JPH0363704B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a galvanic cell type oxygen sensor. More specifically, the present invention relates to a galvanic cell type oxygen sensor composed of a catalytic electrode as a positive electrode, a lead electrode as a negative electrode, an electrolytic solution, and a diaphragm integrally joined to the catalytic electrode.

Galvanic cell-type oxygen sensors are small, lightweight, operate at room temperature, and are inexpensive, so they can be used to check oxygen deficiency conditions in ships and manholes, and to check oxygen concentration in medical equipment such as anesthesia machines and artificial respirators. It is used in a wide range of fields such as monitoring.

Conventional technology A galvanic cell type oxygen sensor generally consists of a catalyst electrode as a positive electrode, a lead electrode as a negative electrode, and a fluororesin diaphragm that allows electrolyte and oxygen to pass through, but does not allow water vapor to pass through. The structure of galvanic cell-type oxygen sensors can be roughly divided into types in which the diaphragm and catalyst electrode are simply in contact (for example, JP-A-58-187846), and types in which both are joined together. type (for example, British Patent No. 1200595). In the former case, the catalytic electrode is composed of a metal disk or cylinder, and oxygen in the sensing gas or sensing aqueous solution first passes through a diaphragm, and then an electrolyte film is formed between the diaphragm and the catalytic electrode. It is dissolved in the liquid and applied to the reaction on the surface of the catalytic electrode. Therefore, it is important to maintain constant contact between the diaphragm and the catalyst electrode at all times so that the thickness of the liquid film does not change. However, there is a problem in that when the pressure of the atmospheric gas changes or the relative humidity changes, the state of contact between the diaphragm and the catalyst electrode changes. From this point of view, it is more advantageous to have a structure in which the diaphragm and the catalyst electrode are integrally joined. Because,
This is because even if the diaphragm swells or dents due to a change in pressure, the catalyst electrode also follows the deformation of the diaphragm.

Problems to be Solved by the Invention In the case of a galvanic cell type oxygen sensor having a structure in which a diaphragm and a catalyst electrode are integrally joined, one problem is how to form a current collection structure. Conventionally, for example, a method has been adopted in which a metal spring as a current collector is pressed against the catalyst electrode, but this method is not very reliable in terms of maintaining constant contact between the spring and the catalyst electrode. Moreover, it is quite complicated to fix the spring in the narrow space of the oxygen sensor. Furthermore, phenomena such as damage to the catalyst electrode and partial separation from the diaphragm may occur.

On the other hand, a current collection method in which a metal wire or a metal screen is pressed against the catalyst electrode is also considered, but in this case as well, there are parts where the current collector is pressed against the catalyst electrode and parts where it is not. Damage to the catalyst electrode is likely to occur.

Means for Solving the Problems The present invention provides a galvanic cell type oxygen sensor having a structure in which a diaphragm and a catalyst electrode are integrally joined, and a current collector consisting of a catalyst electrode and a metal wire, a metal mesh, or a perforated metal plate. The above problem can be solved by interposing a kind of perforated plate made of paper, woven or matted metal fibers, or a sintered version of these perforated plates, between the That is.

Function A porous plate as described above, starting from metal fibers, acts as an intermediate current collector. The diameter of the metal fibers in this perforated plate is extremely thin, ranging from several microns to several tens of microns, and the pores are not that large. ) is small. Therefore, even if this porous plate is pressed against the catalyst electrode, the catalyst electrode is not easily damaged. Furthermore, it is much easier to house and fix such a perforated plate in a narrow sensor than in the case of a spring.

On the other hand, a porous plate made of metal fibers as a starting material has a capillary action, so it also has an electrolyte retention function. In other words, if for some reason the electrolyte no longer comes into contact with the catalytic electrode as a positive electrode, this galvanic cell type oxygen sensor will not work properly. When this happens, electrolyte is constantly replenished to the catalyst electrode.

Metal fiber materials include stainless steel,
Nickel or titanium is suitable.

Embodiment FIG. 1 shows a cross-sectional structure of a galvanic cell type oxygen sensor according to an embodiment of the present invention.

Between the container body 1 and the container lid 2 made of ABS resin,
Holding plate 3 with perforations, O-rings 4, 4',
A diaphragm 5 made of a tetrafluoroethylene-hexafluoropropylene copolymer film, a positive electrode 6 as a catalyst electrode made of a gold vapor-deposited film, a perforated plate 7 made of stainless steel fibers once made into paper and then sintered, and a titanium wire. A positive electrode current collector 8 is screwed. In addition,
The diaphragm 5 and the positive electrode 6 are integrally joined.

Inside the container body 1, an electrolytic solution (PH is 6) 9 made of a mixed aqueous solution of acetic acid, potassium acetate, and lead acetate and a negative electrode 10 made of lead are housed.

The electrolyte 9 flows through the positive electrode 6 due to capillary action in the porous plate 7.
will be replenished.

A thermistor 11 and a resistor 12 are connected between the positive electrode and the negative electrode.

Effects of the Invention The galvanic cell type oxygen sensor A obtained in the above-mentioned example and the conventional galvanic cell type oxygen sensor B in which there is no porous plate using metal fibers as a starting material in the above-mentioned example were each When sensor A was left in air at a temperature of °C and a relative humidity of 10% for 70 days, no abnormality was observed in the sensor output, while sensor B showed no abnormality in the sensor output. It has dropped to 30% of normal. Also, for both sensors, the electrolyte weight is 10
% decreased. Furthermore, when both sensors were disassembled and inspected, no abnormality was found in sensor A, but in the case of sensor B, the positive electrode was partially separated from the diaphragm.

From these facts, first of all, when the water in the electrolyte evaporates and the internal pressure of the sensor drops considerably, a force acts to bend the diaphragm-positive electrode assembly downward, causing sensor B to bend. In the case of sensor A, the sensor output decreased because the current collector was embedded in the positive electrode, whereas in the case of sensor A, the perforated plate made of metal fibers acted as a kind of barrier and prevented the current collector from entering. It is presumed that no abnormality occurred because the penetration into the positive electrode was avoided.

[Brief explanation of drawings]

FIG. 1 shows a cross-sectional structure of a galvanic cell type oxygen sensor according to an embodiment of the present invention. 1... Container body, 2... Container lid, 5... Diaphragm,
6... Positive electrode, 7... Porous plate, 8... Current collector, 9...
...Electrolyte, 10...Negative electrode.

Claims (1)

[Claims] 1. In a galvanic cell oxygen sensor composed of a catalytic electrode as a positive electrode, a lead electrode as a negative electrode, an electrolyte, and a diaphragm, the catalytic electrode is integrally bonded to one side of a diaphragm made of fluorine resin. Adjacent to the catalyst electrode, a perforated plate made of metal fibers made of paper, fabric, or mat, or a sintered perforated plate with metal fibers, is used to hold the electrolyte and serve as an intermediate current collector. A galvanic cell type oxygen sensor, characterized in that a perforated plate having a function is disposed, and a current collector made of a metal wire, a metal net, or a perforated metal plate is further disposed adjacent to the perforated plate. .