JPH05264494A - Moisture-sensitive element - Google Patents

Abstract

PURPOSE:To reduce change with time by using a porous sintered body ceramic blending and containing PbO and Ta2O5 for a main component consisting of TiO2 and SiO2. CONSTITUTION:A particle which is obtained by weighting in a ratio of approximately 0.1-8 pts.mol PbO and approximately 0.005-2 pts.mol Ta2O5 is blended to a main component with 100 pts.mol consisting of approximately 45-90mol% TiO2 and approximately 10-55mol.% SiO2, is formed to a specified shape, and then is calcined at approximately 1,200-1,400 deg.C, thus obtaining a ceramic of porous sintered body and assembling a desired moisture sensor using it as a moisture-sensitive element. The moisture-sensitive element consisting of this sort of ceramic reduces change with time and can be used over a wide detection measurement moisture range and at the same time improves response to moisture change.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic moisture sensitive element suitable for a humidity sensor used in an air conditioner, a humidity control system, a hygrometer or the like.

[0002]

2. Description of the Related Art Hitherto, as a humidity sensitive element used in a humidity sensor, there is one that obtains humidity by measuring the electric resistance by utilizing the property that the electric resistance changes according to the humidity. It is said that a ceramic oxide sintered body is superior to an organic one in terms of deterioration of the material itself, heat resistance, and the like.

[0003]

However, even the moisture-sensitive element made of the above-mentioned ceramics, the conventional one is limited to a region having a humidity detection range, and further has good characteristics in the initial stage. However, even if it is used, there is a big drawback that it tends to change with time when used for a long time. For this reason, a humidity sensor in which a heating cleaning heater for reproduction is attached in the vicinity of the sintered ceramics has been put into practical use, but this method has a drawback that the size becomes large and the power consumption becomes large. In addition, in recent years, coupled with the diversification of applications of humidity sensors,
Although responsiveness to changes in humidity has also been demanded, the fact is that the conventional ones are not sufficiently satisfactory. In view of the above-mentioned inconvenience, the present invention has a wide detection and measurement range for humidity,
Furthermore, while significantly reducing the change with time described above,
It is an object of the present invention to provide a humidity sensitive element having improved responsiveness.

[0004]

In order to achieve the above object, the moisture-sensitive element of the present invention comprises 45 to 90 parts by mole of TiO ₂ and S.
With respect to 100 parts by mole of the main component consisting of 10 to 55 parts by mole of iO ₂ ,
PbO 0.1 to 8 parts by mole and Ta ₂ O ₅ 0.005 to 2 parts by mole are mixed and contained, and the sintered body is made of a porous sintered ceramics. Further, the humidity-sensitive element according to the present invention is affected by the particle diameter of SiO ₂ in the humidity-resistance characteristic, so that the average particle diameter of SiO ₂ is preferably in the range of about 1 to 25 μm. Humidity is 5 to 50 when the average particle size is less than 1 μm.
%, The change in resistance is relatively slow, and when it exceeds 25 μm, the change in resistance tends to be slow in the entire low to high humidity range. More preferably approximately 2.5-20 μ
It is in the range of m.

Further, in order to specifically obtain the moisture-sensitive element of the present invention, TiO _{2 is} 45 to 90 mol% and SiO _{2 is} 10 to 55 mol%.
The powder was weighed in a ratio of 0.1 to 8 mol parts of PbO and 0.005 to 2 mol parts of Ta ₂ O ₅ to 100 mol parts of the main component consisting of ~
By firing at 1400 ° C., it is obtained as a ceramic of a porous sintered body, and a desired humidity sensor is assembled by using this as a humidity sensitive element.

[0006]

In the moisture-sensitive element of the present invention, the main components of the composition are TiO ₂ 45 to 90 mol% and SiO ₂ 10 to 55 mol%, where TiO ₂ acts as a base material of the humidity sensitive element. However, SiO ₂ has the effect of making it porous when it is used as a sintered ceramics. However, if TiO ₂ is less than 45 mol%, that is, if SiO ₂ is more than 55 mol%, the resistance value of the obtained sintered ceramics becomes large, the rate of change in resistance value with respect to humidity change becomes dull, and the burning is slow The strength of the bound ceramics is also reduced, which is not preferable. or,
Conversely, when TiO ₂ exceeds 90 mol%, that is, Si
If the O ₂ content is less than 10 mol%, the resulting sintered ceramics will not be sufficiently porous and the porosity will decrease, which is not preferable because the tendency of the resistance change with respect to the humidity change becomes dull.

Next, as an additive component, PbO has the effects of greatly reducing the change with time and improving the responsiveness. Therefore, PbO is a main component composed of TiO ₂ and SiO _2.
When the amount is less than 0.1 part by mol relative to 0 part by mol, the change with time becomes large and the responsiveness to changes in humidity deteriorates.
On the other hand, when PbO exceeds 8 parts by mole, the resistance value of the sintered ceramics becomes large and the sensitivity of the resistance value change to humidity change becomes unfavorable.

Next, Ta ₂ O ₅ acts as a valence control agent for TiO ₂ , and when it is less than 0.005 parts by mole with respect to 100 parts by mole of the above main component, the resistance value of the sintered ceramics is It is not preferable because it becomes large. On the other hand, if the amount exceeds 2 mol parts, the resistance value of the sintered body increases and the resistance change width in the high humidity region narrows, which is not preferable. As described above, TiO ₂ constitutes the base material of the moisture-sensitive element of the present invention, and the predetermined amount of SiO ₂
By simultaneously adding PbO and Ta ₂ O ₅ ,
For the first time, excellent moisture sensitivity characteristics can be exhibited.

[0009]

EXAMPLES The present invention will be described below based on examples. With respect to sample Nos. 1 to 29 shown in Table 1, raw materials for each component were weighed so as to have a predetermined composition. The average particle size of TiO ₂ at this time was 0.7 μm, and PbO and Ta ₂ O were used.
Those of ₅ were 2.2 μm and 1.1 μm, respectively. SiO ₂
The average particle size of was changed as shown in Table 1. This was mixed in a wet ball mill for 20 hours. After the mixture was dried, a small amount of a binder made of polyvinyl alcohol was added and stirred. Then pass through a 80 mesh screen, 1
The granulated powder was one that did not pass through a 50-mesh sieve. The granulated powder was molded into a disc shape having a diameter of 10 mm and a thickness of 0.8 mm at a pressure of 0.7 ton / cm ² . Next, this was fired in air at a temperature of 1280 ° C. for 1 hour to obtain a porous sintered ceramics.

Next, a RuO ₂ paste was baked on both surfaces of this sintered ceramics, and lead wires were attached thereto to provide a pair of electrodes. For each sample thus obtained, the relative humidity (5% RH, 30%
RH, 55% RH, 95% RH) at 25 ° C
Humidity changes at 10% RH to 90% RH
% RH to 10% RH), each sample was evaluated at 40 ° C, 65% R.
Table 1 also shows the rate of change of the resistance value after leaving it in the H. atmosphere for 4800 hours (the increase in the resistance value was defined as +). The resistance is measured by LCR meter (HEWLETT PA
CKARD impedance analyzer 4192A)
The resistance value is the value when an alternating voltage of 1 V and 1 kHz is applied, and the response time is measured at 0 second when the humidity sensitive element is moved into a different humidity atmosphere, and the resistance value is ± 10 of the final resistance value.
The required time (seconds) to enter the range of% was obtained as the response time.

[Table 1] From the above results, it can be seen that the moisture sensitive element of the present invention also has the following characteristics. That is, it has been found that it functions against a wide range of humidity changes of 5 to 95% RH, and since the rate of change in resistance is large in this wide range, humidity (relative humidity) can be measured accurately. In addition, the resistance value in the low humidity range is 5
Since it is within the practical measurement range of about 2000 KΩ or less at% RH, it is very advantageous not only in accuracy but also in device design such as size reduction. Also, it can be seen that the response time to the humidity change is short and the response is good, and further, the change in resistance value after using for 4800 hours is small and the durability is good.

[0011]

EFFECTS OF THE INVENTION The humidity sensitive element made of the ceramics of the present invention can greatly reduce the change with time, can be used in an extremely wide range of detected and measured humidity, and can greatly improve the responsiveness to changes in humidity. Therefore, a humidity sensor made of this is extremely small in size, high in precision, and excellent in durability, and therefore has a great utility value.

Claims (1)

[Claims] 1. TiO ₂ 45 to 90 parts by mole and SiO ₂ 10 to
PbO for 100 parts by mole of the main component consisting of 55 parts by mole
A moisture-sensitive element comprising a porous sintered ceramics obtained by mixing and sintering 0.1 to 8 parts by mole and Ta ₂ O ₅ 0.005 to 2 parts by mole.