JPS58624B2 - gas sensing element - Google Patents

Description

[Detailed description of the invention] The present invention relates to a gas-sensitive element with excellent selectivity.

Gas-sensitive elements are known that utilize the fact that the specific resistance of the surface of an oxide semiconductor changes when gas comes into contact with the surface of the oxide semiconductor.

For example, ZnO, SnO2, Fe2O exhibiting N-type semiconductivity
When a reducing gas comes into contact with the 3rd grade, the resistance value decreases, and when an oxidizing gas comes into contact with the 3rd grade, the resistance value increases.

Further, in an oxide semiconductor exhibiting P-type conductivity, the increase/decrease in resistance value shows an inverse relationship.

In the above-mentioned oxide semiconductors, the reactivity or selectivity with various gases is determined by the semiconductor surface temperature, surface electron level structure, porosity, pore size, etc.
Generally, an oxide semiconductor alone has low sensitivity as a gas-sensitive element and cannot be said to have sufficient selectivity.

Therefore, attempts have been made to increase the sensitivity by adding a catalyst such as Pt or Pd to the oxide semiconductor.

In this case, a certain degree of selectivity can be obtained by selecting the element temperature.

For example, a gas sensitive material in which Pt is added has high sensitivity to isobutane gas, but does not react much to hydrogen gas or carbon monoxide gas.

On the other hand, when Pd is added, high sensitivity is exhibited to isobutane gas, hydrogen gas, and carbon monoxide gas.

However, both exhibit high sensitivity to alcohol-based gases such as ethyl alcohol gas.

Therefore, in the above-mentioned devices, especially in ordinary homes,
In the same way as LPG gas, it is sensitive to alcohol-based gases generated by foods, hair products, cosmetics, etc., which has been a major problem in practical use.

In view of the above points, it is an object of the present invention to provide a highly reliable sensitizing gas element for LPG that is highly sensitive to isobutane gas without being sensitive to alcohol gas.

The present invention includes a pair of electrodes, a gas sensitive body made of a zinc oxide semiconductor provided between the electrodes, Rh of 0.005 to 8% by weight, and 1.5 to 30 times of this Rh at a molar ratio of 0.005 to 8% by weight. P
and a catalyst layer provided on the surface of the gas sensitive body.

In the present invention, the amount of Rh added is set to 0.005 to 8% by weight, because if it is less than 0.005% by weight, the sensitivity to isobutane gas will be low, and if it exceeds 8% by weight, it will be sensitive to alcohol gas. This is because it becomes easier to feel.

In addition, the amount of P added is 1.5 to 1.5 in molar ratio to the amount of Rh added.
The reason why it is set to 30 times is because if it is less than 1.5 times, there will be no noticeable difference between the sensitivity to isobutane gas and the sensitivity to alcohol-based gases, and the sensitivity to isobutane gas will be small, and if it is more than 30 times, the sensitivity to isobutane gas will be small. This is because the sensitivity to LPG becomes smaller.

Further, in the present invention, the zinc oxide-based semiconductor is an oxide semiconductor composed of zinc oxide alone or zinc oxide as a main component to which subcomponents are added.

As the subcomponent, various substances such as Cr2O3 are used.

In either case, similar effects can be obtained by providing a catalyst layer having the above composition.

The present invention will be explained in detail below using structural examples.

First, the gas-sensitive element according to the present invention has a pair of electrodes 2 on the outer peripheral surface of a cylindrical insulating base 1, as shown in cross section in FIG. A gas sensitive body 3 made of a zinc oxide semiconductor is provided.

Furthermore, a predetermined amount of Rh and P are on the surface of the gas sensitive body 3.
A catalyst layer 4 made of silica-alumina containing .

Further, the gas-sensitive element constructed as described above is assembled on a pin plate, for example, as shown in perspective in FIG.

In FIG. 2, 5 represents a lead wire, 6 represents an insulating plate, and 7 represents a heater.

The heater 7 is provided to improve the sensitivity of the gas sensitive element, and can be provided as appropriate if necessary.

Note that the catalyst layer 4 does not necessarily need to completely cover the surface of the gas sensitive body 3.

Further, in the above, silica alumina is used as a carrier for the catalyst layer, but other materials may be selected as appropriate, and the same effect can be obtained even when no carrier is used.

The gas-sensitive element according to the present invention is manufactured, for example, as described above.

For example, when using Zn0Cr203 as a zinc oxide semiconductor, ZnO and Cr2O3 powders are weighed out in a predetermined composition ratio, mixed, water or a binder is added to form a paste, and a pair of electrodes 2 are provided as shown in Figure 1. It is coated on an insulating substrate 1, dried, and then fired at 300 to 1100°C to form a gas sensitive body.

On the other hand, the catalyst layer is composed of, for example, RhCl3.3H2O and H3PO.
4. Add NH4H2PO41 to make an aqueous solution with a suitable pH, mix it so that the composition falls within the composition range of the present invention, and add silica/alumina powder as a carrier to make a slurry.

After thoroughly mixing and drying this slurry,
Calcinate at ℃ and crush into fine powder.

After adding water and a suitable binder to this fine powder and making it into a paste, it was applied to the surface of the gas sensitive body and dried to a
The gas-sensitive element according to the present invention is obtained by firing at 000°C.

Next, the performance of the gas-sensitive element according to the present invention as described above was measured, and the results are shown in FIGS. 3 and 4.

FIG. 3 shows Rh and P in the gas-sensitive element according to the present invention.
The sensitivity to 0.2vol% isobutane gas with respect to the addition amount of is shown.

Note that the sensitivity is expressed as Ro/Rg, which is the ratio of the resistance value R0 in air to the resistance value Rg in gas, and the larger the value, the easier gas detection is.

Moreover, FIG. 4 shows the sensitivity Ro/Rg to 0.2vol% alcohol gas.

As is clear from FIGS. 3 and 4, when the amounts of Rh and P added in the catalyst layer are within the range of the present invention, the catalyst layer exhibits excellent sensitivity to isobutane gas and is hardly sensitive to alcohol gas.

Next, a gas-sensitive element in which no catalyst is used, a catalyst layer containing only P, a catalyst layer containing only Rh, and a catalyst layer containing P and Rh as in the present invention. The sensitivity Ro/Rg to various gases at 0.2vo1% was measured and shown in Table 1.

As is clear from the results in Table 1, in the case of no catalyst, the overall sensitivity is low and the sensitivity to alcohol gas is higher than to isobutane gas.

Further, when a catalyst layer containing only P or only Rh was used, a similar tendency was exhibited, and it was difficult to detect only isobutane gas.

On the other hand, the gas-sensitive element according to the present invention exhibits excellent sensitivity only to isobutane gas, and can be said to have excellent selectivity with almost no change in sensitivity to other gases.

Although the reason for the excellent selectivity in the present invention is not clear, the reactivity is high because Rh and P are mixed, and at least a portion of the Rh and P added in the catalyst layer manufacturing process is This is thought to be because it is compounded.

Further, in the above embodiment, ZnO-C is used as the gas sensitive material.
Although an r2O3-based semiconductor is used, it goes without saying that other zinc oxide-based semiconductors may be used as needed to achieve similar effects.

In addition to the above, the gas-sensitive element according to the present invention has the following effects: 1) Even if the heater voltage fluctuates by about ±10%, Rg in isobutane gas is hardly affected;
No heater voltage stabilization circuit is required.

2) Eliminates malfunctions (initial alarms) due to adsorption of miscellaneous gases in the air when left unused for long periods of time.

In other words, in the past, if the sensor was left unused for a long period of time, miscellaneous gases would be adsorbed to the surface of the gas sensor, and an alarm could be issued even if there was no gas to be detected when the sensor was energized again.

In contrast, in the present invention, although the element resistance decreases when left unused for a long period of time, the width of this decrease is extremely small, so no alarm is issued, and the return to the steady level is quick.

Further, in the present invention, since the catalyst layer and the gas sensitive body are separated, it is easy to manufacture and has the advantage of having excellent aging characteristics.

Furthermore, when Rh and P are mixed in the gas sensitive material, it is thought that the selectivity will be improved compared to the conventional one.

As described above, by using the gas-sensitive element according to the present invention, it has high sensitivity only to isobutane gas, so L
It can be said that it is extremely effective for use in all-sensing all-sensing gas elements for PG.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing a configuration example of a gas-sensitive element according to the present invention, FIG. 2 is a perspective view showing an example of a device using the gas-sensitive element according to the present invention, and FIGS. FIG. 3 is a curve diagram showing an example of the characteristics of such a gas-sensitive element. 3... Gas sensitive body, 4... Catalyst layer.

Claims (1)

[Claims] 1 A pair of electrodes, a gas sensitive body made of a zinc oxide semiconductor provided between the electrodes, and containing Rh in an amount of 0.005 to 8% by weight and P in a molar ratio of 1.5 to 30 times that of Rh. , and a catalyst layer provided on the surface of the gas-sensitive element.