KR20040069404A - Preparation method of ceria particles with nano-size - Google Patents

Abstract

PURPOSE: Provided is a preparation method of nano-sized ceria powder(CeO2) with no agglomeration by forming hollow or porous ceria precursor powder by thermal spraying ceria precursor solution containing organic materials. CONSTITUTION: The CeO2 powder is prepared by the following steps of: (i) preparing ceria precursor solution, having 0.02-3M of Ce, by dissolving cerium salt selected from acetate, nitrate, chloride or hydroxide of cerium and organic additives comprising carboxylic acid and glycol(or multivalent alcohol) into water or alcohol, wherein cerium salt and organic additives are mixed in a molar ratio of 1 : 0.001-2, and 0.1-0.3M of ethylenediaminetetraacetic acid(EDTA) is optionally added to form polymeric materials. The organic additives are carboxylic acid(citric acid, malic acid or pyruvic acid), and glycol(ethylene glycol, propylene glycol or polyethylene glycol) or multivalent alcohol(trivalent alcohol or tetravalent alcohol), wherein carboxylic acid and glycol or multivalent alcohol are mixed in a weight ratio of 1 : 0.1-10; (ii) thermal spraying precursor solution to form liquid drops(0.01-100micrometer size); (iii) thermal drying liquid drops at 200-1500deg.C for 0.1-10sec to form hollow or porous ceria precursor powder by decomposing organic or polymeric precursors; (iv) sintering ceria precursor powder at 500-1200deg.C for 10-600min and milling. Also, 1-50mol% of at least one metal selected from Y, Gd, Sm, Zr, Zn, Sc, Yb, etc. is optionally added to the step(i) for the preparation of metal-doped ceria powder.

Description

Preparation method of nano-sized ceria {PREPARATION METHOD OF CERIA PARTICLES WITH NANO-SIZE}

The present invention relates to a mass production method of ceria powder having a nanoparticle size, and more particularly, an additive such as an organic carboxylic acid, glycol or a polyhydric alcohol, or a derivative thereof to a reaction solution for preparing a ceria powder having a particle size. And spraying into droplets by spray pyrolysis to prepare precursor powders in a very hollow or porous form, and to obtain them as non-aggregated nano-ceria powders by firing and milling by milling. .

The ceria powders synthesized by the general spray pyrolysis process have a hollow micron size. However, these solid micron sized powders cannot provide non-agglomerated nano ceria powders even after milling.

In the present invention, when synthesizing the nano ceria powder by spray pyrolysis process, by adding an organic additive and changing its type and amount, manufacturing process, post-treatment temperature and time, milling process conditions, the ratio of several nanometers to several hundred nanometers Cohesive Ceria Nano Powder Mass Synthesis Technology

In other words, the present inventors have found that the precursor particles obtained in the spray pyrolysis process using the gas emitted by decomposition of the organic additives by adding organic additives to the precursor spray solution for the mass synthesis of nano-ceria powder by the spray pyrolysis process are very hollow or porous. It is induced to have a shape and then calcined at a constant temperature to obtain a nanophase powder having crystallinity and pulverized by a simple milling process to be applied as a base material for phosphor synthesis, electrolyte of fuel cell, and semiconductor wafer polishing agent. These possible non-aggregating nano ceria powders were synthesized.

1 to 4 are electron micrographs before milling of ceria powder prepared when the calcination temperature was 1000 ° C., 1050 ° C., 1100 ° C. and 1200 ° C. after pyrolysis in a 1000 ° C. tubular reactor according to Example 1, respectively.

5 to 7 are electron micrographs after a 20-hour milling process after firing of the ceria powder prepared when the firing temperatures were 1050 ° C., 1100 ° C. and 1200 ° C. according to Example 1, respectively.

FIG. 8 is an electron micrograph of ceria powder milled for 20 hours after firing at 1100 ° C. when the amount of citric acid and ethylene glycol was 0.22 M and 0.15 M in Example 2, respectively;

9 is an electron micrograph of the ceria powder, which was subjected to a milling process for 20 hours after firing at 1100 ° C. when the amounts of citric acid and ethylene glycol were 0.44 M and 0.3 M in Example 2, respectively;

10 is an electron micrograph of the gadolinium-doped ceria powder subjected to the milling process for 20 hours after firing at 1050 ℃ in Example 3,

FIG. 11 is an electron micrograph of a yttrium-doped ceria powder which was milled for 20 hours after firing at 1050 ° C. in Example 3,

12 and 13 are electron micrographs of pure ceria powder, respectively, after firing at 1000 ° C. before milling and after milling for 20 hours according to Comparative Example 1. FIG.

1) preparing a ceria precursor solution by dissolving a ceria precursor material and an additive selected from organic carboxylic acid and glycol and a polyhydric alcohol in a solvent; 2) generating droplets from the precursor solution; And 3) drying, firing, and milling the generated droplets to obtain nano-seria powder.

The nano-sized ceria manufacturing method according to the present invention will be described in more detail by dividing each process as follows.

1) First Step: Preparation of Ceria Particle Precursor Solution

In order to obtain the ceria powder according to the present invention, first, the ceria precursor materials are dissolved in a solvent such as water, an alcohol or an aqueous weak acid solution to obtain a precursor solution. As the precursor material, cerium salts such as cerium acetate, nitrate, chloride, hydrate, oxide, and the like, which are easily dissolved in a solvent such as water or alcohol, may be used. By the combination of the optimal composition can be derived.

In the present invention, in the preparation of the precursor solution, additives such as organic carboxylic acid, glycol or polyhydric alcohol, or derivatives or mixtures thereof are used for synthesizing ceria precursor powder in a hollow or porous form by generating gas inside the precursor droplet. It is characterized by.

The organic carboxylic acid may be citric acid, malic acid, meso tartaric acid, grape acid and meconic acid, and the like, and the glycol may be ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, triethylene glycol, tetra Ethylene glycol, butanediol-1,4-hexylene glycoloxylene glycol, and the like, and polyhydric alcohols include trihydric alcohols such as glycerin and other tetrahydric or pentahydric alcohols.

The additives produce a polymer at a high temperature, and the amount of each additive has a great influence on the viscosity, molecular weight, and the like of the polymer solution, and thus functions as an important variable in the form of the finally obtained ceria powder. Mixtures of the organic carboxylic acids and glycols or polyhydric alcohols are preferably used, where the mixing ratio may preferably range from 1: 0.1 to 10 weight ratios.

The additives may be used in amounts ranging from 0.001 to 2 moles relative to cerium salts. If the concentration of the additive is less than 0.001 mole, the effect as an additive cannot be expected, and if it is more than 2 moles, it may be decomposed in the pyrolysis process or the calcination process in the reactor to act as impurities.

In addition, ethylenediamine sodium tetraacetate (EDTA) or the like may be used to produce the polymeric material. The amount of EDTA can be used in an amount ranging from 0.01 to 0.3 moles, but if the amount is less than 0.01 moles, the additive effect function is lost.

The concentration of cerium component in the precursor solution is preferably in the range of 0.02 to 3M. If the concentration is less than 0.02 M, the effect of addition cannot be expected. If the concentration is more than 3 M, the concentration of the solution increases, and the droplets do not occur smoothly.

2) second process: spraying of droplets

In order to produce ceria powder by spray pyrolysis using the precursor solution obtained as described above, the solution is sprayed into a droplet using a spray device.

In this case, as a spray device for spraying the precursor droplets, an ultrasonic atomizer, an air nozzle sprayer, an ultrasonic nozzle sprayer, a filter expansion aerosol generator (FEAG), a disk type droplet generator, and the like may be used. . The droplets may be 0.1-100 μm in diameter.

According to the present invention, even if the final synthesized hollow or porous precursor powders have a wide size distribution, internally, they consist of uniform nano-sized primary particles, so that they have a uniform size after milling. Therefore, the droplet size or size distribution in the droplet spraying step does not significantly affect the size formation of the final ceria powder. Therefore, even if the above various droplet generating devices are applied, it is possible to mass-produce nanoseria powder of uniform size.

3) Third process: generation of nano ceria powder

A spray pyrolysis or spray drying process is then performed to convert the droplets into precursors of ceria particles in a hot tubular reactor. At this time, a temperature of 200 to 1500 ℃ is preferable for drying the precursor materials. By such high temperature heating, ceria precursor powders in a very hollow or porous form are synthesized by gases emitted by decomposition of organic or polymer precursors contained in the reaction solution. The time for the droplets to react in the tubular reactor is maintained between 0.1 and 10 seconds. If the reaction time is less than 0.1 seconds, the droplets do not cause drying and pyrolysis. If the reaction time is more than 10 seconds, it is not suitable for mass production conditions within a predetermined time.

The hollow ceria precursor powders obtained by spray pyrolysis or spray drying may be nanopowdered directly through a milling process. Preferably, the ceria precursor powders may be nanopowdered in a range of 500 to 1200 ° C. for a time of 10 minutes to 10 hours. Firing and nanophasing is then followed by milling to a uniform nano size.

The milling process can be carried out using conventional milling means, for example a ball mill, suitably for a time ranging from 10 minutes to 100 hours.

According to the invention, it is also possible to prepare ceria powder doped with a third metal by further using other metal element-containing salts in preparing the ceria precursor solution. As the third metal, one or more selected from Y, Gd, Sm, Zr, Zn, Sc, Yb, La, Al, Si, and Ti may be used in an amount ranging from 1 to 50 mol% based on the cerium salt.

The ceria powders synthesized by the modified spray pyrolysis process according to the present invention are non-aggregated and uniform nano-sizes, and thus are used as raw material powders in the polishing process of semiconductor wafers, electrolytes in fuel cells, and phosphors. Application is possible. In addition, since the process is simple and mass production is possible, it will have an excellent cost competitiveness compared to the existing ceria nano powder manufacturing process.

Hereinafter, the present invention will be described in more detail with reference to the following examples, which are only intended to explain the present invention more specifically, and the scope of the present invention according to the gist of the present invention to these examples. It will be apparent to one of ordinary skill in the art that the present invention is not limited thereto.

Example 1: Preparation of Nano Ceria Powder

A precursor solution was prepared by adding 21.7 g of cerium nitrate and 2.07 ml of ethylene glycol per 100 ml of distilled water. The total concentration of the solution was 0.5 M on a cerium basis.

The precursor solutions thus prepared were generated as micron-sized droplets using an ultrasonic atomizer, and dried and pyrolyzed in a reactor to obtain a powder. At this time, the temperature of the reactor was maintained at 1000 ℃ and the flow rate of the compressed air used as a carrier gas flowed at 30ℓ / min. The ultrasonic atomizer is a device capable of generating a large amount of droplets, was used by connecting six oscillators in series with a frequency of 1.7MHz. The device is a large capacity that sprays 3 liters of solution per hour and is the capacity available in the actual production process.

The ceria powders obtained by the spray pyrolysis were heat-treated for 3 hours while being changed at 50 ° C. intervals in a range of 900˜1200 ° C. in a kiln in an air atmosphere. The ceria precursor powders thus obtained before and after firing were nanopowdered through a milling process. The electron micrographs of the ceria nanopowders obtained by varying the milling time from 1 hour to 20 hours through the ball milling process were analyzed.

1, 2, 3 and 4 are electron micrographs of ceria powders before milling obtained when the calcination temperatures after pyrolysis in a tubular reactor at 1000 ° C. are 1000, 1050, 1100 and 1200 ° C., respectively. 1 to 4, the ceria powder before firing has a spherical shape of a very hollow and porous form, but as the firing temperature increases, the spherical shape disappears and the non-aggregated nanopowder is formed by recrystallization. As the firing temperature increased, the size of the ceria powder increased from several nanometers to 300 nanometers.

5, 6 and 7 are electron micrographs of the powders obtained when the ceria powders obtained in FIGS. 2, 3 and 4 were milled for 20 hours. It can be seen that after milling the spherical shape of the ceria powders disappeared and non-aggregated nanopowders were obtained.

Example 2 Preparation of Nano Ceria Powder According to Changes of Organic Substance Addition

Ceria powders were prepared in the same manner using the same components as in Example 1, but ceria powder was prepared while varying the amounts of citric acid and ethylene glycol, respectively. The precursor ceria powders obtained by the spray pyrolysis process at a reactor temperature of 1000 ° C. were calcined at 1100 ° C. for 3 hours and subjected to a ball milling process for 20 hours.

8 and 9 are electron micrographs of the ceria powders obtained when the addition amounts of citric acid and ethylene glycol were 0.22M, 0.15M, 0.44M, and 0.3M, respectively. From this, it can be seen that the uniformity of the obtained ceria powder increases as the amount of the organic additive is increased.

Example 3: Preparation of Nano Ceria Powder Doped with Other Metal Components

Ceria powders were prepared in the same manner as in Example 1, but a solution in which yttrium and gadolinium were added to the cerium by 10 mol% (each using nitrates) was added as the ceria precursor solution. The precursor ceria powders obtained by the spray pyrolysis process at a reactor temperature of 1000 ° C. were calcined at 1050 ° C. for 3 hours and subjected to a ball milling process for 20 hours.

10 and 11 are electron micrographs of ceria powders to which yttrium and gadolinium were added, respectively. The ceria powders synthesized when yttrium and gadolinium are added also have the same shape and nano size as before. Therefore, these powders can be applied as an electrolyte such as a fuel cell.

Comparative Example 1: Preparation of Micron Size Ceria Powder

Ceria powders were prepared by the same ingredients and methods as in Example 1, except that ethylene glycol was not added.

12 and 13 are electron micrographs of ceria powders obtained before and after milling. They were larger in micron size than the ceria powder prepared according to the present invention, and the powders obtained before milling had a spherical shape with a thick layer and some spherical shapes remained after ball milling. That is, the ceria powder having a dense structure has an irregular shape because nano powdering is difficult in a simple milling process.

According to the present invention, an organic carboxylic acid, glycol or polyhydric alcohol, EDTA, and the like are added to a ceria precursor spray solution in an appropriate amount, and sprayed and dried as droplets by spray pyrolysis to prepare precursor powders in a very hollow or porous form. After firing and milling, non-aggregated nano ceria powder can be produced in large quantities.

Claims (11)

1) preparing a ceria precursor solution by dissolving the ceria precursor material and at least one additive selected from organic carboxylic acids, glycols and polyhydric alcohols in a solvent; 2) generating droplets from the precursor solution; And 3) drying, firing and milling the generated droplets to obtain nano-ceria powder Method for producing a nano-sized ceria powder comprising a. The method of claim 1, Wherein the organic carboxylic acid is at least one selected from citric acid, malic acid, meso tartaric acid, grape acid and meconic acid. The method of claim 1, Glycol is one or more selected from ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, triethylene glycol, tetraethylene glycol, butanediol-1,4-hexylene glycoloxyylene glycol How to. The method of claim 1, And the ceria precursor material is a cerium salt selected from at least one of cerium acetate, nitrate, chloride, hydrate and oxide. The method of claim 1, The solvent is an aqueous solution of water, alcohol or weak acid. The method of claim 1, Wherein the additive is used in an amount ranging from 1: 0.001 to 2 moles per mole of ceria precursor. The method of claim 1, As an additive, a process characterized in that a mixture in the range of 1: 0.1 to 10 weight ratio of organic carboxylic acid and glycol or polyhydric alcohol is used. The method of claim 1, Wherein the concentration of cerium component in the precursor solution ranges from 0.02 to 3M. The method of claim 1, Sodium ethylenediamine sodium acetate (EDTA) is further included in the precursor solution. The method of claim 1, Wherein the precursor solution further comprises a salt of a third element selected from at least one of Y, Gd, Sm, Zr, Zn, Sc, Yb, La, Al, Si and Ti. Nano ceria powder prepared according to the method of any one of claims 1 to 10.