JPH0292817A - Production of yttrium aluminium garnet - Google Patents

Abstract

PURPOSE:To obtain raw material powder of product containing small number of secondary particle, capable of sintering readily and giving high transparent sintered compact by making existence of specific amount of sulfate ion at precipitation in a producing method of adding urea to an acidic aqueous solution containing Y ion and Al ion and precipitating. CONSTITUTION:An acidic aqueous solution containing Y ion and Al ion is neutralized by urea and precipitate is generated, then resultant precipitate is calcined to obtain yttrium aluminium garnet(YAG). In said process, sulfate ion in an amount of 0.1-1.2mol times of total amount of Y ion and Al ion is contained in the acidic aqueous solution. By said method, YAG raw material powder in which growth of secondary particle is small is obtained. Next, 100-2500wt.ppm. SiO2 is added to said powder and the powder is sintered at 1650-1900 deg.C under no oxygen atmosphere to afford polycrystalline YAG sintered material having high light transmittance. With the above-mentioned two critical values of sulfate ion, granular precipitate is obtained for above the lower critical value and only material having low sintering ability is obtained at above the higher critical value.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] This invention provides yttrium aluminum garnet, (
Y3A lso+z, hereinafter simply referred to as YAG. ), relating to a manufacturing method.

[Prior Art] Yttrium aluminum garnet has functions such as a laser host material and a fluorescent material, and is widely used. Recently, the use of polycrystalline yttrium aluminum garnet using ceramic manufacturing methods has progressed, and there is therefore a demand for thick powders with easy reactivity, easy sinterability, and uniformity. Yttrium aluminum garnet is mainly used as an optical material, and a highly transparent sintered body is required. Yttrium aluminum garnet has a cubic crystal structure, so it has no birefringence and no light scattering at grain boundaries. Therefore, it is known that by removing impurities and pores from the crystal, a polycrystalline sintered body with high light transmittance, especially linear transmittance, can be obtained.

The inventors researched a method for producing yttrium aluminum garnet, and found a method in which a mixed acidic aqueous solution of these ions is neutralized with urea to form a precipitate, and the resulting precipitate is calcined to produce yttrium aluminum garnet. (Japanese Patent Application No. 62-248.957). This method is characterized by the following points. Using conventional ammonia precipitate formation, the reaction is difficult to control and produces a jelly-like precipitate that cannot be filtered. Even if the precipitate is forcibly separated by centrifugation, impurities such as ammonium chloride remain in the precipitate and cannot be removed sufficiently. When the obtained precipitate is calcined, impurities such as ammonium chloride that have been mixed in promote crystal growth of yttrium aluminum garnet during calcining, resulting in a material with poor sinterability. On the other hand, in precipitation with urea, the precipitation reaction is slow and easy to control, and a precipitate containing less impurity ions can be obtained.

The inventors proceeded to improve this method. The product obtained by urea precipitation is gel-like and still contains a large amount of impurity ions. When this precipitate is calcined, impurity ions promote the growth of secondary particles. When the secondary particles grow, it is difficult to compress and remove the micropores within the secondary particles during sintering.
It is difficult to obtain a dense sintered body. The inventors have found that the presence of a specific amount of sulfate ions during precipitation plays a decisive role in this regard. The inventor also discovered that by using a precipitate obtained in the presence of a specific amount of sulfate ions,
We have discovered that it is possible to obtain a polycrystalline yttrium aluminum garnet sintered body with high optical transparency.

[Problem of the Invention] An object of the invention is to provide a method for producing thick yttrium aluminum garnet powder in which the growth of secondary particles is small.

Another object of the invention is to obtain a polycrystalline yttrium aluminum garnet sintered body with high light transmittance.

[Structure of the Invention] The invention as set forth in claim 1 is directed to neutralizing an acidic aqueous solution containing yttrium ions and aluminum ions with urea to generate a precipitate, and calcining the obtained precipitate to produce a yttrium aluminum garnet. The method is characterized in that the acidic aqueous solution contains sulfate ions in a molar ratio of 0.1 to 1.2 times the total amount of yttrium ions and aluminum ions.

Next, the invention of claim 2 provides that the yttrium aluminum garnet powder obtained by the method of claim 1 is
The invention of claim l is characterized in that it contains 2500wtppm of 5i02 and is sintered at 1650 to 1900°C in an oxygen-free atmosphere to form a polycrystalline transparent yttrium aluminum garnet sintered body. . When precipitating with urea in the presence of sulfate ions in the mother liquor, a granular precipitate is obtained rather than a gel-like precipitate. Since the precipitate is not gel-like, there is less contamination of impurity ions from the mother liquor. This has the effect that the growth of secondary particles during calcination is small. On the other hand, when starting from a gel-like precipitate, secondary particles grow during calcination due to impurities such as ammonium salts that have entered the gel. It is difficult to remove the pores inside the secondary particles during subsequent sintering, and if a gel-like precipitate is used as a starting material, a dense sintered body cannot be obtained.

There are two critical points in the effect of sulfate ions. By adding sulfate ions in a molar ratio of 0.1 times or more to the total amount of yttrium ions and aluminum ions, a granular precipitate can be obtained. When this precipitate is calcined and then sintered, a dense polycrystalline YAG sintered body is obtained. On the other hand, if the molar ratio of sulfate ions is 1.5 times or more with respect to the total amount of yttrium and aluminum, that is, if you start from a mixed aqueous solution of yttrium sulfate and aluminum sulfate, the particle size of the precipitate increases and the sinterability increases. Only low-quality materials can be obtained. Deterioration of sinterability due to excess sulfate ions occurs at a molar ratio of 1
．． It appears from about 2. Therefore, the preferred sulfate ion content is 0°1-1.2, more preferably 0.
．． 15 to 1.0. Note that the calcination atmosphere is arbitrary, and the temperature is 500 to 1400°C, preferably 900 to 135°C.
0℃ is good.

Next, a method for producing polycrystalline transparent yttrium aluminum garnet using YAG powder after calcination will be described. When the obtained YAG powder is sintered, a dense sintered body is obtained. The conditions for obtaining an optically transparent sintered body are sintering in an oxygen-free atmosphere and a power consumption of 100 to 2500 w for YAG.
tppm1 more preferably 300 to 2000 wtppm
5iO8.

For example, YA with the same 1000w100O 5i02 added
Even with G, only opaque materials can be obtained when sintered in oxygen. On the other hand, a transparent polycrystalline YAG sintered body can be obtained in vacuum, H2, or Ar. Moreover, it is not enough to select the atmosphere; the light transmittance of the sintered body depends on the Sin content. Those without SiO□ are opaque, and those with excess SiO□ are also opaque. The inventor then discovered that 300 to 2000 wtppm of S
(Hereinafter, the wtppm unit is simply expressed as ppm), we succeeded in obtaining high light transmittance with an extinction coefficient of about 0.25 mm.The timing of addition of 5iOz is arbitrary, and the mother liquor It may be added to the precipitate before calcination, or may be added to the YAG powder after calcination.

In addition, to obtain a dense sintered body, the temperature is 0 to 19 at 1650℃ or higher.
Limited to 00℃.

[Example] Example 1 A yttrium nitrate aqueous solution and an aluminum sulfate aqueous solution were mixed in equivalent amounts, that is, according to the composition of YAG, and water was added,
The acidic aqueous solution ILitter was 7 mmol/Litter in terms of YAG. Add to this 51゜4g at room temperature.
of urea (10 times equivalent) was added, heated to 95°C, and reacted for 5 hours with stirring. After the reaction, 2 liters of water was added and cooled to stop the decomposition of urea.

The precipitate was then filtered and washed with water to obtain a granular precipitate. After drying the precipitate, it was calcined in air at 1100° C. for 3 hours, and the product was ground in a ball mill for 10 hours. The product is YAG
The crystal grain size was 0.32 m1 and the specific surface area was 2 m''/g.

Here, 62.5% of the acid ions in the mother liquor were covered by sulfate ions, and the rest were covered by nitrate ions.

Therefore, the molar ratio of sulfate ions to the total amount of yttrium ions and aluminum ions is about 0.94. It is important to note that the precipitation is carried out in the presence of a predetermined amount of sulfate ions, rather than the coexisting nitrate ions. Similar experiments were conducted by replacing nitrate ions with chloride and acetate ions, but the results were all the same.

When urea is added and precipitated, urea becomes ammonia and CO2.
As a result, aluminum and yttrium are precipitated as hydroxides. The precipitation is first preceded by precipitation of aluminum, and then, when the pH increases to 7.5 or higher, yttrium is precipitated. The decomposition reaction of urea is slow, and yttrium does not precipitate quantitatively unless the temperature is 70°C (1 practically, 80°C or higher). Therefore, the temperature during the precipitation reaction is 70°C to the boiling point, more preferably 80°C to the boiling point. Next, when the pH exceeds 9.5, remelting of aluminum begins. However, in precipitation with urea under heating, the pH remains at about 8 due to vaporization of the ammonia produced. Therefore, remelting of aluminum due to an increase in pH is not a problem. According to experiments, it is preferable to add urea at least twice the amount of acid in the mother liquor, preferably 5 to 20 times.

In this example, the inventor attempted to use ammonia instead of a deep cable. That is, ammonia was added at room temperature to adjust the pH of the liquid to 8.5. The resulting precipitate was jelly-like and unfilterable, and although it was washed by repeated centrifugation four times, it did not serve as a preferred starting material. For example, when the precipitate after washing was calcined in air at 1000° C. for 3 hours, the average particle size of the product after ball milling was 0.85 μm.

Further, the YAG powder after calcination was sintered in air at 1700° C. for 5 hours, but the density of the sintered body was only 4.15 g/cm” (91.2% of the theoretical density).

In the case of urea precipitation, when the entire amount was precipitated as nitrate ions, the precipitate was gel-like and occluded a large amount of ammonium nitrate ions.

Example 2 Yttrium chloride 30 mmol and aluminum chloride A50
Add 36 g of urea to an aqueous solution I Litter containing 30 mmol of ammonium sulfate and 30 mmol of ammonium sulfate at room temperature,
The reaction was carried out at 95° C. for 60 minutes with stirring.

After the reaction, the mixture was allowed to cool to room temperature, filtered, washed with water, dried, and calcined in air at 1000°C for 3 hours.

The product obtained by ball milling for 10 hours after calcination (the same applies hereinafter) had an average particle size of 0.35 μm and a specific surface area of 3 m''/g by the BET method.The precipitate was granular and after calcination. There was no growth of secondary particles due to
It was press-molded at ton/cm2 and sintered in air at 1700°C for 3 hours. An opaque sintered body with a sintered density of 4.55 g/cm' (a dense sintered body with a theoretical density) was obtained.

Example 3 6.35 g of yttrium oxide and aluminum hydroxide7.
31g (18.75mmol as YAG) in 11
．． It was dissolved in 40 ml of 6N concentrated hydrochloric acid and 6 ml of 36N concentrated sulfuric acid, and water was added to make 1 Litter. The molar ratio of sulfate ions to the total number of moles of yttrium and aluminum is 0.72. Add 210 g of urea (10 times equivalent to the total amount of hydrochloric acid and sulfuric acid) to this, and stir for 90 minutes.
The reaction was carried out at 5°C for 120 minutes. Thereafter, the mixture was cooled with 2 liters of water, and the precipitate was filtered and washed with water. The precipitate was granular. The precipitate was dried, calcined in oxygen at 1300° C. for 1 hour, and ground in a ball mill for 10 hours. The product after pulverization was a YAG1 phase, with an average particle size of 0.4 μm and a specific surface area of 1 m 2 /g. This was press-molded at a pressure of 2Ton/Cm'' and sintered in oxygen at 1600℃ for 30 hours.The relative density of the sintered body was 99.3% (density 4.52g/cm).
There was a cm.

Regarding this example, the effect of sulfate ions was investigated in the same manner except that the amount of sulfuric acid was changed. Table 1 shows the average particle diameter after calcination and pulverization in a ball mill, and the relative density after sintering at 1600°C.

Table 1 Effect of sulfate ion SO, 7 (Y + A I) Particle size (μm) Density (%) (Molar ratio) 0.15 0.72 1.2 1.5 0.4 96 0.4 99 or more 0. 4 99.3 0.4 99 or more 0.5 98 From Table 1, sulfuric acid ions with a molar ratio of 0.15 or more improve the sintered density, making it possible to obtain a transparent polycrystalline YAG sintered body. This is because it suppresses the formation of gel-like precipitates and prevents the growth of secondary particles during calcination. However, when sulfate ions are added at a molar ratio of 1.5 or more, the particle size after calcination increases and The crystallization activity decreases, and a dense YAG sintered body cannot be obtained.

Example 4 The YAG sintered body prepared in Example 2 was dense but opaque. Similarly, the sintering temperature of the raw material YAG powder obtained in Example 1.3 was increased to obtain a dense powder, but it was all opaque. Therefore, we considered producing a polycrystalline YAG sintered body with excellent light transmittance by using a sintering atmosphere and additives. Note that all the knowledge regarding the production of YAG calcined powder in Examples 1 to 3 also applies to this example.

Colloidal silica (Na
We added ion-free silica sol) to examine the effect of adding silica. In addition, the sintering atmosphere was set to air, oxygen, vacuum, hydrogen, and Ar, and the influence of the atmosphere was investigated. A sintered body having the theoretical density was obtained for each sample. The extinction coefficient of the obtained sample for beam-shaped light at 589 nm was measured. The results are shown in Table 2.

Table 2 Extinction coefficient In oxygen In air 11000pp Opaque to the naked eye 11000pp Same as above In vacuum In hydrogen In Ar In vacuum In vacuum In vacuum In vacuum In vacuum In vacuum In vacuum 1000 ppm 1000 ppm 11000 pp No additives 0 ppm 00 ppm 2000 ppm 3000 ppm 3 wt% 0.25 0.25 0 .26 Opaque to the naked eye 0.26 0.25 Opaque to the naked eye Sin, content is the amount added to the weight of YAG, wtp
Shows pm.

pm From these results, in order to obtain a transparent YAG polycrystalline sintered body, 100 to 2500 ppm of 8102 is required in an oxygen-free atmosphere.
, more preferably 300-2000 ppm of 510. It can be seen that it is necessary to add and sinter. The extinction coefficient of 0.25 mm'' corresponds to a transmission coefficient of 78% at a thickness of 1 mm, which is an extremely high value.
Attempts were made to add iO□ at different times: after the formation of the precipitate and before calcination, and after calcination and before sintering, but the results were the same in both cases. Furthermore, no dependence on the addition form of SiO□ was found. Furthermore, if the purity of the yttrium or aluminum raw material is reduced, SiO2 may be mixed in from the raw material. Since the same effect was obtained even with such Sin, what is important is the amount of 5in2 present relative to YAG.

The reason why the optical properties differ depending on the presence of 5102 and the sintering atmosphere is as follows. The presence of 5in2 eliminated the crystal grain size distribution inside the YAG sintered body and eliminated abnormally grown particles and microparticles. Therefore, scattering and refraction of light inside the sintered body can be reduced. However, on the other hand, when an excessive amount of 3 wt % of Si○ was added, pores were formed in the sintered body, making it opaque. On the other hand, sintering under oxygen atmosphere resulted in an irregular distribution of grain size and reduced optical properties.

Next, regarding the sintering temperature, if it is below 1650°C, it is not possible to obtain a dense sintered body, and the irregular distribution of crystal grain size cannot be resolved. However, on the contrary, at temperatures above 1900℃,
The evaporation of YAG was severe and favorable results could not be obtained.

Therefore, the preferred sintering temperature is 1650°C to 1900°C.

Although specific embodiments have been described in the above description, the present invention is not limited thereto. For example, various additives for YAG are already known. Therefore, the addition of such additives is not excluded.

[Effects of the Invention] According to the invention of claim 1, it is possible to obtain a method for producing a yttrium aluminum garnet raw material powder in which the growth of secondary particles is small.

Further, according to the second aspect of the invention, a polycrystalline yttrium aluminum garnet sintered body having high light transmittance can be obtained.

Claims (2)

[Claims] (1) In a method in which an acidic aqueous solution containing yttrium ions and aluminum ions is neutralized with urea to form a precipitate, and the resulting precipitate is calcined to produce yttrium aluminum garnet, the acidic aqueous solution contains yttrium ions. The molar ratio to the total amount of aluminum ion and aluminum ion is 0.1 to 1.2.
A method for producing yttrium aluminum garnet, characterized by containing double the amount of sulfate ions. (2) The yttrium aluminum garnet after calcination contains 100 to 2500 wtppm of SiO_2, and is heated to 1650 to 190 wtppm in an oxygen-free atmosphere.
The method for producing yttrium aluminum garnet according to claim 1, characterized in that it is sintered at 0°C to form a polycrystalline transparent yttrium aluminum garnet sintered body.