JP2883522B2 - Method for producing rare earth oxide fine powder - Google Patents

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 a rare earth element oxide fine powder having no agglomeration and having good dispersibility useful as a raw material for a rare earth element sintered body and a sintering aid for ceramics such as silicon nitride and aluminum nitride. It is about.

[0002]

2. Description of the Related Art Conventionally, fine powders of rare earth element oxides are prepared by adding a precipitant to a rare earth element mineral salt aqueous solution to form a water-insoluble precipitate, which is separated by filtration, washed with water, dried and calcined. Had been manufactured. However, agglomeration and coagulation occur during drying and firing, and the fired material becomes granular matter of about several mm. Therefore, the material is crushed after firing (often wet grinding using a dispersant). However, coarse particles due to agglomeration remain, which is not preferable as a ceramic raw material, and requires a sieving step after crushing, which is troublesome, and has the disadvantages of high cost and impurity contamination.

[0003]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for producing a rare earth element oxide fine powder which does not require crushing after firing.

[0004]

The present inventors have studied the crystallization conditions of the rare-earth water-insoluble salts with respect to the above-mentioned problems. As a result, by coexisting a surfactant, there is no aggregation during drying and firing, It has been found that a rare earth element oxide fine powder that does not require crushing can be obtained, and various conditions have been sufficiently studied to complete the present invention. The gist of the invention is that a rare earth element mineral salt aqueous solution is added with a precipitant. After adding a surfactant and crystallizing the water-insoluble salt of the rare earth element, or after crystallizing the water-insoluble salt of the rare earth element with the precipitant, adding and mixing the surfactant, the water-insoluble salt is removed. The method for producing a rare earth element oxide fine powder is characterized in that the rare earth element is finely filtered, washed with water as necessary, and then calcined, wherein the water-insoluble salt of the rare earth element is a rare earth element ammonium oxalate double salt NH ₄ Re (C _{20 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.

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

The most important feature of the present invention is that a surfactant is added and stirred simultaneously with addition of ammonium oxalate or oxalic acid as a precipitant and aqueous ammonia to form a rare earth element ammonium oxalate double salt on the surface. The surfactant is adsorbed and separated by filtration, washed with water if necessary, dried and calcined. Alternatively, after the entire amount of the rare earth element ammonium oxalate double salt has been crystallized, the surfactant is added to the surface of the rare earth element ammonium oxalate double salt formed by stirring, and the surfactant is adsorbed and separated by filtration. After rinsing accordingly, drying and baking may be performed.

As the surfactant, any of cationic, anionic and nonionic surfactants can be used. Among them, cationic surfactants are particularly effective.
Acetamine 24 (trade name, manufactured by Kao Corporation, alkylamine salt-based cationic), Emar AD-25R (trade name, manufactured by Kao Corporation, alkyl sulfate salt-based anionic ), Nonipol 140 (Sanyo Chemical Industries, Ltd.) (Trade name, polyoxyethylene-based nonionic), and the like. The addition amount is 0.01 to 10 g per liter of the total amount of the pure surfactant, preferably 0.1 g.
05 to 5g is good. If the amount is less than 0.01 g / L, the effect of addition is not exhibited, and if it exceeds 10 g / L, no further effect can be expected and it is uneconomical. The filtration may be performed by a conventional method, and the washing may be performed as needed. The washed rare earth element oxalate double salt is dried and fired if necessary. The firing temperature and time are also important factors, and it is preferable to set the temperature at 800 to 1,000 ° C. for 1 to 4 hours in order to completely replace the double oxalate with the oxide. The fired product of the rare-earth element oxide thus obtained is a smooth and fluid powder having no need to be crushed, and is used as a raw material for a rare-earth-element oxide sintered body, such as silicon nitride and aluminum nitride. It is extremely useful in handling as a binder.

[0008]

[Function] When ammonium oxalate or oxalic acid and ammonia water are used as the precipitant, the action of the surfactant added is such that the surfactant is adsorbed on the surface of the precipitated particles of the rare earth element oxalate double salt, and the surfactant is added in the drying stage. It is considered to be to prevent the adhesion of salts. As the precursor of the rare earth element fine powder, in addition to the rare earth element ammonium double salt, hydroxides, carbonates, etc. are used. The effect is most pronounced. The applicable range of the rare earth element in the present invention is La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb containing Y.
And one or more mixed rare earth element oxides selected from the group consisting of and Lu.

[0009]

EXAMPLES Hereinafter, embodiments of the present invention will be described specifically 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, the solution temperature was maintained at 15 to 20 ° C., 1,160 ml of the previously adjusted yttrium nitrate solution was added in 3 minutes to crystallize, and stirring was continued for 5 minutes. After that, acetamine 24
4.5 g of Kao Corporation's brand name of cationic surfactant
added. After stirring was further continued for 10 minutes, the mixture was filtered with a Buchner funnel and sprinkled with 4,500 ml of pure water for washing. The resulting cake was transferred to a quartz container and placed in an electric furnace for 2 hours.
The temperature was raised to 900.degree. C., and calcined at 900.degree. When the fired product was passed through a stainless steel sieve having an opening of 425 μm, the whole amount passed within 3 minutes, and 89.0 g of a smooth and flowable powder was obtained. When the particle size distribution of this powder was measured by laser diffraction method (Microtrac), 0.9% or less contained 50% by weight and 2.3% or less contained 90% by weight, and coarse particles exceeding 5.0μm were detected. Did not.

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 passed within 3 minutes, and 151.9 g of a smooth and flowable 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, and 2.6% or less contained 90% by weight of the whole, and coarse particles exceeding 5.0m were not detected.

Example 3 Example 4 was repeated except that 4.5 g of Emal AD-25R (trade name of an anionic surfactant manufactured by Kao Corporation) was added instead of acetamine 24 using yttrium oxide as a starting material. Under the same conditions as in 1, a cake of double yttrium ammonium oxalate 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 smooth and flowable 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 and 2.7μm or less contained 90% by weight of the whole, and coarse particles exceeding 5.0μm were not detected.

Example 4 Using yttrium oxide as a starting material, 4.5 g of Nonipol 140 (trade name of a nonionic surfactant manufactured by Sanyo Chemical Industries, Ltd.) instead of acetamine 24
A cake of ammonium yttrium 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 whole amount passed within 5 minutes, and 89.0 g of a smooth and flowable powder was obtained. The particle size distribution of this powder was measured by a laser diffraction method.
90% by weight of the total weight was contained below μm, and coarse particles exceeding 5.0 μm were not detected.

(Example 5) Using yttrium oxide as a starting material, acetamine 24 (4.5 g) was added to an ammonium oxalate solution before adding the yttrium nitrate solution to the ammonium oxalate solution, and a surfactant was added after precipitation. A cake of ammonium yttrium oxalate double salt was obtained under the same conditions as in Example 1 except that this was not performed. 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 smooth and flowable powder was obtained. The particle size distribution of this powder was measured by a laser diffraction method.
90% by weight of the total weight was contained below μm, and coarse particles exceeding 5.0 μm were not detected.

Comparative Example 1 A precipitate of ammonium yttrium oxalate double salt was formed under the same conditions as in Example 1. Fifteen
After stirring for minutes, the mixture was filtered off on a Buchner funnel without adding a surfactant. The obtained cake was calcined and sieved in the same manner as in Example 1. By 60 minutes, 75.7 g passed through a sieve having an opening of 425 μm, but 12.9 g still remained on the sieve and passed through the sieve. The object was also composed of coarse particles visible to the naked eye. The particle size distribution of the powder passing through a 425 μm sieve was measured by laser diffraction method.
50% by weight, 13.6μm or less contains 90% by weight of the whole, 10%
Particles exceeding μm accounted for 22.5% by weight of the whole, and required crushing and re-sieving for some applications.

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. It consisted of visible coarse particles. The particle size distribution of the powder that passed through the 425 μm sieve was measured by laser diffraction method. 3.9 μm or less contained 50 wt% of the whole, 13.7 μm or less contained 90 wt% of the whole, and particles exceeding 10 μm
16.4% by weight.

[0016]

According to the present invention, a rare earth element oxide fine powder having no agglomeration and excellent dispersibility and excellent fluidity useful as a raw material for a rare earth element sintered body and a firing aid for ceramics can be reduced in a simple process. It can be manufactured at low cost, and its industrial value is extremely high.

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-4-238813 (JP, A) JP-A-64-14142 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C01F 17/00 C04B 35/42-35/49

Claims (2)

(57) [Claims] 1. A water-insoluble salt of a rare earth element is crystallized by adding a surfactant together with a precipitant to an aqueous solution of a mineral salt of a rare earth element to crystallize a water-insoluble salt of the rare earth element. A method for producing a rare earth element oxide fine powder, which comprises adding a surfactant, mixing the resulting mixture, filtering out a water-insoluble salt, washing with water if necessary, and calcining. 2. A water-insoluble salt of a rare earth element is a rare earth element ammonium oxalate double salt NH ₄ Re (C ₂ O 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 a rare earth element oxide fine powder according to claim 1, which is a hydroxide or a rare earth element carbonate.