JPH0426700B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for manufacturing a gas detection element and a temperature compensation element used in a catalytic combustion type gas sensor.

[Conventional technology]

As shown in FIG. 3, the gas detection element used in the catalytic combustion type gas sensor is made of a hot wire 10 made of a coiled wire made of a material with a high temperature coefficient of resistance, such as platinum.
is coated with a carrier 12 such as activated alumina, and a catalyst with excellent oxidation performance against combustible gases is attached to this carrier 12, and the temperature compensating element is coated with a catalyst that is inert to combustible gases. It has the same shape as a gas detection element except for the following points. In the actual sensor, as shown in FIG. 4, a bridge is formed with resistors 15 and 16 so that the gas detection element 13 and temperature compensation element 14 are located in adjacent branch paths, and the bridge is connected to the power supply 17. Element 13,1
4 and the connection point between resistors 15 and 16.

This gas sensing element and temperature compensation element are usually
It is manufactured by a method in which a carrier is attached to a hot wire and then an appropriate heat treatment is performed to fix the carrier to the hot wire. Furthermore, for gas detection elements, a method is usually used in which a carrier is fixed and then an appropriate catalyst is supported on it. A method of attaching it to the strips may also be used.

One of the methods for coating hot filaments with a carrier is a method using electrophoresis, as described in Japanese Patent Application Laid-open No. 83890/1983. Figure 5 shows an apparatus for carrying out the general method of forming a coating layer on hot wires by this electrophoresis method. An electrode 5 made of platinum or the like is immersed in the hot filament 10 to which the carrier is to be attached, and the electrode 5 and the hot filament 10 are connected to each pole of a DC power source 6 to reduce the electrical charge of the carrier powder in the dispersion medium. The carrier is attached to the surface of the hot filament 10 by applying a potential of opposite sign to the hot filament 10. This method has the advantage of being able to control the amount of carrier attached by controlling the voltage value, voltage application time, etc., making it easy to align the size of the elements, reducing variations in sensor performance, and being excellent in mass production. There is. However, although this method of forming elements by electrophoresis has the above-mentioned advantages, it also has the following manufacturing technology problems.

That is, when the apparatus shown in FIG. 5 is used as it is, the carrier will adhere to all parts of the hot wire that are immersed in the dispersion medium. however,
In an actual sensor, both ends of the hot wire need to be connected to conductive terminal rods, so these parts must not be covered with an electrically insulating carrier. Furthermore, the commonly used hot wire has a coiled shape as shown in FIG. 3, and it is desirable to attach the carrier only to this coiled portion. For this reason, when attaching a carrier to the hot wire using the apparatus shown in FIG. It is necessary to perform operations such as coating the areas on which you do not want to adhere with an electrically insulating resin film in advance, attaching the carrier by electrophoresis, and then burning and removing the insulating film by heating at a high temperature. Therefore, these methods are unfavorable in terms of mass production because they increase the number of work steps such as removing the carrier once attached and coating the insulating film.

In addition, in the above-mentioned Japanese Patent Application Laid-open No. 48-83890, a coating layer is formed on the surface of the hot filament by electrophoresis, but there is no specific method for coating only the necessary parts of the hot filament. is not described.

[Problem that the invention seeks to solve]

The problem to be solved by the present invention is that when manufacturing the gas detection element and temperature compensation element of a catalytic combustion gas sensor by electrophoresis, the carrier or the carrier with catalyst is attached only to a limited part of the hot wire. The goal is to obtain equipment that can.

[Means for solving problems]

According to the present invention, the above-mentioned problems are solved in an apparatus for manufacturing a catalytic combustion gas sensor comprising a gas sensing element and a temperature compensating element in which the surface of a hot wire is coated with a carrier or a carrier with a catalyst by electrophoresis. (1) Means for flowing slurry in which coated particles are dispersed through a dropper-shaped opening provided in the electrophoresis tank (2) Means for inserting the portion of the hot wire to be coated into the flowing slurry (3) Means for inserting the portion of the hot wire to be coated into the flowing slurry (3) The hot wire and the inside of the electrophoresis tank This problem is solved by having means for applying a DC voltage between the electrodes.

As a means for draining the slurry in the apparatus of the present invention, it is preferable to allow the slurry to fall naturally through a dropper-shaped opening.In this case, the falling speed is determined by a needle valve installed at the top of the electrophoresis tank that adjusts the amount of outside air introduced. The slurry can be controlled by the opening degree of the slurry, but in addition to this natural falling method, it is also possible to adopt a method in which the slurry is forced to flow out using a pump or the like.

Further, the shape of the slurry flowing out depends on the flow rate and the cross-sectional shape of the dropper-like opening, but shapes such as a droplet shape, a cylindrical shape, and a band shape can be used.

[Effect]

In the present invention, by forming a dropper-like narrow opening in a part of the electrophoresis tank charged with slurry, the amount of slurry flowing out from the opening is restricted, and the slurry is applied only to a limited part of the hot wire. By applying a voltage while the two are in contact with each other, the carrier or the carrier with catalyst can be attached only to the necessary portions of the hot wire.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

In FIG. 1, reference numeral 1 denotes an electrophoresis tank, which is equipped with a thin dropper-shaped opening 2 at the lower end, and a slurry inlet 3 and a needle valve 4 at the upper end. An electrode 5 is disposed within the electrophoresis tank 1, and the electrode 5 is connected to one pole of a DC power source 6.

In manufacturing, first, a slurry 7 in which a carrier or a carrier powder with a catalyst is dispersed is injected into the electrophoresis tank 1 through the slurry inlet 3 until the electrode 5 is submerged in the slurry. Next, droplets 8 of the slurry are formed in the opening 2 at the lower end of the electrophoresis tank 1, or the slurry is allowed to flow down continuously from the opening 2.
In this case, the flow rate of the slurry from the opening 2 can be adjusted by the opening degree of the needle valve 4.

Next, a metal U-shaped jig 9 is inserted into the formed droplets 8 or into the continuously flowing slurry fluid.
By inserting the part to be covered of the coiled hot wire 10 fixed above and connecting the jig 9 to the DC power source 6, the dispersed particles in the slurry 7 are transferred to the hot wire 10.
The carrier or the carrier with catalyst is attached to the desired location of the hot wire.

Note that during the electrophoretic adhesion operation, it is possible to stop the outflow of the droplets and keep the droplets stationary.
It is also possible to make the droplet fall intermittently by placing a hot wire inside the droplet that has not yet separated from the opening.

Example 1 Using the apparatus shown in FIG. 1, a slurry consisting of activated alumina fine powder, alumina sol, and water is injected from the slurry inlet 3, the inlet 3 is closed, and the needle valve 4 is operated to fill the lower end of the opening 2. formed droplets. On the other hand, both ends of a hot wire made of platinum wire with a wire diameter of 30μ, a coil outer diameter of 0.8 mm, and a number of turns of 10 are welded onto a U-shaped nickel jig, so that the coil part of the hot wire enters the inside of the droplet. set in position. In this state, a direct current voltage was applied using the hot wire as a cathode and the electrode as an anode, thereby causing carrier particles to adhere to the coil portion of the hot wire. Next, remove this hot filament from the jig,
It was heated to 800°C in an electric furnace to fix the adhered carrier particles to the hot wire. The thus obtained element had a cylindrical shape in which only a predetermined position of the coil portion 11 of the hot wire was covered with a carrier 12, as shown in FIG.

Example 2 Using the apparatus shown in FIG. 1 and using the same slurry as in Example 1, the opening degree of the needle valve 4 was adjusted so that the falling rate of droplets from the opening 2 was set to 1 per 5 seconds.
It was made to be about the size of a drop. Next, prepare the same jig and hot wire as in Example 1, install the coil part of the hot wire inside the droplet at a position that has not yet separated from the opening, and attach the coil in the same manner as in Example 1. A carrier was attached to the portion and heat treatment was performed in the same manner as in Example 1. As a result, an element having a shape similar to that shown in FIG. 2 was obtained.

Example 3 Using the apparatus shown in FIG. 1 and using the same slurry as in Example 1, the opening degree of the needle valve 4 was adjusted so that the slurry continuously flowed down from the opening 2. Next, the same jig and hot wire as in Example 1 were prepared, and they were set so that the coil portion of the hot wire was located inside the cylindrical slurry formed near the opening. A carrier was attached to the part. Note that during this operation, electrophoresis tank 1
The slurry charge and slurry flow rate were adjusted so that the electrode 5 inside was located inside the slurry during one deposition operation. The shape of the element in which the carrier was attached by continuously flowing the slurry in this manner was also the same as that shown in FIG. 2.

The area covered by the hot filament is determined by the size of the droplet or the continuously flowing fluid; for example, if the inner diameter of the opening is 0.5 mmφ, the area covered by the hot filament is determined by the size of the droplet or the continuously flowing fluid. The length is approximately 1.5mm.

〔Effect of the invention〕

The apparatus of the present invention allows slurry to flow out in the form of droplets, cylinders, or strips from a dropper-shaped opening provided in an electrophoresis tank when manufacturing gas detection elements and temperature compensation elements used in catalytic combustion gas sensors. Since this device has a means for electrophoresis and a hot wire is inserted into the inside of the flowing slurry to perform electrophoresis, droplet-like particles formed at the openings,
By adjusting the size of the cylindrical or band-shaped slurry, the area of the hot filaments covered with the carrier can be limited to a predetermined position.

Furthermore, according to the device of the present invention, it is possible to effectively utilize the inherent features of the electrophoresis method, such as less variation in element shape and excellent mass productivity, thereby improving the performance and mass productivity of catalytic combustion gas sensors. It can make a significant contribution to the

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of the device of the present invention, Fig. 2 is a partially cutaway perspective view of an element manufactured by the device of the present invention, and Fig. 3 is a part of a gas detection element generally used in a catalytic combustion type gas sensor. A cutaway perspective view, Figure 4 is a circuit connection diagram used in a catalytic combustion gas sensor,
FIG. 5 is a block diagram of a conventional device. ... Electrophoresis tank, 2 ... Opening, 3 ... Slurry inlet, 4 ... Needle valve, 5 ... Electrode,
6... DC power supply, 7... Slurry, 8... Slurry droplets, 9... U-shaped jig, 10... Hot wire,
11... Coil portion of hot wire, 12... Carrier.

Claims (1)

[Claims] 1. In a manufacturing device for a catalytic combustion gas sensor consisting of an element in which a coating layer is formed on the surface of a hot wire by electrophoresis, a slurry in which particles to be coated are dispersed is flowed out from a dropper-shaped opening provided in an electrophoresis tank. a means for inserting a portion of the hot filament to be coated into the flowing slurry; and a means for applying a DC voltage between an electrode in an electrophoresis tank and the hot filament. Manufacturing equipment.