JPH1172454A - Sensor for detecting very little moisture quantity in gas and production therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure very little moisture quantity of a specific value or less in gas by sticking calcium chloride to voids of a hydrophilic fluoroplastic film at least in a specific amt. or more and providing electrodes on both surfaces of the hydrophilic fluoroplastic film. SOLUTION: Calcium chloride is struck to the interiors of open-cell voids of a hydrophilic fluoroplastic film 2 with a film thickness or 80 μm, a void size of 0.2 μm, porosity or 71% and a wt. of 5.0 mg/cm<2> as a water absorbable conductive substance 4 and electrodes 5 are formed on both surfaces of the hydrophilic film 2 by the vapor deposition of gold. Calcium chloride is used as the water absorbable conductive substance and the hydrophilic fluoroplastic film is immersed in a 0.1 M calcium chloride aq. soln. for 10 hr or more and the impregnated film is dried under vacuum to stide 50 mg/cm<3> of calcium chloride to the open-cell of the hydrophilic fluoroplastic film. Subsequently, a gold membranes with a thickness of 1000 Åis vapor-deposited on both sides of the hydrophilic fluoroplastic film as electrodes under such a condition that a vacuum degree is 5×10<3> Pa, atmospheric temp. is 80 deg.C, a vapor deposition speed is 3 Å/sec and the distance between a vapor deposition source and the film is 20 cm by using the Mo board (0.5 kw) filament of a vacuum vapor deposition apparatus.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detection sensor for detecting an extremely small amount of water contained in various gases.

[0002]

2. Description of the Related Art As is well known, if a gas containing moisture is compressed and sealed in a cylinder even in an extremely small amount of less than 5000 ppm, there is a danger that hydrate will be generated and pipes will be blocked. To prevent it beforehand, 50
It is necessary to detect and remove even a very small amount of water of less than 00 ppm.

Conventionally, as a sensor for detecting a minute amount of water in a gas, there is a chemical sensor disclosed in Japanese Patent Application Laid-Open No. 6-186194. In this chemical sensor, potassium chloride (KCL) or sodium sulfite (Na ₂ SO ₃ ) is attached as a reactant to a porous fixed body, and a conductive electrode is provided on the surface thereof. Due to the low electric conductivity, it was not possible to measure an ultra-small water content of 5000 ppm or less.

[0004] It is possible to measure an ultra-small water content of 5000 ppm or less by using a moisture sensor made of Panamethrisk (USA) with gold deposited on the surface of an aluminum oxide thin film, but this sensor is very expensive. In addition, it was easily broken and inconvenient to handle.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a conventional chemical sensor based on the above-mentioned porous fixed body of 5000 pp.
In addition, it is impossible to measure an ultra-small water content of less than m, and in view of the fact that the moisture sensor based on the aluminum oxide thin film is expensive and difficult to handle, it is inexpensive and easy to handle. It is a technical problem to provide a sensor.

[0006]

The above technical objects can be achieved by the present invention as described below.

That is, a first aspect of the present invention is that at least 50 mg / c of calcium chloride is contained in pores of a hydrophilic fluororesin membrane.
m ³ is deposited over a super small water content detection sensor in the gas, characterized by comprising an electrode on both sides of the hydrophilic fluorine resin film.

A second aspect of the present invention is that a hydrophilic fluororesin film is immersed in an aqueous solution of calcium chloride having a concentration of 0.1 M or more and dried in a vacuum to form pores in the open cells of the hydrophilic fluororesin film. A method for producing a sensor for detecting an ultra-small water content in a gas, comprising depositing at least 50 mg / cm ^{3 of} calcium chloride and then depositing gold electrodes on both front and back surfaces of the hydrophilic fluororesin film.

The hydrophilic fluororesin membrane used in the present invention has a pore diameter of 0.1 to 10 μm, a porosity of 50 to 90%, a film thickness of 100 to 1 μm, and a density of 0.3 to 1.0 g / cm ³ . It is suitable. If the film thickness is 100 μm or more, the measurement sensitivity is poor because moisture is insufficiently penetrated into the film, and if the film thickness is 1 μm or less, it is difficult to manufacture, and even if it can be manufactured, it is fragile and not practical.

The water-absorbing conductive material used in the present invention includes calcium chloride (CaCl ₂ ) and lithium chloride (LiCl ₂ ).
, Sodium chloride (NaCl), sodium sulfate (Na ₂ SO _4),
Sodium sulfite (Na ₂ SO ₃ ) etc. can be applied,
In particular, calcium chloride is preferable, and even if the same water-absorbing conductive material is used, lithium chloride, sodium chloride, sodium sulfate, and sodium sulfite are not suitable for the present invention because their electric conductivity at the time of water absorption is low.

The adhesion of the water-absorbing conductive material to the hydrophilic fluororesin film is performed by immersing the hydrophilic fluororesin film in an aqueous solution of calcium chloride having a concentration of 0.1 M or more for 10 hours or more, followed by vacuum drying to obtain the hydrophilic fluororesin. At least 50 mg / cm ^{3 of} calcium chloride needs to adhere to the pores of the resin film. If the amount is less than 50 mg / cm ³ , the electric conductivity is insufficient, the impedance (MΩ) proportional to the water concentration is not generated, and the measurement sensitivity cannot be controlled.

When the amount of calcium chloride adhered is 50 mg / cm ³ or more, sufficient electric conductivity can be obtained, and the measurement sensitivity can be controlled.

The amount of calcium chloride deposited is 50 mg / cm ³
In the above case, the impedance can be estimated to change in proportion, so the upper limit of the amount of adhesion is not limited.

The electrodes are formed on one or both sides of a hydrophilic fluororesin film on which a water-absorbing conductive material is adhered. The electrode is preferably formed by a vapor deposition method, such as a sputtering method or a plating method.

As a material of the electrode, gold is suitable.
Platinum, nickel, silver, tin oxide, copper and the like may be used. When these conductors are deposited, the degree of vacuum is 5 × 10 ⁻³ Pa or less and the temperature is 100 ° C. or less. For example, in the case of gold, the distance between the deposition source and the film is 10 to 20 cm, and the Mo boat is 0.1 to 0 cm. .5
Using a kw filament, vapor deposition is performed at a deposition rate of 1-5 / sec.

Calcium chloride is used as a water-absorbing conductive material.
By forming electrodes independently on both the front and back surfaces of a hydrophilic fluororesin film having a film thickness of 100 μm to 1 μm adhered at 0 mg / cm ³ or more, a film-shaped film having a constant distance between the electrodes is formed.
A pole-integrated sensor can be configured.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an ultra-small water content detection sensor according to the present invention will be described below with reference to FIG.

Ultra-small water content detection sensor 1 according to the present invention
Has a film thickness of 80 μm and a pore diameter of 0.2 μm as shown in FIG.
calcium chloride as a water-absorbing conductive material 4 is adhered into the open-cell-like pores 3 of the hydrophilic fluororesin film 2 having an open cell of m ² , a porosity of 71%, and a weight of 5.0 mg / cm ^2. Electrodes 5 and 5 are formed on both front and back surfaces of a fluororesin film 2 by vapor deposition of gold.

Calcium chloride is used as the water-absorbing conductive material 4. As a means for adhering, a hydrophilic fluororesin film is immersed in a 0.1 M (mol) calcium chloride aqueous solution for 10 hours or more, and then dried in vacuum. Then, 50 mg / cm ^{3 of} calcium chloride was adhered in the open pores 3 of the hydrophilic fluororesin membrane.

Next, using a known vacuum evaporation apparatus, gold was used as the electrode 5 at a degree of vacuum of 5 × 10 ⁻³ Pa, an atmosphere temperature of 80 ° C., and
Deposition rate 3Å / sec, distance between deposition source and film 20cm, thin film 1000Å using Mo boat (0.5kw) filament
Was deposited.

FIG. 2 shows an experimental set for evaluating a moisture sensor, in which a gas cylinder 6, a moisture generator 7, a moisture sensor 8, a glass cell 9, an LCR meter (impedance measuring device) 10, and a display 11 are arranged in series. The ultra-small water content detection sensor 1 according to the present invention is set in the glass cell 9 as an evaluation target.

In the experimental set, nitrogen (N ₂ ) gas was used as a carrier gas, and the water content in the nitrogen gas was changed by the water generator 7 in order to obtain water of various concentrations. In order to check the sensitivity of the micro moisture detection sensor 1, the impedance change of the ultra-small moisture detection sensor 1 set in the glass cell 9 using a moisture sensor 8 manufactured by Panametrics (USA) for comparative calibration. To Hewlett-Packard LCR meter 1
0 was measured and displayed on the display 11.

Next, the performance when the ultra-small water content detection sensor 1 having the above configuration is used is plotted with the water concentration (ppm) in nitrogen gas on the horizontal axis and the impedance (MΩ) on the vertical axis. This will be described with reference to the graph of FIG.

Ultra-small water content detection sensor 1 having the above configuration
As shown in FIG. 3, in the case of (a state 24 hours after the electrode deposition), the impedance changed almost linearly to 35 MΩ in response to a change in the water concentration of 5000 ppm or less.

On the other hand, in the case where nothing is attached to the hydrophilic fluororesin film, or when sodium chloride or sodium sulfate is attached, the water concentration is 200
There was no change in impedance even when it changed to nearly 00 ppm.

Therefore, the water concentration (ppm) when the amount of calcium chloride adhered to the hydrophilic fluororesin film is changed.
FIG. 4 shows the relationship between the impedance and the impedance (MΩ).

FIG. 4 shows that a 35 μm-thick hydrophilic fluororesin film was coated on a 0.01 M aqueous solution of calcium chloride at a concentration of 0.01M.
After soaking for 10 hours each at 1M, 1.0M and 2.0M, vacuum drying and 10mg / cm ³ , 80 respectively
mg / cm ^3, to adhere the calcium chloride 400 mg / cm ³ and 770 mg / cm ^3, then shows the relationship between water concentration and the impedance of the four water content detection sensor was vacuum deposited gold as each electrode But 0.0
In the case of 1M, that is, the amount of calcium chloride deposited is 10 mg / c
water concentration 4000 in each case, except for m ³
It shows that accurate impedance can be measured corresponding to the change to ppm.

That is, the present inventors have confirmed that the water concentration of calcium chloride and the amount of calcium chloride adhering to the pores of the hydrophilic fluororesin membrane are in a proportional relationship, and the amount of calcium chloride adhering is adjusted. By doing so, it is possible to detect a very small amount of water concentration based on the impedance corresponding to each amount of adhesion.

FIG. 5 shows that a 35 μm-thick hydrophilic fluororesin film different from that used in the measurement shown in FIG.
Immersed in an aqueous solution of calcium chloride for 10 hours, vacuum dried to deposit 50 mg / cm ³ of calcium chloride, and then immediately after the preparation and one week after the preparation of the ultra-small water content detection sensor on which gold was deposited as an electrode A water concentration-impedance diagram for checking reproducibility later is shown. As is clear from FIG. 5, there was no change in the impedance measurement immediately after the vapor deposition and one week later, and reproducibility was confirmed.

FIG. 3 also shows the results obtained by attaching various water-absorbing conductive materials to an 80 μm-thick hydrophilic fluororesin film, and FIG. 4 shows the results of a 35 μm-thick hydrophilic fluororesin film. The results for the case where calcium chloride was adhered to the resin film with various concentrations of calcium chloride aqueous solution are also shown. The impedance with respect to the moisture concentration of the case where calcium chloride was adhered was 80 μm and 80 μm. Although the sensitivity is different from that of 35 μm, the same tendency is shown in each case, so that there is no practical problem as an ultra-small water content detection sensor.

An experiment was conducted on the adhesion of calcium chloride from the viewpoint of the extent to which the thickness of the hydrophilic fluororesin film can be applied. However, 50 mg / cm ³ of calcium chloride can be adhered to it.
The measurement results were almost the same as those of the μm.

Therefore, it can be estimated from the above results that a hydrophilic fluororesin film having a thickness of about 100 μm to 1 μm can be applied in the present invention.

Further, the same experiment as above was conducted for a hydrophobic fluororesin film instead of the hydrophilic fluororesin film as the substrate. As a result, the sensitivity was better than that of the hydrophilic fluororesin film, but the response was higher. It was considered unstable and not suitable for practical use.

[0034]

In the ultra-small water content detection sensor according to the present invention, calcium chloride having a high water-absorbing ability is attached to a hydrophilic fluororesin film as a water-absorbing conductive material, and gold is deposited as a conductive electrode. Because it is formed by
If this sensor is used, it can be widely used as a sensor capable of detecting an ultra-small water content of 5000 ppm or less contained in various gases such as city gas, LP gas, nitrogen gas, air, and argon gas.

Further, the following effects can be obtained in the sensor for detecting an extremely small amount of water according to the present invention. (a) As the hydrophilic fluororesin membrane, a commercially available product widely used for a membrane filter or the like can be used, so that it can be easily obtained at low cost. (b) The hydrophilic fluororesin film is flexible, hard to break and can easily be restored to its original state even when bent, and does not hurt even when touched by a human body, and does not cause harm due to a chemical reaction or the like. (c) By adjusting the amount of calcium chloride adhered to the hydrophilic fluororesin film as a water-absorbing conductive material, the electric conduction between the electrodes can be controlled even when various gases contain ultra-low moisture of 5000 ppm or less. Because you can read the change in degree,
By measuring the impedance at that time, the amount of ultra-small water in the gas can be detected quickly and accurately. (d) Since the operation of depositing calcium chloride is simple and the electrode deposition operation is easy, the ultra-small water content detection sensor according to the present invention can be provided at low cost.

Therefore, it can be said that the industrial applicability of the present invention is very large.

[Brief description of the drawings]

FIG. 1 is a partially enlarged sectional view of an ultra-small water content detection sensor according to the present invention.

FIG. 2 is an explanatory diagram of an experimental set of an ultra-small water content detection sensor.

FIG. 3 is a graph showing the performance of an ultra-small water content detection sensor for various water-absorbing conductive substances.

FIG. 4 is a graph showing the performance of an ultra-small water content detection sensor depending on the concentration of various calcium chloride aqueous solutions.

FIG. 5 is a graph showing the reproducibility of the ultra-small water content detection sensor according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ultra-small moisture detection sensor 2 Hydrophilic fluororesin film 3 Open-celled pore 4 Water-absorbing conductive material 5 Electrode 6 Gas cylinder 7 Moisture generator 8 Moisture sensor 9 Glass cell 10 LCR meter 11 Display

Claims (2)

[Claims] An ultra-fine gas in a gas, characterized in that at least 50 mg / cm ^{3 of} calcium chloride is adhered to pores of a hydrophilic fluororesin film, and electrodes are provided on both front and back surfaces of the hydrophilic fluororesin film. Micro moisture detection sensor. 2. A hydrophilic fluororesin membrane is immersed in an aqueous solution of calcium chloride having a concentration of 0.1 M or more, and dried by vacuum, so that calcium chloride is at least 50 mg / cm 2 in the open pores of the hydrophilic fluororesin membrane. ^A method for producing a sensor for detecting an ultra-small amount of moisture in a gas, comprising depositing ^three or more gold electrodes on both front and back surfaces of the hydrophilic fluororesin film.