JPH0785071B2 - Carbon dioxide detection sensor and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a solid electrolyte type carbon dioxide gas sensor.

[Conventional technology]

The solid electrolyte type sensor currently being developed is usually constructed by providing electrodes on opposite surfaces of a solid electrolyte chip made of an ionic conductor.

As such a solid electrolyte type carbon dioxide sensor, for example, a NASICON (general formula Na _1-X Z having a structure as shown in FIG. 2 is used.
There are carbon dioxide gas sensors using sodium ion conductors such as r ₂ P _3-X S _iX O ₁₂ ) (Nikkei New Materials, November 20, 1989, page 92). This carbon dioxide sensor is a gold electrode serving as a reference electrode c on both opposing sides of a pellet b made of NASICON on a substrate a provided with a heater e.
The one to which La _0.5 Sr _0.5 CoO ₃ is attached is also used as the detection electrode d.
A gold electrode having Na ₂ CO ₃ adhered thereto is provided, and the sensing electrode d portion is covered with a gas permeable film f and the other portions are covered with a gas blocking film g, which has a complicated structure. .

[Problems to be Solved by the Invention]

The conventional carbon dioxide gas sensor having such a structure has a limitation in downsizing, and has a drawback that the sensitivity is lowered if the gas blocking line g has an incomplete sealing property, and the substrate a, the pellet b, There is also a problem that distortion occurs due to the difference in the coefficient of thermal expansion of the gas permeable film f, the gas blocking film g, etc., and the sensitivity changes, and deterioration easily occurs.

The present invention solves the above-mentioned problems in the prior art and provides a highly reliable carbon dioxide detection sensor which has a simple structure and can be easily miniaturized, and consumes less power. This is the purpose.

[Means for Solving the Problems]

The carbon dioxide gas detection sensor of the present invention that can achieve the above object is a reference electrode layer on a gas-impermeable ceramic substrate, and an oxygen ion conductive solid electrolyte thin film that completely covers the reference electrode layer. A layer, an ion-permeable detection electrode layer, and a detection material layer made of a mixture of an alkali metal carbonate and an alkaline earth metal carbonate are sequentially laminated.

The carbon dioxide gas detection sensor having such a configuration is a solid electrolyte thin film of oxygen ion conductivity that completely covers the reference electrode layer by a known film formation method after forming the reference electrode layer on a gas-impermeable ceramic substrate. After forming a layer and further laminating an ion-permeable sensing electrode layer facing the reference electrode layer through the solid electrolyte thin film layer, a part or all of the sensing electrode layer is treated with an alkali metal carbonate and an alkali. It can be manufactured by coating with a sensing material layer composed of a mixture with an earth metal carbonate.

The reference electrode layer and the detection electrode layer used in the carbon dioxide gas detection sensor of the present invention include, for example, platinum, palladium, rhodium, ruthenium, iridium, gold, silver, etc., which are vacuum-deposited or sputtered, or a noble metal, etc., as a conductive material. It can be formed by an appropriate method such as printing a conductive paste or the like. Among the electrode layers thus formed, the detection electrode layer in particular needs to be ion-permeable, and is preferably a thin film that allows sodium ions, oxygen ions, and the like to easily pass therethrough. preferable.

Further, as the oxygen ion conductive solid electrolyte thin film layer in the carbon dioxide detection sensor of the present invention, for example, ZrO ₂ —Y ₂ O ₃
System, ZrO ₂ -CaO system, ZrO ₂ -Yb ₂ O ₃ system, CeO ₂ -CaO system, CeO ₂
An oxygen ion conductive ceramic such as —Sm ₂ O ₃ system is used, and it is formed by a known film forming method such as sputtering so as to completely cover the reference electrode layer.

Further, the sensing material layer provided on the sensing electrode layer is, for example, an alkali metal carbonate such as lithium carbonate, sodium carbonate or potassium carbonate and an alkaline earth metal carbonate such as magnesium carbonate, calcium carbonate, strontium carbonate or barium carbonate. Alkali metal carbonates and alkaline earth metal carbonates selected from these are formed into a plate-like or pellet-like form by uniformly mixing the respective powders. Is molded into. The molded sensing material is fixed by a method of placing it on the sensing electrode layer provided on the solid electrolyte thin film layer and then heating and fusing it. The size of the sensing material may only cover a part of the sensing electrode layer, or may be such that it can completely cover the sensing electrode layer.

The structure of such a carbon dioxide detection sensor of the present invention is, for example, as shown in FIG.

In the figure, 1 is a gas-impermeable ceramic substrate, on the lower surface of which, for example, platinum, palladium, rhodium,
The heater 6 is provided by a method such as vacuum deposition, sputtering, or plating of an electric resistance film of a noble metal such as ruthenium, iridium, gold, or silver, or a method of printing a conductive paint using these noble metals as a conductive material. Has been. A reference electrode layer 2 is provided on the upper surface of the substrate 1, and an oxygen ion conductive solid electrolyte thin film layer 3 is formed so as to completely cover the reference electrode layer 2, and a detection electrode layer 4 is formed thereon. Further, a detection material layer 5 is provided on it.

[Work]

In the carbon dioxide gas detection sensor of the present invention, when the gas to be measured is brought into contact with the heater while being energized and heated, an electromotive force corresponding to the concentration of carbon dioxide gas in the gas is output between both electrodes. Since the carbon dioxide gas detection sensor of the present invention uses a detection material made of a mixture of an alkali metal carbonate and an alkaline earth metal carbonate, it has a stable detection output characteristic and a measurement error due to humidity is almost eliminated. Does not happen.

[Example 1] A heating resistance wire was formed by sputtering platinum on the back surface of a gas-impermeable alumina sintered body substrate of 4 mm x 3 mm x 0.25 mm to form a heater.

Further, a 2 mm × 2 mm platinum reference electrode and a platinum lead wire were formed on the upper surface of this substrate by sputtering.

Next, stabilized zirconia containing 8 mol% of yttrium trioxide was subjected to high frequency sputtering so as to cover the reference electrode to form a solid electrolyte thin film layer, and subsequently, a detection electrode similar to the reference electrode was formed thereon.

On the other hand, sodium carbonate and barium carbonate in a molar ratio of 1: 1.
Mix to 7 and press-mold at a pressure of 10 Kg / cm ² to 3
mm × 3 mm × 0.3 mm detection material pellets were placed on the above-mentioned detection electrodes, and then the heater was energized to fuse and fix the pellets on the detection electrodes.

The carbon dioxide detection sensor A having the structure as shown in FIG. 1 prepared in this way is incorporated in the chamber 11 of the measuring device of FIG. 3, heated to a predetermined temperature by the heater 5, and then the flowmeters 7, 8 Air, oxygen and carbon dioxide were mixed so as to obtain a predetermined gas concentration through Nos. 9 and 9, and further passed through a water tank 10 to be adjusted to a predetermined humidity and then supplied to the chamber 11. Thus, the electromotive force between the detection electrode 3 and the reference electrode 4 is measured by a voltmeter.
Measured at 12. In addition, 13 is a water tank for shutting off outside air, and 14 is an exhaust port.

In this way, with the element temperature set to 550 ° C., the detection output characteristics with respect to the carbon dioxide concentration of 200 to 5000 PPM in humid air and dry air were measured, and the results are shown in FIG.

From this result, it can be seen that the carbon dioxide sensor A of the present invention has almost the same detection output characteristics as in dry air even in the air of 60% humidity, and is hardly affected by the humidity.

Example 2 Example 1 was repeated except that lithium carbonate and calcium carbonate were mixed at a molar ratio of 1: 1 to form a sensing material pellet.
The carbon dioxide detection sensor B was assembled in the same manner as.

The detection output characteristics of this carbon dioxide detection sensor B were measured in the same manner as in Example 1, and the results are shown in FIG.

The results show that the carbon dioxide sensor B of the present invention has higher sensitivity than the carbon dioxide sensor A of the first embodiment, and has almost the same detection output characteristics in dry air as in the air of 60% humidity. However, it can be seen that it is hardly affected by humidity.

〔The invention's effect〕

As described above, the carbon dioxide detection sensor of the present invention has the feature that the detection output characteristics are not affected by humidity, consumes less power, is less deteriorated, and is easily miniaturized.
Further, there is also an advantage that the manufacturing is easy because the structure is simple without the need of providing a gas blocking film or the like.

[Brief description of drawings]

FIG. 1 is a block diagram of a carbon dioxide gas sensor of the present invention, FIG. 2 is a block diagram of a carbon dioxide gas sensor which is an example of a conventional technique, and FIG. 3 is a block diagram of a detection output characteristic measuring device of a carbon dioxide gas sensor. FIG. 4 is a carbon dioxide detection sensor A which is Embodiment 1 of the present invention.
FIG. 5 is a detection output characteristic diagram with respect to carbon dioxide concentration in humid air and dry air, and FIG. 5 is a carbon dioxide detection sensor B which is Embodiment 2 of the present invention.
FIG. 5 is a detection output characteristic diagram with respect to carbon dioxide concentration in humid air and in dry air. 1 ... Ceramic substrate, 2 ... Reference electrode layer, 3 ... Solid electrolyte thin film layer, 4 ... Detection electrode layer, 5 ... Detection material layer, 6
...... Heater, 7, 8, 9 …… Flowmeter, 10 …… Water tank, 11…
… Chamber, 12 …… Voltmeter, 13 …… Water tank, 14 …… Exhaust port.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-256043 (JP, A) JP-A-2-103457 (JP, A) JP-A-124555 (JP, U)

Claims (3)

[Claims] 1. A reference electrode layer, an oxygen ion conductive solid electrolyte thin film layer that completely covers the reference electrode layer, an ion permeable detection electrode layer, and an alkali on a gas impermeable ceramic substrate. A carbon dioxide gas detection sensor, characterized in that a detection material layer made of a mixture of a metal carbonate and an alkaline earth metal carbonate is sequentially laminated. 2. The carbon dioxide detection sensor according to claim 1, wherein a heater is provided on the back surface of the gas-impermeable ceramic substrate. 3. An oxygen ion conductive solid electrolyte thin film layer that completely covers the reference electrode layer is formed by forming a reference electrode layer on a gas-impermeable ceramic substrate, and further, After laminating an ion-permeable detection electrode layer facing the reference electrode layer through the solid electrolyte thin film layer,
3. The detection material layer according to claim 1, wherein a part or the whole of the detection electrode layer is covered with a detection material layer made of a mixture of an alkali metal carbonate and an alkaline earth metal carbonate. Carbon dioxide detection sensor manufacturing method.