JPH10101411A - Production of fine powder of yttrium aluminum garnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce YAG fine particle powder excellent in dispersibility with low coagulation without using urea. SOLUTION: A mineral acid salt aqueous solution containing a mixture of a yttrium salt and an aluminum salt so that these yttrium and aluminum salts may give the garnet composition are admixed to an aqueous carbonate solution of 7.5-11.0pH by addition of an alkali to crystallize out a water-insoluble salt of yttrium ion and aluminum ion. Then, the reaction mixture is aged, filtered, washed with water, and fired to form a fine particle powder of yttrium aluminum garnet. Since this fine particle powder is less coagulable with high dispersibility, YAG fine particle powder excellent in sintering properties can be produced. Urea is not needed and the precipitation can be formed at a lowered temperature and the anions which cause the secondary particle growth can be readily removed and the environmental problems caused by liberation of ammonia or the remaining urea can be reduced.

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 YAG powder useful for producing translucent YAG ceramics which can be used for an oscillator for a laser, an envelope for a discharge lamp, a window material as a substitute for sapphire, a decorative article and the like. It is. YA
The composition of G is Y3Al5O12 and the theoretical density is 4.55 g / cm.
³

[0002]

2. Description of the Related Art Translucent YAG ceramics have been produced by hot pressing (US Patent:
No. 3,767,745), and a direct sintering method by ball mill mixing of oxide fine powder and CIP molding (hydrostatic molding) (Japanese Patent Application Laid-Open No. 3-218963). In the hot press method, the equipment is expensive and the mass productivity is poor, and it is difficult to manufacture a complex-shaped product which is an important feature of ceramics. The oxide fine powder mixing method can provide a sintered body with good translucency.However, in order to increase the reactivity and suppress the separation of yttria and alumina due to the difference in specific gravity during mixing, ultrafine yttria powder is used. Must be used. Therefore, it is necessary to produce yttria and alumina separately. Further, since the ultrafine powder is used, the molding density is low, and as a result, shrinkage during sintering increases, and dimensional accuracy decreases. Further, when an extrusion molding method or an injection molding method is applied as a mass production method, the molding pressure is increased, and contamination due to wear of a kneader or a screw is increased. As a result, high quality ceramics cannot be obtained.

As a method for producing a single-phase YAG fine powder, a sol-gel method and a hydroxide precipitation method have been reported so far. I do not have. This is because the precipitated particles of the precursor are gel-like fine particles, and as a result of drying and agglomeration, seizure and grain growth of the particles during calcination become remarkable, and the dispersibility of the primary particles decreases. As an example in which this point is improved, a direct decomposition method of sulfate (JP-A-59-207555) is disclosed. However, this method causes air pollution due to sulfur dioxide gas generated by decomposition, so that it is necessary to recover sulfur dioxide gas. Furthermore, since it contains a large amount of sulfate, the sulfate must be decomposed at a high temperature, and the growth of primary particles during calcination becomes remarkable. Therefore, a good translucent sintered body cannot be obtained without a sintering aid such as MgO or SiO2.

[0004] Such a problem was solved by a urea method, which is a kind of uniform precipitation method, as disclosed in Japanese Patent Laid-Open No. 2-928.
No. 17 publication. According to this, sulfate ions are added to an aqueous solution of a mixture of mineral salts mixed with a YAG composition, urea is added thereto, and the mixture is heated, and a granular precipitate is formed by ammonia generated by hydrolysis of urea. The resulting precipitate is in the form of granules, which are filtered, washed with water, dried and calcined to obtain Y having good dispersibility.
AG fine powder. However, in this method, in order to accelerate the hydrolysis of metal ions, urea is required at least 7 times the amount required for neutralization. The generated ammonia has a bad smell, and the undecomposed urea contained in the wastewater pollutes the environment.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to produce a YAG fine powder having low cohesiveness and excellent dispersibility without using urea.

[0006]

According to the present invention, an alkali is added to pH 7.
A mineral salt aqueous solution in which a yttrium salt and an aluminum salt are mixed so as to have a garnet composition is added to an aqueous carbonate solution having a concentration of 5 to 11.0 to crystallize a water-insoluble salt of yttrium ion and aluminum ion. Thereafter, the reaction solution is aged, filtered, washed with water, and calcined to obtain fine yttrium aluminum garnet powder.

Preferably, the aging is performed at least by the pH of the reaction solution.
Is reached, and preferably the total concentration of the yttrium salt and the aluminum salt in the aqueous mineral salt solution is 0.005 to 1.0 mol / L.

The yttrium aluminum garnet fine powder (hereinafter referred to as YAG fine powder) obtained by the present invention has little aggregation and the average primary particle size is, for example, 0.01 to 0.2 μm.
m and excellent dispersibility, it can be used for producing a transparent YAG sintered body. In this specification, the particle size means an average particle size.

The precipitate (water-insoluble salt) obtained in the present invention is crystallographically amorphous, but the form is particulate,
Filtration and washing with water are easy as in the case of the particulate precipitate obtained by the urea method. The composition of the precipitate with carbonate or basic carbonate, because it is not a precipitation of hydroxides, Cl are contained in the raw material base salt causes of secondary grain growth ^- the removal of such extraneous anions ^- and NO3 Is easy. In another experiment, the inventors found that irrelevant anions in the precipitate, that is, anions released from the precipitate, promoted secondary particle growth during calcination and hindered the sinterability of the YAG fine powder. I found it. The concentration of irrelevant anions in the precipitate is the value after washing with water, 2000 wt.
ppm or less is preferred.

In the present invention, since urea is not used for precipitation, the precipitation reaction can be carried out at room temperature, and there is no need to use a large excess of a precipitating agent which does not directly participate in the precipitation reaction as in the case of urea. Similarly, there is little odor due to ammonia, and there is no environmental impact due to urea in wastewater.

In the present invention, inorganic salts of yttrium and aluminum, such as hydrochloric acid, nitric acid, and sulfuric acid, that is, mineral salts are dissolved in water. Then, for example, these solutions are prepared by adjusting the total metal ion concentration of yttrium and aluminum to, for example, 0.00.
Mix according to the YAG composition so as to be 5 to 1.0 mol / L. When the metal ion concentration is higher than the above range, the contact between the particles during the precipitation is increased, so that the particles are seized by calcination, resulting in a powder having low dispersibility. The metal ion concentration may be lower than 0.005 mol / L, but is preferably 0.005 mol / L or more because productivity is reduced.

The above mineral salt solution is added dropwise, for example, with stirring to an aqueous solution of carbonate adjusted to pH 7.5 to 11.0 by adding an alkali. The method of addition is not limited to dropping, and any method may be used as long as a mineral salt aqueous solution is gradually added to a carbonate aqueous solution. The aqueous solution of the carbonate is not particularly limited, but ammonium carbonate, ammonium hydrogen carbonate,
Ammonium hydrogen carbonate, sodium carbonate,
An aqueous solution such as sodium hydrogencarbonate can be used. After completion of the dropwise addition, the mixture is aged for 30 minutes to 100 hours with stirring. The pH of the carbonate aqueous solution decreases as the yttrium and aluminum mineral salt aqueous solution is dropped, and thereafter gradually increases to a constant value. Therefore, the aging may be performed at least until the pH rises and reaches a constant value, and there is no difference in the sinterability even after aging for a long time. The ripening temperature is not particularly limited. However, if the temperature is too high, the ripening proceeds rapidly, and the particle size distribution of the resulting precipitated particles tends to be widened.
~ 60 ° C is preferred. The mechanism of aging is not clear, but the particle size is small immediately after dropping, and the YAG raw material powder produced without aging increases the seizure of particles during calcination as a result of dry agglomeration and dispersibility. It will be low.

The precipitate obtained after aging is dried after repeating filtration and washing with water, for example, several times. At this time, Cl ^- or NO
Concentration of irrelevant anions such as 3 ^- and SO4 ^2- is 2000wtp
pm or more, secondary particle growth during calcination becomes remarkable,
It is preferable to sufficiently perform washing until the concentration becomes lower than this concentration. The obtained precipitate is calcined, for example, after drying to obtain a YAG fine powder. The calcination temperature is not particularly limited.
If the temperature is lower than 50 ° C., the precipitate is not sufficiently decomposed.
At a temperature of 500 ° C. or higher, sintering of the particles progresses and dispersion becomes difficult even by pulverization by a ball mill. Therefore, 6
It is appropriate to calcine at 50 to 1500 ° C. The YAG fine powder thus obtained has less agglomeration and an average primary particle size of, for example, 0.01 to 0.2 μm and is excellent in dispersibility.

According to the present invention, a YAG fine powder which is useful as a raw material of a translucent YAG ceramic and has excellent sinterability due to its low agglomeration and good dispersibility can be produced by a simple process at a low cost. Further, there are no problems such as a bad smell due to ammonia and contamination of waste water due to excess urea. Examples will be described below, but the present invention is not limited to these examples.

[0015]

Example 1 0.5 mol / L yttrium nitrate aqueous solution 30
0 ml and 500 ml of a 0.5 mol / L aqueous solution of aluminum nitrate were placed in a 1 L beaker and mixed to obtain a mixed solution having a YAG composition. This solution was added to 800 ml of a 2M aqueous solution of ammonium bicarbonate adjusted to pH 8.0 by adding aqueous ammonia.
It was added dropwise at a rate of ml / min. At this time, the mixed solution of the YAG composition and the aqueous solution of ammonium bicarbonate were both placed in a thermostatic oven for 2 hours.
Maintained at 5 ° C. The minimum value of the pH during the dropping is 7.0.
After about 3 hours from the completion of the dropwise addition, the pH reached a constant value of 8.0. After completion of the dropping, the mixture was aged at 25 ° C. for 24 hours, and then filtered and washed with water four times. In the embodiment, ripening (curing) is continued even after the pH becomes constant, but the ripening may be stopped when the pH becomes constant. By repeated filtration and washing with water, the concentrations of irrelevant anions, in this case, nitrate ions and free carbonate ions, in the precipitate were reduced to 2000 wtppm or less. The precipitate after washing with water is amorphous, but the form is granular and can be easily filtered and washed with water, and the composition is carbonate or basic carbonate.

After drying the amorphous precipitate in air at 120 ° C., it is calcined in air at 1300 ° C. for 3 hours to obtain primary particles having excellent dispersibility and an average particle size of 0.1 μm.
YAG fine particles of 0.18 μm in secondary particles were obtained. After 2 g of the obtained YAG fine particles were primarily molded at a pressure of 100 kgf / cm ² using a 20φ mold, 2To
CIP molding was performed at a pressure of n / cm ² and vacuum sintering was performed at 1650 ° C. for 3 hours. The sintered body has reached the theoretical density, and both sides of the sintered body are mirror-polished to a thickness of 2 mm.
The measured linear light transmittance at 0 nm was 79%.

[0017]

Examples 2 to 16 An aqueous yttrium chloride solution and an aqueous aluminum chloride solution were mixed so as to have a YAG composition having a predetermined concentration. 10 L of the mixed solution was added to 8 L of an aqueous carbonate solution adjusted to a predetermined pH by adding aqueous ammonia to a volume of 150 ml / ml.
It was dropped at a rate of minutes.

The following operations were carried out in the same manner as in Example 1 except for the points specifically pointed out, and YAG fine powder was prepared by variously changing the metal ion concentration, the kind and concentration of carbonate, pH, aging time and calcination temperature. (Tables 1 and 2) were vacuum-sintered at 1650 ° C. for 1 hour. Table 2 shows the linear transmittance of the obtained sample.
In addition, filtration and washing were repeated four times for each precipitate, and the concentration of irrelevant anions in the precipitate was set to 2000 wtppm or less. In addition, in each sample, the pH once decreased during the course of the dropping of the mineral salt, and then increased again to reach a steady value. In Comparative Example 5, the aging time in Example 1 was shortened, and the aging was stopped before the pH reached a steady value.

As is apparent from Tables 1 and 2, the pH of the aqueous solution of the mineral salt at the time of dropping is lower than 7.5 (Comparative Examples 1 and 2) or higher than 11.0 ( Comparative Examples 3 and 4),
A transparent sintered body cannot be obtained. If the pH is not aged until it reaches a steady value (Comparative Example 5), the light transmittance decreases. Similarly, if the metal ion concentration exceeds 1.0 mol / L (Comparative Example 6).
Light transmittance decreases. From these facts, the pH at the time of dropping the aqueous solution of the mineral acid salt is limited to 7.5 to 11.0, the metal ion concentration is preferably 0.005 to 1.0 mol / L, and the ripening is p
It is preferable to carry out until H reaches a steady value.

[0020]

Table 1 Precipitation conditions for YAG raw material * Metal ion concentration Carbonate Carbonate concentration pH Reaction / curing Curing time (mol / L) Type (mol / L) Temperature (° C) (hr) Example 2 0.005 NH4・ H ・ CO3 1.0 7.5 35 12 Example 3 0.008 NH4 ・ H ・ CO3 2.0 9.0 35 12 Example 4 0.008 (NH4) 2 ・ CO3 2.0 9.0 35 48 Example 5 0.008 (NH4) 2 ・ CO3 2.0 10.5 35 8 Example 6 0.025 NH4 ・ H ・ CO3 1.5 10.0 10 24 Example 7 0.025 NH4 ・ H ・ CO3 1.5 10.0 10 48 Example 8 0.025 NH4 ・ H ・ CO3 1.5 10.0 10 100 Example 9 0.025 Na2CO3 2.0 7.9 60 4 Example 10 0.025 NaHCO3 2.0 7.9 60 12 Example 11 0.025 NaHCO3 2.0 9.2 60 12 Example 12 0.025 NaHCO3 2.0 10.0 60 12 Example 13 0.3 NH4 ・ H ・ CO3 1.0 8.0 35 24 Example 14 1.0 NH4 ・ H ・ CO3 1.0 8.0 35 72 Example 15 0.6 (NH4) 2 ・ CO3 2.0 8.0 35 24 Example 16 0.3 (NH4) 2 ・ CO3 2.5 8.0 35 24 Comparative Example 1 0.02 NH4 ・ H ・ CO3 1.0 5.5 35 72 Comparative Example 2 0.02 NaHCO3 1.5 6.2 35 72 Comparative Example 3 0.02 NaHCO3 2.0 12.0 5 36 Comparative Example 4 0.02 NH4 ・ H ・ CO3 2.5 12.0 5 36 Comparative Example 5 0.5 NH 4 ・ H ・ CO3 2.0 8.0 25 1/3 Comparative Example 6 2.0 NH4 ・ H ・ CO3 2.0 8.0 35 72 * The metal ion concentration is the total concentration of yttrium ions and aluminum ions. * (NH4) 2.CO3 is actually ammonium hydrogen carbonate carbamate. * pH is the value before dropping the mixed aqueous solution of yttrium salt and aluminum salt. * Curing means ripening, except for Comparative Example 5, ripening until the pH reaches a steady value.

[0021]

Table 2 Ceramic properties of YAG fine powder * Calcination temperature Primary particles Secondary particles Sintered density Transmittance (° C) Diameter (μm) Diameter (μm) (g / cm ³ ) (%) Example 2 1150 0.16 0.21 Theoretical density 60.2 Example 3 1150 0.11 0.18 〃 69.9 Example 4 800 0.04 0.35 〃 69.9 Example 5 1150 0.11 0.19 〃 67.4 Example 6 1300 0.07 0.30 〃 71.3 Example 7 1300 0.09 0.25 〃 72.6 Example 8 1300 0.09 0.14 〃 72.6 Example 9 1200 0.18 0.25 〃 65.3 Example 10 1200 0.18 0.25 〃 65.3 Example 11 1300 0.15 0.21 〃 62.2 Example 12 1500 0.20 0.28 〃 59.9 Example 13 1150 0.15 0.23 〃 61.1 Example 14 1150 0.15 0.21 〃 62.0 Example 15 650 0.01 0.35 〃 68.8 Example 16 1150 0.14 0.19 〃 69.2 Comparative Example 1 1200 0.008 0.98 4.21 0 Comparative Example 2 1150 0.009 1.21 4.33 0 Comparative Example 3 1350 0.03 0.92 4.23 0 Comparative Example 4 800 0.008 1.51 4.20 0 Compare Example 5 1300 0.008 0.62 4.55 35.5 Comparative Example 6 1300 0.008 0.70 4.55 30.2 * Particle size was evaluated by TEM observation. * Theoretical density 4.55 g / cm ³ . * The linear light transmittance is measured at a wavelength of 600 nm.

Claims (3)

[Claims] 1. A mineral salt aqueous solution in which a yttrium salt and an aluminum salt are mixed so as to have a garnet composition is added to an aqueous carbonate solution adjusted to pH 7.5 to 11.0 by adding an alkali to form a yttrium ion. And crystallize a water-insoluble salt with aluminum ions, and then the reaction solution is aged,
A method for producing fine yttrium aluminum garnet powder, comprising filtering, washing with water, and firing to obtain fine yttrium aluminum garnet powder. 2. The method for producing fine yttrium aluminum garnet powder according to claim 1, wherein the aging is performed at least until the pH of the reaction solution reaches a certain value. 3. The total concentration of the yttrium salt and the aluminum salt in the aqueous mineral salt solution is 0.005 to 1.0 mol / L.
The method for producing fine yttrium aluminum garnet powder according to claim 1, characterized in that: