JPH0471462B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field The present invention controls the ratio of air and fuel supplied to combustors such as stoves and boilers, and internal combustion machines such as automobiles and engines by measuring changes in the electrical resistance of a sensor sensitive body. Regarding sensors. Conventional Technology Conventionally, there is a sensor made of a stabilized zirconia solid electrolyte as an air-fuel ratio control sensor for combustion in a lean region, that is, a region in which there is excess air relative to complete combustion of fuel (Japanese Patent Application Laid-Open No. 59-60253, Showa 59-
Publication No. 83048). In the sensor made of the stabilized zirconia solid electrolyte described above, the pump current for causing oxygen ions to flow through the zirconia changes in proportion to the oxygen concentration. In response, the inventors previously filed a patent application for a sensor that can specifically change the resistance of a sensor sensitive body at a given oxygen concentration by changing the current flowing through an oxygen ion conductive solid electrolyte. I went to Problems to be Solved by the Invention The above-mentioned invention provides that in the conventional sensor, a large amount of oxygen flows into the sensitive body from outside the sensor, and the ability of the solid electrolyte as an oxygen pump is low in an atmosphere with a high oxygen concentration. It was not possible to lower the oxygen partial pressure in the gas atmosphere of the reactor to near the main mass point. Means for solving the problem A porous ceramic layer is formed to cover the entire oxygen pump consisting of stabilized zirconia and electrodes. Function A porous ceramic layer is formed to cover the entire oxygen pump, which reduces the amount of oxygen flowing in from the outside, allowing it to function as an oxygen pump even in high oxygen concentration atmospheres. Examples Example 1 ZrO ₂ 8 mol% Y ₂ O ₃ in a concave cylindrical mold with a diameter of 11 mm
Stabilized zirconia expressed ^as
Baked in air at 1500℃ for 8 hours. The dimensions of the molded body after firing are 10 mm in diameter and 3 cm in length. A hole with a diameter of 4 mm and a depth of 2 cm is made in the center, and a Pt conductive porous layer is placed along the surface of the hole to a thickness of 0.1 mm. The one coated with the paste is the positive electrode 4 for the oxygen pump shown in Figure 1.
It is. Further, a similar Ag paste is applied to the outer surface of the cylindrical stabilized zirconia solid electrolyte 3,
This is referred to as a negative electrode 5 for an oxygen pump. and from above
Sr _0.5 La _0.5 Co _0.5 Fe _0.5 O ₃ +50mol%, CaZr _0.8 Al _0.2 O ₃
The mixed sintered powder was sprayed to a thickness of 0.2 mm by hydrogen flame spraying.
The sensor sensitive body 2 is sprayed to a size of about mm. On top of this, as shown in FIG.
After coating with Pt paste, alumina powder is applied by plasma spraying to cover the sensor sensitive body 2.
Spray to about 0.2 mm to form porous alumina 1. FIG. 1 is a cross-sectional view of the cylindrical sensor made as described above. The sensor characteristics are as follows: The sensor is placed in a tube furnace and maintained at 600℃, a mixed gas of O ₂ , N ₂ , and CO is passed through, the O ₂ concentration is kept constant at 1%, the amount of CO gas inflow is varied, and an oxygen pump electrode is used. Apply a voltage from 0 to 1.0V to 4,
We investigated whether it could be used as a lean burn sensor by measuring the current value at which the electrical resistance of the sensor sensitive body 2 changes significantly. The results are shown in Figure 2. When the CO gas inflow concentration was changed from 0% to 2.1% without applying direct current to the oxygen pump, the electrical resistance of the sensor sensitive body changed approximately 30 times from 80Ω to 2.5KΩ. However, when the inflow concentration of CO gas is set from 0% to 1.0%, the electrical resistance of the sensor sensitive body hardly changes, which means that if a sensor made of this material is used as a sensor for combustion control, the combustion It can be seen that control can only be performed near the equivalence point. When the inflow concentration of CO gas is constant at 1% and a DC current is applied to the oxygen pump, approximately 2.5KΩ at 30μA
It changed to Furthermore, the inflow concentration of CO gas was reduced to 0.5%.
and 0.0%, the DC current value flowing through the oxygen pump changed to approximately 2.5KΩ at 50μA and 80μA, respectively. These results are based on the fact that by passing a direct current through the stabilized zirconia solid electrolyte, it acts as an oxygen pump and lowers the oxygen partial pressure within the sensor sensitive body to a partial pressure at which a sudden change in electrical resistance occurs. Example 2 As a sensor sensitive material, Sr _0.5 La _0.5 Co _0.7 Fe _0.3 O ₃ +
A sensor was prepared using a mixed sintered body of 60 mol% SrTi _0.8 Al _0.2 O ₃ in the same manner as in Example 1, and its characteristics were examined. The results are shown in Figure 3. Also, adjust the furnace temperature to 700℃ and 800℃ using the same method as above.
4 and 5 show characteristic diagrams of the electrical resistance of the sensor sensitive body when the temperature is set to .degree. C., respectively. Figures 3 and 4
As can be seen from FIG. 5, these three types of characteristic diagrams are completely the same even though they have changed. In other words, when the sensor material of this discovery is used as a sensitive body, the electrical resistance at temperatures above 600℃ remains constant regardless of temperature, and when used as a lean burn sensor,
This eliminates the need to maintain the entire sensor at a constant temperature, making it maintenance-free regardless of temperature. Note that in this example

A mixture of [Formula] and AB _1-y Al _y O ₃ and sintering was used as the reactor, but almost the same results were obtained when a mixture of the two was used. In the above embodiment, the porous ceramic layer was formed by plasma spraying alumina powder, but other materials may be used, or hydrogen spraying or the like may be used. Effects of the Invention By forming a porous ceramic layer such as alumina on the outer surface of the oxygen pump, the amount of external gas flowing into the sensitive body is reduced, so that the sensitive body can function as a sensor within the capacity of the oxygen pump. did it.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the main body of a lean burn sensor according to an embodiment of the present invention, FIG. 2 is a characteristic diagram of the same lean burn sensor, and FIG. 3 is a characteristic diagram of a lean burn sensor according to a different embodiment of the present invention. 4 and 5 are characteristic diagrams of the same lean burn sensor at different temperatures. 1...Porous alumina membrane, 2...Sensor sensitive body, 3...Stabilized zirconia solid electrolyte, 4...
Positive electrode for oxygen pump, 5... Negative electrode for oxygen pump.

Claims (1)

[Claims] 1. An oxide represented by the chemical formula [formula] (Me is at least one element selected from Fe, Mn, Cr, and V, O≦x≦1, O≦δ≦0.5) and the chemical formula AB _{1 -y} Al _y O ₃ (A=Ca or Sr,
B=One type of element selected from Ti, Zr, Hf, O≦y
A mixture or mixed sintered body of oxides represented by ≦1) is used as a sensor sensitive body, an oxygen pump made of stabilized zirconia and an electrode is provided to cover the sensor sensitive body, and a porous electrode is provided to cover the entire oxygen pump. A lean burn sensor characterized by forming a high quality ceramic layer. 2. The lean burn sensor according to claim 1, wherein the electrode is an alloy of at least two of Pt, Pd, and Ag.