JPS5811723B2 - moisture sensing element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a humidity sensing element made of metal oxide and detecting changes in humidity as changes in electrical resistance.

Conventional moisture-sensitive elements of this type include those in which fine powder of metal oxide is applied to the surface of an inorganic insulating substrate to form a moisture-sensitive film, and those in which electrodes are attached to a sintered body of metal oxide. Both utilize the fact that the electrical resistance changes in response to changes in humidity.

However, although some of the above-mentioned conventional moisture-sensitive elements have excellent sensitivity in the initial stage, all of them have five drawbacks, such as a large change in resistance value over time when used for a long period of time.

In order to overcome this drawback, a heater is installed in the temperature/humidity element made of a sintered body of metal oxide, and the humidity sensing element is temporarily heated before use, and the surface of the humidity sensing element is regenerated into a high temperature state. Devices that detect humidity are also known.

In other words, by utilizing the thermal stability of a sintered body of metal oxide and raising the temperature to a high temperature immediately before detecting humidity, the humidity sensing element is returned to its initial state and reproducibility is ensured.

However, since this humidity sensing element needs to be heated immediately before detecting humidity, continuous humidity detection is not possible.

Another drawback is that it requires a complicated mechanism such as a heater and a heater control circuit.

In addition, in order to enable continuous humidity detection, various moisture-sensitive element materials have been studied. For example, a moisture-sensitive element made of Zn0-LiZnVO4 (Japanese Patent Application No. 1983-97020) has been proposed as one with improved aging characteristics. It will be done.

Although this moisture-sensitive element has excellent aging characteristics in high humidity without undergoing regeneration treatment such as a heater, it can be used at room temperature and humidity.
When used for a long period of time under conditions (25° C., 50-60% R, H), sufficient aging characteristics and reproducibility may not always be obtained.

The present invention eliminates the above-mentioned drawbacks and provides a
Even after long-term use at 40°C, 30% R, H to 90% R, H), there is almost no change in the resistance of the moisture-sensitive element, and the reproducibility is excellent.
The purpose is to provide a moisture sensitive element with excellent reliability.

That is, the present invention uses zinc oxide (99 to 85 mol%) and LiZn consisting of zinc oxide, lithium carbonate, and vanadium oxide.
VO4 (spinel compound) (0.5 to 10 mol%) and at least one oxide selected from chromium oxide and iron oxide (
0.5 to 5 molar ratio).

The reason for limiting the composition range in the present invention is that LiZ
If the spinel compound consisting of nVO4 is less than 0.5 molty, the sensitivity to humidity (change in resistance value to changes in humidity) will be small, making it unsuitable for practical use.

On the other hand, if it exceeds 10 molts, the change in resistance at room temperature and humidity (change over time) becomes large, resulting in poor reproducibility and reliability.

Furthermore, if the content of chromium oxide or iron oxide is less than 0.5 mol%, the sensitivity will be low, and if it exceeds 5 mol%, the resistance value of the moisture sensing element will increase, making detection of resistance value changes practically inappropriate.

Further, ZnO was placed in the i range because sufficient moisture sensitivity characteristics cannot be obtained outside the range of 85 to 99 mol.

The present invention will be described in detail with reference to its implementation.

Next, the present invention will be explained by giving specific examples.

First, Li2cD3. znO and v20. were accurately weighed to give a composition ratio of 2=1 in terms of molar ratio, and mixed well using a ball mill.Then, this mixture was pre-calcined at 700°C for 1 hour, and then pulverized using a ball mill to form LiZnV.
O4 powder was obtained.

The thus obtained LiZnVO4 powder, ZnO powder and Cr
After weighing a predetermined amount of 203eFe203 powder, mixing it,
The raw materials were adjusted and prepared.

Next, polyvinyl alcohol (binder) is added to the raw material powder.
was added, press-molded at a pressure of 1.0 g/cd2, and then heated and sintered.

At this time, if the firing temperature is less than 1,100°C, the strength of the moisture-sensitive element will be weak, and if it exceeds 1,300°C, the moisture-sensitive characteristics will deteriorate, so it is preferable to set the firing temperature in the range of 1,100 to 1,300°C.

As shown in Figs. 1 and 2, the shape of the moisture-sensitive element is a disc 1 with a thickness of 1 rn and a diameter of 10 mm, and a pair of electrodes are baked on the double-sided surfaces of this disc in the form of a lattice. 2 and 2' were provided, and the lead wires 3 were connected by thermocompression bonding to produce moisture-sensitive elements, respectively.

Next, 63 as an example and a comparative example manufactured as above.
251.30% obtained for each moisture sensitive element of the species
Resistance value of R, H R1, 25C, 90% Resistance value of R, H
2 and the sensitivity iR0/R2 are shown in the following table.

As a result, it was confirmed that the moisture sensitive element according to the present invention had practically sufficient sensitivity and resistance value.

Next, the change over time of the humidity sensing element according to the present invention was investigated.

First, as for the aging characteristics in high humidity, sample No.

10.15.20 (implementation row) and sample No. 63 (comparative example) were each heated at 25°C under the conditions of 90-95% R and H.
The resistance change rate (9e) after being left for 000 hours was as shown in FIG.

Note that in FIG. 3, curve A is for sample No. 10, and curve A is for sample No. 10.

63 cases are shown respectively.

Moreover, sample No. 15.20 showed the same results as the above curve A.

Furthermore, the aging characteristics at room temperature and humidity are as follows: 25℃, 50℃
The rate of change in resistance (a) when left for 1000 hours under %R,H conditions is shown in FIGS. 4 to 8.

FIG. 4 and FIG. 8 are comparative examples, with FIG. 4 showing sample No. 63, and FIG. 8 showing sample No. 25, 45, or 62.

On the other hand, FIGS. 5 to 7 show changes over time in Examples according to the present invention, and the curve A1 in FIG. 5 is sample No.

5, L, 14 or 19, curve A2 in Fig. 5 is sample N.
o, 6, 10, 11, 15 or 16, curve A3 in Figure 6 is sample No. 30, 34 or 39, curve A3 in Figure 6 is sample No. 31, 35, 36° 40 or 41
Curve A in FIG. 7 is sample No.

50.54 or 58, and the curved line in Fig. 7 is sample N.
o, 51, 55 or 59 respectively.

As is clear from the above results, the examples according to the present invention showed only a change in resistance value of 2% or less over 1000 hours, and were confirmed to have excellent stability.

In addition, in the table, trial I No. 24.25,44,45
Sample No. 48 has high sensitivity but poor aging characteristics, and sample No. 48 has too high a resistance value to be practical.

Further, for sample No. 16 as an example and sample No. 63 as a comparative example, 30% ROH ~ 9
As a result of repeating the humidity cycle of 0% R and H 1000 times, there was a change in resistance value of only about 2 to 5% at most in the example, and about 5 to 8% in the comparison row.

As a result, the humidity sensing element according to the present invention has high sensitivity in the practical resistance range, excellent aging characteristics in high humidity and normal humidity ranges, and stable characteristics against humidity cycles. The matter was confirmed.

Since it has such stable moisture sensitivity characteristics, it is possible to continuously and accurately detect humidity, and it can be said to be of great practical value.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIGS. 1 and 2 are perspective views and sectional views showing the structure of a moisture-sensitive element according to the present invention, and FIGS. FIGS. 4 and 8 are curve diagrams showing characteristic examples of the moisture-sensitive element according to the invention, and FIGS. 4 and 8 are curve diagrams showing characteristic sequences of comparative examples.

Claims (1)

[Scope of Claims] I A sintered body containing 99 to 85% #% of ZnO, 40.5 to 10% of LiZnVO, 0.5 to 5% of Me2O3 (at least one selected from Me20B=Cr203zFe203) Features a moisture-sensitive element.