JPH0814566B2 - Limiting current type gas concentration sensor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an improvement in a limiting current type gas concentration sensor, and more particularly, to the position of a gas diffusion hole that communicates the gas diffusion space of the sensor with the external atmosphere. It is about improvement.

[Prior Art] Conventionally, as a gas concentration sensor for oxygen, hydrogen, water, etc., a limiting current type gas concentration sensor using a solid electrolyte having ion conductivity of a predetermined gas is known.

As shown in FIG. 2, the structure is such that a solid electrolyte plate 31 made of stabilized zirconia having ion conductivity of a predetermined gas such as oxygen gas has a porous electrode made of platinum on both sides.
32A and 32B are formed, and the protective cap 33 is sealed on one surface of the protective cap 33 by covering one electrode 32A, and a gas diffusion space 36 is formed between the protective cap 33 and the solid electrolyte plate 31. The protective cap 33 is provided with a gas diffusion hole 34 that communicates the gas diffusion space 36 with the external atmosphere. In the figure, 37A and 37B are lead wires connected to the electrodes 32A and 32B, respectively.

Further, a structure shown in FIG. 3 has been proposed as an improvement in the molding processability of the protective cap 33 and the adhesiveness between the protective cap 33 and the solid electrolyte plate 31 in the above structure. That is, the porous electrodes 42A, 42B are formed on both sides of the solid electrolyte plate 41, and in order to protect them and form a gas diffusion space, the porous fired body 43 is formed on one side or both sides thereof, together with the firing of the solid electrolyte plate 41. It is provided by being fired and integrally bonded, and a glass coating layer 44 having a fine crack is provided on the surface of one side thereof. Here, the above-mentioned porous fired body 43 is the protective cap 33 of FIG.
In addition, many holes of the porous fired body 43 are the gas diffusion spaces shown in FIG.
36 and the fine cracks of the glass coating layer 44 correspond to the gas diffusion holes 34 in FIG. 2, respectively. In the figure, 45
A and 45B are lead wires connected to the electrodes 42A and 42B, respectively.

In this limiting current type gas concentration sensor, the size of the gas diffusion hole has one of the significant effects on the sensitivity of the sensor.

[Problems to be Solved by the Invention] In any of the conventional gas concentration sensors described above, gas diffusion holes for taking in an external atmosphere are provided in a protective cap for protecting a solid electrolyte plate which is an ion conductor.
In the case of the protective cap 33 shown in FIG. 2, the ceramic powder is formed into a columnar shape, the ultrafine fibers of plastic are passed through the central axis thereof, compression molding is performed, and this is cut into disc-shaped pellets and then fired. Made by. At this time, the gas diffusion holes 34 are formed by burning and removing the ultrafine fibers of the plastic, which have been passed in advance, when the disk-shaped pellets of the ceramic powder are fired. Even if the shape of the hole is slightly deformed, the length of the hole is longer than the fine hole diameter, so that the dispersion of the gas diffusion resistance becomes large, and the yield of the product having the gas diffusion hole within the desired range is increased. Deteriorate.

Further, as described above, the large number of holes of the porous fired body 43 having the glass coating layer 44, which is the protective cap of the sensor shown in FIG. 3, mainly serve as a gas diffusion space as described above. Since it has a slightly larger role as a gas diffusion hole and has a larger diameter, the glass coating layer
It is necessary to form fine cracks that penetrate the inside and outside of the layer, but it is very difficult to control the size and number of the cracks when forming them.

[Means for Solving the Problem] The present invention is to solve these problems, in which porous electrodes are formed on both surfaces of a solid electrolyte plate having ion conductivity, and one of the porous electrodes is formed. A porous fired body is provided in close contact with one surface of the solid electrolyte plate so as to cover the surface of the solid fired body, and the surface of the porous fired body is covered with a non-porous glass coating layer. The electrodes are provided with gas diffusion holes penetrating them.

[Operation] The gas to be measured diffuses into the porous fired body through the gas diffusion holes, and the numerous holes of the porous fired body function as gas diffusion spaces. Since the gas diffusion holes are formed so as to penetrate through the solid electrolyte plate and the porous electrodes on both surfaces thereof, the length of the gas diffusion holes is 1 / th that of the case where the gas diffusion holes are formed in the protective cap.
Since it is about 10, even if there is some deformation during firing of the solid electrolyte plate, there is little effect on the diameter of the gas diffusion holes.

Further, there is no need for a step of forming fine cracks in the glass coating layer on the surface of the porous fired body by controlling the size and the number thereof.

[Embodiment] An embodiment of the present invention will be described with reference to the drawings. In FIG. 1, reference numeral 21 is a solid electrolyte plate having ion conductivity of a predetermined gas, 22A and 22B are porous electrodes made of platinum formed on both surfaces of the solid electrolyte plate 21, and 23 is a penetrating solid electrolyte plate 21. A gas diffusion hole provided in 24, 24 is a porous fired body provided to cover one electrode 22A on one surface of the solid electrolyte plate 21, 25 is formed to cover the entire surface of the porous fired body 24 The domed non-porous glass coating layers 26A and 26B are lead wires connected to the porous electrodes 22A and 22B, respectively.

[Effect of the Invention] According to the limiting current type gas concentration sensor of the present invention, since the gas diffusion holes are provided so as to penetrate the solid electrolyte plate and the porous electrodes on both sides thereof, the solid electrolyte plate is Since it is about 1/10 of the thickness of the protective layer cap having gas diffusion holes, even if a slight deformation occurs due to firing of the solid electrolyte plate, it has almost no effect on the diameter of the gas diffusion holes, It is possible to manufacture a sensor element having a gas diffusion hole having a hole diameter within a desired range with higher yield.

Further, in the present invention, the glass coating layer, it is not necessary to provide fine cracks difficult to control the size and number,
The formation process of the non-porous glass coating layer becomes very easy.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an embodiment of a limiting current type gas concentration sensor of the present invention, and FIGS. 2 and 3 are side sectional views showing another embodiment of a conventional limiting current type gas concentration sensor. 21 ... Solid electrolyte plate, 22A, 22B ... Porous electrode, 23 ...
Gas diffusion holes, 24 ... Porous fired body, 25 ... Glass coating layer.

Claims (1)

[Claims] 1. A porous electrolyte is formed on both sides of a solid electrolyte plate having ion conductivity, and a porous fired body is adhered to one side of the solid electrolyte plate so as to cover one of the porous electrodes. The surface of the porous fired body is covered with a non-porous glass coating layer, and the solid electrolyte plate and the porous electrodes on both sides thereof are provided with gas diffusion holes penetrating them. Limiting current type gas concentration sensor.