JPS60159632A - Hydrogen sensor - Google Patents

Abstract

PURPOSE:To detect only hydrogen selectively by adhering the thin film made of palladium, etc. to an element having piezoelectric effect. CONSTITUTION:Electrodes 2 attached with lead wires is fixed at both side surfaces of a thin plate-shaped oscillator 1 having piezoelectric effect, and the surface is covered with a vapor-deposited film 3 of palladium, etc. to constitute a hydrogen sensor 4. A detector cell 5 attached with the sensor 4 is connected to a gas supplying apparatus 7 with piping through a flowmeter 6, and the lead wires are connected to an oscillator 8. Since the resonance frequency of the sensor 4 is varied by the transmission of hydrogen contained in the gas through the palladium film, this variation is read by a frequency counter 9 and the hydrogen concn. is measured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hydrogen sensor, and more particularly to a hydrogen sensor that selectively detects only aqueous systems.

Conventionally, the following methods are known as detectors for detecting water contained in gas.

(1) A method called the thermal conduction method that takes advantage of the fact that the thermal conductivity of gas changes when an aqueous system is present. (2) A phenomenon in which hydrogen is burned on a catalyst and the resulting heat increases the resistance of a resistor such as a platinum filament. (3) A method called catalytic combustion method that utilizes the sintered body of a metal oxide semiconductor such as tin oxide, and when it comes into contact with hydrogen, the electrical conductivity of the semiconductor changes. However, none of these methods has the ability to distinguish and detect only aqueous systems in the coexistence of hydrogen and other combustible gases. That is, since hydrogen, hydrocarbons, carbon monoxide, etc. can be detected with almost similar sensitivities, this has caused great inconvenience as a water-based detector.

In order to improve these shortcomings, the inventors of the present invention have made extensive studies and have covered an element that exhibits the piezoelectric effect in a thin film with a special metal, attached electrodes to this thin metal film, and used it as a sensor. When an electric circuit including a sensor is made to oscillate,
The present invention was achieved by discovering that the oscillation frequency changes only depending on the presence or absence of hydrogen.

That is, the present invention is a hydrogen sensor in which a detection end is a vibrator in which a patent characterized by at least one metal selected from palladium, gold, and platinum is attached to an element having a piezoelectric effect.

Examples of the piezoelectric element used in the present invention include quartz crystal, itziel salt, barium titanate, lead titanate, lead zirconate titanate (PZT), and lead lanthanum zirconate titanate (PLZT). The shape of the piezoelectric element is not particularly limited, but examples thereof include plate shapes such as a circle, an elliptical square, a rhombus, and a rectangle.

In the present invention, palladium, gold, and platinum may be used as materials for the thin film to be attached to the piezoelectric element, and these may be used alone, or two or more may be used in the form of an alloy or the like. Furthermore, small amounts of silver and/or copper may be contained in these metals.

As a method for attaching the metal thin film to the piezoelectric element, conventionally known methods such as vacuum deposition, chemical vapor deposition (CVD), and sputtering can be applied. There is no particular limit to the thickness of the metal, but it is preferably 5000A or less for ease of processing.

The present invention will be explained in more detail below with reference to the drawings.

FIG. 1 is a sectional view of the hydrogen sensor of the present invention, and FIG. 2 is a configuration diagram of a hydrogen detection device incorporating the hydrogen sensor of the present invention.

The surfaces of the vibrator 1 and the electrodes 2, 2 are covered with a vapor deposited film 6.5 of palladium or the like to form a hydrogen sensor.

In FIG. 2, a detector cell 5 to which a hydrogen sensor 4 of the present invention is attached is connected via a flow meter 6 to a gas supply device 7 via piping, and a lead wire led from the detector cell 5 is connected to an oscillator 8. The oscillator 8 is connected to a frequency counter 9 and a stabilized power supply 10 by wiring, respectively, to form a hydrogen detection device. The water system contained in the gas causes the oscillator 8 and the hydrogen sensor 4 to resonate while flowing the gas from the gas supply device 7 through the flow meter 6 to the detector cell 5, and changes in the resonance frequency and wave number are measured by the frequency counter 9. Detected by reading.

By using the hydrogen sensor of the present invention, only hydrogen can be selectively and continuously detected with high precision even in a gas flow where flammable gases other than hydrogen coexist without being affected by these flammable gases. can do.

Example 1 (Production of Hydrogen Sensor) After attaching electrodes to a quartz crystal resonator plate, palladium was vacuum-deposited on the surface in an air atmosphere to produce a water-based sensor. The thickness of the produced palladium thin film was 3000A.

(Measurement of Resonance Frequency) The above hydrogen sensor was set in the device configured as shown in Figure 2, and the resonance frequency of the oscillator of the 7jCg sensor was measured by flowing air at a rate of 200 d/min from the gas supply device, and the result was 601543 BHz. This frequency remained unchanged even when the air flow rate changed.Also, no change in the resonant frequency was observed when nitrogen or argon was flowed instead of air.

(Response when flowing hydrogen-containing gas) Nitrogen gas containing 5120 PPM of hydrogen was added to the above equipment at 1490 d/
Figure 3 shows the results of measuring the number of resonant frequencies divided by the change while flowing at a minimum speed. After about 2 minutes (indicated by a), the resonant frequency rose to 6015455 Hz, an increase of 17 Hz compared to the case of gas containing no hydrogen, and reached a steady state. Next, hydrogen-free air was flowed at 26,611 Ll/min, and after about 1 minute (indicated by b), the resonance frequency returned to its original state of 60,154.5 BHz.

(Response when flowing other gases) Approximately 1.000PP for each of methane, ethane, and propane
Although nitrogen gas containing M was flowed through the above device, no change was observed in the resonance frequency. Also, sulfur dioxide 10,000
PPM.

Carbon dioxide 5000PPM, nitrogen dioxide 97PPM
Although nitrogen gas containing each of these was flowed, no change was observed in the resonant frequency. These results show that the oscillator of this hydrogen sensor has extremely high hydrogen selectivity in that it acts specifically with only the hydrogen contained in the gas, changing its resonance frequency.

Example 2 5120 in nitrogen in the same equipment used in Example 1
As a result of investigating the influence of the flow rate on the resonant frequency of the vibrator of the hydrogen sensor using gas containing hydrogen in PPM, as shown in FIG. 4, almost no influence of the gas flow rate was observed.

Furthermore, as a result of examining the effect of gas flow rate on response time, almost no effect was observed as shown in FIG.

Moreover, as shown in FIG. 6, almost no effect of gas flow rate on the recovery time was observed.

FIG. 7 shows the influence of ambient temperature on the resonance frequency. It was observed that the sensitivity tends to increase as the ambient temperature decreases.

FIG. 8 shows the influence of ambient temperature on response time (indicated by white circles) and recovery time (indicated by black circles). It was found that both become shorter as the temperature increases.

Example 3 In air using the same equipment used in Example 1 (indicated by a white circle)
FIG. 9 shows the results of examining the change in resonance frequency for each level of hydrogen concentration in nitrogen (indicated by black circles). It was recognized that both people had an almost linear relationship.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of the hydrogen sensor. Figure 2 is a configuration diagram of the hydrogen detection device. Figure 3 is a diagram showing the change in resonance frequency depending on the presence or absence of hydrogen. Figure 4 is the effect of gas flow velocity on resonance frequency. Figure 5 shows how the gas flow rate affects the response time. Figure 6 shows how the gas flow rate affects the recovery time. Figure 7 shows how the ambient temperature affects the resonance frequency. FIG. 8 is a diagram showing the influence of ambient temperature on response time and recovery time. FIG. 9 is a diagram showing changes in resonance frequency due to hydrogen concentration. In the drawings, 1... Vibrator 2... Electrode 6... Vapor deposited film 4.
...Hydrogen sensor 5...Detector cell 6...mi
A: Total 7... Gas supply device 8... Oscillator 9...
・Frequency counter and 10... Clean t' of the stabilized power supply drawing (no change in pi capacity) Book 1 Fig. 7'. Pit 3 diagram #4 diagram 1% IJI (+n1nl i jj (rnl/n
(2) Procedural amendment (spontaneous) March 14, 1980 Commissioner of the Japan Patent Office Kazuo Wakasugi t Indication of the case 1982 Patent Application No. 14564 2, Title of the invention Hydrogen sensor 3, relationship to the case of the person making the amendment Patent applicant address: 1-1-6 Nishi-Shinbashi, Minato-ku, Tokyo "Name of the invention in the specification", "Claims in the specification" , "Column for detailed explanation of the invention in the specification", "Column for brief explanation of drawings in the specification", and "Drawings" (no change).

Claims (1)

[Claims] A hydrogen sensor whose detection end is a vibrator made of a piezoelectric element with a thin film mainly composed of at least one metal selected from palladium, gold, and platinum.