JP2673161B2 - Method for manufacturing yttrium aluminum garnet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to yttrium aluminum garnet,
(Y ₃ Al ₅ O ₁₂ , hereinafter sometimes simply referred to as YAG).

[Prior Art] Yttrium aluminum garnet has a function as a laser host material, a fluorescent material, etc. and is widely used. Recently, the use of polycrystalline yttrium aluminum garnet using a ceramics manufacturing method has progressed, and therefore, a raw material powder having easy reactivity, easy binding and uniformity is demanded. Further, yttrium aluminum garnet is mainly used as an optical material, and a sintered body having high transparency is required. Since yttrium aluminum garnet has a cubic crystal structure, there is no birefringence and no light scattering at grain boundaries. Therefore, it is known that a polycrystalline sintered body having high optical transparency, particularly linear transparency, can be obtained by removing impurities and pores from the crystal.

The inventors have studied a method for producing yttrium aluminum garnet, developed a method of neutralizing a mixed acidic aqueous solution of these ions with urea to form a precipitate, and calcining the formed precipitate to obtain yttrium aluminum garnet. (Japanese Patent Application No. 62-248,957). The characteristic of this method is that
There are the following points. Using normal ammonia precipitate formation, the reaction is difficult to control and an unfilterable jelly-like precipitate is formed. Even if the precipitate is forcibly separated by centrifugation, impurities such as ammonium chloride remain in the precipitate,
This cannot be removed sufficiently. When the obtained precipitate is calcined, impurities such as ammonium chloride mixed in promote the crystal growth of yttrium aluminum garnet at the time of calcining, and only a material having poor sinterability can be obtained. On the other hand, in the case of precipitation with urea, the precipitation reaction is slow and easy to control, and a precipitate containing a small amount of impurity ions can be obtained.

The inventors have advanced the improvement of this method. The product obtained by urea precipitation is a gel and still contains a large amount of impurity ions. When this precipitate is calcined, the impurity ions promote the growth of secondary particles. When the secondary particles grow, 2
Since it is difficult to compress and remove the micro pores in the secondary particles, it is difficult to obtain a dense sintered body. In this regard, the inventor has found that the presence of a certain amount of sulfate ions during precipitation plays a crucial role. The inventor has also found that a polycrystalline yttrium aluminum garnet sintered body having high light transmittance can be obtained by using a precipitate obtained in the presence of a specific amount of sulfate ion.

[Problem of the Invention] An object of the invention of claim 1 is to obtain a method for producing a yttrium aluminum garnet raw material powder in which secondary particles grow little.

Moreover, the invention of claim 2 has as an object to obtain a polycrystalline yttrium aluminum garnet sintered body having high light transmittance.

[Structure of the Invention] In the invention according to claim 1, an acidic aqueous solution containing yttrium ions and aluminum ions is neutralized with urea to form a precipitate, and the obtained precipitate is calcined to obtain yttrium aluminum garnet. In the method, the acidic aqueous solution is characterized by containing 0.1 to 1.2 times the amount of sulfate ion with respect to the total amount of yttrium ion and aluminum ion.

Next, the invention of claim 2 provides the yttrium aluminum garnet powder obtained by the method of claim 1 in an amount of 100 to 250.
It is characterized by containing 0 wtppm of SiO ₂ and sintering this at 1650 to 1900 ° C. in an oxygen-free atmosphere to obtain a polycrystalline transparent yttrium aluminum garnet sintered body.

The invention of claim 1 will be described. Precipitation with urea in the presence of sulfate ions in the mother liquor gives a granular rather than a gel-like precipitate. Since the precipitate is not in the form of gel, contamination of impurity ions from the mother liquor is small. This brings about the effect that the growth of secondary particles is small at the time of calcination. 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 penetrated into the gel. It is difficult to remove the pores inside the secondary particles by subsequent sintering, and if a gel-like precipitate is used as a starting material, a dense sintered body cannot be obtained.

The effect of sulfate ion has two critical points. A granular precipitate can be obtained by adding 0.1 times or more of the sulfate ion in molar ratio to the total amount of yttrium ion and aluminum ion. When this precipitate is calcined and then sintered, a dense polycrystalline YAG sintered body is obtained. On the other hand, when the molar ratio of sulfate ions is 1.5 times or more the total amount of yttrium and aluminum, that is, when starting from a mixed aqueous solution of yttrium sulfate and aluminum sulfate, the particle size of the precipitate increases and the sinterability is low. Only the material can be obtained. The decrease in sinterability due to excessive sulfate ion appears from about 1.2 in molar ratio. Therefore, the preferable sulfate ion content is 0.1 to 1.2, and more preferably 0.15 to 1.0 in the above molar ratio. The calcination atmosphere is arbitrary, and the temperature is 500 to 1400 ° C, more preferably 900 to 1350 ° C.

Next, a method for producing a polycrystalline transparent yttrium aluminum garnet using the YAG powder after calcination will be described. By sintering the obtained YAG powder, a dense sintered body can be obtained. The conditions for obtaining an optically transparent sintered body are sintering in an oxygen-free atmosphere and addition of 100 to 2500 wtppm, and more preferably 300 to 2000 wtppm of SiO ₂ to YAG.

For example, even the same YAG containing 1000 wtppm of SiO ₂ can only give an opaque material when sintered in oxygen. On the other hand, a transparent polycrystalline YA can be used in vacuum, H ₂ and Ar.
A G sintered body can be obtained. Moreover, it is not enough to select the atmosphere, and the light transmittance of the sintered body depends on the SiO ₂ content.
Those without added SiO ₂ are opaque and those with added excess SiO ₂ are also opaque. And the inventor is 300 ~ 2000wtp
We have succeeded in obtaining high light transmittance with an extinction coefficient of about 0.25 mm ^-1 with SiO ₂ at pm (hereinafter, wtppm unit is simply expressed as ppm). The SiO ₂ may be added at any time, and may be added to the mother liquor, to the precipitate before calcination, or to the YAG powder after calcination.

Further, a temperature of 1650 ° C or higher is required to obtain a dense sintered body, and conversely, at 1900 ° C or higher, melting and evaporation of YAG starts, so the sintering temperature is limited to 1650 to 1900 ° C.

[Example] Example 1 An yttrium nitrate aqueous solution and an aluminum sulfate aqueous solution were mixed in an equivalent amount, that is, in accordance with the composition of YAG, water was added, and Y was added.
An acidic aqueous solution of 7 mmol / Litter in terms of AG was used as 1 Litter. To this was added 51.4 g of urea (10 equivalents) at room temperature, heated to 95 ° C. and reacted for 5 hours under stirring. After the reaction, 2 Litter of water was added and cooled to stop the decomposition of urea. Then, the precipitate was 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 crushed by a ball mill for 10 hours. The product was the YAG1 phase with no other phases mixed in, the crystal grain size was 0.3 μm and the specific surface area was 2 m ² / g.

Here, 62.5% of the acid ions in the mother liquor were not covered with sulfate ions, and the others were covered with nitrate ions. Therefore, for the total amount of yttrium ions and aluminum ions,
The molar ratio of sulfate ion is about 0.94. It is important to note that precipitation is carried out in the presence of a predetermined amount of sulfate ions, not the coexisting nitrate ions. The same experiment was conducted by changing the nitrate ion to chloride ion or acetate ion, but the results were all the same.

When urea is added to cause precipitation, urea will react with ammonia and CO ₂
And aluminum and yttrium are precipitated as hydroxides. The precipitation is preceded by the precipitation of aluminum first, and then the ytnium precipitates when the PH is increased above 7.5. The decomposition reaction of urea is slow, 70
Yttrium does not precipitate in low amounts unless it is above 80 ° C, practically 80 ° C. Therefore, the temperature during the precipitation reaction is 70 ° C to the boiling point, more preferably 80 ° C to the boiling point. Next, when PH exceeds 9.5, remelting of aluminum begins. However, during the precipitation with urea under heating, the pH remained at around 8 due to the vaporization of the produced ammonia. Therefore, remelting of aluminum due to an increase in PH is not a problem. According to experiments,
Urea is preferably added in an amount of 2 times or more, more preferably 5 to 20 times, the acid of the mother liquor.

The inventor tried to use ammonia instead of urea in this example. That is, add ammonia at room temperature,
The pH of the liquid was 8.5. The resulting precipitate was jelly-like and non-filterable and was washed by repeating centrifugation four times, but it was not a preferable 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. The calcined YAG powder was sintered in air at 17,000 ° C. for 5 hours, but the density of the sintered body was only 4.15 g / cm ³ (91.2% of theoretical density).

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

Example 2 Yttrium chloride 10 mmol and aluminum chloride 50 mmol,
And 1 Litter of an aqueous solution containing 30 mmol of ammonium sulfate,
36 g of urea was added at room temperature, and the mixture was reacted at 95 ° C. for 60 minutes under 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 below) had an average particle size of 0.35 μm and a non-surface area by the BET method of 3 m ² / g.
The precipitate was granular and did not grow secondary particles due to calcination, and was crushed by a ball mill, press-molded at ² Ton / cm ² and sintered at 1700 ° C. for 3 hours in air. An opaque sintered body having a sintered density of 4.55 g / cm ³ (a dense sintered body of almost theoretical density) was obtained.

Example 3 6.35 g of yttrium oxide and 7.31 g of aluminum hydroxide
(18.75 mmol as YAG) was dissolved in 40 ml of 11.6 N concentrated hydrochloric acid and 6 ml of 36 N concentrated sulfuric acid, and water was added to make 1 Litter. The molar ratio of sulfate ion to the total number of moles of yttrium and aluminum is 0.72. To this, 210 g of urea (10 times equivalent to the total amount of hydrochloric acid and sulfuric acid) was added, and the mixture was stirred at 95 ° C for 12 hours.
The reaction was performed for 0 minutes. Then, it was cooled with 2 Litter of water, and the precipitate was filtered and washed with water. The precipitate was granular. The precipitate is dried, calcined in oxygen at 1300 ° C for 1 hour, and ball-milled to 10
Crushed for hours. The product after pulverization was the YAG1 phase, having an average particle size of 0.4 μm and a specific surface area of 1 m ² / g. 2Ton / c
It was pressed at a pressure of m ² and sintered at 1600 ° C. for 30 hours in oxygen. The relative density of the sintered body was 99.3% (density 4.52 g / cm ³ ).

With respect to this example, the effect of sulfate ion was examined in the same manner except that the amount of sulfuric acid was changed. Table 1 shows the average particle size after calcination and crushing with a ball mill, and the relative density after sintering at 1600 ° C.
Shown in

From Table 1, it is possible to obtain a transparent polycrystalline YAG sintered body by improving the sintering density by the sulfate ion having a molar ratio of 0.15 or more. This is because the formation of gel-like precipitate was suppressed and the growth of secondary particles during calcination was prevented. However, the molar ratio is 1.5
When the above-mentioned sulfate ions are added, the grain size after calcination increases and the sintering activity decreases, so that 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 YAG powders obtained in Examples 1 and 3 was increased to obtain dense ones, but they were all opaque. Therefore, it was studied to manufacture a polycrystalline YAG sintered body having excellent light transmittance by using a sintering atmosphere and additives. In addition, the knowledge about the production of the calcined powder of YAG of Examples 1 to 3,
All also apply to this example.

In the mother liquor before precipitation in Example 2, colloidal silica (Na
Ion-free silica sol) was added to examine the effect of silica addition. The sintering atmosphere was air, oxygen, vacuum, hydrogen, or Ar, and the effect of the atmosphere was examined. A sintered body having a theoretical density was obtained for all the samples.
The extinction coefficient for the beam-like light at 589 nm was measured for the obtained sample. Table 2 shows the results.

* SiO ₂ content is the amount added to the weight of YAG, ppm is wtppm
Shows up.

These results, in order to obtain a transparent YAG polycrystal sintered body, that of SiO ₂ 100~2500ppm in an oxygen-free atmosphere, and more preferably it is necessary to sinter the addition of SiO ₂ of 300~2000ppm I understand. And the extinction coefficient at 0.25 mm ^-1 is 7 at 1 mm thickness.
Corresponding to a transmission coefficient of 8%, it is an extremely high value. The inventor tried to change the time of addition of SiO ₂ between after the formation of precipitate and before calcination and after calcination and before sintering, but the results were the same. Furthermore, we could not find a dependency on the addition form of SiO ₂ . Further, if the purity of the yttrium or aluminum raw material is lowered, SiO ₂ may be mixed from the raw material.
Since similar effects were obtained even with such SiO ₂ ,
What is important is the amount of SiO ₂ present in YAG.

The reason why the optical properties differ depending on the presence of SiO ₂ and the sintering atmosphere is as follows. The presence of SiO ₂ eliminated the distribution of crystal grain size inside the YAG sintered body, and eliminated abnormally grown grains and fine grains. Therefore, it is possible to reduce scattering and refraction of light inside the sintered body. However, on the contrary, the excess amount of 3 wt
% SiO _{2 was} added, pores were formed in the sintered body and it became opaque. On the other hand, sintering in an oxygen atmosphere resulted in an irregular distribution of the crystal grain size and reduced the optical properties.

Regarding the sintering temperature, a dense sintered body could not be obtained below 1650 ° C, and the irregular distribution of the crystal grain size could not be eliminated. However, on the contrary, at 1900 ° C or higher, the evaporation of YAG was severe and the preferable result was not obtained. Therefore, the preferable sintering temperature is 1650 ° C to 1900 ° C.

Although the above description shows a particular embodiment, it is not so limited. For example, various additives have been already known as additives to YAG. Therefore, the addition of such additives is not excluded.

EFFECTS OF THE INVENTION In the invention of claim 1, it is possible to obtain the method for producing the yttrium aluminum garnet raw material powder in which the growth of the secondary particles is small.

According to the invention of claim 2, a polycrystalline yttrium aluminum garnet sintered body having a high light transmittance can be obtained.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akio Watanabe 3-106-105 Takezono, Tsukuba-shi, Ibaraki (72) Inventor Yasuhiro Matsumoto 3502-1, Takuma, Takuma-machi, Mitoyo-gun, Kagawa Inventor Takayoshi Yanagiya Ibaraki 1-9-7 Ninomiya, Tsukuba, Japan

Claims (2)

(57) [Claims] 1. An acidic aqueous solution containing yttrium ions and aluminum ions is neutralized with urea to form a precipitate,
In the method of calcining the obtained precipitate to yttrium aluminum garnet, the acidic aqueous solution contained 0.1 to 1.2 times the amount of sulfate ion in a molar ratio to the total amount of yttrium ion and aluminum ion. A method for producing yttrium aluminum garnet, comprising: 2. The yttrium aluminum garnet after calcination contains 100 to 2500 wtppm of SiO ₂ .
The method for producing yttrium aluminum garnet according to claim 1, characterized by sintering this at 1650 to 1900 ° C in an oxygen-free atmosphere to obtain a polycrystalline transparent yttrium aluminum garnet sintered body.