JPH01212342A - Gas detector and preparation thereof - Google Patents

Abstract

PURPOSE:To prevent deterioration due to a change with the elapse of time, by impregnating a porous gas-sensitive layer with a solution of a compound based on a metal and precipitating a conductive material on the interface of an anode and the gas-sensitive layer by electroplating. CONSTITUTION:An electrode pattern 16 consisting of detection electrode patterns 16a, 16b and a heat resistance electrode 16e is formed on a ceramic substrate 12 and the ceramic laminated sheet 18 unified with the substrate is laminated to said pattern 16. A window part 20 is formed to the laminated sheet 18 and a gas-sensitive layer 24 based on TiO2 is formed within the window part 20. Since a conductive material (based on a platinum group metal) 16c is interposed to the interface of the electrode pattern 16a on an anode side brought into contact with the layer 24, the layer 24 and the anode 16a have a three- dimensionally with contact area. Therefore, even when oxygen deficiency is reduced in the vicinity of the anode 16a by the bias applied between the anode 16a and the cathode 16b, sufficient oxygen deficiency remains in the layer 24 brought into contact with the anode 16a. By this constitution, a rise in the resistance value between the anode 16a and the layer 24 is suppressed and the voltage signal corresponding to gas partial pressure is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention utilizes a gas-sensitive metal oxide whose resistance value changes depending on the type and/or concentration of a specific gas component. There are some related to gas detectors for detecting gas and their manufacturing methods.

[Conventional technology]

Oxygen gas detectors have traditionally been used as gas detectors to detect the presence of gas or its concentration.

Combustible gas detectors have been put into practical use.

Some of these use gas-sensitive metal oxides that have the property of changing their electrical resistance when they come into contact with gas. For example, oxides of transition metal elements such as TiO2゜Cod and NiO are a! Use as an elementary sensor! Wear.

The transition metal oxides shown here are non-stoichiometric compounds! be. The amount of charge carriers (holes, electrons) in this non-stoichiometric compound changes depending on the partial pressure of the surrounding oxygen gas. For this reason, the conductivity changes depending on the surrounding oxygen gas partial pressure.

The gas detector described above is configured as shown in FIG. 9 in order to output a change in the electrical resistance value of the gas detection element due to the partial pressure of the gas to be detected as a voltage signal. A resistor Rc is provided in series with the gas detection element, and this resistor Rc
Applying a DC voltage V to the series circuit of and gas detection element A,
The voltage Vo generated across the resistor Rc is detected as a voltage signal.

i.e. by changes in the partial pressure of the gas being measured.

When the resistance value of the gas detection element A is smaller than the comparison resistor Rc, the voltage vO generated across the resistor Re increases; conversely, when the resistance value of the gas detection element A is larger than the comparison resistance RcK, the voltage Vo increases. becomes smaller.

[Problem that the invention seeks to solve]

Tokoro 1. Since the gas detector described above uses a change in the electrical resistance of the detection element as a means of gas detection, the electrical connectivity between the gas sensitive body and the electrode is extremely important in maintaining a stable detection function. .

However, one of the above oxygen senna, for example TiO2
The sensor is in a high temperature oxidizing atmosphere! Due to the ion current caused by the bias between the cathode and the anode, the anode side f becomes deficient in Ti4+ and in excess of 02-, resulting in fewer oxygen defects. Therefore, the resistance between the anode and the TiO2 gas-sensitive layer increases, and the resistance value of the gas-sensitive layer becomes different from the initial state and deteriorates. As a result, there was a problem that an accurate voltage signal for gas partial pressure detection could not be obtained.

The present invention was made as a result of investigating the problems of the above-mentioned conventional technology! The object of the present invention is to provide a gas detector that is less susceptible to deterioration due to changes over time.

[Means for solving problems]

The above problem is caused by a pair of electrodes consisting of an anode and a cathode,
A gas detector comprising a porous gas-sensitive layer that covers the pair of electrodes and includes a gas-sensitive metal oxide and whose electrical resistance changes depending on the surrounding gas component and/or its concentration. A gas detector characterized in that a conductive material is interposed at the interface with a gas-sensitive layer, a pair of electrodes consisting of an anode and a cathode, a gas-sensitive metal oxide covering the pair of electrodes, and a gas-sensitive metal oxide in the surroundings. The gas-sensitive layer of a gas detection element, which is equipped with a porous gas-sensitive layer whose electrical resistance changes depending on the gas component and/or its concentration, is impregnated with a compound solution containing metal as the main component, and electroplated to The problem was solved by a method of manufacturing a gas detector consisting of depositing a conductive material at the interface between the anode and the gas-sensitive layer.

Here, the electrode is not particularly limited as long as it is a heat-resistant conductor; however, it is usually made of tungsten, molybdenum, gold, or a platinum group metal as a main component.

The gas-sensitive metal oxide used in the gas-sensitive layer may be selected depending on the gas component to be detected.
TiO2゜5n02. C
Transition metal oxides such as 0, ZnO, Nb2O5, Cr2O5, NiO, etc. may be mentioned, and in the present invention, any one or a combination of two or more of these may be used.

The metal used for the conductive material is not particularly limited, but metals containing platinum group metals as the main component are usually used because of their heat resistance, corrosion resistance, ease of plating, and the like.

Electroplating uses a base solution of a metal used as a conductive material as an electrolyte, and uses the electrode as an anode, which becomes the cathode of a gas detector, and the electrode, which becomes the anode of the gas detector, as a cathode, and energizes it.
K to deposit the metal at the interface between the cathode and the gas-sensitive layer
Do more. The conditions for electroplating are the commonly used conditions f.

The gas detector of the present invention can be manufactured, for example, by providing a gas-sensitive layer on a ceramic substrate using a hybrid technique such as a thick film technique. or.

A disk type or beat type 1 in which a thermistor or the like is used may be formed without using thick film technology or the like.

Furthermore, a heating element may be provided near the gas-sensitive layer for the purpose of reducing fluctuations in the temperature characteristics of the gas detector during measurement. A part of this heating element may be connected to one electrode of the gas tester to apply a voltage to the gas sensitive layer, thereby reducing the number of terminals and simplifying the measurement circuit.

Also for the purpose of protecting the gas-sensitive layer.

A coating layer may be provided over the gas-sensitive layer or the upper layer. This coating layer adsorbs and captures toxic substances such as lead on the gas-sensitive metal oxide and prevents the toxic substances 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.

[For production]

In the gas detector of the present invention configured as described above, when a high bias is applied between the anode and the cathode at high temperatures, an ionic current is generated in the gas-sensitive metal oxide forming the gas-sensitive layer by K. As a result, the metal oxide near the anode becomes deficient in metal ions and in excess of oxygen, and the number of oxygen defects near the anode decreases.As a result, the internal resistance on the anode side increases.

Due to the conductive material present at the interface between the gas-sensitive layer and the anode, the gas-sensitive layer and the anode have a large three-dimensional contact area. Sufficient oxygen defects remain in the contacting gas-sensitive layer. This suppresses an increase in the resistance value between the anode and the gas-sensitive layer, and provides a voltage signal corresponding to the gas partial pressure. As a result, accurate detection of gas partial pressure can be carried out. [Example] The present invention will be specifically explained below with reference to Examples.

However, the present invention is not limited to this embodiment only.

Example Embodiments of the present invention will be described using the drawings. In addition.

For illustration purposes, the scale of each figure is different.

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

This embodiment is an oxygen gas detector 101 using TiO2 as a gas-sensitive layer.

As shown in the partially broken perspective view of FIG. 1, on the ceramic substrate 12 are detection electrode patterns 16a, 16b and a thermal resistance electrode 16e connected to platinum lead wires 14a, 14b, 14eK through terminals 15a, 13b, IAe. An electrode pattern 16 is formed on the ceramic substrate 1.
A ceramic laminate 18 integrated with the ceramic substrate 12 is laminated on the ceramic substrate 2 and the electrode pattern 16.

A conductive material 16c is interposed at the interface of the anode-side electrode pattern 16a in contact with the gas-sensitive layer 24 among the electrode patterns 16.

A window 20 is formed in the ceramic laminate 18, and a gas-sensitive layer 24 containing TiO2 as a main component is formed within the window 20. Spherical granulated particles 22 are interposed between the gas-sensitive layer 24 and the ceramic substrate 12 to prevent them from peeling off.

The gas-sensitive layer 24 supports a catalyst made of Pt and Rh precious metal catalysts. Further, on the gas-sensitive layer 24, A
A! A coat layer 26 made of 203 is formed.

Next, the manufacturing process of the oxygen gas detector 10 will be explained according to FIGS. 2 to 6.
%, magnesia, 5 wt%, and sintering aids (silica,
5 wt% of calcia, etc.) was mixed in a bot mill for 20 hours. Thereafter, 12 wt% of polyvinylzotellal and 4 wt% of dizotyl phthalate were added to the mixture as an organic binder.
t%, remove the solvent, and add methyl ethyl ketone, toluene, etc. Furthermore, green sheets 12A and 18A for substrates and for lamination are formed by a doctor blade method.

The shape of the green sheet above is the green sheet for substrates)
12 Affi47.8 mmX 4. OmmX O,
8mmt, green sheet for lamination 18Affi47.8
ynmX4.0mmX0.26mm'-T! be. Sleigh, Te, for the above MN/! j -y sheet 18 A&
C&05mmX2. A window portion 2o of 0 mm is formed.

■ Next, mix platinum black and striped platinum at a ratio of lk 2:1, add 10 wt% of the green sheet material mixture used in step (■) above, and add solvents such as decyl carbitol and ethocel. In addition, it is used as a paste for electrodes.

(2) Next, by thick film printing using the electrode paste prepared in (2), turns 16 are formed at the electrodes on the substrate green sheet 12A. As described above, the electrode pattern 16 includes the detection electrode nozzle turn 16a.

16b and a heat resistance electrode pattern 16e serving as a heater for heating the gas-sensitive layer 24, and both of the putters 716.
Terminal patterns 13a and 15b serve as terminals.

13e (Fig. 2 (a), (b)).

■ After that, the above terminal pattern 13ae '3b*1
3e, platinum leads 14a, 14b with a diameter of 0.2m+n
, 14e (Fig. 6 (a), (b))
.

(2) Next, the laminating green sheet 18A is laminated and thermocompressed onto the substrate green sheet 12A to form a laminate. At this time, the window portion 2 of the laminating green sheet 18A is
0, the tips of the detection electrode patterns 16a and 16b are exposed. and.

After dispersing and adhering 80 to 150 meshes of spherical granulated particles (secondary particles) 22 made of the same material as the f-adjusted green sheet into the window portion 20, the laminate was
Calcinate for 2 hours in an atmosphere that is almost the same as ℃1 air.K
Thus, an integrated ceramic substrate 12 and ceramic laminate 18 are formed (FIGS. 4(a), (b), and (c)).

When the spherical granulated particles 22 are dispersed and adhered as described in 5 and fired, the particles 22 are dispersed on the ceramic substrate 12 to form an uneven surface.

■ Next, Ti is placed inside the window 20 of the ceramic laminate 18.
A gas-sensitive metal oxide whose main component is O2 is to be filled, but first a TiO2 paste is prepared.

That is, 2 parts by weight of 3 parts by weight of ethyl cellulose as a binder are added to 100 parts by weight of TiO2 powder with an average particle size of 1.2 μm calcined at 1200°C for 1 hour in the air, and these are mixed with butycarpitol. (trade name of 2-(2-cytoxyethoxy)ethanol) and 3
A TiO2 paste is prepared with a viscosity of 0.00/ise.

Then, this TiO2 base is coated to a thickness of 200 to 500 μm on the electrode patterns 16a and 16b within the window portion 20 (FIGS. 5(a) and 5(b)).

Next 1. Fire in the air at 1200°C for 12 hours.

(2) Next, 16 cft of conductive material 2 is formed at the interface between the gas-sensitive layer 24 and the anode 16a.
:2oo#/l) to 2.0μ! , dripped onto the gas-sensitive layer 24, and using a 507FLA constant current power source, energized for 10 seconds using the anode 16a as the cathode and the cathode 16b as the anode,
Pt in the chloroplatinic acid aqueous solution impregnating the gas-sensitive layer 24
2+ ions are electrolytically deposited on the anode 16a using the cathode, and a conductive material 16c is formed at the interface of the electrode 16a. According to this method, the amount of the conductive material 16C is completely defined by the current value during electrolysis x electrolysis time = total amount of electricity, and can be kept constant without variation.

The gas-sensitive layer 24 on which the conductive material 16c has just been formed is washed with water to remove the remaining chloroplatinic acid aqueous solution, and then heated to 150°C.
Dry for 10 minutes.

(2) Next, a catalyst is supported on the gas-sensitive layer 24, and a mixed aqueous solution of chloroplatinic acid and chlororhodic acid prepared to have Pt:Rh=io:1 (total catalyst amount 2oo) is used.
m//) was dropped onto the gas-sensitive layer 24 at 1.0 μE.

Next, the catalyst is thermally decomposed at 600°C for 1 hour in the atmosphere to uniformly disperse and support the catalyst.
After applying the paste consisting of 12o3, the laminate which has undergone the above steps is left to stand in the atmosphere at 1200° C. for 1 hour and fired (FIGS. 6(a) and 6(b)).

Internal resistance RT of the gas detector 10 created in this way
is first measured in a Pro-A burner with a gas temperature of 350° C., with the air-fuel ratio set to λ=0.9. The method for measuring this internal resistance RT is to apply a voltage of +12V to the lead wire 14e,
Connect lead wire 14a to ground - P wires 14a and 14
A resistor of 50KO is connected between the This is K
The data thus obtained is called "initial data."

Next, in order to examine changes over time in the gas detector of the present invention, a durability test of the gas detector was conducted. First, 1 lead wire 14 in the atmosphere
Apply a voltage of +20V to the lead wires 14b and 1.
Connect 4e to ground, 100100 at about 1000℃
The interstitial gas layer 24 is heated. After heating, the internal resistance RTf of the gas detector 10 is
Measure t. The data obtained in this way is referred to as "post-endurance data." As a comparison of this initial data and post-durability data, Table 1 shows the results of the examples of the present invention and comparative examples.

Table 1 (Note)-1: A conductive material is not formed on either the anode 16a or cathode 16b interface.

rV&lL2. A conductive material is also formed at the interface between the anode 16a and the cathode 16b.

3. A conductive material is formed only on the interface of the cathode 16b - NlX4. 6 In which the conductive material is formed only on the interface of the anode 16a 6 As is clear from Table 1, Example f of the present invention in which the conductive material is formed only on the interface of the anode 16a has a high internal resistance RT after durability.
There is no change at all. As a result, the voltage signal for detecting the gas partial pressure can be obtained accurately even after the durability test, with no change from the initial state.
' On the other hand, in Comparative Example f, the change in internal resistance RT after durability was remarkable.
N11L3 formed only at the b interface shows the largest change (50 times the initial value). NCL1 where conductive material is not formed on either the anode or cathode, N[L2 where conductive material is formed on both
Although the absolute value of RT is different, the rate of change after durability is both 1.
0 times 1 equal. In other words, it is shown that even if the conductive material is uniformly formed on both the anode and cathode, it is not possible to suppress changes after durability.

Furthermore, in order to more clearly confirm the above-mentioned effects of the invention, the inventors conducted the following experiment.

That is, as shown in FIG. 7, the buried electrode aott made of a platinum wire of 0.1 f1 is provided at a position equidistant from the anode side electrode pattern 16a and the cathode side electrode pattern 16b in the gas sensitive layer 24. The internal resistance R■ between this buried electrode 80 and the electrode pattern 16a on the anode side and the buried electrode 80
The internal resistance Rθ between the electrode pattern 16b on the cathode side and the electrode pattern 16b on the cathode side was measured in the same manner as in the above experiment, and the change in resistance value at the initial stage and after durability was measured.

The data obtained by this measurement is shown in Figure 2g8.

Solid line in Figure 8! What is shown is the change in internal resistance RT between the electrode pattern 16a on the anode side and the electrode pattern 16b on the cathode side, and what is shown with a dashed line is the change in the internal resistance RT between the buried electrode 80 and the electrode pattern 16a on the anode side. What is shown by the dotted line 1 is the buried electrode 80.
There is a change in the internal resistance Re between the electrode and the cathode side turn 16b.

As is clear from FIG. 8, the increase in internal resistance RT due to the durability test is due to the increase in internal resistance R on the anode side.

That is, in the first embodiment of the present invention in which the conductive material 16c is formed at the interface between the anode side electrode pattern 16a and the gas-sensitive layer 24, the increase in the internal resistance R(E) on the anode side is small, and therefore the overall internal resistance RT is small. The increase is also small.

Thereby, a detection signal corresponding to the partial pressure of the gas to be measured can be extracted, and the gas partial pressure can be detected accurately.

〔Effect of the invention〕

As detailed above, in the gas detector of the present invention,
11 A conductive material is formed at the interface between the anode and the gas-sensitive layer.
There is little change in the internal resistance between the two electrodes over time. Therefore, it is possible to extract a voltage signal corresponding to the gas partial pressure that does not change at all times, and it is possible to accurately detect the gas partial pressure.

[Brief explanation of the drawing]

' Figure 1 is a partially cutaway perspective view of a gas detector of the present invention, and Figures 2 to 6 are diagrams showing the assembly procedure of the gas detector. (A) is a front view, (B) is an end view taken along the line A-A, (/ is a detailed view of the main parts, Figure 7 is an explanatory diagram showing the method for measuring the internal resistance of each electrode, and Figure 8 is a durability test. A graph showing changes in internal resistance in Figure 9 is an electrical circuit diagram showing a conventional gas detector. 10...Gas detector 12...Ceramic substrate 16a...Anode) turn 16b:-・Cathode noso turn 16c... Conductive material 16e... Heat resistance electrode (6 others) M 1 Figure 2 Figure 3 Ward (a)
(b) (b)
(b) A-A sweetfish product I! I
Egoro Kosho No. 4
5 Figure 6 Figure 6 (c) Figure 7 Figure 8 Figure 9

Claims (2)

[Claims] (1) A pair of electrodes consisting of an anode and a cathode, and a porous material covering the pair of electrodes that contains a gas-sensitive metal oxide and whose electrical resistance changes depending on the surrounding gas component and/or its concentration. 1. A gas detector comprising a gas layer, characterized in that a conductive material is interposed at the interface between the anode and the gas-sensitive layer. (2) A pair of electrodes consisting of an anode and a cathode, and a porous material covering the pair of electrodes that contains a gas-sensitive metal oxide and whose electrical resistance changes depending on the surrounding gas component and/or its concentration. A gas detector comprising: impregnating a gas-sensitive layer of a gas-sensing element with a compound solution containing metal as a main component, and depositing a conductive material at the interface between the anode and the gas-sensitive layer by electroplating. manufacturing method.