JPH06224003A - Humidity sensitive element - Google Patents

Abstract

PURPOSE:To greatly diminish the with-time fluctuation while improving the responsibility by a method wherein the title sensitizing element is composed of a porous sintered body ceramics comprising the mixture of the main component constituting specific amount of TiO2, SiO2 with Bi2O3 and SnO2, Ta2O5 to be baked later. CONSTITUTION:The humidity sensitizing element is mainly composed of 45-90mol% of TiO2 and 10-55mol% of SiO2. Next, the particles weighed at the-ratio of 0.1-8mol% of at least one kind of groups comprising Bi2O3 and SrO2 and 0.005-2mol% of Ta2O5 are mixed with 100mol% of said main component. Next, the mixture molded in a specific shape is baked at the temperature of 1200-1400 deg.C into a porous sintered body ceramics to be used as the title humidity sensitive element. Through these procedures, the with-time fluctuation can be notablly diminished while enabling the title element to be applied in extremely extensive range of humidity measurement by a hydroscope as well as the responsibility to the fluctuation in humidity to be notably improved.

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 Heretofore, 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 the metal-based sintered ceramics are superior to the organic-based ceramics 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 ,
0.1 to 8 parts by mole of at least one member selected from the group consisting of Bi ₂ O ₃ and SnO ₂ and 100 ₂ parts by mole of Ta ₂ O _{5 to} 0.005 to ₂ parts by mole with respect to 100 parts by mole of the main component consisting of 10 to 55 parts by mole of SiO _2. The composition is made of porous sintered ceramics obtained by mixing and sintering and. 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, the moisture sensitive element of the present invention is specifically obtained.
Has TiO₂45 to 90 parts by mole and SiO₂10-55 parts by mole
For 100 mol parts of the main component consisting of₂O₃And S
nO ₂0.1 to 8 mol of at least one of the group consisting of
Department and Ta₂O_FiveWeighed at a ratio of 0.005 to 2 parts by mole
After mixing the powder and forming it into the specified shape, the temperature is 1200 ~ 14
Porous sintered ceramic by firing at 00 ℃
As a moisture-sensitive element,
The degree sensor is assembled.

[0006]

In the moisture-sensitive element of the present invention, the main components of its composition are TiO ₂ 45 to 90 parts by mole and SiO ₂ 10 to 55 parts by mole, where TiO ₂ acts as a base material for the humidity-sensitive element. However, SiO ₂ exerts an influence on the porosity of the sintered ceramics. However, if TiO ₂ is less than 45 parts by mole, that is, if SiO ₂ is more than 55 parts by mole, the resistance value of the obtained sintered ceramics becomes large, the rate of change in resistance value with respect to humidity change becomes slow, and the sintering is slowed down. The strength of the bound ceramics is also reduced, which is not preferable. or,
Conversely, when TiO ₂ exceeds 90 parts by mole, that is, Si
If the O ₂ content is less than 10 parts by mole, the resulting sintered ceramics will not be sufficiently porous and the porosity will decrease, which is not preferable because the tendency of resistance change with respect to humidity change becomes dull.

Next, as an additive component, Bi ₂ O ₃ and / or SnO ₂ have the effects of greatly reducing the change with time and improving the responsiveness. Therefore, Bi ₂ O ₃ and / or Sn
If O ₂ is less than 0.1 part by mol with respect to 100 parts by mol of the main components consisting of TiO ₂ and SiO ₂ , the change with time becomes large and the responsiveness to changes in humidity deteriorates. on the other hand,
When Bi ₂ O ₃ and / or SnO ₂ 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 low. 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 Bi ₂ O ₃ and / or SnO ₂ and Ta ₂ O ₅ , 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 35 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 Bi ₂ O ₃ and Sn were used.
O ₂ and Ta ₂ O ₅ are 2.2 μm and 2.0 μm, respectively.
, 1.1 μm. The average particle size of SiO ₂ was changed as shown in Table 1. This was mixed in a wet ball mill for 20 hours. After drying this mixture, a small amount of a binder consisting of polyvinyl alcohol was added and stirred. Next, granulated powder was passed through an 80-mesh screen and did not pass through a 150-mesh screen. 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) resistance value at 25 ℃
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 measuring method of the resistance value is the 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 seconds 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.

[0011]

[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.

[0012]

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
Bi _{2 is} added to 100 parts by mole of the main component composed of 55 parts by mole.
At least one selected from the group consisting of O ₃ and SnO ₂
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.