JPH0645249Y2 - Galvanic battery oxygen sensor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a galvanic battery type oxygen sensor. More specifically, the present invention relates to a galvanic cell type oxygen sensor using a plastic container.

2. Description of the Related Art Conventional galvanic cell type oxygen sensors generally have a positive electrode consisting of a catalyst electrode that controls the electrolytic reduction reaction of oxygen, a negative electrode consisting of a lead electrode, and an aqueous solution of an alkali hydroxide or a mixed aqueous solution of an organic acid and an organic acid salt. And the like, a fluororesin diaphragm for suppressing oxygen diffusion and preventing electrolyte leakage, and a plastic container for housing these sensor components (for example, ,
See Japanese Patent Publication No. 54-35111 and Japanese Patent Publication No. 58-187846).

Problems to be Solved by the Invention The plastic container constituting the galvanic cell type oxygen sensor has water vapor permeability to a greater or lesser degree, depending on its material and wall thickness. Therefore, during long-term operation of the oxygen sensor, the water content in the electrolyte decreases,
Increase. If the water content in the electrolyte decreases,
As the internal pressure of the sensor decreases, the ability of the electrolyte to dissolve lead in the negative electrode into the discharge products decreases. When the internal pressure of the sensor decreases, in the case of a sensor in which the diaphragm and the positive electrode are in contact with each other, the diaphragm bends inward and the degree of adhesion between the diaphragm and the positive electrode increases. Therefore, the diaphragm is interposed between the diaphragm and the positive electrode. The electrolyte is depleted, the number of reaction sites on the positive electrode becomes extremely small, and finally the electrolytic reduction reaction of oxygen on the positive electrode does not occur, and the sensor life ends. Further, in the case of a sensor in which the diaphragm and the positive electrode are integrally bonded, the diaphragm-positive electrode assembly is curved inward, the positive electrode is separated from the diaphragm, and the electrolyte solution leaks from the end of the assembly. Cause.

On the other hand, in general, the electrode reaction of the negative electrode is Pb + 2OH ⁻ → PbO + H ₂ O + 2e ⁻ when an aqueous solution of alkali hydroxide is used as the electrolytic solution, and Pb + H ₂ O → PbO + 2H ⁺ + 2e ⁻ when the acidic electrolytic solution is used. ^- there is a a, but the life of the galvanic cell type oxygen sensor comes determined by the solubility of the electrolytic solution of PbO which is a negative electrode reaction product described above. However, the electrolyte concentration of the galvanic cell oxygen sensor is usually adjusted so that the solubility in PbO is maximized at the beginning of its operation, but when the water content of the electrolyte decreases, the electrolyte concentration increases. As a result, the solubility of PbO is also reduced, and the life is shortened accordingly.

On the other hand, when the water content in the electrolytic solution increases, the internal pressure of the oxygen sensor rises, and the electrolytic solution easily leaks from the end of the diaphragm. Further, in the case of an oxygen sensor of a type in which the diaphragm and the positive electrode are in contact with each other, the gap between the diaphragm and the positive electrode becomes too large, so that the arrival speed of oxygen to the positive electrode surface becomes slow, and the polarization characteristics of the positive electrode are There is a problem that the oxygen sensor deteriorates and eventually the linearity between the output voltage of the oxygen sensor and the oxygen concentration is lost.

Also, when the water content of the electrolyte increases, the electrolyte concentration decreases,
The solubility of PbO is also reduced, which shortens the sensor life.

Means for Solving the Problems The present invention covers the surface of a plastic container with a heat-shrinkable plastic film vapor-deposited with aluminum, and heats the heat-shrinkable plastic film to shrink the heat-shrinkable plastic film. It is intended to prevent the permeation of water vapor through the container and to solve the above problems.

Function The life of the conventional galvanic battery type oxygen sensor using an aqueous solution of alkali hydroxide as an electrolyte was short, about 1 year. In such a short-life oxygen sensor, the permeation of water vapor through a plastic container and the various problems associated with it, which have been mentioned above, have not been revealed. On the other hand, the inventors of the present invention use a mixed aqueous solution of an organic acid and an organic acid salt having a pH in the range of 4 to 7 as the electrolytic solution, so that the life of the galvanic battery type oxygen sensor is 10 years or more. It has been discovered (see Japanese Patent Application Laid-Open No. 58-187846).

With the advent of such a long-life oxygen sensor, it has been found for the first time that the water vapor permeability of the plastic container as described above becomes a problem. In the case of conventional galvanic cell oxygen sensors, which proves to be the case, the plastic container does not have any consideration or treatment for preventing permeation of water vapor.

In any case, when ABS resin is used as the material of the plastic container of the galvanic cell oxygen sensor, the water permeability coefficient at 60 ° C is 2 × 10 ^-2 g · mm / cm ² ·.
In contrast to the day / atm, by coating the surface of the plastic container with the laminated film of aluminum and the heat-shrinkable plastic film as in the present invention, the water permeability coefficient becomes almost zero.

Embodiment Hereinafter, one embodiment of the present invention will be described in detail.

FIG. 1 shows a sectional structure of a galvanic cell type oxygen sensor according to an embodiment of the present invention. Cylindrical ABS resin container body 1
Between the container cover 2 made of ABS resin and the cover 2 made of ABS resin, O-rings 4, 4
A diaphragm 5 made of fluorinated ethylene-6 fluorinated propylene polymer, a positive electrode 6 made of gold integrally bonded to the diaphragm 5, a carbon paper 7 as a current collector, and a titanium wire 8 also used as a current collector. It is pinched. Further, in the container body 1, an electrolytic solution 9 made of a mixed aqueous solution of acetic acid, potassium acetate and lead acetate and a negative electrode 10 made of lead are stored. The positive electrode 6 and the negative electrode 10 are connected outside the sensor via a resistor 11 and a thermistor 12. Each side surface of the container body 1 and the container lid 2 of such a galvanic cell type oxygen sensor is covered with a heat-shrinkable tube composed of an aluminum vapor deposition film layer 13 and a heat-shrinkable polyvinyl chloride film layer 14, and heated. Heat shrunk.

The galvanic battery-type oxygen sensor obtained in this way was used at a temperature of 60.
When tested under the conditions of ℃ and relative humidity of 10%, which are much more severe than the atmosphere where an oxygen sensor is usually used, after 150 days, the reduction rate of water content in the electrolyte solution was only 2%. No abnormality was found in the output characteristics of the sensor.

On the other hand, for comparison, the conventional galvanic cell type oxygen sensor in the case of not covering the laminated film composed of the aluminum vapor deposition film layer 13 and the heat-shrinkable polyvinyl chloride film layer 14 in the embodiment of the present invention under the same conditions. After a 150-day test, the water content in the electrolyte after 65 days decreased to 65%, the sensor output also dropped significantly, and the service life was exhausted.

As described above, according to the present invention, in a galvanic battery type oxygen sensor using a plastic container, it is possible to prevent the electrolyte solution from decreasing and increasing over a long period of time, and to maintain the sensor output characteristics well. The excellent advantage that it is possible can be achieved.

[Brief description of drawings]

FIG. 1 is a view showing a sectional structure of a galvanic cell type oxygen sensor according to an embodiment of the present invention. 1 ... Container main body, 2 ... Container lid, 5 ... Separation film, 6 ... Positive electrode, 9 ... Electrolyte, 10 ... Negative electrode, 13 ... Aluminum vapor deposition film layer, 14 ... Polyvinyl chloride film layer

Claims (1)

[Scope of utility model registration request] 1. A galvanic battery type oxygen sensor using a plastic container, wherein the plastic container is covered with a laminated film of aluminum and a heat-shrinkable plastic film.