Coating processes – Particles – flakes – or granules coated or encapsulated
Patent
1995-06-15
1997-04-08
Beck, Shrive
Coating processes
Particles, flakes, or granules coated or encapsulated
427215, 4272551, 4272552, 4272553, 4272557, 4274191, 4274192, 4274193, 423610, 423611, 423612, 423613, 423622, 423625, 118715, 118716, B05D 700, C01G 23047
Patent
active
056185804
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method for producing ceramic fine particles and an apparatus used therefor. More specifically, it relates to a method for continuously producing ceramic fine particles comprising vaporizing one or more kinds of metal compounds to give gaseous starting materials, and then subjecting the gaseous starting materials to chemical reaction, namely by the CVD method (Chemical Vapor Deposition method), or a method for continuously producing ceramic fine particles comprising treating a solution containing one or more kinds of metal salts to form fine starting material droplets, and then subjecting the starting material droplets to pyrolyric reaction, namely a spray pyrolysis method, and it also relates to a production apparatus used for these production methods.
BACKGROUND ART
In general, ceramic fine particles include fine particles of oxides, such as TiO.sub.2, ZnO, Al.sub.2 O.sub.3, and SiO.sub.2, those of carbides, such as-SiC and TiC, and those of nitrides, such as Si.sub.3 N.sub.4, TiN, and AlN. Having various properties, such as photoconductivity, piezoelectricity, fluorescence, and catalytic effects, the fine particles are frequently used in various industrial fields.
Among the ceramic fine particles, titanium oxide fine particles, for instance, have diversified industrial applications, and they are used as white pigments, magnetic starting materials, abrasives, pharmaceuticals, and ultraviolet shielding materials.
Also, SiC fine particles, for instance, have diversified industrial applications, and they are used, for instance, for thermistors utilizing their resistivity stability and for varistors utilizing their non-linearity of voltage-current relationship. Other ceramic fine particles also have various industrial applications.
As mentioned above, although ceramic fine particles have very great industrial applications, it is important to produce uniform fine particles with a narrow particle diameter distribution in order to optimize their performance. In other words, by producing fine particles, specific surface areas thereof are increased, and the proportion of number of molecules located on the surface of the fine particles based on the entire number of molecules constituting the fine particles increases. Therefore, the surface energy of the fine particles is increased, and the performance of the fine particles per unit weight is markedly enhanced. In addition, no variation in the performance of the fine particles is found, because the particle diameter distribution is narrow.
Also, by forming a concentric, multi-layered structure, the ceramic fine particles can enjoy the combined functions of the ceramic constituting the respective layers, and the improved properties for the surface of the substances forming the core. In order to exhibit an optimum performance of the fine particles having a multi-layered structure mentioned above, each of the layers constituting the ceramic fine particles has to be uniformly coated. By uniformly and evenly coating the outermost layer, in particular, it is possible to inhibit the properties of the surface of the inner layer from directly affecting the outer portion, and to uniformly exhibit the properties of the outermost layer.
The methods for producing ceramic fine particles of having extremely important industrial applications as mentioned above can be roughly divided into a liquid-phase method and a vapor phase method.
Examples of the liquid-phase methods include a method for producing zinc oxide fine particles comprising hydrolyzing a metal alkoxide thereof, to give zinc oxide fine particles (Japanese Patent Laid-Open No. 2-59425). Also, in general, a long-time method used comprises adding an acid or alkali solution to a metal salt to cause a reaction in the liquid-phase, to give desired ceramic fine particles.
As for fine particles having a multi-layered structure, for example, a method comprising the steps of adding a metal salt to an aqueous suspension of, for instance, TiO.sub.2 fine particles, and coating
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Kokubo Sachiko
Nishimura Toru
Numata Toshiharu
Oshima Kentaro
Tsuto Keiichi
Beck Shrive
Kao Corporation
Maiorana David M.
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