JPS6350841B2 - - Google Patents

Description

Detailed Description of the Invention <Technical Field> The present invention relates to a moisture-sensitive resistance element using a chemical combination of zirconium silicate and phosphorus as a moisture-sensitive material.

<Prior art> Humidity-sensitive resistance elements whose electrical resistance changes in response to atmospheric humidity have conventionally been made using tin oxide (SnO ₂ ), iron oxide (Fe ₂ O ₃ or Fe ₃ O ₄ ), and oxidized Those using metal oxides such as titanium (TiO ₂ ) or sintered bodies of composite metal oxides, those using porous metal oxide films obtained by anodizing metals such as aluminum, and those using chloride. Lithium (LiCl)
Other known methods include those using electrolyte salts such as , and those using hygroscopic resins, organic polymer membranes, and thermistors.

In general, moisture-sensitive resistance elements using metal oxides or composite metal oxides have the advantage of having a wide moisture sensitivity range and excellent heat resistance, but on the other hand, they have instability peculiar to metal oxides. It has the drawback of poor reproducibility of humidity characteristics, and tends to change over time even at room temperature and humidity. In particular, in these metal oxide sintered bodies, moisture-sensitive characteristics such as sensitivity and response speed are affected not only by the properties of the material itself but also by its microscopic structure such as pore size distribution and porosity. Therefore, it is not always easy to manufacture devices with good moisture sensitivity characteristics with good reproducibility. In addition, there is a problem in that the moisture-sensing properties deteriorate in a relatively short period of time due to the formation of hydroxide due to chemical adsorption of water on the metal oxide surface or a reduction in the moisture-sensitive surface area due to dirt. Ta. For this reason, a method has been proposed and implemented in which chemically adsorbed water and other deposits are removed by periodically heating the humidity sensing element. Furthermore, with conventional methods, it is not always easy to obtain a humidity sensitive element having good exponential characteristics over the entire humidity range.

<Purpose> The present invention was made in order to eliminate the drawbacks of the conventional moisture-sensitive resistance elements made of metal oxides or composite sintered bodies thereof as described above. At the same time, a sintered body is obtained by firing zirconium silicate with uniform particle size and a phosphorus compound,
By creating a network-like chemical bond consisting of zirconium silicate and phosphorus, it has excellent mechanical and thermal properties, little change over time, good exponential properties, and high reproducibility. The present invention provides a moisture-sensitive resistance element characterized by having a moisture-sensitive characteristic. The present invention will be described in detail below with reference to Examples.

<Example> FIG. 1 shows a schematic structural diagram of a moisture-sensitive resistance element according to the present invention.

In the figure, reference numeral 1 denotes a moisture-sensitive resistor having at least a chemical bond of zirconium silicate and phosphorus formed on its surface, and is produced, for example, through the steps described below. Moisture-permeable electrodes 2 are placed on both sides of the moisture-sensitive resistor 1.
is formed, and a lead wire 3 is drawn out.

The moisture-sensitive resistor 1 uses zirconium silicate particles and phosphoric acid (H ₃ PO ₄ ) as starting materials, which are mixed at a weight ratio of 20:5. Further dry on a hot water bath. Next, mold this to a thickness of 0.3mm and an area of 5×
Make pellets of ^5mm2 . The pellets are calcined at a temperature of 350°C for about 10 hours. Furthermore, this pellet
It was created by firing in air at a temperature of 1000°C for about 3 hours.

A ruthenium oxide film having an area of 4×4 mm ² was formed as a moisture-permeable electrode 2 on both sides of the moisture-sensitive sintered body 1 thus obtained, and a lead wire 3 was attached to this to form a moisture-sensitive resistance element.

FIG. 2 shows an example of the humidity sensitivity characteristics (direct current resistance value vs. relative humidity characteristics) at an ambient temperature of 26° C. of the humidity sensitive resistance element produced according to this example. As seen in this figure, it was confirmed that it was sensitive over almost the entire humidity range and had extremely stable and good exponential characteristics against changes in relative humidity.

This is because the moisture-sensitive resistor 1 is created through a process of adding a phosphorous compound (phosphoric acid in the above example) to zirconium silicate and sintering it. This is thought to be due to the formation of a network structure in which zirconium and phosphorus (or ions) are chemically bonded via oxygen atoms on the surface of the zirconium silicate particles. Since the moisture-sensitive resistance element according to the above embodiment operates in response to only the physically adsorbed water contained in the moisture-sensitive sintered body, its moisture-sensitive characteristics exhibit extremely good exponential characteristics with respect to relative humidity. Because surface hydroxyl groups are unlikely to be reformed due to moisture absorption, they are stable with little change over time.

The humidity-sensitive resistor 1, which is sintered by adding a phosphorus compound to the above-mentioned zirconium silicate, has a relationship between resistance value and relative humidity that is second to none even after being left at room temperature and humidity for 10 days.
There is almost no change from the curve in the figure, and the characteristics have stable characteristics with no change over time.

Incidentally, Figure 3 shows the humidity-sensitive characteristics at an ambient temperature of 25°C of a humidity-sensitive resistance element fabricated in the same manner as in the above example without adding phosphoric acid but with aluminum oxide particles instead. show. In FIG. 3, curve a shows the initial characteristics of pellets fired for 3 hours at a firing temperature of 1000°C. Curve b shows the characteristics of the moisture-sensitive resistance element shown in curve a after being left at room temperature and humidity for about 4 days.

In this way, it was confirmed that the moisture sensitivity characteristics of the product to which phosphorus was not added changed in a relatively short period of time even in a normal temperature and normal humidity atmosphere.

As is clear from FIG. 2, the humidity sensitivity of the humidity-sensitive resistance element of the above embodiment is extremely high, and the resistance changes by 6 to 7 orders of magnitude over the entire humidity range.

Further, the other starting material is not limited to phosphoric acid (H ₃ PO ₄ ), and phosphorus compounds such as niline trioxide and ammonium phosphate may also be used.

<Effects> As detailed above, according to the present invention, a moisture-sensitive resistance element having stable and excellent moisture-sensitive characteristics over the entire humidity range can be easily produced with good reproducibility.

Although zirconium silicate is used as a starting material in the present invention, it is thought that the presence of silicon can improve mechanical strength compared to when zirconium oxide is used as a starting material. When using a moisture-sensitive resistance element as a humidity sensor in a place where external vibrations occur (for example, a clothes dryer or an air conditioner), if the mechanical strength is weak, cracks will occur and it will not be possible to obtain the desired resistance change. However, since the humidity-sensitive resistance element according to the present invention has high mechanical strength, stable humidity detection can be performed regardless of external vibrations.

[Brief explanation of drawings]

FIG. 1 is a schematic structural diagram of a moisture-sensitive resistance element according to the present invention. FIG. 2 shows an example of the humidity-sensitive characteristics of a humidity-sensitive resistance element in one embodiment of the present invention. FIG. 3 shows an example of the humidity-sensitive characteristics of a humidity-sensitive resistance element not according to the present invention. 1: Moisture-sensitive resistor, 2: Moisture-permeable electrode, 3: Lead wire.

Claims (1)

[Scope of Claims] 1. In a humidity-sensitive resistance element comprising a humidity-sensitive member whose electrical resistance value changes in response to relative humidity or absolute humidity, the entirety or surface layer of the humidity-sensitive member contains silicic acid. A moisture-sensitive resistance element characterized by forming a chemical bond of zirconium and phosphorus. 2. A method for manufacturing a humidity-sensitive resistance element comprising a humidity-sensitive element whose electrical resistance value changes in response to relative humidity or absolute humidity, characterized in that the element is produced by firing a mixture of zirconium silicate and phosphorus at a high temperature. A method for manufacturing a moisture-sensitive resistance element.