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Rare earth metal compound in aqueous solvent, method for producing same, and method for producing ceramic powder using sameRelated Patent Categories: Colloid Systems And Wetting Agents; Subcombinations Thereof; Processes Of, Continuous Liquid Or Supercritical Phase: Colloid Systems; Compositions An Agent For Making Or Stabilizing Colloid Systems; Processes Of Making Or Stabilizing Colloid Systems; Processes Of Preparing The Compositions (e.g., Micelle; Thickening Agent; Protective Colloid Agent; Composition Containing An Emulsifying Agent With No Dispersant Disclosed; Organic Liquid Emulsified In Anhydrous Hf), Aqueous Continuous Liquid Phase And Discontinuous Phase Primarily Solid (e.g., Water Based Suspensions, Dispersions, Or Certain Sols*, Of Natural Or Synthetic Ester-wax, Beeswax, Carnauba Wax; Or Latex Dispersion), The Solid Is Primarily Inorganic Material (e.g., Mercurous Halide), The Material Primarily Contains Compound Containing Both Metal And Oxygen (e.g., Silver Nitrate), The Metal Present In The Greatest Amount Is Yttrium, Scandium, Or Rare Earth (e.g., Hydrated Ceric Dioxide)Rare earth metal compound in aqueous solvent, method for producing same, and method for producing ceramic powder using same description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070010587, Rare earth metal compound in aqueous solvent, method for producing same, and method for producing ceramic powder using same. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] The present invention relates to a water-based rare earth metal compound sol, a manufacturing method thereof, and a method for manufacturing a ceramic powder using the same. BACKGROUND ART [0002] Heretofore, as a dielectric ceramic composition having a high dielectric constant, a BaTiO.sub.3-based ceramic has been widely practically used. In order to adjust the temperature properties of the dielectric constant and to improve the sintering properties, addition of various subcomponents has been generally performed. As for multilayer capacitors, the thickness thereof has been decreased year by year in order to increase the static capacity, and in recent years, a product in which the thickness per layer is decreased to several micrometers or less has been commercially available. In this type of capacitor which is composed of thinner layers as described above, the uniformity of materials thereof is increasingly required as compared to that in the past. Hence, subcomponents are required to be particularized. [0003] In order to uniformly mix particularized subcomponents with a major component such as BaTiO.sub.3, aggregation of fine particles of the subcomponents must be prevented, and hence before being mixed with the major component such as BaTiO.sub.3, the subcomponents are preferably present in the form of sol (colloid solution). [0004] Accordingly, in Patent Document 1, a method for manufacturing an organic sol containing a rare earth metal, which is one of the subcomponents, has been proposed. Patent Document 1: PCT Japanese Translation Patent Publication No. H11-501609 DISCLOSURE OF INVENTION Problems to be Solved by the Invention [0005] However, since the conventional rare earth metal compound sol disclosed in Patent Document 1 is an organic sol, when the sol is manufactured or is used, an explosion-proof apparatus is required, and as a result, there has been a problem in that the manufacturing cost cannot be easily reduced to a lower level. [0006] The present invention was made in consideration of the current situations described above, and an object of the present invention is to provide a water-based rare earth metal compound sol, which will not cause aggregation of fine particles of a rare earth metal compound, which can be easily handled, and which will not require an explosion-proof apparatus, and is to provide a manufacturing method of the above water-based rare earth metal compound sol. In addition, it is also an object of the present invention to provide a method for manufacturing a ceramic powder, which can manufacture a ceramic powder containing a rare earth metal element uniformly dispersed therein. Means for Solving the Problems [0007] A water-based rare earth metal compound sol described in Claim 1 of the present invention is a water-based rare earth metal compound sol containing a rare earth metal compound dispersed in water. In the water-based rare earth metal compound sol described above, the rare earth metal compound contains a carboxylic acid or a carboxylate, which has at least three carbonyl groups, and at least one rare earth metal selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and the molar ratio (carbonyl group/rare earth metal) of the carbonyl group of the carboxylic acid or the carboxylate to the rare earth metal is in the range of 1.2 to 3. [0008] In addition, in the water-based rare earth metal compound sol described in Claim 2 of the present invention, the carboxylic acid or the carboxylate, described in Claim 1 of the present invention, is citric acid or a citrate, respectively. [0009] In addition, a method for manufacturing a water-based rare earth metal compound sol, described in Claim 3 of the present invention, comprises: a step of preparing an acidic or an alkaline aqueous solution of at least one rare earth metal selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, or a water-based dispersion solution in which a hydroxide of the aforementioned rare earth metal is dispersed; and a step of adding a carboxylic acid or a carboxylate, which has at least three carbonyl groups, to one of the above solutions so that the molar ratio (carbonyl group/rare earth metal) of the carbonyl group to the rare earth metal is in the range of 1.2 to 3. [0010] In addition, in the method for manufacturing a water-based rare earth metal compound sol, described in Claim 4 of the present invention, the carboxylic acid or the carboxylate, described in Claim 3 of the present invention, is citric acid or a citrate, respectively. [0011] In addition, a method for manufacturing a ceramic powder, described in Claim 5 of the present invention, comprises: using the water-based rare earth metal compound sol described in Claim 1 or 2 as a subcomponent ingredient. ADVANTAGES [0012] According to Claims 1 to 4 of the present invention, the water-based rare earth metal compound sol, which will not cause aggregation of fine particles of a rare earth metal compound, which can be easily handled, and which will not require an explosion-proof apparatus, and the manufacturing method of the above water-based rare earth metal compound sol can be provided. [0013] In addition, according to Claim 5 of the present invention, there can also be provided a method for manufacturing a ceramic powder in which a rare earth metal element is uniformly dispersed therein. BEST MODE FOR CARRYING OUT THE INVENTION [0014] Next, a method for manufacturing a water-based rare earth metal compound sol, according to the present invention, will be described. [0015] First, a rare earth metal compound in the form of liquid is prepared as an ingredient. The liquid may be either an acidic aqueous solution or an alkaline aqueous solution. In addition, a water-based dispersion solution in which a hydroxide is dispersed in water may also be used. While this aqueous solution or the water-based dispersion solution is being well stirred, a carboxylic acid or a carboxylate, having at least three carbonyl groups, is added so that the molar ratio (carbonyl group/rare earth metal) of the carbonyl group to the rare earth metal is in the range of 1.2 to 3. In order to advance the reaction, heating may be performed. In this step, the rare earth metal ions and the carboxylic acid react with each other to form a polymeric product. When the size of this polymeric product is appropriate, a water-based rare earth metal compound sol (hereinafter simply referred to as "sol") may be formed; however, when the size is excessively large, precipitation occurs, and as a result, the liquid becomes clouded. When the liquid becomes clouded, the pH is adjusted, for example, by operation of adding ammonia water. When the pH of the liquid is increased, the bonds in the polymeric product are appropriately dissociated, and as a result, the size thereof is decreased so that the precipitate is not formed. That is, the liquid is turned into a sol. In order to prevent the precipitation and to form a sol, the average particle diameter must be approximately 150 nm or less. At this stage, the viscosity of the liquid may increase in some cases (gelation), and in this case, dilution is performed using purified water. [0016] When the carboxylic acid or the carboxylate which is to be added has only one or two carbonyl groups, the stability of complexes formed of rare earth metal ions and carboxylic acid becomes insufficient, and as a result, the sol, a polymeric product of the complexes, is also unstable, so that a hydroxide precipitate is formed. Continue reading about Rare earth metal compound in aqueous solvent, method for producing same, and method for producing ceramic powder using same... 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