JP4067390B2 - Method for producing oxygen radical-containing calcium aluminate sintered body - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is an oxidation catalyst, applications expand, such as an ion conductor is expected, O ₂ is active oxygen species ^- and O ^- process for the preparation of calcium aluminate sintered body containing oxygen radicals at a high concentration.
[0002]
[Prior art]
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 solid surfaces of various oxides (see, for example, Non-Patent Document 1). In most of these studies, O ₂ ⁻ is produced by irradiating the surface of an oxide compound with high-energy radiation such as γ-rays.
[0003]
[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
[0004]
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 Not suitable for uses such as the body.
[0005]
In 1970, H.C. B. Bartl et al., In a 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 and exist in the crystal. It claims to exist as “free oxygen” in the space inside the cage (see Non-Patent Document 2).
[0006]
[Non-Patent Document 2]
H. B. Bartl and T.W. Scheller, Neues Jarhrb. Mineral. , Monash. 1970, 547
[0007]
Hosono et al. Have about 1 × 10 ¹⁹ / cm ³ in a C ₁₂ A ₇ crystal synthesized by 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. O ₂ ^- is found that it is the clathrate from the measurement of electron spin resonance, part of the free oxygen O ₂ ^- proposes a model that exists in cages in the form of (non-patent document 3 reference ).
[0008]
[Non-Patent Document 3]
H. Hosono and Y. Abe, Inorg. Chem. 26, 1193, 1997
[0009]
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, oxidation catalyst, ion conductor, etc. It is expected that it can be used for various purposes.
[0010]
Hosono et al. Further studied C ₁₂ A ₇ that includes O ₂ ⁻ , and used CaCO ₃ , Ca (OH) ₂ or CaO, and Al ₂ O ₃ or Al (OH) ₃ as raw materials. O ₂ ⁻ or O ⁻ that is an active oxygen species is obtained by baking to 1200 ° C. or more and less than 1415 ° C. 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 to cause a solid phase reaction. C ₁₂ A ₇ which is included at a high concentration of 10 ²⁰ / cm ³ or more is obtained (see Patent Document 1).
[0011]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-3218
[Problems to be solved by the invention]
However, when C ₁₂ A ₇ that contains active oxygen species at a high concentration found by Hosono et al. Is used industrially, there are further problems to be solved.
[0013]
In other words, 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 sufficiently exert the function depending on the use. It needs to be shaped.
[0014]
With respect to the shape products, usually the sintered body with increased strength so as to have a resistance to handling at the time of use is used, a sintered body having a simple shape such as a plate or rod, as a raw material C ₁₂ A ₇ powder or a mixed powder of calcium compound-containing powder and aluminum compound-containing powder can be relatively easily manufactured by forming into a predetermined shape using a mold or the like and then firing.
[0015]
On the other hand, depending on the application, for example, it is necessary to produce a sintered body having a complicated shape such as a dish type, a crucible type, a flask type, or a test tube type. In this case, for example, the raw material powder is molded with a mold or the like. Thereafter, a method is often applied in which a calcined body that can be processed by firing at a temperature lower than the sintering temperature is manufactured, and sintered after being processed into a predetermined shape. However, this method is not only complicated with many steps but also uneconomical because a large amount of processing waste is generated, and there are some methods that cannot be processed depending on the shape.
[0016]
In addition, the present inventors have made various means for diversifying the shape of the C ₁₂ A ₇ sintered body. For example, the C ₁₂ A ₇ powder is suspended in water to form a slurry, and then absorbed in water. Although it is possible to cope with a relatively complicated shape by casting in a mold having the properties of casting, once C ₁₂ A ₇ comes into contact with water, not only does it release the oxygen radicals encapsulated, After that, C ₁₂ A ₇ could not include high concentration oxygen radicals, so that it was difficult to apply the slurry casting as it was.
[0017]
The object of the present invention is to solve the above-mentioned problems, and can be applied to oxidation catalysts and ion conductors. It contains a high oxygen radical, and has a complex shape calcium aluminate sintered body with good reproducibility. The purpose is to provide it cheaply.
[0018]
[Means for Solving the Problems]
The present inventors, or release oxygen radicals when C ₁₂ A ₇ is in contact with the organic solvent, oxygen radicals Noting that no or packaging contact properties is impaired, non-aqueous and C ₁₂ A ₇ powder It is suspended in a solvent to form a slurry, which is cast into a slurry, calcined at a predetermined temperature and in an oxygen concentration atmosphere, and then baked at a predetermined temperature and oxygen concentration atmosphere, so that it contains a high concentration of oxygen radicals, a dish type, crucible type, flask type or test tube Recalling that a calcium aluminate sintered body having a complicated shape such as a mold can be manufactured easily and stably, this has been experimentally confirmed, and the present invention has been achieved.
[0019]
That is, in the present invention, a raw material powder containing a Ca / Al molar ratio of 0.77 or more and 0.96 or less is made into a slurry suspended in a non-aqueous solvent, cast into the slurry, and then the oxygen content. Oxygen radical-containing calcium aluminate firing having 12CaO.7Al ₂ O ₃ (hereinafter referred to as C ₁₂ A ₇ ) as a main phase by heating to a melting temperature of 1100 ° C. or higher and under a pressure of 4 × 10 ⁴ Pa or higher. It is a manufacturing method of the calcium aluminate sintered compact characterized by setting it as a ligature.
[0020]
Further, the present invention is characterized in that the raw material powder is obtained by preheating a mixed powder of a calcium compound-containing powder and an aluminum compound-containing powder so that C ₁₂ A ₇ is a main phase powder. Calcium aluminate sintered body, preferably having a specific surface area of 1.5 m ² / g or more and an average particle size of 10 μm or less. It is a manufacturing method of a body.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
In the calcium aluminate sintered body obtained in the present invention, the main elements are Ca, Al, and oxygen (O), and the main mineral phase is C ₁₂ A ₇ .
[0022]
The calcium aluminate sintered body obtained in the present invention can contain unavoidable impurity components other than Ca, Al, and oxygen, depending on the purpose of use, but is applied to oxidation catalysts and ion conductor applications. Is required to have as little impurities as possible and have a high purity, and the total amount of Ca, Al, and oxygen is preferably 95% by mass or more, and more preferably 98% by mass or more.
[0023]
The calcium aluminate sintered body obtained by the present invention, from the constituent element is formed of a single phase or mixed phase composed of various calcium aluminate described later, the main phase is a C ₁₂ A ₇ . This is because the calcium aluminate other, 3CaO · _Al 2 _{O 3} (hereinafter, referred to as _{C 3 A), CaO · Al} 2 O 3 ( hereinafter, referred to as _{CA), CaO · 2Al 2 O} 3 (CA 2), CaO.6Al ₂ O ₃ (CA ₆ ) and the like. This is because only C ₁₂ A ₇ has the property of including oxygen radicals at a high concentration of 10 ²⁰ / cm ³ or more. In the present invention, “C ₁₂ A ₇ is the main phase” means that the peak of the maximum peak of C ₁₂ A ₇ with respect to the total peak height of the mineral layer in the X-ray diffraction chart. It means that the height is 90% or more.
[0024]
In the present invention, in order to set the main phase of the calcium aluminate sintered body to C ₁₂ A ₇ , the molar ratio of Ca and Al contained in the raw material is set in the range of 0.77 to 0.96, What is necessary is just to heat to 1100 degreeC or more. In the range a molar ratio of Ca and Al is other than the _{above, C} 12 the amount of calcium aluminate other than _{A 7 C 3} A and CA is increased, _C calcium aluminate sintered body to be obtained 12 _{A 7} The amount is reduced, and accordingly, the properties of the calcium aluminate sintered body that include oxygen radicals are impaired.
[0025]
Examples of the Ca source material used as a raw material for the calcium aluminate sintered body of the present invention include limestone (CaCO ₃ ), slaked lime (Ca (OH) ₂ ), and quicklime (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.
[0026]
In the present invention, as described above, a raw material powder blended in a predetermined composition or a raw material powder previously formed with C ₁₂ A ₇ as a main phase is made into a slurry using a non-aqueous solvent, and this is cast and molded. Then, it is based on the knowledge that a calcium aluminate sintered body containing oxygen radicals in a high concentration can be obtained by sintering under predetermined conditions. The reason for this is not clear, but from the above circumstances, the present inventor found that when C ₁₂ A ₇ is produced from the raw material and forms a sintered body, when it comes into contact with a large amount of water even once, ₁₂ a ₇ is coupled with the water, are interpreted as the heating conditions for inclusion of oxygen radicals in C ₁₂ a ₇ shows that water was the binding is not removed.
[0027]
Nonaqueous solvents that can be used in the present invention include alcohols such as methanol, ethanol, isopropanol, and n-butanol, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, methyl acetate, ethyl acetate, butyl acetate, and the like. Esters, dioxane, ethers such as tetrahydrofuran, cellosolves such as methyl cellosolve and butyl cellosolve, hydrocarbons such as n-hexane and cyclohexane, chlorinated hydrocarbons such as chloroform and methylene chloride, toluene, xylene and the like Organic solvents such as aromatics can be used. Among these, alcohols, particularly ethanol can be preferably used, and some of ethanol and the like contain water as an azeotropic component, but as long as the object of the present invention is not hindered. This can be used in
[0028]
In the present invention, a calcium aluminate raw material powder (hereinafter simply referred to as “C”), which is previously heated and synthesized from a mixed powder of a calcium compound-containing powder and an aluminum compound-containing powder so that C ₁₂ A ₇ is the main phase. ₁₂ A ₇ powder), or a mixed powder of calcium compound-containing powder and aluminum compound-containing powder as a raw material, and the non-aqueous solvent, if necessary, using a ball mill or the like to prepare a slurry. Is done. At this time, a slurry having a viscosity suitable for pouring into a mold is prepared by appropriately adjusting the amount ratio of the raw material powder and the organic solvent.
[0029]
The raw material powder used for the slurry adjustment preferably has a specific surface area of 1.5 m ² / g or more and an average particle size of 10 μm or less. This is because the raw material powder having a specific surface area of less than 1.5 m ² / g or an average particle diameter of more than 10 μm is likely to settle, and may not be uniformly embedded in the mold during casting. The mold having liquid absorbency used in the present invention may be made of any material as long as it can absorb a non-aqueous solvent from the slurry and obtain a molded body having a desired shape. Since it is inexpensive and easily available, gypsum can be preferably used.
[0030]
The casting molding method is either a waste mud casting method in which excess slurry is discharged after solid content of a predetermined thickness has been deposited on the mold surface, or a solid casting method in which all solid content is deposited in the mold. Also good. After the inking, the cast body is dried at a temperature slightly lower than the boiling point of the organic solvent, and the molded body is obtained by removing the mold from the mold after drying.
[0031]
A binder such as nitrocellulose, polyacrylic acid ester, polyvinyl butyral, polymethacrylic acid ester, or ethyl cellulose is used as necessary to impart strength to the molded article during and after demolding. Among these, polyvinyl butyral can be preferably used. These binders can be used by dissolving in an organic solvent in advance.
[0032]
The sintered body obtained in the present invention is produced by firing the molded body at 1100 ° C. or more, preferably 1200 ° C. or more and the melting temperature or less. If the sintering temperature is equal to or higher than the melting temperature, the sintered body melts and deforms irregularly, or once melted, oxygen radical inclusion becomes difficult. The melt temperature, _C 12 _{A 7} powder as the raw material, the calcium compound-containing powder, aluminum compound containing powder of particle size will vary depending on the heating atmosphere, it is usually about from 1380 to 1,420 ° C..
[0033]
In the present invention, C ₁₂ A ₇ in the calcium aluminate sintered body is clathrated with a high concentration of oxygen radicals, and the molded body is sintered to form a calcium aluminate sintered body. A non-melting temperature range of 1100 ° C. or higher is specified in an atmosphere having an oxygen partial pressure of 4 × 10 ⁴ Pa or higher.
[0034]
If the heating for inclusion of oxygen radicals is once after C ₁₂ A ₇ is formed, as in calcium aluminate powder, any stage during powdering, green firing or after sintering You can go there. However, when applied after sintering, a phase different from C ₁₂ A ₇ , such as C ₃ A or CA, is generated near the surface of the sintered body, and oxygen enters C ₁₂ A ₇ inside the sintered body. May be hindered. In order to prevent this phenomenon, the surface of the sintered body may be ground and polished to remove C ₃ A and CA and expose C ₁₂ A ₇ to the surface.
[0035]
In addition, when separately performing an operation to sinter the molded body to obtain a calcium aluminate sintered body and a heating operation to include high concentration oxygen radicals in C ₁₂ A ₇ in the calcium aluminate sintered body, The former can be performed in the atmosphere.
[0036]
【Example】
(Example) 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. A white powder was obtained by firing for a period of time. This was cooled, wet-pulverized in ethanol using a ball mill, and dried to obtain a powder having a specific surface area of 2.1 m ² / g and an average particle diameter of 4.0 μm. This powder was confirmed by X-ray diffraction measurement to contain C ₁₂ A ₇ as a main component and slightly contain CA.
[0037]
The powder, ethanol, and polyvinyl butyral (# 3000-K, manufactured by Denki Kagaku Kogyo) were blended at a mass ratio of 100: 100: 0.5, and mixed with a ball mill for 1 hour to prepare a slurry. . The slurry was cast into a test tube-shaped gypsum mold having a diameter of 20 mm and a depth of 300 mm, and cast molding was performed by an exhaust mud casting method in which excess slurry was discharged. The cast body was dried at 70 ° C. for 1 day and then demolded to obtain a molded body.
[0038]
The molded body was sintered by heating in the atmosphere at 1370 ° C. for 3 hours. The obtained sintered body has a test tube shape with an outer diameter of 16.4 mm, an inner diameter of 13 mm, and a length of 230 mm. The color is light brown, and it is confirmed again by X-ray diffraction measurement that C ₁₂ A ₇ is a main component. did. The bulk density was measured by the method of JIS R 1634, and the relative density was calculated to be 97%.
[0039]
The sintered body was further heated at 1250 ° C. for 2 hours in an atmosphere with an oxygen partial pressure of 5.8 × 10 ⁴ Pa. After cooling, a part of the sintered body was pulverized, and an ESR spectrum at room temperature and 77 K was measured. , _{O 2} from the intensity of the respective absorption band ^- ion radicals and O ^- was determined the concentration of ions radicals were respectively 4 × ¹⁰ 20 ^{cm -3.}
[0040]
(Comparative Example) As a comparative example, the C ₁₂ A ₇ powder obtained in the example was used, water was used instead of ethanol, and polyvinyl alcohol was used instead of polyvinyl butyral. Slurry was produced, cast and molded, dried and sintered to obtain a sintered body. The obtained sintered body has a test tube shape with an outer diameter of 16.8 mm, an inner diameter of 13.2 mm, and a length of 235 mm, and is white in color. This is mainly composed of CA and C ₃ A by X-ray diffraction measurement. It was found that only a small amount of C ₁₂ A ₇ was produced.
[0041]
This sintered body further in the same manner as in Example were heated under an atmosphere of an oxygen partial pressure of 5.8 × 10 4 ^Pa, after cooling, O ₂ by measuring the ESR spectrum ^- ion radicals and O ^- concentration of ion radicals Were found to be below the detection limit (1 × 10 ¹⁸ cm ⁻³ ), respectively.
[0042]
【The invention's effect】
According to the present invention, a calcium aluminate sintered body containing oxygen radicals in a high concentration and having a complicated shape, for example, a dish shape, a crucible shape, a flask shape, or a test tube shape, can be stabilized. And since it can provide easily, application to the new use of an oxygen radical containing calcium aluminate sintered compact is attained, and it is very useful industrially.

Claims (3)

A raw material powder containing a Ca / Al molar ratio of 0.77 or more and 0.96 or less is made into a slurry suspended in a non-aqueous solvent, cast into the slurry, and then subjected to an oxygen partial pressure of 4 × 10 ⁴ Pa. By heating to 1100 ° C. or higher and the melting temperature or lower in the above atmosphere, an oxygen radical-containing calcium aluminate sintered body having 12CaO · 7Al ₂ O ₃ (hereinafter referred to as C ₁₂ A ₇ ) as a main phase is obtained. A method for producing a sintered calcium aluminate. 2. The calcium according to claim 1, wherein the raw material powder is obtained by previously heating a mixed powder of a calcium compound-containing powder and an aluminum compound-containing powder to obtain a powder of C ₁₂ A ₇ as a main phase. Manufacturing method of aluminate sintered body. The method for producing a calcium aluminate sintered body according to claim 2, wherein the raw material powder has a specific surface area value of 1.5 m ² / g or more and an average particle size of 10 µm or less.