JP3025157B2 - Method for producing spherical rare earth oxide - 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 spherical rare earth oxide useful as a raw material for a phosphor.

[0002]

2. Description of the Related Art Rare earth oxides are used as a raw material for phosphors such as fluorescent lamps and CRTs. As the phosphors become closer to spheres, the coating performance and luminous efficiency are better, and the rare earth oxide spheres are better. The demand for particles is strong. Phosphors are generally obtained by mixing rare earth oxides with other raw materials and fluxes in a powder form and firing the mixture. If the rare earth oxide particles are spherical, the phosphor particles obtained using the same are also used. It tends to be spherical. JP-A-3-271117, JP-A-3-2711
No. 18 discloses that spherical rare earth oxalate particles can be obtained by maintaining the temperature at 20 ° C. or lower until rare earth oxalate particles are obtained, and spherical rare earth oxides can be obtained by firing the particles. However, in all of these examples, oxalate precipitates which were separated by filtration for the purpose of removing adhering water were washed with methanol.However, in consideration of industrialization, recovery to prevent spillage as a work environment and as a countermeasure against wastewater pollution. It is not suitable for mass production because of problems such as the cost of regeneration and the possibility of explosion in the firing furnace unless methanol is completely volatilized before subsequent firing. Further, the rare earth oxides obtained according to the above-mentioned JP-A-Hei Hei 9-203 are generally excellent in terms of spherical particle shape and uniformity of particle size distribution, but those having an average particle size of about 5 μm or less are slightly difficult to make. , Tends to be slightly distorted.

[0003]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks, and it is an object of the present invention to provide a method for producing spherical particles having a uniform particle diameter stably and easily.

[0004]

Means for Solving the Problems The inventors of the present invention have studied to solve the above-mentioned problems, and have found a method for producing a spherical rare earth oxide having a uniform particle size, which can be easily processed in large quantities and industrialized. The gist of the present invention has been established. The gist of the present invention is that in the precipitation reaction between rare earth ions and oxalic acid, the temperature is kept at -5 ° C or more and 20 ° C or less and the coexistence of an organic base from the start of the reaction to filtration and washing with water. Precipitate the rare earth oxalate below, filter, wash with water and place in a stream of steam-saturated air at -5 ° C to 20 ° C, or vacuum dry at -20 ° C to 20 ° C or freeze-vacuum drying Water attached per mole of rare earth
A method for producing a spherical rare earth oxide, characterized in that the total of water and crystallization water are removed to 4.5 mol or less, followed by firing, wherein ethanolamines or hexamethylenetetramine is used as an organic base.

Hereinafter, the present invention will be described in detail. The applicable range of the present invention is yttrium as a rare earth element and lanthanoids having an atomic number of 57 to 71, and is particularly suitable for lanthanoids having an atomic number of 63 or more (63: europium) and yttrium. The spherical shape in the present invention is a true sphere,
And a substantially spherical particle having a ratio of major axis to minor axis of 1.5 or less. This is a range sufficient for applications, and spherical rare earth oxides, in which most of the particles are composed of such particles, have better fluidity than those composed of ordinary amorphous particles. Some angles of repose are small and bulk density is large. The average particle size (D ₅₀ ) is expressed on a volume basis, and 50% of the total particle volume is occupied by particles smaller than the average particle size. The measurement was performed using a Coulter counter (trade name, manufactured by Coulter Corporation). The angle of repose was measured by the tilt method. Bulk density is the loose apparent specific gravity. Non-aggregated means that individual particles are present independently and have substantially no aggregated portion.

As a method for producing a spherical rare earth oxide, first, a rare earth ion and oxalic acid are reacted at a temperature of -5 ° C. or more and 20 ° C. or less to precipitate a spherical rare earth element oxalate.
Examples of the rare earth ion source include aqueous solutions of compounds soluble in water such as rare earth chlorides and nitrates. The kind of the rare earth element may be one kind or two or more kinds. If the total rare earth concentration is too low, productivity is poor. Therefore, the rare earth element is usually at least 0.02 mol / L, preferably in the range of 0.05 to 0.5 mol / L. The reaction formula of oxalic acid and rare earth ions is as follows, and 2R ³⁺ + 3H ₂ C ₂ O ₄ ─ → R ₂ (C ₂ O ₄ ) ₃ + 6H ⁺ hydrogen ions are by-produced. Since the presence of the hydrogen ions has the effect of increasing the particle size of the rare-earth oxalate, it is necessary to neutralize the rare-earth oxalate. However, it is preferable to neutralize with an organic base in consideration of the above-mentioned reason. As the organic base, ethanolamines such as triethanolamine, and hexamethylenetetramine are preferable in view of safety, workability such as odor, and strength of the basicity, and the amount of addition is free from the amount originally present in the rare earth solution. In addition to neutralizing the acid, the amount is preferably 3 mol or less per 1 mol of rare earth, and the larger the amount, the smaller the particle size tends to be.

The amount of oxalic acid is a molar ratio with respect to the total amount of rare earths.
The range of 1.5 to 2.0 is good. If it is less than 1.5, the rare earth is not completely precipitated and the yield is poor, and 2.0 is sufficient. To carry out the reaction, an aqueous solution of a rare earth, an aqueous solution of oxalic acid and, if necessary, an aqueous solution of an organic base are prepared.
Mix after keeping below. The organic base may be previously added to the rare earth aqueous solution or oxalic acid aqueous solution. The temperature at the time of this mixing is important, and the lower the temperature, the better the sphericity tends to be obtained.
It is better to do the following. The mixing speed of the liquid also affects the particle size. The total amount of the rare earth aqueous solution and the oxalic acid aqueous solution, which is added later, is preferably added in 1 to 30 minutes. The longer the time, the larger the particle size. If the time is extremely short, the particles become finer and hardly spherical. However, when oxalic acid is added as a solid, the oxalic acid which is dissolved gradually reacts, so that it may be added quickly.

The resulting spherical rare earth oxalate is separated from the mother liquor and washed with water. As the separation, filtration, inclination, centrifugation and the like can be adopted. The water washing may be performed by dispersing or sprinkling washing using water several times the volume of the oxalate. The temperature of water used at this time is 20 ° C
It must be: The oxalate separated and washed with water immediately enters a drying step. The greatest feature of the present invention lies in this drying method. The drying is performed under a steam-saturated stream of -5 ° C or more and 20 ° C or less, or the oxalate is dried at a temperature of 20 ° C or less under vacuum drying or freeze vacuum drying. Just do it. In the case of flash drying, the smaller the amount of water vapor in the gas to be sent, the better. In the case of air, the absolute humidity is desirably 10 g / m ³ or less. As for the degree of drying, it is necessary that the total amount of adhering water and crystallization water per mole of rare earth is 4.5 mol or less, preferably 4 mol or less. If left at room temperature in excess of 4.5 mol, grain growth accompanied by a change in crystal structure occurs, and the sphere cannot be maintained. The amount of this water is calculated from the weight of the oxalate and the weight of the oxide obtained by calcining the oxalate by the chemical formula R of the oxalate.
It can be determined in consideration of ₂ (C ₂ O ₄ ) ₃ (R: rare earth element). Vacuum drying is performed at 10 to 15 ° C under a vacuum of 1.5 Pa.
It will be below the above moisture in 24 hours. Freeze-vacuum drying keeps the hydrated oxalate which has been separated and washed with water, quickly frozen to -30 to -20 ° C and dried at 0 to 5 ° C for 24 to 40 hours under a vacuum of 50 to 100 Pa to keep the spheres during crystal precipitation. The resulting spherical oxalate is obtained.

If the oxalate from which adhering water is removed is calcined at a temperature of 600 ° C. or more, a spherical rare earth oxide can be obtained. The firing conditions are not limited as long as the drying is sufficient, but it is preferable that the heating rate be 600 ° C./hr or less.

[0010]

EXAMPLES Hereinafter, the embodiments of the present invention will be described specifically with reference to examples, but the present invention is not limited to these. Example 1 1.5 L of an aqueous solution of yttrium nitrate having a concentration of 0.3 mol / L and a pH of 1.5 was charged into a 3 L beaker equipped with a baffle, a thermometer, and a stirring blade, and kept at 5 ° C. Concentration 0.5
A 1.5 L mol / L oxalic acid aqueous solution was separately prepared and kept at 7 ° C. 74.2 g of triethanolamine while stirring at 300 rpm
Was added all at once. Next, the whole amount of the oxalic acid aqueous solution was added over 7 minutes while keeping stirring at 5 ° C. After stirring for further 5 minutes, the mixture was filtered off with a Buchner funnel, sprinkled and washed with 2 L of water at 10 ° C, and then placed in a freezer at -20 ° C. After 30 minutes, remove from the freezer and place in a closed container kept at 2 ℃ -40 ℃
Degassed with a vacuum pump through a cold trap kept at a pressure of 60 Pa or less, and dried for 24 hours under a pressure of 60 Pa or less.
0.2 g was obtained (H ₂ O / Y = 3.9 (molar ratio)). Next, place it in a magnetic crucible and place it in an electric furnace at 850 ° C at 5 ° C / min.
The temperature was maintained at 850 ° C. for 1 hour, and then allowed to cool to obtain 50.2 g of yttrium oxide. When this oxide was observed with an electron microscope, it was composed of non-agglomerated, spherical particles, with an average particle size of 4.2 μm, a repose angle of 46 °, and a bulk density of 1.39 g /
It was cm ^3.

(Example 2) The precipitation of oxalate was carried out in Example 1.
The same was done. After filtering off with a Buchner funnel, washing with 2 L of water at 10 ° C and draining, place it in a constant temperature / humidity room at a temperature of 17 ° C and an absolute humidity of 6 g / m ³ , where a steady gentle wind is flowing.
It was dried for 70 hours to obtain 130.3 g of dry oxalate (H ₂
O / Y = 3.9 (molar ratio)). Next, this was placed in a magnetic crucible and calcined under the same conditions as in Example 1 to obtain 50.3 g of yttrium oxide composed of non-agglomerated spherical particles. This average particle size is
It was 4.0 μm, the angle of repose was 47 °, and the bulk density was 1.36 g / cm ³ .

(Example 3) Precipitation of oxalate, separation and washing with water were carried out in the same manner as in Example 1. The collected oxalate was placed on a metal plate fitted with a heater, a thermometer was inserted into the cake, the whole was put into a closed container, and degassed by a vacuum pump through a cold trap. The temperature of the cake is maintained at 10 to 15 ° C while maintaining the temperature of the cake at 10 to 15 ° C for 17 hours while drying by heating gently with a heater to supply latent heat of evaporation, and 127.8 g of dried oxalate (H ₂ O / Y = 3.7 Molar ratio)).
This was fired in the same manner as in Example 1 to obtain 50.0 g of yttrium oxide. Particle shape is non-agglomerated spherical particles, average particle size
It was 4.4 μm, the angle of repose was 42 °, and the bulk density was 1.31 g / cm ³ .

(Example 4) A mixed aqueous solution of yttrium nitrate and europium nitrate having a concentration of 0.3 mol / L and a pH of 1.4 (Eu /
(Y = 0.034 mol ratio) In the same manner as in Example 1 except for using (Y = 0.034 mol ratio), 128.3 g of dried oxalate was obtained. This was fired in the same manner as in Example 1 to obtain a mixed oxide of yttrium and europium.
51.5 g were obtained. When observed with an electron microscope, it consisted of non-agglomerated spherical particles, with an average particle size of 3.9 μm and an angle of repose of 49.
° and bulk density was 1.34 g / cm ³ .

Example 5 157.3 g of oxalate (H ₂ O / Gd = 3.5 (molar ratio) in the same manner as in Example 1 except that an aqueous solution of gadolinium nitrate having a concentration of 0.3 mol / L and a pH of 1.3 was used. )) And calcined in the same manner as in Example 1 to obtain 80.8 g
Gadolinium oxide was obtained. Observation with an electron microscope revealed that the particles were spherical and had an average particle size of 3.6 μm, a repose angle of 48 °, and a bulk density of 2.04 g / cm ³ .

(Example 6) In place of triethanolamine, 69.7 g of hexamethylenetetramine was added and completely dissolved, and the subsequent steps were carried out as in Example 1. 12
7.7 g of dry oxalate (H ₂ O / Y = 3.7 (molar ratio)) were obtained. This was fired in the same manner as in Example 1 to obtain 50.1 g of yttrium oxide. It was composed of spherical particles, and had an average particle size of 4.3 μm, a repose angle of 40 °, and a bulk density of 1.45 g / cm ³ .

(Example 7) An aqueous solution of oxalic acid having a concentration of 0.4 mol / L
2.5 L of the solution was charged into a 3 L beaker equipped with a baffle, a thermometer, and a stirring blade, and kept at 5 ° C. To this 11
4.9 g of triethanolamine was added and mixed uniformly. 1.2 mol / L while keeping at 5 ℃ while stirring at 300rpm
Then, 500 ml of an aqueous solution of yttrium nitrate having a pH of 1.0 was added over 4.5 minutes. Thereafter, the same treatment as in Example 1 was performed to obtain 158.6 g.
Was obtained (H ₂ O / Y = 3.4 (molar ratio)).
This was fired in the same manner as in Example 1 to obtain 67.0 g of yttrium oxide. Consisting of spherical particles, average particle size 3.4μ
m, the angle of repose was 46 °, and the bulk density was 1.38 g / cm ³ .

Comparative Example 1 Oxalates formed, separated and washed under the same conditions as in Example 1 were calcined under the same conditions as in Example 1 without the drying step of removing adhering water, and 50.3 g of oxidized water was oxidized. Yttrium was obtained. Observation with an electron microscope revealed that the particles consisted of rod-shaped, plate-shaped, and amorphous particles with an average particle size of 3.2
μm, angle of repose was 70 ° or more, measurement was difficult, and bulk density was 0.53 g / cm ³ .

(Comparative Example 2) The oxalate formed and separated under the same conditions as in Example 1 was dried by leaving it in a blow dryer kept at 45 ° C. for 14 hours, and dried 124.5 g of oxalate (H ₂ O / Y =
3.2 (molar ratio)). This was fired in the same manner as in Example 1 to obtain 50.4 g of yttrium oxide. When observed with an electron microscope, it consisted of angular particles of various sizes from fine to coarse, with an average particle size of 10.9 μm and a repose angle.
It was 64 ° and the bulk density was 0.74 g / cm ³ .

(Comparative Example 3) 140.8 g of dry oxalate (H ₂ O / Y = 5.2 (molar ratio) in the same manner as in Example 1 except that the time for placing the frozen cake in a vacuum was 11 hours. )
I got This was fired in the same manner as in Example 1 to obtain 50.2 g of yttrium oxide. Observation with an electron microscope showed that more than half of the particles were spherical, but the rest were irregular particles that seemed to have collapsed from spherical, with an average particle size of 6.1μ
m, angle of repose was 48 ° and bulk density was 1.08 g / cm ³ .

Comparative Example 4 125.2 g of dry oxalate (H ₂ O / Y = 3.4 (molar ratio)) was prepared in the same manner as in Example 1 except that the liquid temperature during precipitation was kept at 25 ° C. Obtained. This was fired in the same manner as in Example 1 to obtain 50.0 g of yttrium oxide. Observation with an electron microscope revealed that the particles were mainly elongated plate-like particles, the average particle diameter was 8.5 μm, the angle of repose was 70 ° or more, measurement was difficult, and the bulk density was 0.66 g / cm ³ .

Comparative Example 5 128.7 g of a dry oxalate (H ₂ O / Y = 3.8 (molar ratio)) was obtained in the same manner as in Example 1 except that the addition of triethanolamine was omitted. This was fired in the same manner as in Example 1 to obtain 50.2 g of yttrium oxide. Although this oxide was non-agglomerated and spherical, the average particle size was as large as 6.8 μm, the angle of repose was 38 °, and the bulk density was 1.49 g / cm ³ .

[0022]

According to the present invention, non-agglomerated spherical rare earth oxide particles can be stably and easily obtained, and their industrial value is extremely high.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C01F 17/00 C09K 11/08-11/78

Claims (2)

(57) [Claims] In the reaction between rare earth ions and oxalic acid, the mixture is kept at -5 ° C or more and 20 ° C or less from the start of the reaction to filtration and washing with water, and rare earth oxalate is precipitated in the presence of an organic base, followed by filtration and washing with water. After that, place in a steam-saturated air stream of -5 ° C or more and 20 ° C or less, or apply vacuum drying or freezing vacuum drying at -20 ° C or more and 20 ° C or less per mole of rare earth.
A method for producing a spherical rare earth oxide, which comprises firing after removing the sum of water landing and crystallization water to 4.5 mol or less . 2. The method for producing a spherical rare earth oxide according to claim 1, wherein the organic base is ethanolamines or hexamethylenetetramine.