JPS6355763B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrical resistance type moisture sensing element having a resistance value that is highly reliable and easy to use. Conventionally, many electrical resistance type moisture sensing elements have been proposed, and some are commercially available. For example, the most common one is the Dunmore type electric hygrometer. This is a high-precision product in which an absorbent alkali salt such as lithium chloride, which is a moisture-sensitive material, is thinly and uniformly applied to the surface of an insulating support. However, if this material is left in high humidity for a long period of time, it absorbs a large amount of water and dissolves, causing the lithium chloride to flow and become unevenly distributed, resulting in changes in its properties. For this reason, various materials such as polystyrene glass fiber and vegetable pulp have been considered for the support, but nothing definitive has been found. In addition, since sublimation of the moisture-sensitive material itself occurs, correction is sometimes necessary. Therefore, in order to obtain a highly reliable moisture sensitive element,
A moisture-sensitive element made by mixing and firing a metal oxide and a semiconductor glass powder has also been reported (Japanese Patent Application Laid-Open No. 18386-1983).
Although this is capable of measuring a wide range of 10%RH to 100%RH, its resistance value is as high as 30MΩ to 1MΩ, which has been a major obstacle in practical use. An object of the present invention is to provide a humidity sensing element that maintains excellent reliability even during long-term use and has a resistance value that is easy to design when designing a circuit as a humidity detector. The present invention includes a pair of electrodes, and a moisture sensitive element provided between the electrodes and made of a porous metal oxide sintered body and an alkali ion conductive glass coated on the surface of the crystal grains of the sintered body. This is a moisture-sensitive element. In other words, in the present invention, alkali ion conductive glass, which is stable even under high humidity, is uniformly dispersed in a porous metal oxide sintered body by performing a high temperature melting process using ordinary ceramic technology.
Optimal moisture sensitivity characteristics can be obtained for coating crystal particles. The characteristics of this moisture sensitive element are 30%
It has an easy-to-use resistance value of 1MΩ or less and 4KΩ or more in the humidity range of RH to 90% RH, and has good responsiveness, and has no deterioration even under high humidity and operates stably over a long period of time and is highly reliable. In addition, as the alkali ion conductive glass in the present invention, lithium ion conductive glass, sodium ion conductive glass, etc. can be used.In practice, lithium ion conductive glass, lithium oxide-boron oxide-lithium chloride, etc. can be used. Glass, lithium oxide - lithium chloride - phosphorus pentoxide glass, lithium oxide - lithium fluoride - boron oxide glass, lithium oxide - germanium oxide -
Vanadium pentoxide glass and lithium oxide
It is preferable to use at least one type of vanadium pentoxide glass and sodium oxide-aluminum oxide-phosphorus pentoxide glass as the sodium ion conductive glass. Further, the content of the alkali ion conductive glass is preferably 1 to 10% by weight based on the moisture sensitive element in order to improve reliability (change in resistance value over time) at low humidity and high humidity. Furthermore, the porous metal oxide sintered body in the present invention is a high melting point metal oxide having a low viscosity such that the alkali ion conductive glass used in the present invention coats the crystal particle surface of the metal oxide. It is preferable that the sintered body made of the metal oxide becomes porous when fired at a temperature, and in particular, the porosity of the porous body is 15 to 30%. Further, the crystal grain size is preferably about 1 μm. Specifically, aluminum oxide, magnesium oxide, zirconium oxide, titanium oxide, chromium oxide, tin oxide, magnesium oxide-chromium oxide spinel, zinc oxide-chromium oxide spinel can be used as the porous metal oxide sintered body. preferable. The present invention will be explained below using specific examples. Example 1 25 mole% Li ₂ O, 58 mole% B ₂ O ₃ and 17 mole
% Licl of Li ₂ O−B ₂ O ₃ −Licl
We have fabricated a lithium-ion conductive glass.
Li ₂ CO ₃ , B ₂ O ₃ , and LiCl reagents were weighed and mixed so as to have the above-mentioned composition ratio, and then placed in a platinum crucible and melted at 800° C. for 30 minutes using an electric furnace. after that,
It was poured onto an iron plate and made into a glass plate. After coarsely pulverizing the glass plate, it was subjected to wet pulverization using an acetone solution for one day and night in an alumina ball mill. The average particle size of the glass at this time was 2 μm. The lithium ion conductive glass powder thus obtained and aluminum oxide were blended as shown in Table 1 and mixed by stirring in an agate mortar. A 1 wt % PVA solution was added to the mixture, and a disk with a diameter of 10 mm and a thickness of 1 mm was formed using a mold press, and this was fired at 1300° C. for 1 hour.

[Table] The sample thus obtained (moisture-sensitive element) was polished using a SiC abrasive material until its thickness became 0.25 mm, and then, as shown in Fig. 1, a disc-shaped sample 1 was A pair of metal electrodes 2 and 3 were printed and baked on the top and bottom, and lead wires 4 and 5 were drawn out to produce a moisture-sensitive element. Figure 2 shows the moisture sensitivity characteristics. By adding more than 1wt% of ion conductive glass, the resistance value at 30%RH is less than 1MΩ, making it easy to use. When these elements were left at 40°C, 90% RH, and extremely high humidity for 3 months, the element resistance value increased for the one with 0.1 wt% addition, and the resistance value increased at 30% RH. 15%RH
A change was observed. For those containing 1 to 10 wt%, the fluctuations were within ±10% RH. When this element is then left in a normal humidity atmosphere, its characteristics return to their initial values after one week, and are sufficiently durable for practical use at room temperature and humidity. On the other hand, with 15wt% and 20wt% additive elements, the resistance value at 90%RH decreases, each by ±15%.
A significant change was observed in RH and +20RH. In this way, there is a relationship between the amount of ion conductive glass added and the variation in characteristics under high humidity.
It was found that when 10 wt% was added, the humidity remained within ±10% RH even under high humidity conditions of 40°C and 90% RH, making it a good moisture-sensitive element for use at room temperature and humidity. Example 2 The moisture-sensitive element of the present invention utilizes the phenomenon of adsorption and desorption of moisture on the surface of crystal grains of a porous metal oxide sintered body, so the effect of its porosity on characteristics such as response characteristics is small. expected to be large. Therefore, we investigated the relationship between porosity and moisture sensitivity characteristics.
In Example 1, a sample with an additive amount of 5wt% was selected, and the added sample was heated at 1200℃, 1250℃, and 1300℃.
The porosity was changed by changing the firing temperature: ℃, 1350℃, and 1380℃. After polishing to a thickness of 0.5 mm, the porosity of each sample was 38% when fired at 1200°C, 30% when fired at 1250°C, and 30% at 1300°C, as measured by a mercury porosimeter.
It was 22% at 1,350℃, 15% at 1,400℃, and 5% at 1,400℃.
The crystal grain sizes of these obtained samples were uniform at 1 μm. Figure 3 shows the pore size distribution of the material fired at 1300°C. The pore diameter was distributed from 0.01 μm to 0.1 μm, and the average was 0.08 μm. Those fired at 1250°C had an average pore diameter of 0.5 μm, and those fired at 1350°C had an average pore diameter of 0.05 μm, and the preferable range for a moisture-sensitive element was 0.05 to 0.5 μm. Moisture sensitive elements similar to those shown in FIG. 1 were made from these samples and their characteristics were measured. The results are shown in FIG. The one with 5% porosity (B-1) has an order of magnitude change in moisture sensitivity (logR30%).
logR90%) is less than one digit, which means that the sensitivity to humidity is poor, and the resistance value is high. On the other hand, 15% (B
-2), 22% (B-3) and 30% (B
-4) and 38% (B-5) have two orders of magnitude change and have sufficient sensitivity. In order to conduct further practical studies on these elements, we measured their response speeds. Next, after the above element was placed under high humidity of 90% RH and the characteristics stabilized, when the humidity was lowered to low humidity of 30% RH,
The resistance values of the elements with 15%, 22%, and 30% porosity increased and returned to stable normal values within 5 minutes. on the other hand
38% required 20 minutes to reach stable normal values. When considering applications such as humidity control in air conditioners as a normal temperature and humidity sensor, it was found that a sensor with a porosity of 38% has a problem with response, and a sensor with a porosity of 15% to 30% is better. Example 3 Moisture-sensitive elements were produced using various alkali ion conductive glasses in the same manner as in Example 1. Second
The table shows the composition of the additive lithium and sodium ion conductive glass, as well as the vitrification temperature.
5wt% of these glass samples were added to titanium oxide, mixed, and formed into a disk sample, followed by firing at 1300°C for 1 hour. When the porosity was measured after polishing to a thickness of 0.5 mm, all of them were in the range of 15 to 30%. The moisture sensitivity characteristics of these elements are shown in FIG. In the case of titanium oxide, which is a semiconductor, the resistance value is lower than that of alumina oxide, which is an insulator in Example 2, and the resistance value is from 200KΩ to 4KΩ, which is an easy-to-use value in the humidity range of 30%RH to 90%RH. It's getting old. Similarly to Example 1, in the high humidity storage test at 40° C. and 90% RH for 3 months, the fluctuation was within ±10% RH.

[Table] Example 4 25mole% Li ₂ O, 58mole% B ₂ O ₃ and 17mole
% LiCl of Li ₂ O−B ₂ O ₃ −LiCl
A moisture-sensitive element was prepared in the same manner as in Example 1 by adding 5 wt% of the lithium ion conductive glass to various metal oxides. Table 3 shows the metal oxides and firing temperatures studied, as well as the porosity and crystal grain size of the obtained moisture-sensitive elements.

[Table] In Table 3, when fired at 1300°C, the porosity of all samples except ZnO was in the range of 15% to 13%, and the crystal grain size was small and uniform at 1 μm. Grain growth occurs, with an average crystal grain size of 12 μm and a low porosity of 6%. To obtain porous ZnO samples, the calcination temperature had to be lowered to 1000°C (D-8). FIG. 6 shows the moisture sensitivity characteristics of each element. MgO, ZrO ₂ , Cr ₂ O ₃ , SnO ₂ as metal oxides,
When using MgCr ₂ O ₄ and ZnCr ₂ O ₄ , the order of change is 2
It was more than an order of magnitude higher, and was sufficient as an initial characteristic. Furthermore, in a high-humidity test at 40°C and 90% RH, these elements showed fluctuations within ±10% RH over a period of 3 months, and were sufficiently usable for practical use at room temperature and humidity.
On the other hand, in the case of ZnO, when fired at 1300℃ (D-7),
The change digit is within 1 digit and the resistance is high. This is because the porosity is as low as 6%. 1000℃ firing (D-8)
However, in a high humidity test at 40℃ and 90%RH for 3 months, the resistance increased and a change of -17%RH occurred. , even after leaving it in the atmosphere, it did not return to its initial value. This is presumed to be caused by the following reasons. That is, at 1000°C, the viscosity of the ion-conducting glass is high and the surface of the porous ZnO particles, which is the skeleton, cannot be sufficiently covered, and the remaining ZnO surface itself seems to deteriorate. At 1300℃, where the viscosity of ion conductive glass is sufficiently low, ZnO sinters,
Grain growth occurs and the material becomes dense, making it impossible to obtain a porous moisture-sensitive element. As seen in the examples, if alkali ion conductive glass is used as the moisture sensitive element, it can be used for a long period of time even under extreme conditions of high humidity (40°C, 90%), although there is a fluctuation range. , the leaving condition is medium,
When the humidity returns to low, the device characteristics return to their initial values. This is thought to be because the lithium and sodium ions, which play an important role as a moisture-sensitive element, are retained in the solid so as not to leak out without damaging their properties. Lithium and sodium ion conductive glass uniformly coats the particles of the porous metal oxide sintered body, which is the skeleton, by melting through high-temperature treatment, resulting in stable properties. In this case, the amount added is preferably 1 to 10 wt%. Further, when the porosity is 15 to 30%, the response speed is within 5 minutes and the sensitivity is good enough for practical use. In addition, these elements have a practical humidity range of 30%RH to 90%RH, and their resistance values are as low as 1MΩ to 4MΩ, making them very easy to use. In the above embodiment, a moisture sensing element having a structure as shown in Fig. 1 was used, but the structure can be changed as appropriate, and rare earth oxides etc. can also be used as the porous metal oxide sintered body. can.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a humidity sensing element used in an embodiment of the present invention, and FIGS. A curve diagram showing the obtained characteristics. 1... Disc fired body, 2, 3... Electrode, 4, 5...
…Lead.

Claims (1)

[Scope of Claims] 1. A sensor comprising a pair of electrodes, a porous metal oxide sintered body, and an alkali ion conductive glass coated on the surface of the crystal grains of the sintered body, which is provided between the pair of electrodes. A moisture sensing element characterized by comprising a moisture body. 2. A moisture-sensitive element according to claim 1, characterized in that the alkali ion conductive glass is contained in an amount of 1 to 10% by weight. 3. A moisture-sensitive element according to claim 1 or 2, characterized in that the moisture-sensitive element has a porosity of 15 to 30%. 4. A moisture-sensitive element according to claim 1, 2, or 3, characterized in that at least one of lithium ion conductive glass and sodium ion conductive glass is used as the alkali ion conductive glass. 5 In claim 4, the lithium ion conductive glass is lithium oxide-boron oxide-lithium chloride glass, lithium oxide-lithium chloride-phosphorus pentoxide glass, lithium oxide-lithium fluoride-boron oxide glass, lithium oxide- 1. A moisture-sensitive element characterized in that at least one of germanium oxide-vanadium pentoxide glass and lithium oxide-vanadium pentoxide glass is used, and sodium oxide-aluminum oxide-phosphorus pentoxide glass is used as the sodium ion conductive glass. 6 In claim 1, aluminum oxide, magnesium oxide, zirconium oxide, titanium oxide, chromium oxide, tin oxide, magnesium oxide-chromium oxide spinel, zinc oxide-chromium oxide spinel are used as polytopic metal oxide sintered bodies. A moisture-sensitive element characterized by using.