JPH03140860A - Oxygen sensor - Google Patents

Abstract

PURPOSE:To reduce the manufacturing cost of a sensor and to improve an oxygen concentration detecting characteristic by providing a solid-electrolyte layer on a first electrode shaped in a thin film and formed on a porous substrate and by providing a second electrode shaped in a thin film and formed on the layer. CONSTITUTION:First, a first electrode 3 is prepared by forming a platinum Pt film of a thickness 5,000Angstrom approx. on a porous substrate 1 by a sputtering method. Next, a solid-electrolyte layer 4 of a thickness 60 mum is formed on the porous substrate 1 by a plasma spray method. As for a solid electrolyte, LaF3 is used. As for material powder for plasma spray, LaF3 powder of an average particle size 1 mum is used. The average particle size of the LaF3 powder is preferably 2 mum or below. Moreover, a platinum film of a thickness 5,000 Angstrom approx. is formed on the solid-electrolyte layer 4 by the sputtering method, so as to prepare a second electrode 5. According to this method, it is possible to reduce the manufacturing cost of a sensor and to improve an oxygen concen tration detecting characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to an oxygen sensor using lanthanum fluoride as a solid electrolyte.

B6 Summary of the Invention The present invention uses lanthanum fluoride, which can operate as a sensor even at low temperatures, as a solid electrolyte, and forms a first electrode in the form of a thin film on a porous substrate. A solid electrolyte layer of lanthanum fluoride is formed on the first electrode by spraying the powder using a plasma spray method, and a thin film-like second electrode is formed on this solid electrolyte layer to construct an oxygen sensor. , which has good durability and can be manufactured at low cost.

C1 Prior Art In general, oxygen sensors using solid electrolytes have been put into practical use to measure oxygen in combustion gas.

Stabilized zirconia is usually used as the solid electrolyte. However, oxygen sensors using stabilized zirconia
The disadvantage is that it can only be used at high temperatures. If the temperature is low,
It does not generate an electromotive force and must normally be used at temperatures above 400°C.

For this reason, oxygen sensors that operate even at low temperatures are currently being researched; for example, one using fluoride (LaF3) as a solid electrolyte has been proposed (Japanese Patent Laid-Open No. 6
1-132855).

D3 Problems to be Solved by the Invention The above-mentioned oxygen sensor using LaF3 is a monocrystalline LaF3
3 must be used, making it very expensive. For this reason, it is not commercially suitable and has not been put into practical use.

Here, it is possible to reduce the thickness of LaF3 and manufacture it at low cost. Thin film manufacturing techniques include resistance heating evaporation, E, B,
There are vapor deposition methods, sputtering methods, and CVD methods, and there is also a spray method (thermal spray method) if the film thickness is 50 μm or more.

However, there are problems in obtaining good oxygen sensors using either thin film manufacturing technique.

In the resistance heating evaporation method and the E, B, evaporation method, the formed L
a The F3 membrane has a columnar structure (columnar structure),
When used as an oxygen sensor for a long time, La
There is a problem in that the F3 film is cracked and no electromotive force is generated.

In addition, the sputtering method has a very slow film formation rate.
Poor productivity. Further, in the CVD method, even in the case of the thermal decomposition CVD method, it is not possible to obtain an extremely smooth film-like film.

Furthermore, it is difficult to form a dense (gas-tight) film using a spray method, even when using a plasma spray method.

In view of these circumstances, the present invention has been developed using La, which can be manufactured using inexpensive film forming technology and has good durability.
The present invention aims to provide an oxygen sensor according to F.

E. Means for Solving the Problems In order to achieve the above object, the present invention provides an oxygen sensor equipped with the following means.

■ Thin film-like first electrode formed on a porous substrate.

(2) A solid electrolyte layer formed on the first electrode by thermally spraying small-particle-sized LaFa powder using a plasma spray method.

■ A second electrode in the form of a thin film formed on this solid electrolyte layer.

F1 Effect According to the present invention, the solid electrolyte layer is formed by a plasma spray method using small-particle-sized LaF3 powder, so it has a relatively dense structure.

Furthermore, since the thin film-like first and second electrodes are formed on both surfaces by a thin film manufacturing technique such as sputtering, the strength of the solid electrolyte layer is improved.

Furthermore, since the first electrode is formed on the porous substrate,
Adhesion between the substrate and the solid electrolyte layer is improved.

Therefore, even if used for a long time, it is possible to realize a highly durable oxygen sensor that is unlikely to crack or peel.

G. Example Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 shows an oxygen sensor according to one embodiment of the invention.

In this figure, the film thickness is exaggerated for convenience of explanation.

The manufacturing process of this oxygen sensor will be explained.

1 is a porous substrate (SUS316L, manufactured by Ball Co., Ltd., PO5
, pore diameter 0.5 μm, porosity approximately 40%). This porous substrate 1 is welded to a pipe (SUS316L) 2.

First, a platinum (PT) film with a thickness of about 5,000 layers is formed on this porous substrate 1 by sputtering.
This is called electrode 3.

Thereafter, a solid electrolyte layer 4 having a thickness of 60 μm is formed on the porous substrate 1 by a plasma spray method. LaF3 is used as the solid electrolyte.

Here, in this plasma spray method, LaF3 powder with an average particle size of 1 μm is used as raw material powder for plasma spray. The average particle size of the LaF powder is preferably 2 μm or less. In addition, a fine powder quantitative supply device (Fine Feeder, manufactured by Mizuta Iron Works) and a plasma spraying device (manufactured by Mizuta Iron Works, 5QKW class system) capable of supplying fine powder are used.

Plasma spray conditions are: ■Atmosphere: Air, ■Substrate temperature: Room temperature, ■Plasma spray gun-to-substrate distance: ]55
0mm ■Spray speed = 0.6Kg/h, ■Used gas:
A r-H2, ■Current: 600A1■Voltage 70DC
It was set to V.

Further, on this solid electrolyte layer 4, a platinum film having a thickness of about 5,000 wafers is formed by sputtering to form the second electrode 5. The method for forming the first electrode 3 and the second electrode 5 is not limited to the sputtering method, but may also be a method in which, for example, a paste containing platinum is applied and fired.

In this example, since LaF3 powder is used as the raw material, a significant cost reduction can be expected compared to an oxygen sensor using single crystal LaF3.

Next, the characteristics of this oxygen sensor will be explained.

The first electrode 3 side of the oxygen sensor is set as the standard air side, exhaust gas with low oxygen concentration is sent to the second electrode 5 side, and the picture electrode 3,
The electromotive force generated during this period was measured.

The results are shown in FIG. This measurement was performed at a temperature of 300°C.

In FIG. 2, (a) shows the characteristics of the oxygen sensor according to the present example, and (b) shows the characteristics of the comparative example. A comparative example is
5,000 platinum electrodes were formed on both sides of a single-crystal LaF3 layer with a diameter of 10 mm and a thickness of 0.4 mm by sputtering.

As a result of this measurement, the La film formed by the plasma spray method
It was found that the electromotive force generated by F3 is almost the same as that of single crystal aF3, and the response speed to oxygen concentration is faster than that of single crystal.

The following two points can be considered as reasons for the increased response speed.

First, the solid electrolyte layer 4 is thin.

In this example, since the solid electrolyte layer 4 is formed by a plasma spray method, it can be made much thinner than the comparative example using single crystal LaF+.

Second, the picture electrodes 3 and 5 are porous. By forming the first electrode 3 on the porous substrate 1'', the first electrode 3 becomes porous. Furthermore, since the surface of the solid electrolyte layer 4 has appropriate irregularities, the second electrode 5 also becomes porous. Since the picture electrode 3.5 is porous, it is thought that the catalytic action on the surface of the picture electrode 3.5 proceeds significantly more quickly than in the comparative example.

We also conducted a strength test that applied thermal strain to the oxygen sensor.

Comparative examples are LaF by resistance heating evaporation and E, B, evaporation.
This is an oxygen sensor in which a solid electrolyte layer is formed by depositing No. 3 into a film. As a result, in the comparative example, under conditions where cracks occur in the solid electrolyte layer or the solid electrolyte layer peels off from the substrate, in this example, the solid electrolyte layer 4 does not crack or peel off from the substrate. Ta.

This experiment confirmed that in this example, the solid electrolyte layer 4 had high strength and good adhesion to the substrate.

The reason for this is that by using LaF3 powder with a small particle size, a relatively dense LaF3 film can be obtained.
Furthermore, by forming electrodes 3.5 on both sides of the LaF film, the strength is further increased and it is believed that the adhesion to the substrate is also improved.

As described in detail of the H6 invention, according to the present invention, a solid electrolyte layer is formed by a plasma spray method using LaF3 powder [2 powder. Therefore, since it is not necessary to use single crystal LaF, lower manufacturing costs can be expected.

In addition, a dense LaF3 film is formed using a small particle size LaF3 powder, and thin film-like first and second electrodes are formed on both sides using thin film manufacturing techniques such as sputtering.
By forming the electrodes, the strength of the solid electrolyte layer and the adhesion between the substrate and the solid electrolyte layer are ensured.

Furthermore, since the thickness of the solid electrolyte layer can be reduced and the electrode is porous, there is an advantage that the response speed to oxygen concentration is improved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of an oxygen sensor according to an embodiment of the present invention, and FIG. 2 is an explanatory diagram showing the output characteristics of the oxygen sensor shown in FIG. 1. DESCRIPTION OF SYMBOLS 1... Porous substrate, 3... 1st electrode, 4... Solid electrolyte layer, 5... 2nd electrode.

Claims (1)

[Claims] (1) A first electrode in the form of a thin film formed on a porous substrate, and a solid electrolyte layer formed on this first electrode by spraying small-particle lanthanum fluoride powder using a plasma spray method. , and a thin film-like second electrode formed on the solid electrolyte layer.