JPH0552801A - Oxygen sensor - Google Patents

Abstract

(57) [Summary] (Corrected) [Purpose] Regarding the oxygen sensor used for measuring and controlling the atmosphere in the furnace such as carburizing and non-oxidizing treatment, the purpose is to realize an oxygen sensor that does not have harmful effects due to carbon deposition. To do. [Structure] A wire net 20 containing a catalyst for preventing carbon deposition is provided so as to cover the pores 9 and 21 for introducing the atmosphere to be measured and for burnout provided at the tip of the detection unit, and further in a direction different from the pores. A device provided with pores that can introduce the measurement target atmosphere and exhaust the burnout air to the detection unit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oxygen sensor, and more particularly to an oxygen sensor used for measuring and controlling the atmosphere in a furnace such as carburizing or nonoxidizing treatment.

[0002]

2. Description of the Related Art FIG. 3 shows a cross section of a detecting portion of a conventionally used oxygen sensor. Generally, one end of zirconia is exposed to a furnace atmosphere and the other end is a reference air (normal air). When exposed to, the oxygen that has become ionized due to the difference in oxygen concentration at both ends is transferred, and appears as an electromotive force between the electrodes at both ends.

Therefore, first, the zirconia element 1
The platinum electrode 2 is attached to the inner end and the protruding portion (only a part of which is shown in cross section in FIG. 3A), and the inner electrode 3 is provided so as to come into contact with the platinum electrode 2 in a coil shape. ..
This internal electrode 3 is placed in an air passage 4 in which reference air exists, and this air passage 4 is connected to an air hole 11 shown in FIG. This reference air hole 11 is used for the internal electrode 3
As shown in the figure, they are arranged in parallel in the alumina tube 6.

A ceramic filter 7 is provided on the outer circumference of the alumina tube 5, and an external electrode 8 functioning as a protective tube is provided on the outer circumference of the ceramic filter 7. Pores 9 are formed in the external electrode 8 and an external electrode 10 as another protective tube is fitted to fix the tip of the zirconia element 1. Reference numeral 12 is a thermocouple for measuring the temperature in the furnace, and the oxygen sensor can also measure the temperature.

In such an oxygen sensor, a standard atmosphere is supplied from the reference air hole 11 and touches the internal electrode 3 through the air passage 4. The internal electrode 3 is further connected to the platinum electrode 2. Are in contact. This platinum electrode 2
The zirconia element 1 in contact with is in contact with the atmosphere in the furnace as the measurement target atmosphere that passes through the pores 9 of the external electrode 8 and the ceramic filter 7.

Therefore, even if a slight difference occurs between the oxygen concentration in the atmosphere in the furnace and the oxygen concentration in the atmosphere, a potential difference occurs between the electrodes 3-8, and the oxygen partial pressure in the furnace can be measured by this. Can be done.

However, when such an oxygen sensor is used for a long time, the atmosphere in the furnace contains CO and hydrocarbon-based gas.

[Chemical 1] Becomes solid carbon (C) by the reaction of, and in the case of a hydrocarbon-based gas,

[Chemical 2] Similarly, solid carbon (C) is formed by the reaction due to, and this penetrates into the inside of the ceramic filter 7 through the pores 9,
Furthermore, it covers the surface of the zirconia element 1,
This makes it impossible to detect the correct oxygen concentration.

Therefore, as shown in FIG. 3 (A), burnout of solid carbon (soot) is carried out by periodically sending burnout air from the ceramic filter 7 and discharging it from the pores 9. ..

[0009]

However, in such a conventional oxygen sensor, since the tip portion of the zirconia element 1 is a blind alley, burnout cannot be sufficiently performed when carbon deposition is extremely large. Sometimes there was a problem that it had to be disassembled and cleaned.

Therefore, it is an object of the present invention to realize an oxygen sensor which does not have a harmful effect due to carbon deposition.

[0011]

In the oxygen sensor according to the present invention, a wire mesh containing a catalyst for preventing carbon deposition is provided so as to cover the pores for introducing the atmosphere to be measured and for burnout provided at the tip of the detecting portion. It is characterized by

Further, in the present invention, pores which can introduce the atmosphere in a direction different from the above-mentioned pores and which exhausts the burnout air may be provided at the tip of the detecting portion.

[0013]

In the present invention, the atmosphere to be measured is first introduced from the atmosphere introducing and burnout pores provided at the tip of the detecting portion of the oxygen sensor. At this time, the atmosphere is provided so as to cover the pores. Carbon (C) due to decomposition of CO and hydrocarbon gas in the atmosphere by the catalyst in the wire mesh
Can be prevented.

Further, in the present invention, in the unlikely event that carbon deposits and burnout is necessary, the burnout air can be exhausted from the pores and the burnout air is provided at the tip of the detecting portion separately from the pores. The burnout air can be exhausted in the other direction from the pores for introducing the atmosphere to be measured and also for burnout, so that the burnout can be performed efficiently.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a detection portion of an oxygen sensor according to the present invention. In this embodiment, a measurement target atmosphere introduction / burnout pore is provided at the tip of the detection portion of the oxygen sensor. A wire net 20 containing a catalyst for preventing carbon deposition is provided so as to cover 9. In this case, the wire net 20 need only be fitted to the tip of the detection part of the oxygen sensor.

As shown in FIG. 2B, the wire net 20 is composed of an outer wire net 20a and an inner wire net 20b.
A commercially available catalyst 22 of Ni (nickel) catalyst is placed between both of the metal nets 20a and 20b. When viewed from the front, the wire net 20 has a shape as shown in FIG.
A wire mesh with a heat resistance of mm (heat resistance temperature is about 1000 ° C) is used.

Further, as shown in FIG. 1, the pores 21 capable of introducing an atmosphere in a direction B different from the suction / exhaust direction A of the pores 9 and discharging the burnout air constitute a tip of the detecting portion. It is provided in the tube 10. For other configurations, the same configuration as the conventional example shown in FIG. 3 can be used.

When such an oxygen sensor is used in a furnace,
The atmosphere in the furnace passes through the wire net 20 and the catalyst 22 therein and is introduced into the sensor through the atmosphere introducing pores 9 and 21 of the external electrode 8. At this time, the catalyst 22 made of Ni is a hydrocarbon. Since it is used as a gas that decomposes a system gas into an endothermic reaction gas (the main components are CO 24% and H ₂ 29%), carbon (CO) generated by decomposition of CO or hydrocarbon gas in the furnace atmosphere ( It has the effect of preventing the precipitation of C).

Therefore, the atmosphere sucked from the pores 9 becomes difficult to be decomposed into carbon, and the surface of the ceramic filter 7 and the zirconia element 1 is hardly polluted.

Further, when carbon is deposited little by little and deposited until it becomes necessary to perform burnout, the burnout air can be exhausted not only from the pores 9 but also from the pores 21. In this case, the burnout direction is A
Since B and B are in different directions, carbon on the surface of the zirconia element 1 and the ceramic filter 7 can be efficiently removed.

[0021]

As described above, in the oxygen sensor according to the present invention, the wire net containing the catalyst for preventing carbon deposition is provided so as to cover the pores for introducing the atmosphere to be measured and for the burnout provided at the tip of the detecting portion, Furthermore, since the atmosphere for measurement can be introduced in a direction different from that of the pores and the pores for exhausting the burnout air are provided at the tip of the detection portion, the precipitation of carbon due to the decomposition of CO or hydrocarbon gas is prevented. As a result, a clean oxygen sensor can be realized, and burnout can be efficiently performed even if carbon is contaminated.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an embodiment of a detection unit of an oxygen sensor according to the present invention.

FIG. 2 is a view showing an example of a metal mesh containing a catalyst used in the oxygen sensor according to the present invention.

FIG. 3 is a cross-sectional view showing a conventional example.

[Explanation of symbols]

 1 Zirconia Element 2 Platinum Electrode 3 Internal Electrode 7 Ceramic Filter 8 External Electrode 9,21 Pore for Introduction of Atmosphere for Measurement and Burnout 11 Reference Air Hole 20 Wire Mesh 22 Catalyst

Claims (2)

[Claims] 1. An oxygen sensor, comprising: a wire mesh containing a catalyst for preventing carbon deposition, which covers the pores for introducing the atmosphere to be measured and for burnout provided at the tip of the detection unit. 2. The oxygen sensor according to claim 1, wherein a porosity through which the atmosphere to be measured can be introduced in a direction different from the porosity and the burnout air is exhausted is provided at the tip of the detection portion.