JPH03165253A - Oxygen sensor - Google Patents

Abstract

PURPOSE:To improve a thermal impact characteristic and to obtain stable characteristics by forming a gas sensitive part consisting of a thin film on a porous base body which is strong to thermal impact. CONSTITUTION:Yttria-stabilized zirconium has a good electrical conductivity and is stable in a reducing atmosphere and is, therefore, most generally used as a solid electrolyte for an oxygen sensor. The sintered body of the yttria- stabilized zirconia is, however, poor in the thermal impact resistant characteristic and the sintered body thereof is sometimes broken down when exposed to an abrupt temp. change. The oxygen ion conductive solid electrolete 3, such as yttria-stabilized zirconia is, thereupon, made into a thin film and this thin film is laminated together with an electrode 2 on the porous base body 1 strong to the thermal impact, by which the gas sensitive part is formed.

Description

[Detailed description of the invention] Industrial application field Invention 41 Various combustion equipment Used for boilers, automobiles, etc. This relates to an oxygen sensor used for conventional technology.This type of sensor (1) has a structure in which a pair of platinum electrodes is provided on a sintered body of yttria-stabilized zirconia, which is an oxygen ion conductive solid electrolyte. The sensor uses an oxygen concentration cell type, and the combustion equivalence point (stoichiometric air-fuel ratio)
Problems to be solved by the invention Although a large change in electromotive force is obtained due to a sudden change in the oxygen partial pressure that occurs at the boundary, itria-stabilized zirconia has good conductivity and is stable even in a reducing atmosphere. Although it is most commonly used as a solid electrolyte for sensors, sintered bodies of yttria-stabilized zirconia generally have poor thermal shock resistance, and are likely to be destroyed if exposed to sudden temperature changes. Therefore, it is not suitable to use this type of sensor in applications involving such environmental conditions. In the oxygen sensor of the present invention, an oxygen ion conductive solid electrolyte such as yttria-stabilized zirconia is made into a thin film with a porous structure that is resistant to thermal shock. In the oxygen sensor of the present invention, a gas-sensitive part is formed by laminating a thin film on a porous base that is resistant to thermal shock. 8. Improved thermal shock characteristics and exhibits stable characteristics over a long period of time.

Embodiment FIG. 1 is a schematic cross-sectional view showing an embodiment of the sensor according to the present invention. 1 is a porous mullite substrate (7 mmφ×
0.5mmt, average pore diameter 0. 1 μm), 2 is the chemical formula L as, *ss r @, esco *, t
An electrode (approximately 1.5 μmt) formed by depositing a perovskite-type composite oxide represented by Fes, sOs-δ by sputter deposition, 3 is 8mol 1% Y2O3-92mO deposited by sputter deposition
Oxygen ion conductive solid electrolyte M consisting of 1% Zrap (
4 is a pre-formed platinum conductor for lead extraction; 5 is a heat-resistant dense tube-shaped sensor support 4*; 6 is an electrode lead wire; 7 is a communication hole for atmosphere B; 4 is a sensor element; The first electrode is in contact with the atmosphere B through the porous substrate 1 and the communication hole 7, and the second electrode is in contact with the atmosphere A through the porous substrate 1 and the communication hole 7. Furthermore, even if atmospheres A and B are separated from each other by a partition wall (not shown) - 8 mol% Y20 heat - 92 m
Disc-shaped dense sintered body of oxygen ion conductive solid electrolyte consisting of ol%Zr0a (7mmφ, 0°5mmt)
A sensor was fabricated in which a sensor element having a pair of platinum electrodes deposited by sputter deposition was fixed to a support in the same manner as in the previous example, and the initial characteristics of the sensor were determined using the sensor fabricated as described above and used as a conventional example. First, the initial output characteristics of the sensors of the example and conventional example were measured.The sensor was installed in an electric furnace and the temperature was controlled. The temperature was set to a predetermined temperature, the atmosphere B was a reference gas atmosphere, L air was supplied at a predetermined flow rate, and the atmosphere A was a test gas atmosphere, and gases adjusted to various oxygen partial pressures were supplied to the electrodes. Measure the electromotive force generated between
rs, aac os, tF es, aO and δ function normally as electrodes. It has become clear that the sensor of the present invention exhibits excellent output characteristics. Especially Las, *sS
The sensor with ri, ssc os, vF es, 5os-δ electrodes exhibits an electromotive force close to the theoretical value even at a low temperature of 400°C.
es, sOw-δ has excellent conductivity and high redox catalytic activity.It is unlikely that this is because the electrode reaction rate is high even at low temperatures, and the electrode reaction proceeds smoothly. This may be due to the fact that we were able to obtain an electromotive force close to the theoretical value.It is also clear that gas permeation is almost negligible even when using a porous substrate9.On the other hand, in the case of conventional sensors, the electromotive force is small at temperatures below 500°C. In the case of platinum, since the electrode reaction rate at low temperatures is lower than that of perovskite oxides, it is thought that the theoretical electromotive force cannot be obtained. In order to confirm this, a thermal shock test was carried out.9 The sensors of the example and the conventional example were held in an electric furnace at 900°C for 15 ml, and the mold was immediately taken out.
As a result of a total of 10 repeated tests on 20 sensors that were forcibly cooled by blowing air at approximately 10°C, cracks were found in the solid electrolyte substrate in 11 of the conventional sensors (l(t)). Occurrence 9 In contrast, no abnormality was observed in any of the 20 sensors of the example.
The measurement results of the output characteristics at 800° C. of the sensors for which no abnormality was observed in the appearance are shown in FIGS. 3(a) and 3(b) together with the initial output characteristics using the same method as described above. The electromotive force showed a value almost close to the theoretical value, and it became clear that there was almost no deterioration of the sensor element in the thermal shock test.9 However, in the output characteristics of the conventional sensor, a decrease in the electromotive force was observed. Table: Catalytic activity decreases due to advanced sintering of platinum.
Although this is thought to be due to a decline in electrode function, it is common (ζ
The strength of the sensor is required to have thermally and mechanically stable properties.The sensor of the present invention has been shown to have excellent properties that satisfy these requirements. We will discuss the case where a perovskite oxide is used as f-o Ln and La
, use Sr as A, and use Fe as Me.
0. 65, the case where y=0.3 is shown! ＞
<, when Ln is Ce, Pr, Nd, or when it is two or more elements among La, Ce, Pr, Nd, when A is Ca, Ba, or when Sr, Ca,
When two or more elements of Ba are present, Me becomes Ni, M
In the case of n, Cr, V, or N 11 Fe,
Similar results can be obtained when two or more elements of Mn, Cr, and V are added, or when other composition ratios are used. When the element is added, it shows the effect of increasing the redox catalytic ability of oxygen without impairing the uniformity of electrode characteristics. The amount of SrMe' Ox mixed is 80 mol for the perovskite complex oxide.
% or less (preferably 40 to 70 mol%) is preferably 1 to
In addition, in order to judge the superiority of using a porous substrate, a sensor element was fabricated using platinum instead of perovskite oxide as the material for the sphere electrode, and a thermal shock test similar to that described above was conducted.1. As a result, similar to the conventional example above, although a decrease in electromotive force was observed, which was thought to be due to the sintering of platinum, the device did not break, demonstrating the superiority of using a porous substrate against thermal shock. As an example, a mullite material is used as the porous substrate, and 8 mo 1 is used as the oxygen ion conductive solid electrolyte.
The force using %Y*Os -92m o I%ZrO* (it is not limited to this as long as it has a similar function °C The sensor shape is not limited to the example, and it is consistent with the gist of the invention) The sensor may be manufactured in any form as long as it does not contradict the present invention.The method for manufacturing the sensor is not limited to the embodiments, and vacuum deposition, thermal spraying, and other known methods may be used. The oxygen sensor has extremely excellent characteristics and can be used as a highly reliable sensor for a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross section of an oxygen sensor according to an embodiment of the present invention. FIGS. 2(a) and (b) are diagrams showing output characteristics of an embodiment and a conventional sensor, respectively. ,(b)
1. Porous substrate 2. Electrode 3. Oxygen ion conductive solid electrolyte 4. Lead extraction electrode & 5...

Claims (4)

[Claims] (1) An oxygen sensor characterized by forming a gas-sensitive portion having a structure in which a first electrode, an oxygen ion conductive solid electrolyte, and a second electrode are sequentially laminated on a porous substrate made of a material with excellent thermal shock resistance. sensor. (2) At least one electrode has the general formula Ln_1_-_x
A_xCo_1_-_yMe_yO_3_-δ (Ln is at least one element selected from La, Ce, Pr, Nd, A is at least one element selected from Sr, Ca, Ba, Me is Ni, Fe, Mn, Cr,V
At least one element selected from 0≦x≦1, 0
The oxygen sensor according to claim 1, characterized in that it is made of a perovskite-type composite oxide represented by ≦y≦1, and δ is the amount of oxygen vacancies. (3) SrMe'O_3 (Me' is Ti, Z
3. The oxygen sensor according to claim 1, wherein 0 to 80 mol%, preferably 40 to 70 mol% of at least one element selected from r, Hf is added to the perovskite composite oxide. (4) The oxygen sensor according to claim 1, 2 or 3, wherein at least one platinum group element is added to the perovskite oxide in the electrode material.