JP3995637B2 - Method for producing laminate of oxygen radical-containing calcium aluminate film - 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 ^- includes oxygen radicals in high concentrations, high ionic conductivity of these radical ions The present invention relates to a method for manufacturing a laminate of calcium aluminate films.

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 this research, O ₂ ⁻ is created by irradiating the surface of an 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 with a melting point of 1415 ° C. If the amount of O ₂ ^{— included} is increased and continuous 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, so that O ₂ ^— and O ⁻ that are active oxygen species 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, when C ₁₂ A ₇ containing active oxygen species at a high concentration found by Hosono et al. Is used industrially, there is a problem to be further solved.

That is, when C ₁₂ A ₇ containing a high concentration of oxygen radicals is applied to an oxidation catalyst or an ion conductor, various functions suitable for each application can be used in order to fully exhibit the function corresponding to the use. It needs to be in form.

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, it is conceivable to form a laminate by forming a C ₁₂ A ₇ film, which is relatively easy to increase in area, on a base material having oxygen ion conductivity. Specific methods of film formation include physical vapor deposition (PVD) methods such as sputtering and laser abrasive methods, sol-gel methods, and the like, but each has 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 that can include oxygen radicals at a high concentration, it is necessary to further heat-treat at a high temperature of 1000 ° C. or higher after film formation.

Although it is possible to directly form crystalline C ₁₂ A ₇ by the CVD method, the substrate must be kept at a high temperature of 1000 ° C. or higher. Accordingly, if the thermal expansion coefficients of the C ₁₂ A ₇ film and the substrate do not match, the film peels off from the substrate during cooling or cracks occur in the film.

As described above, in the above-described method, the substrate for obtaining a crystalline C ₁₂ A ₇ film that can include oxygen radicals at a high concentration can withstand a high temperature of 1000 ° C. or higher, and C ₁₂ A ₇ A material that does not react and must have a thermal expansion coefficient that matches C ₁₂ A ₇ , but has oxygen ion conductivity and a thermal expansion coefficient that matches C ₁₂ A ₇ up to 1000 ° C. or higher. However, it was practically impossible to produce a laminate by the film forming method.

C ₁₂ For such problems of the A ₇ layer, without heating the substrate can be deposited C ₁₂ A ₇ crystalline directly be solved by using a film forming method called spraying method . However, even in such a case, the laminate must be heated to 700 to 900 ° C. in order to continuously take up and release oxygen radicals after film formation. When the thermal expansion coefficient and the base material have a large mismatch in thermal expansion coefficient, the film is peeled off from the base material due to repeated heating and cooling.

As a base material having oxygen ion conductivity, zirconium oxide is generally used. Zirconium oxide is usually used as stabilized zirconium oxide in which cubic crystals, which are high-temperature stable phases, are stabilized to room temperature using various additives in order to avoid sudden volume changes due to phase transition. However, the thermal expansion coefficient of the stabilized zirconium oxide at room temperature to 900 ° C. is 10 to 11 × 10 ⁻⁶ / ° C., which is larger than the thermal expansion coefficient of C ₁₂ A ₇ (7 × 10 ⁻⁶ / ° C.). For this reason, when heating and cooling at room temperature to 900 ° C. are repeated on the laminate of the C ₁₂ A ₇ sprayed film and the stabilized zirconium oxide base material, the film peels off from the base material.

The present inventors can solve the above-mentioned problems of the laminate of the base material and the C ₁₂ A ₇ film only when a base material of a specific material is used, and the film can be obtained by repeated heating and cooling. It has been found that a laminate that does not peel from the substrate can be easily obtained with high reproducibility, and has led to the present invention.

That is, the present invention relates to a laminate obtained by forming an oxygen radical-containing calcium aluminate film on a substrate, and the substrate has a partially stabilized oxidation with a bulk density of 5.5 to 6.1 g / cm ^3. zirconium (hereinafter P artially S tabilized Z irconium Oxide, abbreviated as PSZ) a sintered body, and wherein the oxygen radical-containing calcium aluminate film is formed by thermal spraying using oxygen radicals containing calcium aluminate powder It is the manufacturing method of the laminated body to perform.

In the present invention, the present inventor uses a PSZ sintered body as a base material for an oxygen radical-containing calcium aluminate film, thereby obtaining a laminate in which the film does not peel from the base material even by repeated heating and cooling. Based on what you found.

In the PSZ according to the present invention, stabilized zirconium oxide stabilizes the cubic crystal to room temperature by the addition of the stabilizer, whereas by reducing the amount of the stabilizer, the cubic crystal is added to the cubic parent phase. Also, a stable tetragonal dispersed phase is precipitated at a low temperature.

Since a part of the tetragonal crystal transitions to a monoclinic crystal which is a low temperature stable phase at 900 ° C. or lower, PSZ becomes a mixed phase of cubic, tetragonal and monoclinic crystals at 900 ° C. or lower. When heating from room temperature, this monoclinic phase reversely transforms to tetragonal crystal, but at this time, volume contraction occurs, so that the thermal expansion coefficient of PSZ is smaller than that of stabilized zirconium oxide.

The thermal expansion coefficient of PSZ at room temperature to 900 ° C. is about 5.5 to 8.0 × 10 ⁻⁶ / ° C., although it depends on the type and amount of stabilizer to be added, and the thermal expansion coefficient of C ₁₂ A _7. It is close to (7 × 10 ⁻⁶ / ° C.). This is why the oxygen radical-containing calcium aluminate film based on PSZ of the present invention does not peel from the substrate even by repeated heating and cooling.

The raw material powder of the PSZ sintered body in the present invention is a mixed powder of pure zirconium oxide powder (monoclinic crystal) and stabilized zirconium oxide powder (cubic crystal). By adding pure zirconium oxide to stabilized zirconium oxide, a structure in which tetragonal crystals are precipitated in a cubic parent phase is formed.

Examples of the stabilizer in the present invention include yttrium oxide (Y ₂ O ₃ ), magnesium oxide (MgO), calcium oxide (CaO), scandium oxide (Sc ₂ O ₃ ), lanthanum oxide (La ₂ O ₃ ), and oxidation. It is an oxide of a lanthanide element such as samarium (Sm ₂ O ₃ ) or gadolinium oxide (Gd ₂ O ₃ ).

The calcium aluminate in the present invention is composed of Ca, Al, and oxygen (O) as main elements, and crystalline 12CaO.7Al ₂ O ₃ (C ₁₂ A ₇ ) whose main mineral phase is crystalline. Other calcium aluminates include 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 )), but only crystalline C ₁₂ A ₇ has the property of including oxygen radicals at a high concentration of 10 ²⁰ / cm ³ or more.

In order to make the main component of calcium aluminate C ₁₂ A ₇ , the molar ratio of Ca and Al contained in the raw material may be 0.77 to 0.96. 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, it is not suitable for the present invention.

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 raw materials, the oxygen radicals can be 10 ²⁰ / cm ³ by directly causing a solid phase reaction under controlled conditions of atmosphere and temperature, or by maintaining the conditions of controlled atmosphere and temperature after the solid phase reaction. Calcium aluminate can be obtained which can be included at the above high concentration. A specific example of the conditions for controlling the atmosphere and temperature is, for example, 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, and a temperature of 1200 ° C. or more and less than 1415 ° C.

The calcium aluminate clathrated with the high concentration oxygen radicals obtained by the above operation is adjusted to a particle size of 10 to 100 μm, preferably 10 to 50 μm by a method such as pulverization or sieving, and is suitable as a raw material for thermal spraying. Powdered.

The thermal spraying method in the present invention may be any of plasma spraying method, flame spraying method, explosive spraying method or laser spraying method, etc., but the uniformity of the film and the adhesion between the film and the substrate are good, and it is safe. A plasma spraying method that is excellent in properties and economy is particularly preferable.

The reason why the thermal spraying method is selected in the present invention is not clear, but the present inventor considers as follows. That is, in a general thermal spraying apparatus used for a thermal spraying method, raw materials such as powder are conveyed to a part called a thermal spray gun, and at the same time, heated at a high temperature by a plasma or a flame, and at least the surface becomes liquid. It is said that a film is formed by continuously spraying from the tip of the material and adhering to the surface of the substrate and then solidifying.

Unlike the film obtained by the PVD method, the sol-gel method or the CVD method, the calcium aluminate film obtained by the thermal spraying method is crystalline despite being formed without heating the substrate. This is because, unlike PVD, sol-gel, or CVD, the raw material in the thermal spraying method does not cause a significant change in state due to vaporization or chemical reaction, and simply solidifies on the substrate after the surface or its vicinity melts at a high temperature. This is because the composition and crystal structure of the raw material are easily reflected in the film as they are.

The present invention is also a method for producing a laminate comprising an oxygen radical-containing calcium aluminate film formed on a substrate, wherein the substrate is a partially stabilized zirconium oxide sintered body, and the oxygen radical A method for producing a laminate, wherein the calcium aluminate film is formed by thermal spraying using an oxygen radical-containing calcium aluminate powder.

As described above, according to the present invention, a crystalline calcium aluminate film is obtained, and since the spraying method is adopted, if the spray gun is moved during spraying, a large-area substrate or curved surface is obtained. It is also possible to easily form a film on a substrate having If necessary, the base material may be subjected to a surface roughening pretreatment in order to improve adhesion to the film.

The laminate of the present invention has oxygen ion conductivity, and in particular, a calcium aluminate film containing a high oxygen radical is formed on the surface of a PSZ sintered body having a thermal expansion coefficient close to that of crystalline calcium aluminate (C ₁₂ A ₇ ). Therefore, it is particularly suitably used as an ion source that provides oxygen radicals or oxygen ions that require repeated heating and cooling.

Calcium carbonate (CaCO ₃ ) powder and alumina (γ-Al ₂ O ₃ ) powder were mixed so that the molar ratio of Ca and Al was 0.82: 1, and then fired at 1300 ° C. for 3 hours in the air. A white powder was obtained. After cooling, X-ray diffraction measurement was performed to confirm that the powder was C ₁₂ A ₇ .

Further, the powder 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. The ESR spectrum after cooling at room temperature and 77K were measured, _{O 2} from the intensity of the respective absorption band ^- ion radicals and O ^- was determined the concentration of ions radicals, were respectively 6 × ¹⁰ 20 ^{cm -3} (hereinafter This powder is referred to as “oxygen radical-containing C ₁₂ A ₇ powder”).

Commercially available PSZ powder (Tosoh's TZ-3YS, mixed powder of Y ₂ O ₃ stabilized zirconium oxide and monoclinic zirconium oxide, Y ₂ O ₃ amount 5.2 mass%) is molded at a pressure of 10 MPa using a mold. Thereafter, CIP was performed at a pressure of 200 MPa to form a disk shape having a diameter of 28 mm and a thickness of 5 mm. This was fired in the atmosphere at 1500 ° C. for 2 hours to obtain a sintered body having a thermal expansion coefficient of 7.2 × 10 ⁻⁶ / ° C. and a bulk density of 6.1 g / cm ^{3 from} room temperature to 900 ° C. It was confirmed by X-ray diffraction measurement that the sintered body was PSZ.

After processing this sintered body into a disk having a diameter of 20 mm and a thickness of 2 mm, one side was blasted with an Al ₂ O ₃ blast material of # 54 to prepare a base material.

The oxygen radical-containing C ₁₂ A ₇ powder is pulverized and sieved to prepare a powder of 10 to 50 μm, loaded into a plasma spraying machine, and then a mixed gas of argon and hydrogen is used as a plasma gas, and a current value of 500 amperes. Then, spraying was performed on the substrate surface under the conditions of a voltage value of 64 volts and a spraying distance of 100 mm to prepare a laminate.

The resulting sprayed film of the laminate, it is in close contact without gaps to the substrate in a thickness of about 120 [mu] m, it is C ₁₂ A ₇ crystalline, O ₂ ^- is the concentration of ion radical ^- ion radical and O , Each confirmed to be 4 × 10 ²⁰ cm ⁻³ . In addition, as a result of repeatedly heating and cooling the laminate from room temperature to 900 ° C. 100 times, no cracks or peeling occurred in the sprayed film. Further, it was operable at 750 ° C. as an ion source for continuously supplying oxygen ions.

25 mm of a commercially available PSZ sintered body (SZM-H manufactured by Shinagawa Fine Ceramics, Stabilizer MgO, thermal expansion coefficient of room temperature to 900 ° C. 6.9 × 10 ⁻⁶ / ° C., bulk density 5.5 g / cm ³ ) Thermal spraying of oxygen radical-containing C ₁₂ A ₇ powder was performed on a square plate of × 60 mm × 1 mm in the same manner as in Example 1 to prepare a laminate.

The resulting sprayed film of the laminate, it is in close contact without gaps to the substrate in a thickness of about 90 [mu] m, it is C ₁₂ A ₇ crystalline, O ₂ ^- is the concentration of ion radical ^- ion radical and O , Respectively, were confirmed to be 5 × 10 ²⁰ cm ⁻³ . In addition, as a result of repeatedly heating and cooling the laminate from room temperature to 900 ° C. 100 times, no cracks or peeling occurred in the sprayed film. In addition, it was operable at 800 ° C. as an ion source for continuously supplying oxygen ions.

(Comparative Example 1) A commercially available stabilized zirconium oxide powder (8YSZ, Y ₂ O ₃ stabilized zirconium oxide powder, 13.7% by mass of Y ₂ O ₃ manufactured by Daiichi Elemental Chemistry) was molded in the same manner as in Example 1. And it baked at 14750 degreeC in air | atmosphere for 2 hours, and obtained the sintered compact of the thermal expansion coefficient of 10.5 * 10 < ^-6 > / degreeC and the bulk density of 6.1 g / cm < ³ > from room temperature to 900 degreeC. The sintered body was confirmed to be cubic stabilized zirconium oxide by X-ray diffraction measurement. This sintered body was processed in the same manner as in Example 1, and further, the above-mentioned oxygen radical-containing C ₁₂ A ₇ powder was sprayed to produce a laminate.

The resulting sprayed film of the laminate, it is in close contact without gaps to the substrate in a thickness of about 100 [mu] m, it is C ₁₂ A ₇ crystalline, O ₂ ^- is the concentration of ion radical ^- ion radical and O And 4 × 10 ²⁰ cm ⁻³ respectively. Moreover, as a result of repeatedly heating and cooling the laminated body from room temperature to 900 ° C., the sprayed film was peeled off during the fifth heating.

(Comparative example 2) Commercially available stabilized zirconia sintered body (YSZ-8 manufactured by Nikkato, stabilizer Y ₂ O ₃ , coefficient of thermal expansion of 10.1 × 10 ⁻⁶ / ° C. from room temperature to 900 ° C., bulk density of 6. A 0 g / cm ³ ) disk having a diameter of 25 mm and a thickness of 2.8 mm was sprayed with oxygen radical-containing C ₁₂ A ₇ powder in the same manner as in Example 1 to prepare a laminate.

The resulting sprayed film of the laminate, it is in close contact without gaps to the substrate in a thickness of about 120 [mu] m, it is C ₁₂ A ₇ crystalline, O ₂ ^- is the concentration of ion radical ^- ion radical and O , Each confirmed to be 4 × 10 ²⁰ cm ⁻³ . Moreover, as a result of repeatedly heating and cooling the laminated body from room temperature to 900 ° C., the sprayed film was peeled off during the third heating.

According to the present invention, a calcium aluminate film containing oxygen radicals at a high concentration is formed on the surface of a substrate having a desired shape and oxygen ion conductivity, so that oxygen radicals can be continuously taken in and released repeatedly. A laminated body in which peeling or cracking does not occur in the film even by heating / cooling is suitable for use in, for example, oxidation catalysts and ion conductors, and is industrially useful.

Claims (1)

A method for producing a laminate obtained by forming oxygen radicals containing calcium aluminate film on a substrate, portions wherein the substrate bulk density of 5.5~6.1g / cm ³ stabilized zirconia sintered A method for producing a laminate, wherein the oxygen radical-containing calcium aluminate film is thermally sprayed using an oxygen radical-containing calcium aluminate powder.