JP2009203126A - Mayenite type compound - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a material having good discharge characteristics such as discharge efficiency and discharge delay, chemically stable and power saving in PDP. <P>SOLUTION: A conductive mayenite type compound wherein a part of a free oxygen ion of a mayenite type compound wherein a part of Al is substituted with M (M is Ga or In) is substituted with an electron, and having an electron density of ≥1×10<SP>15</SP>cm<SP>-3</SP>, having a high oxidation resistance and chemically stable is provided. The compound is represented by Ca<SB>12</SB>(Al<SB>1-x</SB>M<SB>x</SB>)<SB>14</SB>O<SB>33</SB>and x is preferably ≥0.001 and ≤0.05. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a composition of a mayenite type compound having improved oxidation resistance.

The mayenite type compound is a 12CaO · 7Al ₂ O ₃ (hereinafter referred to as C12A7) crystal and an isomorphous compound having a crystal structure equivalent to that of the C12A7 crystal, and is a three-dimensionally connected void (cage having a diameter of about 0.4 nm). ). The skeleton constituting this cage is positively charged and forms 12 cages per unit cell. One-sixth of this cage is occupied by oxygen ions to satisfy the electrical neutrality condition of the crystal, but these oxygen ions have characteristics that are chemically different from other oxygen ions constituting the skeleton. Therefore, it is particularly called free oxygen ions. From the above, the C12A7 crystal may be expressed as [Ca ₂₄ Al ₂₈ O ₆₄ ] ^{4 +} · 2O ²⁻ (see Non-Patent Document 1).

Patent Document 1 discloses that when a C12A7 crystal is subjected to reduction treatment using an alkaline earth metal vapor, free oxygen ions in the cage can be replaced with electrons to produce a mayenite type compound having conductivity with the C12A7 crystal. . Since the clad electrons are loosely bound to the cage and can move freely in the crystal, conductivity is imparted to the mayenite type compound. A C12A7 compound in which all free oxygen is replaced with electrons may be represented as [Ca ₂₄ Al ₂₈ O ₆₄ ] ⁴⁺ (4e ⁻ ).

  In Patent Documents 2 to 4, a mayenite type compound in which part or all of C12A7 Ca is substituted with Sr, a mayenite type compound in which a part of Al is substituted with Si or Ge, and free oxygen atoms are substituted with anions. A method for producing a conductive mayenite type compound from the prepared mayenite type compound is described.

  However, the conductive mayenite type compound obtained by reducing the C12A7 crystal (hereinafter referred to as C12A7 electride) has a fast electron diffusion in the cage and is immediately replaced with free oxygen ions. For this reason, when C12A7 electride is subjected to high-temperature heat treatment when used for long-term storage in air, plasma display panel (hereinafter referred to as PDP), etc., the electron density in C12A7 electride decreases, and as a result Characteristics such as the secondary electron emission coefficient deteriorate. For this reason, even if it heat-processed at 250-500 degreeC in presence of air, there existed a need for the mayenite type compound excellent in thermal stability and oxidation resistance with the above characteristic deterioration few. Non-Patent Document 3 discloses that the oxidation resistance can be improved by replacing a part of Ca in the C12A7 electride with a large amount of Mg and replacing a part of Al with a large amount of B. ing.

International Publication No. 2005-000741 Pamphlet International Publication No. 2005-077859 Pamphlet International Publication No. 2006-129674 Pamphlet International Publication No. 2006-129675 Pamphlet F. M.M. Lea and C.M. H. Desch, The Chemistry of Cement and Concrete, 2nd ed. , P. 52, Edward Arnold & Co. London, 1956. O. Yamaguchi, A .; Narai and K. Shimizu, J. et al. Am. Ceram. Soc. 1986, 69, C36. Mi-Yeon Lee and Yong-Seog Kim, International Display Workshop 2006, PDPp2-7.

  As described above, the C12A7 electride is easily oxidized in the air, and particularly easily oxidized during the heat treatment, the electron density in the C12A7 electride is reduced, and the Ne or Xe gas sealed in the PDP. There are problems such as deterioration of characteristics such as secondary electron emission coefficient. For this reason, it has been difficult to apply the C12A7 electride to a device such as a PDP with heat treatment.

In the present invention, a part of Al of a mayenite type compound containing Ca, Al and oxygen is substituted with M (M represents at least one atom selected from Ga and In), and an atomic ratio of M / (Al + M) Is a mayenite type compound in which 0.001 or more and 0.05 or less, and at least a part of free oxygen ions in the mayenite type crystal structure is substituted with electrons, and an electron density of 1 × 10 ¹⁵ cm ⁻³ or more A mayenite type compound is provided. The mayenite type compound of the present _{invention, Ca 12 (Al 1-x} M x) 14 mayenite type compound having a composition represented by _{O 33} (x is 0.001 to 0.05) is preferably.

  The electroconductive mayenite type compound of the present invention does not decrease the electron density even when heat treatment is performed in air, is chemically stable, and has excellent oxidation resistance.

  In the present invention, the mayenite type compound refers to a C12A7 crystal and a homomorphic compound having a crystal structure equivalent to that of the C12A7 crystal. The mayenite type compound has a cage structure and encloses oxygen ions therein. The oxygen ions included in the cage are hereinafter referred to as “free oxygen ions” in accordance with usual cases. The mayenite type compound referred to in the present invention includes an isotype compound in which a cation or an anion in the skeleton or cage is partially substituted within a range in which the cage structure formed by the skeleton of the C12A7 crystal lattice and the skeleton is retained. included.

  As long as the mayenite type compound has a crystal structure of C12A7 crystal composed of Ca, Al and oxygen, a part or all of at least one atom selected from Ca, Al and oxygen is another atom or atomic group. May be substituted. For example, a part of Ca may be substituted with atoms such as Mg, Sr, and Ba, and a part of Al may be substituted with Si, Ge, B, and the like. Moreover, the free oxygen atom may be substituted with an anion. Examples of the anion include a halogen ion, a hydrogen anion, an oxygen ion, and a hydroxide ion.

Specific examples of the mayenite type compound include, but are not limited to, the following compounds (1) to (4).
(1) C12A7 a mixed crystal part of Ca of the skeleton is substituted with magnesium or strontium compound, calcium magnesium aluminate (Ca _{1 over y Mg y) 12 Al 14 O} 33 and calcium strontium aluminate _{Ca 12- z} Sr _z Al ₁₄ O _33. Y and z are preferably 0.1 or less.
(2) Ca ₁₂ Al ₁₀ Si ₄ O ₃₅ which is a silicon-substituted mayenite.
(3) Free oxygen ions in the cage are anions such as H ⁻ , H ₂ ⁻ , H ²⁻ , O ⁻ , O ₂ ⁻ , OH ⁻ , F ⁻ , Cl ⁻ , Br ⁻ , S ²⁻ or Au ^−. It substituted by, for _{example, Ca 12 Al 14 O 32:} 2OH - or _{Ca 12 Al 14 O 32: 2F} -.
(4) cations and anions are both substituted, for example Wadaraito _{Ca 12 Al 10 Si 4 O 32} : 6Cl -.

  The conductive mayenite type compound of the present invention is a mayenite type compound containing at least Ca, Al and oxygen, and a compound in which a part of Al is substituted with M. As long as the mayenite type compound of the present invention is a compound in which a part of Al is substituted with M, as described above, a part of at least one atom selected from Ca, Al and oxygen is another atom or atom. It may be replaced with a group. For example, a part of Ca may be substituted with atoms such as Mg, Sr, and Ba, and a part of Al may be further substituted with Si, Ge, B, etc. in addition to M. As an atom for substituting a part of Ca, Mg or Sr is preferable, and Mg is particularly preferable. Further, the free oxygen atom may be further substituted with an anion as long as at least a part thereof is substituted with an electron. The anion is preferably a halogen ion or a hydroxide ion.

M in the conductive mayenite type compound of the present invention is a compound in which M represents at least one atom selected from Ga and In, and a part of Al is substituted with one or both of these atoms. . M is particularly preferably Ga in which characteristics such as ion size are close to those of Al. The ratio of Al substituted by M is 0.001 or more and 0.05 or less, expressed as an atomic ratio of M / (Al + M). In the conductive mayenite type compound of the present invention, at least a part of free oxygen ions in the mayenite type crystal structure is substituted with electrons, and the electron density is 1 × 10 ¹⁵ cm ⁻³ or more.

  In the conductive mayenite type compound of the present invention, if x is less than 0.001, the effect of improving the oxidation resistance of the mayenite type compound cannot be sufficiently obtained. When x is more than 0.05, the proportion of C12A7 crystals decreases, and not only mayenite type compounds but calcium aluminates containing various crystals and amorphous oxides as described below are obtained. Decreases rapidly. Here, the calcium aluminate in the present invention may contain not only calcium oxide and aluminum oxide but also atoms of other elements in part.

The above-mentioned various crystals include a CaAl ₂ O ₄ crystal (hereinafter referred to as a CA crystal), a Ca ₃ Al ₂ O ₆ crystal (hereinafter referred to as a C3A crystal), and a Ca ₅ Al ₆ O ₁₄ crystal (hereinafter referred to as a C5A3 crystal). And so on). Each of the CA crystal, the C3A crystal, and the C5A3 crystal has a crystal structure different from that of the C12A7 crystal, has no cage in the structure, and is insulative.

  Conductivity is represented by the product of electron density and mobility. However, if a cage containing electrons peculiar to the C12A7 crystal is separated by an insulating crystal such as a CA crystal, electrons cannot easily move between the cages. , Mobility decreases. This decrease in mobility is thought to reduce the conductivity of calcium aluminate containing various crystals and amorphous oxides. In particular, when the proportion of C12A7 crystals in the calcium aluminate oxide is 80% or less, the conductivity is estimated to be extremely low.

In addition, when Ga is substituted for Al, if X is greater than 0.05, Ga ₂ O ₃ remains in the C12A7 crystal without being dissolved, so that when the reduction treatment is performed, Ga precipitates and the ratio of the C12A7 crystal Is significantly reduced. From the above viewpoint, X is preferably 0.01 to 0.04.

  The reason why the oxidation resistance of the mayenite type compound in which Al is substituted with at least one atom of Ga or In which is a Group 13 element is improved is that these atoms are atoms having a higher electronegativity than Al. It is believed that there is. Although the mechanism of action for improving the oxidation resistance of the mayenite type compound substituted with atoms having a higher electronegativity than Al is not clear, the localization of the electrons responsible for conductivity in the cage increases oxygen ions. It is presumed that the substitution rate with is reduced and the oxidation resistance is improved.

The mayenite type compound according to the present invention has an electron density of 1 × 10 ¹⁵ cm ⁻³ or more. From the viewpoint of conductivity, it is preferably 1 × 10 ¹⁹ cm ⁻³ or more. In particular, 2.3 × 10 ²¹ cm ⁻³ corresponding to the electron density of the C12A7 compound in which all free oxygen is replaced with electrons is preferable. The electric conductivity of the mayenite type compound having conductivity is preferably 1.0 × 10 ⁻⁴ S / cm or more, more preferably 1.0 S / cm or more, and 100 S / cm or more. Is more preferable. The maximum value of electrical conductivity can be about 1000 S / cm.

As the mayenite type compound of the present invention, a mayenite type compound having a composition substantially composed only of Ca, Al, M and O is preferable. The composition of this mayenite type compound (hereinafter also referred to as precursor) before the free oxygen ions are replaced with electrons is preferably a compound represented by Ca ₁₂ (Al _1-x M _x ) ₁₄ O _33. . X in this composition formula is 0.001 or more and 0.05 or less as described above. The precursor in which all of the free oxygen ions are substituted with electrons can be expressed as [Ca ₂₄ (Al _1-x M _x ) ₂₈ O ₆₄ ] ⁴⁺ (4e ⁻ ).

The mayenite type compound of the present invention is preferably a mayenite type compound in which a part of Al of the mayenite type compound is replaced with M and a part of Ca is further replaced with Mg or Sr. In particular, a mayenite type compound in which a part of Ca is substituted with Mg is preferable because a part of Ca is further substituted with Mg, thereby further improving the oxidation resistance and chemical stability of the mayenite type compound. The composition of this precursor is represented as (Ca _1-y Mg _y ) ₁₂ (Al _1-x M _x ) ₁₄ O ₃₃ . The ratio y in which Ca is replaced by Mg is preferably 0.002 to 0.1 in terms of the high retention rate of C12A7 crystals. A particularly preferable range of y is 0.003 to 0.08. This is because a mayenite type compound having a high retention rate of C12A7 crystal has high conductivity.

  The conductive mayenite type compound of the present invention may have electrons and a part of the free oxygen ions may remain. Furthermore, an anion of an atom having an electron affinity smaller than that of an oxygen atom may be included in the cage structure together with the electron. Such a conductive mayenite type compound can be produced by substituting a part of anions with electrons from a precursor obtained by using a raw material compound containing an anion source. For example, instead of a Ca source such as calcium oxide or calcium carbonate, a raw material compound having Ca and halogen such as calcium fluoride or calcium chloride is used to produce a mayenite type compound which is a precursor having a halogen ion as an anion. be able to. Then, the electroconductive mayenite type compound of this invention can be manufactured by substituting a part of halogen ion of a precursor for an electron. By substituting all of these anions with electrons, it is also possible to obtain a conductive mayenite type compound that does not contain these anions.

Here, the electron affinity is the energy required to generate an anion from an atom, and is equal to the work required to separate an electron from the anion. In general, for any atom Q, the process of generating an anion from the atom, that is, the enthalpy change of Q → Q ⁻ is defined as the electron affinity. As the electron affinity of the oxygen atom in the present invention, a value for the change of O → O ²⁻ is used. Further, the electron affinity of atoms in the present invention includes not only Q → Q ⁻ but also enthalpy change in the process of Q → Q ²⁻ .

The comparison of the magnitude of electron affinity is more accurate when the value in the cage of the mayenite type compound is used. However, if the value in the vacuum is used, the existing data can be referred to, and it is considered that there is no great difference between the value in the cage and the value in the vacuum, so the value in the vacuum can be used. As described above, from the value of the electron affinity in vacuum, as anions having an electron affinity smaller than that of oxygen atoms, H ⁻ , H ₂ ⁻ , H ²⁻ , O ⁻ , O ₂ ⁻ , F ⁻ , Cl ⁻ , Br ⁻ , I ⁻ and S ^{2− and the} like can be mentioned. Since these anions easily donate electrons into the cage as compared with oxygen ions, the secondary electron emission coefficient is increased and the electron emission characteristics are improved.

For example, when a part of the electrons is replaced with H ⁻ , which is an anion of an atom having an electron affinity smaller than that of an oxygen atom, the result of introduction of electrons into the cage in the process shown in the equation (1) This is preferable because the electron emission characteristics are improved, for example, the secondary electron emission coefficient is increased.

H ⁻ → H ⁰ + e ⁻ (1).

  In the present invention, a part of the electrons of the mayenite type compound is replaced with an anion of an atom having an electron affinity smaller than that of an oxygen atom, so that the oxidation resistance is remarkably improved. Although the details of this mechanism of action are unknown, it is presumed that it is as follows.

  Since the mayenite type compound is a highly reducing compound, electrons are more likely to be released from the cage at higher temperatures than free oxygen ions. For this reason, when a mayenite type compound that only includes electrons is exposed to a high temperature such as 500 ° C. in the atmosphere, oxygen in the atmosphere is changed to oxygen ions by electrons donated from the cage, Oxygen ion uptake reaction occurs easily. This is because the skeleton forming the cage structure of the mayenite type compound has a positive charge, so negatively charged oxygen ions are taken into the cage, but electrically neutral, oxygen molecules or oxygen atoms are taken up. This is because it is difficult.

  From the above, compared to the mayenite type compound that includes only electrons, the mayenite type compound that has a small electron donating property to oxygen in the atmosphere suppresses the oxygen ion generation reaction from the oxygen molecule, and the oxygen ion This makes it possible to reduce the speed of uptake into the cage.

  In the present invention, by replacing a part of the electrons of the mayenite type compound with an anion of an atom having an electron affinity smaller than that of the oxygen atom, a mayenite type compound having a small electron donating property as described above can be realized. It is estimated that the oxidation resistance is improved.

A conductive mayenite type compound in which a part of Al which is a preferred embodiment of the present invention is substituted with Ga can be produced, for example, as follows. In addition, other manufacturing methods can be used, or manufacturing conditions can be changed. A predetermined component ratio, for example, a molar ratio of CaO, Al ₂ O ₃ and Ga ₂ O ₃ is 12: 7 (1-x): 7x (wherein x of Ga to be substituted is 0.001 to 0.05) The mayenite type compound (precursor) containing Ga in 12CaO · 7Al ₂ O ₃ is heated and held at 1300 to 1450 ° C. in air and then cooled in the air. ) Is obtained.

Furthermore, the oxygen partial pressure is reduced to 10 Pa or lower by flowing a gas such as N ₂ with a reduced partial pressure of oxygen or water vapor through the atmosphere using a closed electric furnace. By conducting the reduction treatment, a conductive mayenite type compound having an electron density of 1 × 10 ¹⁵ cm ⁻³ or more is obtained.

When heat treatment is performed in the carbon container, the heat treatment temperature is preferably 1300 ° C. or higher. If it is less than 1300 ° C., calcium aluminate having C5A3 crystal or CA crystal having no cage structure other than the mayenite type compound is produced. For this reason, since electrons are not taken into the cage, sufficient conductivity cannot be obtained. If it exceeds 1415 ° C., the precursor may be melted. When the precursor melts, after cooling and solidifying, a step of crystallizing a mayenite type compound having an electron density of 1 × 10 ¹⁵ cm ⁻³ or more is required.

  The heating rate during the heat treatment is preferably 50 ° C./hour or more, more preferably 200 ° C./hour or more. If the rate of temperature increase is 50 ° C./hour or less, the heat treatment may take a long time and productivity may be reduced. As a cooling method, rapid cooling is preferable in order to keep the reduced electron concentration at a high concentration. This is because, when slowly cooled, the reducing power of C12A7 is higher than that of carbon at 1000 ° C. or lower, and C12A7 is oxidized by carbon. For this reason, it is preferable that a cooling rate is 100-700 degreeC / min.

Preferred examples of the method for setting the oxygen partial pressure to 10 Pa or less include atmospheres of various inert gases not containing oxygen gas, for example, nitrogen gas, rare gases such as argon, and vacuum. When the precursor and the reducing agent include a component that is easily nitrided, such as Al, when nitrogen gas is used as an inert gas, electrons of 1 × 10 ¹⁵ cm ⁻³ or more are obtained by nitriding the precursor or the reducing agent. There is a possibility that a mayenite type compound having a density cannot be obtained. In that case, the heat treatment is preferably performed in a rare gas such as argon or in a vacuum.

A mayenite type compound in which a part of Ca of the present invention is substituted with Mg and a part of Al is substituted with Ga can be similarly produced. A predetermined component ratio, for example, a molar ratio of CaO, MgO, Al ₂ O ₃ and Ga ₂ O ₃ is 12 (1-y): 12y: 7 (1-x): 7x (provided that Ga to be substituted) The raw material prepared and mixed so that x is 0.001 to 0.05 and y of Mg to be replaced is 0.002 to 0.1 is heated and maintained at 1300 to 1450 ° C. in air, Next, by cooling, a mayenite type compound (precursor) containing Ga and Mg in a part of 12CaO.7Al ₂ O ₃ is obtained.Preferable ranges of the heating rate and cooling rate during heat treatment are the above-mentioned Al. This is the same as the mayenite type compound in which a part of is substituted with Ga.

A powder or sintered body of a mayenite type compound (precursor) in which a part of Al produced as described above is substituted with Ga is heated at a temperature of 800 to 1415 ° C. with a water concentration of 100 ppm or less. heat treatment in an atmosphere containing (. hereinafter referred to hydrotreating) by performing a part of free oxygen ions H ^- mayenite type compound is substituted with (a precursor) is obtained. The partial pressure of hydrogen gas in the hydrotreatment is preferably 1 × 10 ^{4 to} 1.1 × 10 ⁵ Pa because a sufficient H ⁻ concentration can be obtained. For example, the above hydrogen gas partial pressure can be obtained by flowing a mixed gas of hydrogen gas and nitrogen gas into an electric furnace equipped with an alumina core tube and setting the hydrogen gas concentration to 20% by volume.

When the mayenite type compound (precursor) in which a part of the free oxygen ions is substituted with H ⁻ is irradiated with ultraviolet rays of 140 to 380 nm, electrons desorbed from H ⁻ are introduced into the cage, and free oxygen ions or A mayenite type compound having an electron density of 1 × 10 ¹⁵ cm ⁻³ or more in which a cage in which H ⁻ is present and a cage in which electrons are present is obtained.

Further, when a mayenite type compound (precursor) in which a part of the free oxygen ions is substituted with H ⁻ is irradiated with an electron beam, electrons are introduced into the cage, and free oxygen ions or H ⁻ are present. It is also possible to obtain a mayenite type compound having an electron density of 1 × 10 ¹⁵ cm ⁻³ or more in which a cage and a cage in which electrons exist coexist.

Further, by holding the hydrogenated mayenite type compound in the plasma, a conductive mayenite type compound in which a cage in which free oxygen ions or H ⁻ are present and a cage in which electrons are present can be obtained. .

A mayenite type compound having an electron density of 1 × 10 ¹⁵ cm ⁻³ or more in which a cage containing free oxygen ions or H ⁻ and a cage containing electrons coexisted as described above is 2.8 eV and 0.8. Light absorption occurs at 4 eV. The electron density can be obtained by measuring this light absorption coefficient. When the sample is a powder, the electron density can be easily obtained by using the diffuse reflection method. In addition, since electrons in the cage have spin activity, the electron density in the cage can be measured using electron spin resonance (ESR).

The hydrogen ion H ⁻ concentration of the conductive mayenite type compound can be quantified using a secondary ion mass spectrometer (SIMS). At this time OH ^- in order to distinguish, for example, infrared absorption spectrum (IR) was measured, OH ^- it is desirable to quantify the concentration of. By subtracting the concentration of OH ⁻ determined from IR from the total amount of H ⁻ concentration determined by SIMS, the concentration of only H ⁻ can be accurately determined.

Furthermore, as another method for quantifying the H ⁻ concentration, the hydrogen atom H ⁰ generated by desorption of electrons from H ⁻ (H ⁻ → H ⁰ + e ⁻ ) can be quantified using ESR. . When performing this measurement, it is desirable that the sample temperature be 200K or less.

In order to obtain a mayenite type compound (precursor) in which the anion substituted with free oxygen ions is Cl ⁻ or F ⁻ , the following method is exemplified.

A raw material prepared by mixing and mixing CaCO ₃ and Al ₂ O _{3 so} that the molar ratio of (CaO / Al ₂ O ₃ ) is 11: 7 is obtained by heating to 1100 to 1350 ° C. in air. The calcined product (hereinafter referred to as C11A7) and CaCl ₂ were mixed so that the molar ratio of Ca to Al was 12: 7, and then this mixture C11A7 · CaCl ₂ was mixed in the air at 900 to 1300 ° C. By holding in, a mayenite type compound Ca ₁₂ Al ₁₄ O ₃₂ : 2Cl ⁻ in which Cl ⁻ is introduced into the cage can be obtained. Further, after mixing C11A7 and CaF _{2 so} that the molar ratio of Ca to Al is 12: 7, this mixture C11A7 · CaF ₂ is kept in the air at 900 to 1300 ° C. the F ^- mayenite type compound introduced _{is, Ca 12 Al 14 O 32:} 2F - is obtained.

In addition, the hydration reaction, and between H 2 _O and the mayenite type compound is reacted, OH to mayenite type compound ^- can be introduced. For example, the hydration reaction can also be carried out by putting a powdered body of a mayenite type compound in a solvent such as ethanol containing pure or moisture, and holding it at room temperature for 1 hour while stirring. Alternatively, hydration can be performed in the gas phase using water vapor.

The free oxygen ions thus obtained, Cl ^-, or, F ^- mayenite type compound obtained by replacing at the (precursor), free oxygen ions or,, Cl ^-, or F ^- the cage and the electrons are present In order to obtain a conductive mayenite type compound coexisting with the existing cage, it can be produced by irradiating the mayenite type compound with ultraviolet rays, electron beams, or holding in plasma.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to the following description. Examples 1 to 5 are examples, and examples 6 to 8 are comparative examples.

(Example 1)
The molar ratio of calcium carbonate, aluminum oxide and gallium oxide was 12: 6.93: 0.07, that is, the mixture was prepared so that x of Ga substituting Al was 0.01, mixed, put into an alumina crucible, In an air atmosphere, the temperature was raised to 1300 ° C. at a rate of temperature increase of 400 ° C./hour, then held for 6 hours for solid phase reaction, and gradually cooled at a temperature decrease rate of 400 ° C./hour to obtain a white crystal.

  This was once pulverized, put again into an alumina crucible, heated to 1300 ° C. at a temperature rising rate of 400 ° C./hour in an air atmosphere, held for 6 hours, and gradually cooled at a temperature falling rate of 400 ° C./hour. The obtained crystal was white and was an insulator. This is designated as sample A.

  Sample A was irradiated with Kα rays at 200 mA and 50 V using an X-ray diffractometer, and an X-ray diffraction pattern was measured. An X-ray peak characteristic at 2θ = 18.1 ° appears in the mayenite type compound. From the X-ray spectrum of sample A, it was found that sample A was a mayenite type compound having C12A7 crystals.

Next, the sample A was pulverized, put into a carbon container with a lid, put into a nitrogen atmosphere furnace having an oxygen concentration of 1% or less, and heated to 1300 ° C. at a temperature rising rate of 60 ° C./min. This state was maintained for 2 hours, and the carbon container was taken out into a glove box filled with a nitrogen atmosphere of 50 ppm or less while being covered. When the temperature of the carbon container was measured with a radiation thermometer, the average cooling rate was 120 ° C./min. After the carbon container reached room temperature, the carbon container was taken out of the glove box and the lid was opened. As a result, this mayenite type compound was green. The obtained sample is designated as sample A ′. Sample A ′ was pulverized, a diffuse reflection spectrum was measured using U3500 manufactured by Hitachi, and converted to a light absorption spectrum by the Kubelka-Munk method. From the light absorption spectrum, it was found that the electron density was 2.3 × 10 ¹⁹ / cm ³ .

  Further, the sample A ′ was wrapped with platinum foil, placed in an infrared heating furnace, and heated in an air atmosphere at 400 ° C. for 10 minutes. The obtained powder was grayish white. A diffuse reflection spectrum was measured for this grayish white powder using Hitachi U3500 and converted to a light absorption spectrum by the Kubelka-Munk method. It has been found that it has crystallization properties.

  Further, from the X-ray diffraction analysis, the X-ray diffraction pattern of the sample A ′ is the same as the X-ray diffraction pattern of the C12A7 crystal. Therefore, it was found that the sample A ′ was composed only of the mayenite type compound crystal.

(Example 2)
A mayenite type compound containing Ga was prepared in the same manner as in Example 1 except that x of Ga substituting Al was set to 0.02. This is designated as Sample B. From the X-ray diffraction pattern, it was confirmed that Sample B was a mayenite type compound having C12A7 crystals. Similarly to Sample A, Sample B was subjected to reduction treatment in a carbon container with a lid. The obtained sample is designated as sample B ′. From the light absorption spectrum of Sample B ′, it was found that the electron density was 2.3 × 10 ¹⁹ / cm ³ .

  Furthermore, sample B ′ was heated for 10 minutes at 400 ° C. in an air atmosphere using an infrared heating furnace in the same manner as sample A ′, and the electron density was 0.046 times that of the heat treatment and had high oxidation resistance. I understood.

  Further, from the X-ray diffraction analysis, the X-ray diffraction pattern of the sample B ′ is the same as the X-ray diffraction pattern of the C12A7 crystal, and thus it was found that the sample B ′ consists only of the mayenite type compound crystal.

(Example 3)
A mayenite type compound containing Ga was produced in the same manner as in Example 1 except that x of Ga substituting Al was changed to 0.03. This is designated as Sample C. From the X-ray diffraction pattern, it was confirmed that Sample C was a mayenite type compound having C12A7 crystals. Similarly to Sample A, Sample C was subjected to reduction treatment in a carbon container with a lid. The obtained sample is designated as sample C ′. From the light absorption spectrum of Sample C ′, it was found that the electron density was 1.9 × 10 ¹⁹ / cm ³ .

  Further, sample C ′ was heated in an air atmosphere at 400 ° C. for 10 minutes in the same manner as sample A ′, and when it was heated for 10 minutes, the electron density was 0.088 times that of the heat treatment and had high oxidation resistance. I understood.

  Further, from the X-ray diffraction analysis, the X-ray diffraction pattern of the sample C ′ was the same as the X-ray diffraction pattern of the C12A7 crystal, and thus it was found that the sample C ′ consisted of only the mayenite type compound crystal.

(Example 4)
A calcium aluminate crystal containing Ga was produced in the same manner as in Example 1 except that x of Ga substituting Al was changed to 0.04. This is designated as Sample D. From the X-ray diffraction pattern, in addition to the C12A7 crystal, Sample D includes C3A (each characteristic X-ray diffraction peak is 2θ = 30.6 °), C5A3 crystal (2θ = 30.1 °) and CA crystal (2θ = 25.4 °) peak was observed. From the height of the X-ray diffraction peak (2θ = 18.1 °) value, it was found that Sample D contained 90% or more of C12A7 crystals. Similarly to Sample A, Sample D was subjected to reduction treatment using a carbon container with a lid. The obtained sample is designated as sample D ′. From the light absorption spectrum of sample D ′, it was found that the electron density was 1.9 × 10 ¹⁹ / cm ³ .

  Furthermore, sample D ′ was heated for 10 minutes at 400 ° C. in an air atmosphere using an infrared heating furnace in the same manner as sample A ′, and the electron density was 0.056 times that of the heat treatment and had high oxidation resistance. I understood.

  Further, from the X-ray diffraction analysis, the X-ray diffraction pattern of the sample D ′ was the same as the X-ray diffraction pattern of the C12A7 crystal, and thus it was found that the sample D ′ consisted of only the mayenite type compound crystal.

(Example 5)
A calcium aluminate crystal containing Ga was produced in the same manner as in Example 1 except that the molar ratio x of Ga was set to 0.05. This is designated as Sample E. From the X-ray diffraction pattern, it was found that Sample E contained CA crystal, C3A crystal, C5A3 crystal and other crystals in addition to the C12A7 crystal. From the height of the peak value of X-ray diffraction (2θ = 18.1 °), it was found that Sample E contained 80% or more of C12A7 crystals. Similarly to Sample A, Sample E was subjected to a reduction treatment in a carbon container with a lid. The obtained sample is designated as sample E ′. From the light absorption spectrum of Sample E ′, it was found that the electron density was 1.9 × 10 ¹⁹ / cm ³ .

  Further, sample E ′ was heated in an air atmosphere at 400 ° C. for 10 minutes using an infrared heating furnace in the same manner as sample A ′, and it was found that the electron density was 0.069 times that before the heat treatment and had high oxidation resistance. It was.

(Example 6)
A calcium aluminate crystal containing Ga was produced in the same manner as in Example 1 except that the molar ratio x of Ga was 0.1. This is designated as Sample F. From the X-ray diffraction pattern, the sample F contains a large amount of crystals other than the C12A7 crystal such as CA crystal, C3A crystal, C5A3 crystal, etc., and from the height of the peak value of X-ray diffraction (2θ = 18.1 °), the C12A7 crystal. Was found to be only about 30% of the case where no substitution was made with Ga. From the light absorption spectrum of Sample F, it was found that the electron density was 1.0 × 10 ¹⁹ / cm ³ .

(Example 7)
A calcium aluminate crystal containing Ga was prepared in the same manner as in Example 1 except that the molar ratio x of Ga was 0.2. This is designated as sample F ′. From the X-ray diffraction pattern, the sample F contains a large amount of crystals other than the C12A7 crystal such as CA crystal, C3A crystal, C5A3 crystal, etc., and from the height of the peak value of X-ray diffraction (2θ = 18.1 °), the C12A7 crystal. Was found to be scarcely present compared to the case where no substitution was made with Ga.

(Example 8)
A calcium aluminate crystal containing no Ga was prepared in the same manner as in Example 1 except that the molar ratio x of Ga was 0. This is designated as Sample G. From the X-ray diffraction pattern, it was found that Sample G consisted of C12A7 crystals only. Similarly to Sample A, Sample G was subjected to reduction treatment using a carbon container with a lid. The obtained sample is designated as sample G ′. From the light absorption spectrum of Sample B ′, it was found that the electron density was 1.8 × 10 ¹⁹ / cm ³ .
Furthermore, when the sample G ′ was heated at 400 ° C. for 10 minutes in an air atmosphere using an infrared heating furnace in the same manner as the sample A ′, white crystals were obtained. From the light absorption spectrum, the electron density was only 0.017 times that before the heat treatment, and the oxidation resistance was low.

Table 1 below shows the results obtained when the Ga addition rate x (CaO: Al ₂ O ₃ : Ga ₂ O ₃ = 12: 7 (1-x): 7x) was changed from 0 to 0.10. The ratio of C12A7 crystals revealed from X-ray diffraction of mayenite type crystals, the electron density of the sample after the reduction treatment, and the residual ratio of the electron density after the heat treatment at 400 ° C. for 10 minutes in an infrared heating furnace Summarized. Here, in Table 1, when the ratio of the C12A7 crystal in FIG. 1 is 90% or more, ◯, 80% or more but less than 90% is △, and 80% or less is ×. .

  According to the production method of the present invention, a bulk body and a powder of a mayenite type compound that can suppress a decrease in electron concentration even when heat treatment is performed in air can be produced.

  In addition, since the decrease in electron concentration due to heat treatment is small, it can be used as an electrode material that requires high-temperature heat treatment, such as a PDP protective film material or a charge injection material in an organic EL device.

The graph which shows the crystal phase of Ga addition calcium aluminate obtained when the addition rate x of Ga was changed, and its characteristic X-ray diffraction peak intensity

Claims (6)

A part of Al of the mayenite type compound containing Ca, Al and oxygen is substituted with M (M represents at least one atom selected from Ga and In), and the atomic ratio of M / (Al + M) is 0.001. A mayenite type compound having a Mayenite type compound having an electron density of 1 × 10 ¹⁵ cm ⁻³ or more, wherein the Mayenite type compound is at least a part of the free oxygen ion in the Mayenite type crystal structure. Type compound. The composition before the free oxygen ions of the mayenite type compound are replaced with electrons is represented by Ca ₁₂ (Al _1-x M _x ) ₁₄ O ₃₃ , and x in the composition is 0.001 or more and 0.05 or less. The mayenite type compound according to claim 1, wherein   The mayenite type compound according to claim 1 or 2, wherein M is Ga. The mayenite type compound according to claim 1, 2 or 3, wherein the mayenite type compound has an electron density of 1.0 × 10 ¹⁹ cm ⁻³ or more.   The mayenite type compound according to claim 1, wherein a part of Ca of the mayenite type compound is substituted with Mg.   The mayenite type compound according to claim 1, wherein a part of the electrons constituting the mayenite type compound is substituted with an anion having an electron affinity smaller than that of oxygen.

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