JPS5919309B2 - Halogen gas sensing element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an element that senses halogen gas by utilizing changes in electrical resistance due to adsorption and desorption of halogen gas.

For example, Freon gas is used as a refrigerant in refrigerators, and methyl chloride gas is used as a refrigerant in large refrigerators.

However, it is necessary to prevent or promptly detect leakage of these halogen-based gases as refrigerants in order to reduce the refrigerating capacity and to maintain hygiene. By the way, sensing of halogen or halide gas is carried out by the following means. For example, a platinum resistor is provided in an oxide semiconductor such as sno2 or ZnO, and the platinum resistor is placed close to a heating filament or a means for sensing halogen gas based on the thermal conductivity associated with adsorption and desorption of halogen gas, or the change in resistance value of the platinum resistor due to temperature. A known method uses a method in which one electrode is arranged and the ionic current flowing between the heating filament and the electrode changes depending on the presence of a halogen gas. However, with these methods, in the case of a thermally conductive element, 1000 pμ
It could only be detected at a high concentration of 1 to 100 ppm, and could not be detected at a low concentration of about 1 to 100 ppm. On the other hand, the method of detection based on changes in the ion current between electrodes requires a high voltage source of about 300 V, requires several watts of heater power, and increases the size of the device.

Furthermore, although this ion current method has high sensitivity, it has drawbacks such as a long recovery time when it comes into contact with a highly concentrated gas and a short life span of the device. Furthermore, in conventional halogen gas sensitive materials, the resistance changes as the gas concentration increases, similar to reducing gases such as isoptane gas, so there was a problem in distinguishing between halogen gas and reducing gas.

In view of the above points, it is an object of the present invention to provide a halogen gas sensing element that does not require a high voltage source, can easily sense halogen gas at low concentrations with good reproducibility, and has excellent gas selectivity.

The present invention uses Zn099.9 to 40% and AuX in molar ratio.
3 (where X is at least one of Cl, Br, and I) a halogen gas sensitive body made of a sintered body with a composition containing 0.1 to 60%, and a pair of electrodes provided on the halogen sensitive body. This is a halogen gas sensing element characterized by:

The reason why the molar ratio of ZnO is 99.9 to 40% is 9.
This is because if it exceeds 9.9%, the rate of change in resistance value due to gas adsorption and desorption will be small, resulting in a decrease in sensitivity, and if it is less than 40%, sinterability will be poor. Further, the reason why AUX3 is set to 0.1 to 60% in terms of molar ratio is that the desired effect is not exhibited even if it is less than 0.1% or exceeds 60%. The halogen gas sensing element according to the present invention can be manufactured as follows.

For example, powder in which ZnO and AUX3 are selected at a predetermined composition ratio is thoroughly mixed in a ball mill or the like to obtain an adjusted powder. Next, an aqueous solution of polyvinyl alcohol as a binder is added to this prepared powder to form a paste, and then two metal wires 2
'' are wound in parallel, and the paste-like material 3 is applied and filled at least between the metal wires. Then, it is dried and
By sintering in an air atmosphere at 900°C, Zn
A halogen sensing element is obtained by forming an O-Aux3-based gas sensitive material.

In the above, even if an acid such as HAuCl4.4H20 which easily decomposes into AuCl3 is used as AUX3, the same effect can be obtained.

Furthermore, the characteristics of the gas sensitive body included in the halogen gas sensing element according to the present invention can be adjusted by adjusting the types and composition ratios of ZnO and AuX. For example, AuCl3 exhibits better properties in terms of proper sensitivity to low concentration gases, response speed, stable operation, etc. On the other hand, AuBr3・Au
I3zu☆ not only greatly contributes to the linear relationship between concentration and resistance value, but also has superior performance in terms of sensitivity not changing even when it comes into contact with high concentration halogen gas, and suppressing the effects of temperature. show. Next, examples of the present invention will be described.

ZnO powder and AuX3 (where X is Cl, .BrlI
At least one of these powders was selected at a predetermined composition ratio to obtain 30 mixtures including reference examples, and each mixture was thoroughly mixed in a ball mill to obtain 9 adjusted powders.

After that, 0.5% of polyvinyl alcohol was added to these prepared powders.
% aqueous solution was added to each to form a paste. Next, as shown in Fig. 1, two metal wires 2 and 2' were wound in parallel around the outer surface, and the inner diameter was 0.81'', the thickness was 0.2 m, and the length was 4.
The paste-like material 3 was applied and filled onto the outer peripheral surface of the cylindrical insulating substrate 1 of No. n, and after drying, a sintering treatment was performed at 750° C. to produce a halogen gas sensing element.

Regarding the above-mentioned halogen gas sensing element, the resistance value R is at room temperature (25°C) and a halogen gas concentration of 0 ppm.

and resistance value R when CCl2F2 gas concentration is 100 ppm
g, and table the resistance change rate Rg/RO along with the composition ratio.
Shown in 1. CHClF2 was also measured in the same manner, and the results are also shown in Table 1. Next, for these halogen gas sensing elements, the relationship between the concentration of CCl2F2 as a halogen gas and the rate of change in resistance was investigated and is shown in FIG.

In FIG. 2, curve a shows Example 11, curve b shows Example 5, and curve c shows the rate of change in resistance with respect to reducing gas (isobutane gas) concentration for Example 11. As is clear from FIG. 2, the rate of change in resistance varies depending on the concentration of rogen gas, so the concentration can also be detected from the resistance value.
In addition, the relationship between the concentration of reducing gas (isobutane gas) and the rate of change in resistance shows a tendency opposite to that of halogen gas, so it becomes clear to distinguish between halogen gas and reducing gas. Furthermore, for the above halogen gas sensing element, 10% of CCl2F2 was added.
The response characteristics when brought into contact with and released from air containing 0 ppm were investigated and shown in Figure 3.

In FIG. 3, curve a shows the case of Example 11, and curve b shows the case of Example 5. As is clear from FIG. 3, the responsiveness is also excellent. As described above, the present invention can be said to be a halogen gas sensing element that is sensitive enough to detect a halogen gas of about 10 ppm, has excellent responsiveness, and has excellent selectivity between halogen gas and reducing gas. Although this example shows an example using CCl2F2 and CHClF2, other halogen gases such as CHBrF2 can also be used.
2 shows similar characteristics.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a configuration example of a halogen gas sensing element according to the present invention, and FIGS. 2 and 3 are curve diagrams showing various characteristics of the halogen gas sensing element according to the present invention.
...Insulating base, 2,2'...Metal wire,
3...Halogen gas sensitive body.

Claims (1)

[Claims] 1 molar ratio of ZnO99.9-40% and AuX_3
(However, X is at least one of Cl, Br, and I.) A halogen gas sensitive body made of a fired body having a composition containing 0.1 to 60%, and a pair of electrodes provided on the halogen gas sensitive body. A halogen gas sensing element that is characterized by: