JPH09255331A - Production of monodispersed hyperfine particles of oxide of rare earth element by inverse micelle method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain hyperfine particles of a monodispersed rare earth oxide having a very small average particle diameter by forming inverse micelle of a surfactant in a nonpolar org. solvent, solubilizing an aq. soln. contg. ions of a rare earth element and a precipitant in the micelle and allowing them to react with each other after mixing. SOLUTION: Inverse micelle formed by a surfactant in a nonpolar org. solvent such as cyclohexane is used as a reaction field, an aq. soln. contg. ions of a rare earth element and a precipitant such as an ammonia soln. are solubilized in the micelle and they are allowed to react with each other after mixing to produce the objective monodispersed hyperfine particles of oxide of the rare earth element having <=5nm average particle diameter. When an aq. soln. of salts of various rare earth elements is used as starting material, hyperfine particles of multiple oxide of the rare earth elements are easily produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for easily producing ultrafine particles of rare earth oxides and complex oxides having an extremely small average particle size and excellent monodispersibility.

[0002]

2. Description of the Related Art Conventional rare-earth oxide fine particles have a large particle size and a wide particle size distribution, and the shapes of the particles are uneven. Therefore, electronic materials, functional ceramic materials, phosphor materials, catalyst materials, etc. In particular, when used in a field requiring a high degree of precision, it requires processes such as pulverization and classification for making the particle diameter uniform. For this reason, there arises a problem that the operation in the particle manufacturing process is complicated and complicated, and the impurities are mixed therewith.

[0003]

The object of the present invention is to obtain monodisperse particles having an extremely small average particle diameter, which cannot be achieved by conventional production methods such as coprecipitation method, hydrolysis method, uniform precipitation method and hydrothermal method. The present invention provides ultrafine particles of rare earth oxides and ultrafine particles of complex oxides, and a method for producing them.

[0004]

In order to achieve the above object, it is effective to prevent grain growth by advancing a hydrolysis reaction in a reaction field of physically limited size. In the present invention, an aqueous solution of a rare earth salt including a rare earth nitrate is solubilized inside a reverse micelle, and a reverse micelle solution of a precipitating agent such as ammonia water or urea which is also solubilized in the reverse micelle, and at room temperature under normal pressure. The ultra-fine particles of rare earth oxides such as yttrium oxide and cerium oxide, and the ultrafine particles of complex oxide are produced in a monodispersed state by the reaction.

[0005]

In the present invention, it is possible to produce ultrafine particles of rare earth oxide and ultrafine particles of complex oxide which are monodisperse and have an extremely small average particle diameter, without using a high pressure and high temperature process.

In the production, an aqueous solution containing a predetermined amount of rare earth ions is added to a non-polar organic solvent in which a surfactant and, if necessary, cosurfactant are dissolved, and solubilized by forming reverse micelles. It can be easily performed by mixing aqueous ammonia or urea with a solution solubilized in the reverse micelle. The formed precipitate particles are subjected to high speed centrifugation and washed with hydrocarbon, alcohol, acetone, petroleum ether or the like.

Further, in the present invention, since a high-purity reagent can be used as a starting material, it is also useful as a means for obtaining extremely high-purity oxide ultrafine particles. Further, by using a solution containing two or more kinds of metal ions as the raw material, it is possible to produce monodispersed composite oxide ultrafine particles at room temperature under normal pressure in the same manner as the binary oxide.

[0008]

EXAMPLES Monodispersed ultrafine particles of various oxides including rare earth oxides or composite oxides can be manufactured by the operations and manufacturing steps shown in FIG.

The operation and manufacture were carried out by the following steps. Into a nonpolar organic solvent such as cyclohexane, a surfactant or a mixed solution of a surfactant and an intermediate alcohol having 4 to 8 carbon atoms, which is a cosurfactant, is added to form a reverse micelle of the surfactant. An aqueous solution containing various rare earth ions and a precipitant that causes a hydrolysis reaction are solubilized in the reverse micelles, respectively, and both are mixed at room temperature,
The mixture was stirred and reacted, and the formed precipitate was washed with hydrocarbon, acetone and alcohol. As a result, various rare earth oxide ultrafine particles having an extremely small average particle diameter such as cerium oxide were obtained.

Observation of the obtained ultrafine particles with a transmission high-resolution electron microscope confirmed the formation of nanometer-sized ultrafine particles having very uniform particle diameters. From the selected area electron diffraction ring, it was confirmed that the obtained ultrafine particles were already oxides.

FIG. 2 is a particle size distribution diagram of cerium oxide ultrafine particles synthesized by reacting a reverse micelle solution in which an aqueous cerium nitrate solution is solubilized with a solution in which aqueous ammonia is similarly solubilized. From the figure, it was found that the particle diameters of the produced particles were distributed in the range of 1.6 to 5.6 nm, and the average value was 3.4 nm.

Furthermore, the standard deviation of the particle size distribution is 0.72 nm.
Thus, it was revealed that the obtained ultrafine particles were extremely excellent in monodispersity.

[0013]

The present invention is a technique for easily producing monodisperse rare earth oxide ultrafine particles and composite oxide ultrafine particles having extremely small particle diameters. Therefore, it is possible to easily produce the target rare earth oxide ultrafine particles by using various rare earth salt aqueous solutions as starting materials, and by using a solution containing a plurality of metal ions as the starting material It is also possible to produce ultrafine composite oxide particles.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram of monodisperse rare earth oxide ultrafine particles having a reaction field inside a reverse micelle.

FIG. 2 is a particle size distribution diagram of cerium oxide ultrafine particles produced by the reverse micelle method.

Claims (2)

[Claims] 1. Ultrafine monodisperse rare earth oxide particles and ultrafine composite oxide particles having an average particle diameter of 5 nm or less. 2. An aqueous solution containing various rare earth ions solubilized in the reverse micelle as a reaction field in a reverse micelle formed by a surfactant in a nonpolar organic solvent, and a precipitant similarly solubilized. A technology for producing nanometer-sized monodisperse rare earth oxides and composite oxide ultrafine particles by mixing and reacting and inside the reverse micelles.