JPS6156841B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a moisture-sensitive element, and more particularly, to a highly reliable moisture-sensitive element whose moisture-sensitive characteristics are less likely to deteriorate over time. Various devices are known for measuring the amount of water vapor in the air, that is, humidity, and a wet/psychrometric bulb hygrometer and a dew point hygrometer are representative examples.
Although these are inexpensive, they have drawbacks in their maintenance and operability. For example, in a psychrometric and wet bulb hygrometer, it is necessary to replenish the wet bulb with water, and depending on the water quality, the humidity reading may be slightly affected. Furthermore, in the case of a dew point hygrometer, a high degree of skill or equipment is required to accurately detect the presence or absence of dew condensation on the surface of a mirror-polished metal plate. For this reason, the use of these wet and dry bulb hygrometers or dew point hygrometers is mostly limited to mere humidity measurement, and there are very few cases where they are incorporated, for example, for signal transmission in automatic equipment. On the other hand, devices have been proposed that use microwaves or laser beams to measure humidity from phenomena such as absorption or scattering by water vapor, but these devices are large-scale and expensive, so they are not widely applied. We haven't reached that point yet. In recent years, moisture sensing elements have been proposed that utilize the phenomenon of water vapor adsorption onto the surface (or inside) of a solid. This humidity sensing element reads changes in the amount of water vapor adsorbed to the element due to differences in humidity from changes in the electrical resistance of the element, and has an extremely simple structure and is easy to handle. It is expected to have a wide range of applications because it can extract changes (changes) as electrical signals. Generally, a moisture-sensitive element has a pair of electrodes attached to opposite or the same surfaces of a porous plate-shaped sintered body made by sintering metal oxide powder, and a pair of leads are drawn from the electrodes. It is composed of. An impedance measuring circuit is disposed between the leads to read changes in the electrical resistance of the element based on changes in the amount of water vapor adsorbed on the surface or inside the internal pores of the element. However, in this case, if the surface or internal pores of the moisture sensing element adsorb oil mist, dust, or a small amount of miscellaneous gas along with water vapor,
The humidity-sensitive element may change its humidity-sensitive resistance region, or may even cease to exhibit moisture-sensitive characteristics (responsiveness as an electrical resistance value to humidity). Therefore, it is necessary to separate and remove these impurities from water vapor. Of these, oil mist, dust, etc. can be separated and removed to some extent by, for example, attaching a fine filter to the moisture sensing element, but it is extremely difficult to separate and remove miscellaneous gases from water vapor. For this reason, in general, a heater is placed around the humidity sensing element, and before the humidity sensing element is activated, the humidity sensing element is sufficiently heated to remove the oil mist, dust, etc. that have been adsorbed. A method (thermal cleaning method) of incinerating the material and removing miscellaneous gases to regenerate it as a moisture-sensitive element having the conventional moisture-sensing characteristics has been carried out. However, with this heating cleaning method, the above effects cannot be obtained unless the moisture sensitive element is heated to 400°C or higher, and therefore the power required for heating is large, making it difficult to apply to ordinary electronic control circuits. In addition, the surrounding parts of the humidity sensing element are limited to nonflammable materials, and furthermore, the normal operation of the humidity sensing element after heating cleaning is usually 30 minutes to 1 hour, and the heating Since the element cannot be operated during cooling and cooling,
This method has drawbacks such as difficulty in continuously measuring humidity or applying it to automatic control devices, and lacks versatility. SUMMARY OF THE INVENTION An object of the present invention is to eliminate such drawbacks, provide a highly reliable moisture-sensing element that has excellent moisture-sensing characteristics, is capable of continuous humidity measurement. That is, the moisture-sensitive element of the present invention contains chromium oxide (Cr ₂ O ₃ ): 30 to 80 mol % selected from nickel oxide (NiO), cobalt oxide (CoO), and manganese oxide (Cr 2 O 3 ) (MnO). At least one kind of metal oxide: 20 to 70 mol% of at least one kind of element or oxide selected from phosphorus and sulfur is supported on a porous sintered body. It is characterized by The porous sintered body according to the present invention is a sintered body of chromium oxide ( ) and at least one metal oxide selected from nickel oxide, cobalt oxide ( ), and manganese oxide ( ). This sintered body may further contain magnesium oxide. In the sintered body, when chromium oxide () exceeds 80 mol%, its electrical resistance value becomes extremely high (approximately
5000KΩ), which causes difficulties in its measurement. Also, 30
When the amount is less than mol %, the change in humidity-sensitive resistance of the humidity-sensitive element obtained from the sintered element becomes extremely small, making it difficult to determine the humidity-sensitive property as a change in electrical resistance with respect to humidity. This sintered body can usually be obtained by the following method. That is, first, powder of chromium oxide () and powder of at least one metal oxide selected from nickel oxide, cobalt oxide (), and manganese oxide () are mixed in a predetermined composition ratio (mol%). They are weighed and blended, and then wet mixed with a small amount of a non-aqueous solvent such as ethyl alcohol or ethylene glycol. The obtained mixed powder is further kneaded with a binder such as polyvinyl alcohol, polyethylene glycol, or liquid paraffin to prepare a kneaded product, which is air-dried and then pressurized at room temperature using a mold of a predetermined shape. It is molded into, for example, a plate-shaped molded product. Next, this molded body is sintered by a conventional method to obtain a sintered element. At this time, it is necessary that the sintered body has a proper porous structure, and in the present invention, the cumulative volume of the pores of 37 Å or more is usually 0.1 to the weight (g) of the sintered body. It is preferable to have a porous structure of ~0.02 cc/g. The sintered body of the present invention having such a porous structure is produced in the above-mentioned manufacturing process, usually with the particle size of the raw material powder: 0.1 to 2.0μ; the molding pressure during molding of the kneaded product: 500 to 2000 kg. /cm ² ; Sintering temperature of compact:
It can be obtained by setting the conditions of 1200-1400°C; sintering time: 0.5-2 hours. A commonly used paste such as gold paste, platinum paste, ruthenium oxide paste, carbon paste, etc., is applied to the opposing surfaces or the same surface of the sintered body thus obtained, and then baked. The moisture sensitive material of the present invention is produced by attaching a pair of electrodes consisting of phosphorus and sulfur, and then supporting at least one element or oxide selected from phosphorus and sulfur on the surface and in the internal pores of the element body. An element is formed. In the present invention, supporting of phosphorus, sulfur, or oxides on the sintered body is carried out as follows. That is, a method is preferably applied in which the sintered body obtained as described above is impregnated with a solution containing at least one selected from phosphorus and sulfur, and then heated and thermally decomposed at a predetermined temperature. Ru. In this method, the impregnating solution is thermally decomposed to leave at least one element or oxide selected from phosphorus and sulfur on the surface of the sintered body or on the walls of the internal pores during the next heat treatment. For example, in the case of phosphorus, triethyl phosphite, trimethyl phosphate, tributyl phosphate, tri-p-cresyl phosphate, tri-p-cresyl phosphate, etc.
Examples include organic phosphoric acid compound solutions such as o-cresyl, and inorganic phosphoric acid compound solutions such as orthophosphoric acid, phosphorous acid, and pyrophosphoric acid. In the case of sulfur, ethyl sulfide, vinyl sulfide, phenyl sulfide,
Examples include solutions of organic sulfur compounds such as benzyl sulfide, methyl sulfide, triethylphosphine sulfide, and diethyl sulfide. These solutions can be used alone or as a mixed solution if necessary. Further, during this impregnation treatment, in order to uniformly impregnate the center of the sintered body with the solution, it is preferable to carry out the treatment under reduced pressure or in a vacuum. The sintered body thus impregnated is then heat-treated at a predetermined temperature. At this time, the solution impregnated into the sintered body is thermally decomposed to produce phosphorus and
At least one element or oxide selected from sulfur is attached to the surface of the sintered body or the wall surface of the internal pores. In the present invention, the heat treatment temperature is set to be higher than the thermal decomposition temperature of the components in the solution, and the upper limit of the temperature is 700°C, preferably 550°C. If the heat treatment is performed at a temperature exceeding the upper limit temperature, the effect of improving the moisture sensitivity characteristics of the obtained moisture sensing element will hardly be obtained. In the moisture-sensitive element of the present invention, at least one element or oxide selected from phosphorus and sulfur is added to the sintered element in an amount of 0.1 to 2.0 in terms of phosphorus and sulfur based on the weight of the element. It is preferable that the supported amount is less than 0.1% by weight,
Since the amount of adhesion to the surface of the sintered element or the wall of the internal pores is not sufficient, the moisture sensing characteristics of the moisture sensing element cannot be improved, and if the amount exceeds 2.0% by weight, the electrical resistance of the entire humidity sensing element becomes significant. This makes it extremely difficult to measure resistance to obtain moisture-sensitive characteristics. The moisture-sensitive element of the present invention configured as described above is
Since the improvement effect of the humidity sensitive property, especially the temporal deterioration of the humidity sensitive property is greatly reduced, it becomes possible to continuously measure humidity with high reliability, and it can be incorporated as a humidity sensitive member of an automatic control device. The moisture sensitive element of the present invention will be explained in more detail below based on Examples. Example 1 (1) Preparation of sintered element body (chromium oxide (): 70 mol%, nickel oxide: 30 mol%). Chromium oxide () powder with particle size 0.1~2.0μ
82.7g and 17.3g of nickel oxide powder in the same particle size range.
g and 200 ml of ethyl alcohol using a Teflon pot for about 24 hours. After air-drying the mixed powder at room temperature, 8% by weight of 5% polyvinyl alcohol was added and kneaded for 20 minutes using a sieve machine. A pressure of 1000 Kg/cm ² was applied to form a disc, and then the formed disc was heat-treated in an electric furnace (atmosphere: air) at 1300°C for 2 hours. The sintered body thus obtained was heated to 3000#
Polished with SiC abrasive material to adjust thickness, diameter 10mm
A disk of sintered element having a thickness of 1 mm was obtained. Regarding this sintered disk, the cumulative volume of pores of 37 Å or more was measured in a conventional manner using a mercury porosimeter, and the value was 0.0789 cc/g. Further, when the composition ratio of this sintered disk was analyzed, it was confirmed that it was 70 mol% of chromium oxide () and 30 mol% of nickel oxide. Next, gold paste was applied to both sides of this sintered disk and baked at 750°C to attach and form gold electrodes with a diameter of 8 mm. (2) Supporting phosphorus on the sintered disk. A triethyl phosphite solution containing 18% by weight of phosphorus was prepared. The above sintered disk was immersed in this, and the whole was held at 10 ^-3 Torr for 20 minutes to perform an impregnation treatment. Thereafter, the sintered disk was taken out and dried at 100° C. for 1 hour. Next, this is 550 for electric furnace (atmosphere: air).
A humidity sensitive element was obtained by heat treatment at ℃ for 30 minutes. When elemental analysis of the moisture sensitive element was carried out based on a conventional method, it was confirmed that 0.8% by weight of phosphorus was supported based on the weight of the sintered disk. (3) Measurement of moisture sensitivity characteristics. Copper wires are attached as lead wires to the opposing gold electrodes of the humidity sensing element, and after connecting these to the impedance measurement circuit, the humidity sensing element is placed in a constant temperature/humidity chamber to measure the relative humidity (%) at 25°C. ) and the electrical resistance value (KΩ) appearing in the impedance measurement circuit (initial moisture sensitivity characteristics) was determined. The results are shown in Figure 1. Furthermore, the humidity sensitivity characteristics after the humidity sensing element was left at each relative humidity for 1000 hours were determined, and the results are shown in FIG. For comparison, the same initial moisture sensitivity characteristics and moisture sensitivity characteristics after being left for 1000 hours were determined for a conventional moisture sensing element (composition: 70 mol% chromium oxide, 30 mol% nickel oxide), and the results were compared. Figure 3,
It is shown in Figure 4. As is clear from the results, although the humidity sensing element of the present invention has a somewhat higher electrical resistance value than the conventional one, there is almost no deterioration of its humidity sensing characteristics over time, and it can be used under continuous humidity conditions. It was found that the measurement had extremely high reliability. Example 2 A sintered disk containing 70 mol% of chromium oxide () and 30 mol% of nickel oxide was prepared in the same manner as in Example 1. A sulfur-supported moisture-sensitive element was prepared in exactly the same manner as in Example 1, except that ethyl sulfide having a sulfur concentration of 35% by weight was used as the impregnating solution. The moisture sensitive element carried 1.2% by weight of sulfur. In the same manner as in Example 1, initial moisture sensitivity characteristics and
Moisture sensitivity characteristics were determined after being left for 1000 hours. the result,
The electrical resistance values at 25°C and relative humidity of 30% and 90% were 3400KΩ and 60KΩ, respectively, and after being left for 1000 hours they were 3500KΩ and 70KΩ, respectively, and the deterioration over time was small. Examples 3 to 9 Various moisture sensitive elements having the same shapes as Examples 1 and 2 were prepared based on the specifications shown in Table 1.

[Table] Table 1 shows the composition of the sintered body,
Each component was blended so that the composition ratio of chromium oxide () was outside the range of 30 to 80 mol% (Comparative Example 1,
2) and those in which the heat treatment temperature of the impregnating solution was 700° C. (Comparative Examples 3 and 4) are also shown as comparative examples. Further, the particle size of the raw material powder used was in the range of 0.1 to 2.0 μ in both Examples and Comparative Examples. Regarding the obtained moisture-sensitive element, the component composition ratio (mol%) and the supported amount of phosphorus and sulfur (weight%) relative to the weight of the sintered element were measured, and the results corresponded to the numbers in Table 1. The results are shown in Table 2. For these humidity sensing elements, the initial humidity sensing characteristics and the humidity sensing characteristics after being left for 1000 hours were determined in the same manner as in Example 1, and the respective electrical resistance values at relative humidity of 30% and 90% at 25°C are shown in Table 2. Also listed.

[Table] As is clear from the above results, it was found that the moisture-sensitive element of the present invention showed extremely little deterioration over time in its moisture-sensitive characteristics.

[Brief explanation of the drawing]

1 and 2 show the initial moisture sensitivity characteristics and the moisture sensitivity characteristics after being left for 1000 hours, respectively, of the humidity sensing element obtained in Example 1 of the present invention, and FIGS. The graph shows the initial moisture sensitivity characteristics of a conventional moisture sensing element and the moisture sensitivity characteristics after being left for 1000 hours.

Claims (1)

[Claims] 1 Chromium oxide (): 30 to 80 mol%, nickel oxide, cobalt oxide (), manganese oxide ()
At least one metal oxide selected from: 20 to 70
1. A moisture-sensitive element comprising a porous sintered body consisting of mol% of sulfur and at least one element or oxide selected from phosphorus and sulfur, or both. 2. The supported amount of at least one element or oxide selected from phosphorus and sulfur is 0.1 to 2.0% by weight in terms of phosphorus and sulfur based on the weight of the sintered element. Claim 1
Moisture-sensitive element described in section.