Chemistry of inorganic compounds – Oxygen or compound thereof – Metal containing
Reexamination Certificate
2001-07-26
2003-12-16
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Oxygen or compound thereof
Metal containing
C423S593100, C423S594140, C423S598000, C423S599000, C423S600000, C501S123000, C501S125000, C501S135000, C501S137000, C501S152000
Reexamination Certificate
active
06663843
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for producing a barium-containing composite metal oxide which can be used as a raw material for a powder, paste or a sintered body of functional oxide ceramics used in fluorescent substances, dielectrics or the like.
BACKGROUND OF THE INVENTION
Barium-containing composite metal oxides are widely used as functional materials such as fluorescent substances, dielectrics or the like.
Example of the barium-containing composite metal oxide used as fluorescent substances includes, for example, europium-activated barium magnesium aluminate. The europium-activated barium magnesium aluminate is a compound represented by the composition formula BaMgAl
10
O
17
:Eu, is a fluorescent substance emitting blue color by excitation of vacuum ultraviolet rays or the like, and is therefore used as PDP, rare gas lamps or the like. Further, a compound in which a part of barium in the europium-activated barium magnesium aluminate is substituted with strontium or calcium is known as a blue color emitting fluorescent substance.
Example of a barium-containing composite metal oxide used as a fluorescent substance include, for example, manganese-activated barium aluminate. The manganese-activated barium aluminate is a compound represented by the composition formula BaAl
12
O
19
:Mn, and shows emission of green color by excitation of vacuum ultraviolet rays or the like. Further, a compound in which a part of barium in the manganese-activated barium aluminate is substituted with europium is known as a green color emitting fluorescent substance.
Example of the barium-containing composite metal oxide used as a dielectric includes barium titanate. The barium titanate is a compound represented by the composition formula BaTiO
3
, and shows high dielectric constant. As a result, the barium titanate is widely used for a lamination type capacitor. Further, a compound in which a part of barium in the barium titanate is substituted with strontium also shows high dielectric constant.
Those barium-containing composite metal oxides have conventionally been obtained by a liquid phase method, a gas phase method, a solid phase method, a hydrothermal synthesis method, a flux method or the like. The oxides thus obtained are generally in the form of a powder containing many agglomerated particles.
Japanese Patent Application Laid-open No. Hei 7-187612 discloses a method for producing a composite metal oxide powder by calcining a composite metal oxide precursor powder in a halogen-based gas as a method for producing a composite metal oxide powder having less agglomerated particles and showing narrow particle size distribution. However, this publication does not contain the disclosure regarding barium-containing composite metal oxides.
The barium-containing composite metal oxides are, in many cases, once dispersed in a dispersion medium in the form of paste, a slurry or the like, and then, converted into a final product. For this reason, dispersibility of the oxides to a dispersion medium directly reflects functions and physical properties of the final product. Therefore, the dispersibility of metal oxides is one of the important properties. Further, while dielectrics are usually used in the form of a sintered body, in some cases, its dispersibility gives great influence on the property of sintered body. Therefore, there is a desire for improvement in dispersibility of barium-containing composite metal. In general, dispersibility is improved by decreasing agglomeration proportion of primary particles with each other, and in view of this, there is also a desire for development of barium-containing composite metal oxides having weak agglomerating force of primary particles with each other.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a method for producing a barium-containing composite metal oxide having weak agglomerating force of primary particles with each other, suitably used for functional oxide ceramic powder such as fluorescent substances or dielectrics, raw materials for pastes, or raw materials for sintered bodies.
As a result of extensive investigations to achieve the above object, it has been found that a barium-containing composite metal oxide having weak agglomerating force of primary particles with each other is obtained by calcining raw material compounds thereof in a specific gas atmosphere.
According to the present invention, there is provided a method for producing a barium-containing composite metal oxide, which comprises calcining a mixture of a barium compound and a metal compound comprising at least one metal selected from the group consisting of magnesium, aluminum, europium, manganese, strontium, calcium, terbium, zinc and titanium, or calcining a barium-containing composite metal salt comprising barium and at least one metal selected from the group consisting of magnesium, aluminum, europium, manganese, strontium, calcium, terbium, zinc and titanium, in a gas comprising a hydrogen halide and water vapor.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
The barium compound used in the present invention may be barium oxides, or any barium compound as long as it converts to a barium oxide by decomposition reaction or oxidation reaction when it is calcined.
Similar to the above-described barium compound, the metal compound comprising at least one metal selected from the group consisting of magnesium, aluminum, europium, manganese, strontium, calcium, terbium, zinc and titanium used in the present invention (hereinafter sometimes referred to as a “metal compound”) may be oxides comprising at least one metal selected from the group consisting of magnesium, aluminum, europium, manganese, strontium, calcium, terbium, zinc and titanium, or any compound as long as it converts to a metal oxide by decomposition reaction or oxidation reaction when it is calcined.
The composite metal salt used in the present invention may be any metal salt as long as it comprises at least one metal selected from the group consisting of magnesium, aluminum, europium, manganese, strontium, calcium, terbium, zinc and titanium, and barium, and converts to a barium-containing composite metal oxide described hereinafter by decomposition reaction or oxidation reaction when it is calcined.
Calcination conditions may be exemplified as described hereinafter. Examples of the compound that converts to its oxide by decomposition reaction or oxidation reaction include hydroxides, aqueous oxides, oxyhydroxides, oxyhalides, halides, carbonates, oxalates, sulfates and nitrates.
The above-described barium compound, metal compound and composite metal salt can be produced by conventional methods. For example, the methods include the liquid phase method, the gas phase method, the solid phase method or the like.
The above-mentioned barium compound is mixed with above-mentioned metal compound to obtain the mixture of barium compound and metal compound in a ratio so that a specific composition ratio of a complex metal oxide including barium described later is obtained.
Methods of mixing a barium compound and a metal compound are illustrated as any suitable method now known or developed in the future, and for example, mixing methods using a ball mill, V-shape mixer, and stirring apparatus and the like, may be exemplified.
The order of feeding a barium compound and a metal compound to a mixing apparatus is not particularly restricted, and both of them may be fed simultaneously fed separately, or they may be fed according to a master batch mode.
In a mixture of the barium compound and the metal compound, a barium oxide and a barium compound which converts to a barium oxide by decomposition reaction or oxidation reaction when it is calcined may be used together as the barium compound. Further, a metal oxide and a metal compound which converts to a metal oxide by decomposition reaction or oxidation reaction when it is calcined may be used together as the metal compound, or at least two kinds of the metal compounds or
Miyazaki Susumu
Ono Keiji
Bos Steven
Kuhar Anthony
Sumitomo Chemical Company Limited
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