JP4108448B2 - Method for producing 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 ^- about how the calcium aluminate sintered body containing oxygen radicals at a high concentration and its production ^- and O .
[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 the solid surface of an oxide compound (see Non-Patent Document 1). Most of these studies create O ₂ ⁻ by irradiating the surface of the 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 It cannot be used for purposes such as body.
[0005]
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).
[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 the gauge 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]
This 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, an oxidation catalyst, an ion conductor, etc. It can be expected that the application will be opened.
[0010]
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).
[0011]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-3218
[Problems to be solved by the invention]
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.
[0013]
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 is necessary to form a molded body having a shape, for example, a plate shape, a ring shape, or a tubular shape.
[0014]
Such a molded body is usually obtained by sintering C ₁₂ A ₇ , but the conventional C ₁₂ A ₇ sintered body has a strength of less than 90 MPa in three-point bending strength even after sintering. For this reason, there has been a problem that the sintered body is damaged at the time of handling, particularly in the case of a complicated shape product.
[0015]
[Means for Solving the Problems]
The present inventors have taken various means for improving the strength of the C ₁₂ A ₇ sintered body. As a result, it was newly found that the strength is improved to 90 MPa or more in the three-point bending strength by adding a small amount of silicon oxide (SiO ₂ ) to C ₁₂ A ₇ .
[0017]
In the present invention, an inorganic fibrous substance having an average fiber diameter of 5 μm or less containing SiO ₂ is added to C ₁₂ A ₇ or a mixture of calcium compounds and aluminum compounds as raw materials, and SiO ₂ is 0.05 to 5% by mass. After adding and mixing in such a ratio, it is heated to 1100 ° C. or higher and a melting temperature or lower in an atmosphere having an oxygen partial pressure of 4 × 10 ⁴ Pa or higher.
[0018]
In the present invention, SiO ₂ powder having an average particle size of 5 μm or less is added to C ₁₂ A ₇ or a mixture of calcium compounds and aluminum compounds as raw materials at a ratio such that SiO ₂ becomes 0.05 to 5% by mass. After the addition and mixing, the calcium aluminate sintered body is produced by heating to 1100 ° C. or higher and a melting temperature or lower in an atmosphere having an oxygen partial pressure of 4 × 10 ⁴ Pa or higher.
[0019]
Furthermore, the present invention provides a method for producing a calcium aluminate sintered body by firing a raw material mixture to obtain a calcium aluminate powder containing C ₁₂ A ₇ as a main component. Calcium aluminate powder containing 0.05 to 5% by mass of SiO ₂ , 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.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
In the calcium aluminate sintered body of the present invention, the main elements are composed of Ca, Al, and oxygen (O), and the main components are 12CaO · 7Al ₂ O ₃ (C ₁₂ A ₇ ). More specifically, the amount occupied by all components of Ca, Al, and O is 95% by mass or more. 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 ), and CaO · 6Al ₂ O ₃ (CA ₆ ). and so on. Of these, only C ₁₂ A ₇ has the property of including oxygen radicals at 10 ²⁰ / cm ³ or more.
[0021]
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 11.5: 15 to 12.5: 13. 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.
[0022]
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.
[0023]
As an inorganic fibrous substance with an average fiber diameter of 5 μm or less containing SiO ₂ added to the raw material of the calcium aluminate sintered body of the present invention, for example, alumina fiber containing SiO ₂ (product name, manufactured by Electrochemical Industry, trade name) Denka Alsene), quartz fiber or glass fiber. Examples of the SiO ₂ powder having an average particle size of 5 μm or less, which is added to the raw material of the calcium aluminate sintered body of the present invention, include, for example, ultrafine anhydrous silicon dioxide (manufactured by Nippon Aerosil Co., Ltd., trade name Aerosil) and fine silica filler (electric Chemical trade name, SFP-30M). The addition of SiO ₂ may be performed at the time of mixing raw materials, or may be performed before molding after firing the raw materials into calcium aluminate powder.
[0024]
In the present invention, SiO ₂ amount is 0.05 to 5 mass%. If it is less than 0.05% by mass, the effect of adding SiO ₂ cannot be obtained, and the strength of the sintered body does not exceed 90 MPa. On the other hand, if it exceeds 5% by mass, C ₁₂ A ₇ is hardly generated, and oxygen radicals are not included. For this reason, none is suitable for the present invention. In the present invention, although SiO ₂ calcium aluminate in sintered can not clearly confirmed by X-ray diffraction measurement, present in the sintered body as the calcium rich calcium silicate phase (3CaO · SiO ₂ or 2CaO · SiO ₂₎ It is estimated that
[0025]
In the present invention, calcium aluminate (C ₁₂ A ₇ ) is subjected to a high concentration of oxygen radicals by heating in a non-melting temperature range of 1100 ° C. or higher in an atmosphere having an oxygen partial pressure of 4 × 10 ⁴ Pa or higher. is there. Such heating may be performed at any stage of powder, green firing or after sintering once C ₁₂ A ₇ is formed. However, after sintering, a crystal phase different from C ₁₂ A ₇ such as 3CaO.Al ₂ O ₃ (C ₃ A) and CaO.Al ₂ O ₃ (CA) is formed in the vicinity of the surface of the sintered body. Intrusion of oxygen into the C ₁₂ A ₇ phase inside the body may be inhibited. In this case, the surface of the sintered body must be polished to remove C ₃ A and CA, and C ₁₂ A ₇ must be exposed on the surface before heating.
[0026]
In the present invention, for firing to obtain a sintered body, calcium aluminate powder containing C ₁₂ A ₇ as a main component is formed by containing 0.05 to 5% by mass of SiO ₂ and then 1100 ° C. or higher. Preferably, it is performed at 1200 ° C. or higher and a melting temperature or lower. If the sintering temperature is equal to or higher than the melting temperature, the sintered body is melted and deformed irregularly, or once melted, oxygen radical inclusion becomes difficult, which is not suitable for the present invention. The melting temperature varies depending on the particle size of the raw material C12A7 powder, the amount of added SiO _2, or the heating atmosphere, but is about 1380-1420 ° C. Molding of the powder may be any of general molding methods such as die molding, cold isostatic pressing (CIP) molding, hot press molding, extrusion molding, injection molding, doctor blade molding, or casting molding.
[0027]
The calcium aluminate powder used in the present invention has a specific surface area of 1.5 m ² / g or more and an average particle size of 10 μm or less, more preferably a specific surface area of 2.0 m ² / g or more and an average particle size of 5 μm or less. . When the specific surface area is less than 1.5 m ² / g or the average particle size exceeds 10 μm, the particle size is coarse and the structure of the sintered body becomes nonuniform, which is not suitable for the present invention.
[0028]
The firing atmosphere of the sintered body in the present invention may be either an inert atmosphere such as nitrogen or argon or in the air. Further, when sintering and oxygen radical inclusion are performed simultaneously, the oxygen partial pressure is 4 × 10 ⁴ Pa or more. The atmosphere is fine.
[0029]
【Example】
Hereinafter, the present invention will be further described with reference to Examples and Comparative Examples.
[0030]
(Example 1)
After mixing calcium carbonate (CaCO ₃ ) powder and alumina (γ-Al ₂ O ₃ ) powder so that the molar ratio of Ca to Al is 11.8: 14.4, SiO ₂ 20% by mass is contained. An alumina fiber having an average fiber diameter of 3 μm (Denka Alcene B80 manufactured by Denki Kagaku Kogyo) was added and mixed so that the SiO ₂ content was 0.6% by mass. The mixture was baked in the atmosphere at 1300 ° C. for 3 hours to obtain a white powder containing 12CaO · 7Al ₂ O ₃ (C ₁₂ A ₇ ) as a main component and slightly containing CaO · Al ₂ O ₃ (CA). Further, this was heated at 1250 ° C. for 2 hours in an atmosphere having an oxygen partial pressure of 5.8 × 10 ⁴ Pa. The product was cooled, wet-ground 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 size of 4.0 μm. The ESR spectrum at room temperature and 77K of the powder was measured, _{O 2} obtained from the intensity of the respective absorption band ^- ion radicals and O ^- concentration of ions radicals were respectively 5 × ¹⁰ 20 ^{cm -3.}
[0031]
This powder was die-molded at a pressure of 10 MPa to produce a rectangular molded body, and sintered by heating at 1370 ° C. for 3 hours in the atmosphere. The obtained sintered body by X-ray diffraction measurement with light _{brown, 12CaO · 7A l2 O 3 (} C 12 A 7) was confirmed to be the main component. When the bulk density was measured by the method of JIS R 1634 and the relative density was calculated, it was 98%. Further, a 3 mm × 4 mm × 45 mm test piece was processed from the sintered body, and the three-point bending strength was measured by the method of JIS R 1601, and it was 114 MPa. Also, by grinding a portion of the sintered body was measured ESR spectrum at room temperature and 77K, O ₂ obtained from the intensity of the respective absorption band ^- ion radicals and O ^- concentration of ions radicals, respectively 4 × It was 10 ²⁰ cm ⁻³ .
[0032]
(Example 2)
After mixing quick lime (CaO) powder and aluminum hydroxide (Al (OH) ₃ ) powder so that the molar ratio of Ca and Al is 12.4: 13.8, fine silica filler (manufactured by Electrochemical Industry) , SFP-30M) was added and mixed. The mixture was calcined in the same manner as in Example 1, _12CaO · _7A l2 O ₃ is _(C 12 _{A 7)} in the main component, to obtain a white powder containing slightly _{3CaO · Al 2 O 3 (C} 3 A). Further, the specific surface area was 1.6 m ² / g and the average particle size was 7 by heating, cooling, wet pulverization, and drying in the same manner as in Example 1 except that the atmosphere was an oxygen partial pressure of 4.2 × 10 ⁴ Pa. .8 μm powder was obtained. The powder of ESR spectra were measured in the same manner as in Example 1, _{O 2} obtained from the intensity of the absorption band ^- ion radicals and O ^- concentration of ions radicals were respectively 3.5 × ¹⁰ 20 ^{cm -3.}
[0033]
After adding 25, 10 and 3 parts by mass of ethanol, polyvinyl butyral and polyethylene glycol having an average molecular weight of 400 to 100 parts by mass of this powder, a clay-like slurry was prepared by kneading, and a 2 mm thick green was obtained by an extruder. A sheet was produced. This was dried at 80 ° C. for 12 hours and debinder baked at 600 ° C. for 1 hour, and then heated in argon at 1350 ° C. for 3 hours to obtain a sheet-like sintered body having a thickness of 1.6 mm. The sintered body was light brown, and it was confirmed by X-ray diffraction measurement that 12CaO · 7Al ₂ O ₃ (C ₁₂ A ₇ ) was the main component. When the bulk density was measured in the same manner as in Example 1 and the relative density was calculated, it was 97%. Further, a 1.5 mm × 4 mm × 45 mm test piece was processed from the sintered body, and the three-point bending strength was measured by the method of JIS R 1601, and found to be 145 MPa. Similarly, by measuring the ESR spectrum of Example 1, _{O 2} obtained from the intensity of the respective absorption band ^- ion radicals and O ^- concentration of ions radicals were respectively 3 × ¹⁰ 20 ^{cm -3.}
[0034]
(Example 3)
And CaCO ₃ powder, the _γ-Al 2 _{O 3} powder mixture, adding alumina fibers comprising SiO ₂ as SiO ₂ minutes is 0.07% by weight, except that the mixing in the same manner as in Example 1 A white powder mainly containing C ₁₂ A ₇ was obtained. Further, this was heated, cooled, wet pulverized and dried in an atmosphere with an oxygen partial pressure of 4.5 × 10 ⁴ Pa in the same manner as in Example 1 to obtain a specific surface area of 3.5 m ² / g and an average particle size of 1.8 μm. ion radicals and O ^{- -} give powder, _{O 2} was determined by ESR measured concentration of ions radicals were respectively 3 × ¹⁰ 20 ^{cm -3.}
[0035]
The sintered body obtained by molding and heating this powder in the same manner as in Example 1 was confirmed to have C ₁₂ A ₇ as the main component. The relative density and the three-point bending strength determined in the same manner as in Example 1 were 96% and 92 MPa, respectively. Ion radicals and O ^{- -} further _{O 2} was obtained in the same manner as in Example 1 the concentration of ions radicals were each 2 × ¹⁰ 20 ^{cm -3.}
[0036]
(Comparative Example 1)
Except for adding and mixing alumina fibers containing SiO ₂ to a mixture of CaCO ₃ powder and γ-Al ₂ O ₃ powder so that the SiO ₂ content is 0.03% by mass, the same as in Example 1. A white powder mainly containing C ₁₂ A ₇ was obtained. Further, this was heated, cooled, wet pulverized and dried in an atmosphere with an oxygen partial pressure of 4.5 × 10 ⁴ Pa in the same manner as in Example 1 to obtain a specific surface area of 2.3 m ² / g and an average particle size of 3.8 μm. give a powder, _{O 2} was determined by ESR measurements ^- ion radicals and O ^- concentration of ions radicals were respectively 5 × ¹⁰ 20 ^{cm -3.}
[0037]
The sintered body obtained by molding and heating this powder in the same manner as in Example 1 was confirmed to have C ₁₂ A ₇ as the main component. The relative density calculated in the same manner as in Example 1 was 96%, _{O 2} ^- ion radical and O ^- concentration of ions radicals, was the 4 × ¹⁰ 20 ^{cm -3,} respectively, three-point bending strength It was 68 MPa.
[0038]
(Comparative Example 2)
A white powder containing C ₁₂ A ₇ as the main component in the same manner as in Example 1 except that the mixture containing Ca ₂ was added to the mixture of CaCO ₃ powder and γ-Al ₂ O ₃ powder without adding the component containing SiO _2. Got. Further, this was heated, cooled, wet pulverized and dried in an atmosphere with an oxygen partial pressure of 4.5 × 10 ⁴ Pa in the same manner as in Example 1 to obtain a specific surface area of 2.5 m ² / g and an average particle size of 2.9 μm. give a powder, _{O 2} was determined by ESR measurements ^- ion radicals and O ^- concentration of ions radicals were respectively 5 × ¹⁰ 20 ^{cm -3.}
[0039]
The sintered body obtained by molding and heating this powder in the same manner as in Example 1 was confirmed to have C ₁₂ A ₇ as the main component. The relative density calculated in the same manner as in Example 1 was 96%, _{O 2} ^- ion radical and O ^- concentration of ions radicals, was the 4 × ¹⁰ 20 ^{cm -3,} respectively, three-point bending strength It was 45 MPa.
[0040]
(Comparative Example 3)
The mixture was calcined in the same manner as in Example 2 except that 5.8% by mass of fine silica filler was added to and mixed with a mixture of quicklime (CaO) powder and aluminum hydroxide (Al (OH) ₃ ) powder. The produced white powder is mainly composed of CaO.Al ₂ O ₃ (CA), and then contains 3CaO.Al ₂ O ₃ (C ₃ A) and 3CaO.SiO ₂ , and the content of C ₁₂ A ₇ is slight. It was confirmed by X-ray diffraction measurement. Further, this was heated, cooled, wet-ground and dried in the same manner as in Example 2 to obtain a powder having a specific surface area of 1.8 m ² / g and an average particle size of 6.5 μm. The powder of ESR spectra were measured in the same manner as in Example 2, _{O 2} obtained from the intensity of the absorption band ^- ion radicals and O ^- concentration of ions radicals were respectively 8 × ¹⁰ 18 ^{cm -3.}
[0041]
【The invention's effect】
The present invention is an oxidation catalyst, applications expand, such as an ion conductor is expected, O ₂ is active oxygen species ^- is provided a calcium aluminate sintered body containing oxygen radicals at a high concentration ^- and O is there. The calcium aluminate sintered body obtained by the present invention has a sufficient strength even when provided in various shapes depending on the application, and is very useful industrially because it does not break.

Claims (3)

C ₁₂ A ₇ Alternatively, a mixture of the calcium compound and aluminum compound used as a raw material is mixed with SiO. ₂ Containing an inorganic fibrous material having an average fiber diameter of 5 μm or less containing SiO 2 ₂ Calcium aluminate sintering, characterized by being added and mixed at a ratio such that 0.05 to 5% by mass is heated to 1100 ° C. or higher and a melting temperature or lower in an atmosphere having an oxygen partial pressure of 4 × 104 Pa or higher. Body manufacturing method. C ₁₂ A ₇ Alternatively, a mixture of calcium compound and aluminum compound as a raw material is mixed with SiO having an average particle size of 5 μm or less. ₂ Powder is made of SiO ₂ After adding and mixing at a ratio such that the amount becomes 0.05 to 5% by mass, the oxygen partial pressure is 4 × 10 ⁴ A method for producing a calcium aluminate sintered body, which is heated to 1100 ° C. or higher and a melting temperature or lower in an atmosphere of Pa or higher. Firing the raw material mixture to C ₁₂ A ₇ In the method of producing a calcium aluminate sintered body by obtaining a calcium aluminate powder containing as a main component and firing it after molding, ₂ 0.05 to 5 mass%, specific surface area 1.5 m ² / G and a mean particle size of 10 μm or less, a method for producing a calcium aluminate sintered body.