JP2004037362A - Manufacturing method of gas detection element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To heighten shape stability of a gas detection element and quality stability derived from the shape stability. <P>SOLUTION: A base material wherein a sensitive layer mainly composed of an indium oxide is formed on a noble metal wire coil is prepared. An electrode 2 is stretched on the bottom part of a butt 1 flatly all over the surface. Fluid dispersion S wherein alumina fine particles are dispersed in ethanol is filled in the butt 1. After dipping bridges 3B where the base material is fixed into the fluid dispersion S, a voltage is applied between the bridges 3B and the electrode 2, to thereby perform an electrophoretic process. After drying a formed coating layer, the layer is sintered at a prescribed temperature as long as a prescribed time, to thereby manufacture this gas detection element having a coating layer on the surface of the sensitive layer. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a gas sensing element in which a sensor electrode is provided with a sensitive layer made of a metal oxide sintered body, and a sensor electrode in which a sensitive layer made of a metal oxide sintered body is provided, and wherein the sensitive layer is made of fine particles. The present invention relates to a method for manufacturing a gas detection element provided with a coating layer made of a body.
[0002]
[Prior art]
Conventionally, when forming a sensitive layer of a gas sensing element or a coating layer for the sensitive layer, various manufacturing methods such as pressure molding, screen printing, dipping, physical vapor deposition (vacuum vapor deposition, sputtering), and chemical vapor deposition are applied. Have been.
Among them, pressure molding is a method in which a material is filled in a metal mold and pressure molded, and is not suitable for manufacturing a minute structure. Screen printing is an application of a printing technique, and it is possible to produce a relatively uniform and minute structure, but the shape of the structure is limited to a flat plate. In addition, since physical vapor deposition and chemical vapor deposition are thin film production methods and a layer structure production method with a thickness of 1 μm or less, they are not suitable for forming the sensitive layer or the coating layer which requires a film thickness of about 10 μm or more. There are many. Therefore, for a gas sensing element having a small and complicated shape, the fine particles to be formed with the sensitive layer or the coating layer are immersed in a dispersion liquid of the fine particle material for forming the sensitive layer or the coating layer by dipping and pulled up. A method in which a material is coated on a sensor electrode or the sensitive layer, and then the formed coating layer is dried and sintered, is widely used because a sensitive layer and a coating layer having an arbitrary shape can be formed.
[0003]
[Problems to be solved by the invention]
However, according to the above-described dipping, the thickness of the formed coating layer is difficult to be uniform, and even when the coating layer is formed on a minute base material, the thickness of the coating layer varies greatly. . In addition, the thickness of the coating layer produced in one process is about 10 μm, and if a coating layer having a thickness greater than this is required, the same procedure may have to be repeated. However, there has been a situation in which it is difficult to secure the thickness of the coating layer and the shape stability of the sensitive layer. For this reason, there is a problem that the characteristics of the obtained gas detection element are likely to vary, and the yield is reduced in order to maintain the quality stability.
[0004]
Therefore, an object of the present invention is to improve the shape stability of a gas detection element and the quality stability derived from the shape stability in view of the above-mentioned circumstances.
[0005]
[Means for Solving the Problems]
The feature of the method for manufacturing a gas detection element of the present invention for achieving this object is as follows.
A method for producing a gas sensing element, wherein a sensitive layer made of a metal oxide sintered body is provided on a sensor electrode, and the sensitive layer is provided with a coating layer made of a sintered body of fine particles, wherein the sensitive layer is provided. Electrophoresis in which a voltage is applied between the sensor electrode and the counter electrode in a state where the sensor electrode and the counter electrode are immersed in the dispersion liquid of the fine particles forming the coating layer, and the sensitive layer forms the layer of the fine particles. Performing a sintering step of sintering the formed fine particle layer to form the coating layer.
Further, it is preferable that the dispersion liquid of the fine particles is obtained by dispersing fine particles in a dispersion medium at 2 × 10 ⁻³ to 4 × 10 ⁻¹ mol / L,
Preferably, the sensitive layer is spherical.
[0006]
Furthermore, to manufacture a gas sensing element provided with a sensitive layer made of a metal oxide sintered body on the sensor electrode, in a state where the sensor electrode and the counter electrode are immersed in a dispersion of fine particles forming the sensitive layer, A voltage is applied between the sensor electrode and the counter electrode, an electrophoresis step of forming the fine particle layer on the sensor electrode is performed, and then a sintering step of sintering the formed fine particle layer is performed. , The sensitive layer may be formed.
(Function and effect)
That is, a gas sensing element in which a sensor electrode is provided with a sensitive layer made of a metal oxide sintered body, and the sensitive layer is covered, and a coating layer made of a sintered body of fine particles is provided, By contacting the sensor layer and capturing changes in the physical properties of the sensitive layer, an output corresponding to the type and concentration of the detected gas can be output through the sensor electrode. At this time, the coating layer is generally used to provide a function of removing an interfering gas component in the detection target gas or a toxic substance that deteriorates the sensitive layer, and the gas detection element is provided. It has the effect of improving gas selectivity and durability.
When forming the coating layer, the electrophoresis step is performed in a state in which the sensor electrode and the counter electrode each having the sensitive layer are immersed in a dispersion liquid of fine particles for forming the coating layer. The fine particles are evenly migrated from the dispersion liquid around the electrodes to one of the pair of electrodes according to the electric charge of the fine particles dispersed in the electrode. Here, when the fine particles are caused to migrate toward the sensor electrode, the fine particles uniformly adhere to the surface of the sensitive layer and are deposited in a layer.
Next, when a sintering step of sintering the formed fine particle layer is performed, the fine particle layers are integrated by sintering to form a breathable coating layer. At this time, since the layer of the fine particles is uniformly formed on the sensitive layer, it is possible to easily form a film having no variation.
[0007]
The function of the coating layer can be variously changed by selecting the fine particles. In addition, by appropriately setting the particle diameter of the fine particles, it is possible to set the denseness of the coating layer. Therefore, by appropriately adjusting the dispersion of the fine particles according to the physical properties required for the coating layer, various characteristics can be easily imparted to the coating layer.
Specifically, if aluminum oxide (alumina) is used as the fine particles, a protective layer can be formed, and the durability against substances causing sensor deterioration can be improved. If alumina or the like carrying a noble metal such as palladium or platinum is used as the fine particles, a catalyst layer can be formed, and the sensitivity to ethanol or hydrogen can be suppressed, and a city gas sensor having excellent methane selectivity can be obtained. As the fine particles, in addition to these, various metal oxide materials can be used, and the fine particles can be dispersed in a dispersion medium such as ethanol to form a dispersion.
[0008]
Further, when the dispersion liquid of the fine particles is obtained by dispersing the fine particles in a dispersion medium at 2 × 10 ⁻³ to 4 × 10 ⁻¹ mol / L, the fine particles are uniformly dispersed without aggregation. In addition, since a sufficient amount of fine particles can be deposited in an appropriate time, the electrophoresis step can be performed efficiently in a short time.
[0009]
In addition, when the sensitive layer is spherical, fine particles are uniformly deposited on the sensitive layer without directivity, which is advantageous for forming a uniform coating layer and greatly improves the production efficiency. Is preferred.
[0010]
Further, the sensitive layer of the gas sensing element can be formed by the same method. In other words, to manufacture a gas sensing element provided with a sensitive layer made of a metal oxide sintered body on the sensor electrode, the sensor electrode and the counter electrode were immersed in a dispersion of fine particles forming the sensitive layer, By performing the electrophoresis step, it is possible to form a coating layer that is dense and has a shape suitable for the shape of the sensor electrode without waste. Subsequently, a sintering step is performed, and when the coating layer is fired into a spherical shape to form the sensitive layer, the fine particle layer is integrated by sintering to form a breathable sensitive layer. At this time, since the fine particle layer is formed uniformly on the sensor electrode, it can be easily formed into a uniform shape with little variation.
[0011]
In the electrophoresis step, a voltage can be applied to all of the sensor electrodes and the sensor electrodes coated with the sensitive layer at the same time while the sensor electrodes are immersed in the dispersion liquid. Therefore, according to the present invention, it is possible to obtain a large number of gas detecting elements with little variation in quality with high productivity and high yield.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
(1) As shown in FIG. 2, a Teflon vat 1 is filled with a dispersion liquid S obtained by uniformly dispersing a predetermined amount of metal oxide fine particles in ethanol using a magnetic stirrer or an ultrasonic generator. Further, a platinum mesh 2 is stretched flat on the bottom surface of the bat 1.
On the other hand, the base material 3A of the gas detection element, in which the sensitive layer 32 made of a metal oxide semiconductor such as tin oxide is provided in a spherical shape on the sensor electrode made of a noble metal wire 31 made of platinum, platinum rhodium, platinum palladium, or the like, is formed. deep. The substrate 3A is a bridge 3B formed by being fixed to a fixing jig 33.
A large number of the bridges 3B are immersed in the dispersion S stored in the vat. Here, each of the bridges 3B holds the noble metal wire coil 31 through the fixing jig 33 so as to be able to conduct electricity. The bridge 3B thus held is used as a pair of electrodes having the platinum mesh 2 as a counter electrode, and a predetermined voltage is applied from the power supply 4 between the bridge 3B and the platinum mesh 2. Then, the metal oxide fine particles migrate and deposit on the base material 3A of the gas detection element by electrophoresis to form a coating layer (electrophoresis step).
[0013]
After a predetermined time, the bridge 3B is taken out of the dispersion liquid S, the coating layer is dried, and then sintered at a predetermined temperature for a predetermined time to form a coating layer 34 containing the metal oxide as a main component on the surface of the base material 3A. It could be formed (sintering step), and the spherical hot-wire type gas detection element 3 could be obtained.
[0014]
(2) When the bridge 3B to which the noble metal wire coil 31 is applied is used instead of the base 3A of the gas sensing element in the above embodiment, the sensitive layer 32 can be formed. That is, as in the previous embodiment, a bridge 3B formed by previously fixing the noble metal coil 31 to the fixing jig 33 is prepared, and the electrophoresis process is performed in the same manner as described above. It is possible to form a coating layer by depositing fine particles.
[0015]
After a predetermined time, the bridge 3B is taken out of the dispersion liquid S, the coating layer is dried, and then sintered at a predetermined temperature for a predetermined time, so that the sensitive layer 32 containing the metal oxide as a main component is formed on the surface of the noble metal wire coil 31. Was formed (a sintering step), and a base material 3A of a spherical gas detection element formed by extending a noble metal wire was obtained. The base material 3A may be used as it is as the gas detection element 3, or may further be formed with the coating layer 34 to serve as the gas detection element 3.
[0016]
Note that the bridge 3B is configured so as to be directly mounted on a gas detection circuit board and incorporated in the gas detection device, and is configured to simplify the gas detection device manufacturing process.
Example 1
As shown in FIG. 1, a base material 3A in which a sensitive layer 32 containing indium oxide as a main component is formed in a spherical shape with a diameter of 500 μm on a noble metal wire coil 31 is prepared.
An electrode made of a platinum mesh 2 is flatly spread over the bottom of the Teflon bat 1 of FIG. The Teflon vat is filled with the dispersion S in which the alumina fine particles are dispersed in ethanol to 1.3 × 10 ⁻¹ mol / L. The dispersion S is sufficiently dispersed by an ultrasonic generator or various stirrers so that the alumina fine particles are uniformly contained. After immersing the bridge 3B to which the base material 3A is fixed in the dispersion liquid S, a voltage of 15 volts is applied between the bridge 3B and the platinum mesh 2 for 3 minutes to perform an electrophoresis step. Thereafter, the bridge 3B is pulled up from the solution, and the formed coating layer is dried and then sintered at a predetermined temperature for a predetermined time to produce a gas detection element 3 having a uniform coating layer 34 having a thickness of about 80 μm on the surface of the sensitive layer. We were able to.
[0018]
A durability test was performed in which the gas detection element thus obtained was exposed to a toxic substance (silicone gas) that causes a high sensitivity of the sensor for a predetermined time. As a comparison, the durability was similarly examined for the case where the above-described coating layer 34 (coating) was not formed and the case where the coating layer 34 (coating) was formed by conventional dipping. The result is shown in FIG. FIG. 3 shows that the sensor output of the gas detection element obtained according to the present invention maintains a predetermined value even after a long-term exposure to a toxic substance, and does not tend to increase. It can be seen that the performance was greatly improved.
[0019]
Example 2
The method according to the present invention can be applied to manufacture not only one gas sensing element but also many gas sensing elements at the same time. When 200 pieces of the gas detection elements according to the above-described first embodiment were manufactured at a time, when electrophoresis was performed using the same dispersion liquid S as in the first embodiment, the gap between the bridge 3B and the platinum mesh 2 was determined. By applying a voltage of 30 volts for 15 minutes, a coating layer 34 having a thickness of about 80 μm and containing alumina as a main component could be formed on all the gas detection elements.
[0020]
Example 3
As shown in FIG. 1, a substrate 3A is prepared in which a sensitive layer 32 mainly composed of tin oxide is formed in a spherical shape with a diameter of 150 μm on a noble metal wire coil.
An electrode made of a platinum mesh 2 is flatly spread over the bottom of the Teflon bat 1 of FIG. The Teflon-made vat is filled with a dispersion liquid S in which alumina particles carrying palladium are dispersed in ethanol at 1.3 × 10 ⁻² mol / L. The dispersion S is sufficiently dispersed by an ultrasonic generator or various stirrers so that the alumina fine particles are uniformly contained. After the bridge 3B to which the base material 3A is fixed is immersed in the dispersion liquid S, a voltage of 30 volts is applied between the bridge 3B and the platinum mesh 2 for 1 minute to perform an electrophoresis step. Thereafter, the bridge 3B is pulled out of the solution, and the formed coating layer is dried and then sintered at a predetermined temperature for a predetermined time to produce a gas detection element 3 having a uniform coating layer 34 having a thickness of about 10 μm on the surface of the sensitive layer. We were able to.
[0021]
FIG. 4 shows gas sensitivity characteristics of the obtained gas detection element to methane, hydrogen, and ethanol. As a comparison, gas sensitivity characteristics were also examined for those without the coating layer 34 (coating) and those with the same coating layer 34 (coating) produced by conventional dipping. From these results, it can be seen that the coating layer 34 formed according to the present invention effectively functions as a catalyst layer for improving methane gas selectivity, and reduces hydrogen and ethanol sensitivity and improves methane selectivity while increasing methane sensitivity. You can see that you can do it.
[0022]
Example 4
In Example 3, the coating layer 34 was formed by changing the dispersoid used for the dispersion S to titanium oxide, alumina, zinc oxide, indium oxide, and cerium oxide.
The conditions of the electrophoresis process, the dispersion S concentrations, titanium oxide 1.7 × ¹⁰ -2 mol / L, alumina 1.3 × ¹⁰ -2 mol / L, zinc oxide 1.6 × 10 ^{- 2} mol / L, indium oxide: 4.8 × 10 ⁻³ mol / L, cerium oxide: 7.7 × 10 ⁻³ mol / L, titanium oxide and alumina: 30 volts for 1 minute, zinc oxide, indium oxide Cerium oxide was set at 30 volts for 10 seconds.
As a result, a coating layer 34 made of titanium oxide, alumina, zinc oxide, indium oxide, and cerium oxide having a thickness of about 10 μm was formed on the sensitive layer 32 mainly composed of tin oxide having a diameter of 150 μm.
[0023]
When the sensor outputs for various gases before and after the formation of the coating layer 34 of each gas detection element were examined, the results were as shown in FIG. In each case, it can be seen that the coating layer 34 functions as a catalyst layer and the gas sensitivity characteristics are changed. In particular, when zinc oxide is used, it can be seen that the overall sensitivity is high.
[0024]
According to the present invention, not only the production of a hot-wire type semiconductor gas detection element having a sensitive layer formed on the above-described noble metal wire coil, but also a gas sensitive portion was formed on an electrode of an alumina substrate provided with an electrode and a heater. A coating layer can also be formed on a substrate type sensor. Further, a coating layer functioning as a protective layer, a catalyst layer, or the like can be formed on the contact combustion type sensor.
In this method, as described above, it is possible to produce a gas detection element regardless of the material as long as it is powder particles charged in a solution, and also from mixed powder particles. It is easy to control the thickness of the coating layer and the density of the coating layer.
[0025]
This method is not limited to fine particles such as tin oxide and alumina, and any fine particles charged in a solution can be used regardless of the material. The fine particles used may be a mixture of various fine particles.
[Brief description of the drawings]
FIG. 1 is a partially broken perspective view of a gas detection element. FIG. 2 is a schematic view of an electrophoresis process. FIG. 3 is a graph showing the results of a toxic substance exposure test of Example 1. FIG. FIG. 5 is a graph showing the effect on gas detection characteristics due to differences in coating layers.
31 Noble metal wire coil 32 Sensitive layer 2 Electrode S Dispersion liquid 34 Coating layer 3 Gas detection element

Claims (4)

A method for producing a gas sensing element, wherein a sensitive layer made of a metal oxide sintered body is provided on a sensor electrode, and the sensitive layer is provided with a coating layer made of a sintered body of fine particles, wherein the sensitive layer is provided. Electrophoresis in which a voltage is applied between the sensor electrode and the counter electrode in a state where the sensor electrode and the counter electrode are immersed in the dispersion liquid of the fine particles forming the coating layer, and the sensitive layer forms the fine particle layer. Performing a sintering step of sintering the formed fine particle layer to form the coating layer. The method according to claim 1, wherein the dispersion liquid of the fine particles is obtained by dispersing fine particles in a dispersion medium at 2 × 10 ⁻³ to 4 × 10 ⁻¹ mol / L. The method according to claim 1, wherein the sensitive layer is spherical. A method for manufacturing a gas sensing element provided with a sensitive layer made of a metal oxide sintered body on a sensor electrode, wherein the sensor electrode and the counter electrode are immersed in a dispersion of fine particles forming the sensitive layer, A voltage is applied between the sensor electrode and the counter electrode, and after performing an electrophoresis step of forming the layer of fine particles on the sensor electrode, performing a sintering step of sintering the formed layer of fine particles, A method for manufacturing a gas sensing element for forming the sensitive layer.

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