Chemistry of inorganic compounds – Rare earth compound
Reexamination Certificate
1995-06-09
2001-10-16
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Rare earth compound
C423S608000, C423S618000, C423S624000
Reexamination Certificate
active
06303091
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a metal oxide powder which is used as a raw material powder of an oxide ceramic that is used as a functional material or a structural material, a metal oxide powder which is used in a dispersed state as a filler or a pigment, or a metal oxide powder which is used as a raw material powder for the production of a single crystal or for flame spray coating, and a method for the production thereof.
PRIOR ART
In general, an oxide ceramic which is used as a functional material or a structural material is produced through a molding step and a calcination step from a metal oxide powder as a raw material. Properties of the metal oxide powder to be used as the raw material have a large influence on the production steps, and functions and physical properties of the ceramic product. Then, it is highly desired to provide a metal oxide powder having powder properties which are precisely controlled so that they are suitable for an intended application.
When a metal oxide powder is used in a dispersed state such as a magnetic fine powder, a filler or a pigment, since properties of each particle are reflected directly on the dispersed state, the control of the properties of the powder is more important.
The required properties of the metal oxide powder vary with a kind and application form of the metal oxide. Commonly required properties are a uniform particle size of the metal oxide powder, that is, a narrow particle size distribution, and a weak bond among primary particles, that is, less agglomeration and good dispersibility.
For example, a titanium oxide powder is widely used as a raw material of a white pigment, a raw material of a filler to be added to a resin, a raw material of a material having a high refractive index, a raw material of a UV light absorber, a raw material of a single crystal, a raw material of a photocatalytic active semiconductor, a raw material of a catalyst support, a raw material of an abrasive, a raw material of a dielectric material, and so on.
A zirconium oxide powder is useful as a material to be used in a high temperature material or a mechanical structural material, an ion conductive material, a piezoelectric material and so on, and is used as a raw material of a calcined body and a raw material for melt spray coating.
A magnesium oxide powder is a useful as a raw material of a refractory ceramic, a raw material of a functional ceramic such as an electronics material or an optical material, and the like.
A cerium oxide powder is one of oxides of rare earth elements, and useful as an electrical conductive material, an optical material, or an abrasive.
A tin oxide powder is a valuable material used as an electronics material, a pigment, a catalyst or an abrasive.
Hitherto, these metal oxides are produced by a liquid phase method, a gas phase method, a hydrothermal synthesis method, a direct oxidation method, an electrical fusion method, and the like. The produced metal oxide powders have some problems such as formation of agglomerates, nonuniformity in the particles, a wide particle size distribution, and so on, and they are not necessarily satisfactory. Further, the above production methods themselves have problems such as complicated procedures, problems of apparatuses, costs of raw materials, and so on. Then, it has been desired to develop a metal oxide powder which contains less agglomerated particles and have a narrow particle size distribution, and to develop a method for producing such metal oxide powder generally and advantageously in an industrial production.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a metal oxide containing less agglomerated particles and having a narrow particle size distribution and a uniform particle shape, which is preferably used as a metal oxide powder to be used as a raw material powder of an oxide ceramic that is used as a functional material or a structural material, a metal oxide powder to be used in a dispersed state as a filler or a pigment, or a metal oxide powder to be used as a raw material powder for the production of a single crystal or for flame spray coating.
Another object of the present invention is to provide a production method which can be generally employed in the production of such metal oxide powder and is excellent industrially.
As a result of the extensive study on the metal oxide powders, it has been found that, when a raw material is calcined in a specific atmosphere gas, the above described metal oxide containing less agglomerated particles and having a narrow particle size distribution and a uniform particle shape is obtained, and that such method can be employed generally in the production of various metal oxide powders and excellent industrially, and the present invention has been completed after further investigations.
That is, according to a first aspect of the present invention, there is provided a metal oxide powder except &agr;-alumina, comprising polyhedral particles having at least 6 planes each, a number average particle size of from 0.1 to 300 &mgr;m, and a D
90
/D
10
ratio of 10 or less where D
10
and D
90
are particle sizes at 10% and 90% accumulation, respectively from the smallest particle size side in a cumulative particle size curve of the particles.
According to a second aspect of the present invention, there is provided a rutile type titanium oxide powder comprising polyhedral particles each having at least 8 planes.
According to a third aspect of the present invention, there is provided a method for producing a metal oxide powder except &agr;-alumina, having a narrow particle size distribution, comprising calcining a metal oxide powder or a metal oxide precursor powder in the presence or absence of a seed crystal in an atmosphere containing at least one gas selected from the group consisting of (1) a hydrogen halide, (2) a component prepared from a molecular halogen and steam and (3) a molecular halogen.
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Hasegawa Akira
Koike Hironobu
Mohri Masahide
Saegusa Kunio
Tanaka Shinichiro
Bos Steven
Sughrue Mion Zinn Macpeak & Seas, PLLC
Sumitomo Chemical Company Limited
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