JPH0321858A - Sensor element of oxygen sensor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a sensor element of an oxygen sensor used to determine the oxygen concentration in various atmospheres.

[Conventional technology]

As shown in FIG. 2, the conventional sensor element is made of an ion-conducting solid electrolyte base with a single gas diffusion hole 1a and electrodes 2 formed on both sides (for example, by platinum screen printing). A capsule 4 in which a heater 3 for heating is molded (for example, by screen printing) on a pellet 1 (for example, made of stabilized zirconia) is attached to a gas reaction chamber 5.
It is sealed with a sealing material 6 (for example, glass) with a sealing material 6 (for example, glass) interposed therebetween.

FIG. 3 shows another conventional sensor element, in which a single gas diffusion hole 4a is formed in a capsule 4 sealed with a sealing material 6 to a pellet 1 having an oval electrode 2. ,
In addition, the heater 3 is molded.

In each of these sensor elements, a voltage is applied between the electrodes 2 and the heater 3, and a current using oxygen ions as carriers flows between the electrodes 2 due to the oxygen bombing action of the pellet 1 at a predetermined heating temperature. Gas diffusion holes 1a, 4a
Oxygen molecules entering the gas reaction chamber 5 through the pellet 1 are discharged via the pellet 1 (arrows indicate the transport of oxygen molecules).

At this time, since the flat region of the current that appears in a certain voltage region of the voltage-current characteristic, that is, the limiting current value and the oxygen concentration are in a one-to-one relationship, the electrode 2 and the heater 3
A constant voltage is applied to the sensor element, and the oxygen concentration is determined by δ13 from the temperature of the sensor element and the limiting current value at that time.

[Problem to be solved by the invention]

As mentioned above, conventional sensor elements
Alternatively, since the capsule 4 is provided with a single gas diffusion hole 1a or 4a, the following problems arise.

(a) Pellet 1, capsule 4, and gas diffusion hole la
, 4a requires a high degree of machining accuracy due to the following reasons,
Incurring high costs.

(a) Since the molding thicknesses of the pellets 1 and capsules 4 and the diameters of the gas diffusion holes 1a and 4a are related to each other, unless the two are strictly adjusted, variations in the limiting current value will occur.

(b) If there is an error in the drilling positions of the gas diffusion holes 1a and 4a, a time lag will occur in the diffusion of oxygen molecules to the electrode 2 and pellet 1, which will hinder the conduction of oxygen ions and cause variations in the limiting current value. It becomes a factor of occurrence.

(b) The processability problem described above is an obstacle to thinning and mass production of sensor elements.

(C) Pellet 1 with gas diffusion holes 1a (
2) is subject to restrictions in the molding of the electrode 2, and the capsule 4 having gas diffusion holes 4a (FIG. 3) is subject to restrictions in the molding of the heater 3.

The present invention was devised in view of the above problems, and its purpose is to provide oxygen that does not require a high level of processing precision, enables thinning and mass production, and allows the shapes of electrodes and heaters to be made freely. An object of the present invention is to provide a sensor element for a sensor.

[Means to solve the problem]

In order to achieve the above object, the present invention uses porous crystallized glass as a sealing material for an ion-conductive solid electrolyte pellet with electrodes molded on both sides and a capsule with a heater molded thereon. The reason is that this porous crystallized glass is also used as gas diffusion holes.

[For production]

Oxygen molecules diffuse into the gas reaction chamber through the gas diffusion holes formed in the porous crystallized glass of the sealing material, and due to the oxygen bombing action of the pellet, the current flowing between the electrodes has a limiting characteristic. appear.

〔Example〕

Embodiments of the present invention will be described with reference to the drawings.

Note that the same parts as in the conventional example are given the same reference numerals.

As shown in Figure 1, a pellet 1 of ionically conductive solid electrolyte (e.g. made of stabilized zirconia) with electrodes 2 molded on both sides (e.g. by platinum screen printing)
and a capsule 4 in which a heating heater 3 is molded (for example, by screen printing) are sealed with a sealing material 7 made of porous crystallized glass, and this sealing material 7 is used to seal gas diffusion holes and pellets. 1 and the capsule 4 (arrows indicate the transfer of oxygen molecules).

One embodiment of porous crystallized glass as the sealing material 7 includes crystallized glass (for example, No. 01 manufactured by Asahi Glass Co., Ltd., crystallization temperature of about 850° C.) and carbon (for example, Acetylene Black (manufactured by IBIDEN Co., Ltd.) in advance (for example, at a weight ratio of 5:2) was interposed between the peripheries of the pellets 1 and capsules 4, and heated at a temperature of about 900°C for about 30 minutes. By performing the partial firing, porous crystallized glass that can be used as a large number of gas diffusion holes is formed by gasifying the carbon.

Moreover, the crystallized glass and carbon may be applied at a blending ratio of 5:2 instead of a previously blended ring.

Note that by changing the blend ratio of crystallized glass and carbon, the state of the pores (gas diffusion holes) can be changed.

〔Effect of the invention〕

The present invention has the following effects.

(a) Since the porous crystallized glass that seals the ion-conductive solid electrolyte pellet and capsule also serves as gas diffusion holes, high processing accuracy is required when providing gas diffusion holes in pellets or capsules as in the past. Because it is not
Mass production becomes possible and costs are reduced by 111 times.

(b) Since there are no gas diffusion holes in the pellets or capsules, they can be made thinner in terms of mechanical strength, and the electrodes and heaters can be molded into the desired pattern without being constrained by molding. be able to.

(c) Porous crystallized glass which allows the level of gas diffusion into the gas reaction chamber to be easily changed by changing the blend ratio of crystallized glass and carbon, and which has good reproducibility when the blend ratio is the same. I can do it.

1... Pellet, 2... Electrode, 3... Heater, 4
... Capsule, 7... Sealing material.

Claims (1)

[Claims] An oxygen device characterized in that the sealing part between the ion-conductive solid electrolyte pellet with electrodes molded on both sides and the capsule with a heating heater molded therein is made of porous crystallized glass that also serves as gas diffusion holes. sensor element of the sensor.