Humidity-sensing component composition

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a humidity-sensing component composition which detects relative humidity as a change in the value of the electrical resistance.
2. Description of the Prior Art
Conventionally, materials known as humidity-sensing component compositions are:
(1) Materials using electrolytic quality salts such as lithium chloride;
(2) Materials utilizing organic polymer films such as polyamide or polyethylene films;
(3) Materials using metallic semiconductors such as selenium or germanium; and
(4) Materials utilizing sintered bodies of metallic oxides such as titanium oxide, aluminium oxide, or stannic oxide.
Among these, the materials using sintered bodies of metallic oxides have the merit of being more stable chemically and physically than other humidity-sensing component compositions such as organic polymer films, and these can be said to be effective as humidity-sensing component compositions.
However, these sintered bodies of metallic oxides usually have the following types of drawbacks:
(1) The characteristic resistance value is high, and is not in the practical resistance value range. In regions of low humidity especially, the resistance of the humidity-sensing component composition abruptly becomes high, so the measurement of humidity in regions of low humidity is difficult.
(2) Dependence on temperature in the humidity-sensing characteristics is large, so temperature compensation is necessary.
(3) Hysteresis in the humidity-sensing characteristics is encountered when moisture is absorbed and released.
(4) Resistance to thermal shock is low, and the humidity-sensing characteristics deteriorate.
(5) Products of hydration are absorbed on and foul the surface of sintered bodies of metallic oxides so that the humidity-sensing characteristics deteriorate, making periodic heat cleaning necessary.
For these reasons, the development of a humidity-sensing component composition with high reliability has been greatly desired.
SUMMARY OF THE INVENTION
An object of the present invention is to provide, with due consideration to the drawbacks of such conventional materials, a reliable humidity-sensing component composition.
Another object of the present invention is to provide a humidity-sensing component composition in which the characteristic resistance value is low and is in the practical resistance value range.
Another object of the present invention is to provide a humidity-sensing component composition in which the dependence on temperature in the humidity-sensing characteristics is extremely small so that temperature compensation is unnecessary.
Another object of the present invention is to provide a humidity-sensing component composition in which hysteresis is almost absent in the humidity-sensing component characteristics when moisture is absorbed and released.
Another object of the present invention is to provide a humidity-sensing component composition which can withstand thermal shock.
Another object of the present invention is to provide a humidity-sensing component composition for which special heat cleaning is unnecessary.
Another object of the present invention is to provide a humidity-sensing component composition which exhibits good humidity-sensing characteristics in regions of low humidity, especially in regions of 40% RH and below.
With the above objects in view, the present invention resides in a humidity-sensing component composition including a metallic oxide and a chalcogen oxyacid salt represented by a general formula A.sub.x B.sub.y O.sub.z where A is one of an alkali metal and an alkaline earth metal, B is one of sulphur, selenium, and tellurium, O is oxygen, x is 1 to 2, y 1 to 5, and z 2 to 7, said chalcogen oxyacid salt being blended by an amount of 0.01 to 99.99 mol% in the metallic oxide with the sum of the metallic oxide and the chalcogen oxyacid salt as a reference, the metallic oxide and the chalcogen oxyacid salt being sintered under an atmosphere of molecular oxygen.

BRIEF DESCRIPTION OF THE DRAWINGS
The other objects, features, and advantages of the present invention will become more apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a front elevation showing one embodiment of the humidity-sensing component made from the humidity-sensing component composition of the present invention.
FIG. 2 to FIG. 11 are graphs showing the characteristics of the humidity-sensing component composition of the present invention in which:
FIG. 2 and FIG. 3 show the humidity-sensing characteristics; FIG. 4 and FIG. 5 show the relationship between temperature and the humidity-sensing characteristics; FIG. 6 and FIG. 7 show the hysteresis in the humidity-sensing characteristics after the composition was held under conditions of high humidity; FIG. 8 and FIG. 9 show the humidity-sensing characteristics before and after the composition was subjected to a thermal shock test; FIG. 10 shows the humidity-sensing characteristics before and after the composition was subjected to a water resistance test; FIG. 11 shows the hysteresis in the humidity-sensing characteristics after the composition was held under conditions of high humidity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A humidity-sensing component composition according to the present invention is now described in detail with reference to the drawings.
In the present invention, the metallic oxides used are materials which have humidity-sensing characteristics, and, if course, materials which are conventionally known as effective components of a humidity-sensing component composition are included. MgO, TiO.sub.2, ZrO.sub.2, Nb.sub.2 O.sub.5, TaO, Ta.sub.2 O.sub.5 Cr.sub.2 O.sub.3, MoO.sub.3, WO.sub.3, MnO.sub.2, Mn.sub.3 O.sub.4, FeO, Fe.sub.2 O.sub.3, CoO, Co.sub.2 O.sub.3, NiO, Ni.sub.2 O.sub.3, Ni.sub.3 O.sub.4, ZnO, Al.sub.2 O.sub.3, Ga.sub.2 O.sub.3, In.sub.2 O.sub.3, Tl.sub.2 O.sub.3, SiO.sub.2, GeO.sub.2, SnO, SnO.sub.2, PbO, Sb.sub.2 O.sub.3, Bi.sub.2 O.sub.3, and the like are given as examples of oxides, while Mg.sub.2 Fe.sub.2 O.sub.4, ZnFe.sub.2 O.sub.4, MgAl.sub.2 O.sub.4, MgCr.sub.2 O.sub.3, ZnCr.sub.2 O.sub.3 (above, spinel), 3Al.sub.2 O.sub.3.2SiO.sub.2 (Mullite), and the like are given as examples of compound oxides. Among these, TiO.sub.2, .gamma.-Al.sub.2 O.sub.3, ZnO, MgO, ZrO.sub.2, NiO, MgAl.sub.2 O.sub.2 and the like are particularly desirable. Among the metallic oxides, those refined by thermal decomposition, such as metallic salts, metallic hydroxides, alkoxides, and the like are acceptable. Especially, in providing a humidity-sensing component composition for satisfactory measurement in low humidity regions of 40% RH or less, the use of a combination of metallic oxides such as titanium oxide, and cupric oxide or cuprous oxide is particularly desirable.
Chalcogen oxyacid salt is represented by the following general formula (I).
A.sub.x B.sub.y O.sub.z (I)
wherein A is one of an alkali metal and an alkaline earth metal, B is one of sulphur, selenium, and tellurium, O is oxygen, x is 1 to 2, y 1 to 5, and z 2 to 7.
Specific examples of sulphur oxyacids are the sulphoxylates, sulphites, disulphites (metabisulphites), dithionites, disulphates (pyrosulphates), thiosulphates, and thionates. Specific examples of selenium oxyacids are the selenites and selenates. Specific examples of tellurium oxyacids are the tellurites and tellurates.
The ratios of metallic oxides and chalcogen oxyacid salts in the humidity-sensing component composition of the present convention are based on a reference value of the sum of the metallic oxide component and the chalcogen oxyacid salt component. The chalcogen oxyacid salt component will range from 0.01 to 99.99 mol%, with the desirable range being 0.1 to 99.9 mol%, especially less than 50 mol% in consideration of economy and characteristics. After blending each of the components for this humidity-sensing component composition, the sintered body obtained by means of suitable sintering conditions has an extremely improved humidity-sensing characteristic in comparison with a humidity-sensing component composition prepared from the metallic oxide only.
Particularly when providing a humidity-sensing component composition for satisfactory measurement in low humidity regions of 40% RH or less, a combination of metallic oxides such as titanium oxide, and cupric oxide or cuprous oxide, is used, with a range of 50 to 98 mol% for the titanium oxide, 1 to 40% for the cupric or cuprous oxide, and 1 to 10 mol% for the chalcogen oxyacid salt (alkali metal salt) being desirable. After each of the components are blended in these ranges, the humidity-sensing characteristics of the sintered body obtained under suitable sintering conditions give extremely good agreement with the characteristics obtained from the following equation (II), and an accurate expression of the humidity is obtained by means of a simple logarithmic conversion circuit. The measurement accuracy is considerably improved, especially in low humidity regions (40% RH or less).
H=log K+a (II)
where H is the relative humidity, K is the impedance, and a is a constant.
The humidity-sensing component composition of the present invention can be manufactured in the following manner, using normal ceramics manufacturing technology.
First, after the required amount of each of the respective components has been weighed out, they are adequately blended in a ball mill, shaker mill, or the equivalent by means of a dry method or a wet method using a blended solvent such as water and methyl alcohol. Following this, the blended material is dried as required and calcinated at a suitable temperature, then crushed and prepared as the raw material powder. This raw material powder may be molded or acceptable is the process by which the raw material powder is kneaded together with a binder such as polyvinyl alcohol, polyethylene glycol or the like, then the kneaded material is prepared and dried, after which it is molded. This molded body is sintered under an atmosphere of molecular oxygen (usually air) to give a sintered body. This sintered body desirably has a porous structure, normally with a porosity of 10 to 55% and a pore diameter of 1.mu. or less.
The humidity-sensing component composition of the present invention is usually obtained from a raw material powder with a particle diameter of 0.1 to 3.mu., at a molding pressure of 50 to 1000 kg/cm.sup.2, a sintering temperature of 500.degree. to 1200.degree. C. and a sintering time of 0.5 to 3 hours.
A humidity-sensing component can be constructed from the sintered body obtained in this manner by polishing as required, after which the electrodes are formed, utilizing a commonly used paste, such as gold paste, platinum paste, ruthenium oxide paste or the like. In addition, mass production methods can be used such as the thick film method, making cost reduction possible.
The humidity-sensing component composition of the present invention will now be explained with reference to the following embodiments.
Embodiment 1
Titanium oxide and sodium pyrosulphate (Na.sub.2 S.sub.2 O.sub.7) were respectively weighed out in the mol ratios of 96.5% and 3.5% and mixed in a pot mill for 16 hours using the wet method. The resulting blended material was dried for four hours at 140.degree. C., granulated, and prepared to give a raw material powder. This raw material powder was subjected to a pressure of 500 kg/cm.sup.2 to mold a disc-shaped compacted body 12 mm in diameter and about 2 mm thick. This compacted body was sintered for 3 hours at 900.degree. C., after which ruthenium oxide paste was printed by the seregraphy process in a comb shape onto one side of the sintered body and baked on at about 850.degree. C.
The structure of the humidity-sensing component manufactured in this manner is shown in FIG. 1. In FIG. 1, an electrode 1 and a humidity-sensing component 2 are shown.
This humidity-sensing component was maintained in a constant temperature bath at an ambient temperature of 25.degree. C., the relative humidity was varied from 20 to 100% and the change in its resistance value was investigated during this time. In FIG. 2, the resulting curve A is compared with curve A' which shows the change in resistance value of a humidity-sensing component in which the only component is titanium oxide. As clearly shown in FIG. 2, the resistance value of the humidity-sensing component composition of the present invention at an ambient temperature of 25.degree. C. ranges from 1.04.times.10.sup.6 ohms at a relative humidity of 30% to 4.5.times.10.sup.3 ohms at a relative humidity of 80%, exhibiting over a wide humidity range a change in resistance value, which is known to be an extremely practical resistance value range.
Embodiment 2
Titanium oxide and barium selenite (BaSeO.sub.3) were respectively weighted out in the mol ratios of 96.5% and 3.5% and mixed in a pot mill for 16 hours using the wet method. The resulting blended material was dried for four hours at 140.degree. C., granulated, and prepared the raw material powder. This raw material powder was subjected to a pressure of 500 kg/cm.sup.2 to form a disc-shaped compacted body 12 mm in diameter and about 2 mm thick. This compacted body was sintered for 3 hours at 1000.degree. C., after which ruthenium oxide paste was screen printed in a comb shape onto one side of the sintered body and baked on at about 850.degree. C.
This humidity-sensing component was maintained in a constant temperature bath with an ambient temperature of 25.degree. C. or less, the relative humidity was varied from 20 to 100% and the change in its resistance value (humidity-sensing characteristics) was investigated during this time.
The result is shown in FIG. 3 in which the curve C shows the humidity-sensing characteristics which were obtained. For comparison, curve D shows the humidity-sensing characteristics of a humidity-sensing component made of only titanium oxide. As clearly shown in FIG. 3, the resistance value of the humidity-sensing component composition of the present invention at an ambient temperature of 25.degree. C. ranges from 8.0.times.10.sup.5 ohms at a relative humidity of 30% to 5.0.times.10.sup.4 ohms at a relative humidity of 80%, exhibiting over a wide humidity range a change in resistance value, which is known to be an extremely practical resistance value range.
Embodiments 3 to 11
The compositions were sintered in the same way as in the Embodiment 1 and the humidity-sensing characteristics of the sintered bodies were investigated.
The results are given in Table 1. For comparison purposes, comparative example 1 showing the humidity-sensing characteristics of a sintered body made of only titanium oxide, is also included on the bottom line of the table. In Table 1, component (b) is a chalcogen oxyacid salt.
TABLE 1______________________________________ Composition (mol ratio), humidity sensingEmbodi- Component TiO.sub.2 / characteristics (.OMEGA.)ment (b) Component (b) 30% RH 80% RH______________________________________3 Na.sub.2 S.sub.2 O.sub.3 96.5/3.5 4.2 .times. 10.sup.5 2.8 .times. 10.sup.34 Na.sub.2 S.sub.2 O.sub.4 96.5/3.5 2.9 .times. 10.sup.5 3.6 .times. 10.sup.35 Na.sub.2 S.sub.2 O.sub.5 96.5/3.5 1.8 .times. 10.sup.5 5.8 .times. 10.sup.36 Na.sub.2 S.sub.2 O.sub.6 96.5/3.5 5.0 .times. 10.sup.5 2.3 .times. 10.sup.37 Na.sub.2 SO.sub.3 96.5/3.5 2.6 .times. 10.sup.5 8.5 .times. 10.sup.38 Na.sub.2 SO.sub.4 96.5/3.5 1.2 .times. 10.sup.5 6.4 .times. 10.sup.39 Na.sub.2 TeO.sub.3 96.5/3.5 2.2 .times. 10.sup.5 6.1 .times. 10.sup.310 Na.sub.2 TeO.sub.4 96.5/3.5 1.7 .times. 10.sup.5 2.4 .times. 10.sup.311 Na.sub.2 SeO.sub.4 96.5/3.5 5.2 .times. 10.sup.5 6.3 .times. 10.sup.2Compar- TiO.sub.2 100/0 7.2 .times. 10.sup.6 8.1 .times. 10.sup.5ativeExample______________________________________
Embodiments 12 and 13
The compositions were sintered in the same way as in the Embodiment 2 and the humidity-sensing characteristics of the sintered bodies were investigated.
The results are given in Table 2. For comparison purposes, comparative example 1 showing the humidity-sensing characteristics of a sintered body made of only titanium oxide, is also included on the bottom line of the table.
TABLE 2______________________________________ Composition (mol ratio), humidity sensingEmbodi- Component TiO.sub.2 / characteristics (.OMEGA.)ment (b) Component (b) 30% RH 80% RH______________________________________12 BaSO.sub.4 96.5/3.5 3.0 .times. 10.sup.6 9.0 .times. 10.sup.413 BaTeO.sub.3 96.5/3.5 1.5 .times. 10.sup.6 7.0 .times. 10.sup.4Compar- TiO.sub.2 100/0 7.2 .times. 10.sup.6 8.1 .times. 10.sup.5ativeExample______________________________________
Embodiment 14
In the same way as in the Embodiment 1, a composition containing titanium oxide and potassium selenite (K.sub.2 SeO.sub.3) in the mol% of 96.5% and 3.5% respectively was sintered, and the humidity-sensing characteristics of the sintered body were investigated. The results are given in Table 3.
TABLE 3______________________________________ Composition (mol ratio), humidity sensingEmbodi- Component TiO.sub.2 / characteristics (.OMEGA.)ment (b) Component (b) 30% RH 80% RH______________________________________14 K.sub.2 SeO.sub.3 96.5/3.5 1.4 .times. 10.sup.5 7.5 .times. 10.sup.3______________________________________
Embodiment 15
In the same way as in the Embodiment 2, a composition containing titanium oxide and calcium tellurite (CaTeO.sub.3) in the mol% of 96.5% and 3.5% respectively was sintered, and the humidity-sensing characteristics of the sintered body were investigated. The results are given in Table 4.
TABLE 4______________________________________ Composition (mol ratio), humidity sensingEmbodi- Component TiO.sub.2 / characteristics (.OMEGA.)ment (b) Component (b) 30% RH 80% RH______________________________________15 CaTeO.sub.3 96.5/3.5 9.2 .times. 10.sup.5 5.5 .times. 10.sup.4Compar- TiO.sub.2 100/0 7.2 .times. 10.sup.6 8.1 .times. 10.sup.5ativeExample______________________________________
Embodiments 16 to 28
The compositions were sintered in the same way as in the Embodiment 1 and the humidity-sensing characteristics of the sintered bodies were investigated.
The results are given in Table 5. In Table 5, component (a) is a metallic oxide.
TABLE 5______________________________________ Composition (mol ratio), humidity sensingEmbodi- Component Component (a)/ characteristics (.OMEGA.)ment (a) Na.sub.2 TeO.sub.3 30% RH 80% RH______________________________________16 ZnO 96.5/3.5 5.0 .times. 10.sup.5 1.5 .times. 10.sup.417 MgO 96.5/3.5 5.1 .times. 10.sup.5 1.4 .times. 10.sup.418 ZrO 96.5/3.5 4.8 .times. 10.sup.5 1.3 .times. 10.sup.419 .gamma.-Al.sub.2 O.sub.3 96.5/3.5 8.4 .times. 10.sup.5 1.7 .times. 10.sup.420 NiO 96.5/3.5 1.3 .times. 10.sup.6 3.2 .times. 10.sup.421 Y.sub.2 O.sub.3 96.5/3.5 1.6 .times. 10.sup.5 1.0 .times. 10.sup.422 WO.sub.3 96.5/3.5 5.6 .times. 10.sup.5 3.3 .times. 10.sup.523 MnO.sub.2 96.5/3.5 1.6 .times. 10.sup.6 6.6 .times. 10.sup.424 Fe.sub.2 O.sub.3 96.5/3.5 2.4 .times. 10.sup.5 1.2 .times. 10.sup.425 SiO.sub.2 96.5/3.5 2.5 .times. 10.sup.6 2.6 .times. 10.sup.426 SnO.sub.2 96.5/3.5 4.9 .times. 10.sup.4 2.3 .times. 10.sup.327 Sb.sub.2 O.sub.3 96.5/3.5 6.7 .times. 10.sup.5 8.4 .times. 10.sup.428 MgAl.sub.2 O.sub.4 96.5/3.5 4.0 .times. 10.sup.5 1.2 .times. 10.sup.4______________________________________
Embodiments 29 to 41
The compositions were sintered in the same way as in the Embodiment 2 and the humidity-sensing characteristics of the sintered bodies were investigated. The results are given in Table 6.
TABLE 6______________________________________ Composition (mol ratio), humidity sensingEmbodi- Component Component (a)/ characteristics (.OMEGA.)ment (a) BaSeO.sub.3 30% RH 80% RH______________________________________29 ZnO 96.5/3.5 9.0 .times. 10.sup.5 7.1 .times. 10.sup.430 MgO 96.5/3.5 9.3 .times. 10.sup.5 7.0 .times. 10.sup.431 ZrO.sub.2 96.5/3.5 8.2 .times. 10.sup.5 6.5 .times. 10.sup.432 .gamma.-Al.sub.2 O.sub.3 96.5/3.5 1.0 .times. 10.sup.6 7.3 .times. 10.sup.433 NiO 96.5/3.5 2.2 .times. 10.sup.6 9.1 .times. 10.sup.434 Y.sub.2 O.sub.3 96.5/3.5 6.6 .times. 10.sup.5 6.0 .times. 10.sup.435 WO.sub.3 96.5/3.5 1.2 .times. 10.sup.6 8.4 .times. 10.sup.536 MnO.sub.2 96.5/3.5 6.6 .times. 10.sup.6 1.2 .times. 10.sup.537 Fe.sub.2 O.sub.3 96.5/3.5 7.5 .times. 10.sup.5 6.2 .times. 10.sup.438 SiO.sub.2 96.5/3.5 7.5 .times. 10.sup.6 7.6 .times. 10.sup.439 SnO.sub.2 96.5/3.5 9.9 .times. 10.sup.4 7.3 .times. 10.sup.340 Sb.sub.2 O.sub.3 96.5/3.5 1.4 .times. 10.sup.6 1.8 .times. 10.sup.541 MgAl.sub.2 O.sub.4 96.5/3.5 9.0 .times. 10.sup.5 6.2 .times. 10.sup.4______________________________________
Embodiments 42 to 44
The compositions were sintered in the same way as in the Embodiment 1 and the humidity-sensing characteristics of the sintered bodies were investigated. The results are given in Table 7. In Table 7, the results for Embodiment 9 are also included.
TABLE 7______________________________________ Components humidity-sensing (mol %) characteristics (.OMEGA.)Embodiment TiO.sub.2 Na.sub.2 TeO.sub.3 30% RH 80% RH______________________________________42 99.9 0.1 7.2 .times. 10.sup.5 3.0 .times. 10.sup.4 9 96.5 3.5 2.2 .times. 10.sup.5 6.1 .times. 10.sup.343 50.0 50.0 5.0 .times. 10.sup.5 1.5 .times. 10.sup.344 0.1 99.9 4.0 .times. 10.sup.5 1.0 .times. 10.sup.3______________________________________
Embodiments 45 to 47
The compositions were sintered in the same way as in the Embodiment 2 and the humidity-sensing characteristics of the sintered bodies were investigated. The results are given in Table 8. In Table 8, the results of Embodiment 2 are also included.
TABLE 8______________________________________ Components humidity-sensing (mol %) characteristics (.OMEGA.)Embodiment TiO.sub.2 BaSeO.sub.3 30% RH 80% RH______________________________________45 99.9 0.1 9.2 .times. 10.sup.5 6.6 .times. 10.sup.4 2 96.5 3.5 8.0 .times. 10.sup.5 5.0 .times. 10.sup.446 50.0 50.0 7.0 .times. 10.sup.5 3.7 .times. 10.sup.447 0.1 99.9 3.5 .times. 10.sup.5 1.7 .times. 10.sup.4______________________________________
Embodiment 48
The sintered body of the humidity-sensing component composition used in the Embodiment 9 was maintained at ambient temperatures of 25.degree. C., 40.degree. C., 60.degree. C., and 80.degree. C., the relative humidity was changed from 20 to 100% and its humidity-sensing characteristics were investigated during this time. The results are shown in FIG. 4.
In FIG. 4 the curves E, F, G, and H show the humidity-sensing characteristics at ambient temperatures of 25.degree., 40.degree., 60.degree., and 80.degree. C. respectively. In addition, the humidity-sensing characteristics of a conventional humidity-sensing component composition are shown as dotted line curves in FIG. 4 for comparison purposes. The dotted line curves labelled E' and F' are the humidity-sensing characteristics at ambient temperatures of 25.degree. C. and 40.degree. C. respectively. As clearly shown in FIG. 4, at ambient temperatures from 25.degree. C. to 40.degree. C. the temperature dependency is extremely small so it can be understood that there is no necessity for temperature compensation. Also, in the humidity-sensing component composition of the present invention, the total change in the humidity-sensing characteristics in the ambient temperature range of 25.degree. to 80.degree. C. corresponds to the change in the humidity-sensing characteristics of the conventional composition at ambient temperatures of 25.degree. C. to 40.degree. C. Compared to the conventional composition, it is understood that the temperature characteristics of the humidity-sensing component composition of the present invention are greatly improved.
Embodiment 49
The sintered body of the humidity-sensing component composition used in the Embodiment 2 was maintained at ambient temperatures of 25.degree. C., 40.degree. C., 60.degree. C., and 80.degree. C., the relative humidity was changed from 20 to 100%, and its humidity-sensing characteristics were investigated during this time. The results are shown in FIG. 5.
In FIG. 5 the curves I, J, K, and L show the humidity-sensing characteristics at ambient temperatures of 25.degree., 40.degree., 60.degree., and 80.degree. C. respectively. In addition, the humidity-sensing characteristics of a conventional humidity-sensing component composition are shown as dotted line curves in FIG. 5 for comparison purposes. The dotted line curves labelled I' and J' are the humidity-sensing characteristics at ambient temperatures of 25.degree. C. and 40.degree. C. respectively. As clearly shown in FIG. 5, the temperature dependency at ambient temperatures from 25.degree. C. to 40.degree. C. is extremely small so it can be understood that there is no necessity for temperature compensation. Also, in the humidity-sensing component composition of the present invention, the total change in the humidity-sensing characteristics in the ambient temperature range of 25.degree. to 80.degree. C. corresponds to the change in the humidity-sensing characteristics of the conventional composition at ambient temperatures of 25.degree. C. to 40.degree. C. Compared to the conventional composition, it is understood that the temperature characteristics of the humidity-sensing component composition of the present invention are greatly improved.
Embodiment 50
In the same way as in the Embodiment 1, a composition containing titanium oxide and potassium selenite (K.sub.2 SeO.sub.3) in the mol% ratios of 89.5% and 10.5% respectively was sintered.
After the sintered bodies obtained in this manner had been held in a relative humidity of 98% at an ambient temperature of 25.degree. C. for 24 hours, the hysteresis in the humidity-sensing characteristics was investigated at the above ambient temperatures in a range of relative humidities from 20% to 80%. Also, in the same way as outlined above, the hysteresis in the humidity-sensing characteristics of the sintered body of the composition of the Embodiment 9 was investigated.
The results are shown in FIG. 6. The curves M and N in FIG. 6 show the results of the Embodiments 9 and 50 respectively. As is clearly shown in FIG. 6, the hysteresis in the humidity-sensing characteristics of the sintered body of these compositions is about .+-.3% RH. It is therefore understood that the amount of hysteresis is extremely small, even when the sintered body component is held for 24 hours at a relative humidity of 98%.
Embodiment 51
The sintered bodies of the humidity-sensing component compositions used in the Embodiments 2 and 13 were maintained at an ambient temperature of 25.degree. C. and an ambient relative humidity of 98% for 24 hours, after which, at the same ambient temperature the hysteresis in the humidity-sensing characteristics was investigated over a relative humidity range of 20 to 80%.
The results are shown in FIG. 7. The curves O and P in FIG. 7 show the results of the Embodiments 2 and 13 respectively. As clearly shown in FIG. 7, the hysteresis for the humidity-sensing characteristics of the sintered body of the composition is within .+-.2% RH. It is therefore understood that the amount of hysteresis is extremely small, even when the sintered body component is held for 24 hours at a relative humidity of 98%.
Embodiment 52
The humidity-sensing component composition of the Embodiment 9 was subjected to 50 cycles of a thermal shock test as one cycle of 30 minutes at an ambient temperature of 85.degree. C., and thereafter 30 minutes at an ambient temperature of -25.degree. C. The humidity-sensing characteristics of this humidity-sensing component composition were investigated both before and after the thermal shock tests in the same way as for Embodiment 1.
The results are shown in FIG. 8. In FIG. 8 the curve Q shows the humidity-sensing characteristics before the tests, while the curve R shows the humidity-sensing characteristics after the tests. For purposes of comparison, the humidity-sensing characteristics were also investigated for a conventional humidity-sensing component composition both before and after the identical thermal shock tests and are shown by curves Q' and R' respectively. As clearly shown in FIG. 8, the changes in the humidity-sensing characteristics of this embodiment before and after the thermal shock tests is within 3%. It is therefore understood that compared to the conventional humidity-sensing component composition the composition in this embodiment has an extremely high resistance to thermal shock.
Embodiment 53
The component sintered body used in the Embodiment 13 was subjected to 50 cycles of a thermal shock test as one cycle of 30 minutes at an ambient temperature of 85.degree. C., and thereafter 30 minutes at an ambient temperature of -25.degree. C. The humidity-sensing characteristics of this humidity-sensing component composition were investigated both before and after the thermal shock tests in the same way as for Embodiment 2.
The results are shown in FIG. 9. In FIG. 9 the curve S shows the humidity-sensing characteristics before the tests, while the curve T shows the humidity-sensing characteristics after the tests. For purposes of comparison, the humidity-sensing characteristics were also investigated for a conventional humidity-sensing component composition both before and after the identical thermal shock tests and are shown by curves S' and T' respectively. As clearly shown in FIG. 9, the change in the humidity-sensing characteristics of this embodiment before and after the thermal shock tests is within 3%. It is therefore understood that compared to the conventional humidity-sensing component composition the composition in this embodiment has an extremely high resistance to thermal shock.
Embodiment 54
The humidity-sensing component composition of the Embodiment 50 was held in an environment of an ambient temperature of 85.degree. C. and a relative humidity of 80% for one month. The humidity-sensing characteristics of this humidity-sensing component composition were investigated both before and after this holding test in the same way as for Embodiment 1.
The results are shown in Table 9. As clearly shown in Table 9, the humidity-sensing characteristics of this embodiment show an extremely small amount of change even when held for a prolonged period of time under a severe environment of high temperature and high humidity. Accordingly, it is understood that under normal environmental conditions this humidity-sensing component composition can be used for a long time without requiring special heat cleaning.
TABLE 9______________________________________ humidity-sensing characteristics (.OMEGA.)Relative humidity 30% RH 80% RH______________________________________Initial humidity-sensing 7.0 .times. 10.sup.5 6.5 .times. 10.sup.3characteristicsHumidity-sensing 8.2 .times. 10.sup.5 5.8 .times. 10.sup.3characteristics after test______________________________________
Embodiment 55
The sintered bodies of the humidity-sensing component compositions used in the Embodiments 2 and 13 were immersed in distilled water for one month at a temperature of 25.degree. C., after which they were dried under a current of air. The humidity-sensing characteristics were investigated in the same way as for embodiment 2 both before and after these tests.
The results are shown in FIG. 10. The curves U and U' show the humidity-sensing characteristics of the sintered body of the Embodiment 2, before and after the test respectively, while the curves V and V' show the humidity-sensing characteristics of the sintered body of the Embodiment 13, before and after the test respectively.
As clearly shown in FIG. 10, the humidity-sensing characteristics of these embodiments show almost no change after the test in comparison with the characteristics before the test. Accordingly, it is understood that even under an environment of severe water conditions there is no concern about deterioration of the humidity-sensing characteristics of these humidity-sensing component compositions, so that they can be used for a long time without requiring special heat cleaning.
Embodiment 56
Titanium oxide, cupric oxide, and sodium tellurite (Na.sub.2 TeO.sub.3) were respectively weighed out in the mol ratios of 82%, 15%, and 3% and mixed in a pot mill for 16 hours using the wet method. The resulting blended material was dried for four hours at 140.degree. C., granulated, and prepared the raw material powder. This raw material powder was subjected to a pressure of 500 kg/cm.sup.2 to mold a disc-shaped compacted body 7 mm in diameter and about 0.7 mm thick. This compacted body was sintered for 3 hours at 900.degree. C., after which ruthenium oxide paste was printed by the seregraphy process in a comb shape onto one side of the sintered body and baked on at about 850.degree. C.
The humidity-sensing component manufactured in this manner was maintained in a constant temperature bath at an ambient temperature of 25.degree. C. and the relative humidity was changed from 5% to 100%. The change in the resistance values was investigated during this time. The results are given in Table 10. For comparison purposes, the humidity-sensing characteristics of a sintered body comprising titanium oxide and sodium tellurite in the mol ratios of 96.5% and 3.5% respectively are also included in Table 10 as Comparative Example 2.
TABLE 10______________________________________Em- Humidity-sensingbodi- Components (mol %) characterisitics (.OMEGA.)ment TiO.sub.2 Na.sub.2 TeO.sub.3 Cu.sub.2 O 10% RH 30% RH 80% RH______________________________________56 82 3 15 4.0 .times. 10.sup.5 1.07 .times. 4.1 .times. 10.sup.3 10.sup.5Com- 97 3 0 2.5 .times. 10.sup.7 2.2 .times. 10.sup.5 6.1 .times. 10.sup.3para-tiveExam-ple 2______________________________________
Embodiment 57
Cuprous oxide was substituted for cupric oxide in the Embodiment 56, a sintered body was manufactured in the same way as in the Embodiment 56, and the humidity-sensing characteristics of the sintered body were investigated. The results are given in Table 11.
TABLE 11______________________________________Em- Humidity-sensingbodi- Components (mol %) characterisitics (.OMEGA.)ment TiO.sub.2 Na.sub.2 TeO.sub.3 CuO 10% RH 30% RH 80% RH______________________________________57 87 3 10 4.3 .times. 10.sup.5 1.15 .times. 4.3 .times. 10.sup.3 10.sup.5______________________________________
Embodiment 58
Titanium oxide, cuprous oxide, and potassium selenite (K.sub.2 SeO.sub.3) were respectively weighed out in the mol ratios of 82%, 15%, and 3% and subjected to the same blending, molding, and sintering processes as in the Embodiment 56. The sintered body obtained in this manner was held for 24 hours at an ambient temperature of 25.degree. C. and a relative humidity of 98%, after which, at the same ambient temperature, the relative humidity was varied in the range of 20% to 80% and the hysteresis in the humidity-sensing characteristics was investigated. The results are shown in FIG. 11.
As is clearly shown in FIG. 11, the hysteresis for the humidity-sensing characteristics of the sintered body of this composition is within .+-.2% RH. It is therefore understood that the amount of hysteresis is extremely small, even when the sintered body component is held for 24 hours at a relative humidity of 98%.
In the above manner, by means of the present invention it is possible to provide a humidity-sensing component composition in which, in comparison with the conventional humidity-sensing component compositions, the characteristic resistance value is low and is in the practical resistance value range; the dependence on temperature in the humidity-sensing characteristics is extremely small so that temperature compensation is unnecessary; hysteresis is almost absent in the humidity-sensing component characteristics when moisture is absorbed and released. Also, this composition can withstand thermal shock and special heat cleaning is unnecessary.
In addition, when an alkaline earth metal salt is used as a chalcogen oxyacid salt, it is possible to provide a humidity-sensing component composition with superior water resistance.
Further, when an alkali metal salt is used as a chalcogen oxyacid salt and when titanium oxide and either cupric oxide or cuprous oxide as a metallic oxide are used together, it is possible to provide a reliable humidity-sensing component composition in which, in comparison with the conventional humidity-sensing component compositions, the characteristic resistance value is low and is in the practical resistance value range. This composition also exhibits good humidity-sensing characteristics in regions of low humidity, especially in regions below 40% RH; hysteresis is almost absent in the humidity-sensing component characteristics when moisture is absorbed and released; and special heat cleaning is unnecessary.

Number	Date	Country
61-93211	Apr 1986	JPX
61-93212	Apr 1986	JPX
61-305392	Dec 1986	JPX

Number	Name	Date
4321577	Carlson	Mar 1982
4357426	Murata	Nov 1982
4373391	Johnson	Feb 1983
4462930	Suzuki et al.	Jul 1984
4464647	Yokomizo et al.	Aug 1984
4529540	Uno et al.	Jul 1985
4608549	Fukui	Aug 1986

Humidity-sensing component composition

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