JP4010994B2 - 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 chemical vapor deposition (CVD) methods. there were.

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 It must not react and must have a coefficient of thermal expansion that matches C ₁₂ A ₇ , which greatly limits the material of the substrate.

The above problems of the C ₁₂ A ₇ film can be solved by using a film forming method called a thermal spraying method, but even in such a case, the substrate is used as a substrate at a high temperature suitable for the operation of an oxidation catalyst or an ion conductor. Without using a material having a large oxygen ion conductivity below, oxygen radical ions such as O ₂ ⁻ and O ⁻ cannot be rapidly supplied to the C ₁₂ A ₇ film, and oxygen radicals are continuously taken up. In other words, it becomes difficult to use it as an oxidation catalyst or an ion conductor.

As a base material having oxygen ion conductivity, zirconium oxide (YSZ) stabilized with yttrium oxide is generally used. The oxygen ion conductivity of a laminate of this and a C ₁₂ A ₇ film is 700 ° C. It is only about 1 × 10 ⁻² S · cm ⁻¹ and cannot be said to be sufficient.

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 a laminate excellent in oxygen ion conductivity. Is easily obtained with high reproducibility, and the present invention has been achieved.

That is, the present invention is a laminate formed by forming an oxygen radical-containing calcium aluminate film on a substrate, wherein the substrate is oxidized by adding zirconium oxide, samarium oxide or gadolinium oxide stabilized with scandium oxide. any of the sintered body der cerium is, moreover bulk density of the sintered body is a 5.5~7.0g / cm ^3, wherein the oxygen radical-containing calcium aluminate film is an oxygen radical containing calcium aluminate A method for producing a laminate, which is obtained by thermal spraying using powder.

Furthermore, the present invention is the above-described method for producing a laminate of oxygen radical-containing calcium aluminate films, wherein the oxygen ion conductivity at 700 ° C. is 5 × 10 ⁻² S · cm ⁻¹ or more. .

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 high oxygen ion conductivity at a high temperature, and continuous uptake and release of oxygen radicals. In addition, a laminated body having a high oxygen ion conductivity of 5 × 10 ⁻² S · cm ⁻¹ or higher can be provided, which is suitable for, for example, oxidation catalysts and ion conductor applications.

In the present invention, the present inventor uses a sintered body of either zirconium oxide stabilized with scandium oxide or cerium oxide added with samarium oxide or gadolinium oxide as the base material of the oxygen radical-containing calcium aluminate film. This is based on the finding that a laminated body of oxygen radical-containing calcium aluminate films having high oxygen ion conductivity can be obtained.

As a result of the present inventors experimentally examining various methods for obtaining an oxygen radical-containing calcium aluminate film, the present inventors obtained a calcium aluminate film when spraying calcium aluminate powder as a raw material powder, At this time, since the crystallinity of the calcium aluminate powder is almost maintained, by using this property, the calcium aluminate powder is simply pretreated by containing oxygen radicals. This is based on the finding that a film can be obtained and the problems of the prior art can be solved.

Zirconium oxide (ZrO ₂ ) stabilized with scandium oxide (Sc ₂ O ₃ ) in the present invention is usually used as a stabilizer for stabilizing the cubic crystal, which is a high-temperature stable phase of zirconium oxide, to a low temperature around room temperature. Instead of yttrium oxide (Y ₂ O ₃ ) and calcium oxide (CaO) used, scandium oxide (Sc ₂ O ₃ ) is used. Although the reason is not certain, the oxygen ion conductivity of stabilized ZrO ₂ is improved by using Sc ₂ O ₃ as compared with the case of using Y ₂ O ₃ or CaO.

A suitable addition amount of Sc ₂ O _{3 as} a stabilizer is Sc ₂ O ₃ : ZrO ₂ = 8: 92 to 12:88, preferably 9:91 to 11:89 in mol%. Further, in order to further stabilize the crystal phase, as a second stabilizer, cerium oxide (CeO ₂ ), aluminum oxide (Al ₂ O ₃ ), Y ₂ O ₃ or the like is added to the above composition as necessary. A small amount of about 2 mol% may be added.

On the other hand, CeO ₂ to which samarium oxide (Sm ₂ O ₃ ) or gadolinium oxide (Gd ₂ O ₃ ) in the present invention is added has high oxygen ion conductivity like ZrO ₂ stabilized with Sc ₂ O ₃ . A suitable addition amount of Sm ₂ O ₃ or Gd ₂ O ₃ to CeO ₂ is Sm ₂ O ₃ (or Gd ₂ O ₃ ): CeO ₂ = 5: 95 to 15:85, preferably 8:92 in mol%. It is in the range of ~ 12: 88.

For CeO ₂ to which ZrO ₂ stabilized with Sc ₂ O ₃ or Sm ₂ O ₃ or Gd ₂ O ₃ is added, these powders are molded by die molding, cold isostatic pressing (CIP) molding, extrusion molding, injection molding or After forming into a predetermined shape by a method such as slurry casting, a sintered body is obtained by heating to 1300 to 1700 ° C. in the atmosphere. The shape of the sintered body is appropriately selected from a flat plate, a curved plate, a dish shape, a tubular shape, and the like as necessary.

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 a laminate formed by forming an oxygen radical-containing calcium aluminate film on a base material, the base material being made of zirconium oxide stabilized with scandium oxide, samarium oxide or cerium oxide added with gadolinium oxide. be any of the sintered body, the oxygen radical-containing calcium aluminate film is method for producing a laminate, characterized in that formed by thermal spraying using oxygen radicals 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 is stabilized with scandium oxide, which is a material having a high oxygen ion conductivity of 5 × 10 ⁻² S · cm ⁻¹ or more because the mobility of oxygen ions is particularly high at a high temperature (700 ° C. or higher). As a calcium aluminate film containing high oxygen radicals is formed on the surface of any sintered body of zirconium oxide or cerium oxide to which samarium oxide or gadolinium oxide is added, as an ion source for providing oxygen radicals or oxygen ions Particularly preferably used.

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, from the intensity of each of the absorption bands _{O 2} ^- ion radical and O ^- was determined the concentration of ions radicals were respectively 5 × ¹⁰ 20 ^{cm -3} (hereinafter This powder is referred to as “oxygen radical-containing C ₁₂ A ₇ powder”).

A mixed powder of scandium oxide powder 10 mol% and zirconium oxide 90 mol% (specific surface area 12.2 m ² / g) was molded at a pressure of 10 MPa using a mold, and then CIPed at a pressure of 200 MPa to provide a diameter of 28 mm and a thickness of 5 mm. It was molded into a disc shape. This was fired at 1450 ° C. for 3 hours in the atmosphere to obtain a sintered body having a bulk density of 5.8 g / cm ³ . 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 100 [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 3 × 10 ²⁰ cm ⁻³ . Moreover, it was 6 * 10 ^<-2> S * cm ^{< -1 >} when the oxygen ion conductivity of the thickness direction in 700 degreeC of a laminated body was measured. Further, it was operable at 750 ° C. as an ion source for continuously supplying oxygen ions.

(Examples 2 to 6) In place of the mixed powder of scandium oxide and zirconium oxide of Example 1, the raw material powder shown in Table 1 was used. After molding in the same manner as in Example 1, the sintered body was subjected to the conditions shown in Table 1. Was made. Thereafter, disk processing and blasting were performed in the same manner as in Example 1 to prepare a substrate. An oxygen radical-containing C ₁₂ A ₇ powder was prepared in the same manner as in Example 1, and sprayed on the blasted substrate surface in the same manner as in Example 1 to produce a laminate.

The sprayed film of the resulting laminate, thickness, crystalline phase, O ₂ ^- ion radical and O ^- concentration of ion radicals, as the oxygen ion conductivity in the thickness direction at 700 ° C. of the laminate of Example 1 Measured and shown in Table 2.

(Comparative Examples 1-2) In place of the mixed powder of scandium oxide powder and zirconium oxide 90 of Example 1, a raw material powder obtained by mixing yttrium oxide or calcium oxide and zirconium oxide under the conditions shown in Table 1 is shown in Table 1. After producing a sintered body under conditions, disk processing and blasting were performed in the same manner as in Example 1 to produce a substrate. An oxygen radical-containing C ₁₂ A ₇ powder was prepared in the same manner as in Example 1, and sprayed on the blasted substrate surface in the same manner as in Example 1 to produce a laminate.

The sprayed film of the resulting laminate, thickness, crystalline phase, O ₂ ^- ion radical and O ^- concentration of ion radicals, as the oxygen ion conductivity in the thickness direction at 700 ° C. of the laminate of Example 1 Measured and shown in Table 2.

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 high oxygen ion conductivity at a high temperature, and continuous uptake and release of oxygen radicals. Is suitable for use as, for example, an oxidation catalyst or an ion conductor, and is industrially useful.

Claims (2)

A method for producing a laminate comprising an oxygen radical-containing calcium aluminate film formed on a substrate, wherein the substrate is any one of zirconium oxide stabilized with scandium oxide, samarium oxide or cerium oxide added with gadolinium oxide. The zirconium oxide has a bulk density of 5.5 to 5.9 g / cm ³ , the cerium oxide has a bulk density of 6.8 to 7.0 g / cm ³ , and A method for producing a laminate, wherein an oxygen radical-containing calcium aluminate film is sprayed using an oxygen radical-containing calcium aluminate powder. 2. The method for producing a laminate of oxygen radical-containing calcium aluminate films according to claim 1, wherein oxygen ion conductivity at 700 ° C. is 5 × 10 ⁻² S · cm ⁻¹ or more.