JPS5847664B2 - gas sensing element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas-sensitive element using a gas-sensitive body made of an oxide sintered body.

Among gas-sensitive elements using conventional SnO-based gas-sensitive bodies, those that can obtain a linear resistance change with respect to gas concentration have a small resistance change rate, making it difficult to extract a large output with a detection device.

In addition, with large resistance change books, the linearity was poor and the resistance change was saturated with a small amount of gas, making it difficult to distinguish between gas caused by an accident and gas generated during use of the equipment, making it difficult to handle. .

In addition, liquefied petroleum gas H such as propane gas and butane gas
2. It had many drawbacks, such as being unable to distinguish it from gases such as CO and causing resistance changes due to reducing components such as cigarette smoke.

The present invention improves the above-mentioned conventional drawbacks, and uses ZnO in a molar ratio of 99. 8 5-20%, M”eO
0. 1 to 5o% (However, M'eO is Ca
p S r pBa , Co , Ni , Mn) and M2e20g in an amount of 0.05 to 30
% (However, M2e is Ga, B, In, Fe, A
It is an object of the present invention to provide a highly reliable gas-sensitive element by using a gas-sensitive body made of a sintered body containing at least one of L and Cr.

The gas-sensitive element according to the present invention detects gas by disposing the above-mentioned assembled gas-sensitive body between a pair of electrodes and extracting a change in the electrical resistance of the gas-sensitive body as an electric signal at its own electrode.

The gas-sensitive element according to the present invention has a structure as shown in FIG. 1, for example.

This gas-sensitive element 1 has a pair of metal wire electrodes 3 and 4 wound in parallel on the surface of a cylindrical ceramic insulating substrate 2.
A gas sensitive element 5 is coated and sintered on the same part of this volume and fixed.

However, one of the electrodes 3 and 4 is used as a heater for heating the gas-sensitive body.

In this example, one of the electrodes 3 and 4 is used also as a heater, but a separate heater may be provided.

The gas-sensitive element 1 is manufactured, for example, as follows.

First, ZnO, M1eO (where M'e is Ca, Sr,
At least one of Ba, Co, Ni, Mn) M2
e203 (However, M2e is Ga, B, In, Fe, A
A, at least one of Cr) was weighed out to have a predetermined composition ratio, mixed, water or a binder was added to make a paste, and the paste was placed on the same part of the electrodes 3 and 4 and dried. It is then sintered at 600°C to 800°C to produce a sintered body.

Even if the firing process in this case is performed in an electric furnace, the electrodes 3 and 4
The heating may be carried out by energizing either one of them as a heater.

Further, the atmosphere may be in the air.

Note that the metal oxide Z used in the gas-sensitive body of the gas-sensitive element of the present invention
nO, M'eO (however, M'e is Ca, Sr, Ba
, Co, Ni. At least one type of Mn) M2e
20 (M2e is Ga, B, In, Fe,
Al. At least one type of cr) is a compound that converts into an oxide when heated, such as hydroxide, carbonate, oxalate,
Nitrates can also be used.

The gas-sensitive element of the present invention exhibits the following characteristics.

First, the change in resistance value with respect to the gas concentration of various gases, that is, the sensitivity characteristic, is as shown in Figure 2.The vertical axis shows the resistance value Ro, which is the reference value when no gas exists, and the resistance value Rg in the gas atmosphere. Take the ratio R o /R g and plot the gas concentration Vo on the horizontal axis. When #% is taken to form a curve, the resistance value ratio Ro/Rg of the gas-sensitive element according to the present invention does not saturate and changes linearly even if the gas concentration Vow changes over a wide range, as shown by the solid line.

In addition, in Fig. 2, a reference example using a conventional gas-sensitive body is shown by a dotted line.The change in resistance is smaller than that of the present invention, and it is saturated at a gas concentration of 0.1 ol%. I end up.

In particular, the gas-sensitive body used in the present invention is a hydrocarbon containing two or more carbon elements (C2H5, C3H3 y C4H10...
The more carbon element C there is with respect to ), the better the sensitivity becomes.

This is effective if the gas-sensitive body used in the present invention is used in a measuring device for partial analysis.

Regarding specific embodiments in which the composition or ratio of the gas-sensitive bodies used in the present invention is variously changed, the resistance value Ro when the gas concentration is OVoA'Z is
and this resistance value Ro and the gas concentration o of C4H1o. 1v
o. If the resistance value Rg and Ro/Rg at g% are shown, the first
It will look like a table.

Table 1 also shows examples of gas-sensitive bodies that fall outside the range of the gas-sensitive bodies of the present invention.

The gas-sensitive body used in the gas-sensitive element of the present invention may contain subcomponents such as catalysts within a range that does not impair the effects of the present invention.

For example, the sensitivity can be further improved by adding Pt to the entire composition in an amount not exceeding 10 weight φ.

Note that this Pi is H2PtCl6・H20, NHPtCl
6, K2PtCJ',,K2PtcA6, Na
It may also be added as a compound such as P tc7.

Table 2 shows the resistance value Ro and resistance value change Ro/Rg of various examples when the gas-sensitive element of the present invention was manufactured by adding Pt to the composition of the gas-sensitive body.

Note that Ro and Rg are values measured at the same gas concentration as described above.

The range of the gas-sensitive body used in the present invention is 99.85
ZnO. M' e less than 0.1 molar coefficient
O, 0.0 For M2e203 with less than 5 mol φ, the change in resistance Ro/Rg due to gas adsorption and desorption is small, and for MleO with less than 20 mol Zn0150 mol width
M2e203 which gives rise to 130 moles, or those containing more than 10% of pt in terms of weight ratio, have a small Ro/Rg and a large temperature coefficient with respect to resistance, making them impractical.

That is, the molar ratio is 99.85 to 20, and the M'eO is 0.1 to 20.
The effects of the present invention cannot be obtained unless the gas sensitive body is made of a sintered body containing 50 moles φ and 0.05 to 30 moles M2e203.

The resistance value change with respect to temperature of the gas-sensitive element of the present invention is determined by the third
As shown in the figure, it can be seen that the resistance value remains almost constant against temperature changes.

In addition, Fig. 3 shows the resistance value R at 20°C (20°C
) is the ratio of resistance change AR to JR/R (20℃
), and the horizontal axis shows the temperature near room temperature.

Furthermore, when the gas-sensitive element of the present invention is constructed as a gas-sensitive element with a heater, the heater voltage V applied to the heater is
As shown in FIG. 4, the resistance value changes with respect to fluctuations in the resistance value is extremely small.

However, the curve shown in FIG. 4 is shown as a representative example for Example 51r6) and Example 1 1 7 ('I) shown in the table above.

Regarding the response characteristics, as shown in Figure 5, the specified resistance value is reached within one second after gas injection, and even after the gas is removed, the resistance value returns to the gas-free state within a few seconds, showing excellent characteristics. .

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the appearance of a gas-sensitive element used in an embodiment of the present invention, and FIGS. 2 to 5 are characteristic diagrams showing various performances of the gas-sensitive element of the present invention. 1... Gas-sensitive element, 5... Gas-sensitive body.

Claims (1)

[Claims] 1. In a gas-sensitive element comprising a pair of electrodes and a gas-sensitive body provided between the electrodes, the gas-sensitive body:
In molar ratio composition, ZnO is 99.85~20φ, M'eO is 0.1~50% (however, M''e is Ca, Sr,
At least one of Ba, Co, Ni, Mn)
and M2e203 from 0.05 to 30% (but M2e
A gas-sensitive element comprising a sintered body containing at least one of Ga, B, In, Fe, Al, and Cr.