JPS58210560A - Oxygen concentration detector - Google Patents

Abstract

PURPOSE:To obtain a detector capable of preventing perfect leakage of O2 from a place other than an O2 diffusion hole to a space of the closed end of an element, by providing a plug and a filler having the same quality as the element between the closed end and the opened end of the cup-shaped element made of an oxygen ion conductive ceramic. CONSTITUTION:A cup-shaped element 7 is made by an oxygen ion conductive ceramic consisting of 95mol. ZrO2 -5mol. Y2O3. An O2 diffusion hole 16 is bored at the closed end of the element 7 from the outside and Pt electrodes 10, 10, 11, 11 are provided on the inner and the outer sides of the element and lead Pt pastes 14, 15 are connected to respective inside electrodes 10, 11 and also, lead Pt wires 12, 13 are connected to respective outside electrodes 10, 11. A temporarily calcined plug 8 having the same quality as the element is placed between the closed end and the opened end and the regular calcination is carried out after pouring a ceramic filler 9 which is solidified by the calcination of Al2O3, etc. on the plug 8. In this manner, a highly reliable oxygen concentration detector is obtained without leaking gaseous O2 into a space of the opened end part from a place other than the hole 16.

Description

[Detailed description of the invention] The present invention relates to an oxygen concentration detector.

Conventionally, as this type of oxygen concentration detector, Japanese Patent Application Laid-Open No. 56-1
There is one disclosed in Publication No. 30649. This is the first
It has the structure shown in the figure. To explain this,
1 is a pellet-shaped oxygen ion conductive ceramic such as Z
It is an element made of rO-Y2O3, has PT electrodes 4 on both sides, and has a sealing material 3 attached to both ends of a hollow ceramic tube 2, such as glass frit or ceramic glue.
It is sealed. 5 is a PT lead wire, one of which is connected to the outer electrode 4 and the other connected to the inner electrode 4 through a small hole (not shown) made in the ceramic tube 2. 6. is a small hole provided to enable the diffusion movement of 02 between the inside and outside of the ceramic tube 2, and has a diameter of, for example, about 10-1.

In FIG. 1, the two cells (electrode 4 and element 1) provided at both ends of the ceramic tube 2 have different functions, one being a solid electrochemical pump operation cell P and the other being a solid electrochemical sensor cell S.

That is, P discharges oxygen (hereinafter abbreviated as 02) from inside the ceramic tube 2 through the element 1 due to the flow of the pump operating current 1p, and as a result, S is the 02! A concentration electromotive force Vs is generated due to the difference in partial pressure. Now,
When 1p at P is forced to flow, an equilibrium is achieved between the amount of Ox that is pumped out of the tube 2 by the pumping action and the amount of O2 that diffuses into the tube 2 through the small hole 6. At that time, the electromotive force (Vs) generated in S is the external field 02 partial pressure PQ of tube 2
, Vs= (R↑/4F) i n (PI/PV) from Nernst's equation using the 02 partial pressure pv in 12
It is expressed as (Formula 1). On the other hand, 1p has a small hole 6
1p=tb, (PA PV) (Equation 2) with the coefficient σL representing the characteristics of 0 diffusion. From the above two equations, 1p=P4σL(1-exp (-4FVs/RT)
) (Formula 3) holds true, so Ip that keeps Vs constant has a linear relationship with PA at a constant temperature, and the external partial pressure PA can be detected by measuring 1p. If the voltage is kept constant at 15 mV, the ambient temperature is kept constant at 800° C., and nitrogen gas is used as the carrier gas, the result will be as shown in FIG.

In this way, in the conventional device, there is an equilibrium state between the amount of Ox jt that diffuses into the ceramic tube 2 through the small hole 6 of the ceramic tube 2 and the amount of Ox jt that is discharged to the outside of the ceramic tube 2 through the inside of the element 1. is used.

Therefore, unless 02 is prevented from diffusing into the ceramic tube 2 from other than the small hole 6 of the ceramic tube 2, the characteristics shown in FIG. 2 will fluctuate and the O2 concentration cannot be detected accurately. .

For this reason, the ceramic tube 2 is manufactured so as not to have pores, but since the element 1 is bonded to the ceramic tube 2, the ambient temperature conditions may be such that rapid cooling/heating cycles are repeated. If the temperature is as high as, for example, 900° C., the sealing material 3 sealingly joining the element 1 and the ceramic tube 2 may deteriorate or crack, resulting in a seal failure. Further, sealing defects are likely to occur depending on the manufacturing process. Therefore, due to poor sealing, unnecessary Oz will be diffused into the ceramic tube 2, resulting in variations in characteristics.

Therefore, the present invention has been devised in view of the above points, and its purpose is to prevent unnecessary diffusion of 02.

The present invention will be explained in detail below using specific examples. Third
In the figure, reference numeral 7 denotes an element made of an aS ion-conducting metal oxide in the shape of a knob, for example, 95 moles of ZrO-5 moles of Yz03. Note that the element 7 has an outer diameter of 6N and a wall thickness of 0.
It has dimensions of about 6ms+ and total length IQms. Reference numeral 8 denotes a cylindrical ceramic plug made of the same material as the element 7 and shaped so as to come into close contact with the element 7 during pre-firing. Reference numeral 9 is a filler made by pouring powder slurry of the same material as the element 7 and hardening it by firing to further strengthen the seal between the plug 8 and the element 7 and to secure the inner lead wire as described later. 10
．． Reference numeral 11 denotes a porous electrode formed by applying and baking PT paste, and is provided on the inside and outside of the element 7, and the electrodes 10 and 11 of each pair are semicircular in shape so as not to short-circuit. 12.13 is a PT metal lead wire, and the above electrode 10.1
It is connected to the outer electrode portion of No. 1 by an inorganic adhesive. 1
4.15 is a lead portion, which is formed by applying and baking PT paste. This lead part 14.1
5 is electrically connected to the inner electrode portion of the electrode 10.11 and to the lead wire 17.18. Reference numeral 16 denotes an oxygen diffusion hole having a diameter of, for example, about 0.2 fl provided to measure the diffusion movement of O2 between the inside and outside of the element 7. The lead wires 17 and 18 are made of PT gold metal.

Next, a method for producing each of the above-mentioned components will be outlined. At the same time as the element 7 is molded, the diffusion holes 16 are integrally molded into the element 7. At this time, the element 7 is temporarily fired. Next, 'J'1 paste of each electrode 10.11 and PT paste of lead portion 14.15 are applied to the element 7, and lead wires 12.13.17.18 are arranged. A pre-fired ceramic plug 8 is placed inside the element 7 in advance, and a slurry, which is the precursor of the filler 9, is poured above the ceramic plug 8. Then, the whole is fired. Note that the ceramic stopper 8 in particular needs to be brought into close contact with the element 7;
It is preferable that both materials are made of the same material and have the same shrinkage rate upon firing.

According to the above configuration, the electrode 11 and the element part therebetween constitute a solid electrochemical sensor cell S, and the electrode 10 and the element part therebetween constitute a solid electrochemical pump operating cell P.

Since the operation of each cell is the same as that of the conventional example shown in FIG. 1, the explanation will be omitted.According to this embodiment, the element 7 is shaped like a pot, and the outside of the element 7 is exposed to the gas to be measured. Due to the structure, the diffusion of 02 takes place only through the diffusion hole 16, and therefore an unnecessary amount of Oz is removed from the gas to be measured into the element 7.
There is no way to enter space A through . On the other hand, the inside of the element 7 is sealed with a ceramic plug 8 to prevent Oz from entering from the atmosphere side.

Therefore, there is no seal leakage other than the diffusion hole 16, and the characteristics shown in FIG. 2 do not change.

FIG. 4 shows a structure in which the present invention is applied to an automobile. Referring to FIG. 4, the same reference numerals as those shown in FIG. 3 indicate the same components. Incidentally, in this example, the element 7 has a stepped structure at its middle portion, and is supported by the metal housing 19 at that portion. A ring-shaped metal packing 2o, talc powder 21, an asbestos plate 22, and a caulking ring 23 are arranged between the housing 19 and the element 7, and by cold caulking the upper end of the housing 19, the two are made from strong to airtight. Fixed.

In order to electrically suspend the metal lead wires 12, 13 from the housing 19, the entire outer periphery of the element 7 is coated with a porous ceramic coating layer 24 formed by plasma spraying. Note that the coating layer 24 makes the electrode 10.1
The exhaust side of No. 1 can be protected.

A mounting flange 25 for fixing to an exhaust pipe is welded to the outer periphery of the housing 19, and a protective cover 26 with a number of holes 26a is provided at the lower end of the housing 19.
is fixed by welding.

In the example shown in FIG. 4, lead portions 27 and 28 are formed on the outside of the element 7 up to its upper end, so that the electrodes 10 and 11 are electrically connected to the metal lead wires 12 and 13, respectively. There is.

According to the above embodiment, the ceramic plug 8 is made of the same material as the element 7, but the shrinkage rate is slightly lower than that of the element 7 in order to make the ceramic plug 8 tightly adhere to the element 7 due to shrinkage due to firing of the ceramic plug 8. The ceramic stopper 8 may be made of a ceramic material. For example, as element 7, 95 mol Zn0z
-5 mol Y203, ceramic stopper 8 has 25 mol Z
n0z -75 mol Yz03 may also be used.

Furthermore, the ceramic filler 9 is AlzO3゜A i! 2
03 S'i 02. Any material may be used as long as it is solidified by firing, such as Aβ-Oj-MgO. Furthermore, a glass frit can be poured onto the filler 9 to enhance sealing performance.

As detailed above, according to the present invention, by employing a kelp-shaped element and a ceramic plug, seal leakage does not occur, and therefore, the characteristics can be made more stable than in the past. .

[Brief explanation of drawings]

FIG. 1 is a partial sectional perspective view showing a conventional example, FIG. 2 is a characteristic diagram for explaining the conventional example, FIG. It is a sectional view showing an example of application. 7...Element, 8...Ceramic stopper, 10.11...
- Electrode, 16...diffusion hole. Representative Patent Attorney Takashi Okabe・'I) 1 Figure J Figure 3 'j+': 4. 11! J

Claims (1)

[Claims] A cup-shaped element made of oxygen ion conductive ceramic with one end open and the other end closed, two sets of electrodes provided on the inside and outside of the closed end of the element, and the electrode on the inside of the element. a ceramic plug that is arranged except for a portion where the element is provided and seals the open end, and a space formed between the inside of the closed end side of the element and the ceramic plug is opened to the outside of the element. an oxygen concentration diffusion hole provided in the element, the one set of electrodes and the element part between the electrodes are made into a solid electrochemical sensor cell, and the other set of electrodes and the element part between the electrodes are made into a solid electrochemical sensor cell. Oxygen concentration detector used as a pump operation cell.