CN1241720A - Humidity sensor and its manufacture - Google Patents

Abstract

The humidity sensor includes two oxygen sensors and each oxygen sensor includes one zirconia sheet with one diffusion hole in the center and one first and one second electrodes printed on the two sides of the sheet. The two second electrodes of the two sheets are covered by the same cover to form two separated diffusion chambers. The humidity sensor has the merit of being capable of measuring gas humidity in the temperature range below 250 deg.C. The present invention also discloses the manufacture process of the humidity sensor.

Description

Humidity sensor and manufacturing method thereof

The invention relates to a humidity sensor, in particular to a humidity sensor which is manufactured by utilizing the oxygen measuring principle of a zirconium oxide boundary current type oxygen sensor of a solid electrolyte and can measure the humidity in a gas environment from room temperature to 250 ℃. The invention also relates to a manufacturing method of the humidity sensor.

In many industrial processes or material handling processes where dry gases are used for protection, it is important to monitor the moisture content of these gases. In the field of humidity measurement, humidity sensors made of various materials and using various principles are available.Such as alumina humidity sensor (CN2129414Y), ceramic humidity sensor (CN2168250Y), polymer humidity sensitive element (CN2101237U), composite humidity sensor (CN1177102A), thermistor humidity sensor (CN1142263A), etc. The humidity sensor realizes the measurement of humidity by utilizing the physical adsorption phenomenon of humidity sensing materials to water molecules, and when the ambient temperature is higher than 100 ℃, the adsorption quantity of the humidity sensing materials to the water molecules of the various sensors is very small (close to the physical adsorption limit value), so that when the ambient temperature is higher than 100 ℃, the various humidity sensors cannot measure the humidity in the environment.

The invention aims to provide a humidity sensor which can measure humidity in an environment lower than 100 ℃ and can measure humidity in gas in an environment of 100-250 ℃ and a manufacturing method thereof.

The aim of the invention can be achieved by the following technical measures:

firstly, a zirconia sheet 1 is manufactured by mould forming, the zirconia sheet 1 is put in a high-temperature sintering furnace for sintering, a diffusion hole 2 is manufactured on the sheet 1, then electrodes 3 and electrodes 4 are printed on two sides of the sheet, the electrodes 4 on the two zirconia sheets with the diffusion hole and the electrodes are covered by a same cover part 5, the cover part 5 and the zirconia sheets with the two electrodes 4 are respectively connected in a sealing way, a diffusion chamber 6 is formed between the cover part 5 and the electrodes 4, and the diffusion chamber is communicated with the outside through the diffusion hole on the zirconia sheet.

The invention utilizes the oxygen measuring principle of a solid electrolyte zirconia boundary current type oxygen sensor to measure the humidity. Fig. 1 is a schematic diagram of the operation of the oxygen sensor, which comprises a solid electrolyte zirconia sheet 1, electrodes 3 and 4 printed on both sides of the sheet 1, a diffusion hole 2 in the center of the sheet 1, a cover 5 covering the electrodes 4, and a diffusion chamber 6 formed between the electrodes 4 and the cover 5. As shown in fig. 1, when a voltage V is applied between the electrodes 3 and 4 and the solid electrolyte zirconia flake is heated to 350 ℃ or higher, the following reactions occur at the electrodes 3 and 4 (wherein the electrode 3 is an anode and the electrode 4 is a cathode):

cathode: ……………………(1)

anode:

the reaction is represented by the current I generated on the loop, in dry air, as the voltage V continues to increase to V₁When the voltage V is increased, the current I is not increased any more but becomes a stable current value I₀However, as voltage V continues to increaseExceeds V₂When the current Iis from I₀The current-voltage characteristic of the phenomenon is shown in figure 2, and is a working principle characteristic diagram of the solid electrolyte zirconium oxide boundary current type oxygen sensor. The current I is formed by the flow of oxygen ions, the I of different oxygen concentrations₀All of which differ in value, according to this property, by measuring I₀The value can be calculated to obtain the oxygen concentration value in the gas.

When water vapor exists in the air, the scientific research personnel increase the voltage V value to V₃When the current I has a first stable value I₁Until the voltage is increased to V₄Current value I from I₁Continuously changing when the voltage continues to increase to V₅When the current I has a second stable value I₂Until the voltage increases to V₆When the current Iis from I₂Continuing, as shown in FIG. 3, the microscopic mechanism of this phenomenon is as follows:

cathode: ……………………(1)

…………………(3)

anode:

the value of I is also formed by the flow of oxygen ions, only the oxygen ions are derived from the gas O₂And H₂The sum of the oxygen ions in O that are electrolyzed.

According to the gas diffusion pore restriction Ficks rule of the sensor, the first limiting current I is given on the assumption that the diffusion coefficient of oxygen is equal to that of water vapor₁Value and second limit current value I₂May be represented by the following formulae, respectively: ${\mathrm{<figure-callout\; id="1"\; label="I"\; filenames="A9812184200071.png,A9812184200072.png"\; state="\{\{state\}\}">I</figure-callout>}}_1=-\frac{4\mathrm{FDSP}}{\mathrm{RTL}}\ln (1-\frac{{\mathrm{Po}}_2}{P})$ ${\mathrm{<figure-callout\; id="2"\; label="I"\; filenames="A9812184200071.png,A9812184200083.png"\; state="\{\{state\}\}">I</figure-callout>}}_2=-\frac{4\mathrm{FDSP}}{\mathrm{RTL}}(1+\frac{P_{H_{2}O}}{2P{o}_2})\ln (1-\frac{{\mathrm{Po}}_2}{P})$ ${\mathrm{<figure-callout\; id="2"\; label="Po"\; filenames="A9812184200071.png,A9812184200083.png"\; state="\{\{state\}\}">Po</figure-callout>}}_2=0.21(P-P_{H_{2}O})$ wherein F is a Faraday constant; d is the diffusion coefficient of the mixed gas molecules;

s is the area of the gas diffusion hole; p is the total pressure of the mixed gas;

is the partial pressure of oxygen

Is the water vapor partial pressure;

r is a gas constant; t is the working temperature (K) of the sensor;

l is the length of the gas diffusion hole; 0.21 is the oxygen content in air.

FIG. 3 shows the current of the humidity sensor as a function of voltage and ambient humidity, showing the first threshold current value I₁Value of oxygen partial pressure in the atmosphere

Proportional, the second limiting current law is proportional to the sum of the partial pressure of oxygen and the partial pressure of water in the atmosphere, and therefore, by measuring I₁Value and I₂The value is calculated, and the difference value delta I of the two-stage limit current is calculated, so that the partial pressure of the water vapor in the environment atmosphere can be conveniently detectedThe values, FIG. 4, show the partial pressure P of water vapor

Is related to Δ I.

As the solid electrolyte zirconia limit current type oxygen sensor adopted by the humidity sensor can work at the temperature of 400 ℃ or above, the humidity sensor can work at high temperature, water molecules can react as shown in formulas (1), (2) and (3) as long as the water molecules are in contact with the electrode of the sensor, physical adsorption of the water molecules is not needed, and the contact between the water molecules and the surface of the electrode cannot be influenced by the high temperature, so that the humidity sensor can measure the humidity in a high-temperature environment.

The present invention will now be described more fully hereinafter with reference to the accompanying drawings in which:

FIG. 1 is a diagram of the operating principle of a solid electrolyte zirconia boundary current oxygen sensor.

FIG. 2 is a graph showingcurrent-voltage characteristics of an oxygen sensor in dry gas

FIG. 3 is a graph of current-voltage characteristics of an oxygen sensor in humid gas

FIG. 4 shows a tidePartial pressure of wet water vapor

Graph of dependence on Δ I

FIG. 5 zirconium oxide flakes

FIG. 6 zirconia flakes with diffusion holes

FIG. 7 zirconium oxide flakes with diffusion holes and electrodes

FIG. 8 is a block diagram of a humidity sensor

FIG. 9 is another block diagram of a humidity sensor

Fig. 5 to 8 show a preferred embodiment of the present invention:

1. forming a zirconium oxide sheet: zirconium oxide powder (composition 8% mol Y)₂O₃+ZrO₂) Pressing and processing the zirconium oxide thin sheet by adopting a steel die to form the zirconium oxide thin sheet, sintering the zirconium oxide thin sheet in a high-temperature sintering furnace at the sintering temperature of 1400-1600 ℃ for 4-8 hours, and taking out and naturally cooling.

2. Manufacturing a diffusion hole: and (3) manufacturing diffusion holes in the center of the zirconia sheet by adopting a laser drilling method, wherein the hole diameter is 20-35 mu m.

3. Electrode manufacturing: printing platinum slurry on two sides of the zirconia sheet by adopting a screen printing technology, wherein the concentration of the platinum slurry is 90%, and drying at room temperature.

4. The electrodes 4 on the two zirconia sheets with diffusion holes and electrodes manufactured in steps 1-3 are respectively bonded with the zirconia sheets 5 by using glass enamel 7, the shape and the area of the zirconia sheets 5 with diffusion holes and electrodes are the same, the two zirconia sheets with diffusion holes and electrodes are respectively positioned at two sides of the zirconia sheets 5, and diffusion chambers 6 are formed between the zirconia sheets 5 and the electrodes 4, as shown in fig. 8.

The humidity sensor manufactured by the embodiment has the characteristics of symmetrical and compact structure, uniform heating, accurate measurement and the like, and the embodiment is convenient and easy to operate.

Another embodiment of the present invention is illustrated by fig. 5 to 7 and 9, and unlike the preferred embodiment, the area of the zirconia flakes 5 in this embodiment is 2 to 3 times the area of the zirconia flakes having the diffusion holes and the electrodes, and two zirconia flakes having the diffusion holes and the electrodes are juxtaposed on the same side of the zirconia flakes 5 as shown in fig. 9.

The invention has the following advantages: the humidity sensor has the outstanding characteristic that the humidity sensor can work in a high-temperature, low-humidity or high-humidity environment with the temperature ranging from room temperature to more than 100 ℃, the maximum working temperature is 250 ℃, and the humidity measuring range is 0-50 kPa, so that the blank that various existing polymer, semiconductor, ceramic and electrolyte humidity sensors in the field of the current humidity sensor cannot work in an environment with the temperature of more than 100 ℃ is filled.

Claims (10)

1. A humidity sensor is characterized in that the humidity sensor is formed by combining two solid electrolyte zirconia boundary current type oxygen sensors.

2. The humidity sensor according to claim 1, wherein the diffusion holes of the two solid electrolyte zirconia boundary current oxygen sensors are arranged in the same direction, and the two solid electrolyte zirconia boundary current oxygen sensors are juxtaposed.

3. The humidity sensor according to claim 1, wherein the diffusion holes of said two solid electrolyte zirconia confinement current oxygen sensors are disposed in a back-to-back manner, and said two solid electrolyte zirconia confinement current oxygen sensors are disposed in a back-to-back manner.

4. The method for manufacturing the humidity sensor comprises the following steps of: the method is characterized in that the electrodes 4 on two zirconia sheets with diffusion holes and electrodes are covered by the same cover 5, the cover and the zirconia sheets with the corresponding electrodes are respectively connected in a sealing way, a diffusion chamber 6 is formed between the cover 5 and the electrodes 4, and the diffusion chamber is communicated with the outside through the diffusion holes on the zirconia sheets.

5. A method of manufacturing a humidity sensor as claimed in claim 4, wherein two sheets of zirconia having diffusion holes and electrodes are sealed together on the same side of the lid member.

6. The method of claim 4, wherein two sheets of zirconia having diffusion holes and electrodes are symmetrically placed on opposite sides of the cover member to be hermetically sealed.

7. The method of claim 4, wherein the mold used to formthe zirconia flakes is steel.

8. The method of claim 4, wherein the diffusion holes are formed by laser drilling, and the diameter of the holes is 20-35 μm.

9. The method of claim 4, wherein the zirconia substrate is sintered at 1400-1600 ℃ for 4-8 hours, and electrodes are printed on both sides of the substrate using platinum paste.

10. The method of claim 4, wherein the cover member is a zirconia ceramic wafer, and the cover member is bonded to the zirconia wafer having the diffusion hole and the electrode by sealing with glass enamel.

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