Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group iiia metal or beryllium
Reexamination Certificate
2002-02-14
2004-11-16
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group iiia metal or beryllium
C423S600000, C073S019010, C502S341000, C424S688000, C204S424000, C429S006000, C429S006000, C429S006000, C429S231600
Reexamination Certificate
active
06818192
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a 12CaO.7Al
2
O
3
compound which is an oxide clathrating an O
2
−
ion radical and an O
−
ion radical as active oxygen species in a high concentration (hereinafter, these two ion radicals are referred collectively to as “active oxygen species”). The present invention also relates to a method for producing such a compound and to the use thereof.
BACKGROUND ART
An O
2
−
ion radical is known as one of active oxygen species which has a key role in oxidizing processes of various organic and inorganic materials. Extensive researches have heretofore been made on O
2
−
absorbed on the solid surface of an oxide compound (J. H. Lunsford, Catal, Rev. 8, 135, 1973, M. Che and A. J. Tench, Adv. Catal, 32, 1, 1983). In most of such researches, high-energy gamma rays are irradiated onto the surface of an oxide compound to create O
2
−
ion radicals thereon.
RO
2
(R:alkali metal) is known as a crystal including an O
2
−
ion radical as a constituent anion. However, the related compounds are unavailable for a certain application such as oxidation catalysts or ionic conductors, because all of the compounds will be readily decomposed even at a temperature of 300° C. or less.
As compared to O
2
−
ion radicals, O
−
ion radicals have higher activity. Several articles have reported that a small amount of O
−
ion radicals was included in alkali halide glasses, calcium-aluminosilicate glasses or the like (J. R. Bralsford et al., J. Chem. Physics, Vol. 49, pp 2237, 1968, H. Hosono et al., J. Am. Ceramic. Soc., 70, 867, 1987). However, there has not been known any crystal having an O
−
ion radical as a constituent ion.
In 1970, H. B. Bartl et al. made a point that among sixty-six oxygens within a unit cell containing two molecules in a 12CaO.7Al
2
O
3
crystal, so-called C12A7, two oxygens of them existed within a space of each cage structure in the crystal as “free oxygens” without residing in a network of the crystal (H. B. Bartl and T. Scheller, Neuses Jarhrb. Mineral., Monatsh, 1970, 547).
Based on an electron spin resonance analysis, Hosono, one of the inventors, et al. have discovered that about 1×10
19
cm
−3
of O
2
−
was clathrated in a 12CaO.7Al
2
O
3
crystal synthesized by reacting two raw materials, CaCO
3
and Al
2
O
3
or CaCO
3
and Al (OH)
2
, in a solid phase reaction at a temperature of 1200° C. in ambient atmosphere. They have proposed a model in which a part of free oxygens exists in each cage structure in the form of O
2
−
(H. Hosono and Y. Abe, Inorg. Che. 26, 1193, 1987).
12CaO.7Al
2
O
3
is inherently a stable oxide having a melting point of 1415° C. If a larger amount of active oxygen species can be clathrated in this oxide and then a reversible incorporation and release of oxygen can be achieved, the oxide would have a desirable availability for various purposes, such as oxidation catalysts or ionic conductors.
While one of the inventers, et al. have found out that O
2
−
was clathrated in the 12CaO.7Al
2
O
3
crystal, the concentration of O
2
−
was a relatively low value of 10
19
cm
−3
and any O
−
ion radical having higher activity has not been identified. Further, any effective technique for controlling the amount of O
2
−
and releasing/incorporating it from/into the crystal reversibly has not been achieved.
For using such a compound as high-efficiency oxidation catalysts or antibacterial agents, it is required to clathrate the active oxygen species in a higher concentration and to provide a reversible function for releasing the clathrated active oxygen species and incorporating oxygen from outside. It is also necessary to establish a technique for quantitatively analyzing the concentration of the clathrated active oxygen species.
DISCLOSURE OF INVENTION
The inventers have discovered that a 12CaO.7Al
2
O
3
compound clathrating active oxygen species in a high concentration of 10
20
cm
−3
or more is obtained by preparing a raw material including calcium and aluminum mixed with each other in an atomic equivalent ratio of approximately 12: 14 and then reacting the raw material in a solid phase reaction at a controlled temperature under a controlled atmosphere. The present invention is directed to such a compound itself, a method for producing the same, a method for releasing clathrated ions, and the use of the compound.
More specifically, the present invention provides a 12CaO.7Al
2
O
3
compound produced by preparing a raw material including calcium and aluminum mixed with each other in an atomic equivalent ratio of approximately 12:14, preferably a raw material including calcium carbonate and gamma-aluminum oxide mixed with each other in a molecular equivalent ratio of approximately 12:7, and then reacting the raw material in a solid phase reaction at a sintering temperature of 1200° C. or more, preferably 1300° C., under an atmosphere with an oxygen partial pressure of 10
4
Pa or more and a water-vapor partial pressure of 10
2
Pa or less, preferably an oxygen partial pressure of 10
5
Pa or more and a water-vapor partial pressure of 1 Pa or less. This compound can include 10
20
cm
−3
or more of clathrated active oxygen species. The amount of the clathrated active oxygen species can be determined by an electron spin resonance analysis and a Raman spectrum analysis.
When the sintering atmosphere is arranged in an oxygen partial pressure less than of 10
4
Pa and a water-vapor partial pressure of more than 10
2
Pa, the concentration of the clathrated active oxygen species will be less than 10
20
cm
−3
. Further, even under a dry oxidation atmosphere with an oxygen partial pressure of 10
4
Pa or more and a water-vapor partial pressure of 10
2
Pa or less, when the sintering temperature is arranged in less than 1200° C., it will be difficult to synthesize the desired 12CaO.7Al
2
O
3
compound. Conversely, when the sintering temperature exceeds 1415° C., the raw material will be undesirably molten. Thus, it will also be hard to obtain the desired 12CaO.7Al
2
O
3
compound. In case of synthesizing the 12CaO.7Al
2
O
3
compound through a solid phase reaction, the mixture of calcium carbonate and gamma-aluminum oxide is suitable for the raw material. However, any combination of calcium hydroxide or calcium oxide and aluminum hydroxide or one of various aluminum oxides (alpha, gamma or theta aluminum oxide) may be used as the raw material to synthesize the above compound.
An electron spin resonance (ESR) spectrum (at 77 K) of the 12CaO.7Al
2
O
3
compound clathrating the active oxygen species is formed of a superposition of two spectrums; one defined by gx=2.00, gy=2.01 and gz=2.04, the other defined by gx=gy=2.05 and gz=2.00. These g values correspond to those of O
2
−
ion radicals and O
−
ion radicals in the solid, respectively. Thus, it can be concluded that O
2
−
ion radicals and O
−
ion radicals are clathrated in the 12CaO.7Al
2
O
3
compound.
The absorption band shape in the ESR spectrum is symmetric at room temperature and becomes asymmetric at a low temperature of 77K. This indicates that O
2
−
ion radicals and O
−
ion radicals rotationally move within each cage structures at room temperature, while they are coupled electrostatically with and retained spatially by Ca
2+
ions residing on each wall of the cage structures at low temperature. Each concentration of O
2
−
ion radicals and O
−
ion radicals can be quantitatively determined from the intensity of the absorption band.
In a Raman scattering spectrum of the above compound, a strong scattering peak is exhibited around 1130 cm
−1
. This peak corresponds to the peak of O
2
−
ion radicals which has been reported by K. Nakamoto et al. (K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compound, 1978, Wiley). Since there is a certain dependence between the ESR absorption band and the Raman s
Hayashi Katsuro
Hirano Masahiro
Hosono Hideo
Bos Steven
Japan Science and Technology Corporation
Westerman Hattori Daniels & Adrian LLP
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