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Method for preparing electroconductive mayenite type compound achieved

Foreign code F110005256
File No. BE06001WO
Posted date Aug 29, 2011
Country United States of America
Application number 50324406
Gazette No. 20060276326
Gazette No. 7465433
Date of filing Feb 8, 2005
Gazette Date Dec 7, 2006
Gazette Date Dec 16, 2008
International application number JP2005001848
International publication number WO2005077859
Date of international filing Feb 8, 2005
Date of international publication Aug 25, 2005
Priority data
  • P2004-037203 (Feb 13, 2004) JP
  • 2005JP001848 (Feb 8, 2005) WO
Title Method for preparing electroconductive mayenite type compound achieved
Abstract To provide a method for preparing a mayenite type compound having electroconductivity imparted.
A method for preparing an electroconductive mayenite type compound, which comprises melting a raw material containing Al and at least one element selected from the group consisting of Ca and Sr, holding the melt in a low oxygen partial pressure atmosphere having an oxygen partial pressure of not higher than 10 Pa, followed by cooling or annealing in a low oxygen partial pressure atmosphere or in atmospheric air for solidification, thereby to replace oxygen present in cages by electrons in a high concentration.
Outline of related art and contending technology BACKGROUND ART
Mayenite is a cement mineral naturally produced in Mayen in Germany, and its crystal structure belongs to a cubic system.
The typical composition of the mayenite type compound is 12CaO.7Al2O3 (hereinafter referred to as C12A7) or 12SrO.7Al2O3 (hereinafter referred to as S12A7), or a mixed crystal composition thereof.
However, part of Ca or Sr may be replaced by an alkali metal or alkaline earth metal such as K, Na, Li, Mg or Ba or part of Al may be replaced by a metal element having an ion radius of from about 0.5 to 0.8 .ANG. such as Si or Ge.
Ca or Al is a common component for ceramic materials and has been used mainly as one component for structural materials.
Usually, an oxide of a metal in or before the third period, including such a compound, is electrically dielectric and shows no electroconductivity.
Heretofore, oxide ceramics showing electroconductivity were ones containing a large amount of an oxide of a transition metal or a typical metal in or after the forth period of Periodic Table of Elements, whereby the environmental load was high.
A crystal of the mayenite type compound has, in its crystal lattice, fine voids (cages) having a diameter of 0.6 nm at a rate of 12 cages per unit lattice, and a C12A7 crystal as its typical composition contains two O2- ions per unit lattice in the cages.
Namely, the C12A7 crystal is represented by [Ca24Al28O64]4+.2O2-, and such O2- ions are called "free oxygen" as they are weakly bound (Non-Patent Document 1).
Further, a crystal represented substantially by [Ca24Al28O64]4+.4F- or [Ca24Al28O64]4+.4Cl-, having such free oxygen replaced by fluorine or chlorine, is known (Non-Patent Documents 2 and 3).
Hosono as one of the present inventors, et al, previously found anew that such free oxygen can be replaced by various anions such as O2-, O- and OH- and filed patent applications with respect to inventions relating to the compound itself, a process for its production and applications for such a compound (Patent Documents 1 to 6).
Further, Hosono et al found that when a C12A7 powder as a mayenite type compound obtained by a solid phase reaction, or its sintered product, was subjected to heat treatment in a hydrogen atmosphere to prepare a C12A7 compound having H- taken in the cages, and then, the compound was irradiated with ultraviolet light to have electrons taken in the cages, it was possible to impart electroconductivity.
And, they filed a patent application with respect to the invention relating to the compound itself, a process for its production and applications of such a compound.
However, by such a preparation method wherein H- is clathrated in the above sintered product, followed by irradiation with ultraviolet light, electrons are clathrated only at the surface portion of the sintered product irradiated with the ultraviolet light, and it was not possible to clathrate electrons into the interior of the powder or sintered product being a region not irradiated.
Further, Hosono et al developed a method for preparing a C12A7 single crystal and found it possible to impart electroconductivity to such a crystal by exposing the crystal to an alkaline vapor to have electrons clathrated in cages, and they filed a patent application with respect to the invention relating to the compound itself, a method for its production and applications of such a compound (Patent Document 6).
This preparation method utilizes a reaction to withdraw free oxygen from the C12A7 crystal in a solid state.
However, in such a reaction, diffusion of oxygen in the interior of the solid became a rate-determining step, and it took a long time to have electrons clathrated in a sufficient amount.
On the other hand, the present inventors knew that in a molten state of C12A7 at a high temperature, the diffusion coefficient of the oxygen could be made high as compared with in a solid state, whereby the reaction to withdraw free oxygen proceeded quickly.
However, it was known that when a furnace circulating nitrogen was employed, from the melt having a C12A7 composition, a 3CaO.Al2O3 (hereinafter referred to as C3A) phase and a CaO.Al2O3 (hereinafter referred to as CA phase) could form as decomposition products and no C12A7 crystal would be formed.
Thus, it was usually difficult to simultaneously carry out the reaction to withdraw oxygen and the reaction to form a C12A7 crystal (Non-Patent Document 4).
Hosono et al found that by reducing the surface area of the raw material by employing an isostatistic pressing product having a dense structure as compared with a powder, it was possible to make mild the reaction to withdraw oxygen in the temperature rising process being a reaction which took place at the surface, whereby it was possible to suppress formation of decomposition products, and they invented a method for preparing a C12A7 compound having oxygen in cages replaced by electrons, which comprises melting an isostatistic pressing product of C12A7 powder in a reducing atmosphere or in a covered carbon crucible and filed a patent application (Patent Document 6).
Patent Document 1: JP-A-2002-3218
Patent Document 2: JP-A-2003-40697
Patent Document 3: JP-A-2003-128415
Patent Document 4: JP-A-2002-316867
Patent Document 5: JP-A-2003-238149
Patent Document 6: JP-A-2004-26608
Patent Document 7: Japanese Patent Application No. 2003-183605
Non-Patent Document 1: H. B. Bartl and T. Scheller, Neuses Jarhrb.
Minerai, Monatsh. (1970), 547
Non-Patent Document 2: P. P. Williams, Acta Crystallogr., Sec. B, 29, 1550 (1973)
Non-Patent Document 3: H. Pollmann, F. Kammerer, J. Goske, J. Neubauer, Friedrich-Alexander-Univ.
Erlangen-Nurnberg, Germany, ICDD Grant-in-Aid, (1994)
Non-Patent Document 4: R. W. Nurse, J. H Welch, A. J. Majumdar, Transactions of the British Ceramic Society (1965), 64(9), 409-18

Scope of claims [claim1]
1. A method for preparing an electroconductive mayenite type compound, comprising: melting a raw material containing Al and at least one element selected from the group consisting of Ca and Sr;
holding the melt in a low oxygen partial pressure atmosphere;
and
cooling for solidification;
whereinan oxygen partial pressure of the low oxygen partial pressure atmosphere is not higher than 10 Pa, anda direct current conductivity of the electroconductive mayenite type compound is at least 10-4 S/cm.
[claim2]
2. The method for preparing an electroconductive mayenite type compound according to claim 1, wherein the cooling for solidification is in a low oxygen partial pressure atmosphere.
[claim3]
3. The method for preparing an electroconductive mayenite type compound according to claim 1, wherein the cooling for solidification is in atmospheric air.
[claim4]
4. The method for preparing an electroconductive mayenite type compound according to claim 1, wherein the cooling for solidification is annealing.
[claim5]
5. The method for preparing an electroconductive mayenite type compound according to claim 4, wherein a cooling rate of annealing is at least 200 deg. C./hr and at most 500 deg. C./hr.
[claim6]
6. The method for preparing an electroconductive mayenite type compound according to claim 1, wherein prior to the cooling for solidification the melt is discharged from a crucible.
[claim7]
7. The method for preparing an electroconductive mayenite type compound according to claim 6, wherein a cooling rate is more than 500 deg. C./hr and at most 1,000 deg. C./hr.
[claim8]
8. The method for preparing an electroconductive mayenite type compound according to claim 1, wherein the raw material comprises, as represented by mol % and as calculated as the following oxides, from 15 to 66% of at least one member selected from the group consisting of CaO and SrO, from 14 to 63% of Al2O3, from 0 to 38% of SiO2, from 0 to 38% of GeO2, from 0 to 38% of B2O3, from 0 to 5% of Li2O, from 0 to 5% of Na2O, from 0 to 5% of K2O, from 0 to 10% of MgO, from 0 to 10% of BaO, from 0 to 8% of Fe2O3 and from 0 to 8% of TiO2, and the total of molar ratios of CaO, SrO and Al2O3 is at least 25%.
[claim9]
9. The method for preparing an electroconductive mayenite type compound according to claim 1, further comprising holding the prepared electroconductive mayenite type compound in air at a temperature of at least 500 deg. C. and not more than the melting point of the compound to adjust the electroconductivity.
[claim10]
10. The method for preparing an electroconductive mayenite type compound according to claim 9, wherein the electroconductivity of the prepared electroconductive mayenite type compound is adjusted to be at least 10-10 S and at most 103 S/cm.
  • Inventor, and Inventor/Applicant
  • HOSONO HIDEO
  • HAYASHI KATSURO
  • MIYAKAWA MASASHI
  • HIRANO MASAHIRO
  • KIM SUNGWNG
  • ITO SETSURO
  • NARUSHIMA SATORU
  • JAPAN SCIENCE AND TECHNOLOGY AGENCY
  • ASAHI GLASS
IPC(International Patent Classification)
Reference ( R and D project ) ERATO/SORST Exploring and developing applications for active functions utilizing nanostructure embedded in transparent oxides AREA
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