JPH0541589B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an effective method for manufacturing a novel moisture-sensitive element capable of detecting moisture in gas. (Conventional technology) Recently, not only for weather observation but also for home appliances,
BACKGROUND ART So-called moisture sensing elements that can detect moisture in gases have come to be widely used in medical equipment, automobile parts, and the like. Such moisture-sensitive elements have traditionally been made of nylon ribbons, hair, lithium chloride, etc., but more recently resin-dispersed carbon films, organic polymers, or metal oxide-based materials have been fixed on substrates. Moisture sensing elements have been put into practical use in which electrodes are formed to take advantage of changes in resistance due to humidity in gas. (Problems to be Solved by the Invention) However, the above-mentioned moisture-sensitive elements that have been put into practical use have a narrow operating temperature range (especially difficult to use in high-temperature ranges), a short lifespan, and are expensive. However, it has been desired to develop a moisture-sensitive element that can overcome these drawbacks. Regarding this point, in recent years, a moisture-sensitive ceramic made of a sintered body of a perovskite-type composite oxide and an AMO _3- type oxide has been proposed.
No. 106568), this moisture-sensitive ceramic is said to be able to reduce changes in moisture-sensitive characteristics over time. However, this moisture-sensitive ceramic requires the blending of crystalline, high-melting-point AMO ₃ type oxide (e.g., SrTiO ₃ , etc.), and the molded body is sintered, so it requires high temperature and long sintering times. There were some drawbacks, such as the need for binding, a small adjustable porosity, and a small rate of change in resistance in response to changes in humidity. The present invention has been made in view of the above, and it is an object of the present invention to provide an effective method for manufacturing a moisture-sensitive element that can be used even in a high temperature range, has a long life, and is inexpensive. (Means for Solving the Problems) The structure of the present invention for achieving the above object will be explained based on the attached embodiment drawings. FIG. 1 is a plan view showing an embodiment of the device of the present invention; FIG. 2 is a vertical sectional view taken along the line -- in FIG. 1. That is, the moisture sensitive element according to the present invention includes an insulating substrate 1, and is fixed on the substrate 1 via an adhesive layer 2 of high melting point glass, and has the following general formula:
A moisture sensitive device consisting of a fired porous membrane 3 of perovskite type composite oxide represented by A _1-x A _x ′B _1-y B _y ′O ₃ and an electrode 4 formed on the porous membrane 3. Although it is an element, the gist of the present invention is that the powder of the above composite oxide is
It is made by firing a dried product spray-dried from an aqueous solution whose components have been adjusted in advance or a coprecipitated precipitate into a fine powder, and this composite oxide powder is
A suspension of water and oil and high melting point glass are added to form a paste, the paste of the above composite oxide is applied onto an insulating substrate on which the high melting point glass is baked, and this is fired. The present invention provides a method for manufacturing a moisture-sensitive element, in which a porous film of the composite oxide is fixed on a substrate, and electrodes are formed on the porous film. In the above general formula, A is any one element selected from rare earth elements with atomic numbers 57 to 71, represented by lanthanum (La) and niodium (Nd),
A' is any one element selected from alkaline earth elements represented by calcium (Ca), strontium (Sr), and barium (Ba), B is cobalt (Co), and B' is manganese. (Mn), any one element selected from transition metal elements represented by iron (Fe) and nickel (Ni), and O
represent the oxygen element, and x and y are expressed by the inequalities 0≦x≦1 and 0≦y≦1, respectively. In order to obtain fine and uniform powder of the perovskite-type composite oxide used in the present invention, nitrates, sulfates, carbonates of the above constituent metals (A, A', B, B'),
Adjustment of inorganic acid salts such as phosphates, organic acid salts such as acetates and oxalates, halides such as chlorides, bromides, and iodides, or hydroxides and oxyhalides to a specified ratio. There is a method in which the metal salt aqueous solution is spouted in a mist, dried, and then the resulting powder is fired, or the metal salts are co-precipitated by adjusting the pH of the metal salt aqueous solution, and this precipitate is fired. There is a way to do that. Preferably, such a coprecipitation method involves heating and hydrolyzing a mixed solution of a metal salt aqueous solution and a urea solution whose components have been adjusted in advance to make it alkaline and uniformly precipitating the metal salt to obtain a coprecipitate. Can be adopted. The precipitate prepared by the above spray drying method or coprecipitation method has a molecular weight of 800 to 1100
A powder of the above composite oxide with a uniform and fine crystal structure (perovskite type) can be obtained by short-time firing at ℃, and the synthesis temperature is 300 to 600℃ lower than when synthesizing from component oxides. Economical. In order to obtain the moisture sensitive element of the present invention, a high melting point glass such as borosilicate glass is baked in advance at a temperature of 800°C or higher on an edge substrate 1 such as ceramics to form an adhesive layer 2, and the above-mentioned adhesive layer 2 is formed on this. A suspension obtained by mixing oil (screen oil, castor oil, etc.) and water with 100 parts by weight of the composite oxide, or preferably an emulsion obtained by mixing oil, water, and an emulsifier such as a surfactant. Add 50 to 1000 parts by weight of the liquid and mix, then add 1 to 30 parts by weight of the above-mentioned high melting point glass to bind the oxides together, make a paste, and apply 700 parts by weight.
The composite oxide is fired at ~1100°C to form a porous thin film 3 (thickness: 10-500μ), and then Pt, Au, Au-Pd is formed on this thin film by applying a conductive paste or sputtering. , Ag, RuO ₂ etc. electrode 4
are formed parallel or in a comb shape (parallel in the example),
By attaching the lead wire 5 to the electrode 4 by soldering or conductive paste 6, the results shown in FIGS.
A device as shown in the figure is obtained. The oil and water in the paste evaporate during baking,
After the removal, many voids remain in the layer of the fired body, making the fired body porous. The shape (pore diameter, etc.), number (related to the overall porosity), distribution state, etc. of these voids are closely related to the adsorption and desorption of moisture, and have a large effect on changes in the conductivity (electrical resistance) of the fired body. influence For example, if the pore size is small, the change in conductivity will be large at low humidity (relative humidity, hereinafter the same), and if the pore size is large, the change in conductivity will be large at high humidity. In the present invention,
By adding an oil suspension or emulsion as described above, a porosity of 3 to 85% can be obtained;
When it is less than 85%, the range of change in conductivity with respect to humidity becomes small, and when it exceeds 85%, it tends to be difficult to obtain the strength as an element. In addition, in the present invention, the pore size is adjusted by adjusting the particle size of the raw material composite oxide powder, by changing the amount of water, oil, etc. and high melting point glass powder added to the paste, or by changing the firing conditions. Appropriateness will be achieved according to the purpose. (Function) As described above, when the paste containing the composite oxide is fired, a large number of voids are formed in the paste applied on the substrate 1 due to the volatilization of the oil, water, etc. added thereto. In this state, the high melting point glass softened and melted by the firing temperature binds the composite oxide particles to each other, and after cooling, a porous film 3 of perovskite composite oxide is formed on the substrate 1. Perovskite-type composite oxides (XYO ₃ , where X and Y represent metal elements and O represents oxygen element) are generally insulating, but contain transition metal ions such as Co, Ni, Fe, and Mn at the Y site, and When a rare earth ion is used at the X site, the conductivity, that is, the electrical resistance value becomes low.
The perovskite-type composite oxide used in the present invention is represented by the general formula A _1-x A _x ′B _1-y B _y ′O ₃ , and A,
Since A', B, and B' are filled with the above metal elements, the composite oxide thin film 3 becomes semiconductive,
Moreover, the resistance value changes depending on the humidity. The presence of a large number of voids within the thin film 3 facilitates the adsorption and desorption of moisture, and the range of change in resistance value due to humidity becomes even more remarkable (10 ¹² to 10 ⁶ Ω). Therefore, this porous thin film 3 is fixed on the insulating substrate 1,
If the humidity sensing element of the present invention provided with electrodes 4 and lead wires 5 is incorporated into various control equipment and changes in resistance value due to humidity are converted into electrical signals, household electrical equipment, automobile parts, and various other electronic equipment can be used. It can be used as an extremely accurate sensor for humidity control. In addition, the porous membrane 3 is integrated with the adhesive layer 2 of high melting point glass and fixed on the substrate 1, and has a large amount of voids and a high porosity, so even if it is a porous membrane that is fragile when used alone. Since it is stably supported on the substrate 1, a stable thin film structure is maintained as an entity that performs a moisture sensing function without cracking or breaking. In the humidity sensing element of the present invention, a sintered body is not manufactured by firing a single molded body at high temperature, but a high melting point glass substance is used to bond the particles of the composite oxide, and a thin layer is formed on the substrate. It is carried out as a
Since it is easy to select a high-melting glass with a softening and melting temperature of 1000℃ or less, the firing temperature can be lower than the firing temperature of the sintered body and the firing time can be shortened, which improves productivity compared to the sintering method. This enables superior manufacturing. (Example) Next, an example will be described. Example 1 Borosilicate glass powder is placed on an alumina ceramic substrate and baked at a temperature of 800°C or higher.
Perovskite-type composite oxide with an average particle size of 2μ synthesized by the coprecipitation method; 100 parts by weight of La _0.95 Sr _0.05 Co _0.9 Ni _0.1 O ₃ and the above borosilicate glass powder 7
An emulsion made by mixing oil (screen oil) and water at a weight ratio of 2:1 is added to the mixed powder with the addition of parts by weight.
Add 220 parts by weight to make a paste, apply this paste to the substrate on which the glass is baked by screen printing method, etc. After drying, bake at 820℃ for 5 minutes to form a porous baked film (film thickness) on the substrate. , 80μ)
was formed. Pt, Au, Au-Pd, Ag,
Electrodes such as RuO ₂ were formed in parallel or in a comb shape, and lead wires were attached to the electrodes by soldering or conductive paste to form a moisture-sensitive element. Example 2 510 parts by weight of an emulsion prepared by mixing oil, a surfactant as an emulsifier, and water in a weight ratio of 27:1:14 was added to the mixed powder of composite oxide and glass similar to Example 1 to make a paste. It was coated in the same manner as above on the substrate on which the above glass had been baked, and baked at 820°C for 25 minutes to form a porous film (thickness: 40 μm), as well as electrodes and lead wires as in Example 1. was installed as a humidity sensing element. Example 3 A paste similar to Example 2 was applied to a substrate with baked glass, and after drying, it was baked at 820°C for 15 minutes.
A porous membrane (thickness: 40 μm) was formed, and electrodes and lead wires were attached in the same manner as in Example 1 to form a moisture-sensitive element. A moisture-sensitive element material corresponding to the fired thin film in the moisture-sensitive element membranes obtained in Examples 1, 2, and 3 was separately prepared, and its porosity was measured. The results are shown in Table 1.

[Table] Also, the relative humidity (%
The relationship between changes in RH) and resistance values was investigated. The results are shown in FIG. 3 (Example 1), FIG. 4 (Example 2), and FIG. 5 (Example 3). From these results, in Figure 3, relative humidity of 30~
Shows a linear resistance change of more than 3 orders of magnitude at 100%RH,
In addition, Fig. 4 shows a linear resistance change of more than 5 digits at 40 to 100% RH, and Fig. 5 shows a resistance change of more than 4 digits at 80% RH. It is understood that it is possible to appropriately control the change in resistance value with respect to humidity depending on the firing properties, and that the element can be appropriately prepared depending on the desired use. For example, the case of FIG. 4 (Example 2) is suitable for use as a humidity sensor for air conditioners, etc., and the case of FIG. 5 (Example 3) is suitable for use as a dew condensation sensor. Furthermore, when the fired thin films of each Example were subjected to a peel test, their adhesion was extremely strong. In the above embodiment, the moisture-sensitive element material of the present invention was manufactured by fixing the moisture-sensitive element material on a ceramic substrate, but it is of course possible to use other insulating substrates, and It is not excluded that devices similar to the above may be obtained using other perovskite-type complex oxides other than those of the examples and which do not depart from the scope of the present invention. (Effects of the Invention) As described above, the humidity sensing element of the present invention uses a fired porous film of perovskite type composite oxide and high melting point glass as an entity responsible for its humidity sensing function, and by changing the additive composition, It is possible to adjust the porosity over a wide range, and it is easy to increase the change in resistance with respect to humidity, and it is possible to provide various moisture-sensitive elements with porosity suitable for use as humidity-sensitive sensors. In addition, since the porous film is a fired product, it can be stably fixed on an insulating substrate and can be manufactured by a simple method, so that it can be supplied at low cost. The present invention, which has many advantages as described above, is extremely useful.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an embodiment of the device of the present invention;
FIG. 2 is a vertical sectional view taken along the line -- in FIG. 1, and FIGS. 3 to 5 are graphs showing the relationship between relative humidity and resistance change of the humidity sensing element according to the embodiment of the present invention. (Explanation of symbols) 1... Insulating substrate, 2... Adhesive layer, 3... Porous film, 4... Electrode, 5... Lead wire, 6... Solder or conductive paste.

Claims (1)

[Claims] 1. A general formula obtained by firing a dried product spray-dried from an aqueous solution whose components have been adjusted in advance or a coprecipitated precipitate into a fine powder, A _1-x A _x ′B _1-y B _y ′O ₃ (wherein, A is any one element selected from rare earth elements with atomic numbers 57 to 71, A′ is any one element selected from alkaline earth elements, and B
represents a cobalt element, B′ represents any one element selected from transition metal elements, and O represents an oxygen element, and x and y each represent an inequality, 0≦x≦
1, 0≦y≦1. ) perovskite type composite oxide powder,
A suspension of water and oil and high-melting point glass powder are added to form a paste, and the composite oxide paste is applied onto an insulating substrate on which the high-melting point glass has been baked, and then baked. A method for manufacturing a moisture-sensitive element, comprising: fixing a porous film of the composite oxide on the substrate, and forming an electrode on the porous film. 2. The manufacturing method according to claim 1, wherein A is either lanthanum element or niogium element. 3. The manufacturing method according to claim 1, wherein A' is one of calcium element, strontium element, and barium element. 4. The manufacturing method according to claim 1, wherein B' is any one of manganese element, iron element, and nickel element.