JPS627681B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a humidity sensitive material, and an object thereof is to provide a humidity sensitive material containing a polyheteroacid-based material as a humidity sensitive component (hereinafter referred to as "humidity sensitive component"). Conventional relative humidity sensors have been based on physical phenomena such as changes in the elongation of hair or plant fibers, temperature differences between dry and wet bulbs, or the dew point of water vapor, changes in the electrical conductivity of electrolytes (such as LiCl), and phosphoric acid solutions. Sensors that utilize electrochemical phenomena such as changes in the ionization degree of Sensors are widely known. Among these, electrical sensors are generally superior to other sensors in terms of ease of handling because their devices are small and easy to operate, especially those that use ceramic semiconductors as their sensing bodies. It has the advantage of being easy to mass produce and being inexpensive. However, this type of ceramic-based sensitive material generally has a large surface electrical resistance of 10 ³ to 10 ⁸ (Ωcm).
Therefore, if water vapor condenses or adheres to the surface, the electrical resistance will easily change due to the adhered water, which has the disadvantage of adversely affecting the moisture sensitivity. In view of the above circumstances, the present inventors have developed a ceramic sensor that has the advantages of being small, easy to handle, and inexpensive, as well as eliminating measurement errors due to the influence of water adhering to the surface, i.e., having low electrical resistance. As a result of intensive research into humidity sensitive materials, the inventors discovered that polyheteroacid-based substances are extremely effective as humidity sensitive components, and completed this invention. The drawings show one embodiment of a humidity sensor using a humidity sensitive body according to the present invention, and the present invention will be explained below based on the drawings. In the figure, 1 is a terminal 2 (2 ₁ ,
2 ₂ ) is a humidity sensitive body in which a polyheteroacid-based substance as a sensitive component is in the required form; It is an AC power source that provides an electric field, and 6 is a voltmeter that measures the potential difference between terminals (2 ₁ , 2 ₂ ). The polyhetero acid-based substance used as a moisture-sensitive component in this invention has the chemical formula H
_(8-o) [XY ₁₂ O ₄₀ ]・mH ₂ O is a polyheteroacid, and the amount of crystal water m is 12≦m≦30 depending on the humidity.
, X is an element selected from Si and P having a valence of n, and Y is Mo or W. A preferred specific example is phosphomolybdic acid (H ₃
[PMo ₁₂ O ₄₀ ]・30H ₂ O), phosphotungstic acid (H ₃
[PW ₁₂ O ₄₀ ]・30H ₂ O), silicon molybdic acid (H ₄
Examples include [SiMo ₁₂ O ₄₀ ]・30H ₂ O), silicon tungstic acid (H ₄ [SiW ₁₂ O ₄₀ ]・30H ₂ O), and the like. These polyheteroacid-based substances generally have a water crystallization number of about 30 when the relative humidity is about 70% or higher, and when the relative humidity decreases to about 50%, the crystallization water number decreases to about 12 to 13. In addition, this change in the number of water of crystallization is reversible and the response is rapid, so the number of water of crystallization is determined according to the value of relative humidity. A protective resistor 4 is connected to an AC power source 3 (1KHz10V) to a sensitive body 1 containing this polyheteroacid-based substance as a moisture-sensitive component.
When a current is passed through the terminal (10KΩ1W), the number of crystal water regulates the amount of charge transfer and determines the electrical resistance of the sensitive element 1 according to the relative humidity value, and as a result, the terminal (2
The potential difference between ₁ and 2 ₂ ) appears on the voltmeter 6 as a specific value of the sensitive body at relative humidity, and the humidity is detected. Moreover, since polyheteroacid-based materials generally have low electrical resistance, the electrical resistance value of the sensitive body 1 is 10 ¹ to 10 ⁴ (Ω
cm), which is a small value for practical use, and even if water vapor in the air is deposited, the electrical resistance value does not change significantly like in the past. To manufacture this humidity sensitive body 1, a polyheteroacid material is usually pressure-molded, or a substrate such as a glass nonwoven fabric is impregnated with an aqueous solution of a polyheteroacid material, dried, and then pressurized. ,
It can be formed into a desired shape such as a cylinder, and then terminals made of carbon or the like can be attached to both ends to form a sensitive body with terminals suitable for use as an electrical sensor. Note that the sensitive material 1, which is formed by pressure molding a single polyheteroacid material, tends to dry out at low humidity and deliquesce and break at high humidity, so it should be impregnated into the substrate in places where the relative humidity changes drastically. It is preferable to use a sensitive body. As detailed above, the humidity sensitive material according to the present invention has a humidity sensitive component, which is a polyheteroacid material, which has low electrical resistance and is excellent in practical use. There is no risk of adversely affecting the moisture content, and if used in a humidity sensor, a sensor with excellent handling can be obtained with a simple device. Next, the present invention will be further explained in detail based on Examples. Example 1 Phosphormolybdic acid (H ₃ PMo ₁₂ O _{40.29H 2} O; manufactured by Yoneyama Pharmaceutical Co., Ltd.) was dissolved in pure water at a ratio of 0.5 to 3 mol/l, and then recrystallized at 80°C and RH 20% or less. It was purified by drying for hours. This purified phosphomolybutenic acid is 10 mm long and 2 mm wide.
After pressure molding to 20 mm at a molding pressure of 5 ton/cm ² , carbon terminals were pressure molded at both ends to create a humidity sensitive body with attachment terminals. Examples 2 to 4 Phosphortungstic acid (H ₃ PW ₁₂ O ₄₀・29H ₂ O)
(Example 2), silicon molybdic acid (H ₄ SiMo ₁₂ O ₄₀ ·30H ₂ O) (Example 3), and silicon tungstic acid (H ₄ SiW ₁₂ O ₄₀ ·30H ₂ O) (Example 4), respectively. A humidity sensitive material was prepared in the same manner as in Example 1. Examples 5 to 6 Phosphortungstic acid (Example 5) and phosphomolybdic acid (Example 6) were purified in the same manner as in Example 1, and then dissolved in pure water at a ratio of 2 to 3 mol/l. The solution was impregnated and coated on a glass nonwoven fabric with a width of 5 mm, a length of 15 mm, and a thickness of 0.5 mm, and then dried at 80° C. and RH 20% for 3 hours, and further pressurized at 500 kg/cm ² . Next, carbon terminals were attached to both ends in the same manner as in Example 1 to produce a humidity sensitive body with terminals. The four types of sensitive bodies obtained in Examples 1 to 4 were assembled into the circuit shown in the drawings, exposed to relative humidity of 50% to 90% for 3 hours, and then AC voltage (1KHz 10V) was applied. Electrical resistance of the sensitive bodies. was measured. In Examples 1 and 2, the temperature at the time of measurement was
Examples 3 and 4 were carried out under two conditions: 15°C and 35°C.
The test was carried out under one condition: 30°C. The results are shown in Table 1. The sensitive bodies obtained in Examples 5 and 6 were assembled into a circuit in the same manner as above, and the relative humidity was varied within the range of 50 to 90% under the condition of applying an AC voltage (same conditions as above) to measure the sensitivity to humidity changes. We investigated the body's responsiveness. The temperature was 35°C. The results are shown in Tables 2 and 3.

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[Table] As is clear from the above results, the sensitive material according to the present invention, which has a polyheteroacid-based material as a moisture-sensitive component, has a small electrical resistance value of 10 ¹ to ^{10 4} Ωcm, which is excellent in practical use. It is an excellent humidity sensitive material whose responsiveness reaches an equilibrium value in about 15 minutes for a 10% increase/decrease.

[Brief explanation of the drawing]

The drawing is a schematic diagram of an embodiment of a humidity sensor using a humidity sensitive body made of a polyheteroacid-based material according to the present invention. 1...Humidity sensitive body.

Claims (1)

[Claims] 1. Chemical formula H _(8-o) [XY ₁₂ O ₄₀ ]・mH ₂ O (however,
The amount of crystal water m can be 12≦m≦30 depending on the humidity, and
represents an element selected from Si and P having a valence of n, and Y represents Mo and W, respectively. ) A humidity-sensitive material characterized by using a polyheteroacid-based substance represented by the following as a humidity-sensitive component.