JPH02122252A - Threshold current type gas concentration sensor - Google Patents

Abstract

PURPOSE:To form a gas diffusing hole of a hole diameter within a desired range at a good yield even if a slight deformation arises at the time of calcination of a solid electrolyte plate which is a sensor element by providing the gas diffusing hole to the solid electrolyte plate. CONSTITUTION:Porous electrodes 12A, 12B consisting of, for example, platinum are formed on both surfaces of the solid electrolyte plate 11 having the ion conductivity of a prescribed gas. The gas diffusing hole 13 is provided to the solid electrolyte plate 11 and a protective cap 14 is placed on the porous elec trode 12A side of the one surface. The solid electrolyte plate 11 and the protec tive cap 14 are sealed therebetween by a sealing material 15 in the peripheral edge part thereof. A gas diffusing space 16 is formed between the protective cap 14 and the porous electrode 12A as well as the solid electrolyte plate 11 by the sealing material 15. Lead wires 17A, 17B are respectively connected to the porous electrodes 12A, 12B. The need for providing the gas diffusing hole to the protective cap 14 is eliminated in this way and since the solid electro lyte plate 11 is as thin as about 1/10 the thickness of the protective cap 14, the plate exerts the less influence on the gas diffusing hole 13 even if there is some deformation at the time of calcination.

Description

[Detailed description of the invention] Utilization of U industry-1-! I! The present invention relates to an improvement in a limiting current type gas concentration sensor, and particularly to an improvement in the position of a gas diffusion hole that communicates the gas diffusion space of the sensor with the outside atmosphere.

[Conventional technology 1] Conventionally, as a gas concentration sensor for oxygen, hydrogen, water, etc.
A limiting current type gas concentration sensor using a solid electrolyte has been known for many years to determine the ionic conductivity of a given gas.

As shown in FIG. 3, porous electrodes 32Δ and 32I3 made of platinum are disposed on both sides of a solid electrolyte plate 31 made of stabilized norconia that increases the ionic conductivity of a predetermined gas, such as oxygen gas, by γI. A protective cap 33 is formed on one side of the solid electrolyte plate 31 by sealing 4A35 to cover one electrode 32A.
．． 1! A gas diffusion space 36 is formed between the protective cap 33 and a gas diffusion hole 34 that communicates the gas diffusion space 36 with the outside atmosphere. In addition,
In the figure, 37A, 37 F3 are - electrodes 32Δ, 32B
The wires are connected to each other.

In addition, the structure shown in FIG. 4 has been proposed as a modification of the moldability of the protective cap 33 and the adhesive outer surface of the protective cap 33 and the solid electrolyte plate 31a. ing. 4- That is, porous electrodes 42Δ, 42B are formed on both sides of the solid electrolyte plate 41, and a porous fired body 43 is formed to protect them and form a gas diffusion space.
is baked together with the solid electrolyte plate 4I and joined together on one or both sides thereof, and furthermore, a glass coating layer 44 for preventing minute cracks is provided on one surface. Here, the porous fired body 43 marked with "-" is attached to the protective cap 33 in FIG.
The large number of holes correspond to the gas diffusion holes 3a in FIG. 3, and the fine cracks in the glass coating layer 44 correspond to the gas diffusion holes 34 in FIG. In addition, 45A in the figure,
45RiJ are lead wires connected to the electrodes 42Δ and 42B, respectively.

In this limiting current type gas concentration sensor, the size of the gas diffusion hole is one of the factors that has a significant effect on the sensitivity of the sensor.

[Problem to be Solved by the Invention 1] The above conventional gas concentration sensors all have gas diffusion holes that take in the external atmosphere or are provided in a protective cap that protects a solid electrolyte plate that is an ion conductor. In the case of the protective cap 33 shown in FIG. 3, ceramic powder is formed into a columnar shape, with the center axis of the ceramic powder passed through a set of ultrafine fibers of Plus Deck, compression molded, and this is cut into disc-shaped pellets. After baking, the seaweed is made. At this time, the gas diffusion holes 34 are formed by burning and removing the ultrafine fibers of plastic that are threaded in advance when the disk-shaped pellets of the ceramic powder shown in -]- are fired. Even if the shape of the pores is slightly deformed during this process, the length of the pores is longer than the minute pore diameter, resulting in large variations in gas diffusion resistance. Yield will be poor.

In addition, the large number of pores of the porous fired body 43 on which the glass coated layer 44, which is a protective cap for the sensor, is placed on the surface shown in FIG. Therefore, it plays a role as a gas diffusion hole (j
Since the pore size is a little small, it is necessary to form fine racks penetrating the inside and outside of the glass coating layer 4/I as gas diffusion holes, or to control the size and number of cracks when forming them. That is extremely difficult.

[Means for Solving the Problems 1 This invention solves these problems,
Instead of installing gas diffusion holes on the protective cap side, we installed them on the solid electrolyte plate with ionic conductivity, which is the sensor element.
It's a J thing.

1 Effect] With the above configuration, there is no need to provide gas diffusion holes in the protective cap, and the solid electrolyte plate
Its thickness is about 1/10 that of the protective cap shown in Figure 3, so even if there is some deformation during firing,
The effect on the pore diameter of the gas diffusion holes is extremely small.

[Example] The present invention will be described in detail with reference to the drawings.

First, in FIG. 1, 11 is a solid electrolyte plate having ion conductivity for a predetermined gas, 12Δ, 12B are porous electrodes made of platinum, for example, formed on both sides of the solid electrolyte plate II, and I3 is the solid electrolyte plate 11. 14 is a protective cap placed on one side of the porous electrode I2Δ of the solid 7u electrolyte plate 11; 15 is a gas diffusion hole provided between the solid electrolyte plate II and the protective cap 14; A sealing material 16 seals the peripheral edges of the solid electrolyte plate 11, a gas diffusion space created between the porous electrode 12A and the protective cap 14 by a sealing hole 15, +7A and 7B porous These are lead wires connected to the quality electrodes 12A and +2f3, respectively.

Next, another embodiment of the present invention will be described with reference to FIG. 2■ is a solid electrolyte plate having ionic conductivity for a predetermined gas; 22A and 22B are porous electrodes made of platinum formed on both sides of the solid electrolyte plate 21; and 23 is a porous electrode installed through the solid electrolyte plate 21. 24 is a porous fired body provided on one side of the solid electrolyte plate 21 to cover one electrode 22A; 25 is a glass coating layer formed to cover the entire surface of the porous fired body 24; 26Δ, 2
6B is a lead wire connected to the porous electrodes 22A and 2213, respectively.

[Effects of the Invention] According to the limiting current type gas concentration sensor of the invention, the gas diffusion holes are temporarily installed in the solid electrolyte, so that the solid electrolyte plate can be used for the gas diffusion as shown in FIG. Since it is about 1/1O thinner than the thickness of the protective cap 14 in which the holes 34 are located, even if the solid electrolyte plate is slightly deformed by firing, it will hardly affect the pore diameter of the gas diffusion holes. First, gas diffusion holes having a hole diameter within a desired range can be formed with a higher yield.

In addition, compared to the conventional glass coating layer 44 having minute cracks formed on the surface of the porous fired body 7I3, which is a protective V-yappe shown in FIG.
There is no need to create fine cracks whose size and number are difficult to control, and gas diffusion holes within a desired range can be formed with a high yield in the solid electrolyte.

Furthermore, in this invention, the protective cap does not have a gas diffusion hole, so conventionally, the heater circuit pattern required for sensor operation was limited to being formed on the protective cap with the gas diffusion hole. Unlike No. 1, the present invention does not provide gas diffusion holes in the protective cap, so the heater circuit pattern can be formed without any restrictions.

[Brief explanation of the drawing]

1 and 2 are side sectional views showing different embodiments of the limiting current type gas concentration sensor of the present invention, and FIGS. 3 and 4 are side sectional views showing different embodiments of the conventional limiting current type gas concentration sensor. FIG. 11, 2, 1.3 +, 4+, solid electrolyte plate, +2A. 12B, 22Δ, 22B, 32A, 32B, 42A, 4
2B, porous electrode, 13.23.34. Gas diffusion hole, 1
4.33. Protective cap, I5.35; sealing material, 16.
36; Gas diffusion space, 24.43, Porous fired body, 25
．． Glass coating layer, glass coating layer having 4 fine cracks.

Claims (1)

[Claims] Porous electrodes are formed on both sides of a solid electrolyte plate having ionic conductivity for a predetermined gas, and one side of the solid electrolyte plate is covered with the electrode,
A limiting current type gas concentration sensor in which a protective cap having a gas diffusion space is sealed, characterized in that the solid electrolyte plate is provided with a gas diffusion hole that communicates the external atmosphere of the sensor with the gas diffusion space. A limiting current type gas concentration sensor.