JPS6028202A - Humidity sensitive element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to a moisture sensitive element.

[Technical background of the invention and its problems] Moisture sensing element (humidity sensor) that measures and detects atmospheric humidity
A large number of methods have been proposed and put into practical use. In particular, in recent years, various types of humidity sensors that can directly detect humidity electrically have been proposed. This humidity sensor is attracting attention because it has the feature that not only humidity detection but also humidity control can be easily processed using electrical signals.

By the way, in order to measure the humidity in the atmosphere, the above-mentioned humidity sensor generally causes moisture in the atmosphere to be physically adsorbed on the surface of a humidity sensing element, and then reads the electrical resistance value. Conventionally, the humidity sensing element of such a humidity sensor is a sintered body of a polymeric substance, a metal oxide, or a substrate in which a metal oxide is baked.

However, humidity sensors that use polymeric substances as moisture sensing elements have extremely high resistance values in the low humidity region, ranging from IMΩ to over 10MΩ, so humidity cannot be easily detected using ordinary electrical detection circuits, resulting in high accuracy. It also had the disadvantage of being extremely bad.

Although humidity sensors using metal oxides as moisture sensing elements have excellent initial sensitivity, they all have the drawback of large changes in resistance after long-term use. In order to overcome this problem, a heater was attached to the humidity sensor made of a sintered metal oxide, and the humidity sensor was temporarily heated before humidity measurement to bring it into a high temperature state and regenerate the surface of the humidity sensor. There are also known devices that later detect humidity. Utilizing the thermal stability of the humidity-sensitive element made of a metal oxide, the humidity-sensitive element is returned to its initial state by raising the temperature to a high temperature just before detecting humidity, ensuring reproducibility. However, with such a humidity sensor, continuous humidity detection is impossible because heating must be performed immediately before humidity detection. Moreover, a complicated mechanism such as a heater and a heater control circuit is required, which becomes a cause of high cost.

Due to these problems, Zn08 has recently been used as a humidity sensor.
5~99-t=le%, LiZrVO40,5~10
A device using a moisture-sensitive element body made of a metal oxide having a composition of 0.5 to 5 Mok% and Cr2O3+Fe203% has been developed (Japanese Patent Application Laid-Open No. 56-4204). This humidity sensor can be used stably for a long period of time under normal environmental conditions (0 to 40 degrees Celsius, 30 to 90% Hbl) without any regeneration treatment such as a heater, and has a low resistance value. It is fully applicable to humidity control in air conditioners and humidifiers. However, when such a humidity sensor is used under high temperature conditions, it may not always be possible to obtain sufficient aging characteristics and reproducibility.

[Objective of the Invention] The present invention provides a moisture-sensitive element that can be used stably with almost no change in resistance even when used for a long time under high-temperature conditions, and has an electrical resistance value that is easy to use even in a wide range of humidity. This is what we are trying to provide.

[Summary of the invention] The present invention provides Crz0321-73-e mol%, at least one of ZnO and MgO, 25-55 mol%, P2
This is a moisture-sensitive element made of a sintered body whose essential components are O52.0 to 10.0 mol and Li200.5 to 80 mol 2O50.5 to 8.0 mol. For example, at an ambient temperature of 25°C and a relative humidity of 30%, such a humidity sensing element has a
00 Ω, and at the same temperature and relative humidity of 9 Ω, approximately 15 Ω.
, and has an easy-to-use resistance value in a wide range of humidity,
Moreover, even if left for a long period of time under a high temperature condition of 85° C., it shows little change over time and has high reliability. As described above, the moisture sensitive element of the present invention has excellent characteristics because of CrzO.
3. A small amount of P such as CrzOa or ZnO is added to the grain boundaries of crystalline particles of ZnO (or ZnO and MgO, or MgO alone).
This is presumed to be due to the structure in which the components 2O5, Li 20 and V2O5 are present.

The reason for limiting the blending ratio of C "203" above is that if the amount exceeds 21 momoles, the resistance value as a moisture sensitive property will be generally high, but on the other hand, if the amount exceeds 73 momoles, This is because the change over time becomes large when left at high temperatures.

The reason for limiting the blending ratio of at least one of ZnO and MgO is that if the amount is set to 25 mmol, the change over time when left at high temperatures will be difficult, but if the amount is set to 55 mmol, If it exceeds this value, the resistance value as a moisture sensitive property will generally be high and shaky.

In this case, even if ZnO and MgO are used alone or in combination, similar effects can be exerted.

The reason for limiting the blending ratio of CuO is that the amount is 2.
This is because if the amount is less than 0 mol, the change over time when left at high temperatures will be poor, but if the amount exceeds 10.0 mol, the resistance value will increase on the low humidity side.

The reason for limiting the blending ratios of Li2O and V2O5 is that when the amounts of LizO and V2O5 are each less than 0.5 mol, the resistance value as a moisture sensitive property becomes higher overall, but on the other hand, LizO, This is because when the amount of V2O5 exceeds 8.0 moles each, changes over time when left at high temperatures become large.

[Embodiments of the invention” Next, the present invention will be explained in detail.

Example 1 First, chromium oxide, zinc oxide, and phosphoric acid were used as starting materials.
Fine powders of ammonium, lithium carbonate, and vanadium oxide were used. These starting materials are Cr2O3, ZnO, C
uO, Li2O, V2O5 (7) molar ratio 45%.

Weigh it so that it becomes 45%, 4%, 3%, 3chi,
Thereafter, the mixture was wet mixed in a pot mill for some time.

Subsequently, this mixture was dried at 120°C for 12 hours and then calcined at 800°C. Subsequently, the calcined product was wet-milled for a while in a bot mill, and then dried again at 120'O for 12 hours to prepare a raw material powder.

Next, 2% by weight of polyvinyl alcohol (binder) was added to the raw material powder and granulated using a Leica machine, and the granulated product was pressure-molded at 50 ruts/cr/I to give a diameter of 8 mm. A disk-shaped molded body with a thickness of about 2 mm was made.

Subsequently, this molded body was fired at a temperature of 1300'O for 2 hours, and then both sides of the sintered body were polished to a thickness of 1 knot. Subsequently, after screen printing ruthenium oxide paste on both sides of this sintered body (moisture sensitive element), about 700
Baking was carried out at .degree. C. to form electrodes with a diameter of 6 mm, and a moisture-sensitive element having the structure shown in FIG. 1 was manufactured. Note that 1 in Figure 1
is a moisture sensitive element body, and 2 is an electrode.

Therefore, for the humidity sensing element of Example 1, the ambient temperature was
When the resistance value (humidity sensitivity characteristic) was examined at a constant temperature of 5 DEG C. and the relative humidity was varied from 30 to 90%, the characteristic diagram shown in FIG. 2 was obtained. As is clear from FIG. 2, the humidity sensing element of the present invention has a temperature of 76% at an ambient temperature of 25°C and a relative humidity of 30%.
It can be seen that at 0KQ, the same temperature, and 90% relative humidity, the resistance is 8.6Ω, which is a low resistance value that is extremely easy to use in a wide range of humidity.

In addition, the resistance value (humidity sensitivity characteristics) when the humidity sensing element of Example 1 was left in a constant temperature bath at a temperature of 85° 0 for 1000 hours and the relative humidity was changed from 30 to 90% at an ambient temperature of 5°C.
As a result of investigation, the characteristic diagram shown in Figure 3 was obtained. This third
As is clear from the figure, the humidity sensitive element of the present invention shows almost no change in its moisture sensitive characteristics after being left at high temperatures, and it can be seen that it has stable characteristics over time. Examples 2 to 7 Same as the above examples Six types of humidity sensing elements were manufactured using a method using a sintered body (humidity sensing element) having the composition shown in Table 1 below.

Therefore, the humidity sensing elements of Examples 2 to 7 were tested at an ambient temperature of 25°C, a relative humidity of 30%, a resistance value of 90% (initial moisture sensitivity characteristics), and after being left in a constant temperature bath at 85°C for 1000 hours. The resistance value (moisture sensitivity characteristics after being left at high temperature) at an ambient temperature of 25°C and a relative humidity of 30°C and 90% was investigated. The results are also listed in Table 1. In addition, in Table 1, reference example 1 shows a humidity sensing element equipped with a humidity sensing element outside the composition range of the present invention.
Also listed as ~6.

As is clear from Table 1 above, the humidity sensing element of the present invention has a resistance value that is extremely easy to use in a wide range of humidity, and has stable aging characteristics even under high temperature conditions. In contrast, moisture-sensitive elements (Reference Examples 1 to 6) made of sintered bodies outside the composition range of the present invention have resistance values that are easy to use in the wide range of humidity and stable aging characteristics under high-temperature conditions. Don't satisfy both.

Example 8 First, as starting materials, chromium oxide, magnesium carbonate,
Fine powders of ammonium phosphate, lithium carbonate, and vanadium oxide were used. These starting materials are Cr2O3,M
The molar ratios of gO, P2O5, Li20, and V2O5 were weighed to be 45, 45, 4, 3, and 3, and then wet mixed in a bot mill for U hours.

Subsequently, this mixture was dried at 120υ for 12 hours and then calcined at 800°C. Subsequently, the calcined product was wet-milled in a pot mill for U hours, and dried again at 120° C. for 12 hours to prepare a raw material.

Next, a moisture-sensitive element having the same structure as that shown in FIG. 1 was manufactured in the same manner as in Example 1 using the raw material powder.

Therefore, for the humidity sensing element of Example 8, the ambient temperature was
When the resistance value (humidity sensitivity characteristic) was examined when the relative humidity was changed from 30 to 90 degrees with a constant temperature of 0.degree., the characteristic diagram shown in FIG. 4 was obtained. As is clear from FIG. 4, the humidity sensing element of the present invention has a temperature of 630 KQ at an ambient temperature of 5°C and a relative humidity of 30%.
It can be seen that at the same temperature and relative humidity of 90, it exhibits a low resistance value of 6 or 7 Ω, which is extremely easy to use in a wide range of humidity.

In addition, the resistance value (humidity sensitivity characteristics) when the humidity sensing element of Example 8 was left in a constant temperature bath at a temperature of 85°C for 1000 hours and the relative humidity was changed from 30 to 90% at an ambient temperature of 25°C. As a result of investigation, the characteristic diagram shown in FIG. 5 was obtained. As is clear from FIG. 5, the moisture sensitive element of the present invention shows almost no change in its moisture sensitive characteristics after being left at high temperatures, indicating that it has stable aging characteristics.

Examples 9 to 14 Six types of humidity sensing elements each having a sintered body (moisture sensing element) having the composition shown in Table 2 below were manufactured in the same manner as in Example 1.

Therefore, the humidity sensing elements of Examples 9 to 14 had an ambient temperature of 5°C, a relative humidity of 30%, a resistance value of 90% (initial moisture sensitivity characteristics), and after being left in a constant temperature bath at 85°C for 1000 hours. Ambient temperature 25°C, relative humidity %,
The 90% resistance value (moisture sensitivity characteristics after being left at high temperature) was investigated. The results are also listed in Table 2. In addition, in Table 2, reference examples 7 to 12 also include moisture-sensitive elements having moisture-sensitive elements outside the composition range of the present invention.

As is clear from Table 2 above, the humidity sensing element of the present invention has a resistance value that is extremely easy to use in a wide range of humidity, and has stable aging characteristics even under high temperature conditions. On the other hand, the humidity sensing elements (Reference Examples 7 to 12) made of sintered bodies outside the composition range of the present invention have resistance values that are easy to use in the wide range of humidity and stable aging characteristics under high temperature conditions. Don't satisfy both.

Examples 15 to 19 Six types of humidity sensing elements each having a sintered body (moisture sensing element) having the composition shown in Table 3 below were manufactured in the same manner as in Example 1.

Therefore, the humidity sensing elements of Examples 15 to 19 were subjected to an ambient temperature of 25°C, a relative humidity of 30%, a resistance value of 90% (initial moisture sensitivity characteristics), and were left in a constant temperature bath at 85°C for 1000 hours. Later ambient temperature is 25°C and relative humidity is 30%.

The resistance value (humidity sensitivity characteristics after being left at high temperature) of the 90-meter was investigated and the results are also listed in Table 3. Further, in Table 3, humidity sensing elements having humidity sensing cables outside the composition range of the present invention are also listed as Reference Examples 13 to 14.

As is clear from Table 3 above, the humidity sensing element of the present invention has a resistance value that is extremely easy to use in a wide range of humidity, and has stable aging characteristics even under high temperature conditions. In contrast, the humidity sensing elements (Reference Examples 13 to 14) made of sintered bodies outside the composition range of the present invention have a resistance value that is easy to use in the wide range of humidity and stable aging characteristics under high temperature conditions. Don't satisfy both.

[Effects of the Invention] As detailed above, the present invention has an electrical resistance value (humidity sensitivity characteristic) that is easy to use even in a wide range of humidity, and moreover, the resistance value does not change even when used for a long time under high temperature conditions. It is possible to provide a highly reliable moisture sensing element that can be stably used with almost no occurrence of moisture.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing one form of the moisture-sensitive element of the present invention, and FIG.
The figure is a diagram showing the initial humidity sensitivity characteristics of the humidity sensing element of Example 1, FIG. 3 is a diagram showing the humidity sensitivity characteristics of the humidity sensing element of Example 1 after being left at high temperatures, and FIG. 4 is a diagram of the example. FIG. 5 is a diagram showing the initial humidity sensitivity characteristics of the humidity sensing element of Example 8, and FIG. 5 is a diagram showing the humidity sensitivity characteristics of the humidity sensing element of Example 8 after being left at high temperatures. ■... Sintered body (moisture sensitive element), 2... Electrode. 7 Figure 1 Figure 2 Relative humidity (%) Figure 4 Relative humidity % Figure 3 Figure 5 Supplementary profit (%)

Claims (1)

[Claims] CrzOa 21-73 mol%, ZnO and MgO (
D') Chino at least 1 type 25-55 molti, P2
O52, 0~10.0% Le%, Lis+00.5~8
．． 0 mol%, V2O50.5 to 8.0 (-h).