JPH0769624A - Production of fine powder of rare earth element oxide - Google Patents

Abstract

PURPOSE:To provide a production method of a fine powder of rare earth ele ment oxide which is useful as a source material of a rare earth element sintered body or a sintering aid for ceramics such as silicon nitride and aluminum nitride and has a high dispersibility and excellent fluidity without aggregation. CONSTITUTION:To an aq. soln. of mineral acid salt of rare earth element, a precipitant and a surfactant are added to crystallize a water-insoluble salt of rare earth element. Otherwise, a precipitant is added to crystallize a water- insoluble salt of rare earth element and then a surfactant is added and mixed. The water-insoluble salt is separated by filtering, and if necessary, washed with water and calcined. The obtd. water-insoluble double salt of rare earth element is rare earth ammonium oxialate NH4Re(C2O4)2.nH2O (Re is a rare earth element and n is >=1), rare earth hydroxide, or rare earth carbonate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing fine powders of rare earth element oxides which are useful as raw materials for rare earth element sintered bodies and sintering aids for ceramics such as silicon nitride and aluminum nitride and have good dispersibility without aggregation. It is about.

[0002]

2. Description of the Related Art Conventionally, fine powder of rare earth element oxide is prepared by adding a precipitating agent to an aqueous solution of a mineral acid salt of a rare earth element to form a water-insoluble precipitate, which is filtered, washed with water, dried and fired. It was manufactured. However, since coagulation and coagulation occur during drying and firing, the fired product becomes a granular material of about several mm, so it is crushed after firing (in most cases, wet crushing using a dispersant), but after crushing However, coarse particles due to agglomeration remain, which is not preferable as a ceramics raw material and requires a sieving step after crushing, which is troublesome, and has the disadvantages of high cost and contamination of impurities.

[0003]

SUMMARY OF THE INVENTION The present invention solves the above problems and provides a method for producing fine powder of rare earth element oxide which does not require crushing after firing.

[0004]

Means for Solving the Problems With respect to the above problems, the present inventors have examined the crystallization conditions of rare earth water-insoluble salts, and as a result, coexistence of a surfactant causes no aggregation during drying and firing, The inventors have found that a rare earth element oxide fine powder that does not require disintegration can be obtained, thoroughly studied various conditions, and completed the present invention. After crystallizing a water-insoluble salt of a rare earth element by adding a surfactant together with it, or after crystallizing a water-insoluble salt of a rare earth element with a precipitating agent and adding and mixing a surfactant, a water-insoluble salt is added. In a method for producing a fine powder of a rare earth element oxide, which is characterized by firing, after filtering and washing with water as needed, a rare earth element water-insoluble salt is a rare earth element ammonium oxalate double salt NH ₄ Re (C ₂ 0 ₄ ) ₂・ nH ₂ 0 (Here Re
Is a rare earth element, n is 1 or more), a rare earth element hydroxide or a rare earth element carbonate.

The present invention will be described in detail below. All steps of the method for producing fine powder of rare earth oxide according to the present invention are as follows. As a raw material, a rare earth element oxide is dissolved in mineral acid to obtain a free acid concentration of 1.5 mol / liter or less, and a rare earth element concentration of 0.1
~ 1.0 mol / l of a solution adjusted to a concentration of 1 to 30% by weight, an aqueous solution of oxalic acid in an amount of 2 to 2.5 times the amount of rare earth elements and an aqueous solution of 2 to 4 times the amount of oxalic acid in an amount of 28% by weight of ammonia water while stirring. To do. Examples of the mineral acid include hydrochloric acid, nitric acid, sulfuric acid, and the like, among which nitric acid is preferable. Here, it is not necessary to specify the order of adding the solutions. The formation of ammonium oxalate double salt can be easily confirmed by powder X-ray diffraction.

Here, the greatest feature of the present invention is to add ammonium oxalate or oxalic acid which is a precipitating agent and ammonia water, and at the same time, to add a surfactant and stir, to form a surface on the produced rare earth element ammonium oxalate double salt. The surface active agent is adsorbed, filtered, washed with water if necessary, dried and calcined. Alternatively, after the total amount of the rare earth element ammonium oxalate double salt is crystallized, a surfactant is added and stirred to adsorb the surfactant on the surface of the rare earth element ammonium oxalate double salt, which is then filtered off as necessary. After washing with water, it may be dried and fired.

As the surfactant, any of cationic, anionic and nonionic can be used. Among them, the cationic surfactant is particularly effective.
Acetamine 24 (Kao Co., Ltd. product name, alkylamine salt type cationic), Emar AD-25R (Kao Co., Ltd. product name, alkyl sulfate ester type anionic ), Nonipol 140 (Sanyo Chemical Industries ( Trade name, polyoxyethylene-based nonionic) and the like. The amount added is 0.01 to 10 g, preferably 0.
05-5g is good. If it is less than 0.01 g / L, the effect of addition does not appear, and if it exceeds 10 g / L, no further effect can be expected and it is uneconomical. Filtration may be carried out by a conventional method, and washing with water may be carried out as necessary. The washed rare earth element oxalic acid double salt is dried if necessary and then calcined. The baking temperature and time are also important factors, and in order to completely exchange the oxalic acid double salt for the oxide, it is preferable to set the temperature at 800 to 1,000 ° C for 1 to 4 hours. The rare earth element oxide, which is the fired product thus obtained, becomes a powder having a smooth and good flowability and does not need to be crushed, and the raw material of the rare earth element oxide sintered body, silicon nitride, aluminum nitride, etc. It is extremely useful in handling as a co-agent.

[0008]

[Function] The effect of the surfactant added when ammonium oxalate or oxalic acid and aqueous ammonia is used as the precipitant is that the surfactant is adsorbed on the surface of the precipitated particles of the rare earth element oxalic acid double salt, and the complex is not added in the drying step. It is considered to prevent the adhesion of salts to each other. As precursors of fine powders of rare earth elements, hydroxides, carbonates, etc. are used in addition to ammonium double salts of rare earth elements. Although the effect of adding a surfactant is also recognized for these, in the case of ammonium oxalate double salts The effect is most remarkable. The applicable range of the rare earth element in the present invention is Y containing La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb.
And one or more mixed rare earth element oxides selected from the group consisting of and Lu.

[0009]

EXAMPLES The embodiments of the present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. (Example 1) Yttrium oxide is dissolved in nitric acid to prepare an yttrium nitrate solution having a yttrium concentration of 0.7 mol / L and a free acid concentration of 0.3 mol / L. Separately pure water in a 5L beaker
2,900 ml, 214 g of oxalic acid dihydrate and 268 ml of 28% by weight ammonia water are charged and stirred to prepare an ammonium oxalate aqueous solution. Then, to this ammonium oxalate solution, while stirring at a stirring rotation speed of 280 rpm, while maintaining the liquid temperature at 15 to 20 ° C., 1,160 ml of the yttrium nitrate solution prepared above was added in 3 minutes to crystallize, and stirring was continued for 5 minutes. After the acetamine 24
4.5g of (cationic surfactant brand name manufactured by Kao Corporation)
added. After continuing stirring for a further 10 minutes, it was filtered off with a Buchner funnel and sprinkled with 4,500 ml of pure water for washing. Transfer the obtained cake to a quartz container and put it in an electric furnace for 900
The temperature was raised to ℃, and the temperature was further maintained at 900 ℃ for 1 hour, followed by calcination and then allowed to cool. When the fired product was passed through a stainless steel sieve having a mesh size of 425 μm, the entire amount passed through within 3 minutes, and 89.0 g of a dry powder having good flowability was obtained. The particle size distribution of this powder was measured by the laser diffraction method (Microtrac), and 50% by weight of the whole was contained in 0.9 μm or less and 90% by weight was contained in 2.3 μm or less. There wasn't.

(Example 2) Using erbium oxide as a starting material, a cake of erbium ammonium oxalate double salt was obtained under the same conditions as in Example 1. When the obtained cake was baked and sieved in the same manner as in Example 1, the whole amount was passed within 3 minutes, and 151.9 g of a smooth and free-flowing powder was obtained. When the particle size distribution of this powder was measured by a laser diffraction method, 1.1% or less contained 50% by weight of the whole, 2.6 μm or less contained 90% by weight of the whole, and coarse particles exceeding 5.0 μm were not detected.

Example 3 Using yttrium oxide as a starting material, 4.5 g of Emal AD-25R (trade name of anionic surfactant manufactured by Kao Corporation) was added in place of acetamine 24. Under the same conditions as in 1, a cake of yttrium ammonium oxalate double salt was obtained. When the obtained cake was baked and sieved in the same manner as in Example 1, the whole amount passed within 3 minutes, and 89.1 g of a dry and well-flowing powder was obtained. When the particle size distribution of this powder was measured by a laser diffraction method, 50% by weight of the whole was contained in 1.1 μm or less, 90% by weight of the whole was contained in 2.7 μm or less, and coarse particles exceeding 5.0 μm were not detected.

Example 4 Yttrium oxide was used as a starting material, and 4.5 g of nonipol 140 (a nonionic surfactant manufactured by Sanyo Chemical Industry Co., Ltd.) was used instead of acetamine 24.
A cake of yttrium ammonium oxalate double salt was obtained under the same conditions as in Example 1 except for the addition. When the obtained cake was baked and sieved in the same manner as in Example 1, the entire amount passed through within 5 minutes, and 89.0 g of a dry powder having good flowability was obtained. The particle size distribution of this powder was measured by laser diffractometry to be 1.0 μm or less and 50% by weight of the whole, 2.8
The total weight was 90% by weight or less, and coarse particles exceeding 5.0 μm were not detected.

Example 5 Using yttrium oxide as a starting material, 4.5 g of acetamine 24 was added to the ammonium oxalate solution prior to the addition of the yttrium nitrate solution to the ammonium oxalate solution, and a surfactant was added after the precipitation. A yttrium ammonium oxalate double salt cake was obtained under the same conditions as in Example 1 except that the above procedure was omitted. When the obtained cake was baked and sieved in the same manner as in Example 1, the whole amount passed within 3 minutes, and 88.8 g of a dry powder having good flowability was obtained. The particle size distribution of this powder was measured by laser diffractometry to be less than 0.8 μm, 50% by weight of the total, 2.2
The total weight was 90% by weight or less, and coarse particles exceeding 5.0 μm were not detected.

(Comparative Example 1) Under the same conditions as in Example 1, a precipitate of yttrium ammonium oxalate double salt was produced. 15
After continuing to stir for minutes, it was filtered off with a Buchner funnel without addition of surfactant. The cake thus obtained was calcined and sieved in the same manner as in Example 1. As a result, 75.7 g passed through a sieve having an opening of 425 μm by 60 minutes, but 12.9 g still remained on the sieve and passed through the sieve. The objects were also composed of coarse particles that could be seen with the naked eye. The particle size distribution of the powder that passed through the 425 μm sieve was measured by the laser diffraction method and found to be 3.2 μm or less.
50% by weight, 90% by weight of the whole less than 13.6 μm, 10
Particles having a size of more than μm accounted for 22.5% by weight of the whole particles, which required crushing and re-sieving depending on the use.

(Comparative Example 2) Under the same conditions as in Comparative Example 1, a cake of erbium ammonium oxalate double salt was obtained from erbium oxide. When the obtained cake was baked and sieved in the same manner as in Example 1, 124.8 g passed through the sieve by 60 minutes, but 22.8 g still remained on the sieve, and the cake that passed through the sieve was also visually observed. It consisted of visible coarse particles. The particle size distribution of the powder that passed through the 425 μm sieve was measured by the laser diffraction method. 3.9 μm or less contained 50% by weight of the whole, 13.7 μm or less contained 90% by weight of the whole, and particles larger than 10 μm contained the whole.
It was 16.4% by weight.

[0016]

EFFECTS OF THE INVENTION According to the present invention, a rare earth element fine oxide powder having good dispersibility and good fluidity, which is useful as a raw material for a rare earth element sintered body and a firing aid for ceramics, and has excellent dispersibility, can be prepared in a simple process. It can be manufactured at low cost and its utility value is extremely high in industry.

Claims (2)

[Claims] 1. A water-insoluble salt of a rare earth element is crystallized by adding a surfactant together with a precipitating agent to an aqueous solution of a mineral acid salt of a rare earth element, or by crystallizing a water-insoluble salt of a rare earth element with a precipitating agent. A method for producing a fine powder of rare earth element oxide, which comprises adding and mixing a surfactant after the reaction, filtering the water-insoluble salt, washing with water as needed, and then firing. 2. A water-insoluble salt of a rare earth element is a rare earth element ammonium oxalate double salt NH ₄ Re (C ₂ 0 ₄ ) ₂ · nH ₂ 0 (where Re is a rare earth element and n is 1 or more), a rare earth element. The method for producing fine powder of rare earth element oxide according to claim 1, which is a hydroxide or a carbonate of rare earth element.