JPH01227956A - Oxygen sensor - Google Patents

Abstract

PURPOSE:To obtain an oxygen sensor which operates surely at a sufficiently high response speed at a low temp. by providing perovskite type composite oxide electrodes expressed by the specific formula on the surface of an oxygen ion-conductive solid electrolyte. CONSTITUTION:The oxygen ion-conductive solid electrolyte formed by adding calcium oxide to cerium oxide is used as a sensor element 1. The mixture prepd. by dissolving the perovskite type composite oxide which is expressed by the formula and is pulverized to <=1mum with an org. solvent such as turpentine oil to form the paste thereof and further mixing a small amt. of n-butyl acetate as a diluent with such paste is applied on the inside and outside surfaces of the solid electrolyte element 1 and is sintered at 800 deg.C in air to form the electrodes 3. The solid electrolyte element 1 is mounted to an alumina ceramics pipe 2 and the juncture thereof is sealed with silver. The oxygen sensor produced in such a manner is operatable at 200-300 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an oxygen sensor that is suitable for combustion control such as gas processing and can operate down to low temperatures.

[Conventional technology]

Conventionally, this rR element sensor of Haji is a modified ion specialized Z
Those using solid ``WL analysis'' called stabilized zirconia of r02-Y2O2 yarn and Zr0l-CaO yarn.

This method uses a bokamono half-body consisting of a non-curved and wrinkled composition with several missing lines, such as TiOx-a.

The solid-state*S type plate cable sensor uses a solid-state battery
There are two types of methods: those that use the electromotive force of a solid electrolyte and those that use the rR ion current that flows through the solid electrolyte when a voltage is applied.

On the other hand, the oxide hemicyclic type flI sensor has an electron transfer rate of 24g according to the change in the filtration composition of the oxide under heavy loads:
This method takes advantage of changes in

The solid-state battery type oxygen sensor constitutes an oxygen concentration battery as shown below, and from its electromotive force, P'ol, Ee /Solid substance 1 quality / Ee* '*
(Ee: 1ii [Extreme] This is to determine the block partial pressure PL in the test gas.

The theoretical electromotive force E of this battery is expressed by equation (1).

P'o1: known oxygen partial pressure + pB, cumulative partial pressure in test gas T: loquat vs. pressure, R: gas number, F: Faraday constant number In both the type and the type using semi-dedicated oxide, electrodes are attached to detect the #jL element concentration by electrical signals. Conventionally, platinum has been used as an electrode. The electric body is used to maintain the concentration equilibrium between the partial pressure P''o2 of the gas to be detected and the free ions or oxygen vacancies in the solid. We are looking forward to our role as a place to carry out the
This is an extremely important part of this pyrolithic sensor. Since platinum 'tun' is mentioned in the '1 child biography' note, in the case of a solid-state battery type oxygen sensor, the interface between the three phases of platinum, solid am negative and gas phase is one gas chemical reaction. It becomes a point. The ↓δ response of an oxygen sensor depends on how quickly this 'electrochemical reaction proceeds, and a platinum' electrode is made porous to increase the number of anti-Lb points. However, all conventional oxygen sensors cannot be used in practical operation unless the temperature is approximately 700°C or higher, and the 24-ton temperature (
'In order to ensure 4-element conduction injection, make the electric mk thicker, immediately'
C) When do you run into problems when you have to use a lot of platinum?

Furthermore, when using elementary sensors at high temperatures, the following problems arise.

■ A heat source is required to heat the atmosphere around the sensor.

■ Because it is at the pot temperature, it is easily affected by the outside temperature;
- Maintaining one foot at a time becomes a national bell. As a result, a temperature gradient occurs in the oxygen sensor element, reducing measurement accuracy.

■ Heat loss is also large.

■ Accelerates deterioration of the electrolyzer and electrodes, shortening their lifespan.

Therefore, the present inventors proposed in Japanese Patent Application No. 61-245125 that AI-XA'XBO3-δ (A:L
We proposed a low-temperature-operated jJJfi reformed sensor using a perovskite-type composite oxidation ring represented by a, A': an alkaline earth metal, and B: a transition metal. As shown in the embodiment of this invention, solid 1! As a solution, cerium oxide (Ca
b, ) 10 mol g of calcium oxide (Cab)
1L of La,, Sr as an electrode using
The sensor using 4coo, -ak exhibits buried electromotive force down to a low temperature of 1FJ300°C, and has a fast response speed. On the other hand, the same solid I! A sensor using scale jX and sputtering platinum as an electrode exhibits a theoretical electromotive force of only up to FJ600°C.

[Problem that the invention seeks to solve]

The present invention aims to provide an oxygen sensor that operates reliably at a sufficiently faster response speed at lower temperatures than the above-mentioned low-temperature @ type silicon sensors.

[Taste j! Means for solving liI] The present invention is directed to a perovskite-type complex oxide represented by A1-A'XBO, -δ, which was previously proposed by the present inventors. The aim is to obtain xmt that can advance electrochemical reactions faster than others,
Activation of the sensor by using an electrode represented by AI-Xj" I found a black ink that could further reduce the level of ink and completed the present invention.
ILI-XSFXCOl-7B'70 to -15 (B'=
Ni, Fe, Cu.

The present invention is a gauging sensor characterized by having a perovskite-type composite silicide electrode represented by Mn % x = α1 to α5, y = α01 to α1).

The range of X is the solid solution range of Sr, and beyond this range, X
Linear diffraction has confirmed that other phases are precipitated in addition to the perovskite phase.

The range of y is [Lol is placed jl! The lowest effective value is 8, and preferably 102 or more.

If α1, which is the upper limit of the first order, is exceeded, the opposite effect will occur.

As the oxygen ion conductor, Ce02-CaO thread,
Ce0l-Gd103 yarn, Zr0l-YxOs yarn, Zr
02-CaO yarn fabric Any one of Bi, O, and yarns can be used. It is preferable to add 10 to 40 moles of CaO to Ce01.

[Written by Kawa]

La1-1SrlCO1-yB'y03-δ is At
- Like xA'xBOs-6, it is made of perovskite-type complex oxide with wire defects, and is made of a functional material with parent conductivity that has both oxygen ion conductivity and electron conductivity due to wood block defects◇ Therefore, the solid 1 with rR cumulative ionic conductivity
If the above composite oxide is attached as an electrode to tm material, (
The result is a mixture of gas phase/complex oxide/solid i%S. First, at the (gas phase/a@oxidation'm) interface, stratification of oxygen in the gas phase or desorption of oxygen into the gas phase occurs reversibly even at low levels of oxygen due to the catalytic action of the composite oxide. (A composite oxide/IAI body electrolyte shell) The interface can become a passageway for transferring oxygen ions into the solid electrolyte, since the composite oxide has a high ion density. Of course, if the interface between the three phases of platinum (gas phase, electrode, and electrolyte) is solid, as in the case of the platinum electrode,
This is also a reaction point for electrochemical reactions, but even without a three-phase interface, a composite oxide electrode has a mixed 24-electrity as described above, so electrons and ions can flow as well. Oxygen, which is stratified on the surface of the electrode, receives electrons at any part of the surface of the electrode, becomes ions, moves within the bulk of the electrode, and enters the electrolyte. Demeru. .

As mentioned above, composite oxide electrodes are considered to be superior to platinum electrodes in terms of catalytic action and passage of oxygen ions, and also suggest low-temperature operability of the sensor.

The present invention Iri, Lal-1srzcOO3-(5 CO
Lal-1srz, in which a part of the transition gold element B' is directly replaced.
The 'IIL pole represented by cO1-yB'y03-δ is used, but by substituting -S for Co with B', the self-catalytic action of the previous day is further enhanced, and the next step is that the vaporization proceeds much faster. The emergence of an innovative oxygen sensor that can operate at temperatures as low as 200 degrees Celsius is what led to OT disease.

〔Example〕

Cerium oxide (coos) and calcium oxide (CaO
) with 10 mol % of oxygen ions added (denoted as (ceo, ) at(CaO) H)
can be used as an element in a sensor having the structure shown in Figure 1. Next, the perovskite-type composite oxide is made into fine particles down to 1 μm or less and made into a paste using an organic solvent such as turpentine. M cloth was applied to the inner and outer surfaces of M cord 1 and baked at 800° C. in air to form % pole 5.

The solid electrolyte confectionery 1 was placed in an alumina a-fiber tube 2, and the connection portion was shielded with gold and silver (not shown).

The above oxygen sensor was heated in a gas to be detected, and the electromotive force at that time was measured using four proprietary gold maple lead terminals connected to the T-pole 5.

The test gas is nitrogen gas mixed with oxygen gas at a concentration of 10% and a total flow rate of 300 to 500 d/n.
1 in. (at atmospheric pressure). Pure oxygen gas was used as the reference gas and supplied at 500 d/min (under atmospheric pressure).
.

The configuration of this oxygen sensor is as follows.

P'0s(On), MO/(ClOs) at(
CaO)a+/MQ Po, (0,+N,)MO: Perovskite-type composite oxide 111 electrode Example 1 Material in which 2 mol% of CO in Laa4Sra4COO and δ was directly replaced with Mn by N1 processing, that is, LacnSriaCOa*
5NiaozOi-δ(A) and Laat8raaCOa
wsMnastOi−δ(B)i! The oxygen sensor's operation test was carried out for 5 hours when it was used as a pole. Of these, the sensor electromotive force
・-EMF) foot measurement results are shown in Figure 2 (A) and (B).
It was shown as The double border on the upper left in Figure 2 is indicated by (1) above.
It shows the relationship between the theoretical electromotive force E and one degree at each test oxygen partial pressure (P gas) obtained by formula.

In addition, (ri in the same figure is Laaa8ra4COOi-δ,
(D) This is the electromotive force measurement result of a nine-time sensor using U platinum paste as an electrode and is shown as a comparative example. The baking degree of each electrode is (AXB) (800
°C, (D) is 1000 °C.

As is clear from this comparative example, commonly used platinum 1! The reason why the electromotive force of the eR cumulative sensor with the pole attached follows the theoretical electromotive force is (Cent9t (CaO), which is approximately 600
℃ or higher (b), La, as the invention of the inventor's prior application
The r@4COOm-δ electrode should be installed at temperatures above 300℃ (C).

On the other hand, Laam8raaCOa**Ni of this example
Using a+uOm-J(person)'lLm, fc, the block sensor follows the theoretical electromotive force up to 190℃ as shown in (A) in Figure 2, ft-o. This means that the temperature can be lowered to approximately 200C.

La1LaSraiCOaes, MnaotOs-δ(
B) 'l [pole fl (A) has no effect, but as shown in Figure 2, it follows the theoretical electromotive force up to m, which is slightly lower than (C).

Next, the sensor responsiveness measurement results are shown in Figures 3 and 4. Figure 5 shows the cumulative concentration (partial pressure) p7o in the test gas.
, When fc is suddenly changed from f 1 atm to α1 atm, 1iL4(A)l? It shows the time-lapse situation in which the attached sensor reaches the theoretical electromotive force E expressed by the +11 formula at 198°C, and it takes about 20 minutes. (EMF
The key is pulled to 22 mV and the flat rock indicates E under this condition). The electrode (C) was installed next, and the sensor was also attached in the ninth step of the comparison. Figure 4 ns'1 as pole (A)'
1ftO-VC (B) @Installation is so o of the sensor
↓b response at
m). Also gMF key 27 mV horizontal? # indicates Ei under this condition. '#The sensor with the L pole (A) reaches the theoretical electromotive force E within 1 minute, and the sensor with the electrode (B) reaches the theoretical electromotive force E within 2 minutes. At the pole (C), the theoretical electromotive force is not reached at 198°C as shown in Fig. 3, and at 300°C, the theoretical electromotive force at the electrode (A) shown in Fig. 4 is not reached.
It is clear from the reli in Figure 3 that it is fully loaded for a longer time than in case B). In addition, at electrode (D), 198℃#
The theoretical electromotive force is not reached at any temperature of 500°C.

Implementation 1 Crit 2 Laa4SranCOOi-J's Co'(i-Ni
, Cu material is replaced with Fe, namely, Laa
4Sra4COatiNimssOa-δ(EhaLaa
aSraaCOaeNi, +On-δ (F),
La, Sr a4cOa*5custOs-J(
,0),Laa4SrmiCOaysFems yi0i-
a (H) 1! Construction of oxygen sensor when used as a pole #
The ll test was conducted in the same manner as in Example 1.

Figure 5 shows the EMF measurement results of electrodes (E) and (F).
A) Shown in comparison with (C). In the case of electrodes (E) and (F), 1 is inferior to electrode (A), but up to 210 to 220°C, electrode (C) has excellent low-temperature operation according to the theoretical electromotive force.

Figure 6 shows the responsivity of pole (E) and (F) with '1 as electrode (A).
In comparison with
This is an example of measurement when suddenly changing CL1atmvc from atm.

At the initial stage of P temperamentization, responsiveness is (A) > (E) > (
F), but the time to reach the theoretical electromotive force is almost the same.

FIG. 7 shows the EMF measurement results of the electrodes (()) and (H) in comparison with the m-pole (A). According to the theoretical electromotive force up to 250℃, electrode (A) is not required.

It has better low temperature operability than electrode CC).

Example 3 Material in which 2 mol% of CO in La+uSratCoOs-δ was replaced with N1, i.e., Laa*Sra*C0atsNi
An operation test of the rR cord sensor during 'fc was carried out in the same manner as in Example 1 using aexOiJ (I) as an electrode.

Figure 8 shows electrode (I) and Laa @S as ratio wRPJ.
EM F 1141J fixed lees fruit of r□COOto δ(J) was shown. While the 11L electrode (J) follows the theoretical electromotive force up to about 360°C, the electrode (I) follows the theoretical electromotive force up to F1250°C, achieving a lower operating temperature of about 100°C.

〔Effect of the invention〕

The present invention is designed to adopt the upper se convention,
It can operate at 300°C, expanding the operating temperature range further to the lower temperature side than conventional products, making it possible to expand the range of applications. In addition, the above problems when using the oxygen sensor with emphasis ■～■
It goes without saying that you will get vomiting after it is resolved.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of the Ippuku sealed tube type oxygen sensor used in the example of the present invention, and FIGS. 2 to 8 are diagrams showing the characteristics of the cough cord sensor used in the example. In the turtle 1 diagram, 1 is solid 1! 2 is an alumina porcelain tube, 3 is an electrode, and 4 is a conductive metal lead terminal.

Claims (1)

[Claims] La_1_-_xS on the surface of the oxygen ion conductive solid electrolyte
r_xCo_1_-_yB'yO_3_-_δ(B'=
Ni, Fe, Cu, Mn, x=0.1-0.5, y=0
．． An oxygen sensor comprising a perovskite-type composite oxide electrode represented by 01 to 0.1).