described above, and a paste further adding terpineol After that, it is applied in substantially the same shape so as to extend between the gold electrodes 4A and 4B of the alumina substrate 1, and baked at, for example, about 700 ° C. for 2 hours. Thereafter, an organic silica binder or an alumina sol may be added. An organic silica binder or alumina sol is added and then, for example, 700
By sintering at 1 ° C. for 1 hour, the structural strength of the gas-sensitive body is improved, and sensitivity to VOC and formaldehyde is slightly improved.

By this baking, the element piece 6 made of SnO _2, which is a metal oxide semiconductor, extends between the gold electrodes 4A and 4B.
Are formed on the same substrate 1. After this formation, the electrodes 2A, 2B and 4 on the back side of the alumina substrate 1
Lead wires 5 are connected to A 'and 4B', respectively, and these lead wires 5 constitute a heater connection terminal and an output terminal.

(Embodiment 1) In this embodiment, the detection target gas is V
Gd as a catalyst for developing sensitivity to VOC and formaldehyde as OC and formaldehyde
Gd (gadolinium) is added to the element piece 6 so that 5 atomic percent (atm%) of SnO ₂ containing, for example, 2 wt% (wt%) of Pd is added to each of the element pieces 6. After dripping, and after performing the drying by nature after this dripping, in air 500 degreeC, for example.
For 3 hours to form a gas sensor.

The gas sensor according to this embodiment provides
The ratio of the resistance R at both ends when the gas concentration of VOC or formaldehyde (paraformaldehyde) is changed to the resistance Rair at both ends of the element piece 6 in the air of the gas sensor.
/ Rair), the results shown in FIG. 2A were obtained for VOC, and the results shown in FIG. 2B were obtained for formaldehyde. In contrast,
With respect to the gas sensor to which Gd was not added, the results shown in FIGS. 3A and 3B were obtained for VOC and formaldehyde, respectively. Here, R / Rair indicates that the sensitivity is higher as the value is smaller than 1. As shown in FIGS. 2 and 3, by adding Gd, the sensitivity to VOC and formaldehyde is improved, and 1 ppm or less is obtained. It can be seen that even low concentrations of VOC and formaldehyde can be sufficiently detected. Therefore, a gas sensor that is highly sensitive to low concentrations of VOC and formaldehyde can be obtained.

By the way, when the gas concentration of VOC or formaldehyde is 0.3 ppm, for example, the addition amount of Gd is changed variously (by changing the addition amount of Gd in the range of 0.2 to 50 atm%). When Rair was measured, the results shown in FIG. 4A for VOC and the results shown in FIG. 4B for formaldehyde were obtained for VOC.
To secure the desired sensitivity from this measurement result, approximately 0.2
It is desirable to add about 50 atm% of Gd.

Although the gas-sensitive material was SnO ₂ ,
Similar results as described above were obtained with a mixture of SnO ₂ and Al ₂ O ₃ . (Embodiment 2) This embodiment is similar to Embodiment 1 except that
For example, 5% for SnO ₂ containing 2 wt% of Pd
G so that atm% of Gd (gadolinium) is added.
Each of the nitrate aqueous solutions of d was dropped, and after the dropping, the mixture was naturally dried, and calcined in air at, for example, 500 ° C. for 3 hours. A gas sensor was formed.

With the gas sensor according to the present embodiment,
The ratio of the resistance R at both ends when the gas concentration of VOC or formaldehyde (paraformaldehyde) is changed to the resistance Rair at both ends of the element piece 6 in the air of the gas sensor.
/ Rair), the results shown in FIG. 5 (a) were obtained for VOC, and the results shown in FIG. 5 (b) were obtained for formaldehyde. In contrast,
With respect to the gas sensor to which Gd was not added, the results shown in FIGS. 6A and 6B were obtained for VOC and formaldehyde, respectively. 5 and 6 that the addition of Gd improves the sensitivity to VOC and formaldehyde, and can sufficiently detect VOC and formaldehyde at a low concentration of 1 ppm or less. Therefore, a gas sensor that is highly sensitive to low concentrations of VOC and formaldehyde can be obtained.

Also, comparing FIG. 5 with FIG. 2 of Example 1, the addition of the organic silica binder makes it possible to reduce the VOC.
And that the sensitivity to formaldehyde is improved. In this embodiment, only the case where the organic silica binder is added is shown. However, even if alumina sol is added instead of the organic silica binder, the detection sensitivity of VOC and formaldehyde is improved as in the case where the organic silica binder is added.

In each of the above embodiments, only the case where Gd is added is shown, but instead of Gd, Y (yttrium), La (lanthanum), Nd (neodymium), Cd
a (calcium), Mg (magnesium), or Ba (barium), or a combination of these two elements, when VOC and formaldehyde are added in the same manner as when Gd is added. The detection sensitivity is improved. Here, in order to secure a desired sensitivity, when one kind of element is added, the element is added in an amount of about 0.2 to about 50.
Atm% is desirable, and when two kinds of elements are added, the total of the two kinds of elements is about 0.2 to about 5
It is desirable to add so as to be 0 atm%.

(Embodiment 3) FIG. 7 shows that the above-described gas sensor is operated at room temperature and normal humidity (in this embodiment, the temperature is approximately 20 ° C. and the humidity is approximately 6 ° C.).
Element piece 6 when left in air
5 is a graph showing the measurement results of the change over time of the resistance Rair at both ends of the graph. Where Rair (i) is the initial value of the resistance at both ends,
Rair (r) is the resistance at both ends at the time of each measurement (day) after the start of the measurement. Also, Lee in Figure 7 have been added 5 atm% of Gd with respect to SnO _2, B is the Y relative SnO ₂ 5
Atm% added, G is 5% Gd with respect to SnO ₂
that the Y was added 5 atm% with the addition atm%, two is made by adding 5 atm% of Ca with addition of 5 atm% of La relative SnO _2, E together with added 5 atm% of La relative SnO ₂ Y 5 atm
%. The gas-sensitive material was only SnO ₂ , but similar results were obtained with a mixture of SnO ₂ and alumina.

From the measurement results shown in FIG. 7, it can be seen that the stability over time of the resistance value is better when two or more elements are added to SnO ₂ . In particular, L for SnO ₂
When a is added at 5 atm% and Y is added at 5 atm%, it can be seen that both ends resistance Rair hardly changes and good temporal stability can be obtained. In addition, although the value of the resistance Rair at both ends decreases with the number of days elapsed in (a) to (d),
For the detection sensitivity of VOC and formaldehyde, see 29
Even after the passage of days, there was almost no change in any of the gas sensors A to E.

[0021]

According to the first aspect of the present invention, the above object is achieved.
For this reason, VOC and formaldehyde are
A gas sensor material used for a gas sensor,
SnO _TwoOr SnO_TwoAnd Al_TwoO_ThreeFeeling of a mixture of
Gd, Y, La, Nd, Ca,
One of Mg and Ba is used in a range of approximately 0.2 to approximately 50 atomic par.
Because of the cent addition, the conventional SnO_TwoOr SnO_TwoAnd A
l_TwoO_ThreeVolatile compared to gas-sensitive materials consisting of a mixture of
Improved detection sensitivity for organic compounds and formaldehyde
From high to low concentrations of VOCs and formaldehyde
The effect that a highly sensitive gas sensor can be realized
is there.

According to a second aspect of the present invention, there is provided a gas sensor material used for a gas sensor using VOC and formaldehyde as detection target gases, wherein SnO ₂ or SnO ₂ and Al ₂
Gd, as an additive to a gas-sensitive material comprising a mixture of O ₃
Since at least two of Y, La, Nd, Ca, Mg, and Ba are added in a total amount of about 0.2 to about 50 atomic percent, a conventional gas-sensitive material made of SnO ₂ or a mixture of SnO ₂ and Al ₂ O _3. Since the detection sensitivity of volatile organic compounds and formaldehyde is improved as compared with the above, a gas sensor that is highly sensitive to low concentrations of VOC and formaldehyde can be realized, and has a lower resistance value than the invention of claim 1. There is an effect that a change with time can be reduced.

According to a third aspect of the present invention, there is provided a gas sensor material used for a gas sensor using VOC and formaldehyde as a detection target gas, comprising SnO ₂ or SnO ₂ and Al _2.
Y and L are added as additives to a gas-sensitive material consisting of a mixture of O _3.
a was added in a total amount of about 0.2 to about 50 atomic percent, so that the sensitivity of detecting volatile organic compounds and formaldehyde was lower than that of a conventional gas-sensitive material composed of SnO ₂ or a mixture of SnO ₂ and Al ₂ O _3. As a result, it is possible to realize a gas sensor that is highly sensitive to low concentrations of VOC and formaldehyde, and has the effect of reducing the change over time in the resistance value as compared with the first aspect of the present invention.

[Brief description of the drawings]

FIG. 1A is a perspective view of a gas sensor using a gas sensor material according to an embodiment of the present invention as viewed from the front side.
(B) is the perspective view seen from the back side of the gas sensor same as the above.

FIG. 2 is a graph showing the concentration dependence of a resistance value change in Example 1 of the embodiment.

FIG. 3 is a graph showing the concentration dependence of a change in resistance value in a comparative example with the first embodiment.

FIG. 4 is a graph showing the relationship between the change in resistance value and the amount of Gd added.

FIG. 5 is a graph showing the concentration dependency of a change in resistance value in Example 2 of the embodiment.

FIG. 6 is a graph showing the concentration dependence of a change in resistance value in a comparative example with the above-mentioned Example 2.

FIG. 7 is a graph showing a measurement result of a change with time of the resistance value of Example 3 of the above.

[Explanation of symbols]

 Reference Signs List 1 alumina substrate 2A, 2B gold electrode 3 heater 4A, 4B, 4A ', 4B' gold electrode 5 lead wire 6 element piece

Claims (3)

[Claims] 1. A gas sensor material used for a gas sensor using VOC and formaldehyde as a detection target gas, wherein Gd, Y, La is added as an additive to a gas-sensitive material made of SnO ₂ or a mixture of SnO ₂ and Al ₂ O _3. , Nd,
A gas sensor material comprising one of Ca, Mg, and Ba added at about 0.2 to about 50 atomic percent. 2. A gas sensor material used for a gas sensor using VOC and formaldehyde as a detection target gas, wherein Gd, Y, La is added as an additive to a gas-sensitive material made of SnO ₂ or a mixture of SnO ₂ and Al ₂ O _3. , Nd,
At least two of Ca, Mg, and Ba are used in a total of approximately 0,1.
A gas sensor material comprising 2 to about 50 atomic percent added. 3. A gas sensor material used for a gas sensor using VOC and formaldehyde as a detection target gas, wherein Y and La are added as additives to a gas-sensitive material made of SnO ₂ or a mixture of SnO ₂ and Al ₂ O _3. Total 0.
A gas sensor material comprising 2 to about 50 atomic percent added.