JPS6351364B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a humidity sensing element, and more particularly to a sensor that has an electrical resistance that is easy to use in a wide range of humidity and can be used stably for a long time. A humidity sensor that measures and detects atmospheric humidity is
An extremely large number of methods have been proposed and put into practical use so far. Particularly in recent years, humidity sensors that can directly detect humidity electrically have been proposed. As mentioned above, humidity sensors that directly detect humidity electrically have the advantage of being able to easily process not only detection but also humidity control using electrical signals, and inexpensive ones have also been proposed and put into practical use. It is attracting attention. By the way, some of the humidity sensors using this method have been put into practical use and are commercially available and are inexpensive.In order to measure the humidity in the atmosphere, moisture in the atmosphere is physically adsorbed onto the surface of a humidity sensor and an electric current is used. Humidity sensors such as these generally use a sintered body of a polymer or metal oxide, or even a metal oxide baked onto a substrate. . By the way, the above 2
Human humidity sensors have a resistance value that is relatively easy to use in high humidity areas, and can detect and control humidity easily and with a certain degree of accuracy, but in low humidity areas (20 ~30%R,H, or less)
In this case, the resistance value becomes extremely large, 1MΩ or 10MΩ or more, and humidity cannot be easily detected with a normal electrical detection device, and the accuracy becomes extremely poor.
On the other hand, the latter type of humidity sensor has almost no change in resistance value with respect to humidity in a low humidity region, and similarly cannot be said to be able to accurately detect low humidity.
In this way, a humidity sensor that is inexpensive, can detect low humidity with relatively high accuracy, and is stable over a long period of time has not yet been obtained. By the way, the fields that require simple and accurate detection control in low humidity regions are extremely diverse, including industrial and consumer applications, and there is a strong desire to develop humidity sensors suitable for these applications. As a result of intensive research to meet the above needs, the inventors of the present invention have developed a humidity sensor that has an electrical resistance value that is easy to use in a wide range of humidity, and that can be used relatively stably over a long period of time. I found out. That is, LiZnVO ₄ is 15 to 1 mol% ZnO is 30 to 1 mol%
This is a moisture-sensitive element made of a sintered body containing 80 mol% and 55 to 19 mol% of Al ₂ O ₃ as essential components. The humidity sensing element according to the present invention has an electrical resistance value of approximately 700 KΩ at an ambient temperature of 25° C. and a relative humidity of 10%, which is more than two orders of magnitude lower than that of conventional humidity sensors, making it extremely easy to use. Also, at a relative humidity of 90%, approximately
It has a resistance value of 5KΩ, which makes it easy to use over a wide range of humidity. By the way, it has been confirmed that the humidity-sensing characteristics of the humidity-sensing element according to the present invention change depending on the sintering temperature, although it also depends on the composition ratio. Body porosity was found to be in the range of 15-30%. Example 1 will be described in detail below. First, fine powders of lithium carbonate, vanadium oxide, zinc oxide, and aluminum oxide were used as starting materials. This raw material powder is mixed with LiZnVO ₄ , zinc oxide,
10% and 45 respectively in molar ratio as aluminum oxide
%, 45%, and then wet-mixed in a pot mill for 24 hours. Thereafter, the mixture was dried at 120°C for 12 hours and then calcined at 900°C. Thereafter, the raw material powder was further wet-pulverized in a pot mill for 24 hours, and then dried again at 120° C. for 12 hours. Next, 2% by weight of polyvinyl alcohol was added as a binder to the prepared powder thus obtained, and granulation was performed using a Raikai machine, followed by pressure molding.
Pressure molding was performed at a pressure of 500 kg/cm ² to obtain a disc-shaped molded product with a diameter of 5 mm and a thickness of about 4 mm. The thus obtained compact was sintered at a temperature of 1300° C. for 2 hours, and both main surfaces of the obtained sintered compact were polished with No. 2000 white arundum to obtain a sintered compact with a diameter of 5 mm and a thickness of 3 mm. Next, ruthenium oxide paste was applied by screen printing to both main surfaces of this sintered body, and then
Baked electrodes were formed at a temperature of 700°C to obtain a humidity sensing element as shown in FIG. The humidity characteristics of the humidity-sensitive element according to the present invention thus obtained are shown in FIG. This moisture sensing element is suitable for ambient temperature 25
670KΩ at 10% relative humidity and 90% relative humidity at °C
It has a resistance value of 6KΩ, which is extremely easy to use in a wide range of humidity. Furthermore, when the porosity of the sintered body obtained at this time was measured by mercury intrusion method, it was found that the porosity was 25%. In order to investigate the stability of the humidity sensing element according to the present invention, high humidity (40℃, 90% R, H) and low humidity (10℃, 10% R, H,
Figures 3 and 4 show the results when the moisture sensitive element was left under various conditions of (%R, H, ), respectively. Although the resistance value changed slightly for a while after being left,
After 400 hours, a stable resistance value was exhibited, confirming that the humidity sensing element was sufficiently stable even over a long period of time, and was capable of detecting humidity with high accuracy. Regarding other examples and comparative examples, including Example 1,
Composition and moisture-sensitive characteristics (as moisture-sensitive characteristics)
Shown as 10% R, H and 90% R, H at 25°C. ) are shown in the table.

【table】

[Table] As can be seen from the table, it was confirmed that all of them had resistance values that were easy to use over a wide range of humidity.
Furthermore, when the long-term stability was examined under the same conditions as in Example 1, it was confirmed that changes were almost the same as in Example 1, and that it was stable over a long period of time. By the way, when the composition of Example 1 was sintered at various humidities, the porosity of the sintered body did not change monotonically with the sintering humidity, but changed as shown in FIG. The resistance values at 25°C, 50% R and H at this time are also shown. Similar operations were carried out for other examples, and it was found that the porosity of the sintered body was necessary to obtain good resistance values over a wide range of humidity.
It has been found that a value between 15 and 30% is preferable. As described above, it has been confirmed that the humidity sensing element according to the present invention has a resistance value that is extremely easy to use in a wide range of humidity ranges, and is capable of stable humidity detection even over a long period of time, and its effectiveness is extremely high. This can be said to be remarkable.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a moisture-sensitive element according to the present invention; FIG. 2 is a curve diagram showing the moisture-sensitive characteristics of the moisture-sensitive element according to the present invention;
Fig. 3 A curve diagram showing the stability of moisture sensitivity when left at 40°C, 90% R, H, Fig. 4: 10°C, 10% R,
FIG. 5 is a curve diagram showing the stability of moisture sensitivity characteristics when left at 25° C. and 50% R, H.

Claims (1)

[Scope of Claims] 1. A moisture-sensitive element comprising a sintered body containing 15 to 1 mol% of LiZnVO ₄ 30 to 80 mol% of ZnO 55 to 19 mol% of Al ₂ O ₃ as an essential component. 2. The moisture-sensitive element according to claim 1, wherein the sintered body has a porosity of 15 to 30%.