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12CaO 7Al2O3 COMPOUND AND METHOD FOR PREPARATION THEREOF achieved

Foreign code F110003896
File No. E06006EP
Posted date Jul 6, 2011
Country EPO
Application number 02775366
Gazette No. 1445237
Date of filing Oct 17, 2002
Gazette Date Aug 11, 2004
International application number JP2002010806
International publication number WO2003033406
Date of international filing Oct 17, 2002
Date of international publication Apr 24, 2003
Priority data
  • P2001-321251 (Oct 18, 2001) JP
  • 2002JP10806 (Oct 17, 2002) WO
Title 12CaO 7Al2O3 COMPOUND AND METHOD FOR PREPARATION THEREOF achieved
Abstract There is provided a C12A7 compound capable of selectively and reversibly clathrating X- ions, such as active oxygen radicals, with improved controllability. The C12A7 compound clathrating OH- ions and On- at a concentration of 2 x 1019 cm-3 or less can be prepared by subjecting a mixed material containing Ca and Al to a solid phase reaction at a firing temperature not lower than 1200 ℃ and lower than 1449 ℃ in a dry oxygen atmosphere having an oxygen partial pressure of 0.1 atm or more and a water vapor partial pressure of 10-3 atm or less, keeping the resultant product at a temperature of 1200 ℃ or higher, and cooling rapidly. The C12A7 compound is heat-treated to clathrate OH- ions at a concentration of 2 x 1019 cm-3 or less, and On- at a high concentration of more than 2 x 1019 cm-3. The compound can reversibly clathrate or release On- ion radicals through the elevation or lowering of the temperature thereof in a temperature range of 300 to 850 ℃. The compound is useful for an oxidation catalyst, an anti-bacterial agent, an ion conducting material, an electrode for a solid-electrolyte fuel cell, and the like.
Outline of related art and contending technology Background Art
In 1970, H. B. Bartl et al., stated that in a 12CaO·7Al2O3 crystal, two oxygen atoms of 66 oxygen atoms in a unit cell having two molecules do not belong to the network, but exist as "free oxygen" in a cage in the crystal (H. B. Bartl and T. Scheller, Neuses Jarhrb. Mineral., Monatsh. 1970, 547).
Hosono et al., of the present inventors discovered that 12CaO·7Al2O3 crystal clathrates O2- at a concentration of about 1 x 1019 cm-3 as measured by electron spin resonance. The 12CaO·7Al2O3 crystal was synthesized by subjecting a mixed material containing CaCO3 and Al2O3 or Al(OH)3 to a solid phase reaction at a temperature of 1200°C in air. Hosono et al., proposed a model in which part of the free oxygen exists in the cage in the form of O2- (H. Hosono and Y. Abe, Inorg. Che. 26, 1193, 1987, "Materials Science", Vol. 33, No. 4, pp. 171-172, 1996).
The present inventors subjected a mixed material containing calcium and aluminum at an atomic equivalent ratio of about 12:14 to a solid phase reaction under a controlled atmosphere and temperature, whereby a 12CaO·7Al2O3 compound clathrating active oxygen at a high concentration of 1020 cm-3 or more was found. The present inventors filed patent applications of the compound itself, a method for production thereof, a measure for taking clathrated ions, a method of identification of active oxygen ion radicals, and an application of the compound (Japanese Patent Application Publication No. 2001-49524 = Japanese Unexamined Patent Application Publication No. 2002-003218, PCT/JP01/03252 = WO 01/79115 A1).
The present inventors synthesized a C12A7 compound containing OH- at a concentration of 1021 cm-3 or more by hydrating the powder of the 12CaO·7Al2O3 compound in water, a water-containing solvent, or a water vapor-containing gas and firing it under an oxygen atmosphere, and filed patent applications of the compound itself, a method for production thereof, a method of identification of OH- ions, and an application of the compound (Japanese Patent Application Publication No. 2001-117546).
As to the mechanism by which the C12A7 compound includes the active oxygen radical ions at a high concentration, the present inventors consider that the free oxygen in the C12A7 compound is reacted reversibly with the oxygen molecules entering the C12A7 compound. As to the mechanism by which the OH- ions are included at a high concentration, the present inventors consider that the free oxygen in the C12A7 compound is reacted reversibly with the water molecules entering the C12A7 compound. These mechanisms are described below in detail.
Fig. 1 is a schematic view showing the crystal structure of 12CaO·7Al2O3. 12CaO·7Al2O3 is a cubic crystal system (lattice constant = 11.97 angstrom) belonging to a space group of 143d, including two formula of C12A7 per unit cell, and having a melting point of 1449°C. The crystal has a structure in which Ca2+ ions are coordinate with a network structure where tetrahedrons of AlO4 are aggregated. There is a cavity, i.e., a cage, in the crystal lattice.
2(12CaO·7Al2O3) = Ca24Al28O66 = [Ca24Al28O64]4+·2O2-
O2- is called free oxygen, and exists in the cage. In general, O2- is always coordinated in the form of a cation in a solid structure, and does not exist in the free state. However, the O2- ions in the cage of the 12CaO·7Al2O3 crystal cannot be combined with the cations, and exist in the free state. This state is similar to the case that the ions are adsorbed on a solid surface, and is considered to be very chemically active.
The O2- ions clathrated in the cage are prevented from directly reacting with the external atmosphere. However, when the temperature increases, the case size becomes large due to thermal expansion. Oxygen molecules in the atmosphere can pass through a bottle neck of the cage, to be thus clathrated in the cage. As a result, the reaction proceeds as follows:
O2- (in the cage) + O2 (in the cage) = O- (in the cage) + O2- (in the cage)
Through this reaction, the C12A7 compound clathrates a large amount of active oxygen radical ions.
Two On- are produced from two oxygen ions O2- in the unit cell. The 12CaO·7Al2O3 compound clathrating On- at a high concentration is described as [Ca24Al28O64]4+·(2-m)O2- (2m)On-. In this formula, m ≤ 2, and On- and O2- are clathrated in the cage. The oxygen molecules in the cage and in the atmosphere are equilibrated with the oxygen molecules in the atmosphere in a high temperature region in which the oxygen molecules can pass through the bottle neck of the cage. In general, when the temperature increases, the oxygen atoms in the C12A7 decrease in accordance with the Boyle-Charles law. Accordingly, it is considered that the number of active oxygen ion radicals decrease at a higher temperature.
When the synthesized C12A7 contains H2O, the reaction of O2- (in the cage) + H2O (in the cage or in the interstices of the crystal lattice) = 2OH- (in the cage) proceeds, thus clathrating OH- ions in the cage. The 12CaO·7Al2O3 compound clathrating OH- at a high concentration is described as [Ca24Al28O64]4+·(2-m)O2-(2m)OH-. In this formula, m ≤ 2, and OH- and O2- are clathrated in the cage. The H2O molecules in the cage are equilibrated with the water vapor in the atmosphere in a temperature region in which the H2O molecules can pass through the bottle neck of the cage.
Scope of claims [claim1]
1. A 12CaO·7Al2O3 compound clathrating monovalent anions represented by X- and anion molecules at a concentration of 2 x 1019 cm-3 or less.
[claim2]
2. A 12CaO·7Al2O3 compound according to Claim 1, wherein the X- are OH- ions and On- ion radicals, where n is an integer of 1 or 2.
[claim3]
3. A 12CaO·7Al2O3 compound clathrating OH- ions at a concentration of 2 x 1019 cm-3 or less, and On- at a high concentration of more than 2 x 1019 cm-3.
[claim4]
4. A method for preparing the 12CaO·7Al2O3 compound according to Claim 1 or 2, comprising the steps of:
subjecting a mixed material containing calcium (Ca) and aluminum (Al) to a solid phase reaction at a firing temperature not lower than 1200°C and lower than 1449°C in a dry oxygen atmosphere having an oxygen partial pressure of 0.1 atm or more and a water vapor partial pressure of 10-3 atm or less,
keeping the resultant product at a temperature of 1200°C or higher, and
cooling rapidly.
[claim5]
5. A method for preparing the 12CaO·7Al2O3 compound according to Claim 3, comprising the steps of:
subjecting a mixed material containing calcium (Ca) and aluminum (Al) to a solid phase reaction at a firing temperature not lower than 1200°C and lower than 1449°C in a dry oxygen atmosphere having an oxygen partial pressure of 0.1 atm or more and a water vapor partial pressure of 10-3 atm or less, and
slowly cooling the resultant product to a temperature in the range of 300 to 850°C.
[claim6]
6. A method for preparing the 12CaO·7Al2O3 compound according to Claim 3, wherein the 12CaO·7Al2O3 compound according to Claim 1 or 2 is kept at a fixed temperature in a temperature range of 300 to 850°C in a dry oxygen atmosphere having an oxygen partial pressure of 0.1 atm or more and a water vapor partial pressure of 10-3 atm or less, and is cooled rapidly or slowly to room temperature.
[claim7]
7. A method for reversibly clathrating or releasing On- ion radicals through the elevation or lowering of the temperature of the 12CaO·7Al2O3 compound according to Claim 1, 2 or 3 in a temperature range of 300 to 850°C in a dry oxygen atmosphere having an oxygen partial pressure of 0.1 atm or more and a water vapor partial pressure of 10-3 atm or less.
[claim8]
8. A method for preparing the 12CaO·7Al2O3 compound according to Claim 4 or 5, wherein calcium carbonate, calcium hydroxide, or calcium oxide is used as a raw material for the calcium, and aluminum oxide or aluminum hydroxide is used as a raw material for the aluminum.
[claim9]
9. An oxidation catalyst using the 12CaO·7Al2O3 compound according to Claim 1, 2 or 3.
[claim10]
10. An anti-bacterial agent using the 12CaO·7Al2O3 compound according to Claim 1, 2 or 3.
[claim11]
11. An ion conducting material using the 12CaO·7Al2O3 compound according to Claim 1, 2 or 3.
[claim12]
12. An electrode for a solid-electrolyte fuel cell using the 12CaO·7Al2O3 compound according to Claim 1, 2 or 3.
  • Applicant
  • JAPAN SCIENCE AND TECHNOLOGY AGENCY
  • Inventor
  • HOSONO, Hideo
  • HIRANO, Masahiro
  • HAYASHI, Katsuro
IPC(International Patent Classification)
Specified countries Contracting States: DE FR GB
Reference ( R and D project ) ERATO HOSONO Transparent ElectroActive Materials AREA
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