JPS6024565B2 - 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.

Generally, metal oxides have excellent water absorption properties, and it is known that they can be used as moisture-sensitive elements by taking advantage of this property. That is, Fe203, Fe304, Yama203, Cr
A moisture-sensitive film is formed by coating fine powder of a metal oxide such as No. 203 on the surface of an inorganic insulating substrate, and the change in electrical resistance of this film with respect to humidity is utilized. This type of moisture-sensing element is physically, chemically, and thermally stable, but it generally has a high specific resistance, so even if there is a slight change in resistance due to moisture absorption and desorption, this can be electrically detected with high precision. That's difficult.
In addition, in order to lower the specific resistance, Li20, K20, N
Although there are products containing alkali metal oxides such as A20, they have many drawbacks, such as a relatively long humidity cycle history, poor reproducibility, and large changes in temperature. Further, those utilizing the semiconducting properties of spinel structure oxides have a relatively low resistance value and can detect humidity in the entire range of relative humidity from 0 to 100%. However, if left at room temperature, the resistance value increases and reproducibility is difficult to obtain. Heating has been considered to eliminate this drawback, but
Although reproducibility can be obtained by heating, there are disadvantages in that the temporal characteristics of the electrode properties due to repeated heating are unreliable, and the structure is complicated. The present invention was made in view of the above circumstances, and uses magnesium oxide (Mg0), chromium oxide (Cra03) and vanadium oxide (V2Q).
are 69.95 to 30 mol% and 29.95 to 50 mol%, respectively.
The resistance value is relatively low because it is composed of mol. It has been found that a moisture sensitive element with small hysteresis can be obtained. Therefore, it is an object of the present invention to provide a moisture-sensitive element that exhibits good stability and high reliability due to the formation of crystals. The present invention will be explained in detail below.

The present invention uses Mg.

69.95-30 mol% Cr20329.95-50 mol% V2QO. The burnt striped body has a composition of 1 to 20 mol %, and is used, for example, constructed as shown in FIG.

In the figure, 1 is the sensitive part of the device according to the present invention.
It is a bran body of 31V2Q system. 2 and 3 are electrodes, which are electrode materials that are in close contact with the Akatsuki feeder 1 and have low contact resistance and good moisture resistance;
For example, it is made of gold paste or silver paste. 4
, 5 are terminals attached to the electrodes 2 and 3.

Such a moisture sensitive element of the present invention can be manufactured, for example, by the following method. That is, Mg.

47.5 mol%, Cr20347.5 mol%, V2Q5
Weigh out the mole % and mix it thoroughly using a ball mill or the like.

Next, these mixtures were preliminarily calcined at a temperature of 850 qo for 2 hours, and then ground using a ball mill or the like. Thereafter, a binder such as polyvinyl alcohol is added to and mixed with the powder, and the powder is molded into a desired size under a pressure of about 100 k9/kg to 1.2 on'. Then, this molded body was heated to 1000 to 130
Sinter in an air atmosphere at a temperature of 0° C. for 1 to 5 hours. As shown in FIG. 1, gold paste is applied and baked on both sides of the aggregate 1 to form electrodes 2 and 3, and terminals 4.
5 are connected. The thus obtained moisture-sensitive element according to Example A of the present invention and conventional reference examples B and C
Comparisons of humidity-resistance characteristics and aging characteristics with the humidity-sensitive element according to the above are shown in FIGS. 2 to 5. Reference example B is Zn○-V2Q-Li20 in which an alkali metal oxide is added to a metal oxide.
Reference Example C is an MgCr204 type moisture sensitive element made of a spinel structure oxide, but Example A shows superior results in all cases. In other words, in the humidity-resistance characteristics shown in Figure 2, Reference Example B has high resistance at low humidity;
At high humidity, although the resistance is low and the digit of change is large, the humidity hysteresis is large. Reference Example C has a relatively low resistance value and a large digit of change, but the humidity hysteresis is small.
On the other hand, Example A has a low resistance value, a single digit variation, and a small humidity hysteresis, which has a great advantage over Reference Examples B and C in terms of matching with the measurement circuit. Third
Figures 5 to 5 show a comparison of the characteristics over time between the humidity sensing element of Example A and the humidity sensing element of Reference Example C.
After 100 q hours have passed in an atmosphere of . If the humidity in Figure 3 is 50%, the humidity in Figure 4 is 70%.
In this case, FIG. 5 shows the rate of change when the humidity is 90%. According to this, Example A is stable with almost no change, but Reference Example C has a large rate of change and moves in the negative direction. Next, the reasons for limiting the composition ratios of Mg○, Cr203 and V2Q in the present invention will be explained with reference to FIGS. 6 to 8.
Figure 6 shows the relationship between the composition ratio of Mg0 and the average particle size of non-consolidating particles. exceeds 2rm and the porosity becomes small, which is not desirable as a moisture-sensitive element. Figure 7 shows the relationship between the composition ratio of Cr203 and the average grain size of the competitors.
As in the case of g0, the average particle diameter of the dawn feeder exceeds 2 grains and the porosity becomes small, making it unsuitable for use as a moisture sensing element. Furthermore, Figure 8 shows the relationship between the composition ratio of V2Q and the resistance value, and shows the change in resistance value corresponding to the composition ratio of V205 when the temperature is 60%. The value falls within the range of 1 and ○, but if it is less than 0.1 mol % or exceeds 20 mol %, the resistance value increases and a moisture sensitive element with good aging characteristics cannot be obtained. As is clear from these, Mg069.95-30 mol%, Cr203
29.95-50 mol%, V2QO. It can be seen that the optimum composition range is 1 to 20 mol%. As detailed above, according to the present invention, Mg069.95 to 30 mol%, Cr2
0329.95-50 mol% and V2QO. 1-20
By constructing a competitive body with a composition of mol%, the resistance value is low and the resistance value is stable even when left at room temperature without heating, and the resistance value changes over time.Moreover, we have created a highly reliable moisture sensing element with low humidity hysteresis. Obtainable.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of the humidity sensing element according to the present invention, FIG. 2 is a curve diagram showing humidity-resistance characteristics, and FIGS. 3 to 5
The figures are curve diagrams showing the aging characteristics, Figure 6 is a curve diagram showing the relationship between the composition ratio of Mg0 and the average particle size, and Figure 7 is a curve diagram showing the relationship between the composition ratio of Mg0 and the average particle size.
Curve diagram showing the relationship between the composition ratio and average particle size of No. 203, No. 8
The figure shows the relationship between the composition ratio of V205 and the resistance value. 1... Scale rust body, 2, 3... Electrode, 4,
5...Terminal. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] 1 Magnesium oxide 69.95-30 mol% Chromium oxide 29.95-50 mol% Vanadium oxide 0.1
A moisture-sensitive element made of a sintered body having a composition of ~20 mol%.