JPH10101334A - Production of powdery starting material for yttrium aluminum garnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain powdery starting material for yttrium aluminum garnet having satisfactory dispersibility and giving a transparent sintered compact by adding an org. hydroxy acid to aq. soln. of mineral acid salts of Y and Al mixed in such a ratio as to give a garnet compsn., neutralizing the soln. with urea and calcining the resultant precipitate. SOLUTION: An org. hydroxy acid, one of precursor is added to an aq. soln. of mineral acid salts of Y and Al mixed in such a ratio as to give a garnet compsn., the soln. is neutralized with urea and the resultant precipitate is calcined to produce the objective powdery starting material for yttrium aluminum garnet(YAG) having satisfactory dispersibility and high sinterability and giving a transparent sintered compact. Since sulfuric acid is not used, environmental problem due to gaseous SO2 is not caused at the time of firing. Lactic acid or tartaric acid may be used as the org. hydroxy acid and this acid is added by an amt. (mol) 0.1-5 times the total cocn. of Y and Al ions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a YAG aluminum garnet (YAG) ceramic which is useful for producing a translucent yttrium aluminum garnet (YAG) ceramic which can be used for an oscillator for a laser, an envelope for a discharge lamp, a window material for replacing sapphire, a decorative article and the like. The present invention relates to a method for producing a raw material powder. The composition of YAG is Y3Al
In 5 O12, the theoretical density of 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. In addition, since the ultrafine powder is used, the molding density is low, and as a result, shrinkage during sintering increases, making it difficult to apply to applications requiring dimensional accuracy. 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) and a sulfuric acid-added urea method (JP-A-2-92817) are disclosed.
However, in the direct sulfate decomposition method, a large amount of sulfur dioxide gas generated by decomposition causes air pollution, and enormous cost is required to recover the sulfur dioxide gas. Furthermore, since it contains a large amount of sulfate, the decomposition and firing temperature of sulfate must be increased,
The growth of primary particles becomes significant. For this reason, MgO or Si
Without a sintering aid of O2, a good translucent sintered body cannot be obtained. In the case of the sulfuric acid-added urea method, a translucent sintered body can be manufactured without using a sintering aid. That is, according to this method, an easily sinterable raw material powder having little aggregation and good dispersibility can be obtained. However, since this precipitate contains sulfate, an environmental problem occurs due to sulfurous acid gas at the time of decomposition and firing.

[0005]

An object of the present invention is to provide a transparent YA without using sulfuric acid.
An object of the present invention is to produce an easily sinterable YAG raw material powder that is useful as a raw material for a G sintered body, has low agglomeration and has good dispersibility.

[0006]

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for producing a precipitate by neutralizing an aqueous solution of a mineral acid salt mixed so that the mixing ratio of an yttrium salt and an aluminum salt becomes a garnet composition with urea to form a precipitate. In the method of calcining to obtain yttrium aluminum garnet raw material powder, the mineral salt aqueous solution contains at least one member selected from the group consisting of organic hydroxy acids and precursors thereof.

Here, the organic hydroxy acid is an organic compound having a carboxylic acid group and a hydroxyl group, such as lactic acid, tartaric acid, citric acid and glyceric acid. The substance used is not limited to these organic hydroxy acids, but may be salts or amides of acid anhydrides. However, a substance which is water-soluble and which is present as a hydroxy acid or a salt thereof at the time of formation of a precipitate from the beginning is preferred. As the salt form, an ammonium salt is particularly preferred in order to avoid mixing of foreign metal ions into the precipitate.

Preferably, the concentration of at least one member of the group consisting of the organic hydroxy acids and their precursors is
The molar ratio is 0.1 to 5.0 times the total concentration of yttrium ions and aluminum ions. Within this range, the rate of hydrolysis of aluminum or yttrium can be set to an appropriate value, and a yttrium aluminum garnet raw material powder having particularly high sinterability can be obtained.

[0009]

The operation and effect of the present invention will be described. In the present invention, when a precipitate is formed by the urea method, an organic hydroxy acid or a precursor thereof, that is, a substance which is decomposed during the reaction to act as an organic hydroxy acid, is dissolved in an aqueous solution of a mineral salt comprising a mixture of an yttrium salt and an aluminum salt. To exist. Although the action of the organic hydroxy acid and its precursor is not always clear, a soluble chelate is generated between the organic hydroxy acid and the aluminum ion or yttrium ion, and thereby the hydrolysis rate of aluminum or yttrium is reduced. Conceivable. If the rate of hydrolysis decreases, the amount of precipitate nuclei generated decreases, the grain growth of the individual precipitated particles proceeds, washing and filtration are easy, and the precipitate particles are considered to be easy to handle due to little contact with the precipitated particles. .

[0010] In such a precipitate, since the precipitate is granular, the growth of secondary particles during calcination is suppressed, and an easily sinterable yttrium aluminum garnet fine powder having low cohesiveness and excellent dispersibility is obtained. It is considered to be.

As the organic hydroxy acid and its precursor,
As described above, the organic hydroxy acid itself or a salt thereof such as ammonium is preferable, and particularly preferred is lactic acid, tartaric acid, or a substance which is a member of a salt such as ammonium thereof. The concentration of the organic hydroxy acid and its precursor (hereinafter simply referred to as “organic hydroxy compound”) is determined by the sum of aluminum ion and yttrium ion in order to promote the formation of chelates with aluminum ions and yttrium ions and to delay the generation of precipitation nuclei. The molar ratio to the amount is preferably 0.1 times or more. On the other hand, if the amount of the organic hydroxy compound is too large, a soluble metal chelate complex is stably formed, and the hydrolysis of the metal ion is not completed. Therefore, the amount is preferably 5.0 times or less. In particular, lactic acid or a salt thereof is preferably 1.5 to 3.5 times, and tartaric acid or a salt thereof is preferably 0.5 to 1.0 times.

The particulate precipitate obtained by the present invention is almost the same as the particulate precipitate obtained by the sulfuric acid-added urea method, and the filtration and washing properties are comparable. In addition, since an organic substance is used instead of sulfuric acid as the precipitation modifier, decomposition products at the time of calcination are carbon dioxide gas and water, there is no generation of sulfurous acid gas, and the problems of working environment and air pollution are remarkably improved.

In forming a precipitate, for example, a salt of yttrium and aluminum, such as hydrochloric acid or nitric acid, is dissolved in water, and then, for example, the metal ion concentration is 0.005 to 1.0 mol / L.
And mixed according to the YAG composition. When the metal ion concentration is higher than 1.0 mol / L, the contact between the particles during precipitation is increased, so that the particles are seized at the time of calcination, resulting in a powder having low dispersibility. If it is lower than this, there is no particular problem, but the productivity is reduced.
005 mol / L or more is preferable.

To this solution, urea and preferably an organic hydroxy compound such as lactic acid or tartaric acid or a salt thereof in a molar ratio to metal ions of 0.1 to 5.0 times are added to form a mixed solution. Examples of lactate and tartrate include, but are not limited to, ammonium lactate, sodium lactate, lithium lactate, magnesium lactate, ammonium tartrate, ammonium hydrogen tartrate, sodium tartrate, and the like.

The above mixed solution is reacted at 70 to 100 ° C. for several hours with stirring. Urea decomposes into ammonia and carbon dioxide by heating, whereby aluminum and yttrium precipitate as hydroxides, carbonates or basic carbonates. When the pH of the mixed solution rises to about 4.0, aluminum precipitates first begin to form, and when the pH further rises, yttrium precipitates. The increase in pH can be controlled by the amount of added urea, the amount of the organic hydroxy compound, and the reaction temperature.
A precipitate having any average particle size can be formed. It is sufficient that urea has an amount necessary to neutralize the acid in the reaction solution and hydrolyze the metal ions. If the amount is too small, the hydrolysis of the metal ions is incomplete and the hydrolysis reaction takes time. There is no particular problem if the amount of urea is too large, but it is uneconomical. For these reasons, the urea is suitably used in a molar ratio of 4 to 10 times the molar amount based on the total amount of metal ions.

When the reaction temperature is 70 ° C. or lower, hydrolysis of urea does not occur, and the reaction temperature may be 70 ° C. or higher and the boiling point of the reaction solution or lower. Preferably, after completion of the reaction, the mixture is cooled to room temperature, and the precipitate is washed with water and filtered several times. This removes irrelevant anions during precipitation, for example, chloride ions and nitrate ions to 2000 wtppm or less, and prevents secondary particle growth during calcination. If the washing is insufficient and irrelevant anions are contained in the precipitate, seizure of the particles occurs during calcination. The obtained precipitate is dried, for example, and then calcined at a temperature of, for example, 650 ° C. or more, to obtain a YAG powder.
The YAG powder thus obtained is a fine powder, and becomes a raw material powder of a translucent YAG having little aggregation and excellent dispersibility.

According to the present invention, it is possible to easily and inexpensively produce a fine powder of YAG which is useful as a raw material of a translucent YAG ceramic, has less aggregation, has good dispersibility, and has excellent sinterability. Further, since sulfuric acid is not used, problems of working environment and air pollution can be improved. Examples will be described below, but the present invention is not limited to these examples.

[0018]

Example 1 600 ml of 1 mol / L YCl3 aqueous solution and 1 mol / L
Was placed in a 5 L beaker, and urea and ammonium lactate were added in a molar ratio of 10 times and 2 times, respectively, to the total amount of metal ions. This mixed solution was heated to 95 ° C. and reacted for 3.5 hours. After the reaction solution was cooled to room temperature, filtration and washing with water were repeated seven times to obtain a precipitate having an irrelevant anion concentration of 2000 wtppm or less.

After drying this amorphous precipitate at 120 ° C. in air, it was calcined at 1250 ° C. for 2 hours in air to obtain a YAG raw material powder having excellent dispersibility. Using a 20φ mold, 2 g of the obtained YAG raw material powder was
After primary molding at a pressure of 0 kg / cm ² , 1.5 Ton /
CIP molding (hydrostatic molding) at a pressure of 1 cm ²
Vacuum sintering was performed at 3 ° C. for 3 hours. When the density of the obtained sintered body was measured by Archimedes' method, the theoretical density was 4.55 g / cm ^3, and both surfaces were mirror-polished to obtain a sample having a thickness of 2 mm, and the light linear transmittance at a wavelength of 600 nm was measured. 58 when measured
%Met.

[0020]

Examples 2 to 13 In the same manner as in Example 1, YAG raw material powder was prepared by variously changing the metal ion concentration, the type and amount of organic hydroxy acid (all added as ammonium salts), and the calcination temperature. did. Table 1 shows the preparation conditions for each sample. The primary particle size (average particle size) after calcination,
Table 2 shows the density and the linear light transmittance after vacuum sintering at 670 ° C. From Tables 1 and 2, it can be seen that, in the present invention, Y having good translucency
It can be seen that a raw material powder for an AG sintered body can be obtained. In Examples 2 to 9 in which ammonium lactate was used, the high linear light transmittance was obtained in Examples 3, 4, and 5 in which the molar ratio between ammonium lactate and metal ions was 1.5 to 3.5. , 7,
8 Example 10 using ammonium tartrate
In Examples 10 and 11, the light linear transmittance was high among Examples 13 and 13 in which the molar ratio between ammonium tartrate and metal ions was 0.5 to 1.0.

In each comparative example, despite the use of an organic hydroxy compound, transparent YAG was sintered at 1670 ° C.
No sintered body was obtained. This indicates that when the molar ratio of the organic hydroxy compound to the metal ion is less than 0.1 times or more than 5.0 times, it is necessary to take measures such as increasing the sintering temperature.

[0022]

Table 1 Sample preparation conditions * Human peroxy acid Metal ion concentration Human peroxy acid / metal Calcination temperature (ammonium salt) / (mol / L) (molar ratio) (° C) Example 2 Lactic acid 0.05 0.5 1250 Example 3 Lactic acid 0.05 1.5 1250 Example 4 Lactic acid 0.05 2.0 1250 Example 5 Lactic acid 0.05 3.5 1250 Example 6 Lactic acid 0.05 5.0 1250 Example 7 Lactic acid 0.1 1.5 1300 Example 8 Lactic acid 0.1 3.5 1300 Example 9 Lactic acid 0.1 5.0 1300 Example 10 Tartaric acid 0.05 0.5 1250 Example 11 Tartaric acid 0.05 1.0 1250 Example 12 Tartaric acid 0.05 3.0 1250 Example 13 Tartaric acid 0.05 5.0 1250 Comparative example 1 Lactic acid 0.05 0.05 1250 Comparative example 2 Lactic acid 0.05 7.5 1250 Comparative example 3 Lactic acid 0.05 10.0 1250 Comparative example 4 Lactic acid 0.1 0.05 1300 Comparative Example 5 Lactic acid 0.1 10.0 1300 Comparative Example 6 Tartaric acid 0.05 0.05 1150 Comparative Example 7 Tartaric acid 0.05 7.5 1250 * All organic hydroxy acids are added as ammonium salts. Metal ion concentration is the total concentration of yttrium ion and aluminum ion, metal Regarding the form of ion addition, chloride salt and urea were added in a molar ratio of 10 times the total amount of metal ions. After precipitation, filtration and washing were repeated seven times to reduce the concentration of irrelevant anions to 2000 wtppm or less. The baking atmosphere is air.

[0023]

[Table 2] Table 2 Ceramic properties * Primary particle diameter Sintering density Light linear transmittance (μm) (g / cm ³ ) (%) Example 2 0.19 4.55 45.2 Example 3 0.21 4.55 59.6 Example 4 0.29 4.55 66.3 Example 5 0.34 4.55 64.1 Example 6 0.35 4.55 45.1 Example 7 0.28 4.55 57.5 Example 8 0.33 4.55 63.2 Example 9 0.37 4.55 46.7 Example 10 0.20 4.55 60.4 Example 11 0.27 4.55 68.2 Example 12 0.33 4.55 54.1 Example 13 0.36 4.55 40.1 Comparative example 1 0.11 4.53 0 Comparative example 2 0.43 4.49 0 Comparative example 3 0.46 4.45 0 Comparative example 4 0.16 4.54 0 Comparative example 5 0.50 4.41 0 Comparative example 6 0.02 4.02 0 Comparative example 7 0.44 4.48 0 * Particle size is TEM Evaluated by observation. The sintering condition is 1670 ° C. in vacuum for 3 hours. Theoretical density 4.55 g / cm ³ . Light linear transmittance was measured at a wavelength of 600 nm.

Claims (3)

[Claims] 1. An aqueous solution of a mineral acid salt mixed so that the mixing ratio of an yttrium salt and an aluminum salt becomes a garnet composition is neutralized with urea to form a precipitate, and the obtained precipitate is calcined. A method for producing yttrium aluminum garnet raw material powder, characterized in that the mineral salt aqueous solution contains at least a member of a group consisting of an organic hydroxy acid and a precursor thereof. Method. 2. The concentration of at least one member of the group consisting of the organic hydroxy acid and its precursor is 0.1 to 5.0 times in molar ratio to the total concentration of yttrium ions and aluminum ions. The method for producing yttrium aluminum garnet raw material powder according to claim 1, characterized in that: 3. The substance according to claim 1, wherein the at least one member of the group consisting of the organic hydroxy acids and the precursors thereof is at least one member of the group consisting of lactic acid, tartaric acid and salts thereof. A method for producing yttrium aluminum garnet raw material powder.