JPH0131586B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a galvanic cell type humidity sensor. More specifically, the present invention relates to a humidity sensor characterized by having a proton-conductive solid oxide as a partition wall, which is conveniently used for detecting the water vapor concentration in high-temperature gas.

Conventionally, humidity sensors include a hygroscopic permittivity variable type, a hygroscopic vibration load variable type, and an adsorption conductivity variable type.

However, all of these methods require a voltage or current signal to be supplied to the humidity sensing element itself from the outside, and have the drawback of requiring complicated accessory equipment for this purpose.

Furthermore, all of them are used at relatively low temperatures and have a characteristic defect in that they cannot withstand use at high temperatures. Furthermore, the moisture sensitivity response speed of these products is not sufficiently fast, and there is a risk of deterioration due to adsorption of impurities, etc., and complex treatments are required to periodically regenerate this. It is.

In view of the above-mentioned circumstances, the inventors of the present invention have completed the present invention as a result of extensive research into a humidity sensor that uses a voltage generated by a water vapor partial pressure difference between both surfaces of a partition wall as a signal.

That is, the present invention provides a humidity sensor that uses a proton-conductive solid oxide as a partition wall and detects humidity based on the potential difference generated by the humidity difference between the two sides of the partition wall.

The proton conductive solid oxide used as the partition wall of the present invention is based on oxides of strontium and cerium.

A proton conductive solid oxide containing an oxide of at least one metal of ytterbium, scandium, ytterbium, neodymium, magnesium, praseodymium and zinc is preferably used in the present invention. The general formula of an example of such a solid oxide is shown below.

SrCe _1-x M _x O _3- 〓 (Here, M is Y, Sc, Yb, Nd, Pr, Mg or
(Zn, x represents a value of 0.5 or less, and α represents a value from 0 to 0.5) The atomic ratio of metals constituting such an oxide and its preparation method are as follows.

That is, the amount of strontium and cerium as metal atoms is 30 to 70 mol%, preferably 40 to 60 mol%, respectively, based on the total metal atoms. Further, the content of at least one metal selected from the group consisting of yttrium, scandium, ytribium, neodymium, magnesium, praseodymium, and zinc, which partially replaces cerium, is preferably 0.5 to 25 mol% based on the total metal atoms in the oxide. It is 1 to 20 mol%.

The oxide can be prepared by various commonly known methods. One method is to use a compound containing each of (a) strontium, (b) cerium, and (c) at least one metal selected from the group consisting of yttrium, scandium, ytribium, neodymium, praseodymium, magnesium, and zinc. One method is to fire it.

When obtaining the solid oxide used in the present invention, the firing temperature is usually 500°C to 1500°C in an oxidizing atmosphere.
Preferably a temperature in the range of 600°C to 1450°C is suitable.

In the solid oxide of the present invention, (a) strontium, (b) cerium, and (c) yttrium, scandium, ytterbium, neodymium, praseodymium, as long as the (proton) conductivity of the solid (oxide) is not impaired. It may contain impurities such as metals other than magnesium and zinc.

The solid metal oxide prepared by the method described above is formed into a film by the method described below, and used as a partition wall for a humidity sensor of the present invention. That is,
The oxide obtained by the preparation method described above may be formed into a film, or a method may be used that combines the preparation of the oxide and the film formation. As such a film forming method, for example, a film may be formed by mechanical processing such as cutting or polishing a solid material such as a pellet or sheet;
The powder may be press-molded or made into a paste and applied onto a porous support and sintered.

The film thickness of the solid oxide obtained by the above-described molding method is usually 10 ^-2 to 10 ⁴ μ, preferably 10 ^-1 to
A range of 10 ³ μ is appropriate.

Next, an example of a humidity sensor using the thus obtained membrane as a partition will be described based on the drawings.
Reference numeral 11 in FIG. 1 indicates a gas atmosphere to be measured, which indicates an atmosphere of water vapor, acid, etc. 12 is a porcelain tube, 13 is a partition made of proton conductive solid oxide, and porous electrodes 14 are attached to both sides of the partition walls. 15
indicates a lead wire. A desiccant 16 such as synthetic zeolite or the like may be enclosed in the porcelain tube (sealed chamber) 12 in order to keep the water vapor pressure in the chamber constant. If such a device is used to expose the other side of the partition wall 13 to the gas atmosphere 11 containing an arbitrary water vapor partial pressure, the water vapor partial pressure will be increased by the electromotive force generated between the electrodes on both sides of the partition wall depending on the water vapor partial pressure in the gas. can be detected by the detector 17.

The principle of the present invention will be explained below.

If a proton-conducting solid electrolyte is used as a partition wall and a water vapor partial pressure difference is created on both sides, water vapor will tend to move from the side with higher partial pressure to the side with lower partial pressure, according to Luschatrier's law. Since a proton conductive solid electrolyte exists between both gases, water vapor cannot move directly, but on the high water vapor partial pressure side, H ₂ O → 2H ⁺ (proton conductor) + 2e ^- + 1/2O ₂ on the low water vapor side. , 2H ⁺ (proton conductor) + 2e ^- +1/2O ₂ →H ₂ O electrochemical reaction is about to proceed, and the high water vapor side is charged to the negative electrode and the low water vapor side to the positive electrode, creating a potential difference between the two electrodes. In this case, the electromotive force E can be expressed as E=RT/2FluP _H2O /P゜_H2O (P゜_O2 /P _O2 ) ^1/2 (1) when the electronic conductivity of the electrolyte is negligibly small. Can be done. Here, P° _H2O and P _H2O represent the water vapor pressures in the reference gas and the measured gas, respectively.P° _O2 and _P02 represent the oxygen partial pressures in the reference gas and the measured gas, respectively. R, F and T are the gas constant, Faraday constant and absolute temperature, respectively. The oxygen partial pressure in both gases is constant,
And if P゜_H2O in the reference gas is known (or constant), equation (1) at the measurement temperature is expressed as E = A + BluP _H2O , and there is a relationship between the electromotive force and the logarithm of the water vapor partial pressure in the measured gas. A linear relationship holds true. Therefore, if A and B are determined experimentally, the water vapor partial pressure can be determined from the electromotive force.

Gas concentration measuring instruments based on the principle of concentration batteries have been widely used as oxygen gas concentration meters using oxygen ion conductive solid electrolytes, but the concept of water vapor concentration batteries that utilize the concentration of water vapor has not been known until now. I wasn't there.

This is because conventionally, no solid electrolyte has been found that exhibits good proton conductivity at high temperatures at which such concentration batteries can operate, and generally only aqueous solutions or proton conductive solid electrolytes with extremely high equilibrium water vapor partial pressures are known as battery electrolytes. This is because it was a long time ago.
The present invention was made possible by the inventors' discovery of an oxide that exhibits high proton conductivity at high temperatures. This led to the invention of a water vapor sensor using this principle.

This sensor has traditionally been considered difficult to use250
It can be used at high temperatures of ~1000℃, and the activation force spontaneously generated by the water vapor concentration is extracted as a sensing signal without supplying an electrical signal from an external circuit. It has its features. Furthermore, it has advantages such as fast response speed, high sensitivity, and is not affected by other impurity gases.

Examples in which the proton conductive solid oxide used as the partition wall of the present invention is used as a humidity sensor will be described below with reference to examples, but the present invention is not limited thereto.

Example 1 An example of humidity measurement will be explained based on FIG. 2.

SrCe _0.95 Yb _0.05 O _2.8 sintered plate 2 with diameter 12 mm and thickness 0.5 mm
A porous platinum electrode 22 was attached to the diameter of 7 mm at the center of both sides of the tube, and this was adhered with an inorganic adhesive to the tip of an alumina porcelain tube 23 having an outer diameter of 12 mm, an inner diameter of 9 mm, and a length of 100 mm to form a detection part.

Note that the conductive wires 24 and 25 are taken out from both electrodes,
It was used as an electromotive force detection terminal.

The area around the detection unit is heated to a constant temperature (400°C) by an electric heating coil 26, and air containing 4.58 torr of water vapor is passed through the reference gas inlet 28 and outlet 29 into the porcelain tube 23 as a reference gas to the detection unit. When the tip was exposed to air having various water vapor partial pressures, it was found by the detector 27 that a stable electromotive force was obtained depending on the water vapor partial pressures. The response speed at this time was within 3 seconds. The results are shown in FIG. In FIG. 3, the vertical axis shows the detection voltage (mv), and the horizontal axis shows the water vapor partial pressure (torr). This result shows that there is a linear relationship between the two, and the temperature can be easily determined from the detected voltage.

Example 2 In the humidity measuring device of Example 1, instead of flowing the reference gas, a humidity sensor was installed in which a molecular sieve was sealed inside the porcelain tube as shown in Figure 1.
When exposed to air with various water vapor pressures at 400℃,
Stable electromotive force can be obtained with a response speed of less than 3 seconds.
As shown in the figure, a linear relationship was obtained between water vapor partial pressure and electromotive force.

[Brief explanation of drawings]

FIG. 1 shows one embodiment of the humidity sensor of the present invention, and FIG. 2 shows another embodiment. FIGS. 3 and 4 are measurement examples showing the relationship between water vapor partial pressure (torr) and detection voltage (mv) in the present invention. 11... Gas atmosphere to be measured, 12... Porcelain tube,
13... Partition wall, 14... Porous electrode, 21...
SrCe _0.95 Yb _0.05 O _2.8 sintered plate, 22... Porous platinum electrode, 23... Alumina porcelain tube, 26... Electric heating coil.

Claims (1)

[Claims] 1 A proton-conductive solid oxide comprising an oxide of at least one of yttrium, scandium, ytterbium, neodymium, magnesium, praseodymium, and zinc in an oxide of strontium and cerium is used as a partition, and both sides of the partition A galvanic battery type humidity sensor that detects humidity using the potential difference generated by the humidity difference.