Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2001-02-05
2003-06-03
Le, H. Thi (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S329000, C428S402000, C423S115000, C423S326000, C423S327100, C423S593100, C423S598000, C423S600000
Reexamination Certificate
active
06572964
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an ultrafine mixed-crystal oxide obtained by a vapor phase method, and the production process thereof. More specifically, the present invention relates to an ultrafine mixed-crystal oxide with a mixed-crystal state, prepared from a mixture selectively comprising a plurality of chlorides, bromides, and iodides of titanium, silicon, and aluminum with an arbitrary composition ratio, the production process and the use thereof.
BACKGROUND ART
The fields of industrial application of the ultrafine oxides have been expanding considerably in recent years. For instance, ultrafine titanium oxide is being extensively studied as an ultraviolet-shielding agent, an additive for a silicone rubber, and a photocatalyst. In particular, the application for cosmetics attracts special attention due to the ultraviolet shielding effect of ultrafine titanium oxide, and, in light of the photocatalytic properties of the ultrafine titanium oxide, some attention is also being paid to the application for prevention of fouling, sterilization, and deodorizing. Such applications are supported by the advantages of ultrafine titanium oxide in terms of safety, processability, functional characteristics, and durability. The ultrafine particles have not been exactly defined, but are generally regarded as fine particles with a primary particle diameter of about 0.1 &mgr;m or less.
The specific functions of titanium oxide, that is, scattering and absorption of ultraviolet light, are noteworthy. It is more noticeable that ultrafine particles of titanium oxide are favorably provided with the above-mentioned two functions in combination. For instance, ultrafine titanium oxide with a primary particle diameter of about 80 nm can work to effectively scatter ultraviolet light. In addition, it is known that such ultrafine particles of titanium oxide can effectively absorb ultraviolet light with a wavelength of about 400 nm or less and be excited to generate electrons and/or holes in the portion adjacent to the surface of the particle, thereby exhibiting such photocatalytic performance as to carry out the prevention of fouling, sterilization, and deodorizing, as mentioned above.
However, when titanium oxide having such functions is used for cosmetic applications in practice, there is the possibility that the titanium oxide works improperly unless subjected to a surface treatment (coating). This is because the electrons and holes caused by photo-excitation generate various radicals when allowed to react with oxygen and water in the air, so that they work to decompose organic materials in the air.
Titanium oxide is also used as a high-performance dielectric material. For example, titanium oxide is subjected to a solid phase reaction with barium carbonate at 1,200° C. in accordance with the following reaction formula, thereby providing barium titanate serving as a dielectric material.
BaCO
3
+TiO
2
→BaTiO
3
+CO
2
In this case, barium carbonate decomposes at around 700° C. to generate BaO with high tendency of ionization, which is diffused into TiO
2
particles with covalent bonding characteristics to form a solid solution, thereby producing barium titanate. The particle size of the barium titanate is determined by the crystalline size of the TiO
2
in the course of the reaction. Therefore, the crystallinity and the particle size of the titanium oxide serving as the raw material become significant. To cope with the requirement for a small-size ceramic condenser with a high dielectric constant, there is an increasing demand for ultrafine particles of barium titanate, and consequently, for ultrafine particles of titanium oxide as a raw material.
However, the growth of titanium oxide particles with a particle size of 0.1 &mgr;m or less is striking at the above-mentioned reaction temperature of about 700° C., so that there is the problem that such titanium oxide particles cannot contribute to the provision of ultrafine particles of barium titanate. Ultrafine particles of titanium oxide for achieving the above-mentioned object is desired.
As an example of a method for producing fine particles of a composite containing titanium oxide, a production process is known for finely-divided particles of silica-titania composite material, that is, a production process of allowing a mixture of gaseous halogenated silicon and gaseous halogenated titanium to react with oxidizing gas containing an oxygen at 900° C. or more (Japanese Laid-Open Patent Application No. 50-115190). According to this method, the mixture of gases serving as the raw material is subjected to a reaction under conditions of a high temperature of 900° C. or more without preheating. The resultant composite particles have such a structure that crystalline TiO
2
particles are always deposited on the surface of the composite particles.
Japanese Patent No. 2503370 (European Patent No. 595078) discloses that a mixed oxide of titanium oxide, aluminum oxide, and silicon oxide can be produced by flame hydrolysis (at a reaction temperature of 1000 to 3000° C.) using chlorides as raw materials. The flame hydrolysis produces a mixed oxide of Al
2
O
3
and TiO
2
, or a mixed oxide of SiO
2
and TiO
2
. Similarly, Japanese Patent No. 2533067 (European Patent No. 585544) discloses manufacture of a mixed oxide of aluminum oxide and silicon oxide by flame hydrolysis.
As previously mentioned, the production process for a metal oxide by a vapor phase method, or the production process for a metal oxide or mixed metal oxide by flame hydrolysis is conventionally known. However, the growing mechanism of the product particles that is, in general, seriously influenced by the reaction temperature, the gas flow velocity, the cooling rate, or the like, has not been sufficiently clarified.
DISCLOSURE OF THE INVENTION
In light of the applications of the previously mentioned ultrafine metal oxides, objects of the present invention are to provide a convenient production process for a surface-modified ultrafine mixed-crystal oxide, and to provide the ultrafine mixed-crystal oxide obtained by the process.
The inventors of the present invention have conducted an intensive investigation in view of the prior art. As a result, the above-mentioned problems were solved by producing an ultrafine mixed-crystal oxide comprising primary particles with a mixed crystal state having a BET specific surface area of about 10 to about 200 m
2
/g in such a manner that a mixed gas (hereinafter referred to as “a mixed halogenated metal gas”) comprising at least two compounds selected from the group consisting of chlorides, bromides, and iodides of titanium, silicon (In the present invention, silicon element is grouped together with a metal element), and aluminum and an oxidizing gas are independently preheated to about 500° C. or more prior to a reaction.
Namely, the present invention provides:
(1) a process for producing an ultrafine mixed-crystal oxide characterized by producing an ultrafine mixed-crystal oxide comprising primary particles in a mixed crystal state with a BET specific surface area of about 10 to about 200 m
2
/g, comprising the step of subjecting a halogenated metal to high temperature oxidation with an oxidizing gas to produce a metal oxide by a vapor phase production method, wherein the halogenated metal is in the form of a mixed gas (a mixed halogenated metal gas) comprising at least two compounds each having a different metal element selected from the group consisting of chlorides, bromides, and iodides of titanium, silicon, and aluminum, and the mixed halogenated metal gas and the oxidizing gas are independently preheated to about 500° C. or more prior to a reaction;
(2) the production process of the ultrafine mixed-crystal oxide according to the aforementioned item (1), wherein the mixed halogenated metal gas is prepared by independently vaporizing at least two compounds each having a different metal element selected from the group consisting of chlorides, bromides, and iodides of titanium, silicon, and aluminum, and mixing the compounds i
Tanaka Jun
Tomikawa Shin-ichiro
Le H. Thi
Showa Denko K.K.
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