JPS6366450A - Gas detector and manufacture thereof - Google Patents

Abstract

PURPOSE:To add the temperature compensating function of a gas detector with a simple construction along with a reduction in the number of parts, by providing a thermosensor with a partially sintered porous gas sensing layer varying in the electric resistance according to gas components and density. CONSTITUTION:Electrode patterns 16 such as detection electrode patterns 16a, 16b and 16c and a thermal resistance electrode pattern 16e or the like are formed on a ceramic substrate 12 and a ceramic laminate plate 18 is laminated on the patterns integrally with the ceramic substrate 12. A gas sensing layer 25 mainly composed TiO2 and a thermosensor layer 24 are formed within a window 20 provided on the laminate plate 18 and a coat layer 26 made of Al2O3 is formed thereon. The sensor layer 24 is made of a TiO2 paste controlled on specified conditions which is spread to a thick film over the entire surface of the electrode pattern 16a on the cathode side from a half of the electrode pattern 16c within the window 20 and then, baked. The gas sensing layer 25 is made of the TiO2 likewise, which is spread to a thick film over the entire surface of the electrode pattern 16b from a half of the electrode pattern 16c and then baked on a condition of lessening the sintering as compared with the detecting element layer 24.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is a gas sensor that detects surrounding gas using a gas-sensitive metal oxide whose resistance value changes depending on the concentration of a specific gas component. The present invention relates to a detector and a method for manufacturing the same.

[Prior Art] Conventionally, as this type of gas detector, there is an oxygen sensor as shown in cross section in FIG. 10, for example.

That is, the oxygen sensor 50 has a pair of electrodes 54 a on the ceramic substrate 52 ! 54 b, a ceramic laminate 60 having a window 58 is laminated on the substrate 52 , and T i O 2 is mainly deposited so as to remove @fffi 54 a and 54 b and to close the window 58 . It is a stack of gas-sensitive layers 62 as components, and the electrical resistance of the gas-sensitive layers, which changes depending on the surrounding M partial pressure, is detected between electrodes.

Furthermore, in the conventional vi sensor, the detection level of the gas-sensitive layer varies depending on the temperature even if the gas concentration is the same, so a heater is provided on the ceramic substrate as a means to compensate for this.

A device is known in which the amount of electricity supplied to the heater is controlled so that the oxygen sensor reaches a predetermined temperature based on the temperature detected by a thermistor provided separately from the oxygen sensor.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional technology, since a thermistor that is incorporated separately from the oxygen sensor is used, the number of parts increases, the configuration becomes complicated, and manufacturing is troublesome. There was a problem that.

The present invention was made in order to solve the problems of the above-mentioned conventional technology, and an object thereof is to provide a gas detector that has a small number of parts, a simple configuration, and is easy to manufacture, and a method for manufacturing the same. shall be.

[Means for Solving the Problems] The first invention, which has been made to solve the above problems, comprises a plurality of Ttj electrodes, which cover these electrodes, contain gaseous metal oxides, and which contain gaseous metal oxides. a porous angry gas layer whose electrical resistance changes depending on the components and/or gas concentration, and a temperature detection element is provided by sintering a part of the gas sensitive layer. The gist is the vessel.

Further, the second invention for manufacturing the above-mentioned gas detector includes providing at least three electrodes, covering two of these electrodes with a gas-sensitive metal oxide, and heating and baking the electrodes. forming a temperature sensing element by covering a part of the electrode and/or another electrode with the same material as the gas-sensitive metal oxide;
The gist of the present invention is a method for manufacturing a gas detector, characterized in that an angry gas layer is formed by heating and firing under conditions that cause less sintering than the heating and firing of the temperature sensing element.

Furthermore, the third invention as another manufacturing method provides a porous gas-sensitive material that includes a plurality of electrodes, contains a gas-sensitive metal oxide, and has an electrical resistance that changes depending on gas components and/or gas temperature. The object of the present invention is to provide a method for manufacturing a gas detector, which comprises covering the plurality of electrodes with a layer and applying current between the electrodes so as to convert a part of the gas-sensitive layer into a temperature detection element.

Here, the above-mentioned electrode may be any conductive material that can withstand the firing process, but it is usually made of a material mainly composed of silver, gold, or a platinum group metal.

The transition metal oxide used in the gas-sensitive layer changes depending on the gas component to be detected.
Ti03SnOz, Coo,
Examples include ZnO, Nb2O5, and Cr20t, and in the present invention, it is preferable to use any one or a combination of two or more of these materials.

In addition, for the purpose of protecting the gas-sensitive layer, a coating layer may be provided on the gas-sensitive layer or the upper layer. This coating layer adsorbs and captures toxic substances such as lead on gas-sensitive metal oxides. Is it toxic? Prevents A-kan from reaching the gas-sensitive layer. The material of the coating layer is not particularly limited as long as it is thermally stable, and for example, alumina, magnesia spinel, zirconia, etc. can be used.

As one of the means for forming a part of the gas sensitive layer, in the second invention, a temperature sensing element is formed by changing the heating and baking conditions of the same gas sensitive metal oxide as the gas sensitive layer, Further, in the third aspect of the present invention, a part of the gas-sensitive layer is fired by applying electricity between electrodes in the gas-sensitive layer, thereby forming a temperature detection element.

[Function] In the gas detector of the present invention, when a gas comes into contact with the gaseous gas layer, the electrical resistance of the gaseous gas layer changes depending on the gas concentration, and this resistance change is detected between the electrodes to determine the gas concentration. Measure changes in

Further, since a part of the angry gas layer of the gas detector of the present invention is formed on the temperature detection element, based on the detected temperature from this temperature detection element, for example, a heater formed integrally with the gas detector Pass to Ttit.

Temperature compensation can be performed by controlling the temperature of the gas detector to set the temperature of the gas detector to a predetermined temperature.

Then, as a method for forming a part of the gas-sensitive layer into a temperature detection element, we focused on heating and baking a gas-sensitive metal oxide, and first, in the second invention, we developed a method for forming a gas-sensitive metal oxide. The angry gas layer and the temperature detecting element are formed by changing the firing temperature and time, and in the third invention, the temperature detecting element is formed by sintering a part of the gas sensitive layer by heating with electricity.

[Effects of the Invention] As explained above, according to the present invention, since the temperature detection element is formed in a part of the gas-sensitive layer, the number of parts is small and the temperature of the gas detector can be determined with a simple configuration. A compensation function can be added.

Moreover, in the method for manufacturing a gas detection element, a temperature detection element is formed by heating and firing a part of the angry gas layer by changing the heating and firing conditions for the angry gas layer, and by heating and firing a part of the angry gas layer by heating and firing it with electricity. Since the detection element is formed, manufacturing is also easy.

[Example] An example of the present invention will be described using the drawings. Note that the scales of each figure are different for explanation purposes.

First, one embodiment of the present invention will be described with reference to FIG.

This embodiment is an oxygen gas detector 10 using T i O2 as the gas-sensitive layer.

As shown in the partially broken perspective view of FIG. 1, terminals 13a and 13b are provided on the ceramic substrate 12.

Platinum lead 1 with 13c and ’13e! 14a and 14b.

Electrode pattern 16 connected to 14c, 14e
a.

Electrode patterns 16 such as 16b, 16C1 and a heat resistance electrode pattern 16e are formed, and the ceramic substrate 1 is further formed on the ceramic substrate 12 and the electrode pattern 16.
Ceramic 8 integrated with 2! Laminated plates 18 are laminated.

A window 20 is formed in this ceramic laminate 18, and inside this window 20, a sensitive gas Ni 25 whose main component is TiO2 and a temperature detection element layer 24 are formed (second (Figure), spherical granulated particles 22 are interposed between the gas-sensitive layer 25 and the temperature-detecting element N24 and the ceramic substrate 12 to prevent swordplay between the two.

Furthermore, a coating layer 26 made of Ag2O3 is formed on the angry gas II 25 and the temperature detection element layer 24.

Next, the manufacturing process of the oxygen gas detector 10 will be explained with reference to FIGS. 3 to 7.

(2) 92 vt% alumina, 3 vt% magnesia, and 5 wt% sintering aids (silica, calcia, etc.) are mixed in a bot mill for 20 hours. fL To the mixture were added 12 wt% polyvinyl butyral and 4 vt% dibutyl phthalate as organic binders, and methyl ethyl ketone, toluene, etc. as solvents. In addition, 1 in Botmill
The mixture was mixed for 5 hours to form a slurry, and a double green sheet 12A18A for substrates and II was formed by a doctor blade method.

The shape of the green sheet above is board green sheet 1.
47.8mmX4.0mmX0°8mm' for 2A, 47.8mmX4.0mmX for 18A green sheet for lamination
0. It is 26mm'. Then, 3. A window portion 20 of 0.05 mrn×2.0 mm is formed.

■Next, platinum black and spongy platinum were mixed in a ratio of 2:1, and 10vt% of the green sheet material mixture used in (■) above was added, and a solvent such as butyl calpitol and ethocel was added. and use it as an electrode paste.

(2) Next, the electrode pattern 16 is formed on the substrate green sheet 12A by thick film printing using the electrode paste prepared in (2). As described above, the electrode pattern 16 is the electrode pattern 16a.

16b, 16c, and gas sensitive 1!25 and temperature detection element/! A thermal resistance electrode pattern 16e serving as a heater for heating the pattern 16 and terminal patterns 13a, 13b, 13c, and 13e serving as each terminal of the pattern 16 are formed (FIGS. 2(A) and 2(B)).

(2) After that, the terminal patterns 13a and 13b.

Connect platinum leads 1114a, 14b, 14c, and 14e with a diameter of 0.2 mm to 13c and 13e, respectively (FIGS. 4(a) and 4(b)).

■ Next, place fIN on the board green sheet 12A.
The green sheet 18A layer is thermocompression bonded to form a laminate. At this time, the tips of the electrode patterns 16a, 16b, and 16c are exposed in the window portion 20 of the f1M green sheet 18A. Then, 80 to 150 meshes of spherical granulated particles (secondary particles) 22 made of the same material as the green sheet prepared in step (3) are dispersed and adhered in the window part 20, and then the above laminate is exposed to the atmosphere at 1500°C. The ceramic substrate 12 and the ceramic laminate 18 are integrally formed by firing in substantially the same atmosphere for 2 hours (FIGS. 5(A) and 5(B)).

When the spherical granulated particles 22 are dispersed and adhered and fired as described above, each particle 22 is dispersed on the ceramic substrate 12 to form an uneven surface.

■ Next, in the window 20 of the ceramic laminate 18,
i The temperature sensing element layer 24 and the gas sensitive Ji 25 are filled and fired with an angry metal oxide whose main component is O2.
First, the TiO2 paste is prepared.

That is, for 90 parts by weight of T i O2 powder with an average particle size of 1.2 μm calcined in the atmosphere at 1200°C for 1 hour,
10 parts by weight of platinum black was added as a catalyst, and 2 parts by weight of 3% by weight ethylcellulose was added as a binder, and these were mixed in petit rubitonyl (trade name of 2-(2-butoxyethoxy)ethanol). 300
Adjust the T i O2 paste to the viscosity of Boise.

Then, as shown in FIG. 2, this TiO2 paste is applied from the right half of the electrode pattern 16c in the window 20 to the entire surface of the electrode pattern 16a on the cathode side.
Remove the coating to a thickness of 500 μm.

Subsequently, this is baked at 1450° C. for 2 hours in the atmosphere to form the temperature detection element 1124.

Next, apply the same T i O2 paste as above to half of the electrode pattern 16c to the electrode pattern 16 on the left side in the figure.
Apply a thick film of 50 to 500A1m over the entire surface of b,
The gas-sensitive layer 25 is formed by firing at 1200°C in the atmosphere for 1 hour (Fig. 6 (a) and (b)). It's death time.

■ Next, coat/g26 on the sensitive gas ff120.
After applying a paste made of AQ203, the laminate that has undergone the above steps is left in the atmosphere at 1200° C. for 1 hour and fired (FIGS. 7(a) and 7(b)).

Next, instead of the above step (2), the temperature detection element layer 24 can be formed by performing the following process. In addition,
The other steps are almost the same as in the above embodiment.

That is, first, the same T i O2 paste as in ■,
Three electrode patterns 16a, 16b+16
Apply 50 to 500 μm thick WA on top of c. Then, it is baked at 1200° C. for 1 hour in the atmosphere.

Next, the laminate is inserted into the pipe of a propane burner, and the burner is adjusted to an atmosphere with an air-fuel ratio of λ: 0.9 and a gas temperature of 800° C., and the electrode pattern 16a is formed.

AC 20V is applied between 16c and 16c for 30 seconds. As a result, the gas-sensitive layer is sintered by self-energized heat generation between the electrode patterns, and a portion thereof is formed into a temperature-sensing element layer.

Next, regarding the oxygen senna formed by the above manufacturing method,
Its angry gas function and temperature detection function were demonstrated through the following tests.

After assembling the sample into an oxygen sensor, expose the sample to the exhaust gas of a propane gas burner.

This propane gas burner has an exhaust temperature of 350 degrees Celsius, and the air-fuel ratio changes from fuel surplus (hereinafter referred to as rich, air-fuel ratio λ = 0.9) to fuel deficiency (hereinafter referred to as lean) every second.
λ=1.1), and
The exhaust temperature is varied from 350°C to 900°C. Then, as shown in the circuit diagram of FIG. 8, the platinum lead! 1
Each electrode pattern 16 from 3a, 13bv 13c
a, 16 b.

Monitor the voltage at 16c. The resistance value between each electrode is shown in FIG. 9. In FIG. 9, curves A and B are λ=1.1 and λ
=0.9, which indicates the resistance value of the arbitrary gas Ji25, and curves C and D indicate the interelectrode pattern 16a,
16a at λ=1.1 and λ=0.9, which indicates the resistance value of the temperature detection element layer 24.

As is clear from the figure, the temperature detection element! The resistance value of 24 (Curve C9 track! ID) changes with almost the same temperature dependence as the resistance value of the angry gas layer 25 (Curve A1 track tiB), and furthermore, λ=1.1 and λ= Since it does not change much at 0°9, it has a temperature detection function.

In addition, in the above example, according to the first manufacturing method,
By changing the conditions (time, temperature) for sintering the temperature sensing element 7m24, on the other hand, according to the second manufacturing method, by changing the energization time and voltage, the temperature sensing element can be changed to a desired resistance value. Can be done.

[Brief explanation of the drawing]

Fig. 1 is a partially cutaway perspective view of an embodiment of the invention, Fig. 2 is a sectional view showing the main parts of the embodiment, and Figs. 3 to 7 are explanatory diagrams of manufacturing the embodiment. , Fig. 8 is a circuit diagram of the same embodiment, and Fig. 9C? I is a graph showing the characteristics of an oxygen sensor, and FIG. 10 is a sectional view showing a conventional oxygen sensor. DESCRIPTION OF SYMBOLS 10... Oxygen sensor (gas detector), 12... Ceramic substrate, 16a, 16b, 16cm... Detection electrode pattern, 16e... Heat resistance electrode pattern, 18... Ceramic laminate board. 20... Window portion, 24... Temperature detection element layer 25... Gas sensitive layer,

Claims (1)

[Scope of Claims] 1. A plurality of electrodes, a porous gas-sensitive layer that covers these electrodes, contains a gas-sensitive metal oxide, and whose electrical resistance changes depending on the gas component and/or the gas concentration; A gas detector, characterized in that a temperature detection element is provided by sintering a part of the gas-sensitive layer. 2. At least three electrodes are provided, two of these electrodes are covered with a gas-sensitive metal oxide, and a temperature sensing element is formed by heating and baking, and a part of the above electrodes and / or covering both electrodes with the same material as the gas-sensitive metal oxide over another electrode,
A method for manufacturing a gas detector, characterized in that a gas-sensitive layer is formed by heating and firing under conditions that cause less sintering than the heating and firing of the temperature sensing element. 3. Provide a plurality of electrodes, cover the plurality of electrodes with a porous gas-sensitive layer containing a gas-sensitive metal oxide, and whose electrical resistance changes depending on the gas component and/or gas concentration, and one of the gas-sensitive layers A method for manufacturing a gas detector, characterized in that electricity is applied between the electrodes so as to transform the part into a temperature detection element.