JP4030493B2 - Calcium aluminate laminate and method for producing the same - Google Patents

Description

The present invention is an oxidation catalyst, applications expand, such as an ion conductor is expected, O ₂ is active oxygen species ^- and O ^- oxygen radicals regarding calcium aluminate film and laminates thereof containing a high concentration of.

O ₂ ^- or O ^- oxygen radicals is one of the active oxygen has been known to play an important role in the oxidation process of organic substances and inorganic substances. Extensive research has been conducted on O ₂ ⁻ adsorbed on the solid surface of an oxide compound (see Non-Patent Document 1).
J. et al. H. Lunsford, Catal. Rev. 8, 135, 1973, M.M. Che and A.A. J. et al. Tench, Adv. Catal, 32, 1, 1983.

In the above research, O ₂ ⁻ is produced by irradiating the surface of the oxide compound with high-energy radiation such as γ rays.

RO ₂ (R = alkali metal) is known as a crystal having O ₂ ⁻ as a constituent anion. However, since these compounds are easily decomposed at a low temperature of 300 ° C. or lower, an oxidation catalyst, ion conduction It cannot be used for purposes such as body.

In 1970, H.C. B. Bartl et al., In 12CaO · 7Al ₂ O ₃ (hereinafter referred to as C ₁₂ A ₇ ) crystal, 2 out of 66 oxygen atoms in a unit cell containing 2 molecules are not included in the network, It claims to exist as “free oxygen” in the existing space in the cage (see Non-Patent Document 2).
H. B. Bartl and T.W. Scheller, Neues Jarhrb. Mineral. , Monash. 1970, 547.

Moreover, Hosono et al. 1 × 10 ¹⁹ / cm ³ in a C ₁₂ A ₇ crystal synthesized by a solid phase reaction in air at a temperature of 1200 ° C. using CaCO ₃ and Al ₂ O ₃ or Al (OH) ₃ as raw materials. the degree of O ₂ ^- that is inclusion found from the measurement of electron spin resonance, part of the free oxygen O ₂ ^- form (non-patent literature have proposed a model that exists in the gauge of 3).
H. Hosono and Y. Abe, Inorg. Chem. 26, 1193, 1997.

C ₁₂ A ₇ is a stable oxide having a melting point of 1415 ° C. If the amount of O ₂ ^{− included} is increased and reversible uptake and release are possible, it can be used as an oxidation catalyst, ion conductor, etc. Can be expected to open up applications.

Further, Hosono et al. Examined C ₁₂ A ₇ which includes the O ₂ ⁻ , and used CaCO ₃ , Ca (OH) ₂ or CaO and Al ₂ O ₃ or Al (OH) ₃ as raw materials, and oxygen. In a dry oxidation atmosphere with a partial pressure of 10 ⁴ Pa or more and a water vapor partial pressure of 10 ² Pa or less, firing is performed at 1200 ° C. or more and less than 1415 ° C., and a solid-phase reaction is performed, thereby reducing O ₂ ⁻ and O ⁻ which are active oxygen species to 10 C ₁₂ A ₇ is obtained that is included at a high concentration of ²⁰ / cm ³ or more (see Patent Document 1).
Japanese Patent Laid-Open No. 2002-3218.

However, there is a problem to be further solved when C ₁₂ A ₇ containing active oxygen species at a high concentration found by Hosono et al. Is used industrially.

That is, when C ₁₂ A ₇ containing a high concentration of oxygen radicals is applied to uses such as an oxidation catalyst and an ionic conductor, it is suitable for each use in order to fully exhibit the function corresponding to the use. Various forms are required.

Except when C ₁₂ A ₇ is used in powder form, the form is generally imparted by sintering C ₁₂ A ₇ . The sintered body can be produced by firing a C ₁₂ A ₇ powder or a mixed powder of a calcium compound and an aluminum compound as a raw material into a predetermined shape using a mold or the like and then firing. However, when a large-sized product such as a plate-shaped product with a large area is manufactured, a large-scale molding machine and a firing furnace are required, which is expensive.

As a countermeasure against this, it is conceivable to form a C ₁₂ A ₇ film that is relatively easy to increase in area on a substrate having oxygen ion conductivity capable of supplying oxygen to the film. Specific methods of film formation include physical vapor deposition (PVD) methods such as sputtering and laser ablation methods, sol-gel methods, chemical vapor deposition (CVD) methods, thermal spraying methods, and coating methods. , Each had problems.

That is, the C ₁₂ A ₇ film obtained by the PVD method or the sol-gel method is amorphous and cannot include oxygen radicals as it is. In order to obtain crystalline C ₁₂ A ₇ which can include oxygen radicals at a high concentration, it is necessary to further crystallize by heat treatment at a high temperature of 1000 ° C. or higher after film formation. However, since C ₁₂ A ₇ is accompanied by a large volume expansion when the amorphous material is crystallized, there is a problem that the film peels off.

Although it is possible to directly form a crystalline calcium aluminate film by the CVD method, since a calcium aluminate other than C ₁₂ A ₇ is likely to be formed, a film containing only crystalline C ₁₂ A ₇ Is extremely difficult to obtain.

In the thermal spraying method, a crystalline C ₁₂ A ₇ powder is used as a raw material powder, which is conveyed to a part called a thermal spray gun and heated to a high temperature by plasma or a flame to melt at least the powder surface, and the tip of the thermal spray gun The film is formed by continuously injecting and adhering to the substrate surface and then solidifying.

Unlike the film obtained by the PVD method or the sol-gel method, the calcium aluminate film obtained by the thermal spraying method becomes mostly crystalline C ₁₂ A ₇ . However, when the raw material powder is melted, a small amount of amorphous C ₁₂ A ₇ is generated and remains in the sprayed film. C ₁₂ A ₇ may be heated to a high temperature in order to efficiently extract the contained oxygen radicals to the outside. If amorphous remains in the C ₁₂ A ₇ film at this time, crystals will be generated during heating. As a result, the volume suddenly changes and the film peels off from the substrate.

On the other hand, in the coating method, it is possible to obtain a film containing no amorphous calcium aluminate by applying a slurry containing crystalline calcium aluminate powder and then baking the coating film by heating. . However, yttria (Y ₂ O ₃ ) -stabilized zirconium oxide (YSZ) or calcium oxide-stabilized zirconium oxide having oxygen ion conductivity generally used as a substrate reacts with calcium aluminate powder during baking. As a result, calcium zirconate (CaZrO ₃ ) and the like are produced, and it is extremely difficult to obtain a film containing only crystalline C ₁₂ A ₇ .

The inventors of the present invention are concerned with the above-mentioned problem of the laminate composed of the C ₁₂ A ₇ film and the base material, after applying crystalline C ₁₂ A ₇ powder to the surface of the base material using a base material of a specific material, and then a predetermined atmosphere. And a layered product that can be solved by heating and baking at a temperature to form a C ₁₂ A ₇ film, and that contains oxygen ion radicals in a high concentration and has oxygen ion conductivity, can be easily obtained with high reproducibility. That is, this has led to the present invention.

That is, the present invention is characterized in that a film made of 12CaO · 7Al ₂ O ₃ containing crystalline oxygen radicals is provided on the surface of a sintered zirconium oxide stabilized or partially stabilized with magnesium oxide. It is an aluminate laminate.

Further, in the present invention, a slurry containing crystalline 12CaO · 7Al ₂ O ₃ powder is applied to the surface of a sintered zirconium oxide stabilized or partially stabilized with magnesium oxide, and this is applied to an oxygen partial pressure of 10 ^4. A method for producing a calcium aluminate laminate, comprising heating in a temperature range of 1300 ° C. or higher and 1400 ° C. or lower in an atmosphere of Pa or higher and a water vapor partial pressure of 10 ² Pa or lower.

In the calcium aluminate laminate of the present invention, a film made of crystalline oxygen radical-containing calcium aluminate is provided on the surface of a zirconium oxide sintered body containing magnesium oxide. As a result, the problem that the calcium aluminate film peels off is improved, and a composite having a crystalline calcium aluminate film is obtained, so that stable supply of oxygen negative ions can be achieved. It is suitable for applications such as catalysts and ion conductors, and is industrially useful. In addition, the method for producing a calcium aluminate laminate according to the present invention enables the calcium aluminate laminate having the above characteristics to be stably obtained at a low cost and employs a coating method. A radical-containing calcium aluminate laminate can be obtained, and a calcium aluminate laminate having a curved surface can be easily obtained.

As a result of the present inventors experimentally examining various methods for obtaining a laminated body of oxygen radical-containing calcium aluminate films, the present inventors have used a zirconium oxide sintered body containing magnesium oxide as a substrate, and obtained crystalline calcium aluminate. A slurry containing the powder as a raw material powder is prepared, and this slurry is applied onto the substrate, and then, in a dry oxidation atmosphere having an oxygen partial pressure of 10 ⁴ Pa or more and a water vapor partial pressure of 10 ² Pa or less, 1300 ° C. or more and 1400 ° C. By heating at the following temperature, it is possible to obtain a laminate in which a crystalline calcium aluminate film containing a high concentration of oxygen radicals is baked on the substrate, and at the time of baking, a calcium aluminate powder and It is based on the finding that the above-mentioned problems of the prior art can be solved at once without reacting.

The calcium aluminate in the present invention is 12CaO.7Al ₂ O ₃ (C ₁₂ A ₇ ) in which main elements are composed of Ca, Al, and oxygen (O), and the main mineral phase is crystalline. The calcium aluminate, _{other, 3CaO · Al 2 O 3 (} C 3 A), CaO · Al 2 O 3 (CA), CaO · 2Al 2 O 3 (CA 2), CaO · 6Al 2 O 3 (CA ₆ ) and other mineral phases can be contained.

In order to set the main component of calcium aluminate to C ₁₂ A ₇ , the molar ratio of Ca and Al contained in the raw material may be 0.77: 1 to 0.96: 1. When the molar ratio of Ca and Al is in a range other than the above, the amount of C ₃ A and CA, which are calcium aluminates other than C ₁₂ A ₇ , increases, and the property of including oxygen radicals is impaired. For this reason, the said range is selected preferably.

The calcium aluminate powder used in the present invention can be obtained from various raw materials so as to have the aforementioned composition. Examples of the Ca source material used as the raw material include limestone (CaCO ₃ ), slaked lime (Ca (OH) ₂ ), and quick lime (CaO). Examples of the Al source material include alumina (Al ₂ O ₃ ), aluminum hydroxide (Al (OH) ₃ ), bauxite, and aluminum residual ash. Of these, CaCO ₃ and Al ₂ O ₃ can be particularly preferably used because they are easily available and highly safe.

After mixing the above raw materials, a calcium aluminate whose main component is C ₁₂ A ₇ is obtained by direct solid-phase reaction under controlled conditions of atmosphere and temperature. A specific example of the conditions for controlling the atmosphere and temperature is, for example, a temperature of 1200 ° C. or higher and lower than 1415 ° C. in the air.

The calcium aluminate obtained by the above operation is usually a lump, but is pulverized as necessary to prepare a powder. At this time, as a pulverizer, a coarse pulverizer such as a stamp mill, a top grinder, a jaw crusher, a roll crusher, a fine pulverizer such as a ball mill, a vibration mill, an attrition mill, etc. A machine can be used. However, in order to prevent calcium aluminate from reacting with moisture, the pulverization is usually carried out by a dry method, and pulverized to a particle size suitable for slurrying with an average particle size of 1 to 5 μm and a specific surface area of 1 to 10 m ² / g. The

Since calcium aluminate reacts with water, water cannot be used as a solvent during slurrying. Instead, alcohols such as methanol, ethanol, isopropanol, n-butanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone Ketones such as methyl acetate, esters such as ethyl acetate and butyl acetate, ethers such as dioxane and tetrahydrofuran, cellosolves such as methyl cellosolve and butyl cellosolve, hydrocarbons such as n-hexane and cyclohexane, chloroform and chloride Organic solvents such as chlorinated hydrocarbons such as methylene and aromatics such as toluene and xylene can be used. Of these, alcohols, particularly ethanol, can be preferably used.

Moreover, in order to give intensity | strength to the coating film after application | coating, binders, such as nitrocellulose, polyacrylic acid ester, polyvinyl butyral, polymethacrylic acid ester, or ethylcellulose, are used as needed. Among these, polyvinyl butyral can be preferably used. These binders can usually be used by dissolving in an organic solvent in advance.

In the present invention, since the calcium aluminate powder has undergone the above-described operation, the calcium aluminate powder is crystalline unlike that obtained by the PVD method or the sol-gel method. Further, unlike a film obtained by a CVD method or a conventional coating method, the content of C ₁₂ A ₇ is extremely high. For this reason, in the calcium aluminate laminate obtained by the method of the present invention, the C ₁₂ A ₇ film can contain a high concentration of oxygen radicals, and the oxygen radicals can be efficiently extracted outside during use. In addition to having the characteristics that can be achieved, there is a characteristic that the problem that the film peels off from the substrate even when heated to a high temperature is difficult to occur.

In the present invention, it is characterized by using a sintered body made of zirconium oxide containing magnesium oxide as a substrate, but this knowledge is a knowledge experimentally obtained by the present inventor and contains magnesium oxide. When the sintered body of zirconium oxide to be used is used as a base material, there are many unclear points as to whether the reaction between the base material and calcium aluminate is prevented. In particular, regarding the sintered body made of zirconium oxide containing magnesium oxide, so-called stabilized zirconium oxide or partially stabilized zirconium oxide in which magnesium oxide is dissolved in zirconium oxide is commercially available. It is preferably selected because it is easy.

In the present invention, the base material may be subjected to surface roughening pretreatment as needed to improve the adhesion to the film. According to the results of the experimental study by the present inventor, the maximum height (Rz), which is an index of surface roughness specified in JIS B 0601: 2001, is 5 to 15 μm, and the adhesion between the film and the substrate is high. High and preferable.

Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples.

(Example 1) Calcium carbonate (CaCO ₃ ) powder and alumina (γ-Al ₂ O ₃ ) powder were mixed so that the molar ratio of Ca to Al was 0.86: 1. A white fired product was obtained by firing at 0 ° C. for 3 hours. After cooling, X-ray diffraction measurement was performed, and it was confirmed that this fired product was C ₁₂ A ₇ .

Further, the fired product was fired at 1250 ° C. for 2 hours in a dry oxidizing atmosphere having an oxygen partial pressure of 4 × 10 ⁴ Pa and a water vapor partial pressure of 10 ² Pa. Ion radicals and O ^{- -} After cooling, the fired product, _{O 2} from ESR spectrum was measured, the intensity of each of the absorption band at room temperature and at 77K were determined the concentration of ions radicals, each 5 × ¹⁰ 20 ^{cm -3} there were.

After grinding the baked product for one hour in a stamp mill, a mesh opening dropped sieve with 1mm sieve to prepare a crushed product 500 g, this diameter 10mm zirconia (ZrO ₂₎ manufactured by grinding balls 1500g and 1 liter of ethanol ( About 795 g) was filled in a 2 liter polyethylene container and continuously pulverized with a ball mill at 72 rotations per minute for 15 hours. The obtained powder was filtered, dried, and crushed, and then X-ray diffraction measurement was performed to confirm that it was C ₁₂ A ₇ . The _{O 2} to obtain the ESR spectrum from the measured ^- ion radicals and O ^- concentration of ions radicals were respectively 5 × ¹⁰ 20 ^{cm -3.} Further the average particle size and specific surface area of this powder was measured by a laser diffraction scattering method and BET1 point method, were respectively 3.7μm and 2.0 m ² / g.

This powder was dispersed in a mixed solvent of ethanol and polyvinyl butyral 100: 0.5 (mass ratio ) to make a slurry, and then the surface was sandblasted with # 80 Al ₂ O ₃ blasting material 60 mm long and 25 mm wide. After applying to the surface of a substrate made of a 2 mm thick magnesium oxide partially stabilized zirconium oxide (SZM-H made by Shinagawa Fine Ceramics) sintered body using a brush, oxygen partial pressure 8 × 10 ⁴ Pa, water vapor content The film was baked by heating at 1350 ° C. for 2 hours in a dry oxidation atmosphere with a pressure of 0.5 × 10 ² Pa to perform lamination. The maximum height after sandblasting of the substrate measured using a stylus type surface roughness measuring instrument was 9.4 μm.

It was confirmed by a scanning electron microscope (SEM) that the obtained film of the laminate had a thickness of about 150 μm and was in close contact with the substrate without any gap. In addition, in the X-ray diffraction diagram, a wide range of bulge (halo) peculiar to amorphous was not recognized at all, and it was judged to be crystalline C ₁₂ A ₇ containing no amorphous. After further peeled film from the substrate, the ESR spectrum was measured, _{O 2} ^- ion radical and O ^- was determined the concentration of ions radicals were respectively 4 × ¹⁰ 20 ^{cm -3.}

(Example 2) Calcium carbonate (CaO) powder and alumina (γ-Al ₂ O ₃ ) powder were mixed so that the molar ratio of Ca to Al was 0.82: 1. For 5 hours to obtain a white fired product. After cooling, X-ray diffraction measurement was performed, and it was confirmed that this fired product was C ₁₂ A ₇ .

After grinding the fired product 2 hours a stamp mill, a mesh opening dropped sieve with 1mm sieve to prepare a crushed product 500 g, this diameter 10mm zirconia (ZrO ₂₎ manufactured by grinding balls 1500g and 1 liter of ethanol ( About 795 g) was filled in a 2 liter polyethylene container and continuously pulverized with a ball mill at 72 rotations per minute for 20 hours. The obtained powder was filtered, dried, and crushed, and then X-ray diffraction measurement was performed to confirm that it was C ₁₂ A ₇ . The _{O 2} obtained from ESR spectroscopy ^- ion radicals and O ^- concentration of ions radicals were both less than 1 × ¹⁰ 19 ^{cm -3.} Furthermore, when the average particle diameter and specific surface area of this powder were measured by the laser diffraction / scattering method and the BET one-point method, they were 2.9 μm and 2.6 m ² / g, respectively.

This powder was slurried in the same manner as in Example 1, and then the surface was sandblasted with # 54 Al ₂ O ₃ blasting material. The magnesium oxide partially stabilized zirconium oxide (length: 42 mm, width: 40 mm, thickness: 3 mm) After applying to the surface of the sintered body substrate made of SZM-M made by Shinagawa Fine Ceramics) using a sprayer, in a dry oxidizing atmosphere having an oxygen content of 1 × 10 ⁵ Pa and a water vapor partial pressure of 0.1 × 10 ² Pa The film was baked by heating at 1380 ° C. for 2 hours to laminate.

It was confirmed by a scanning electron microscope (SEM) that the obtained film of the laminate had a thickness of about 40 μm and adhered to the substrate without any gap. Further, it was determined to be crystalline C ₁₂ A ₇ containing no amorphous substance by X-ray diffraction measurement. After further stripped the membrane from the substrate, the ESR spectrum was measured, _{O 2} ^- ion radical and O ^- was determined the concentration of ions radicals, were respectively 3 × ¹⁰ 20 ^{cm -3.}

(Example 3) A plate-like magnesium oxide-stabilized zirconium oxide sintered body (ZR-15M manufactured by Nikkato) having a length of 45 mm, a width of 30 mm, and a thickness of 2.5 mm was used in the same manner as in Example 2 except that it was used as a substrate. Then, lamination with a C ₁₂ A ₇ coating film was performed. It was confirmed by a scanning electron microscope (SEM) that the laminated film had a thickness of about 110 μm and was in close contact with the substrate without any gaps. Further, it was determined to be crystalline C ₁₂ A ₇ containing no amorphous substance by X-ray diffraction measurement. Further measuring the ESR spectrum of the film, _{O 2} ^- ion radical and O ^- was determined the concentration of ions radicals were respectively 5 × ¹⁰ 20 ^{cm -3.} This laminate was operable at 800 ° C. as an ion source of oxygen ions.

(Comparative Example 1) In Example 2, instead of magnesium oxide partially stabilized zirconium oxide, yttria (Y ₂ O ₃ ) stabilized zirconium oxide sintered body (YSZ-8 manufactured by Nikkato) having a diameter of 25 mm and a thickness of 2.8 mm The disc was laminated with the coating film in the same manner as in Example 2 except that the disc made of the above was used as the substrate. As a result, it was confirmed by X-ray diffraction measurement that the baked film was altered to calcium zirconate (CaZrO ₃ ) instead of the original C ₁₂ A ₇ . Was further measured ESR spectra of the membrane, O ₂ ^- ion radical and O ^- ion radicals were detected either.

(Comparative Example 2) In Example 2, a calcium oxide stabilized zirconium oxide disk (ZR-11 manufactured by Nikkato) having a diameter of 21 mm and a thickness of 2 mm was used as the substrate in place of the magnesium oxide partially stabilized zirconium oxide. Was laminated with a coating film in the same manner as in Example 2. As a result, it was confirmed by X-ray diffraction measurement that the baked film was altered not to the original C ₁₂ A ₇ but to CA (CaO.Al ₂ O ₃ ). Was further measured ESR spectra of the membrane, O ₂ ^- ion radical and O ^- ion radicals were detected either.

According to the present invention, calcium aluminate powder composed of crystalline C ₁₂ A ₇ is used as a raw material, and this is slurried and coated on a zirconium oxide substrate stabilized or partially stabilized with magnesium oxide, and then has a high oxygen partial pressure. And a layer of calcium aluminate film containing oxygen radicals at a high concentration can be obtained only by heating in a dry oxidizing atmosphere with a low water vapor partial pressure. A laminate of calcium aluminate films can be easily provided with high reproducibility, and this laminate is suitable for use in, for example, oxidation catalysts and ion conductors, and is very useful in industry.

Claims (2)

A calcium aluminate laminate, wherein a film made of 12CaO.7Al ₂ O ₃ containing crystalline oxygen radicals is provided on the surface of a sintered zirconium oxide stabilized or partially stabilized with magnesium oxide. A slurry containing crystalline 12CaO · 7Al ₂ O ₃ powder is applied to the surface of a sintered zirconium oxide stabilized or partially stabilized with magnesium oxide, and this is applied to an oxygen partial pressure of 10 ⁴ Pa or more and a water vapor partial pressure. A method for producing a calcium aluminate laminate, comprising heating in a temperature range of 1300 ° C. to 1400 ° C. in an atmosphere of 10 ² Pa or less.